*8.70 In this problem we investigate whether, as an alternative to cascoding, we can simply increase the channel length L of the CS MOSFET. Specifically, we wish to compare the two circuits shown in Fig. P8.70(b) and (c). The circuit in Fig. P8.70(b) is a CS amplifier in which the channel length has been quadrupled relative to that of the original CS amplifier in Fig. P8.70(a) while the drain bias current has been kept constant.
(a) Show that for this circuit VOV is double that of the original circuit, gm is half that of the original circuit, and Vo vi is double that of the original circuit.
(b) Compare these values to those of the cascode circuit in
Fig. P8.70
(c), which is operating at the same bias current and has the same minimum voltage requirement at the drain as in the circuit of Fig. P8.70(b).