11.9 R 0.2 mA K0,02 mA 9 k +3 V w ov. 0.2 mA R₁ 1 k R₂ 川 11-3 taken as the current Io. It is required to design the circuit to obtain a closed-loop gain lo/V, that approaches 100 mA/V for large loop gain. Deter- mine the required value of Rp. Then analyze the circuit to determine the actual value realized for Io/Vs and the output resistance Rout! Let each of Q1 Q3 have gm 5 mA/V and to simplify matters, you may neglect ro of cach of the three transistors except when determining Roul. For the purpose of determining Rol, assume that 03-50k 11.11 R v, -R Figure 11.9.1 Figure 11.9.1 shows a series-shunt feedback amplifier in which the three BJTs have VBE = 0.7V, B=100, and 14 = 100 V. The current sources have incremental output resistances equal to 500 k2. (a) Show that the feedback is negative. (b) Give the circuit and find. (c) Assuming the loop gain to be large, what do you expect the closed-loop gain Vo/V, to be approximately? (d) If V, has a zero de component, perform a de analysis of the circuit to determine the de collector current of each of Q1, Q2. and Q3 and deter- mine the de voltage at the output. To simplify the analysis, ignore all base currents. (e) Find the circuit. Calculate the gain of each of the three stages and the overall voltage gain, A. (f) Find A Va/Vs. By what percentage does the value differ from the approximate value obtained in (b)? (g) Find the input resistance Rin (h) Find the output resistance Rout Note: This is a rather long but highly instructive problem. Section 11.5: Other Feedback Voltage Amplifier Types D11.10 Figure 11.11.1 Figure 11.11.1 shows a popular configuration for a feedback transconductance amplifier. It consists of a differential voltage amplifier with a voltage gain, where 1, and a very high input resis- tance, a MOSFET characterized by its gee and ro. and a feedback resistance R. Assume RT- (a) If the loop gain is large, what is the closed-loop transconductance Io/V₂? (b) Use feedback analysis to derive expressions for Io/V, and Rout (c) For R-2002, -1000, gm-2 mA/V, and 20k, find lo/V, and Rout Po D11.12 π- = HV₁ (a) Consider the circuit in Fig. 11.5.1 as a feedback transconductance amplifier, that is, with the output Figure 11.12.1 continues

Fig: 1