Question

Vcc Rc C3 Si C1 rs RG R1 Vs Figure -Q2 (2Marks) (b) Draw the low frequency ac equivalent h-parameter model for the above circuit in Figure-Q2. (a) Find Vos. (4Marks) (6Marks) (8Marks) . VL (c) Find the mid-band voltage gain (d) Find the lower cutoff frequency for the above amplifier.

Answer 1

DC Equivalent of the given circuit is open circuit all capacitors Redrawn V_B = C_x = (12 V) [10 k/10 k + 10 k] = 6 V R_th = 10 k Vertical-bar Vertical-bar 10 k = 5 k beta = h f_c = alpha/1 - alpha = h f_b/1 - h f_b = -0.99/1 - 0.99 = 99 Assume V_BC = 0.7 I_B = 6 - 0.7 - V_DS/5 k I_C = 12 - V_DS/10 k \r\n I_C = beta I_B 12 - V_DS/10 k = 99 [6 - 0.7 - V_DS/5 k] 12 - V_DS = 2 times 99 [5.3 - V_DS] 12 - V_DS = 1049.4 - 198 V_DS 197 V_DS = 1037.4 V_DS = 5.26 V Low frequency AC Equivalent nodal: Cap short circuit DC supply grounded hoe = 0.2 mu s 1/h o e = 1/0.2 times 10^6 = 5 m Ohm hoe R_L' = hoe (R_C Vertical-bar Vertical-bar R_L) = 0.2 mu s(10 k Vertical-bar Vertical-bar 500 k) = 0.2 mu s (11 k) = < 0.1