Determine the closed-loop input and output resistances

Question

The circuit shown in given Figure has the same parameters as described in given Problem, except that R_i = 20 k Ω and R_o = 50 k Ω. Determine the closed-loop input and output resistances, R_if and R_of , respectively.

Problem

Consider the circuit in Figure. The input resistance of the op-amp is R_i = ∞ and the output resistance is R_o = 0. The op-amp has a finite gain, so that  = A_gvε . The current gain of the transistor is h_FE.

(a) Write the closed-loop transfer function in the form

where Ag is the open-loop gain of the system.

_{(b) What} is the expression for βz?

(c) If A_g = 5 × 10⁵ mS and A_g f = 10 m_S, what is the required β_z and R_E?

(d) If A_g increases by 10 percent, what is the corresponding percent change in A_gf?