8.2SomeProperties of NegativeFeedbackGain desensitivity1.dAdAf(1+ Aβ)2dA,1 dAAf1+Aβ Athe percentage change in Ar (due to variations insome circuit parameter) is smaller than thepercentage change in A by the amount of feedbackForthisreasontheamountoffeedback.1 +Aβ, is also known as the desensitivity factor.Microelectronic Circuits
Microelectronic Circuits 8.2 Some Properties of Negative Feedback 1. Gain desensitivity A dA A A dA A dA dA f f f + = + = 1 1 (1 ) 2 the percentage change in Af (due to variations in some circuit parameter) is smaller than the percentage change in A by the amount of feedback. For this reason the amount of feedback, 1 + Aβ, is also known as the desensitivity factor
Some Properties of NegativeFeedback2. Bandwidth extensionAMA(s)A,(s) :A(s)=1+βA(s)1+s/OHAM/(1+AMB)S1+s/0H(1+AMP)OLOLfOHf=O(1+AMP)1+AMβNote that the amplifier bandwidth is increased by the samefactor by which its midband gain is decreased, maintainingthe gain-bandwidth product at a constant value.MicroelectronicCircuits
Microelectronic Circuits 2. Bandwidth extension Some Properties of Negative Feedback Note that the amplifier bandwidth is increased by the same factor by which its midband gain is decreased, maintaining the gain-bandwidth product at a constant value
Some Properties of NegativeFeedback3. Noise reductionSIN=V,/V,(a)BVA,A2Al1+A,A2BA,A2B+Vsl1ANVhMicroelectronic Circuits
Microelectronic Circuits Some Properties of Negative Feedback 3. Noise reduction
Some Properties of NegativeFeedback4. Reduction in nonlinear distortionXX(a)D:\模电课件\(b)负反馈.exeMicroelectronicCircuits
Microelectronic Circuits Some Properties of Negative Feedback 4. Reduction in nonlinear distortion
Some Properties of NegativeFeedback4. Reduction in nonlinear distortionVo(V)A(a)(b)43210.020.060.020.040.08-0.060.040.08u(V)-2-3MicroelectronicCircuits
Microelectronic Circuits Some Properties of Negative Feedback 4. Reduction in nonlinear distortion