Homework 4, ECE 403, NCSU, Prof. Bilbro due before lecture on Friday, 2/13/09 1)Drawa pmos current mirror with two matched p-channel FETs that is biased with ideal current source Ibias, and that is connected to some arbitrary circuit represented only by Ioutand Vout(i.e. you can’t assume anything about the relation between Ioutand Vout.) For concreteness, let’s label the transistors like the current mirror in J&M’s figure 3.4, so that the bias pmos is M3 and the load pmos M2. Showthat the low-frequency small-signal model of your current mirror is a simple passive resistor connecting voutto (small-signal) ground with rds2= 1 / ( λpmosIbias ) . 2)Consider the C-S amp from J&M Figure 3.4 and assume that M3 and M2 are matched (i.e. that both of these pmosfets have the same W and L as well as the same current model) . a)Show that the small signal low-frequency gain of this amp is (2911101222biasbiasmVdsdspmosnmospmosnmosbiaskk IIgAggIllll= -= -= -+++if the amp is unloaded (i.e. if it’s not connected to any external load.)
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Small-signal model, Early effect, PMOS current mirror, Cload Cload, total capacitance Cload