The op amp in Problem 12.4 is used with the CMFB scheme shown in Fig. 12.17. The circuit is perfectly balanced except that the CM-sense resistors are mismatched with the upper resistor R_cs1= 10.1 kΩ and the lower resistor R_cs2= 9.9 kΩ. Assume the source followers and the CM-sense amplifier are ideal with gains of unity.

(a) Compute the gains a_cms and a_dmˆ’cms in (12.106).

(b) Compute the low-frequency op-amp gains v_od / v_id, v_oc / v_ic, v_od / v_ic, and v_oc / v_id with the CMFB active.

(c) Use SPICE to simulate these gains.

Figure 12.17:

Transcribed Image Text:

Vo1 Res o =Voc- VGs Res CS Vo2 .V. сте - V CM V ems Vсм - VGS