Section 11.1: The General Feedback Structure 11.1 A newly constructed feedback amplifier under- goes a performance test with the following results: With the feedback connection removed, a source signal of 1 mV is required to provide a 1-V out- put; with the feedback connected, a 1-V output requires a 0.1-V source signal. For this amplifier, identify values of A,B, and Aẞ, the closed-loop gain, and the amount of feedback in dB. Section 11.2: Some Properties of Negative Feedback 11.2 An amplifier with a midband gain of 1000 V/V has a lower 3-dB frequency f of 100 Hz and an upper 3-dB frequency fH of 100 kHz. The gain falls off at a rate of 20 dB/decade at both the low and the high-frequency ends. If negative feedback is applied to this amplifier so that its midband gain becomes 10 V/V, find the 3-dB frequencies of the closed-loop amplifier. Also, sketch a Bode plot for the magnitude of both the open-loop and closed- loop gains, in the same figure. If the open-loop gain has a tolerance of ±10%, what do you expect the tolerance of the closed-loop gain to be? much as ±1% variation in ẞ, to what value must A be raised to ensure the required minimum gain? Section 11.3: The Feedback Voltage Amplifier D11.4 R₁ Figure 11.4.1 VDD 1=300 μA R₁ Rom D11.3 It is required to design an amplifier to have a nominal gain of 20 V/V using a battery-powered amplifier whose gain drops to one-third its nor- mal full-battery value over the life of the battery. If only a 5% drop in closed-loop gain is desired, what nominal open-loop amplifier gain must be used in the design? Also, what is the value of B? (Note that since the change in A is large, it is inaccurate to use differentials.) If component- value variation in the ẞ network may produce as 11-1 Figure 11.4.1 shows a current-mirror-loaded dif- ferential amplifier to which series-shunt feedback is applied through the voltage divider (R1, R2), where R₁+R2470 k2. All MOSFETs have VA 6 V and are operated at |Vorl=0.15 V. The input signal source has a zero de component. (a) Find the loop gain Aẞ and hence the value of A. (b) Find the values of R1 and R2 that result in a closed-loop gain Vo/Vs of exactly 6 V/V.

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