Chapter : 6 - Field Effect Transistors

Example : 6.9.1 - Page No : 6-26

In [5]:
from __future__ import division
from numpy import pi
# Given data
q = 1.6 * 10**-19;# in C
N_D = 10**15;# in electrons/cm**3
N_D = N_D * 10**6;# in electrons/m**3
epsilon_r = 12;
epsilon_o = (36 * pi * 10**9)**-1;
epsilon = epsilon_o * epsilon_r;
a = 3 * 10**-4;# in cm
a = a * 10**-2;# in m
V_P = (q * N_D * a**2)/( 2 * epsilon);# in V
print "The Pinch off voltage = %0.1f V" %V_P
# V_GS = V_P * (1-(b/a))**2
b = (1-0.707) *a;# in m
print "The value of b = %0.3f µm" %(b*10**6)
print "Hence the channel width has been reduced to about one third of its value for V_GS = 0"
# Note : The unit of b in the book is wrong since the value of b is calculated in µm.

The Pinch off voltage = 6.8 V
The value of b = 0.879 µm
Hence the channel width has been reduced to about one third of its value for V_GS = 0

Example : 6.9.2 - Page No : 6-26

In [4]:
from math import sqrt
# Given data
I_DSS = 8;# in mA
V_P = -4;# in V
I_D = 3;# in mA
V_GS = V_P * (1 - sqrt(I_D/I_DSS));# in V
print "The value of V_GS = %0.2f V" %V_GS
V_DS = V_GS - V_P;# in V
print "The value of V_DS = %0.2f V" %V_DS

The value of V_GS = -1.55 V
The value of V_DS = 2.45 V

Example : 6.9.3 - Page No : 6-27

In [1]:
from __future__ import division
# Given data
V_P = -4;# in V
I_DSS = 9;# in mA
I_DSS = I_DSS * 10**-3;# in A
V_GS = -2;# in V
I_D = I_DSS * ((1 - (V_GS/V_P))**2);# in A
print "The drain current = %0.2f mA" %(I_D*10**3)

The drain current = 2.25 mA

Example : 6.9.4 - Page No : 6-27

In [2]:
# Given data
I_DSS = 12;# in mA
I_DSS = I_DSS * 10**-3;# in A
V_P = -(6);# in V
V_GS = -(1);# in V
g_mo = (-2 * I_DSS)/V_P;# in A/V
g_m = g_mo * (1 - (V_GS/V_P));# in S
print "The value of transconductance = %0.2f mS" %(g_m*10**3)

The value of transconductance = 3.33 mS

Example : 6.9.5 - Page No : 6-28

In [3]:
# Given data
I_DSS = 10;# in mA 
I_DSS = I_DSS * 10**-3;# in A
V_P = -(5);# in V
V_GS = -(2.5);# in V
g_m = ((-2 * I_DSS)/V_P) * (1 -(V_GS/V_P));# in S
g_m = g_m * 10**3;# in mS
print "The Transconductance = %0.f mS" %g_m
I_D = I_DSS * ((1 - (V_GS/V_P))**2);# in A
print "The drain current = %0.1f mA" %(I_D*10**3)

The Transconductance = 2 mS
The drain current = 2.5 mA