p-Amp Voltage-Follower Voltmeter
The operational amplifier voltage-follower voltmeter in Figure 4-6 is comparable to the
simple emitter-follower circuit. However, unlike the emitter-follower, there is no baseemitter
voltage drop from input to output. The voltage-foLLower also has a much higher
input resistance and lower output resistance than the emitter-follower. The voltagefoLLower
input (£8) is applied to the op-amp noninverting input terminaL, and the
feedback from the output goes to the inverting input The very high internal voltage
gain of the operational amplifier, combined with the negative feedback, tends to keep
the inverting terminal voltage exactly equal to that at the noninverting terminal. Thus.
the output voltage (Vo) exactly follows the input. As discussed earlier, the attenuator
selects the voltmeter range.