7.4 For the amplifier in Fig. 7.10, let VDD = 5 V, RD = 10 kΩ, Vt = 1V, = 20 µA/V2, W/L = 20, VGS = 2V, and λ = 0.
(a) Find the dc current ID and the dc voltage VDS.
(b) Find gm.
(c) Find the voltage gain.
(d) If vgs = 0.2 sin ωt volts, find vds assuming that the small-signal approximation holds. What are the minimum and maximum values of vDS?
(e) Use Eq. (7.28) to determine the various components of iD. Using the identity , show that there is a slight shift in ID (by how much?) and that there is a second-harmonic component (i.e., a component with frequency 2 ω). Express the amplitude of the second-harmonic component as a percentage of the amplitude of the fundamental. (This value is known as the second-harmonic distortion.)
(a) 0.2 mA, 3 V; (b) 0.4 mA/V; (c) – 4 V/V; (d) vds = −0.8 sin ωt volts, 2.2 V, 3.8 V; (e) iD = (204 + 80 sin ωt – 4 cos 2 ωt) µA, 5%