Chapter 11, Problem 11.10EP

The diff-amp circuit in Figure 11.30 is biased at $I_Q=0.4\text{mA}.$ The transistor parameters are $\beta =120,V_{A1}=V_{A2}=150\text{V},$ and $V_{A3}=V_{A4}=90\text{V}$ (a) Determine the open-circuit ( $R_L=\infty$ ) differential-mode voltage gain. (b) Find the differential-mode voltage gain when $R_L=250\text{k}\Omega .$ (c) Determine the differential-mode input resistance. (d) Find the output resistance looking back from the load $R_L$ . (Ans. (a) 2163, $(b)$ 1018, $(c)$ 31.2 $\text{k}\Omega ,(\text{d})281\text{k}\Omega$ ).