Analog Fundamentals: Amplifiers

-October 06, 2013

Analog to digital converters (ADCs). Digital to analog converters (DACs). Sensors. Actuators. Amplifiers. These are all terms that are used when it comes to describing the analog world we live in. How are they connected and how do they work? In order to better understand, we will review the basics on amplifiers. 

Amplifiers, also referred to as amps, allow designers to connect the sensors and actuators to their converters as shown in Figure 1. Amplifiers turn a low level, high source impedance signal into a high level, low source impedance signal that converters can understand.



Figure 1. Analog to Electronic Signal Processing

There are several types of amplifiers, which include:

  • Operational amplifiers (op amps)
  • Power amplifiers
  • RF amplifiers
  • Instrumentation amplifiers

The most common device is the operational amplifier, which is a three-terminal device that can amplify small signals that are present at its inputs. They are called operational because it can be configured to perform different operations or functions, such as positive amplification, inverting amplification and filtering. Operational amplifiers are typically used as the fundamental building blocks for analog design. Op amps can do virtually anything:  amplify, filter, level shift, compare and drive ADCs. The circuit design sometimes becomes difficult when the system is a little bit more complex and requires multiple amplifiers, multiple passives or good matching between the passives. The most complex amplifiers are built using a combination of op amps.  


Instrumentation amplifiers are typically used for amplifying bridges as well as biopotentials.  A bridge creates a small differential signal between its two terminals.  Because of the high source impedance of a bridge, a high input impedance is required as well as high gain.  This is why an instrumentation amplifier is the perfect solution for this type of problem. 

Figure 2. The Generic Instrumentation Amplifier (In-Amp)

To dig deeper on amplifiers, I recommend listening to my ADI colleague, Gustavo Castro, who will be discussing the ins and outs of amplifiers on-demand at Design Conference: Virtual Event during his presentation: “Amplifiers: Capture Signals and Drive Precision Systems.”

If you have any questions leave a comment. Good luck designing!


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