# Chapter 10 : FET biasing¶

## Example 10.1, Page No 381¶

In [1]:
import math
#initialisation of variables

Vdd=22.0
Rd=2.0*10**3

#Calculations
print("when Id=0")
Id=0
Vds=Vdd-Id*Rd
print('at point A Vds = %.2f V' %Vds)
Vds=0
Id=Vdd/Rd

#Results
print("when Vds=0")
print('at point A Id = %.2f mA' %(Id*10**3))

when Id=0
at point A Vds = 22.00 V
when Vds=0
at point A Id = 11.00 mA


## Example 10.4, Page No 387¶

In [2]:
import math

#initialisation of variables

Idss=8.0*10**-3
Vpmax=6.0
Vgs=2.3
Vgsmax=6

#Calculations
Id=Idss*(1-(Vgs/Vgsmax))**2
Idss=4*10**-3
Vp=3
Idmin=Idss*(1-(Vgs/Vp))**2

#Results
print('at point A Idmin = %.2f mA' %(Idmin*10**3))

at point A Idmin = 0.22 mA


## Example 10.6 Page No 393¶

In [3]:
import math

#initialisation of variables
Vdd=25.0
R2=1.0*10**6
R1=3.8*10**6
Rs=2.5*10**3
Rd=2.5*10**3

#Calculations
Vg=(Vdd*R2)/(R1+R2)
print("when Id=0")
Id=0
Vgs=Vg-Id*Rs
print(" plot point A at Id=0")
print('at point A Vds = %.2f A/s' %Vds)
Vgs=0
Id=Vg/Rs
print(" plot point B Vgs=0")
print('at point A Id = %.2f A/s' %Id)
Idmax=3*10**-3
Idmin=2.3*10**-3
Vdsmin=Vdd-Idmax*(Rd+Rs)
Vdsmax=Vdd-Idmin*(Rd+Rs)

#Results
print('The value of Vdsmax = %.2f V' %(Vdsmax))

when Id=0
plot point A at Id=0
at point A Vds = 0.00 A/s
plot point B Vgs=0
at point A Id = 0.00 A/s
The value of Vdsmax = 13.50 V


## Example 10.7, Page No 401¶

In [4]:
import math
#initialisation of variables

Id=3.0*10**-3
Vgs=-2.3
Vdsmin=10.0
Vdd=25.0
Vgsoff=-6
Idss=8.0*10**-3

#Calculations
Vgs=Vgsoff*(1-math.sqrt(Id/Idss))
Rd=(Vdd-Vdsmin)/Id

#Results
print('The value of Td = %.2f kohm' %(Rd/1000))

The value of Td = 5.00 kohm


## Example 10.8 Page No 403¶

In [5]:
import math
#initialisation of variables
Id=3.0*10**-3
Vds=10.0
Vdd=25.0
Vgs=2.3

#Calculations
Rs=Vgs/Id
Rd=((Vdd-Vds)/Id)-Rs

#Results
print('The value of Rd = %.2f ohm' %(Rd/1000))

The value of Rd = 4.23 ohm


## Example 10.9 Page No 405¶

In [6]:
import math

#initialisation of variables
Id=3.0*10**-3
Vds=10.0
Vdd=25.0
Vg=5.2
Vgsoff=-6
Idss=8.0*10**-3
R2=1.0*10**6

#Calculations
R=(Vdd-Vds)/Id#R=(Rs+Rd)/2
Rd=R/2
Rs=Rd
Vgs=Id*Rs
Vgs=Vgsoff*(1-math.sqrt(Id/Idss))
Vs=Id*Rs
Vg=Vs-(-Vgs)
R1=((Vdd-Vg)*R2)/Vg

#Results
print('The value of R = %.2f Mohm' %(R1/10**6))

The value of R = 3.83 Mohm


## Example 10.11, Page No 412¶

In [7]:
import math
#initialisation of variables

Vee=20.0
Id=3.0*10**-3
Vds=9.0
Vbe=.7
Vb=0
Ve=Vee-Vbe

#Calculations
Re=Ve/Id
Re=6.8*10**3#satnadard value
Id=Ve/Re
Idss=16*10**-3
Vgsoff=-8
Vgs=Vgsoff*(1-math.sqrt(Id/Idss))
Vs=Vb-Vgs
Vrd=Vee-Vds-Vs
Rd=Vrd/Id

#Results
print('The value of Rd = %.2f V' %(Rd/1000))

The value of Rd = 2.24 V


## Example 10.12 Page No 415¶

In [8]:
import math

#initialisation of variables
Idss=5.0*10**-3
Vgsoff=6.0
Rs=3.3*10**3
Vdd=20.0
Rd=Rs

#Calculations
print("when Id=0 % Vgs=Vs=0")
Id=0
Vgs=0
Vs=0
print(" at point A universal transfer characteristic Id/Idss and Vgs/Vgsoff=0")
Id=1.5*10**-3
Vgs=Id*Rs
y=Id/Idss
x=Vgs/Vgsoff
print(" point B the universal transfer charecteristic x=.825 and y=.3")
Id=.2*Idss
Vds=Vdd-Id*(Rd+Rs)

#Results
print('The value of Vds = %.2f V' %(Vds))

when Id=0 % Vgs=Vs=0
at point A universal transfer characteristic Id/Idss and Vgs/Vgsoff=0
point B the universal transfer charecteristic x=.825 and y=.3
The value of Vds = 13.40 V


## Example 10.13 Page No 416¶

In [9]:
import math
#initialisation of variables

Idss=9.0*10**-3
Vgsoff=7.0
Vdd=22.0
R1=4.7*10**6
R2=1.0*10**6
Rs=2.7*10**3
Rd=Rs

#Calculations
Vg=(Vdd*R2)/(R1+R2)
print("when Vgs=0 % Vgs/Vgsoff=0")
Id=Vg/Rs
print("when Vgs/Vgsoff=.5")
Vgs=.5*(-Vgsoff)
Id=(Vg-Vgs)/Rs
x=Id/Idss
print(" point Y on universal characteristic x=.3 and Vgs/Vgsoff=.5")
print("draw voltage divider bias line through X nad Y where bisa line intersect transfer curve")
Id=.29*Idss
Vds=Vdd-Id*(Rd+Rs)

#Results
print('The value of Vds= %.2f V' %(Vds))

when Vgs=0 % Vgs/Vgsoff=0
when Vgs/Vgsoff=.5
point Y on universal characteristic x=.3 and Vgs/Vgsoff=.5
draw voltage divider bias line through X nad Y where bisa line intersect transfer curve
The value of Vds= 7.91 V


## Example 10.14 Page No 419¶

In [10]:
import math

#initialisation of variables

Vdd=40.0
R2=1.0*10**6
R1=5.6*10**6
Rd=4.7

#Calculations
Vg=(Vdd*R2)/(R1+R2)
print("from the point where the bias line intersect the transfer curve")
Id=6.2
Vds=Vdd-Id*Rd

#Results
print('The value of Vds= %.2f V' %(Vds))

from the point where the bias line intersect the transfer curve
The value of Vds= 10.86 V


## Example 10.16, Page No 422¶

In [11]:
import math

#initialisation of variables
rDS=25.0
Vgsoff=10.0
Vds=200.0*10**-3
Vdd=12.0

#Calculations
Id=Vds/rDS
Rd=Vdd/Id
Vi=-(Vgsoff+1)

#Results
print('The value of Vi= %.2f V' %(Vi))

The value of Vi= -11.00 V


## Example 10.17, Page No 424¶

In [12]:
import math
#initialisation of variables

Vdd=50.0
Rd=10.0
R2=1.0*10**6
rDS=0.25

#Calculations
Id=Vdd/Rd
print(" from transfer curve at Id=5 and Vgs=5.7")
Vgs=5.7
R1=((Vdd-Vgs)*R2)/Vgs#use 6.8Mohm to make Vgs>5.7V to ensure that the FET is biased on
Vds=Id*rDS

#Results
print('The value of Vds= %.2f V' %(Vds))

 from transfer curve at Id=5 and Vgs=5.7
The value of Vds= 1.25 V