Consider the op-amp circuit presented in Figure Q.1. Assume non-ideal operational amplifiers are used. OpAmp1 has a differential input impedance Zin1 = 2 MΩ, an output impedance Zout1 = 25 Ω, and a differential gain (open loop gain) Ao1 = 10000 at DC. OpAmp2 has a differential input impedance Zin2 = 1 MΩ, an output impedance Zout2 = 5 Ω, and a differential gain (open loop gain) Ao2 = 10000 at DC.
R1 = 1 kΩ, R2 = 50 kΩ, and R3, R4, and R5 are all 1 kΩ resistors.
1) Calculate the DC input resistance Rin seen at plan B as depicted in Figure.
2) Calculate the DC output resistance Rout1 seen at plan B as depicted in the circuit Figure.
3) Is it necessary to propose a solution in the form of a circuit, to be placed after plan B and just before R1, to mitigate the loading effect at the output of Op-Amp1? Explain why?
Plan
Rin Rout1
OpAmp1
Vin
Zin1 - 2 MΩ Zout1 - 25 Ω Ao1 - 10000 @ DC
Vout
Zin2 - 1 MΩ Zout2 - 5 Ω Ao2 - 10000 @ DC