Question

Problem 2 The diode in the circuit below has a saturation current Is = 10-13 A and n=1. Its ID-VD curve is illustrated below for your convenience. a) Using the graphical method, determine the value of R that would result in a diode current Ip 4mA. What is the resulting voltage Vp? b) With R as calculated above, a sinusoidal signal v, 100 sin(ot) mV is superimposed on the DC source. Draw the small signal model and find the output voltage across the diode. 0.01 0.009 0.008 0.007 0.006 0.005 0.004 0.003 0.002 0.001 D. = 1.4V v, 100 sin(ut) mv 文 0 01 0.2 0.3 0.4 0.5 06 07 0.8 09 1 11 12 13 14 15

Answer 1

a) I_D = 4 MA I_D = I_s E V_D/n V_T V_D = (n^V T) ln (I_D/I_s) = (26 m)ln (4m/10^-13) V_D = 0.635 V KVL I_D = 1.4 -V_0 /R R = 1.4 -0.635 /4m R = 191.25 Ohm AC analysis r_d = n V_I/ I_D = 26 m/4m = 6.5 Ohm V_d = V i (r d/rd + R) = vi (6.5/6.5 + 191.25) = 100 sm (wt) mv times (0.0328) v_d = 3.28 sin wt MV output voltage across diode, v_d = V_D + v_d V_d = (0.635 V)+ (3.28 sin wt MV)