Question

D **7.124 The MOSFET in the amplifier circuit of Fig. P7.124 has V, 0.6 V and 5 mA/V'. We shall assume that Vis sufficiently large so that we can ignore the Early effect. The input signal v has a zero average. (a) It is required to bias the transistor to operate at an overdrive voltage 0.2 V. What must the dc voltage at the drain be? Calculate the dc drain current Ip. What value must Rp have? (b) Calculate the value of g at the bias point (c) Use the small-signal equivalent circuit of the amplifier to show that sig Rp and R+R2 where (d) Evaluate v,lvg and R VDD =+ 10V 0.5 ΜΩ 0.5 ΜΩ Figure P7.124

Answer 1

V_0v = V_as - v_t implies V_as = v_0 v + v_t = 0.2 + 0.6 = 0.8 V V_as = I_R_1 R_1 implies I_R_1 = V_as/R_1 = 0.8/0.5 times 1066 = 1.6 u/A since for MOSFET I_a = 0 implies I_R_1 = I_R_2 V_0 - V_as/R_2 = I_R_2 implies V_0 = V_as + R_2 I_R_2 = 0.8 + (0.5 times 10^6 times 1.6 times 106-6) implies V_0 = 1.6 V I_D = 1/2 K_n V_ov^2 = 1/2 times 5 times 106-3 times (0.2)62 implies I_D = 0.1 Ma V_DD = (I_D + I_R_2) R_D + V_D implies R_D = V_DD - V_D/I_D + IR_2 = 10 - 1.6/0.1 times 106-3 + 1.6 times 10^-6 implies R_D = 82.677 k r i_n = 2 I_D/V_v = 2 times 0.1 times 106-3/0.2 implies I_n = 1mA/V The small - signal equivalent model can be drawn as and apply KCL at node G V_g3 + V_3 I g/R_1 + in V_gs + V_0 - v_sig/R_0 + V_0/R_d = 0 Since V_A os along r_0 is infinite and open