# Chapter 7: Field effect Transistors¶

### Example 7.1 page no. 262¶

In [1]:
#Exa 7.1
#What is Resistance between gate and source

#given data
VGS=10			#in Volt
IG=0.001		#in uA
IG=IG*10**-6		#in A

#calculation
RGS=VGS/IG		#in ohm

#result
print"Resistance between gate and source is  ",RGS/10**6,"ohm"

Resistance between gate and source is   10000.0 ohm


### Example 7.2 page no.262¶

In [2]:
#Exa 7.2
#What is AC drain resistance of JFET

#given data
delVDS=1.5			#in Volt
delID=120			#in uA
delID=120*10**-6		#in A

#Calculation
rd=delVDS/delID			#in Ohm

#Result
print"AC drain resistance of JFET in Kohm ",rd*10**-3,"kohm"

AC drain resistance of JFET in Kohm  12.5 kohm


### Example 7.3 page no. 262¶

In [3]:
#Exa 7.3
#Determine Transconductance
import math
#given data
VP=-4.5			#in Volt
IDSS=10.0			#in mA
IDS=2.5			#in mA

#Calculation
VGS=VP*(1-math.sqrt(IDS/IDSS))		#in Volt
gm=(-2*IDSS/VP)*(1-VGS/VP)		#in mA/Volt

#Result
print"Transconductance is",round(gm,2),"mA/v"

Transconductance is 2.22 mA/v


### Example 7.4 page no. 262¶

In [6]:
#Exa 7.4
#calculate Vgs off

#given data
gm=10			#in mS
IDSS=10			#in uA
IDSS=IDSS-10**-6	#in Ampere

#Calculation
VGS_OFF=-2*IDSS/gm

#Result
print"VGS(OFF) is =",round(VGS_OFF),"mV"

VGS(OFF) is = -2.0 mV


### Example 7.5 page no. 262¶

In [6]:
#Exa 7.5
#Determine The minimum value of VDS for pinch-OFF region is equal to VP.

#given data
VP=-4.0			   #in Volt
IDSS=10.0			 #in mA
IDSS=IDSS*10**-3	#in Ampere
VGS=-2.0              #in Volt

#Calculation
ID=IDSS*(1.0-VGS/VP)**2	#in mA

#result
print "Drain current=",ID*1000,"mA"
print"VDS(min) is : ",VP,"V"

Drain current= 2.5 mA
VDS(min) is :  -4.0 V


### Example 7.6 page no. 263¶

In [4]:
#Exa 7.6
#Find the value of Id , gmo, gm

#given data
VP=-3.0			#in Volt
IDSS=8.7		#in mA
IDSS=IDSS*10**-3	#in mA
VGS=-1			#in Volt

#calculation
ID=IDSS*(1-VGS/VP)**2	#in Ampere
gmo=-2*IDSS/VP		#in mS
gm=gmo*(1-VGS/VP)	#in mS

#result
print"ID is ",round(ID*1000,1),"mA"
print"gmo is",round(gmo*1000,1),"mS"
print"gm is  ",round(gm*1000,1),"mS"

ID is  3.9 mA
gmo is 5.8 mS
gm is   3.9 mS


### Example 7.7 page no.263¶

In [5]:
#Exa 7.7
#Find gm

#given data
VP=-3.0 		#in Volt
IDSS=8.4 	#in mA
VGS=-1.5 	#in Volt

#calculation
ID=IDSS*(1-VGS/VP)**2 		#in mA
gmo=-2*IDSS/VP 			#in mS
gm=gmo*(1-VGS/VP) 		#in mS

#result
print"Drain current=",ID,"mA"
print"Transconductance is ",gm,"mS"

Drain current= 2.1 mA
Transconductance is  2.8 mS


### Example 7.8 page no.263¶

In [17]:
#Exa 7.8
#What is gm

#given data
VP=-4.5 		   #in Volt
IDSS=9 			#in mA
IDSS=IDSS*10**-3   #in Ampere
IDS=3 			 #in mA
IDS=IDS*10**-3 		#in Ampere

#calculation
import math
VGS=VP*(1-math.sqrt(IDS/IDSS)) 	#in Volt
gm=(-2*IDSS/VP)*(1-VGS/VP) 		#in mS

#result
print"IDS = 3 mA when gm is ",round(gm*1000,2),"mS"

IDS = 3 mA when gm is  2.31 mS


### Example 7.9 page no.271¶

In [2]:
#Exa 7.9
#given data :
Vp=-4.0 			   #in Volt
IDSS=10.0 		    #in mA
#From eq 7.1
Vgs1=0
Id1=IDSS                 # mA, at Vgs=0
Vgs2=1
Id2=Id1*(1-Vgs2/Vp)**2   #mA, at Vgs=1
Vgs3=-1
Id3=Id1*(1-Vgs3/Vp)**2   #mA, at Vgs=1
Vgs4=-2
Id4=Id1*(1-Vgs4/Vp)**2   #mA, at Vgs=-2
Vgs5=-4
Id5=Id1*(1-Vgs5/Vp)**2   #mA, at Vgs=-4

print "Transfer Characteristics are in mA ",Id1,Id2,Id3,Id4,Id5

#Plot
%matplotlib inline
import matplotlib.pyplot as plt
fig = plt.figure()

Vgs=[-4,-2,-1,0,1]
Id=[0,2.5,5.625,10,15.625]
plt.xlabel("Vgs  (V)")
plt.ylabel("Id  (mA)")
plt.xlim((-4,2))
plt.ylim((0,18))
ax.plot([0], [10], 'o')
ax.annotate('(Idss)', xy=(0,10))

a=plt.plot(Vgs,Id)

print "Transfer Characteristics for N channel MOSFET Type"
plt.show(a)

Transfer Characteristics are in mA  10.0 15.625 5.625 2.5 0.0
Transfer Characteristics for N channel MOSFET Type


### Example 7.10 page no.275¶

In [20]:
#Exa 7.10
#Determine the drain current

#given data
ID_on=5 		#in mA
VGS=6 			#in Volt
VGS_on=8.0 		#in Volt
VGST=4 			#in Volt

#calculation
K=ID_on/(VGS_on-VGST)**2 		#in mA/V**2
ID=K*(VGS-VGST)**2 			#in mA

#result
print"When VGS=6V the drain current is ",ID,"mA"

When VGS=6V the drain current is  1.25 mA