Using the Shockley equation, the small-signal diode resistance r D of the diode can be derived about some operating point (Q-point) where the DC bias current is I Q and the Q-point applied voltage is V Q . To begin, the diode small-signal conductance g D is found, that is, the change in current in the diode caused by a small change in voltage across the diode, divided by this voltage change, namely: