1) (2 pts) Given two voltages, v1(t) and v2(t), and given a differential voltage defines as vd(t) = v2(t) - v1(t), write v1(t) and v2(t) in terms of the common-mode and differential-mode voltages.
2) (2 pts) In order to keep a BJT operating such that the linearized small signal models are reasonably accurate, the small signal component of the base-emitter voltage needs to be on the order of 10mV. Yet for a differential pair, the magnitude of the differential input signal can be about twice that. Why?
3) (3 pts) Draw the basic PNP-based BJT Differential Pair.
4) (3 pts) We have found that the differential voltage gain of the basic BJT differential pair is given by Ad = gm*RC. How would you respond to the claim that, without changing anything else in the circuit, the gain can be made arbitrarily large by either increasing the transconductance or collector resistance. In other words, what mechanism prevents this from being true?