14.6. Output Buffer Stage
It is evident from the gain result, (14.29), that the high gain depends on having a high resistance at the output; a relatively small load resistor can reduce the gain substantially. For example, suppose that the amplifier is to be used as a resistance feedback amplifier as shown in Fig. 14.6. The input is at the gate of M2, and the feedback resistor is connected back to the gate of M1. The load at the output is Rf + R2 || RO.
Figure 14.6. Opamp with feedback resistor Rf. The feedback circuit adds load Rf + R2 in parallel with external load, RO, at the output.
For a specific example, assume that RO >> Rf >> R2 such ...