Chapter 6 : Field Effect Transistors

Example 6.1, Page No. 184

In [4]:
# drain resistance transconductance and amplification factor

import math
from array import array
#Variable declaration
Vgs=array('d', [0.0, 0.0, 0.3])     #in V
Vds=array('d',[5.0, 10.0, 10.0])    #in V
Id=array('d',[8.0, 8.2, 7.6])       #in mA

#Calcualtions
dVds=Vds[1]-Vds[0]                  #in V
dId=Id[1]-Id[0]                     #in mA
rd=(dVds/dId)                       #in kilo-ohm
dVgs=Vgs[2]-Vgs[1]                  #in V
dId1=Id[1]-Id[2]                    #in mA
gm=dId1/dVgs                        #in mA/volt
mu=gm*rd                            #A/V

#Result
print("(i)  A.C. Drain resistance is ,(kilo-ohm)= %.f"%rd)
print("(ii) Transconductance is ,(mS)           = %.f"%gm)
print("(iii) Amplification factor is ,          = %.f"%mu)
#Transconductance and Amplification factor are calculated wrong in the textbook

(i)  A.C. Drain resistance is ,(kilo-ohm)= 25
(ii) Transconductance is ,(mS)           = 2
(iii) Amplification factor is ,          = 50

Example 6.2, Page No. 184

In [15]:
# mutual conductance

import math
#Variable declaration
I1=1.0                  # in mA
I2=1.2                  # in mA
V1=-3.0                 # in V
V2=-2.9                 # in V

#Calculations
del_ID=(I2-I1)
del_VGS=V2-V1           # in V
gm=del_ID/del_VGS

#Result
print("mutual conductance,gm(mS) = %.f"%gm)

mutual conductance,gm(mS) = 2

Example 6.3, Page No. 185

In [17]:
# pinch off voltage

import math
#Variable declaration
a=5.6*10**-6/2                  # channel width in m
epsilon0=8.86*10**-12           # in F/m
epsilon=12*epsilon0             # in F/m
Nd=10**21                       # in m^-3
e=1.6*10**-19                   # in V

#Calculations
Vp=e*Nd*a**2/(2*epsilon);

#Result
print("Pinch off voltage,Vp(V) = %.1f"%Vp)

Pinch off voltage,Vp(V) = 5.9

Example 6.4, Page No. 185

In [2]:
# ID gm and gmo

import math
#Variable declaration
I_DES=8.7                 # in mA
V1=-3.0                   # in V
V_GS=-1.0                 # in V


#Calculations
gmo=-(2*I_DES/V1)
ID=I_DES*(1-(V_GS/V1))**2
gm=gmo*(1-(V_GS/V1));

#Result
print("(i).  ID(mA)  = %.3f"%(math.floor(ID*1000)/1000))
print("(ii). gmo(mS) = %.1f"%gmo)
print("(iii).gm(mA)  = %.3f"%(math.floor(gm*1000)/1000))

(i).  ID(mA)  = 3.866
(ii). gmo(mS) = 5.8
(iii).gm(mA)  = 3.866

Example 6.5, Page No. 186

In [25]:
# Vgs

import math
#Variable declaration
ID=3.0                         # in mA
I_DSS=9.0                      # in mA
Vp=-4.5                        # in V

#Calculations
Vgs=-Vp*(math.sqrt(ID/I_DSS)-1)


#Result
print("Vgs(V) = %.1f"%Vgs)

Vgs(V) = -1.9

Example 6.6, Page No. 196

In [27]:
# voltage amplification

import math
#Variable declaration
gm=3                  #Transconductance in mS
rl=10                 #load resistance in kilo-ohm

#Calculations
av=gm*rl
#Result
print("the voltage aplification is ,= %.f"%av)

the voltage aplification is ,= 30

Example 6.7, Page No. 196

In [3]:
# output voltage

import math
#Variable declaration
Rl=20.0                   #in kilo-ohm
Rs=1.0                    #in kilo-ohm
Rg=1.0                    #in M-ohm
Cs=25.0                   #in micro-F
mu=20.0                   #amplification factor
rd=100.0                  #in kilo-ohm
vi=2.0                    #in V
f=1.0                     #in kilo-Hz

#Calculations
Xc=((1/(2*math.pi*f*10**3*Cs*10**-6)))
A=((mu*Rl*10**3)/((rd+Rl)*10**3))
Vo=A*vi

#Result
print("amplifier output signal voltage is ,(V)= %.2f"%(math.floor(Vo*100)/100))

amplifier output signal voltage is ,(V)= 6.66