9.37 This problem explores the linearization of the transfer characteristics of the differential pair achieved by including emitter-degeneration resistances Re in the emitters (see Fig. 9.17). Consider the case I = 200 μA with the transistors exhibiting Vbe = 690 mV at iC = 1 mA and assume α ?1
(a) With no emitter resistances Re, what value of VBE res lts when vid = 0?
(b) With no emitter resistances Re, use the large-signal model to find iC1 and iC2 when vid = 20 mV.
(c) Nowfind the value of Re that will result in the same iC1 and iC2 as in (b) but with vid = 200 mV. Use the large-signal model.
(d) Calculate the effective transconductance Gm as the ratio of the difference current, (iC1 - iC2), to vid in the cases without and with the Re's. By what factor is Gm reduced? How does this factor relate to the increase in vid? Comment.
