The circuit shown in given Figure has the same parameters as described in given Problem, except that Ri = 20 k Ω and Ro = 50 k Ω. Determine the closed-loop input and output resistances, Rif and Rof , respectively.
Problem
Consider the circuit in Figure. The input resistance of the op-amp is Ri = ∞ and the output resistance is Ro = 0. The op-amp has a finite gain, so that 
= Agvε . The current gain of the transistor is hFE.
(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 Ag = 5 × 105 mS and Ag f = 10 mS, what is the required βz and RE?
(d) If Ag increases by 10 percent, what is the corresponding percent change in Agf?
