Question:

(a) The circuit of FIGURE is known as a transimpedance circuit used for the measurement of very small currents. Derive the relationship between the output voltage V and the input current I; i.e. if V = KI find k in terms of R₁, R₂ and R_f.

(b) Calculate the current I if R_f = 10 MΩ, R₁ = 90 MΩ. R₂ = 10 kΩ and V -0.1 V.

(c) Model the circuit of FIGURE using PSPICE (using an ideal op-amp] and use the model to confirm the calculation made in (b).