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Practice Problems P1.17: An FM radio receiver has an input resistance of 75 Ohm. The input signal provided by a distant transmitter is 5 µV rms, and the receiver supplies 5 V rms to an 8 Ω loudspeaker. Calculate the power gain of the receiver. P1.33: An amplifier has a voltage gain of 30 dB, and a current gain of 70 dB. What is the power gain in dB? If the input resistance is 100 KΩ, what is the load resistance? P1.63: A differential amplifier has vo (t) = A1v1(t) – A2v2(t), If A1 = 1000, and A2 = 999, determine the CMRR. Answers: P1.17: 9.375 x 1E12 P1.33: GdB = 50, RL = 1 KΩ P1.63: CMRR = 60 dB Answer: -20 dB and CMRR = 114 dB 1 Chapter 2: The Operational Amplifier (Op Amp) 2 The Operational Amplifier continued Summing Point Constraint: This concept refers to the fact that under negative feedback conditions: (i) The differential input voltage will be zero in ideal op-amps (or very close to it in non-ideal ones) as the gain is ideally infinite (ii) The input current will also be zero as there is no voltage and the resistance is very high (ideally infinite) 3 The Operational Amplifier continued Note here that the resistor R2 provides the negative feedback to the input of the op-amp. This means that, as the i/p voltage increases, the negative o/p voltage also increases, and tends to reduce the input to the opamp by feedback, to provide a finite gain. 4