1 Q34.7kC21nC11n1.3kQ22k5.1kRL1k3kVsigQ14.7kECE2280 Homework #8 Spring 2007 1. Assume the transistors at the right have a finite ß and an infinite Early voltage. Write an expression for the input resistance Rin in the circuit shown below. Your expression should include only real resistances (R1, R2, R3, R4, or a subset of these) and possibly ß, re1 or rπ1, and re2 or rπ2. (Assume all transistors have the same ß.) Circle your answer 2. The transistors below are identical, use VBE=0.7, β=100, gm=80m A/V, rπ=1250Ω, C1=C2=100µF. (a) Find the complete frequency response for Vo/Vsig, ignore ro and the parasitic capacitors. (b) Find the low frequency pole values. 3. Use the following circuit for both problems #3 and #4: β=100, |VBE|=0.7 Find VE1, VC1, VC2, VE2, VE3, VC3, IE1, IE2, and IE3. 4. Analyze the circuit to find the midband gain Vo/Vsig, Rin(ignore input source, Vsig), and Rout(ignore RL=1k). RSig=100 ~ Vsig C1 C2 Vo vO -VCC VCC R1 R3 R2 Rin Q1 Q2 R4 VCC VCC -10V +10V Vout Rin Rout2 5. The input and output curves vs time are are shown below. Explain in detail why this circuit is not amplifying the signal and is instead 0V. VCE_SAT=0.2V, VBE=0.7V, and β=100. 6. β can range from 40 to 200. For the two extreme values of β(β=40 and β=200) find IE, VE, VB, Rin(ignore the source resistance 10k), and the midband voltage gain Vout/Vsig. Time0s 0.5ms 1.0ms 1.5ms 2.0ms 2.5ms 3.0ms 3.5ms 4.0msV(R4:2) V(C5:1)-1.0mV-0.5mV0V0.5mV1.0mVTime 1mV 0.5mV 0V -0.5mV -1mV V9FREQ = 1kVAMPL = 1mVOFF = 0V410VC3100mVR45kVR51kQ1Q2N3904C510mR21kV84V+ - + - VsigC2C1 100k10k1kQ11k+9V Vout