1 Find a the gain b output voltage vO c input resistance Rid

1. Find:

(a) the gain.

(b) output voltage, v_O

(c) input resistance, R_id, of the amplifier

(d) output resistance, R_out, of the amplifier

(e) If the 0.5mA current source was constructed using two matched NPN transistors (simple current source), what will the output resistance of the current source be?

+ 15V Q3 Q4 Vo pip Papn 200 Vr=25mV Vid 2 -Vid 2 ) 0.5 mA - 10V

Solution

(a) Replace the circuit seen looking into the drain with its Norton equivalent circuit as shown in Fig. 5. Solve for id(sc). id(sc) = Gmgvtg = Gmgvi R1kR2 Ri + R1kR2 Gmg = 1 rs + Rtskr0 r0 r0 + Rts Figure 5: Norton drain circuit. (b) Solve for vo. vo = id(sc)ridkRDkRL = Gmgvi R1kR2 Ri + R1kR2 ridkRDkRL rid = r0 + rskRts 1 Rts/ (rs + Rte) = r0 µ 1 + Rts r0 s ¶ + Rts (c) Solve for the voltage gain. Av = vo vi = Gms R1kR2 Ri + R1kR2 ridkRDkRL (d) Solve for rin. rin = R1kR2 (e) Solve for rout. rout = ridkRD (d) Special case for Rts = 0. Gmg = 1 rs = gm rid = r0