Question

(10) In the following cascoding circuits, Qi, Q, Q, are all DC biased in saturation mod DC current of Ip 0.4 mA. They have transconductance of Kni Km-4 mis and The Early voltage for the NMOS' İs V·,-10 V, and VAP-12 V for PMOS,,respec a) (3) Determine the overdrive voltage l'or for each Mosnr. b) (7) Calculate the intrinsic voltage gain (van) of each circuit Voo lo Vet Q2 v.

Answer 1

"I_D = 0.4mA V_A - N = 10V rightarrow NMOS V_A - P = 12V rightarrow PMOS gm1 = gm2 = 4ms V_ov = (VGS - vt) rightarrow over drive voltage Current equation in saturation is I_D = 2k(VGS - Vt)^2 I_D = 2(V_ov)^2 rightarrow 1 and gm = 2k(VGS - Vt) gm = 2k(V_ov) rightarrow 2 K = gm/2(V_ov) rightarrow 3 from 1 and 3 I_D = 2 times gm/2V_ov times (V_ov)^2 I_D = gmV_ov a) For Q1: - I_D = gm1.V_ov1 V_ov1 = I_D/gm1 = 0.4mA/4ms = 0.1v V_ov1 = 0.1v For Q2""- I_D = gm2.V_ov2 V_ov2 = 0.4mA/gm2 = 0.4MA/4ms V_ov_2 = 0.1v For Q3: - I_b = gm3V_ov3 V_ov3 = ID/gm3 = 0.4mA/2ms V_ov_3 = 0.2v gm3 is not clearly visible so it is assumed as 2ms. b) Voltage gain: - v_0/v_in = -gm1r01 gm1 = 4ms r01 = VA - N/I_D = 10v/0.4mA r01 = 25Kohm so voltage gain = -gm1r01 = -4 times 10^-3 times 25 times 10^3 v_0/v_in = -100 small signal circuit is: - Now V_0 = -gm1vgsr01 r01 = VA - N/ID = 10v/0.4mA r01 = 25kohm = -4 times 10^-3 times 25 times 10^3 vgs v0 = -100vgs and vgs = vi from the above circuit so v0 = -100vi gain v0/vi = -100"