D 13.42 It is required to use the current I5 in Fig. 13.14 to bias an npn differential pair. The transistor Q5 is identical to Q2, and R5 is equal to R2. The differential pair has two equal collector resistances RC connected to VCC, and the output voltage vO is taken between the two collectors.
(a) Find an expression for the differential gain Ad in terms of (RC/R5) and (IS5/IS1). Comment on the expected temperature dependence of Ad. Neglect the effect of finite βN.
(b) Specify the values of R5 and RC required for I = 20 µA and Ad = 6 V/V. Let the emitter areas of Q1 and Q5 be in the ratio 1:4.