Figure 931
for the Amplifier in Fig $Q_{3}$ And $Q_{4}$ Have Very High

Essay

Figure 9.3.1
For the amplifier in Fig. 9.3.1:
(a) Assuming $Q_{3}$ and $Q_{4}$ have very high $\beta$ values, determine the value of $R$ that will provide a dc current of $0.25 \mathrm{~mA}$ for each of $Q_{1}$ and $Q_{2}$ . (b) Assuming $Q_{1}$ and $Q_{2}$ have very high $\beta$ values, determine the value of $R_{C}$ that results in a dc voltage of $+3 \mathrm{~V}$ at the collectors of $Q_{1}$ and $Q_{2}$ .
(c) What is the input common-mode range for this differential amplifier?
(d) Determine the value of the differential voltage gain $v_{O} / v_{i d}$ .
(e) Determine the value of the input differential resistance, $R_{i d}$ . Assume $\beta_{1}=\beta_{2}=100$ .
(f) If it is required to raise the value of $R_{i d}$ by factor of 5 by including a resistance $R_{E}$ in the emitter of each of $Q_{1}$ and $Q_{2}$ , what value of $R_{E}$ is required? What is the resulting value of the differential gain?
(g) If the transistors have an Early voltage $V_{A}=50 \mathrm{~V}$ , calculate the worst-case value of the common-mode gain resulting from the resistances $R_{C}$ having finite tolerances of $\pm 1 \%$ . Hence, find the value of the CMRR of the original amplifier (i.e., the one without the resistances $R_{E}$ included).
(h) With the two input terminals grounded, calculate the value of the worst-case differential dc voltage at the output resulting from the resistances $R_{C}$ having finite tolerances of $\pm 1 \%$ . Hence, find the input offset voltage of the original amplifier (i.e., the one without $R_{E}$ 's).