Chapter 7: Field-effect Transistors (FETs)

Example 7.1, Page Number: 217

In :
%matplotlib inline
Welcome to pylab, a matplotlib-based Python environment [backend: module://IPython.zmq.pylab.backend_inline].
In :
# variable declaration
V_GS_off=-4;       # voltage in volt
I_DSS=12*10**-3;    # current in ampere
R_D=560;           # resistance in ohm

#calculation
V_P=-1*V_GS_off;  # volt
V_DS=V_P;         # Vds in volt
I_D=I_DSS;        # current accross resistor
V_R_D=I_D*R_D;    #voltage across resistor
V_DD=V_DS+V_R_D;  # Vdd in volt

# result
print "The value of V_DD required to put the device in the constant"
print " current area of operation of JFET = %.2f volt" %V_DD
The value of V_DD required to put the device in the constant
current area of operation of JFET = 10.72 volt

Example 7.2, Page Number: 218

In :
print('The p-channel JFET requires a positive gate to source voltage.')
print('The more positive the voltage, the lesser the drain current.')
print('Any further increase in V_GS keeps the JFET cut off, so I_D remains 0')
The p-channel JFET requires a positive gate to source voltage.
The more positive the voltage, the lesser the drain current.
Any further increase in V_GS keeps the JFET cut off, so I_D remains 0

Example 7.3, Page number: 219

In :
I_DSS=9.0*10**-3;
V_GS_off=-8.0;
V_GS=0.0;
I_D=9.0*10**-3
I_D=I_DSS*(1-(V_GS/V_GS_off))**2;
print('Value of I_D for V_GS=0V is %f A '%I_D)
V_GS=-1.0
I_D=I_DSS*(1-(V_GS/V_GS_off))**2;
print('Value of I_D for V_GS=-1V is %f A'%I_D)
V_GS= -4.0
I_D=I_DSS*(1-(V_GS/V_GS_off))**2;
print('Value of I_D for V_GS=-4V is %f A'%I_D)
Value of I_D for V_GS=0V is 0.009000 A
Value of I_D for V_GS=-1V is 0.006891 A
Value of I_D for V_GS=-4V is 0.002250 A

Example 7.4, Page Number: 220

In :
#Variable Declaration
I_DSS=3.0*10**-3;
V_GS_off=-6.0;
y_fs_max=5000.0*10**-6;
V_GS=-4.0;
g_m0=y_fs_max;

#Calculation
g_m=g_m0*(1-(V_GS/V_GS_off));
I_D=I_DSS*(1-(V_GS/V_GS_off))

#Result
print('forward transconductance = %f Siemens'%g_m)
print('value of I D = %f A'%I_D)
forward transconductance = 0.001667 Siemens
value of I D = 0.001000 A

Example 7.5, Page Number: 221

In :
# variable declaration
V_GS=-20.0;         # voltage in volt
I_GSS=-2*10**-9;   # current in ampere

#calculation
R_IN1=abs((-20/(2*10**-9))) # resistance in ohm
R_IN=R_IN1/(10**9)

# result
print "Input resistance = %d Giga ohm" %R_IN
Input resistance = 10 Giga ohm

Example 7.6, Page Number: 223

In :
# variable declaration
V_DD=15;         # voltage in volt
V_G=0;           # voltage in volt
I_D=5*10**-3;     # current in ampere
R_D=1*10**3;      # resistance in ohm
R_G=10*10**6;     # resistance in ohm
R_S=220;         # resistance in ohm

# calculation
V_S=I_D*R_S;       # source voltage in volt
V_D=V_DD-I_D*R_D;  # drain voltage in volt
V_DS=V_D-V_S;      # drain to source voltage in volt
V_GS=V_G-V_S;      # gate to source voltage in volt

# result
print "Drain to source voltage = %.2f volts" %V_DS
print "Gate to source voltage = %.2f volts" %V_GS
Drain to source voltage = 8.90 volts
Gate to source voltage = -1.10 volts

Example 7.7, Page Number: 224

In :
# variable declaration
V_GS=-5.0;        # voltage in volt
I_D=6.25*10**-3;   # current in ampere

#calculation
R_G=abs((V_GS/I_D)) # resistance in ohm

# result
print "Gate resistance = %d ohm" %R_G
Gate resistance = 800 ohm

Example 7.8, Page Number: 224

In :
I_DSS=25.0*10**-3;
V_GS_off=15.0;
V_GS=5.0;
I_D=I_DSS*(1-(V_GS/V_GS_off))**2
R_S=abs((V_GS/I_D))
print('Drain current = %f Amperes'%I_D)
print('Source resistance = %.0f Ohms'%R_S)
Drain current = 0.011111 Amperes
Source resistance = 450 Ohms

Example 7.9, Page Number: 225

In :
# variable declaration
V_D=6;         # drain voltage in volt
V_GS_off=-3;   # off voltage in volt
V_DD=12;       # voltage in volt
I_DSS=12*10**-3;   # current in ampere

#calculation
I_D=I_DSS/2;    #MIDPOINT BIAS
V_GS=V_GS_off/3.4;    #MIDPOINT BIAS
R_S=abs((V_GS/I_D))   #resistance i voltage
R_D=(V_DD-V_D)/I_D    #resistance in voltage

# result
print "Source resistance = %.2f ohm" %R_S
print "Drain resistance = %d ohm" %R_D
Source resistance = 147.06 ohm
Drain resistance = 1000 ohm

Example 7.10, Page Number: 227

In :
import pylab
import numpy

# variable declaration
R_S=680.0;           # resistance in ohm
I_D=0;           # current in ampere

#calculation
V_GS=I_D*R_S;    #FOR I_D=0A

I_DSS=4*10**-3;    # current in ampere
I_D=I_DSS;        # currents are equal
V_GS1=-1*I_D*R_S;    #FOR I_D=4mA

# result
print "V_GS at I_D=0amp is %d volt" %V_GS
print "V_GS at I_D=4mA is %.2f volt" %V_GS1
print "Plotting load line using the values of V_GS at I_D=0 and 4mA,"
print " we find the intersection of load line with transfer characteristic"
print " to get Q-point values of V_GS=-1.5V and I_D=2.25mA"

#########PLOT######################
idss=4
vgsoff=-6
vgs=arange(-6.0,0.0,0.0005)
idk=arange(0.0,4.0,0.0005)
ids=arange(0.0,2.25,0.0005)
vgsk=-idk*0.68
i_d=idss*(1-(vgs/vgsoff))**2
text(-3.00,2.25,'Q Point',size=13)
text(-3.25,2,'(-1.5V, 2.25mA)')
plot(vgs,i_d)
plot(vgsk,idk,'b')
plot(-1.5,2.25,'o')
ylim( (0,5) )
title('Transfer characteristic curve')
xlabel('Vgs')
ylabel('Idss')
V_GS at I_D=0amp is 0 volt
V_GS at I_D=4mA is -2.72 volt
Plotting load line using the values of V_GS at I_D=0 and 4mA,
we find the intersection of load line with transfer characteristic
to get Q-point values of V_GS=-1.5V and I_D=2.25mA
Out:
<matplotlib.text.Text at 0xd95b60c> Example 7.11, Page Number: 228

In :
# variable declaration
V_DD=12;        # voltage in volt
V_D=7;          # voltage in volt
R_D=3.3*10**3;   # resistance in ohm
R_S=2.2*10**3;   # resistance in ohm
R_1=6.8*10**6;   # resistance in ohm
R_2=1*10**6;     # resistance in ohm

#calculation
I_D=(V_DD-V_D)/R_D;   # drain current in ampere
V_S=I_D*R_S;          # source voltage in volt
V_G=(R_2/(R_1+R_2))*V_DD; # gate voltage in volt
V_GS=V_G-V_S;          # gate to source voltage in volt

# result
print "Drain Current = %.4f Ampere" %I_D
print "Gate to source voltage = %.4f volts" %V_GS
Drain Current = 0.0015 Ampere
Gate to source voltage = -1.7949 volts

Example 7.12, Page Number: 229

In :
# variable declaration
R_1=2.2*10**6;        # resistance in ohm
R_2=R_1;             # resistance in ohm
V_DD=8;              # voltage in volt
R_S=3.3*10**3;        # resistance in ohm

#calculation
V_GS=(R_2/(R_1+R_2))*V_DD;    #FOR I_D=0A
V_G=V_GS;                   # voltage in volt
I_D=(V_G-0)/R_S;    #FOR V_GS=0V

# result
print "V_GS = %d volt" %V_GS
print "at V_GS=0V. I_D = %.4f ampere" %I_D
print "Plotting load line using the value of V_GS=4V at I_D=0"
print " and I_D=1.2mA at V_GS=0V, we find the intersection of"
print " load line with transfer characteristic to get Q-point"
print " values of V_GS=-1.8V and I_D=1.8mA"
V_GS = 4 volt
at V_GS=0V. I_D = 0.0012 ampere
Plotting load line using the value of V_GS=4V at I_D=0
and I_D=1.2mA at V_GS=0V, we find the intersection of
load line with transfer characteristic to get Q-point
values of V_GS=-1.8V and I_D=1.8mA

Example 7.13, Page Number: 235

In :
I_DSS=10.0*10**-3;
V_GS_off=-8.0;
V_GS=-3.0;
I_D=I_DSS*(1-(V_GS/V_GS_off))**2;
print('Drain current when V_GS=-3V is %f Amperes'%I_D)
V_GS=3;
I_D=I_DSS*(1-(V_GS/V_GS_off))**2;
print('Drain current when V_GS=3V is %f Amperes'%I_D)
Drain current when V_GS=-3V is 0.003906 Amperes
Drain current when V_GS=3V is 0.018906 Amperes

Example 7.14, Page Number: 236

In :
#variable Declaration
I_D_on=500.0*10**-3;
V_GS=10.0;
V_GS_th=1.0;
K=I_D_on/((V_GS-V_GS_th)**2)
V_GS=5.0;
I_D=K*(V_GS-V_GS_th)**2;
print('Drain current = %f A'%I_D)
Drain current = 0.098765 A

Example 7.15, Page Number: 237

In :
# variable declaration
I_DSS=12*10**-3;    # currenin ampere
V_DD=18;            # voltage in volt
R_D=620;            # resistance in oh

#calculation
I_D=I_DSS;          # currents are equal
V_DS=V_DD-I_D*R_D;  # drain to source voltage

# result
print "Drain to sorce voltage = %.2f volt" %V_DS
Drain to sorce voltage = 10.56 volt

Example 7.16, Page Number: 238

In :
#variable Declaration
I_D_on=200.0*10**-3;
V_DD=24.0;
R_D=200.0;
V_GS=4.0;
V_GS_th=2.0;
R_1=100.0*10**3;
R_2=15.0*10**3;

#Calculation
K=I_D_on/((V_GS-V_GS_th)**2)
V_GS=(R_2/(R_1+R_2))*V_DD;
I_D=K*(V_GS-V_GS_th)**2;
V_DS=V_DD-I_D*R_D;

#Result
print('Drain to Source voltage = %f V'%V_DS)
print('Gate to Source voltage = %f V'%V_GS)
Drain to Source voltage = 11.221172 V
Gate to Source voltage = 3.130435 V

Example 7.17, Page Number: 239

In :
# variable declaration
V_GS_on=3;         # voltage in volt
V_GS=8.5           #voltage displayed on meter
V_DS=V_GS;         # voltages are equal
V_DD=15;           # voltage in volt
R_D=4.7*10**3;      # resistance in ohm

#calculation
I_D=(V_DD-V_DS)/R_D;  # drain current

# result
print "Drain current = %.4f ampere" %I_D
Drain current = 0.0014 ampere