Chapter 4 : Field Effect Transistors and MOSFETs¶
Example 4.1, Page No. 257¶
In [2]:
# find the drain current
import math
#variable declaration
Idss=15.0 # maximum drain current in mili-ampere
VgsOFF=-5.0 # pinch off voltage in volts
Vgs1=0.0 # gate source voltage in volts
Vgs2=-1.0 # gate source voltage in volts
Vgs3=-4.0 # gate source voltage in volts
#Calculations
Id1=Idss*(1-(Vgs1/VgsOFF))**2
Id2=Idss*(1-(Vgs2/VgsOFF))**2
Id3=Idss*(1-(Vgs3/VgsOFF))**2
#Result
print("drain current (mA) = %.f"%Id1)
print("drain current (mA) = %.1f"%Id2)
print("drain current (mA) = %.1f"%Id3)
Example 4.2, Page No. 257¶
In [6]:
# find the drain current
import math
#variable declaration
Idss=12.0 # maximum drain current in mili-ampere
VgsOFF=-20.0 # pinch off voltage in volts
Vgs1=0.0 # gate source voltage in volts
Vgs2=-5.0 # gate source voltage in volts
Vgs3=-10.0 # gate source voltage in volts
Vgs4=-15.0 # gate source voltage in volts
Vgs5=-20.0 # gate source voltage in volts
#Calculations
Id1=Idss*(1-(Vgs1/VgsOFF))**2;
Id2=Idss*(1-(Vgs2/VgsOFF))**2;
Id3=Idss*(1-(Vgs3/VgsOFF))**2;
Id4=Idss*(1-(Vgs4/VgsOFF))**2;
Id5=Idss*(1-(Vgs5/VgsOFF))**2;
#Result
print("Vgs(V)\tId(mA)")
print(" %.f\t%.f"%(Vgs1,Id1))
print(" %.f \t%.f"%(Vgs2,Id2))
print(" %.f \t%.f"%(Vgs3,Id3))
print(" %.f \t%.f"%(Vgs4,Id4))
print(" %.f \t%.f"%(Vgs5,Id5))
Example 4.3.a, Page No.258¶
In [7]:
# Plot the min transconductance curve
import math
import matplotlib.pyplot as plt
%matplotlib inline
from array import array
#variable declaration
#VGS_off=-2 to -6 volt
#IDSS=8 to 20 mA
#Formula : ID=IDSS*[1-VGS/VGS_off]^2
#Let take some values for plotting
IDSS=8.0 # in mA
VGS= array("f", [0, -0.5, -1.0, -1.5, -2.0]) #in Volt
VGS_off=-2 # in Volt
ID=array("f")
print(" Minimum Transcunductance Values:\n Vgs \t Id")
for i in range(0,5):
ID.append(IDSS*(1-VGS[i]/VGS_off)**2)
print("%.1f \t%.1f"%(VGS[i],ID[i]))
plt.plot(VGS,ID)
plt.title(" Minimum Transconductance Curve")
plt.xlabel("Gate to source voltage (Vgs)")
plt.ylabel("Drain current in milli ampere(Id)")
plt.show()
Example 4.3.b, Page No.258¶
In [10]:
# Plot the max transconductance curve
import math
import matplotlib.pyplot as plt
%matplotlib inline
from array import array
#variable declaration
#VGS_off=-2 to -6 volt
#IDSS=8 to 20 mA
#Formula : ID=IDSS*[1-VGS/VGS_off]^2
#Let take some values for plotting
IDSS=20.0 # in mA
VGS= array("f", [0, -2.0, -4.0, -6.0]) #in Volt
VGS_off=-6 # in Volt
ID=array("f")
print(" Maximum Transcunductance Values:\n Vgs \t Id")
for i in range(0,4):
ID.append(IDSS*(1-VGS[i]/VGS_off)**2)
print("%.1f \t%.1f"%(VGS[i],ID[i]))
plt.plot(VGS,ID)
plt.title(" Maximum Transconductance Curve")
plt.xlabel("Gate to source voltage (Vgs)")
plt.ylabel("Drain current in milli ampere(Id)")
plt.show()
#Drain current value correspond to Vgs = -4 is wrong in the book.
Example 4.4, Page No. 261¶
In [31]:
# drain current and transconductance
import math
#variable declaration
Idss=20.0 # maximum drain current in mili-ampere
Vp=-8.0 # pintc off voltage in volts
gmo=5000.0 # in micro seconds
Vgs=-4.0 # gate to source voltage in volts
#Calculations
Id=Idss*(1-(Vgs/Vp))**2
gm=gmo*(1-(Vgs/Vp));
#Result
print("drain current (mA) = %.f"%Id)
print("transconductance (micro-second) = %.f"%gm)
Example 4.5, Page No.279¶
In [11]:
# drain resisitance
import math
#variable declaration
Id=0.4 #drain current in mili-ampere
Vd=1.0 #drain voltage in volts
Vs=-5.0 #dc voltage in volts
Vss=-3.0 #dc voltage in volts
Vdd=5.0 #dc voltage in volts
MuCox=20.0 #in micro-ampere/volts
W=400.0 #in micro-metre
l=10.0 # in micro-metre
#Calculations
Id=((1.0/2)*(MuCox)*(W/l))
Rs=(Vss-Vs)/(Id*10**-3)
Rd=(Vdd-Vd)/(Id*10**-3)
#Result
print("The values of the resistances are as follows : ")
print("Resistance Rs is %.f K-ohm"%Rs)
print("Resistance Rd is %.f K-ohm"%Rd);
Example 4.6, Page No. 279¶
In [13]:
# drain resisitance
import math
#variable declaration
Vdd=10.0 # in volt
ID=0.4 # in mA
mu_nCox=20.0 # in uA/V^2
W=100.0 # in um
L=10.0 # in um
Vt=2.0 # in Volt
#Calculations
#Formula : ID=mu_n*Cox*W*(VGS-Vt)^2/(2*L)
VGS=math.sqrt(2*L*ID/(mu_nCox*10**-3*W))+(Vt)
Vd=VGS
R=(Vdd-Vd)/ID
#Result
print("Drain resistance is %.f k-ohm"%R)
Example 4.7, Page No. 280¶
In [20]:
# drain to source resisitance
import math
#variable declaration
Vdd=5.0 #in volt
knwl=1.0 #in mA/V^2
Vd=0.1 #drain voltage
Vt=1.0 #in Volt
#Calculations
Id=Vt*((Vdd-Vt)*Vd- (1.0/2)*0.01) #drain current in milli ampere
Rd=(Vdd-Vd)/Id #resistance in killo ohms
Rds= Vd/Id #resistance in killo ohms
#Result
print("Effective drain to source resistance is %.f ohm"%(Rds*1000))
Example 4.8, Page No. 280¶
In [22]:
# Analyse the circuit
import math
#variable declaration
Vdd=10.0 #in volt
ID=0.4 #in mA
knwl=1.0 #in mA/V^2
Vg=5.0 #gate voltage in volys
Vt=1.0 #in Volt
Rd=6.0 #drain resistance in killo ohms
Id=0.5 #in mA after solving the qudratic equation
#Calaculations
Vs= Id*Rd #source voltage in volts
Vd= Vdd-Rd*Id #drain voltage in volts
Vgs= Vg-Rd*Id #gate to source voltage in volts
#Result
print("source voltage = %.f V"%Vs)
print("drain voltage = %.f V"%Vd)
print("gate to source voltage = %.f V"%Vgs)
print("drain current = %.1f mA"%Id)
print("\nAs Vd>Vg-Vt, the transistor is operating at saturation as initially assumed.")
Example 4.9, Page No.281¶
In [26]:
# drain resisitance
import math
#variable declaration
Vdd=5.0 #in volt
Id=0.5 #in mA
knwl=1.0 #in mA/V^2
Vt=-1.0 #in Volt
#Calcualtions
#Formula : ID=mu_n*Cox*W*(VGS-Vt)^2/(2*L)
VGS=math.sqrt((2*Id/knwl))+(Vt)
Vd=3
Rd1=Vd/Id #drain resistance in killo ohms
Vdm= Vd-Vt #saturation mode operation
Rd2=Vdm/Id #drain resistance in killo ohms
#Result
print("Drain resistance is %.f k-ohm"%Rd1)
print("Largest value of drain resistance maintaining saturation-region is %.f k-ohm"%Rd2)
Example 4.10, Page No.282¶
In [30]:
# channel width to channel length ratio and drain resisitance
import math
#variable declaration
Id=100.0 # drain current in micro-ampere
kn=20.0 # in micro-ampere per volt^2
Vt=-1.0 # in volts
Vgs=0.0 # gate source voltage in volts
Vdd=5.0 # dc voltage in volts
Vd=1.0 # drain voltage in volts
#Calculations
wl=(2*Id/(kn*(Vgs-Vt)**2))
Rd=(Vdd-Vd)/(Id*10**-3)
#Result
print("channel width to channel ratio (W/L) = %.f"%wl)
print("drain resistance (in k-ohm) = %.f"%Rd)
print("\nRd can vary in the range 0 to 40 k-ohm")
Example 4.11, Page No. 282¶
In [32]:
# drain to source resisitance
import math
#variable declaration
Vdd=10.0 # in volt
knwl=1.0 # in mA/V^2
Vd=0.1 # drain voltage
Vt=-1.0 # in Volt
#Calculations
Id=1*((-Vt)*Vd- (1.0/2)*0.01)# drain current in milli ampere
Rd=(Vdd-Vd)/Id # resistance in killo ohms
Rds= Vd/Id # resistance in killo ohms
print("Drain to source resistance is %.f k-ohm"%Rds)
Example 4.12, Page No.287¶
In [34]:
# input resistance
import math
#variable declaration
Vdd=15.0 # in volt
knwl=0.25 # in mA/V^2
Va=50.0 # voltage
Vt=1.5 # in Volt
Id=1.06 # drain current in milli ampre
Vd= 4.4 # drain oltage in volt
Rd=10.0 # drain resistance in killo ohms
Rg=10.0 # gate resistance in killo ohms
Rl=10.0 # load resistance in killo ohms
Ii=4.3 # input current in milli ampere
#Calculations
Vgs=Vd
gm=knwl*(Vgs-Vt) # transconductance in mA/V
ro=Va/Id # output resistance in killo ohms
x=(Rd*Rl)/(Rd+Rl)
Av= -gm*((x*ro)/(x+ro))
Ri= Rg/Ii # input resistance in mega ohms
print("Input resistance (Rin) = %.2f Mega-ohm"%Ri)