Transcript Series-Shunt Feedback (Voltaje amplifier

Feedback
Feedback Concepts
Expresion General de Circuitos Retroalimentados
Efectos de la Retroalimentación Negativa
Bandwidth with Feedback
Effect of feedback on (a) the pole location and (b) the frequency response of an
amplifier having a single-pole open-loop response.
Gain Stability 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.
Amplifier Types
1.
2.
3.
4.
Voltaje Amplifier
Current Amplifier
Transconductance Amplifier
Transresistance Amplifier
Característica del Puerto de un Amplificador
(Variable Voltaje)
Rs
Rs
+
+
Vs
Xout
vin
Vs
vin
R in
Xout
-
-
Amplificador de Voltaje Ideal
Amplificador de Voltaje Real
R out
+
+
-
Axin
Carga
Xin
vout
+
-
+
Xin
Axin
Carga
vout
-
Amplificador de Voltaje Ideal
Amplificador de Voltaje Real
Característica del Puerto de un Amplificador
(Variable Corriente)
+
+
Is
Rin=0
Rs
Xout
Iin=Is
Is
Rin
Rs
-
Carga
R out
Carga
Axin
+
Axin
Xin
vout
Amplificador de Corriente Ideal
vout
+
Rout=oo
-
Amplificador de Corriente Ideal
-
Amplificador de Corriente Ideal
Xin
Xout
Iin=Is
Amplificador de Corriente Real
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
The Four Basic Feedback Topologies
a)
b)
c)
d)
Voltage-mixing voltage-sampling (series–shunt) topology.
Current-mixing current-sampling (shunt–series) topology.
Voltage-mixing current-sampling (series–series) topology.
Current-mixing voltage-sampling (shunt–shunt) topology.
1. Series-Shunt Feedback Voltaje Amplifier
(b) Equivalent Circuit.
𝑅𝑖𝑓 = 𝑅𝑖 (1 + 𝐴𝛽)
(a) Ideal Structure
1. Series-Shunt Feedback Voltaje Amplifier
𝑅𝑜𝑓
𝑅𝑜
=
(1 + 𝐴𝛽)
Measuring the Output Resistance of the Series-Shunt Feedback Amplifier Rof : Vt/I.
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
1. Series-Shunt Feedback (Voltaje amplifier)
Summary of the rules for finding the A circuit and  for the voltage-mixing voltagesampling case
1. Series-Shunt Feedback (Voltaje amplifier)
Example 1
Series-Shunt Feedback -Voltaje Amplifier
Example 1
Series-Shunt Feedback -Voltaje Amplifier
Af 
1 R1  R2

β
R2
Example 1
Series-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.
2. Series-Series Feedback Transconductance Amplifier
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 currentsampling (series–series) case
2. Series-Series Feedback transconductance Amplifier
Example 2
Series-Series Feedback Transconductance Amplifier
Example 1
Series-Series Feedback Transconductance Amplifier
Example 2
Series-Series Feedback Transconductance Amplifier
Some of the output current is directed
back in series with the input.
Example using a BJT:
Feedback gain (Af):
Af 
Io
A


Vs 1  βA
 hfe hie
 hfe

  hfe  hie  hfeRE
1  (  RE)

 hie  RE 
3. Shunt-Shunt Feedback Transresistance Amplifier
Ideal Structure
3. Shunt-Shunt Feedback Transresistance Amplifier
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 voltagesampling (Shunt-Shunt ) case.
Example 1
Shunt-Shunt Feedback Transresistance Amplifier
Example 1
Shunt-Shunt Feedback Transresistance Amplifier
Example 2
Shunt-Shunt Feedback Transresistance Amplifier
The output voltage is fed back in parallel with the input.
Example of an op-Amp circuit:
Feedback gain (Af):
Af  
Ro
Ri
4. Shunt-Series Feedback Current Amplifier
Ideal Structure
4. Shunt-Series Feedback Current Amplifier
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 currentsampling (shunt–series) case.
Example 1
Shunt-Series Feedback - Current Amplifier
Example 1
Shunt-Series Feedback - Current Amplifier
Example 1
Shunt-Series Feedback - Current Amplifier
Example 2
Shunt-Series Feedback - Current Amplifier
Summary of Each Type of Feedback and the Effects on
Impedance
A. Voltage
A. Transconductance
A. Transresistance
A. Current
Summary of Each Type of Feedback and the Effects on
Gain
A. Voltage
A. Transconductance A. Transresistance
A. Current