Feedback

Feedback

Feedback Concepts

Expresion General de Circuitos Retroalimentados

Efectos de la Retroalimentación Negativa

Effect of feedback on (a) the pole location and (b) the frequency response of an amplifier having a single-pole open-loop response.

Bandwidth with Feedback

Gain calculations with feedback are often based on external resistive elements in the circuit. By removing gain calculations away from internal variations of and gm, the gain becomes more stable.

Gain Stability with Feedback

Amplifier Types

1. Voltaje Amplifier 2. Current Amplifier3. Transconductance Amplifier4. Transresistance Amplifier

Axin

Xout

+ -Carga

Rin

Axin

vinXoutVsvin

+ -

Rout

Amplificador de Voltaje Real

+ -

-Xin

-+

Amplificador de Voltaje Real

Cargavout

Amplificador de Voltaje Ideal

vout+

+ -

Vs

Rs Rs

Xin

Amplificador de Voltaje Ideal

Característica del Puerto de un Amplificador (Variable Voltaje)

Característica del Puerto de un Amplificador (Variable Corriente)

Amplificador de Corriente Ideal

Xin RoutCarga

+ -

Amplificador de Corriente Ideal

Xout

Amplificador de Corriente Real

+ -

RsIs

Axin

Iin=Is

Rout=oo

Is

+

-

Rin=0

Cargavout vout

Xout

Axin

+

-

Rin

Amplificador de Corriente Ideal

Xin

RsIin=Is

Feedback Connection Types

1. Voltaje Amplifier (series–shunt) voltage-mixing voltage-sampling topology.

2.Current Amplifier (shunt–series) current-mixing current-sampling

topology

3.Transconductance Amplifier (series–series)

voltage-mixing current-sampling topology

4. Transresistance Amplifier (shunt–shunt)

current-mixing voltage-sampling topology

a) Voltage-mixing voltage-sampling (series–shunt) topology.b) Current-mixing current-sampling (shunt–series) topology.c) Voltage-mixing current-sampling (series–series) topology. d) Current-mixing voltage-sampling (shunt–shunt) topology.

The Four Basic Feedback Topologies

(a) Ideal Structure

1. Series-Shunt Feedback Voltaje Amplifier

(b) Equivalent Circuit.

𝑅𝑖𝑓 =𝑅𝑖(1+ 𝐴 𝛽)

1. Series-Shunt Feedback Voltaje Amplifier

Measuring the Output Resistance of the Series-Shunt Feedback Amplifier Rof : Vt/I.

𝑅𝑜𝑓=𝑅𝑜

(1+𝐴 𝛽)

1. Series-Shunt Feedback Voltaje Amplifier

Derivation of the A circuit and circuit for the series–shunt feedback amplifier. (a) Block diagram of a practical series–shunt feedback amplifier. (b) The circuit in (a) with the feedback network represented by its h parameters.

1. Series-Shunt Feedback Voltaje Amplifier

Summary of the rules for finding the A circuit and for the voltage-mixing voltage-sampling case

1. Series-Shunt Feedback (Voltaje amplifier)

1. Series-Shunt Feedback (Voltaje amplifier)

Example 1 Series-Shunt Feedback -Voltaje Amplifier

Example 1 Series-Shunt Feedback -Voltaje Amplifier

2

21f

RRR

β1A

Example 1Series-Shunt Feedback -Voltaje Amplifier

Ganancia del Amplificador retroalimentado Af

Resistencia de entrada real del amplificador

Resistencia de salida real del amplificador

Example 2 Series-Shunt Feedback - Voltaje Amplifier

2. Series-Series FeedbackTransconductanceAmplifier

(a) Ideal Structure (b) Equivalent Circuit.

2. Series-Series Feedback Transconductance Amplifier

Measuring the Output Resistance of the Series-Series Feedback Amplifier Rof : Vt/I.

Derivation of the A circuit and circuit for the series–series feedback amplifier. (a) Block diagram of a practical series–series feedback amplifier. (b) The circuit in (a) with the feedback network represented by its h parameters.

2. Series-Series Feedback Transconductance Amplifier

2. Series-Series Feedback Transconductance Amplifier

Summary of the rules for finding the A circuit and for the voltage-mixing current-sampling (series–series) case

2. Series-Series Feedback transconductance Amplifier

2. Series-Series Feedback transconductance Amplifier

Example 2Series-Series Feedback Transconductance Amplifier

Example 1Series-Series Feedback Transconductance Amplifier

Example 2Series-Series Feedback Transconductance Amplifier

Efeie

fe

Eie

feE

iefef

Rhhh

Rhh)R(1

hhβA1

AVsIoA

Feedback gain (Af):

Some of the output current is directed back in series with the input.

Example using a BJT:

3. Shunt-Shunt Feedback Transresistance Amplifier

Ideal Structure

Block diagram for a practical shunt–shunt feedback amplifier.

3. Shunt-Shunt Feedback Transresistance Amplifier

Summary of the rules for finding the A circuit and for the current-mixing voltage-sampling (Shunt-Shunt ) case.

3. Shunt-Shunt Feedback Transresistance Amplifier

Example 1Shunt-Shunt Feedback Transresistance Amplifier

Example 1Shunt-Shunt Feedback Transresistance Amplifier

The output voltage is fed back in parallel with the input.Example of an op-Amp circuit:

RiRoAf

Feedback gain (Af):

Example 2Shunt-Shunt Feedback Transresistance Amplifier

4. Shunt-Series Feedback Current Amplifier

Ideal Structure

Block diagram for a practical shunt–shunt feedback amplifier.

4. Shunt-Series Feedback Current Amplifier

Summary of the rules for finding the A circuit and for the current-mixing current-sampling (shunt–series) case.

4. Shunt-Series Feedback Current Amplifier

Example 1Shunt-Series Feedback - Current Amplifier

Example 1Shunt-Series Feedback - Current Amplifier

Example 1Shunt-Series Feedback - Current Amplifier

Example 2Shunt-Series Feedback - Current Amplifier

Summary of Each Type of Feedback and the Effects on Impedance

A. Voltage A. CurrentA. Transconductance A. Transresistance

Summary of Each Type of Feedback and the Effects on Gain

A. Voltage A. Transconductance A. Transresistance A. Current