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Unformatted text preview: ECE 488: RF Circuits and Systems Spring 2009 HOMEWORK 7: Negative Res. Osc., Hybrids, T-Line Reflections, TR Switches Reference: Lectures 1518; Chapters 8, 13, 20 Due: March 25 Problem 1. The three amplifiers in the balanced amplifier circuit in Figure 1 have the same gains and noise figures given by G1=G2=G3=21 dB, and NF1=NF2=NF3=6 dB. The temperatures of R1, R2, R3, and R4 are 400 K, 500 K, 600 K, and 700 K, respectively. The characteristic impedance of all the hybrids is 50 , and the value of all the resistors is 50 . (Remember that T = 290 K , and Boltz- manns Constant is = 1 . 3807 10 23 J/ K.) [24 points] a. What is the overall gain of the circuit expressed in dB? b. Why is it not likely that this circuit would ever be implemented? c. If amplifier G2 fails, what is the new gain? (As- sume the failure causes no impedance mis-matches.) (We will return later to this circuit in a study of Noise Figures.) Figure 1: A tri-balanced amplifier. Problem 2: Figure 2 shows a model of a negative resistance oscillator. [20 points] a. With an R NEG of- 1500 and an R L of 3500 , what is the total effective resistance of the circuit...
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- Summer '08