We start with the filters as we said last time, the word is active. The active filter essentially stand for the word, there is an active device during filtering. So some property of an active device has been used, otherwise we shall see soon that even a normal RC or LRC filters can do as much a good job as otherwise but why active we will see later. Another filter requirements as I shown you last day was we have four kinds of filter we may use. One is something which passes almost everything except up to a frequency, we call it low pass. Something which passes all of it from starting from some frequency below which it is nothing is passed, so it is called high pass. You are allowed to pass between two frequencies the signal but otherwise block everywhere or do not pass anything there, here or here and the finally you are passing everywhere except some band of frequencies. So these band reject, band pass, high pass and a low pass. These are the four filters which we will be using in any of the circuits which we will use in your whole career. We are right now as the word filter says does not say whether it should be analog filter or it can be a digital filter. You can actually have either kind of them. Normally even if I am doing a analog sorry digital filter, we actually convert partly to digital in a half way and what we call switch capacitor filters, these are essentially digital filters but actually copy out most of the analog functions. So the basic filtering still could be said to be an analog filter. Of course there are many digital interesting filter, your signals and system theory and communication system theory will deal with many more of them later in your career or later in your classes.  This is typically ideal filter, this is what I am expecting ideally but when I actually pass through any active filtering system, what I see is till certain frequency called omega p, see certainly the transfer function does not show a constant value but repels up that is keeps on changing and till this point which is essentially a pole, at this point the gain starts falling or the transfer function starts falling its value because that is a pole we said. And ideally it should have reached to 0 at this point but it did not, it actually crossed that point and before it actually settles to 0 again repels, again repels. So the way we defined is, this is of course called the ripple which is passing through and we may assume it is a universal one frequency ripple in real life that also is not to ripple itself will have different components but right now assume single frequency ripples. Ideally what did we want, we want flat response here and sharp fall there, this is ideally a filter low pass filter was asking for. What we are essentially getting a fixed value and plus ripple up to a frequency where the pole starts that band we call pass band that means where the transfer function is such that everything is passing beyond this depends on the number of poles, this may be 20 dB down, 40 dB down or 60 dB down whatever it is the value start going down and when it reaches the so called ideal filter value we essentially say that we have reached, there is a band between the pass band and before everything becomes 0 let us say this band is called transition band that means from higher to low the frequency range is called transition band. Ideally what was, do we really need transition band, ideally we want transition band should be 0 okay that is what ideally we are looking but what we are seeing in real life there is a transition band, there is a fall time or fall, there is up to which it will keep falling. Beyond this we would have expected something to become constant but it did not but it also ripples and maybe finally it settles to the value which you are expecting. The band in which nothing is passed as for the low pass requirement we call it stop band. So for any low pass filter we are interested in what is the ripple magnitude, ripple frequency, what is the expected pass band you are getting, what is the transition band you are getting and what is the stop band you are getting and of course as I say ripple frequency itself will be varying but assume right now it is single frequency ripple occurs. So this is a definition for any filter this, so ideally for a low pass I have expect a max be 0 okay that means this should have come here. I want transition band frequency omega this low minus omega p should be as 0 as possible and again this a max be 0. Ideally this is what was expected and if that occurs we say we have a ideal low pass filter. If you look at the other band pass requirement it is similar a typical good band pass filter would have expected to have this transition between this frequency and this frequency the transfer function should have value which is constant and everything is passing okay. Below this frequency we do not want anything to pass so we say lower stop band beyond this frequency nothing should pass we say it is upper stop band. So there is a lower side stop band and upper stop band in between there is a pass band. However in real life this is not starting from here it actually again ripples and some kind of a Gaussian function one gets or rather signum function it gets and then that means beyond this value stop band I mean pass band is this but there is a ripple over it here then it goes down so there is a pole there is a somewhere 0 starting here there is a pole going down and one can say it again ripples before it actually reaches to 0 okay. So essentially in our design what are we expected to do that where it starts where it ends and what is this ripple magnitude is going to be exactly that is what we must do and what should we do minimize them as much as possible same way this is some transition band there is a transition band I also want transition band to be as close to 0 as is possible. We have already said that a pass this band pass filter is essentially a combination of low pass and high pass if I say this is my FL and if I say this is my FH please remember I repeat listen that is why I gave the name separately this is my FL this is my FH that means first there is some high pass starts and then there is a low pass starts so in between both are passing and so done the band pass. If I separate the upper frequency if I make this as FH and if I make that as FL that means high pass sorry low pass followed by after certain frequency high pass there is a frequency band in which nothing is passing so we said say band reject so basic design of a filter is essentially this and this is just a setting of the frequencies to suit your band pass or band reject requirement so in design of course in this course we should have done all of them time is not enough so we will only do one good low pass and one good high pass and if we get that then we say okay this is the circuit which can be then manipulated to create a band pass as well as a band reject filter. Now having showed you this is my requirement and this is what ideally and non ideally I am going to get I want to come closer to ideal but before we go to act networks active networks I just want to see a network itself okay normal network itself we are done this earlier as well if you have a RC network okay 1R and 1C okay if I take a transfer function of this V0 by VNS which is 1 upon CS upon 1 upon CS plus R which is 1 plus RCS or it can be written as 1 upon 1 by RC if I define a frequency cutoff frequency is 1 upon RC this is nothing but 1 upon S by omega 0 what does that mean there is a pole in negative half minus omega 0 and if I plot the board S plot therefore at this the gain will start falling so a simple RC network actually acts like a which filter low pass filter now one can think little interestingly if you see now ideally I wanted this sharp fall is that correct I must all my design why I am doing active filters all my in any passive filter this is going to occur is that clear so what I say can I do some mischief okay or close to this I have come closer to ideal and the active part should help me in getting these as close to the ideal value as is possible if I do that then I will actually create a filter which is close to ideal low pass so why active part is necessary because I want to shift the slope down if I do so something else may happen I will say whether I can tolerate that or not I will check that but at least I want fall to be as sharp as possible let us say it is 120 dB down at this point is that clear so it will swap very shortly is that clear so essentially I am trying to see I have done this pole 0 theory and I am now started looking here is some way there should be multiple poles coming there if they are they occur at very close phase or same point then my fault can be but if I look at the other filter equivalence of this which is interesting okay so basically a active low pass filter ideally could be a RC circuit as I just now did followed by a voltage follower is that correct follows by a voltage follower so whatever is the voltages here will be transferred here because a voltage follower so this is the easiest way of making a low pass filter we are not seen as transfer function so far so we do not know whether it is going closer to ideal but this should do as a low pass filter with an active device what is the purpose of all over here if any load occurs at the capacitor it will load that out this buffer will separate your input response from the output loads is that clear that is why I put a buffer in which is my voltage follower by doing this I am still achieving one upon RC kind of requirements and I am getting low pass with of course 20 dB down gain falling I can do similar thing for and as I say high pass is just the opposite of low pass and I say okay replace R by C and C by R wherever there so I put a C here or here again derive this transfer function which I get S by Omega 0 upon S by Omega 0 plus 1 where 1 upon RC is Omega 0 now you see how many things are happening here how many poles are there how many zeros are there there is a 0 at S is equal to 0 itself and there is a pole at S is equal to minus Omega 0 is that clear so there is a 0 and there is a pole so till Omega 0 which will dominate the 0 will start dominating is that correct so initially what could occur you can see from here 20 dB 0 means 20 dB per decade rise start rising okay at the pole what is the fall should be minus 20 dB but what is it rising already with 0 plus 20 dB so at this point onwards 20 minus 20 0 dB gain becomes or output function becomes constant is that high pass requirement at frequency above 1 upon RC I want transfer function to have unity value or no attenuation just passes out inputs is that correct so how do I create in this case you have a CR here pass way follower and this will act like a high pass filter this is 0 this is 0 and pole together constant okay so obviously now one thing you must have got from there if I have a low pass I would avoid zeros is that actually 0 should be at infinite okay if I am looking for high pass I will bring 0 whenever I want flatness to start is that clear so that means I have now a trick that if I have a S in the numerator I am creating 0 S plus something also but S is in the numerator and S plus something in the denominator if that kind of function I create then what I will create high pass if only one upon S plus something I create I will create a low pass is that point here this is the trick of filtering that okay create properly zeros and poles such that you actually achieve low pass and high pass values the only thing trick is how much to get whether this value should be 1 or it should have gain function if I want to gain function what should I do I should do actually are here then it will also give me some gain out of it like a normal amplifier I may amplify it also okay now this tricks are always played in many of the filter designs but using this what is the main problem we saw that that 20 dB is the all that we could get in you cannot have fast rise or fast falls so this though this is a filter no pass high pass can be always realized by this try yourself one and you will see as it will cut off somewhere and it will show you but the response will not be closer to ideal but why should you always have ideal yeah the reason is okay so there is something you must remember many circuits do not mind for example that it should actually be cut off completely as far as anyway it is like a noise going on a different letter anyway I do not care very much what happens but if I do care it single end system I will worry about it so depending on the what is going it going to dry or where from the next stage will be your choice may not be you should not see that I should have a ripple or should not hurt now way I have figured out and that is who will work today are not necessarily I will complete I have figured out basically if I see a function as I am getting I know any conic section take any conic section straight line parabola hyperbola circle ellipse or for that matter any curve for that matter can always be represented by a very simple functions what is that function is called polynomials if I write a 0 plus a 1x plus a 2x square up to n polynomials I assure you that any curve can be fitted okay it may require thousand terms to actually get closer to the curve you are looking for it is a fit function technique so I figured out that if I can generate some functions which also gives to be like those 0s and poles which I am looking then I can have a this equivalent of a I repeat what I said I create a polynomial or I create a function whose numerator and denominator looks like 0s and poles but their values can be tailored then I can say I am right now creating a filter for that function is that okay because that response will be something closer to filter is that correct this is the technique which most designers are most circuits in the analog we use that we actually create some kind of a known functions whose values mathematically we can derive and then try to fit it on those on a circuit and we say how close we are getting these two filters which we shall see little later one is called Butterworth filter the other is called Shabashio filters why I am showing you because in Butterworth filter the ripple can be minimized what is the advantage of a Butterworth filter that the ripples are very small and therefore it is called maximally flat maximally flat so all Butterworth filters are so designed that their ripples are very close to small value of 0 kind it is a flat here but the price I pay because of the function I am using to create the ripple 0 or ripple small there will be a transition band is that correct there will be a transition if I want to reduce transition band then I will say the number of poles which are required higher and higher that number of remember each pole will require let us say one circuit of this kind equivalently saying I just now showed you each pole requires one such circuit if there are n poles I will require n such circuits so I figure out that if I want I use a Butterworth filter then I can maximize the flatness but to reduce this transition band I may require larger number of poles is that correct on the contrary Shabashio filters are more this they say we cannot reduce very much the ripple okay but for a smaller number of poles I can reduce the transition band is the two difference clear in the maximally flat filters Butterworth filters ripple is smaller small very small at the cost if I want to reduce the transition band I will require larger number of poles or larger number of sections as I call in the case of Shabashio I say I cannot reduce this very much I tolerate ripple okay but for a smaller number of poles I will give better transition or at least same transition I would have got in Butterworth okay with a smaller number what is the advantage of smaller number of sections of smaller poles a circuit is smaller numbers what is the cost cost reduces if your number of sections goes down the price goes down but price going down at what cost the ripple is that correct so if you want a very good filter then you pay price okay higher price is that correct so maximally flat filters will require larger sections but will care much less ripples is that correct this is something all designers must keep in mind all IC designers are always told that anything I use because we have a silicon area known area let us say few millimeters by few millimeters say 1 centimeter at best I may have both side so many million transition I am putting if I do not put additional hardware I can put something else there is that clear that means the price of silicon is very very high area silicon what is any equivalently we say like in Mumbai we say it is a real estate silicon is a real estate any small micron by micron you throw you are losing money okay so whole trick and integrate circuit design sir how to minimize area or increase density is that correct so if you are doing the same function with larger circuit oh yeah it will do better but you paid price high price for that okay so one must understand some chips we sell very heavily high at high price if someone like young man says I want exactly this filter this should do this this man says no no I do not have only this much money so the trick of design is what is the customer wants okay so in all our engineering this part is never explained till maybe graduate of course dual degree will learn in 4th year we are never telling that all this our theory etc is as good as the money in your pocket that is it okay so this has to be understood why we learn all the tricks because we do not know what customer at the end will give me a response you say it may make or not okay so I have now suggest you here is a circuit active filter which is a generalized two pole filter how much how many what do you mean by two poles how many capacitor RC should be two RCs this is generalized why I say generalized what does that mean generalized means all four filter should be clear can be created out of this is that great generalized I never say it is low pass high pass band pass I from this circuit by proper choice of the Y1's and Y2's and Y3's and Y4 I should be able to create low pass high pass band pass band is that clear to you what is the advantage of such generalized network then because this is one time created any user during design can just manipulate this and say okay here is a low pass so he does not what is the other constant design do you know what is the cost of design is the time taken by so many engineers are called man years or man hours is the cost larger the circuit redesigned by you every blog then it will be costly every time so if I have ready met block which can be manipulated to create different things I have saved a lot of money that is essentially called semi custom something is prepared and used again and again so this is something equivalent of a semi custom that means a generalized block can be configured as either low pass high pass or any other is that clear to you why I shown to you this is something which all designers should know analysis why this is not very great this is same as what low pass high pass we did but here is some analysis I will show you I have an input V in to one of the conduct it can be admittance or conductance why is G plus JB why is G is the conductance B is admittance so why is equal as we said Z is equal to R plus JX same way it is the opposite of that so I say okay here is a Y1 component Y2 component Y3 component feedback this is two feedback this is our follower which I am not disturbing please remember this follower I have kept as it is there is another feedback which I have brought here to output let us say Kishchoff law at node VA what are the current what is the current entering V in minus VA into Y1 is that correct is the current passing through Y network theory simple trivial. Yabadokonse branch janeh currents K from VA to VB and VA to V0 is that there are two more branch current so branch current at VA must be 0 total current so this current must be this plus this so I write VA minus VB into Y2 VA minus V0 into Y3 they must be equal Kishchoff law at node VA three current summed up okay same way I summed at VB okay I said node VB VB minus VA a current either a current or what is current here no current enters open that property I used so I say VB minus VA into Y2 equal to VB by Y4 VB into Y4 okay then the third equation I see it since this is a follower this is V0 but that should be same as VB okay by what is the that is active part did you get what is the active part I used opamp properties have been used in actually writing the networks is that correct these equation I could not have written if I have not used opamp properties what properties I used same no current enters same potentials both properties I use and I use this is a follower okay so I use this the property of opamp and then could write such equations if I solve this you solve yourself though I have solved but you solve yourself at then you can do analysis I did just look at the final transfer function you write and verify V0S by VNS which is my either you write TS or you can also write HS whichever way you are writing either T is the transfer function okay normally I have been using H as the transfer function but I do not know from wherever earlier I had taken there was a T so I used so maybe your colleges so I get Y1 Y2 upon Y1 Y2 this kind of function please note down this function rest you do yourself Y1 Y2 upon Y1 Y2 plus Y1 plus Y2 plus Y3 into Y this is the transfer function I have got for the circuit I have given there is that clear simple so Kishav Locos all career or a expressions up V0 by VNS I will now explain a specific example which filter do you want me to do we will see little later but let us do this example now in this I create the first Y1 Y2 I put it as R1 R2 and this Y3 I4 I put as two capacitors in our case G is 1 upon R and Y is CS okay be rather not but why these are why only this is capacitance so CS is the admittance of that and conductance of this is 1 upon R1 and 1 upon R2 this is the expression I just got for the transfer function G1 G2 upon G1 plus G2 plus SC4 G1 G2 SC3 so now you look at it at S is equal to 0 what is the value of HS yeah view all of your expression and please remember all that I had done is I have substituted here the actual Gs and Cs okay so I got G1 G2 upon G1 G2 plus SC4 G1 plus G2 plus SC3 is HS okay at S is equal to 0 what is the value of transfer function S0 hey S0 hey a term Chalagaya G1 G2 by G1 G2 so one what does that what does that means at S is equal to 0 there is already a transfer function has a value one means it could be normalized to some other 0 so it has a value is that correct so which filter I am looking for now initially there is a value which filter I am looking low pass I have a value of the function of the output gain available at this value is that clear now when S tends to infinity so there is a S is equal to j omega when omega tends to infinity one can see the transfer function will go to 0 is that correct that means finally it is going to 0 that I see it is 1 and finally it is going to 0 so your concert characteristic different low pass different this is what we say initially value and then it is going towards 0 so obviously I am looking for a low pass so can you now get this that jibe by just substituting here the proper values of this I can create a low pass filter how many poles you are seeing here two poles so at least fall will be better than one single pole system is that correct it will be better than the single poles. So, I can create a different filter of my choice of different cutoff why different because R and C is in my value of me at me so a generalized system so why it is not so good because it is now once made at best you have only those two poles to manipulate additional is that clear you cannot actually get to this person requirement so this tolerance of yours is how much will be depending on that I said how much money you keep in your pocket that is the way it is it come in a salt curke dikhay hain I may a but I know key a maximally flat let us see whether it is so I wrote the transfer function as it is is it clear what I just substitute G is 1 upon R and vice yes and I get this function if I manipulate it better and I give a definition that Tau 3 is RC 3 and let us assume R are equal my assumption is R are equal but I never said C's are equal R's are equal but see why I do not want to make C is equal because then the time there will be same poles so I okay there are two different poles one is related to RC 3 the other related to RC 4 so this is the transfer function I want please note down HS is 1 upon 2 RC 4 S plus C 4 C 3 R square SS square Kine poles I am a part SS square term I am a part dope holes if I define this I can write a j omega magnitude is the magnitude Rokey the expression I am in a thodasa directly like I you can also think how I have written okay I say a core method of those section if you give me a corner SS square get a car now it is a partial fraction career because separate separate image career 1 upon S minus a into 1 upon S minus B transfer function key theory can gain again because it is equal to a1 into a2 is that correct so a transfer function when I a second function when I say the input the product is that point clear I repeat a transfer action h1 is using one pole a transfer function h2 using second pole is that correct I can create two separate functions output of the first is given to the input so the transfer function will get multiplied so 1 upon S minus a into 1 upon into S minus B automatically appear so is that trick clear to you once you have two poles you actually can create single pole sections and then keep output of that should be given to the next input keep doing so as many sections you will put those many poles you can create is that correct if you put seven sections that is why a word I use section each one pole will create one section I have number of sections so I can create as many poles I want and the trick is they get always multiplied by H1 H2 H3 H4 this is the way we actually implement higher pole functions anyway is come in a value Nikola or maximally flat requirement take that d by this function with the omega should be 0 you see it is the maximum minima karna kele of the differential 0 correct magnitude in a flat renna change so no change of course less than omega 0 for it is co value solve here okay I can get a condition Tau 3 is Tau T4 and C3 is to C4 a condition meet Karna in a so maximally flat situation liars is that point clear I differentiated that below that cutoff and I say at this point if I want no ripple then what should happen if I meet these conditions then I would say I am going to have a maximally flat situation is that correct over ripple kajo party O we can remove by actually choice of proper tauts and seeds is that clear or rather seeds C3 should be twice of C4 in our case if we substitute back in a normal function the cutoff of this transfer function value will occur at 3 dB point what do we 3 dB point means normally in Bode plot what is the 3 dB point is the corner we start right there 20 dB but in real life that is not the point where it start where 3 dB below it starts falling it is a continuous curve it is not Bode what did he suggest that instead of that continuous curve you actually make two points and then you say it is your cutoff point so you can actually see if I substitute here this is 1 upon root 2 dB at omega equal to omega t4 1 upon t4 that is the corner frequency of the Bode is that correct so if I get the pole you can see this is the solution many up on root t4 1 upon root 2 Rc4 why we said in real life actual curve will be something like this sorry a 3 dB isn't it is key over car so Rc4 okay so one can see that I can create a low pass and how much is now fall will start from because I made that condition tau 1 is to tau 4 right here the gain will starts falling by how many dB is 2 poles and I am after a point or dope all of them in a shift key under what condition under this condition the two poles are matching is that clear and the maximally flat situation attained so I got maximally flawed falling down by 40 dB so at least 20 dB ke bhajaya 40 to karbiya meh thoda tha stop transition band ko sharper kiya kum kiya meh and also what did I do flat kiya is meh kitne section lagay doh section aur kuch bada nahi to kya karna padega ek aur section lagau if you aap isko aasai hi chate hain to number of poles should keep on increasing that means number of sections will keep on increasing that is the problem with larger amount of money you spend so you have Butterworth filter have a powerful okay for this kaap na problem hain ki it require larger section to make it sharper okay now if I say I do not use that condition of maximally flat then I must say can I get sharpness with a lower number of poles and then I will call they are Sheveshaw filters we will come back to Butterworth in more details but this theory has to be understood what we are really trying in design of a is that point here please remember only two filters will design low pass hi okay last time if you say bola tha what is a all pass filter which we are not discussed maybe here we can quickly show you what is it up on before we go to the next kaahoga hi isko bolthe hain all pass all pass ka kya meaning hai ye to edhi transfer function bana h ka magnitude nikala h j omega by h 0 samjo is ka value nikala that the constant hai everything is passing to filter do kuch kya nahi usin a flat come a sakta hai iska transfer function kareeb kareeb aisa hona chahiya equivalently hain this is not the exact one what is it trying to tell you this transfer function 0 aur pole ek hi jaga par hain 1 upon RC par hi hain 0 hai a pole hai uska kya meaning hai 20 dB 8 jatah hai to usra minus 20 dB shuru kar deta hai wahi par that every frequency you get flat is that correct. However even if you see this function is ka transfer function to thik hai aisa hai magnitude but is ka kya change hoga iska phase okay phase can vary depending on RC values phase can vary from 0 to 180 degree. So whenever the transfer function filters you create and you want a particular phase at the output between in and out then you connect the last stage of your filter can be all pass filter with proper phase requirements is that clear to you what is the advantage of this is ka gain to one hi ho gya nahi sab kuch pass hai okay but is ka phase adjust kya ja sakta hai kya kya minus plus jo value is ka hai the phase tan inverse nikalingi do is ka phase varying RC par is that correct so the net phase at the output compare to your input need not be just the product of their magnitude h1 h2 h3 h4 but also I can adjust my final phase with the input is that correct many requirement the output should meet should be either 180 degree off or less than 180 for the stability case. So we actually create the last stage as all pass filters okay though it does not change your whatever h1 h2 you brought everything it will pass anyway but it will give you a phase bit whatever phase difference between the final stage of filter to the actual stage where you are connecting so please remember the all pass filter as such word seems to be funny why are if everything is passing what is being filtered nothing is actually phase is also please remember any complex system will have something e to the power j5 magnitude into e to the power j5 so it is the magnitude may be one unity everywhere but the phase is not is that clear and that phase variations can be attained by proper choice of RCs is that clear this essentially is the trick of phase controls we do something called phase control oscillators okay we do use some of some such property there is that correct phase control oscillators okay all the filters which we are going to talk are essentially in real life this can be a polynomial of n by n or m by n it can be s3 s4 sn same way SS b0 s something more up to sn but this may say many square terms he will be luckily so cabling is you know bullies can I am by quadratic the numerator be quadratic function a or denominator be quadratic function so in filter we actually try to see whether both Butterworth or Shebesha functions are by quadratic in nature is that correct we are looking for by quadratic functions what is that now I am talking about it is called implementation of it a real life I will KSA implement so we say okay let us look functions if I have a by quadratic function like this a2 s2 a1 s by 0 upon s2 d1 s0 this is also given in Cedars Smith and me I can have I can be part of this function I can create into low pass by pass band pass high pass whatever it is so look at the numerator may subcurch s terms any zeroes only constant value hey something called K if that functions are K upon SS square omega 0 by Q s SS this plus omega 0 square have any time you heard of the word Q Q cut quality factor omega L by R 1 upon omega RC they are also quality factor now this quality factor. If I apply a step input to any amplifier or any circuit the output essentially does not respond instantaneously is that point clear what did I say if I give okay maybe that figure which I have I can still use if I apply a step input something like this this is my input so the output does not respond immediately it starts rising and let us say trans function as a value one it should have actually reached here it did not so what it did what is this word we call ringing okay ringing we start ringing of course settles okay ideally catch I had a message as a name ring over Jada is got your damping factor is okay it is called Jolly say Niche like a scope will take key mall key rather it is got definition yeah yeah 1 upon 2 Q K which is the damping factor or in some books it will be Zeta it will be called Zeta so Zeta is 1 upon 2 Q so what does that essentially means that ideally I want something to happen like this okay depending on higher value so you can see if I put a very high Zeta 1 ke karib hai so ye asa ho jai it means it may reach at isentotically only to the actual value isentotic come in him kaya infinite pejake one whenever it is in a Zeta come look who are the body Jada ring kar kaya so I have to adjust my Zeta so that very close to that value I will get flatter response is that clear to damping factor has something to do with the quality factor by a function which is this okay so if the transfer function say has a nature of K upon SS square Omega 0 by Omega 0 is the pole Omega cutoff frequency into S sorry upper plus Omega 0 is it quadratic SS square plus S plus something so it is a quadratic term numerator does not have any quadratic term constant as a function low pass the low poles and low pass the however if the numerator has a term which contains SS square it may give up at multiple 0 at 0 multiple to 0 that 0 okay. What do you do? Faster rise kia or bad may SS square SS square term to a new circle cut karengi to a flat hokia Milan co high pass in band pass instead of SS square you now want after another cutoff to occur to ask your S look okay so you can do this analysis but if you have a function which is K dot remember the denominator is same everywhere and in the band reject you should I cut off at some other point so SS square plus Omega 0 square with the as a function hey so it will be band so if I can create by these two names I give Butterworth and Shabesha functions closer to this then I can say I am creating low pass I pass band pass band I say even this function should give me low pass why did I say so it has a 0 okay so initial value can be pumped up okay but then after the pole it actually starts falling down in a way so it is key value we will be just as I the S into S plus Z hey so high pass the manner is exactly so the generally this we may not use but this is also possible in designs we always use these four functions are the easiest to make okay and these are the four functions will realize in either Butterworth form or in Shabesha form what are the advantage of that to Shabesha gives me lesser number of poles circuit to create sharper fall at the cost I will get better word will not give me repel or very little repel but we will take larger number of poles to get the same as if Shabesha of a visual let us say five section but it may take seven sections or eight sections that clear so the at the cost of money real cost I may create Butterworth even for higher poles but ideally I say I can choose either Shabesha or Butterworth to my specifications if this is my quadratic form let us take the low pass one it is H0 upon some constant clear H0 omega 0 say divide kardiya or us come in a H0 kardiya so it is H0 S square upon omega 0 square 1 upon QS upon omega 0 plus 1 yeah transfer function heck how many poles it may take you have to go do poles of H0 create the gain chalega lahir chaiyana H0 kilo gain lagga one or the two ne padta kucho gain factor chaiyai to the amplifier banaya this circuit has an amplifier here is that correct R3 R4 a amplifier a gain function dia me is that point clear Abhi Nikala Kishav law solver KSK transfer function Nikala into gain is made only thing is it into is ka gain be here the J transfer function or what transfer function same aate haikyaan dek sakti it follows the similar pattern then what do we say by quadratic form is type KS may fit bethega the filter karni is that clear there is say you know even buffer will do the same as well as this buffer may I am here to gain then on each other normal amplifier be R2 R1 a graph of it will be organic even open does the same thing what buffer does the only difference between buffer and an open means that we do not want to use any additional components because I do not need gain there if I need gain I will put resistance so essentially if R is shorted here I am going to get a unity gain that is what I am saying even in open that are 0 is still lower only thing is now it will be a function of these value there it with the intrinsic value is that the difference clear now R3 R4 will also affect that R0 value is that clear so R0 will not be same as what we naturally device was giving it will get modified by these feedback factors is that correct so there is slight difference but the nature is same R0 will go down and RI will increase will remain same independent of that is that clear to you only thing we are there we are not interested in actually getting gain out of it we only want resistance transfer natural resistances available so put a buffer in all unity gain follower okay so it is coming a transfer function banana the code abhijay say many banana just directly more say with that I fit said except R1 R2 C1 C2 as a square plus S time bigger bracket C2 plus C2 into R1 R2 plus R1 C1 into 1 minus AB0 bracket close plus one let us say R1 and R2 are same and that is R and let us say C1 and C2 is also same which is C okay then I get this function is R2 C2 S2 RC3 minus AB0 S plus 1 what is this why I am doing this please look at my transfer function for low power SS square Omega 0 by Q into S plus Omega 0 square if I create Q is equal to this and Omega 0 equal to this then I am actually doing bike what is that clear if I choose my Q which is under root R1 R2 C1 C2 divided by this R1 C1 mind this this and I choose my Omega 0 is 1 upon R1 R2 C1 C2 under root of that then I am essentially converting this function into SS square plus Omega 0 by QS plus Omega 0 square which is my bike where transfer function for low pass is that clear abhijay low pass catcher function banana I converted it equivalently in this form this we already said by theory now if it you can see the expression between the two is identical so they are identical only thing the values correspondingly should be like this if these values are there these two functions are identical is that correct that means with these values this function will represent a low pass filter is that clear you see this bike bike ride function which is this SS square Omega this we have already proved by theory this is a bike ride though poles and each I know I equivalent in a sir now please remember what did I do I have to implement this function so I said okay here is a circuit with me I tried this circuit by my earlier theory also but I know I put this circuit I evaluated this transfer function is that okay then I say if I compare with my bike ride function I get these values and if I get these values that this function and that bike ride function is identical is that correct since that was a low pass filter this also should do me a low pass action is that clear with cut off frequency now much 1 upon RC R square C square means 1 upon RC and Q is RC divided by this much is that clear so if I get this the cut off frequency is 1 upon RC Q is 1-3 upon AV 0 and for this can you think why I put this condition Q is AV 0 should be less than 3 what will happen if AV 0 is greater than 3 what will happen look at this function. So minor as poles will go into the right half plane okay so what happened what stability got keep ways margin I am sure 180 save. This come up all I am sure left half may run a right half may jara condition is that now condition clear this low pass filter will keep acting as a low pass as long as AV 0 is less than 3 AV 0 is decided about what is AV 0 value there 1-R2 by R1 or which is a so R3-R3 by R2 R3 by R2 ratio should never be greater than 3 is that correct it should be never be greater than 3 if that value is never greater than 3 then stability will achieve this function will implement a low pass filter is that correct at this cut off what is the fall it will start at this cut off. Is that correct. What I am trying is. What I am trying is then I am not sure whether face stability is guaranteed so what make a filter is that clear I want ideally this so I say okay I want to come as close to the ideal value so poles is that clear so a definition say I am going to be a filter is by quiet function okay. Okay. Is that correct this will become a high pass okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay okay. I already explain you how 0 is a point is say output if you have 2 paths out of phase at a given frequency they have same value then the 0 is created output goes to ? is that correct that condition always can be created by proper choices of frequency as well as the components you use. This is another which is integrated circuit filter, this is an IC filter, this is all component used. What is the difference between operational amplifier and operational trans conductance amplifier? So if I have an amplifier whose output current is controlled by input signal then I have an operational trans conductance amplifier, typically I will not show you the buffer stage which I have not shown you, I will not show you the output, it should be removed, so amplifier is modified a little bit, defam plus gain stage, two gain stages are applied and such is called OTA, operational trans conductance amplifier, forget about what is inside this, OTA, you have its symbol, what is the difference you see, so you have a different signal of V2-V1 or V1-V2 and there is an output current. And there is a bias current called I bias, you see, it is output current I out, so its gain is called Gm, that is transistor Gm or normal Gm of defam, Gm1 plus Gm2 is actually Gm effective, multiplied by K, K is a multiplying factor, so I can improve the trans conductance by this K factor, okay, size double triple, so K is essentially a size factor, okay, a amplifier may a transistor Gm, 2 beta dash W boil into I bias, so this is the function, what is V out, current, please remember, is any current can go here, no current can enter open, so whatever is coming here must go through the capacitance, is that point clear, no current can enter open, the current can only pass through capacitor as it cannot get into this input open, okay, so I out into 1 upon CS is my V out, so I out by V in is capital Gm, which is what the trans conductance amplifier give and assume right now K is 1, okay, so Gm is Gm, however, I out by trans conductance, capital Gm times V in minus V out, so V in minus V out is the difference potential, so Gm times Vd is the actual current which is coming out, correct the terms, so V out by V in is 1 upon CS upon 1 upon Gm, Gm by C per a pole, is that correct, Gm is conductance, so 1 upon Gm is resistance, so 1 upon RCS, low pass filter function, 1 upon RCS, pole is that 1 upon RC, but R is 1 upon Gm, so Gm upon C, this is the pole, is that correct, let us say I want a low pass which has a very high cut off frequency, so what does that mean, that is a filter has a bandwidth of 10 mega hertz or 100 mega hertz, C should be small, but C can be created in a silicon circuit, whatever smallest 0.01 perform, one femto farad, tens of femto farad I may create, but its only proportionally Gm should be reduced, isn't it, sorry Gm should be increased, Gm has to be increased what will happen here, size has to be increased, so if there is such a big transistor and there is such a big capacitor, then bandwidth can be increased, but in real life you will not be allowed to increase W by L 4, 8, 12, so this cannot be increased, this cannot be reduced, this means that bandwidth is always limited, is that correct, why Gmc filters are not very very popular, so they are used, where they will be used, less than a mega hertz cut off you want, 100s of kilo hertz, 500 kilo hertz, so this simple filter can be used, what will happen to you, Gm will have to be increased, alternatively where can we increase Gm, I bias say, but if I bias is increased then power dissipate, okay, so we have to now worry in a chip, how much power I will be given to dissipate, what is the smallest value of capacitor I can create during whatever processing I have and therefore what is the maximum size I will be allowed to because the area constraint, so maximum frequencies can never be greater than a mega hertz, is that correct, why mega hertz, that is maths, but in reality such OTA filters can be used only for limited frequency range up to a mega hertz maximum frequency range, preferably 500 kilo hertz, okay, this is the maximum frequency you will get, okay. This C which you can see, why cannot be small, in this we have just said that there are parasitics, they are all coming in parallel, so you can actually make it small, but the rest of the capacitance you will kill it, one of C1 plus C2, C1, C2, C3, so it is difficult to reduce C, net C, difficult to increase GM and there we say GM by C is limited up to a mega hertz or preferably 500 kilo hertz, most of the low frequency continuous filters are OTA filters, most of the low frequency up to 100 kilo hertz, guarantee it works fantastic, so GMC filter, what is the advantage, low power relatively, very few components, so very small chip, very cheap chip, okay and can filter it up to few kilo hertz, 100 kilo hertz, okay. These filters are extensively used in almost every hardware, where audio signal frequencies are in nature, whatever systems you are looking, mostly in audio, then these filters are ideal. This is also a bike ride, because it also uses the same low pass function, I will tell you a figure, 2 OTAs and 2 capacitors can be manipulated by different signals at V1, V2, V3, V3, 0, 1, 0, 1 and you can create all 4 filters out of that, we will come back to it, like next time I will start on this, just wanted to show you, abhi jo ek dikhaya maine issi ko use krte hua, issi theory ko use krte hua, hum ne ek universal filter banaya hain, jo ki chaaro filter design kr sata hai, but none of them will be good, iss ke honne ke ba, then we will show ke a chahi chahiye toh fir kya ka, toh fir butter berth aur shebe chahi tarah najar nalinga aur achha filter banaya hain, okay, yeh circuit mein aapko fir se batonga, just to show you that same block can be utilized to make universal.


This is Acts chapter 20, I've entitled this message, shepherds and wolves, sheep and goats. Shepherds and wolves, sheep and goats. Look with me at Acts chapter 20, beginning in verse number 17. It says now, from Miletus, he sent to Ephesus and called the elders of the church to come to him. And when they came to him, he said to them, you yourselves know how I lived among you the whole time from the first day that I set foot in Asia, serving the Lord with all humility and with tears and with trials that happened to me through the plots of the Jews or the Jewish leaders. How I did not shrink back from declaring to you anything that was profitable in teaching you in public and from house to house, testifying both to Jews and to Greeks of repentance towards God and faith in our Lord Jesus Christ. And now behold, I am going to Jerusalem, constrained by the Spirit, not knowing what will happen to me there, except that the Holy Spirit testifies to me that in every city, that imprisonment and afflictions await me, but I do not account my life of any value nor as precious to myself if only I may finish my course and the ministry that I received from the Lord Jesus to testify to the gospel of the grace of God. And now behold, I know that none of you or none who are among you whom I have, or whom I've gone about proclaiming the kingdom, you will see my face again. Therefore I testify to you this day that I am innocent of the blood of all, for I did not shrink from declaring to you the whole counsel of God. Pay careful attention to yourselves and to all the flock in which the Holy Spirit has made you overseers. To care for the church of God, which he obtained with his own blood. I know that after my departure, fierce wolves will come in among you, not sparing the flock. And from among you and from among yourselves will arise the men speaking twisted things to draw away disciples after them. Therefore be alert, remembering that for three years I did not cease night or day to admonish everyone with tears.  This is Paul at the end of his third missionary journey. He's circling back and he's revisiting churches that he has established both on his first and second missionary journeys. Ephesus is one of the primary apostolic centers that Paul has established. It at this time becomes the largest church, probably in the world at that time. It's meeting in multiple different locations in the city of Ephesus. It's thriving, it's flourishing, it's filled with the power of the spirit. Miracles are happening, people are getting saved. You can read in the book of Acts about when Paul goes to Ephesus and begins to overturn spiritual darkness, principalities and powers. And there is really a revival that begins to break out in the city of Ephesus. Now, a couple of years later, it's flourishing and it's growing. And Paul is on his way back through knowing that this is probably going to be his last time speaking with these leaders that he's trained and he's led. And so he's traveling by ship in the Mediterranean. He comes to Miletus, he stops there and he calls for the elders of Ephesus to come and meet him. It's 50 miles. These elders, these pastors, these leaders walk 50 miles to come in to meet with Paul. And Paul knows by the Holy Spirit and by discernment, this is going to be his last chance to speak to them, words of encouragement. And Paul is with tears and with passion and mixed emotions, kind of wrapping his spiritual arms around these leaders and he's giving them admonitions, warnings and exhortations. And as we just read, he warns them about a great number of things. And the reason why he's leaving them with this warning is because Paul knows several things. Paul knows that what begins pure can become tainted. Paul knows that what starts powerfully can become weak over time.   And so this is why Paul is speaking to them because all of these things, how is it that something pure becomes corrupted? How is it that something that starts motivated by heaven becomes fueled by hell? How is it that something powerful can become weak and powerless? It all boils down to Satan's primary tactic when it comes to the church. And it's one word, it's the word deception. When deception is introduced into the church, when deception is introduced into the people of God, who are the bulwark and the buttresses, as 1 Timothy says, of truth. When the enemy creeps in either from within or from the outside, his tactic is always to bring deception because deception weakens. Deception undermines, deception decays and it corrodes. It takes away the foundations and the footings and this is what Paul is concerned is going to happen now that he's not going to be there. He tells them, he says, I know, I know, I know. And I've been warning you every time I've been around you with tears and you guys are looking at me like I'm crazy. It's like Paul's meeting with the elders around a conference table and he's in tears every time he's with them, telling them, guys, you gotta keep this pure. Guys, we gotta keep Jesus the main thing. We have to listen to the word of God. We have to be a people of prayer. And the elders are probably looking at him like, Paul, why are you so emotional all the time? Paul, look at the stat books, look at the growth, look at the salvation, look at the baptisms, look at what God's doing, look at how new locations are popping up all over the place in Ephesus. We're overturning idols and there's breakthrough. Can't you just celebrate the victory? But in the back of Paul's mind, he knows. He knows that the enemy is not going to leave what God has started uncontested. He knows that now that I'm not going to be here, the enemy's gonna come in and the way he's going to come in is he's going to work his way in through deception. And Paul's talking to and about three groups of people. In this chapter, there's really four groups of people that are mentioned. There's apostle, that's Paul and his apostolic team. But he's addressing three different groups of people. He's addressing number one, shepherds, which we'll talk about here in a moment. Wolves and the flocks of God. Shepherds, wolves and the flocks of God.  He says, you need to know this for the health of the church and for you to be able to lead the church of Ephesus through challenging waters. You're gonna need to know who these people are. Here's what's interesting. In church history, Ignatius, who's one of the early church fathers, after Paul actually writes in his memoirs that the church of Ephesus went through a season of decline and deception, but actually because they had these words of Paul, prophetically spoken years earlier, the leaders went into a season of prayer and fasting, repented and God renewed the lampstand of first love back to the city of Ephesus. So they adhered, they listened to the admonition of Paul. And I think we need to be careful, even here in the 21st century, because if we're not careful, the tactics of the enemy are the exact same today as they were then. You see, the enemy doesn't have new tricks. Why? Because the old ones work. And his tactics are deception. You know, the devil, when he wants to deceive, never shows up, knocks on the door of the church and says, hello, my name is Satan. I would like to come in and I would like to influence what's going on here and destroy everybody in your church. That's not how it happens. He doesn't do that in a church. He doesn't do that in a denomination. He doesn't do that in a movement and he doesn't do it in a family. He's stealth and he's subtle and he comes camouflaged as something other than he is. So this morning I want to walk us through what are shepherds, what are wolves and what does it mean to be the flock of God? Paul identifies these three groups of people and he calls us to pay special attention to each one of them. Let's talk about shepherds. Who is Paul talking to in Acts chapter 20? Says he gathered the elders together. There are three titles in this chapter that Paul uses three different words that address the same group of people. Number one, it says elders. Those are the spiritual qualifications of the leaders of the church. They're elders, which means they're spiritually mature. The other word that he uses is the word overseers. He addresses them and he says, remember that God has made you overseers of the flock of God. That is from the Greek word that we get Episcopos and it means to be up on a high vantage point, looking down and being able to see things from a higher perspective. It means to be an overseer. And while elders speaks about the spiritual qualifications, an overseer is actually talking about the function of what they do. And then the last title that he uses for this group of people is he calls them shepherds. Why does he call them shepherds? Because the people of God are called the flocks of God, the sheep that God cares for and shepherds are those who lead the sheep and they do it by being in the midst of the people because in many ways, they're sheep too.  It is actually a calling from the Holy Spirit. And that's what Paul says. Remember it was the Holy Spirit who called you to be overseers. You don't appoint yourself to be a pastor. You don't appoint yourself to be an elder. You don't appoint yourself to be a spiritual overseer. It's the work of the Holy Spirit. And here's the definition of a shepherd. It's those who have been called by Jesus to lead his church. And I'm grateful for pastors and shepherds. I'm grateful for those who've pastored me in my life.  The other day during our vacation, I met up at Gull Lake Bible Conference Grounds with another pastor who's been a pastor in Grand Rapids for 39 years of the same church. I've been here 26 years. I'm a rookie compared to him. And every year he comes down here and we'll meet up and we'll go for a walk, a walk and talk. And so we walked that day four miles and he just said, hey, how are things going? I listed off a couple of things that were going on and just kind of random, we sat down and he said, Lee, are you familiar with the game Jenga? I'm like, oh yeah, I don't know. I played that game with our family.  Are you taking care of yourself? And it hit me, it struck me when he said that, that this man is a pastor to pastors and how he was caring for my soul, even though I'm a pastor. You know, pastors need pastors and sheep need pastors. Sheep need shepherds. It's those who are not appointed by men, but they're appointed by the Holy Spirit, have been called by Jesus to lead his church. And here's what Jesus or here's what Paul speaks to shepherds. He says, take heed to yourself. That's the new King James or pay careful attention to yourselves and to the flock of God. A shepherd's number one responsibility is to take care of himself. It's to examine himself. It's to make sure that he's in a faith. So for my example, I can't get up here and preach to you something that Jesus hasn't worked out in me. I can give you information, but I can't give you impartation. I can give you information you can take home and file away in your notebooks, but the things that are gonna be planted in your heart that will bring transformation and change in your life have to be something that I first have examined, submitted and allowed God to do in my own heart. My first responsibility is to be pastored before I can ever pastor. And every true shepherd has to have pastors in their life, but I believe every sheep has to have a shepherd in their life where they recognize, no, these are spiritual leaders that God has appointed in my life. And the responsibility of shepherds is to feed and to lead the flock of God. It's to amplify the voice of Jesus who is the great shepherd. How many are grateful that Jesus is our great shepherd? And he's a wonderful shepherd. He's a beautiful leader. We sang about him this morning, sang to him this morning. He's a powerful leader. He's God, he's good, he's merciful. He knows exactly what we need. Psalm 23 is such a beautiful example that he leads us besides still waters into green pastures. And you know the beautiful thing about Jesus? As our shepherd, it says, yea, though I walk through the valley of the shadow of death, you are with me. You know, Jesus is your shepherd, not just on the mountain tops, but he's your shepherd even in the valleys.  He's a good shepherd. But the job of a shepherd in a church, a pastor, a leader in a church is not to have our own voice, but it's to amplify the voice of the good shepherd, Jesus. And ultimately, it's to defend the flocks of God with our whole lives. It's to pay careful attention to the flocks of God. It's to pay careful attention to what's going on and to defend them from wolves. Jesus said in John 10, verse 11, I am the good shepherd, this is Jesus. He said, the good shepherd lays down his life for the sheep. The hired hand is not a shepherd and he does not own the sheep. So when he sees a wolf coming, he abandons the sheep and he runs away. Why? Because he's preserving themself. The wolf attacks the flock and scatters it, but the man runs away because he's a hired hand and he cares nothing for the sheep.  And Paul is communicating to these leaders, this is your primary responsibility. Number one, take care of yourself and then take care of the flocks of God. Defend them, protect them, nurture them, feed them, lead them and defend them against wolves. Which leads us to the second thing that Paul, the second group of people that Paul identifies, which are wolves. Every time I read this and I think about wolves, I think of, it's not actually a wolf, but I think of the old cartoons I grew up on. Wiley the coyote, anybody remember that? The road runner and Wiley the coyote who is always trying to, he's always trying to get the road runner. He's just Wiley, he's scheming, he's strategic. This is what Paul describes as a wolf. A wolf is a predator. And in this particular case, when Paul's talking about, I know this, that as soon as I leave, as soon as the apostolic leader of this church is no longer there to protect and to pray and to give you a perspective that maybe you guys don't have, I know that the enemy's gonna send in wolves. Fierce, ravenous wolves because that's what wolves do. Wolves are predators. And in this case, wolves are false teachers or voices of influence who present themselves as either sheep or shepherds but have a secret motive or ambition besides bringing the flocks of God to maturity in Christ. They're false teachers. They're false influences that try to come in from the outside or rise up from the inside. Jesus spoke of these false prophets, these false leaders. In Matthew seven, he told his disciples, beware of false prophets who come to you in sheep's clothing but inwardly are ravenous wolves. You will recognize them by their fruits. Grape's gathered from thorn bushes or figs from thistles. So every healthy tree bears good fruit but the diseased trees bear bad fruit. Jesus said, you're gonna know the difference by the fruit of their lives. But he said, beware of wolves. Beware of wolves. And I want you to know today that there are wolves in our world and in our culture who are inspired and fueled by hell whose appetite is their own stomach and you are their prey. And you know what's interesting is a lot of us, a lot of Christianity kind of lives like there is no devil. It's like we believe in God and obviously we believe in one another and we love Jesus and we love the Bible but there's a lot of Christians out there who kind of act as if there's no devil and if there's a devil like he lives in Papua New Guinea someplace and he can't get a ticket out of there to come to America. He only lives among those people that it's not really in America.  It's just kind of he's way over there or maybe he was back in the Bible times.    They come in nice because nobody's threatened by a sheep. Nobody goes to the petting zing goes whoa, a sheep. Stay away, that thing's fierce. No, kids just run up and pet a sheep. They just look soft and fuzzy.   But a wolf is a predator and a wolf is looking for an opportunity. A wolf when it comes from the outside of a flock will circle it and he'll howl to intimidate the flock and then he'll attack from the outside. But according to Jesus sometimes wolves that are deceivers in the church will actually dress up to look like sheep. Why? So they can get into the flock. It's all about access. And sometimes in our day the wolves are dressing up as a YouTube channel, as an Instagram account, as a Facebook post, as a newspaper article, as a book that's been written, as a friend who invites you to come and check out this person who's got deep revelation. That's how he dresses up in sheep's clothing and what they're trying to do is they're trying to get access to your life. They're trying to get access to your soul, why? So that they can consume you for their own benefit, for their own pleasure. How do you know the difference between shepherds and wolves? Well, here's the difference. True shepherds lay down their lives for the flock.  Shepherds will not shrink back from the whole counsel of God. That's what Paul says here. He said, the whole time I was with you, I did not shrink back from proclaiming to you the whole counsel of God. You know, one of the reasons why the church, I believe in this cultural hour, is in the position that it's in, is because over the last 20, 25 years, there are pastors in churches who refuse to preach things that are in the Bible because they did not want to irritate or offend and lose people. And so we've compounded that by 20 years. We just preached the nice, happy stuff. Your life's awesome.  Get rich, prosper, succeed, and achieve. And we want to tell everybody what they want to hear, but not everything in the Bible is rosy and gold and not everything in the Bible. Jesus said, my words are an offense. He intentionally does that. So if we go through the Bible and we cut out all the passages that people don't want to preach, it would account for the malnutrition of the body of Christ over the last two decades. Paul said, no, I'm a shepherd and I'm an apostle. Why? Because I preached to you the whole counsel of God. Oh, do you know how big your church could be if you just don't talk about that issue? Don't go there. Don't say this. Yeah, it doesn't matter. You can have a church full of people who never walk in their inheritance.  See, shepherds are appointed by God and recognized by men. Wolves appoint themselves. Shepherds point and lead to Jesus. Wolves will draw you to themselves away from Jesus. If you're being influenced by a voice that once upon a time you were passionate about the presence of God, you loved the place of prayer, the Bible came alive on the inside of you, you were in awe and worship and now you've grown cold and you become more sophisticated and you're reading more broadly or you're listening to other voices or there's other things that are passionate and it's because of somebody's influence in your life, run because it's a wolf. How do you know if it's a shepherd because they're drawing you towards Jesus? They're echoing the voice of Jesus. Here's a question you've got to ask. Is do they echo the voice of Jesus or are they eclipsing it? Does their life align with the life of Jesus or contradict it? Are they coming to feed you or to feed on you? Is the fruit of their life holiness or licentiousness? That's the difference between sheep and wolves or shepherds and wolves. And today here's some of the deceptions that are facing the flock of God. These are so key. These are the tools that hell and wolves are using right now to try to destroy the underpinnings of the church in Western civilization because he knows that the only answer for turning around this mess that's in our world is a church that is devoted to Jesus. Here are the five weapons that the enemy is using. The deception and what Paul calls in Galatians one, a different gospel. It's a gospel, but it's a different gospel. Number one is syncretism, which is the mixing of spiritual influences with the truth of the gospel of Jesus Christ. I can have a little Buddhism and a little bit of Jesus.  I can dabble in witchcraft. Do you know that the witchcraft is on the rise during the pandemic in 2020? The number one best-selling book among girls 20 years and younger was about wicked witchcraft. It's somebody said, our culture is really becoming secular. Yes, our culture is becoming secular, but it's on its way to becoming pagan. And it's happening even in a church where we're embracing things and we're just kind of mixing it all together. I can have this and that. No, Jesus is the way, the truth and the life, period. Number two is postmodernism. Postmodernism is really more of a philosophy, but it's infecting even the gospel in the church. And here's what it says. Truth is plastic and it's relative. And therefore we have to reshape the gospel to fit our culture. Listen, we build our faith, not on the culture stone, but on the cornerstone who is Jesus. And the word of God remains forever. The grass withers and the flowers fade, but the word of God remains forever. Jesus isn't up in heaven going, I gotta put out the fifth edition of the Bible where we go through and edit some things and shift some things to fit American culture. No, Jesus is in heaven and he has sat down because his work is finished. It is done. He alone is the alpha in the omega, the first and the last, the beginning and the end. Postmodernism says, oh, we gotta tweak and we gotta change, remove some things, form some things, modernize some things. No, we need to go back to the cornerstone of the gospel. Third deception that is in the church is libertarianism. I'm not talking about the political branch, so don't write me emails. Libertarianism, liberty comes from the word freedom and libertarianism, theologically, it's all about grace. It's cheap, greasy, easy, permissiveness that says, go ahead and walk in the flesh. You don't have to walk in the spirit. Do whatever you want. Jesus will forgive you and you're saved. You said a prayer when you were in fifth grade, you're on your way to heaven, that's good enough. That's libertarianism and it contradicts everything that's in the gospel. Universalism is number four that says everyone will ultimately be saved and go to heaven.  Again, you gotta go through the Bible and you gotta tear a bunch of pages out to get there. It sounds like a great message. Oh, all good dogs go to heaven, it's wonderful. Everybody goes to heaven except Chicago Bears fans. But everybody else goes to heaven except, and then you pick out your group of people that you think shouldn't go to heaven but everybody else goes to heaven. That's universalism. But Jesus said, narrow is the way that leads to life. Wide is the path that leads to destruction. The last deception that is facing the flock of God is legalism and legalism says you can save yourself by working, doing more, working harder, being better, striving, keeping the law. If you just perform better and sometimes it's a religious legalism, many times it takes the form of self-helpism. That I can just fix myself. I can improve my life. I can live my best life now. But really all that is is foolish pride and our arrogance because if we could fix ourselves then Jesus had no need to come and die on the cross for us. But Jesus gave it all. He shed his precious blood. Why? Because his blood alone can save. And his Holy Spirit alone can transform and change. These five are the deceptions that are facing the flock of God. And you need to watch out for them, beloved.  Oh, he's got a church or he wrote a book or this person seems like a great person or I follow them on Instagram or I see this post on Facebook. Beware if it's any of these things because those are wolves and sheep's clothing. I wrote this this week, beware of anyone teaching you a doctrine or new perspective of the Bible that has been formed on the anvil of culture and not forged in the fires of the Holy Spirit and attested to by those who paid in martyr's blood. Haven't preached in a while, so my voice. And that has not been paid in martyr's blood throughout the ages of church history. Ours is a faith to be received, theirs is a lie to be deceived. These are the deceptions that we need to be careful for. The third and the final group is the flock. It's the flock of God made up of both sheep and goats. See when you read the Bible and it talks about flocks, there will always be two groups of people or two groups of animals. There's sheep and there's goats. We have a picture here. The other day, Jane and I took our grandson, Owen, to the John Ball Zoo and they have a pitting zoo. So here he is, pitting a sheep. Bah, nice little guy. But then there's this other one, if they'll put the next picture up. That, is that, no, do one more. That is a goat. And while we were standing there, the guy who was taking care of it all came up to Jane and he says, you need to take that thing out of your pocket.  You need to take that out because that goat will come up behind you and it will take it right out of your pocket and chew on you. He didn't say that about the sheep. Said it about the goat.  Jesus said in Matthew 25, at the end of the age, at the judgment, he's gonna separate the sheep from the goats. And the reason for that is today, our animals have been domesticated, but in ancient times, sheep and goats were indistinguishable. They looked like one another. You could only tell the difference by their behavior. That was the only way you could tell the difference between sheep and goats was by their behavior. And what that requires for the shepherd is examination. That's why in Psalm Proverbs 27, the writer tells us, he says, to examine your flocks and know the conditions of your flocks. But it also, for all of us, means we need to examine our own hearts. Am I a sheep or am I a goat? Well, here's the difference. Let me lay it out for you. Number one, here's sheep. Sheep know the voices that are shepherd. They spend time with him and they obey his voice. So whether that's talking about Jesus as the great shepherd ultimately, we spend time with Jesus and we know his voice. And when he speaks, we listen and we obey. That's, we know we're a sheep. When Jesus speaks, that's the authority.  The first voice that they hear is the voice of the shepherd and it bonds them to the shepherd. And that's what happens when we're born again. We get bonded to Jesus. But also, it's also true of spiritual leaders in our life as well. That when we get counsel or advice from spiritual leaders in our life, not in a controlling, dominant way, but we actually are looking for that advice. We're looking for that counsel. Why? Because we know that they care for us. A sheep knows the voice of the shepherd. Here's the second indicator of a sheep. Sheep stick together. They're flock animals. They stick together. In fact, if one sheep goes running off a cliff, the rest of the sheep will follow.  Sheep follow the shepherd wherever he leads them. And sheep are cautious. They don't make quick changes or movements. They need to be protected. And it's the last time you heard of somebody dying from a sheep bite. Doesn't happen. But goats, they're a whole different story. Goats ignore the voice of the shepherd. It's been said in the agricultural world that shepherds lead sheep, but they have to chase goats. Goats are driven by curiosity and their own personal appetites. Goats are independent. They roam, they're stubborn, they're self-willed. Goats will ram the shepherd or other individuals from behind when they're not looking. And goats are reckless and will eat anything, including garbage. I think when Paul is talking to the shepherds and the leaders, he tells them to examine themselves. And there have been many occasions where I've sat in the presence of Jesus and said, Lord, am I being a good sheep or do I have goat tendencies in my heart? Or it's like, thanks for the suggestion, Lord, but I'm gonna go do my thing. Or I've got my own desires and I'm gonna pursue it. Have I bucked at leaders or people that have cared for me from behind when they weren't looking? Have I been stubborn and self-willed? And have I been feeding on garbage? Or Lord, am I being a sheep, which means I'm growing, I'm listening to your voice, I'm following where you're leading, I'm eating and I'm feeding on green pastures because that's where you're taking me and I'm being cautious and taking heed to my own heart. I can't answer that question for you in relationship with your sheep or a goat.  Just like Paul told those pastors, take heed and pay careful attention to yourself and, I want you to stand with me if you would this morning, shepherds, wolves, sheeps and goats, take heed. Paul gathered with the elders of Ephesus with tears in his eyes because he knew the significance and the power of the moment that he was living in and he wanted them to thrive. Verse 32 says, I want you to inherit, I want you to attain the full inheritance that God has for you. And today, that's my desire as a pastor. It's for all of us that we would not just make it to heaven but we would actually walk in the full inheritance that Jesus has for us here and that we would walk free from deception. God's looking for a people that will lean into him, know his voice and be used to demonstrate his glory on the earth. I want to pray over us before we dismiss this morning. Would you just buy your heads with me? Lord Jesus, first and foremost, we recognize you as the head of the church, the cornerstone of all that God is building and the shepherd of our soul. Jesus and we say we love you and we need you. Today, Lord, I'm asking that you would give us eyes of discernment, that you would give us hearts that are soft and pliable. And in the places in our life, maybe we're offense, hurt, bitterness, pride, arrogance, selfish ambition where it's crept in and causes us to miss you or to resist you. Lord, today would you give us pure, clean, unadulterated soft hearts to you that we might follow you and those of us who've been given the task of leading others and every parent, every mom, every dad who's been given the responsibility to lead their families. Lord, that we would lead others as we are led by you with grace, mercy and truth. Creating us a clean heart, oh God. Help us to walk in truth. Help us to walk in power and help us to be victorious overcomers in the day that we live in.


So far we've talked about handwritten notes, but it may well make more sense to use PowerPoint. So in this video I'm going to show how you can record voiceover and annotations on PowerPoint using a Microsoft Surface. So here we have PowerPoint. When you install Camtasia it gives you an add-in. If you click on add-ins you'll see over here there's a record button. I'm not going to press it because I'm already recording obviously. I started to set Camtasia going before I started this. But if we now go back and run the presentation we can go forward or backwards. Down here we can click and get a pen and we can annotate circle things. Go on to the next slide, draw diagrams, point things out, ask questions and so on. This can of course be done in class because anything you write on PowerPoint will appear on the data projector. So it can be a much better way to write complicated stuff than on a whiteboard or blackboard in a large lecture theatre where most people can't see it and where it's not captured by the lecture recording system. But also the whole thing is now being recorded. When you finish, we'll discard the annotations in this particular case. And then if you set it going as an add-in it will ask if you want to stop. In my case I set it going beforehand. So it's recording PowerPoint a good idea or not. Well the research suggests that it's found by most students to be less engaging than handwriting. However if you already have huge numbers of slides and especially if you have detailed equations or diagrams or tables or something then it can be very useful but the recommendation is cut words, write them in. So if you're doing a fair bit of that, circling things, annotating things, writing things in, then it's not so bad.