Question

Given the following Op Amp characteristics: Rin=2.0Mohms, Rout=75ohms and Avol=200,000. Determine the voltage gain, input and output impedance, output voltage. Compare this o/p voltage to that would have occurred if the buffer had not been used.

Answer 1

R_in = 2 m ohm r_out = 75 ohm a = a_vol = 2 times 10^5 beta = 1 input resistance = (1 + a beta) R_in = (1 + 2 times 10^5) 2 = 4 times 10^5 times 10^6 = 40 g ohm out put resistance = R_out/1 + a beta = 75/1 + 2 times 10^5 = 37 . 5 times 10^-5 = 0 . 3 7 5 m ohm voltage gain = a/1 + a beta = 2 times 10^5/1 + 2 times 10^5 = 1 v_o /v_I = 1 v_o = V_I if buffer had not been used V_f = R_in v_o/r_1 + R_in beta = V_f/V_o = R_in/R_1 + R_in voltage