# Chapter 8: Operational Amplifier¶

## Example 8.3, Page 148¶

In [1]:
#Initialisation
f=20*10**3              #bandwidth frequency in KHz

#Calculation
gain=(10**6)/(f)         #gain

#Result
print'Gain = %d'%gain

Gain = 50


## Example 8.4, Page 150¶

In [5]:
#Initialisation
og=2*10**5                          #Open Loop Gain
cg=20                              #Closed Loop Gain
or1=75                              #Output Resistance
ir1=2*10**6                          #Input Resistance

#Calculation
ab=og*cg**-1                           #factor (1+AB)
or2=or1/ab                              #Output Resistance
ir2=ir1*ab                          #Input Resistance

#Result
print'Output Resistance = %.1f mOhm\n'%(or2*1000)
print'Input Resistance = %d GOhm'%(ir2*10**-9)

Output Resistance = 7.5 mOhm

Input Resistance = 20 GOhm


## Example 8.5, Page 150¶

In [12]:
#Initialisation
og=2*10**5                          #Open Loop Gain
cg=20                               #Closed Loop Gain
or1=75                              #Output Resistance
ir1=2*10**6                         #Input Resistance
r1=20*10**3                         #Resistnce in Ohm
r2=10**3                            #Resistnce in Ohm

#Calculation
ab=og*cg**-1                        #factor (1+AB)
or2=or1*ab**-1                          #Output Resistance
#the input is connected to a virtual earth point by the resistance R2,
#so the input resistance is equal to R 2 ,
ir2=r2                              #Input Resistance

#Result
print'Output Resistance = %.1f mOhm\n'%(or2*1000)
print'Input Resistance = %d KOhm'%(ir2*10**-3)

Output Resistance = 7.5 mOhm

Input Resistance = 1 KOhm


## Example 8.6, Page 151¶

In [15]:
#Initialisation
og=2*10**5                          #Open Loop Gain
cg=1                              #Closed Loop Gain
or1=75                              #Output Resistance
ir1=2*10**6                          #Input Resistance

#Calculation
ab=og*cg**-1                        #factor (1+AB)
or2=or1*ab**-1                      #Output Resistance
ir2=ir1*ab                          #Input Resistance

#Result
print'Output Resistance = %d uOhm\n'%(or2*10**6)       #wrong answer in the textbook
print'Input Resistance = %d GOhm'%(ir2*10**-9)

Output Resistance = 375 uOhm

Input Resistance = 400 GOhm