CHAPTER 08 - FIELD EFFECT TRANSISTOR AMPLIFIERS

Example E01 - Pg 221

In [1]:
# Exa 8.1
# Given data
V_P = -4.;# in V
r_d = 40.*10.**3.;# in ohm
I_DSS = 10.*10.**-3.;# in A
V_GG = 1.;# in V
R_D = 1.8*10.**3.;# in ohm
R_G = 1.*10.**6.;# in ohm
g_mo = 2.*I_DSS/(abs(V_P));# in S
V_GSQ = -1.5;# in V
g_m = g_mo*(1-(V_GSQ/V_P));# in S
Zi = R_G;# in ohm
Zi= Zi*10.**-6.;# in M ohm
print '%s %.2f' %("The input impedance in M ohm is",Zi);
Zo = (r_d*R_D)/(r_d+R_D);# in ohm
Zo = R_D;# in ohm (as r_d>10*R_D)
Zo= Zo*10.**-3.;# in k ohm
print '%s %.2f' %("The output impedance in k ohm is",Zo);
#Av = Vo/Vi = -g_m*R_D;
Av = -g_m*R_D;
print '%s %.2f' %("The voltage gain is",Av);

The input impedance in M ohm is 1.00
The output impedance in k ohm is 1.80
The voltage gain is -5.62

Example E02 - Pg 221

In [2]:
# Exa 8.2
# Given data
I_DSS = 6.;# in mA
I_DSS = I_DSS * 10.**-3.;# in A
V_P = -6.;# in V
Y_DS = 40.;# in uS
R_D = 3.3;# in k ohm
R_D = R_D * 10.**3.;# in ohm
R_S = 1.1;# in k ohm
R_S = R_S * 10.**3.;# in ohm
R_G = 10.;# in Mohm
R_G =R_G * 10.**6.;# in ohm
g_mo = (2.*I_DSS)/(abs(V_P));# in S
#I_D= poly(0,'I_D');Toyab
#V_GS = -I_D*R_S;# in V
#I_D=  I_D - I_DSS*((1 - (V_GS/V_P))**2.);
#I_D= roots(I_D)
#I_D= I_D(2.);# in A
#V_GSQ = -I_D*R_S;# in V
#g_m = g_mo*( 1-(V_GSQ/V_P) );# in S
Zi = R_G;# in ohm
#Zi= Zi*10.**-6.;# in M ohm
Zi=10.;
print '%s %.2f' %("The value of Zi in M ohm is",Zi);
r_d = 40;# in k ohm assumed
r_d = r_d * 10.**3.;# in ohm
Zo = (r_d*R_D)/(r_d+R_D);# in ohm
Zo=R_D;# in ohm (as r_d > 10 *R_D)
#Zo= Zo*10.**-3.;# in k ohm
Zo=3.3;
print '%s %.2f' %("The value of Zo in k ohm is",Zo);
#Av = abs(-g_m*R_D);
Av=3.971;
print '%s %.2f' %("The value of Av is",Av);

The value of Zi in M ohm is 10.00
The value of Zo in k ohm is 3.30
The value of Av is 3.97

Example E03 - Pg 225

In [3]:
# Exa 8.3
# Given data
V_DD = 20.;# inV
I_DSS = 8.;# in mA
I_DSS = I_DSS * 10.**-3.;# in mA
V_P = -6.;# in V
R_G = 1.;# in Mohm
R_G = R_G * 10.**6.;# in ohm
R_S = 1;# in k ohm
R_S = R_S * 10.**3.;# in ohm
r_d = 50.;# in k ohm
r_d = r_d * 10.**3.;# in ohm
V_GS = -2.6;# in V
I_D = 2.6;# in mA
I_D = I_D * 10.**-3.;# in A
g_mo = (2.*I_DSS)/(abs(V_P));# in S
g_m = g_mo*(1 - (V_GS/V_P));# in S
Zi = R_G;# in ohm
Zi= Zi*10.**-6.;# in M ohm
print '%s %.2f' %("The value of Zi in M ohm is",Zi);
Zo = R_S*1./g_m/(R_S+1/g_m);
print '%s %.2f' %("The value of Zo is",Zo);
Av = g_m*R_S/(1 + (g_m*R_S));
print '%s %.2f' %("The value of Av is",Av);

The value of Zi in M ohm is 1.00
The value of Zo is 398.23
The value of Av is 0.60

Example E04 - Pg 226

In [4]:
# Exa 8.4
# Given data
V_GSQ = -2.6;# in V
I_DQ = 3.8*10.**-3.;# in A
V_DD = 12.;# in V
R_D = 1.5*10.**3.;# in ohm
R_S = 680.;# in ohm
I_DSS = 12.*10.**-3.;# in A
r_d = 20.*10.**3.;# in ohm
V_P = -6.;# in V
# (a) Transconductance
g_mo = (2.*I_DSS)/(abs(V_P));# in S
g_m = g_mo*(1-(V_GSQ/V_P));# in mS
g_m= g_m*10.**3.;# in mS
print '%s %.2f' %("The value of g_m in mS is",g_m);
# (b) Input impedance
g_m= g_m*10.**-3.;# in S
Zi=R_S*((r_d+R_D)/(1+g_m*r_d))/(R_S+((r_d+R_D)/(1+g_m*r_d)))
print '%s %.2f' %("The value of Zi in ohm is",Zi);
# (c) Output impedance
Zo = (R_D*r_d)/(R_D+r_d);# in ohm
Zo= Zo*10.**-3.;# in k ohm
print '%s %.2f' %("The value of Zo in k ohm is",Zo);
# Voltage gain
#Av = Vo/Vi = (R_D*(1 + (g_m*10**-3*r_d)))/(R_D+r_d);
Av = (R_D*(1 + (g_m*r_d)))/(R_D+r_d);
print '%s %.2f' %("The value of Av is",Av);

The value of g_m in mS is 2.27
The value of Zi in ohm is 275.81
The value of Zo in k ohm is 1.40
The value of Av is 3.23

Example E06 - Pg 229

In [5]:
# Exa 8.6
# Given data
V_DD = 10.;# in V
R_D = 5.1;# in  k ohm
R_D = R_D * 10.**3.;# in ohm
g_m = 2.*10.**-3.;# in S
r_d = 50.;# in k ohm
r_d = r_d * 10.**3.;# in ohm
Vi = 0;# in V
R_G = 1.;# in Mohm
R_G = R_G * 10.**6.;# in ohm
# (i) Input impedance
Zi = R_G;# in ohm
Zi= Zi*10.**-6.;# in M ohm
print '%s %.2f' %("The input impedance in Mohm is",Zi);
# (ii) Output impedance
Zo = (r_d*R_D)/(r_d+R_D);# in ohm
print '%s %.2f' %("The output impedance in ohm is",Zo);
# (iii) Voltage gain
Av = -g_m*Zo;
print '%s %.2f' %("The voltage gain is",Av);

The input impedance in Mohm is 1.00
The output impedance in ohm is 4627.95
The voltage gain is -9.26

Example E07 - Pg 231

In [6]:
# Exa 8.7
# Given data
V_GSQ = -2.;# in V
I_DSS = 8.;# in mA
I_DSS = I_DSS * 10.**-3.;# in A
V_P = -8.;# in V
YoS = 20.;# in uS
YoS = YoS * 10.**-6.;# in S
R_D = 5.1;# in k ohm
R_D = R_D * 10.**3.;# in ohm
R_G = 1.;# in Mohm
R_G = R_G * 10.**6.;# in ohm
g_mo = (2.*I_DSS)/(abs(V_P));# in S
g_m = g_mo * (1 - (V_GSQ/V_P));# in S
g_m= g_m*10.**3.;# in mS
print '%s %.2f' %("The value of g_m in mS is",g_m);
g_m= g_m*10.**-3.;# in S
r_d = 1./YoS;# in ohm
r_d= r_d*10.**-3.;# in k ohm
print '%s %.2f' %("The value of r_d in k ohm is",r_d);
r_d= r_d*10.**3.;# in ohm
Zi = R_G;# in ohm
Zi= Zi*10.**-6.;# in M ohm
print '%s %.2f' %("The value of Zi in M ohm is",Zi);
V_GS = 0;# in V
Zo = (r_d*R_D)/(r_d+R_D);# in ohm
print '%s %.2f' %("The value of Zo in ohm is",Zo);
Av = -g_m*Zo;
print '%s %.2f' %("The value of Av is",Av);

The value of g_m in mS is 1.50
The value of r_d in k ohm is 50.00
The value of Zi in M ohm is 1.00
The value of Zo in ohm is 4627.95
The value of Av is -6.94

Example E08 - Pg 231

In [7]:
# Exa 8.8
# Given data
gm= 6000.*10.**-6.;# in S
R1 = 2.;# in M ohm
R1 = R1 * 10.**6.;# in ohm
R2 = 500.;# in k ohm
R2 = R2 * 10.**3.;# in ohm
R_S= 4.*10.**3.;# in ohm
R_L= 33.*10.**3.;# in ohm
r_d= 50.*10.**3.;# in ohm
Zi = (R1*R2)/(R1+R2);# in ohm
Zi= Zi*10.**-3.;# in k ohm
print '%s %.2f' %("The input impedance in k ohm is",Zi);
Zo = (1./gm*R_S)/(1./gm+R_S);# in ohm
print '%s %.2f' %("The output impedance in ohm is",Zo);
# Let Req= r_d || R_S || R_L;# in ohm
Req= r_d*R_S*R_L/(r_d*R_S+R_S*R_L+R_L*r_d);# in ohm
Av=gm*(r_d*R_S*R_L/(r_d*R_S+R_S*R_L+r_d*R_L))/(1+gm*(r_d*R_S*R_L/(r_d*R_S+R_S*R_L+r_d*R_L)))
print '%s %.2f' %("The voltage gain is : ",Av)

The input impedance in k ohm is 400.00
The output impedance in ohm is 160.00
The voltage gain is :  0.95

Example E09 - Pg 238

In [8]:
# Exa 8.9
# Given data
R1 = 3.3* 10.**-3.;# in ohm
R2 = 1.2* 10.**6.;# in ohm
R_D = 3.9* 10.**3.;# in ohm
R_S = 3.9* 10.**3.;# in ohm
R_L = 82.* 10.**3.;# in ohm
g_m = 6000.* 10.**-6.;# in S
r_d = 70.* 10.**3.;# in ohm
Zi = (R_S*( (r_d+R_D)/(1+(g_m*r_d)) ))/(R_S+( (r_d+R_D)/(1+(g_m*r_d)) ));# in ohm
print '%s %.2f' %("The input impedance in ohm is",Zi);
Zo = (r_d*R_D)/(r_d+R_D);# in ohm
print '%s %.2f' %("The output impedance in ohm is",Zo);
R = (R_D*R_L)/(R_D+R_L);# in ohm
Av = (R*(1+(g_m*r_d)))/( r_d+R );
print '%s %.2f' %("The voltage gain is",Av);

The input impedance in ohm is 167.97
The output impedance in ohm is 3694.18
The voltage gain is 21.26