Chapter 10 , Field Effect Transistors

Example 10.1 , Page Number 344

In [1]:
#Variables

VGS = 10.0                    #Gate-source voltage (in volts)
IG = 0.1 * 10**-6             #Gate current (in Ampere)

#Calculation

RGS = VGS/IG                  #Gate-to-source resistance (in ohm)

#Result

print "Gate-to-source resistance : ",RGS*10**-6,"Mega-ohm."

Gate-to-source resistance :  100.0 Mega-ohm.

Example 10.2 , Page Number 344

In [2]:
#Variables

dVDS = 1.5                  #Change in drain-source voltage (in volts)
dID = 120.0 * 10**-6        #Change in drain current (in Ampere)

#Calculation

rd = dVDS/dID               #AC drain resistance (in ohm) 

#Result

print "AC drain resistance of the JFET : ",rd*10**-3,"kilo-ohm."

AC drain resistance of the JFET :  12.5 kilo-ohm.

Example 10.3 , Page Number 344

In [3]:
#Variables

dID = 0.3 * 10**-3            #Change in drain current (in Ampere)
dVGS = 0.15                   #Changein gate-to-source voltage (in volts)

#Calculation

gm = dID/dVGS                 #Transconductance (in siemen) 

#Result

print "Transconductance : ",gm*10**6,"micro-siemens."

Transconductance :  2000.0 micro-siemens.

Example 10.4 , Page Number 345

In [7]:
#Variables

dVDS = 7.0                  #Change in drain-source voltage (in volts)
dID1 = 0.2 * 10**-3         #Change in drain current1 (in Ampere)
dID2 = -0.7 * 10**-3        #Change in drain current2 (in Ampere)
dVGS = -0.25                #Changein gate-to-source voltage (in volts)

#Calculation

rd = dVDS/dID1              #AC drain resistance (in ohm)
gm = dID2/dVGS              #Transconductance (in Ampere per volt)
u = rd*gm                   #Amplification factor

#Result

print "AC drain resistance : ",rd*10**-3,"kilo-ohm."
print "Transconductance : ",gm*10**3,"mA/V."
print "Amplification factor : ",u,"."

AC drain resistance :  35.0 kilo-ohm.
Transconductance :  2.8 mA/V.
Amplification factor :  98.0 .

Example 10.5 , Page Number 345

In [9]:
#Variables

IDSS = 10.0 * 10**-3                #Drain-source saturation current (in Ampere)
Vp = -4.5                           #Pinch-off voltage (in volts)
IDS = 2.5 * 10**-3                  #Drain-source voltage (in volts)   

#Calculation

VGS = Vp*(1-(IDS/IDSS)**0.5)        #Gate-to-source voltage (in volts)
gm = -2*IDSS/Vp*(1- VGS/Vp)         #Transconductance (in Ampere per volt)  

#Result

print "Transconductance : ",round(gm*10**3,2),"mA/V."

Transconductance :  2.22 mA/V.

Example 10.6 , Page Number 345

In [11]:
#Variables

gm = 10.0 * 10**-3                #Transconductance (in siemens)
IDSS = 10.0 * 10**-6              #Drain-source saturation current (in Ampere)

#Calculation

VGSoff = (-2*IDSS)/gm             #Gate-to-source voltage (in volts)

#Result

print "VGSoff : ",VGSoff*10**3,"mV."

VGSoff :  -2.0 mV.

Example 10.7 , Page Number 345

In [14]:
#Variables

Vp = -4.0              #Pinch-off voltage (in volts)
VGS = -2.0             #Gate-source voltage (in volts)
IDSS = 10.0 * 10**-3   #Drain-source saturation current (in Ampere)

#Calculation

ID = IDSS*(1 - VGS/Vp)**2          #Drain current (in Ampere)
VDSmin = Vp                        #Minimum drain-source voltage (in volts) 

#Result

print "Minimum value of VDS : ",VDSmin,"V."

Minimum value of VDS :  -4.0 V.

Example 10.8 , Page Number 346

In [20]:
#Variables

IDSS = 8.7 * 10**-3    #Drain-source saturation current (in Ampere)
Vp = -3.0              #Pinch-off voltage (in volts)
VGS = -1.0             #Gate-source voltage (in volts)

#Calculation

ID = IDSS*(1 - VGS/Vp)**2          #Drain current (in Ampere)
gmo = -2*IDSS/Vp                   #Transconductance for VGS = 0 (in Ampere per volt)  
gm = gmo*(1 - VGS/Vp)              #Transconductance (in Ampere per volt)

#Result

print "ID : ",round(ID*10**3,4),"mA."
print "gmo : ",round(gmo*10**3,1),"mS."
print "gm : ",round(gm*10**3,3),"mS."

ID :  3.8667 mA.
gmo :  5.8 mS.
gm :  3.867 mS.

Example 10.9 , Page Number 346

In [21]:
#Variables

IDSS = 8.4 * 10**-3    #Drain-source saturation current (in Ampere)
Vp = -3.0              #Pinch-off voltage (in volts)
VGS = -1.5             #Gate-source voltage (in volts)

#Calculation

ID = IDSS*(1 - VGS/Vp)**2          #Drain current (in Ampere)
gmo = -2*IDSS/Vp                   #Transconductance for VGS = 0 (in Ampere per volt)  
gm = gmo*(1 - VGS/Vp)              #Transconductance (in Ampere per volt)

#Result

print "ID : ",round(ID*10**3,4),"mA."
print "gmo : ",round(gmo*10**3,1),"mS."
print "gm : ",round(gm*10**3,3),"mS."

ID :  2.1 mA.
gmo :  5.6 mS.
gm :  2.8 mS.

Example 10.10 , Page Number 346

In [24]:
#Variables

Vp = -4.5              #Pinch-off voltage (in volts)
IDSS = 9.0 * 10**-3    #Drain-source saturation current (in Ampere)
IDS = 3.0 * 10**-3     #Drain-source current (in Ampere) 

#Calculation

VGS = Vp*(1-(IDS/IDSS)**0.5)        #Gate-to-source voltage (in volts)
gm = -2*IDSS/Vp*(1 - VGS/Vp)        #Transconductance (in Ampere per volt)  

#Result

print "VGS : ",round(VGS,3),"V."
print "gm : ",round(gm*10**3,2),"mS."

VGS :  -1.902 V.
gm :  2.31 mS.

Example 10.11 , Page Number 349

In [26]:
#Variables

VGG = 1.5                   #Gate supply voltage (in volts)
VDD = 15.0                  #Drain supply voltage (in volts)
RD = 1.5 * 10**3            #Drain resistance (in ohm)
RG = 2.0 * 10**6            #Gate resistance (in ohm)
IDSS = 15.0 * 10**-3        #Drain current in saturation (in Ampere)
Vp = -4.0                   #Pinch-off voltage (in volts)
VS = 0.0                    #Source voltage (in volts)

#Calculation

VGS = -VGG                  #Gate-to-source voltage (in volts)
ID = IDSS*(1 - VGS/Vp)**2   #Drain current (in Ampere)
VD = VDD - ID*RD            #Drain voltage (in volts)
VDS = VD - VS               #Drain-to-source voltage (in volts)

#Result

print "Drain-source voltage : ",round(VDS,1),"V."

Drain-source voltage :  6.2 V.

Example 10.12 , Page Number 349

In [35]:
#Variables

VGS = VGG = -3.0                #Gate-source voltage (in volts)
IDSS = 12.0 * 10**-3            #Drain current in saturation (in Ampere)
Vp = -6.0                       #pinch-off voltage (in volts) 
VDD = 3.0                       #Drain voltage (in volts) 
RD = 3.5 * 10**3                #Drain resistance (in ohm) 

#Calculation

ID = IDSS*(1 - VGS/Vp)**2   #Drain current (in Ampere)
VDS = VDD - ID*RD           #Drain-source voltage (in volts)
VD = VDS                    #Drain voltage (in volts)
VG = VGG                    #Gate voltage (in volts)
VS = 0                      #Source voltage (in volts) 

#Result

print "ID = ",ID*10**3,"mA."
print "VDS = ",VDS,"V."           
print "VD = ",VD,"V."             
print "VG = ",VG,"V."             
print "VS = ",VS,"V."             

#Calculation error in the value of VDS and VD in the book.

ID =  3.0 mA.
VDS =  -7.5 V.
VD =  -7.5 V.
VG =  -3.0 V.
VS =  0 V.

Example 10.13 , Page Number 350

In [36]:
#Variables

VDD = 25.0               #Drain Supply (in volts)
RD = 3.0 * 10**3         #Drain resistance (in ohm)
RS = 400.0               #Source resistance (in ohm)
ID = 2.0 * 10**-3        #Drain current (in Ampere) 

#Calculation

VDS = VDD - ID*(RD + RS) #Drain-source voltage (in volts)
VGS = -ID*RS             #Gate-source voltage (in volts)

#Result

print "Drain-source voltage : ",VDS,"V."
print "Gate-source voltage : ",VGS,"V."

Drain-source voltage :  18.2 V.
Gate-source voltage :  -0.8 V.

Example 10.14 , Page Number 350

In [46]:
#Variables

VDD = 25.0                  #Drain voltage (in volts)
RG1 = 1.2 * 10**6           #Gate1 resistance (in ohm)
RG2 = 0.6 * 10**6           #Gate2 resistance (in ohm)
ID = 4.0 * 10**-3           #Drain current (in Ampere)
VDS = 8.0                   #Drain-source voltage (in volts) 
Vp = -4.0                   #Pinch-off voltage (in volts)  

#Calculation

VGS = Vp*(1 - (ID/IDSS)**0.5)    #Gate-source voltage (in volts)
VG = VDD*RG2/(RG1 + RG2)    #Gate voltage (in volts)
RS = (VG - VGS)/ID          #Source voltage (in ohm)   

#Result

print "RS : ",round(RS*10**-3,1),"kilo-ohm."

RS :  2.5 kilo-ohm.

Example 10.15 , Page Number 350

In [52]:
#Variables

Vp = -2.0                       #pinch-off voltage (in volts)
IDSS = 5.0 * 10**-3             #Drain current in saturation (in Ampere)
RL = 910.0                      #Load resistance (in ohm)
RF = 2.29 * 10**3               #Resistance (in ohm)
R1 = 12.0 * 10**6               #Resistance1 (in ohm)
R2 = 8.57 * 10**6               #Resistance2 (in ohm)
VDD = 24.0                      #Drain supply voltage (in volts)

#Calculation

VG = VDD*R2/(R1 + R2)           #Gate voltage (in volts)
ID = 4.46 * 10**-3               #Drain current (in Ampere)  
VGS = VG - ID*RF                #Gate-source voltage (in volts)
ID1 = (VG - VGS)/RF             #Drain current at operating point (in Ampere)

#Result

print "Drain current at operating point : ",round(ID1*10**3,3),"mA."
print "Since , value of ID at operating point is almost equal to previously computed value of Id. Therefore , FET is operated in pinch-off region."

Drain current at operating point :  4.46 mA.
Since , value of ID at operating point is almost equal to previously computed value of Id. Therefore , FET is operated in pinch-off region.

Example 10.16 , Page Number 353

In [55]:
#Variables

gm = 2500.0 * 10**-6       #Transconductance (in siemens)
RL = 12.0 * 10**3          #Load resistance (in ohm)

#Calculation

A = -gm*RL                 #Voltage gain  

#Result

print "Voltage gain : ",A,"."

Voltage gain :  -30.0 .

Example 10.17 , Page Number 353

In [57]:
#Variables

gm = 4000.0 * 10**-6       #Transconductance (in siemens)
RL = 15.0 * 10**3          #Load resistance (in ohm)
RD = 10.0 * 10**6          #Drain resistance (in ohm)

#Calculation

A = -gm*RD*RL/(RD + RL)    #Voltage gain

#Result

print "VOltage gain : ",round(A,1),"."

VOltage gain :  -59.9 .

Example 10.18 , Page Number 353

In [62]:
#Variables

VGS = -1.0              #Gate-source voltage (in volts)
VDS = 4.0               #Drain-source voltage (in volts)
IDS = 1.0 * 10**-3      #Drain-source current (in Ampere)
gm = 5.0 * 10**-3       #Transconductance (in siemens)
RDS = 20.0 * 10**3      #Drain-source resistance (in ohm)
RG = 500.0 * 10**3      #Gate resistance (in ohm)   
VDD = 10.0              #Drain supply voltage (in volts)

#Calculation

RS = abs(VGS/IDS)             #Source resistance (in ohm)
RD = (VDD - VDS)/IDS - RS     #Drain resistance (in ohm) 
Av = -gm*(RD*RDS/(RD + RDS))  #Voltage gain
Rin = RG                      #Input impedance (in ohm)
Rout = RD*RDS/(RD + RDS)      #Output impedance (in ohm)

#Result

print "RD : ",RD*10**-3,"kilo-ohm."
print "RS : ",RS*10**-3,"kilo-ohm."
print "Av : ",Av,"."
print "Rin : ",Rin*10**-3,"kilo-ohm."
print "Rout : ",Rout*10**-3,"kilo-ohm."

RD :  5.0 kilo-ohm.
RS :  1.0 kilo-ohm.
Av :  -20.0 .
Rin :  500.0 kilo-ohm.
Rout :  4.0 kilo-ohm.

Example 10.19 , Page Number 355

In [64]:
#Variables

RL = 25.0 * 10**3               #Load resistance (in ohm)
RS = 2.5 * 10**3                #Source Resistance (in ohm)
R1 = 4.0 * 10**6                #Resistance1 (in ohm)
R2 = 2.0 * 10**6                #Resistance2 (in ohm)
gm = 2500.0 * 10**-6            #Transconductance (in siemens)

#Calculation

Zin = R1*R2/(R1 + R2)           #Input impedance (in ohm)
Zout = RS*1/gm/(RS + 1/gm)      #Output impedance (in ohm)
Av = gm*RS*RL/(RS + RL)/(1 + gm*(RS*RL)/(RS + RL))       #Voltage gain

#Result

print "Input impedance : ",round(Zin*10**-6,2),"Mega-ohm."
print "Output impedance : ",round(Zout),"ohm."
print "Voltage gain : ",round(Av,2),"."

Input impedance :  1.33 Mega-ohm.
Output impedance :  345.0 ohm.
Voltage gain :  0.85 .

Example 10.20 , Page Number 369

In [69]:
#Variables

IDon = 5.0 * 10**-3              #Drain current in on state (in Ampere)
VGS = 8.0                        #Gate-source voltage (in volts)
VGST = 4.0                       #Gate-source T voltage (in volts)
VGS1 = 6.0                       #Gate-source voltage1 (in volts)

#Calculation

K = IDon/(VGS - VGST)**2         #K (in Ampere per volt-square) 
ID = K*(VGS1 - VGST)**2          #Drain current (in Ampere) 

#Result

print "Drain current : ",round(ID*10**3,2),"mA."

Drain current :  1.25 mA.

Example 10.21 , Page Number 369

In [83]:
#Variables

IDon = 4.0 * 10**-3              #Drain current in on state (in Ampere)
VGS = 8.0                        #Gate-source voltage (in volts)
VGST = 4.0                       #Gate-source T voltage (in volts)
gm = 2000.0 * 10**-6             #Transconductance (in siemens)
VDD = 15.0                       #Drain supply voltage (in volts)
RD = 6.0 * 10**3                 #Drain resistance (in ohm)
RD2 = 40.0 * 10**3               #Resistance (in ohm)
RD1 = 60.0 * 10**3               #Resistance (in ohm) 

#Calculation

VGS = VDD/(RD1 + RD2)*RD2        #Gate-source voltage (in volts)
K = IDon/4**2         #K (in Ampere per volt-square)
ID = K*(VGS - VGST)**2           #Drain current (in Ampere)
VDS = VDD - ID*RD                #Drain-source voltage (in volts)
Av = gm*RD                       #Voltage gain
Vout = Av*0.08                   #Output voltage (in volts)

#Result

print "VGS : ",VGS,"V."
print "ID : ",ID,"A."
print "VDS : ",abs(VDS),"V."
print "Av : ",Av,"."
print "Vout : ",Vout,"V."

VGS :  6.0 V.
ID :  0.001 A.
VDS :  9.0 V.
Av :  12.0 .
Vout :  0.96 V.