In some cases, we need amplifiers that have high gain when the input voltage is low and decreasing gain as the input voltage increases. So this is an amplifier whose gain depends upon the input voltage! An op amp circuit such as that in Figure 51 can provide this response. Here diodes are used to isolate feedback resistors via their forward voltage drop until the output voltage rises above predefined levels.

For the circuit in given Figure, assume the forward voltage drop of the diodes is 1.4 V (i.e., they do not begin to conduct until the voltage across them is above 1.4 V). Prepare a plot of output voltage versus input voltage for this circuit.

(Hint: When diode begins to conduct, the output must be V, and this effectively just puts the 100- resistors in parallel.)