SAFFRONY INSTITUTE TECHNOLOGY FEEDBACK AMPLIFIER SUBMITTED BY : Suchit Darji GUIDED BY: Prof. Nipa Modi

EE3110 Feedback Amplifiers Introduction of Two-Port Network Negative Feedback (Uni-lateral Case) Feedback Topology Analysis of feedback applications Close-Loop Gain Input/Output resistances Ref:080130HKN EE3110 Feedback Amplifiers

Two-Port Network (z-parameters) (Open-Circuit Impedance) Open-circuit input impedance At port 1 Open-circuit reverse transimpedance At port 2 Open-circuit forward transimpedance Open-circuit output impedance Ref:080130HKN EE3110 Feedback Amplifiers

Two-Port Network (y-parameters) (Short-Circuit Admittance) At port 1 At port 2 Short-circuit forward transadmittance Short-circuit input admittance Short-circuit reverse transadmittance Short-circuit output admittance Ref:080130HKN EE3110 Feedback Amplifiers

Two-Port Network (h-parameters) (hybrid) At port 1 At port 2 Short-circuit forward current gain Short-circuit input impedance Open-circuit reverse voltage gain Open-circuit output admittance Ref:080130HKN EE3110 Feedback Amplifiers

Two-Port Network (g-parameters) (inverse-hybrid) At port 1 At port 2 Open-circuit forward current gain Open-circuit input admittance Short-circuit reverse current gain Short-circuit output impedance Ref:080130HKN EE3110 Feedback Amplifiers

EE3110 Feedback Amplifiers z-parameter example Note: (1) z-matrix in the last circuit = sum of two former z-matrices (2) z-parameters is normally used in analysis of series-series circuits (3) Z12 = Z21 (reciprocal circuit) (4) Z12 = Z21 and Z11 = Z22 (symmetrical and reciprocal circuit) Ref:080130HKN EE3110 Feedback Amplifiers

EE3110 Feedback Amplifiers y-parameter example Ref:080130HKN EE3110 Feedback Amplifiers

y-parameter example (Cont’) Note: the y-matrix is equal to the sum of two former ones. Therefore, y-parameters is normally used in analysis of shunt-shunt circuits What connection should be for h- or g- parameters? Ref:080130HKN EE3110 Feedback Amplifiers

General Feedback Structure A : Open Loop Gain A = Vo / V  : feedback factor  = Vf / Vo Ref:080130HKN EE3110 Feedback Amplifiers

Negative Feedback Properties Negative feedback takes a sample of the output signal and applies it to the input to get several desirable properties. In amplifiers, negative feedback can be applied to get the following properties Desensitized gain : gain less sensitive to circuit component variations Reduce nonlinear distortion : output proportional to input (constant gain independent of signal level) Reduce effect of noise Control input and output impedances by applying appropriate feedback topologies Extend bandwidth of amplifier All of these properties can be achieved by trading off gain Ref:080130HKN EE3110 Feedback Amplifiers

EE3110 Feedback Amplifiers Gain De-sensitivity Feedback can be used to desensitize the closed-loop gain to variations in the basic amplifiler. Assume  is constant. Take differentials of the closed loop gain equation gives, Divided by Av, the close loop gain sensitivity is equal to, This result shows the effects of variations in A on ACL is mitigated by the feedback amount. (1+A) is also called the desensitivity amount. Differential respected with A Ref:080130HKN EE3110 Feedback Amplifiers

Basic Feedback Topologies Depending on the input signal (voltage or current) to be amplified and form of the output (voltage or current), amplifiers can be classified into four categories. Depending on the amplifier category, one of four types of feedback structures should be used. (Type of Feedback) (Type of Sensing) (1) Series (Voltage) Shunt (Voltage) (2) Series (Voltage) Series (Current) (3) Shunt (Current) Shunt (Voltage) (4) Shunt (Current) Series (Current) Ref:080130HKN EE3110 Feedback Amplifiers

Feedback Structure (Series-Shunt) Voltage Gain Calculation: Voltage amplifier voltage-controlled voltage source Requires high input impedance, low output impedance Voltage-voltage feedback Ref:080130HKN EE3110 Feedback Amplifiers

Input/Output Resistance (Series-Shunt) Input Resistance: Output Resistance (Closed loop output resistance with zero input voltage) Ref:080130HKN EE3110 Feedback Amplifiers

EE3110 Feedback Amplifiers h-parameter Modeling Only uni-lateral case will be considered : NO reverse dependent signal found in the amplifier network. |h12a| = 0 NO reverse dependent signal found in the feedback network. |h21f| = 0 Ref:080130HKN EE3110 Feedback Amplifiers

EE3110 Feedback Amplifiers Uni-lateral Ref:080130HKN EE3110 Feedback Amplifiers

EE3110 Feedback Amplifiers Series-Shunt Example It is observed that: Series connection in input ports Shunt connection in output ports  Series-Shunt connection h-parameter should be used. Equivalent circuit Ref:080130HKN EE3110 Feedback Amplifiers

EE3110 Feedback Amplifiers h-parameter analysis 1 Ref:080130HKN EE3110 Feedback Amplifiers

EE3110 Feedback Amplifiers Ref:080130HKN EE3110 Feedback Amplifiers

Feedback Structure (Series-Series) Ref:080130HKN EE3110 Feedback Amplifiers

Input/Output Resistance (Series-Series) Input Resistance: Output Resistance (Closed loop output resistance with zero input voltage) Ref:080130HKN EE3110 Feedback Amplifiers

Series-Series Example CE amplifier with an un-bypassed emitter ac small signal equivalent circuit Ref:080130HKN EE3110 Feedback Amplifiers

Feedback Network with z-parameter Reduce equivalent circuit Ref:080130HKN EE3110 Feedback Amplifiers

EE3110 Feedback Amplifiers Close loop analysis Ref:080130HKN EE3110 Feedback Amplifiers

EE3110 Feedback Amplifiers Final Rin and Rout Ref:080130HKN EE3110 Feedback Amplifiers

Feedback Structure (Shunt-Shunt) Ref:080130HKN EE3110 Feedback Amplifiers

Input/Output Resistance (Shunt-Shunt) Input Resistance: Output Resistance (Closed loop output resistance with zero input voltage) Ref:080130HKN EE3110 Feedback Amplifiers

EE3110 Feedback Amplifiers Shunt-Shunt Example CE amplifier ac small signal equivalent circuit Shunt-Shunt connection found!  y-parameter Ref:080130HKN EE3110 Feedback Amplifiers

EE3110 Feedback Amplifiers Feedback Network y-parameter modeling Ref:080130HKN EE3110 Feedback Amplifiers

EE3110 Feedback Amplifiers Ref:080130HKN EE3110 Feedback Amplifiers

Feedback Structure (Shunt-Series) Ref:080130HKN EE3110 Feedback Amplifiers

Input/Output Resistance (Shunt-Series) Input Resistance: Output Resistance (Closed loop output resistance with zero input voltage) Ref:080130HKN EE3110 Feedback Amplifiers

EE3110 Feedback Amplifiers Summary Feedback Structure Close loop gain Input impedance Output impedance Parameter used Series-Shunt h-parameter Series-Series z-parameter Shunt-Shun y-parameter Shunt-Series g-parameter Ref:080130HKN EE3110 Feedback Amplifiers

EE3110 Feedback Amplifiers Supplementary Find the input and output resistance from - Two port network, and - Circuit theory Ref:080130HKN EE3110 Feedback Amplifiers

EE3110 Feedback Amplifiers Circuit Theory Ref:080130HKN EE3110 Feedback Amplifiers

EE3110 Feedback Amplifiers Two Port Network  Ref:080130HKN EE3110 Feedback Amplifiers

EE3110 Feedback Amplifiers Ref:080130HKN EE3110 Feedback Amplifiers

EE3110 Feedback Amplifiers THANKYOU Ref:080130HKN EE3110 Feedback Amplifiers