Chapter- 7 FET Biasing

Example-7.1 Page Number-416

In [4]:
#from the given figure:
Vdd=16.0                  #supply  voltage in volts
Idss=10.0                 #drain source saturation current in mA
Vp=-8.0                   #pinch off voltage in volts
Rd=2.0                    #drain resistance in kohm
Vgg=-2.0                  #gate voltage in volts

#calculation:
Vgs=Vgg                 #gate source voltage in volts
X=(1-Vgs/Vp)**2         #temporary variable
Id=Idss*X               #drain current in mA
Vds=Vdd-Id*Rd           #drain source voltage in volts
Vd=Vds                  #drain voltage in volts
Vg=Vgs                  #gate voltage in volts
Vs=0                    #source voltage in volts

print "Vgs=",Vgs,"V"
print "Id=",Id,"mA"
print "Vds=",Vds,"V"
print "Vd=",Vd,"V"
print "Vg=",Vg,"V"
print "Vs=",Vs,"V"

Vgs= -2.0 V
Id= 5.625 mA
Vds= 4.75 V
Vd= 4.75 V
Vg= -2.0 V
Vs= 0 V

Example-7.2 Page Number-419

In [6]:
#from the given figure:
Vdd=20.0                  #supply  voltage in volts
Idss=8.0                  #drain source saturation current in mA
Vp=-6.0                   #pinch off voltage in volts
Rd=3.3                    #drain resistance in kohm
Rg=1.0                    #gate resistance in Mohm
Rs=1                      #source resistance in kohm

#drawing the load line and characterstics curve:
#calculation:
Id=2.6                  #drain current in mA
Vds=Vdd-Id*(Rd+Rs)      #drain source voltage in volts
Vs=Id*Rs                #source voltage in volts
Vg=0                    #gate voltage in volts
Vd=Vds+Vs               #drain voltage in volts

print "Id=",Id,"mA"
print "Vds=",Vds,"V"
print "Vs=",Vs,"V"
print "Vg=",Vg,"V"
print "Vd=",Vd,"V"

Id= 2.6 mA
Vds= 8.82 V
Vs= 2.6 V
Vg= 0 V
Vd= 11.42 V

Example-7.5 Page Number-424

In [9]:
#from the given figure:
Vdd=16.0                  #supply  voltage in volts
Idss=8.0                  #drain source saturation current in mA
Vp=-4.0                   #pinch off voltage in volts
Rd=2.4                    #drain resistance in kohm
R1=2.1                    #resistance in Mohm
R2=270.0                  #resistance in kohm
Rs=1.5                    #source resistance in kohm

#drawing the load line and characterstics curve:
#calculation:
Vg=1.82                  #gate voltage in volts         
Id=2.4                   #drain current in mA
Vgs=-1.8                 #gate source voltage in volts
Vd=Vdd-Id*Rd             #drain voltage in volts
Vs=Id*Rs                 #source voltage in volts
Vds=Vdd-Id*(Rd+Rs)       #drain source voltage in volts
Vdg=Vd-Vg                #drain gate voltage in volts 

print "Id=",Id,"mA"
print "Vgs=",Vgs,"V"
print "Vd=",Vd,"V"
print "Vs=",Vs,"V"
print "Vds=",Vds,"V"
print "Vdg=",Vdg,"V"

Id= 2.4 mA
Vgs= -1.8 V
Vd= 10.24 V
Vs= 3.6 V
Vds= 6.64 V
Vdg= 8.42 V

Example-7.6 Page Number-427

In [12]:
#from the given figure:
Vdd=12.0                  #supply  voltage in volts
Idss=12.0                 #drain source saturation current in mA
Vp=-6.0                   #pinch off voltage in volts
Rd=1.5                    #drain resistance in kohm
Rs=680                    #source resistance in ohm

#drawing the load line and characterstics curve:
#calculation:
Vg=0                     #gate voltage in volts         
Id=3.8                   #drain current in mA
Vgs=-2.6                 #gate source voltage in volts
Vd=Vdd-Id*Rd             #drain voltage in volts
Vs=Id*Rs                 #source voltage in volts
Vds=Vd-Vs/1000           #drain source voltage in volts

print "Id=",Id,"mA"
print "Vgs=",Vgs,"V"
print "Vd=",Vd,"V"
print "Vg=",Vg,"V"
print "Vs=",round(Vs/1000,2),"V"
print "Vds=",round(Vds,2),"V"

Id= 3.8 mA
Vgs= -2.6 V
Vd= 6.3 V
Vg= 0 V
Vs= 2.58 V
Vds= 3.72 V

Example-7.7 Page Number-430

In [19]:
#from the given figure:
Vdd=18.0                  #supply  voltage in volts
Idss=6.0                  #drain source saturation current in mA
Vp=-3.0                   #pinch off voltage in volts
Rd=1.8                    #drain resistance in kohm
R1=110                    #resistance in Mohm
R2=10.0                   #resistance in Mohm
Rs=750.0                    #source resistance in ohm

#drawing the load line and characterstics curve:
#calculation:
Vg=1.5                   #gate voltage in volts         
Id=3.1                   #drain current in mA
Vgs=-0.8                 #gate source voltage in volts
Vds=Vdd-Id*(Rd+Rs/1000)       #drain source voltage in volts

print "Id=",Id,"mA"
print "Vgs=",Vgs,"V"
print "Vds=",round(Vds,2),"V"

Id= 3.1 mA
Vgs= -0.8 V
Vds= 10.1 V

Example-7.8 Page Number-431

In [20]:
#from the given figure:
Vdd=18.0                  #supply  voltage in volts
Idss=6.0                  #drain source saturation current in mA
Vp=-3.0                   #pinch off voltage in volts
Rd=1.8                    #drain resistance in kohm
R1=110                    #resistance in Mohm
R2=10.0                   #resistance in Mohm
Rs=150.0                    #source resistance in ohm

#drawing the load line and characterstics curve:
#calculation:         
Id=7.6                   #drain current in mA
Vgs=0.35                 #gate source voltage in volts
Vds=Vdd-Id*(Rd+Rs/1000)       #drain source voltage in volts

print "Id=",Id,"mA"
print "Vgs=",Vgs,"V"
print "Vds=",round(Vds,2),"V"

Id= 7.6 mA
Vgs= 0.35 V
Vds= 3.18 V

Example-7.9 Page Number-432

In [22]:
#from the given figure:
Vdd=20.0                  #supply  voltage in volts
Idss=8.0                  #drain source saturation current in mA
Vp=-8.0                   #pinch off voltage in volts
Rd=6.2                    #drain resistance in kohm
Rs=2.4                    #source resistance in kohm
Rg=1                      #gate resistance in Mohm

#drawing the load line and characterstics curve:
#calculation:         
Id=1.7                   #drain current in mA
Vgs=-4.3                 #gate source voltage in volts
Vds=Vdd-Id*(Rd+Rs/1000)       #drain source voltage in volts

print "Id=",Id,"mA"
print "Vgs=",Vgs,"V"
print "Vds=",round(Vds,2),"V"

Id= 1.7 mA
Vgs= -4.3 V
Vds= 9.46 V

Example-7.10 Page Number-433

In [23]:
#from the given figure:
Vdd=20.0                  #supply  voltage in volts
Idss=10.0                 #drain source saturation current in mA
Vp=-4.0                   #pinch off voltage in volts
Rd=1.5                    #drain resistance in kohm
Vgs=0                      #gate source voltage in volts

#calculation:  
#since Vgs=0V, Id=Idss=10mA  
Id=10                      #drain current in mA
Vd=Vdd-Id*Rd               #drain voltage in volts

print "Id=",Id,"mA"
print "Vgs=",Vgs,"V"
print "Vd=",round(Vd,2),"V"

Id= 10 mA
Vgs= 0 V
Vd= 5.0 V

Example-7.14 Page Number-442

In [28]:
#from the given figure:
Vdd=16.0                  #supply  voltage in volts
Idss=8.0                 #drain source saturation current in mA
Vp=-4.0                   #pinch off voltage in volts
Rc=3.6                    #collector resistance in kohm
Rb=470                    #base resistance in kohm
Rs=2.4                    #source resistance in kohm
B=80
Vbe=0.7                   #base emitter voltage in volts

#drawing the load line and characterstics curve:
#calculation:         
Id=1.0                   #drain current in mA
Vgs=-2.6                 #gate source voltage in volts
Ie=Ic=Id                 #emitter current and collector current in mA
Ib=Ic/B                  #base current in mA
Vb=Vdd-Ib*Rb             #base voltage in volts
Ve=Vd=Vb-Vbe             #base voltage in volts

print "Id=",Id,"mA"
print "Vgs=",Vgs,"V"
print "Ie=",Ie,"mA"
print "Ib=",round(Ib*1000,2),"microA"
print "Vb=",round(Vb,3),"V"
print "Ve=",round(Ve,2),"V"

Id= 1.0 mA
Vgs= -2.6 V
Ie= 1.0 mA
Ib= 12.5 microA
Vb= 10.125 V
Ve= 9.43 V

Example-7.16 Page Number-444

In [31]:
#from the given figure:
Vdd=16.0                  #supply  voltage in volts
Rd=1.8                    #drain resistance in kohm
R1=91.0                   #resistance in kohm
R2=47.0                   #resistance in kohm
Vd=12                     #drain voltage in volts
Vgs=-2                    #gate source voltage in volts

#calculation:         
Id=(Vdd-Vd)/Rd                     #drain current in mA
Vg=(R2*Vdd)/(R2+R1)                #gate voltage in volts
Rs=(Vg-Vgs)/Id                     #source resistance in kohm

print "Id=",round(Id,2),"mA"
print "Vg=",round(Vg,2),"V"
print "Rs=",round(Rs,2),"kohm"

Id= 2.22 mA
Vg= 5.45 V
Rs= 3.35 kohm

Example-7.17 Page Number-444

In [34]:
#from the given figure:
Idon=4.0                    #drain current in mA
Vgson=6.0                   #gate source voltage in volts
Vgsth=3.0                   #gate source threshold voltage in volts

#calculation:
Id=Idon                           #drain current in mA
Vgs=Vgson                         #gate voltage in volts
Vdd=Vgs*2                         #drain voltage in volts
Vds=Vdd/2                         #drain source voltage in volts
Rd=(Vdd-Vds)/Idon                 #drain resistance in ohm

print "Vdd=",round(Vdd,2),"V"
print "Rd=",round(Rd,2),"kohm"

Vdd= 12.0 V
Rd= 1.5 kohm