9.31 Consider the BJT differential amplifier when fed with a common-mode voltage VCM as shown in Fig. 9.15(a). As is often the case, the supply voltage VCC may not be pure dc but might include a ripple component vr of small amplitude and a frequency of 120 Hz (see Section 4.5). Thus the supply voltage becomes VCC + vr. Find the ripple component of the collector voltages, vC1 and vC2, as well as of the difference output voltage vod ≡ vC2 − vC1. Comment on the differential amplifier response to this undesirable power-supply ripple.