Chapter 12:Feedback in amplifiers¶

Example 12.1 Page no.395¶

In [1]:
A=100.0                                 #Internal Gain
B=0.1                            #Feedback Factor

#Calculation
Af=A/(1+A*B)                # Gain of Feedback Amplifier
# Result
print " The Value of the Gain of Feedback Amplifier is = ",round(Af,2)

 The Value of the Gain of Feedback Amplifier is, =  9.09


Example 12.2 Page no. 395¶

In [2]:
Af=100.0                                            #Voltage Gain
Vin=.05                            #V , Input Signal without Feedaback Gain
Vi=0.6                                              #V , Input Signal with Feedaback Gain

#Calculation
Vo=Af*Vi
A=Vo/Vin
B=((A/Af)-1)/A
#Result
print "The Value of the Internal Gain A is, A =  ",A
print " The Value of the Feedback Gain B is, B =  percent ",round(B*100,2)

The Value of the Internal Gain A is, A =   1200.0
The Value of the Feedback Gain B is, B =  percent  0.92


Example 12.3 Page no. 401¶

In [3]:
A=1000                                            #60dB    Voltage Gain
B=0.005                                            #Negative Feedback
dAbyA=-0.12                                 #dA/A = 12 %

#Calculation
dAfbyAf=1/(1+A*B)*dAbyA    #dAf/Af=1/(1+A*B)*dA/A

# Result
print " The change in overall Gain of the Feedback Amplifier is",dAfbyAf
print "Therefore the overall gain of feedback amplifier will be reduce by ",-dAfbyAf*100,"%"

 The change in overall Gain of the Feedback Amplifier is -0.02
Therefore the overall gain of feedback amplifier will be reduce by  2.0 %


Example 12.4 Page no. 401¶

In [4]:
Zi=1000.0                                #Ohms
A=1000.0                                #Voltage Gain
B=0.01                                    #Negative Feedback

#Calculation
Zid=(1+A*B)*Zi
# Result
print " The Value of the Input Impedance of the Feedback Amplifier is, Zid =  ",Zid/10**3,"K ohm"

 The Value of the Input Impedance of the Feedback Amplifier is, Zid =   11.0 K ohm


Example 12.5 Page no. 401¶

In [6]:
A=1000.0                                    #60dB, Voltage Gain
Zo=12000.0                                #Ohms
Zod=600.0                                 #Ohms
dAbyA=0.1                               #dA/A = 10 %

#Calculation
B=((Zo/Zod)-1)/A                             #Zod=Zo/(1+A*B)
dAfbyAf=1/(1+A*B)*dAbyA       #dAf/Af=1/(1+A*B)*dA/A
# Result
print " The Feedback Factor of the Feedback Amplifier is, B = ",B*100,"percent"
print " The change in overall Gain of the Feedback Amplifier is, dAf/Af = ",dAfbyAf*100,"percent"

 The Feedback Factor of the Feedback Amplifier is, B =  1.9 percent
The change in overall Gain of the Feedback Amplifier is, dAf/Af =  0.5 percent