# Chapter 15 : Operational Amplifier¶

## Example 15.1a, Page No 572¶

In [1]:
import math
#initialisation of variables
v11=50.0      #in microV
v21=-50.0     #in microV
#Second Set of Input Signal
v12=1050.0    #in microV
v22=950.0     #in microV
p=100.0      #Common Mode Rejection Ratio

#Required Formulae
#vo = Ad*vd*(1+vc/p*vd) .... p = commom mode rejection ratio

#Calculations
#First Set of Values
vd1=v11-v21#in microV
vc1=(v11+v21)/2#in microV
Vo1 = vd1*(1+vc1/(p*vd1))

#Second Set of Values
vd2=v12-v22#in microV
vc2=(v12+v22)/2#in microV
Vo2 = vd2*(1+vc2/(p*vd2))

#Results
print("Percentage difference in output signal = %.2f v " %(100*(Vo2-Vo1)/Vo1))

Percentage difference in output signal = 10.00 v


## Example 15.1b, Page No 572¶

In [2]:
import math

#initialisation of variables
v11=50.0    #in microV
v21=-50.0   #in microV
#Second Set of Input Signal
v12=1050.0  #in microV
v22=950.0  #in microV
p=100.0    #Common Mode Rejection Ratio

#Required Formulae
#vo = Ad*vd*(1+vc/p*vd) .... p = commom mode rejection ratio

#Calculations
#First Set of Values
vd1=v11-v21#in microV
vc1=(v11+v21)/2#in microV
Vo1 = vd1*(1+vc1/(p*vd1))

#Second Set of Values
vd2=v12-v22#in microV
vc2=(v12+v22)/2#in microV
Vo2 = vd2*(1+vc2/(p*vd2))

#Now we have to calculate the same thing with common mode rejection ratio = 10000

p=10000#Common Mode Rejection Ratio

#First Set of Values
vd1=v11-v21#in microV
vc1=(v11+v21)/2#in microV
Vo1 = vd1*(1+vc1/(p*vd1))

#Second Set of Values
vd2=v12-v22#in microV
vc2=(v12+v22)/2#in microV
Vo2 = vd2*(1+vc2/(p*vd2))

#Results
print("Percentage difference in output signal = %.2f v " %(100*(Vo2-Vo1)/Vo1))

Percentage difference in output signal = 0.10 v


## Example 15.2 Page No 576¶

In [3]:
import math

#initialisation of variables
Vbe1=0.7
Vce3=0.2
I3=5.0
R3=0.4
Vee=5
Vcc=5
Ic1=2.5
Rc=1.0

#Calculations
Vcmmin=Vbe1+Vce3+(I3*R3)-Vee
Vcmmax=Vcc-(Ic1*Rc)+0.6

#Results
print("The Vcm can vary from = %.2f v to " %Vcmmin)
print("%.2f v " %Vcmmax)

The Vcm can vary from = -2.10 v to
3.10 v


## Example 15.3 Page No 583¶

In [4]:
import math

#initialisation of variables
Vbe2=0.7
Vce1=0.2
I1=0.99
R1=2.2
Vee=6
Vcc=6
Ic2=0.495
R2=7.75
Vbc2=0.6

#Calculations
Vcmmin=Vbe2+Vce1+(I1*R1)-Vee
Vcmmax=Vcc-(Ic2*R2)+0.6

#Results
print("The Vcm can vary from = %.2f v to " %Vcmmin)
print("%.2f v " %Vcmmax)

The Vcm can vary from = -2.92 v to
2.76 v


## Example 15.4 Page No 596¶

In [5]:
import math

#initialisation of variables

f=32.0    #feedback in dB
#from the Bodes plot we get that Avo = 2510
Avo = 2510.0   #gain
print('The parameters are R , r (for Rdash), C (for Cdash)')
#Desensivity D = B*Rmo = Avo*(R/(R+r))
#20log10(D ) = f

#Calculations
k = f - (20*math.log(Avo,10))
#Let (R+r)/R = l
l = 1.0/(10**(k/20))
#R/(R+r) = fp/fz
#For 45degree phase margin and 32dB of low frequency feedback we find by trial and error method from the graph
fz = 10#in MHz
fp = fz*l
#to determine c we can arbitrarily choose R
R = 1000.0   #in ohm

#Results
print("R = %.2f ohm " %R)
r = (l-1)*R
print("r = %.2f ohm " %r)
C = 1/(2*math.pi*fz*r*10**-6)
print("C = %.2f pF " %C)

The parameters are R , r (for Rdash), C (for Cdash)
R = 1000.00 ohm
r = 62048.35 ohm
C = 0.26 pF