Chapter 30 : Field Effect Transistors

Example No. 30_1 Page No. 984

In [3]:
# Determine Id for each value of Vgs (a) 0V# (b) -0.5V# (c) -1V (d) -2V (e) -3V

# Given Data

Vgs1 = 0#           # Voltage Gate-Source 1=0 Volts
Vgs2 = -0.5#        # Voltage Gate-Source 2=-0.5 Volts
Vgs3 = -1.#          # Voltage Gate-Source 3=-1 Volts
Vgs4 = -2.#          # Voltage Gate-Source 4=-2 Volts
Vgs5 = -3.#          # Voltage Gate-Source 5=-3 Volts
Vgsoff = -4.#        # Voltage Gate-Source(off)=-4 Volts
Idss = 10.*10**-3     # Idss = 10m Amps

a = (1-(Vgs1/Vgsoff))
b = (1-(Vgs2/Vgsoff))
c = (1-(Vgs3/Vgsoff))
d = (1-(Vgs4/Vgsoff))
e = (1-(Vgs5/Vgsoff))

# Vgs = 0 Volts

Id1 = Idss*a*a
print 'The Value of Id for Vgs is 0 Volts = %0.2f Amps'%Id1
print 'i.e 10 mAmps'

# Vgs = -0.5 Volts

Id2 = Idss*b*b
print 'The Value of Id for Vgs is -0.5 Volts = %0.4f Amps'%Id2
print 'i.e 7.65 mAmps'

# Vgs = -1 Volts

Id3 = Idss*c*c
print 'The Value of Id for Vgs is -1 Volts = %0.4f Amps'%Id3
print 'i.e 5.62 mAmps'

# Vgs = -2 Volts

Id4 = Idss*d*d
print 'The Value of Id for Vgs is -2 Volts = %0.4f Amps'%Id4
print 'i.e 2.5 mAmps'

# Vgs = -3 Volts

Id5 = Idss*e*e
print 'The Value of Id for Vgs is -3 Volts = %0.4f Amps'%Id5
print 'i.e 0.625 mAmps'
The Value of Id for Vgs is 0 Volts = 0.01 Amps
i.e 10 mAmps
The Value of Id for Vgs is -0.5 Volts = 0.0077 Amps
i.e 7.65 mAmps
The Value of Id for Vgs is -1 Volts = 0.0056 Amps
i.e 5.62 mAmps
The Value of Id for Vgs is -2 Volts = 0.0025 Amps
i.e 2.5 mAmps
The Value of Id for Vgs is -3 Volts = 0.0006 Amps
i.e 0.625 mAmps

Example No. 30_2 Page No. 985

In [5]:
# Find the minimim and maximum value of Id and Vds if Vgs=-1.5 Volts

# Given Data

Idssmin = 2.*10**-3#      # Idss(min)=2m Amp
Idssmax = 20.*10**-3#     # Idss(max)=20m Amp
Vgs = -1.5#             # Voltage Gate-Source=-1.5V
Vgsoffmin = -2.#         # Voltage Gate-Source(off)(min)=-2 Volts
Vgsoffmax = -8.#         # Voltage Gate-Source(off)(max)=-8 Volts
Vdd = 2.0#               # Supply Voltage(Drain)=20 Volts
Rd = 1.*10**3#            # Drain Resistance=1k Ohms

a = 1-(Vgs/Vgsoffmin)#
b = 1-(Vgs/Vgsoffmax)#

# Calculation using Minimum Values

Id1 = Idssmin*a*a#
print 'The Value of Id = %0.4e Amps using Minimum Values'%Id1
print 'i.e 125 uAmps'

Vds1 = Vdd-Id1*Rd#
print 'The Value of Vds = %0.2f Volts using Minimum Values'%Vds1

# Calculation using Maximum Values

Id2 = Idssmax*b*b#
print 'The Value of Id = %0.4f Amps using Maximum Values'%Id2
print 'i.e 13.2 mAmps'

Vds2 = Vdd-Id2*Rd#
print 'The Value of Vds = %0.2f Volts using Maximun Values'%Vds2

Vp = -Vgsoffmax#

Vdsp = Vp+Vgs#
print 'The Value of Vds(p) = %0.2f Volts using Maximun Values'%Vdsp
The Value of Id = 1.2500e-04 Amps using Minimum Values
i.e 125 uAmps
The Value of Vds = 1.88 Volts using Minimum Values
The Value of Id = 0.0132 Amps using Maximum Values
i.e 13.2 mAmps
The Value of Vds = -11.20 Volts using Maximun Values
The Value of Vds(p) = 6.50 Volts using Maximun Values

Example No. 30_3 Page No. 989

In [6]:
# Calculate the value of Vd

# Given Data

Vs = 1.#         # Voltage at Resistor Rs=1 Volts
Rs = 200.#       # Source Resistor=200 Ohms
Vdd = 10.#       # Supply Voltage(Drain)=10 Volts
Rd = 1.*10**3#    # Drain Resistor=1k Ohms

Is=Vs/Rs#

Id = Is#

Vd = Vdd-Id*Rd#
print 'The Drain Voltage Vd = %0.2f Volts'%Vd,
The Drain Voltage Vd = 5.00 Volts

Example No. 30_4 Page No. 991

In [10]:
# Calculate Vg, Vs, Id, Vd.

# Given Data

R1 = 390.*10**3#      # Resistor 1=390k Ohms
R2 = 100.*10**3#      # Resistor 2=100k Ohms
Rd = 1.*10**3#        # Drain Resistor=1k Ohms
Vdd = 15.#           # Supply Voltage(Drain)=15 Volts
Vgs = -1.#           # Voltage Gate-Source=-1 Volts
Rs = 800.#           # Source Resistor=800 Ohms

Vg = (R2/(R1+R2))*Vdd#
print 'The Value of Vg = %0.2f Volts'%Vg
print 'i.e 3 Volts'

Vs = Vg-Vgs#
print 'The Value of Vs = %0.2f Volts'%Vs
print 'i.e 4 Volts'

Id = Vs/Rs#
print 'The Value of Id = %0.2e Amps.'%Id
print 'i.e 5 mAmps'

Vd = Vdd-Id*Rd
print 'The Value of Vd = %0.2f Volts'%Vd
print 'Approx 10 Volts'
The Value of Vg = 3.06 Volts
i.e 3 Volts
The Value of Vs = 4.06 Volts
i.e 4 Volts
The Value of Id = 5.08e-03 Amps.
i.e 5 mAmps
The Value of Vd = 9.92 Volts
Approx 10 Volts

Example No. 30_5 Page No. 992

In [11]:
# Calculate the value Drain Current Id and Drain Voltage Vd.

# Given Data

Vdd = 15#           # Supply Voltage(Drain)=15 Volts
Vbe = 0.7#          # Voltage Base-Emitter=0.7 Volts
Re = 2.2*10**3#      # Emitter Resistor=2.2 kOhms
Rd = 1*10**3#        # Drain Resistor=1 kOhms
Vee = 15#           # Supply Voltage(Emitter)=15 Volts


Ic = (Vee-Vbe)/Re#

Id = Ic#
print 'The Drain Current Id = %0.2e Amps'%Id
print 'i.e 6.5 mAmps'

Vd = Vdd-Id*Rd#
print 'The Drain Voltage Vd = %0.2f Voltage'%Vd
The Drain Current Id = 6.50e-03 Amps
i.e 6.5 mAmps
The Drain Voltage Vd = 8.50 Voltage

Example No. 30_6 Page No. 997

In [14]:
# Calculate the Voltage Gain Av and Output Voltage Vo

# Given Data

Rd = 1.5*10**3#      # Drain Resistor=1.5 kOhms
Rl = 10*10**3#       # Load Resistor=10 kOhms
Idss = 10*10**-3#    # Idss=10 mAmps
Vgs = -1#           # Voltage Gate-Source=-1 Volts
Vgsoff = -4.#        # Voltage Gate-Source(off)=-4 Volts
Vin = 0.2#          # Input Voltage=0.2 Volts(p-p)

gmo = 2*Idss/(-Vgsoff)#

gm = gmo*(1-(Vgs/Vgsoff))#

rl = (Rd*Rl)/(Rd+Rl)#

Av = gm*rl#
print 'The Voltage Gain Av =%0.2f'%Av
print 'Approx 4.875'

Vo = Av*Vin
print 'The Output Voltage Vo = %0.3f Volts(p-p)'%Vo
The Voltage Gain Av =4.89
Approx 4.875
The Output Voltage Vo = 0.978 Volts(p-p)

Example No. 30_7 Page No. 998

In [15]:
# Calculate Av, Vo & Zo.

# Given Data

Rs = 240.#           # Source Resistor=240 Ohms
Rl = 1.8*10**3#      # Load Resistor=1.8 kOhms
Vgsoff = -8.#        # Voltage Gate-Source(off)=-8 Volts
Vgs = -2.#           # Voltage Gate-Source=-2 Volts
Idss = 15.*10**-3     # Idss=15 mAmps.
Vin = 1.#            # Input Voltage=1 Volts(p-p)

rl = ((Rs*Rl)/(Rs+Rl))#
gmo = 2*Idss/-Vgsoff#
gm = gmo*(1-(Vgs/Vgsoff))#

Av = gm*rl/(1+gm*rl)#
print 'The Voltage Gain Av =%0.2f'%Av

Vo = Av*Vin#
print 'The Output Voltage Vo = %0.2f Volts(p-p)'%Vo

A = (1/gm)#
Zo = ((Rs*A)/(Rs+A))#
print 'The Output Impedence Zo = %0.2f Ohms'%Zo
The Voltage Gain Av =0.37
The Output Voltage Vo = 0.37 Volts(p-p)
The Output Impedence Zo = 143.28 Ohms
Approx 143.5 Ohms

Example No. 30_8 Page No. 1000

In [17]:
#Calculate Av, Vo, Zin.

# Given Data

Rd = 1.2*10**3#      # Drain Resistor=1.2 kOhms
Rl = 15.*10**3#       # Load Resistor=15 kOhms
gm = 3.75*10**-3#    # Transconductance=3.75 mSiemens
Vin = 10.*10**-3#     # Input Voltage=10 mVpp
Rs = 200.#           # Source Resistor=200 Ohms

rl = ((Rd*Rl)/(Rd+Rl))#

Av = gm*rl#
print  'The Voltage Gain Av =%0.2f'%Av

Vo = Av*Vin#
print  'The Output Voltage = %0.2e Volts(p-p)'%Vo
print 'Approx 41.6 mVolts(p-p)'

A = (1/gm)#

Zi = ((Rs*A)/(Rs+A))#
print 'The Output Impedence Zi = %0.2f Ohms'%Zi
print 'Approx 114 Ohms'
The Voltage Gain Av =4.17
The Output Voltage = 4.17e-02 Volts(p-p)
Approx 41.6 mVolts(p-p)
The Output Impedence Zi = 114.29 Ohms
Approx 114 Ohms

Example No. 30_9 Page No. 1001

In [19]:
#Determine Id for each value of Vgs (a) 2V# (b) -2V# (c) 0V

# Given Data
Vgs1 = 2.#           # Voltage Gate-Source 1=2 Volts
Vgs2 = -2.#          # Voltage Gate-Source 2=-2 Volts
Vgs3 = 0#           # Voltage Gate-Source 3=0 Volts
Vgsoff = -4.#        # Voltage Gate-Source(off)=-4 Volts
Idss = 10.*10**-3#    # Idss = 10m Amps

a = (1-(Vgs1/Vgsoff))#
b = (1-(Vgs2/Vgsoff))#
c = (1-(Vgs3/Vgsoff))#

# Vgs = 2 Volts

Id1 = Idss*a*a#
print 'The Value of Id for Vgs is 2 Volts = %0.2e Amps'%Id1
print 'i.e 22.5 mAmps'

# Vgs = -2 Volts

Id2 = Idss*b*b#
print 'The Value of Id for Vgs is -2 Volts = %0.2e Amps'%Id2
print 'i.e 2.5 mAmps'

# Vgs = 0 Volts

Id3 = Idss*c*c#
print 'The Value of Id for Vgs is 0 Volts = %0.2e Amps'%Id3
print 'i.e 10 mAmps'
The Value of Id for Vgs is 2 Volts = 2.25e-02 Amps
i.e 22.5 mAmps
The Value of Id for Vgs is -2 Volts = 2.50e-03 Amps
i.e 2.5 mAmps
The Value of Id for Vgs is 0 Volts = 1.00e-02 Amps
i.e 10 mAmps

Example No. 30_10 Page No. 1002

In [18]:
# Calculate the value of Rd to provide an Id(on) of 10m Amps.

# Given Data

Vdd = 15.#           # Suppy Voltage(Drain)=15 Volts
Vgson = 10.#         # Voltage Gate-Source(on)=10 Volts
Idon = 10.*10**-3#    # Drain Current(on)=10m Amps

Rd = (Vdd-Vgson)/Idon#
print 'The Drain Resistance = %0.2f Ohms'%Rd

print 'A 470 Ohms resistor would provide the proper biasing voltage at the  gate'
The Drain Resistance = 500.00 Ohms
A 470 Ohms resistor would provide the proper biasing voltage at the  gate