4 CALCULATE THE BIAS-POINT AND SMALL-SIGNAL LOW-FREQUENCY GAIN OF THE COMMON SOURCE AMPLIFIER FROM FIGURE 12

12. - SOLUTIONS
SOLUTIONS

12.4 Calculate the bias-point and small-signal low-frequency gain of the common

source amplifier from Figure 12.46 if V

t

= 0.7, β = 240 µA/V

2

, and the nMOS out-

put impedance is infinite. Let V

BIAS

= 3 V, V

DD

= 15 V, and R

L

= 10 kΩ.

At the bias point of V GS = 3, I DS = 240•10 -6 • (3-0.7) 2 / 2 = 0.65 mA and

thus the output voltage is V OUT = 15 - I DS R L = 8.5V. g m = 240•10 -6 • (3-

0.7) = 0.55 mA/V. v out = -g m R L v in , or the gain A = v out /v in = -g m R L = -