ee541F10HW01-02 - U niversity of S outhern C alifornia U SC...

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U niversity of S outhern C alifornia USC Viterbi School of Engineering Ming Hsieh Department of Electrical Engineering EE 541: Homework Assignment #01-02 Fall, 2010 Due: 09/09/2010 Choma Problem #01: The model shown within the symbolic network “box” in Figure (P1) is a linearized equivalent circuit of an emitter-degenerated, common emitter amplifier. The ampli- fier is driven by a voltage source whose Thévenin resistance is R s , and its load termination con- sists of a resistance, R l in shunt with a capacitance, C l . In this problem, R s = 50 Ω , R l = 1.2 K , R e = 120 , and C l = 300 fF . The transistor model parameters are r b = 90 , r π = 2.8 K , r o = 25 K , and β = 120 amps/amp . β I + V s R s R e r b r π C l R l I r o I 2 V 2 I 1 V 1 R out R in Figure (P1) (a). Derive analytical expressions for each of the four h-parameters of the degenerated common emitter amplifier. (b). Using the h-parameter expressions deduced in Part (a), derive analytical expressions for the low frequency, open loop values of voltage gain, V 2 /V s , input resistance, R in , and output resistance, R out . (c). Using the h-parameter expressions deduced in Part (a), derive an analytical expression for the low frequency loop gain of the amplifier. Discuss the influence that the emitter degen- eration resistance, R e , has on this loop gain. (d). Using appropriate preceding results, compute numerical, low frequency values for: i. the open loop input resistance; ii. the driving point input resistance; iii. the open loop output resistance; iv. the driving point output resistance; v. the loop gain; vi. the open loop voltage gain; vii. the closed loop voltage gain. (e). Can the analytical expressions for the closed loop voltage gain deduced in Part (b) and the loop gain deduced in Part (c) be adequately approximated by relatively simple algebraic
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EE 541 University of Southern California Viterbi School of Engineering Choma expressions? If said expressions can be approximated, explain the conditions that render the approximations valid and submit the resultant approximate expressions. (f). In terms of the h-parameters and suitable other circuit variables, give a general expression for the 3-dB bandwidth of the circuit. Numerically evaluate this bandwidth. Problem #02: Consider the two-stage feedback amplifier of Figure (P2), where biasing is not shown in the interests of preserving topological simplicity. Each transistor has the simpli- fied small signal equivalent circuit that is also shown in the figure.
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ee541F10HW01-02 - U niversity of S outhern C alifornia U SC...

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