模电英文课件ch123.pptVIP

12.3 Feedback improving performance parameters 12.3.1 Gain Stability 12.3 Feedback improving performance parameters 12.3.2 Reducing nonlinear distortion 12.3 Feedback improving performance parameters 12.3.3 Bandwidth Extension 12.3 Feedback improving performance parameters 12.3.4 Feedback influence input and output resistances 12.3 Feedback improving performance parameters General rules for design of feedback 12.3 Feedback improving performance parameters Steps of analysis feedback circuits * Sensitivity of Af becomes very small. When Af only depends on feedback network, so feedback components should be linear and stable. Since Taking derivative of Af with respect to A ?=0.099 Af becomes small, but linearity is improved. Since Upper 3dB is extended by a factor of (1+A?) Open-loop Closed-loop Lower 3dB is reduced by a factor of (1+A?) Shunt output connection — Decrease output resistance. Stabilize output voltage. Series input connection — Increase input resistance Shunt input connection — Decrease input resistance Series output connection — Increase output resistance. Stabilize output current. Stabilize output voltage — Stabilize dc quantity — Stabilize ac quantity — Stabilize output current — Use dc neg. feedback Use ac neg. feedback Shunt output connection Series output connection Increase input resistance — Series input connection Decrease input resistance— Shunt input connection 1. Recognize basic amp and feedback network 2. Recognize positive or negative feedback 3. Recognize ac or dc feedback 4. Determine feedback circuit configuration 5. Symbol input, output feedback quantities 6. Calculate A, ?, and Af in an ideal feedback circuit. end *