# Chapter 7:Junction Rectifier,Transistos and Devices¶

## Example 7.2,Page No:7.7¶

In [2]:
import math

#variable declaration
#given Is2/Is1 =150
#Is2/Is1 =2**(T2-T1)/10
#dT=10ln(I)/ln(2)
I  = 150;

#Calculations
dT  = 10*math.log(I)/float(math.log(2));       #increase in temperature in °C

#Result
print'Increase in temperature necessary to increase Is by a factor by 150 is %3.2f '%dT,'°C';

Increase in temperature necessary to increase Is by a factor by 150 is 72.29  °C


## Example 7.3,Page No:7.7¶

In [3]:
import math

#variable declaration
Io  = 0.25*10**-6;        # large reverse biased current in A
V   = 0.12;               # applied voltage in V
Vt  = 0.026;              # Volt-equivalent of temperature in V

# Calculations
I   = Io*(math.exp(V/float(Vt))-1);     #current in A

# Result
print'Current flowing through germanium diode = %g '%(I*10**6),'uA';

Current flowing through germanium diode = 25.0067  uA


## Example 7.4,Page No:7.12¶

In [5]:
import math

#variable declaration
k   = 1.38*10**-23;          # boltzmann constant (m**2)*(kg)*(s**-2)*(K**-1)
e   = 1.6*10**-19;           # charge of electron in coulombs
ue  = 0.19                   # mobility of electron  in m**2.V**-1.s**-1
uh  = 0.027;                 # mobilty of holes in m**2.V**-1.s**-1
T   = 300;                   # temperature in K

#Calculations
Dn  = ((k*T)/float(e))*ue;           # diffusion constant of electrons in cm**2/s
Dh  = (k*T/float(e))*uh;             # diffusion constant of holes in cm**2/s

#Result
print'Diffusion co-efficients of electrons = %3.2e'%Dn,'m**2/s';
print'Diffusion co-efficients of holes = %3.2e '%Dh,'m**2/s';

Diffusion co-efficients of electrons = 4.92e-03 m**2/s
Diffusion co-efficients of holes = 6.99e-04  m**2/s


## Example 7.6,Page No:7.13¶

In [4]:
import math

#variable declaration
I1  = 20;           #current in mA
V1  = 0.8;          #voltage in volts
V2  = 0.7;          #voltage in volts
I2  = 10;           # current in mA
v3  = -10;          #voltage in volts
I3  = -1*10**-6;     # current in mA

# Calculations
R   = (V1 - V2)/(I1 - I2);     #resistance in ohm
Vreb  = v3/I3;                 #velocity in volts

#Result
print'resistance = %d'%(R*10**3),'ohm';
print'Vreb = %3.1e'%Vreb,'ohm';


resistance = 10 ohm
Vreb = 1.0e+07 ohm


## Example 7.7,Page No:7.13¶

In [5]:
import math

#variable declaration
T   = 300;                 # temp in kelvin
k   = 1.38*10**-23;        # Boltzmann constant (m**2)*(kg)*(s**-2)*(K**-1)
e   = 1.602*10**-19;       # charge of electron in coulombs
ue  = 3650;                # mobility of electrons
uh  = 1720;                # mobility of holes

#Calculations
De  = (ue*k*T)/float(e);       # diffusion constant of electrons in cm**2/s
Dh  = (uh*k*T)/float(e);       # diffusion constant of holes in cm**2/s

# Result
print'Diffusion constant of electrons = %3.1f'%De,'cm**2/s';
print'Diffusion constant of electrons = %3.1f'%Dh,'cm**2/s';

Diffusion constant of electrons = 94.3 cm**2/s
Diffusion constant of electrons = 44.4 cm**2/s


## Example 7.8,Page No:7.23¶

In [6]:
import math

#variable declaration
p   = 2;                 # resistivity in ohm-m
er  = 16;                 #relative dielectrivity of Ge cm**2/s
up  = 1800;               # mobility of holes in cm**2/s
e0  = 8.85*10**-12;       #permitivity in (m**-3)*(kg**-1)*(s**4)*(A**2)
a   = 2*10**-4;           #channel height in m

# Calculations
qNa  = 1/float(up*p);
e    = e0*er;                      #permitivity in F/cm
Vp   = (qNa*(a**2))/float(2*e);       # pinch-off voltage in V

#Result
print'Pinch-off voltage = %3.2e'%Vp,'V';
print' Note:calculation mistake in text book ,e value is taken as 14.16*10**-12 instead of 141.6*10**-12';

Pinch-off voltage = 3.92e-02 V
Note:calculation mistake in text book ,e value is taken as 14.16*10**-12 instead of 141.6*10**-12


## Example 7.9,Page No:7.23¶

In [7]:
import math

#variable declaration
a       = 3.5*10**-6;               #channel width in m
N       = 10**21;                   #number of electrons in electrons/m**3
q       = 1.6*10**-19;              #charge of electron in coulombs
er      = 12;                       #dielectric constant F/m
e0      = 8.85*10**-12;             #dielectric constant F/m

#calculation
e      = (e0)*(er);                     #permitivityin F/m
Vp     = (q*(a**2)*N)/float(2*e);        #pinch off voltage in V

#result
print'pinch off velocity =%2.1f'%Vp,'V';

pinch off velocity =9.2 V


## Example 7.10,Page No:7.23¶

In [8]:
import math

#variable declaration
IDSS       = 10;               #current in mA
IDS        =2.;                # current in mA
Vp         = -4.0;             #pinch off voltage in V

#formula
#IDS   = IDSS*((1-(VGS/Vp))**2)
#calculation
VGS        = Vp*(1-(math.sqrt(IDS/float(IDSS))));
gm         = ((-2*IDSS)/float(Vp))*(1-(VGS/float(Vp)));    #transconductance in m*A/V

#result
print'transconductance =%3.2f'%gm,'m*A/V';

transconductance =2.24 m*A/V


## Example 7.11,Page No:7.24¶

In [9]:
import math

#variable declaration
VGS       = -3;                       #pinch off voltage in V
IDSS        =10*10**-3;                # current in A
Vp         = -5.0;                     #pinch off voltage in V

#calculation
IDS   = IDSS*((1-(VGS/float(Vp)))**2);    #current in mA

#result
print'current =%3.2f'%(IDS*10**3),'mA';

current =1.60 mA


## Example 7.12,Page No:7.24¶

In [10]:
import math

#variable declaration
IDS        = 2*10**-3;               #current in mA
IDSS       = 8*10**-3;                # current in mA
Vp         = -4.5;                    #pinch off voltage in V
VGS1       = -1.902;                   #pinch off voltage  when IDS =3*10**-3 A

#formula
#IDS   = IDSS*((1-(VGS/Vp))**2)
#calculation
VGS        = Vp*(1-(math.sqrt(IDS/float(IDSS))));
gm         = ((-2*IDSS)/float(Vp))*(1-(VGS1/float(Vp)));   #transconductance in m S

#result
print'transconductance =%3.2f'%(gm/10**-3),'m S';

transconductance =2.05 m S


## Example 7.13,Page No:7.25¶

In [11]:
import math

#variable declaration
VGS        = 26;                #gate source voltage in V
IG         = 1.6*10**-9;        #gate current in A

#calculation
R          = VGS/float(IG);           #gate to current resistance in ohms

#result
print'resistance =%3.2e'%R,'ohms';

resistance =1.62e+10 ohms


## Example 7.14,Page No:7.25¶

In [12]:
import math

#variable declaration
ID1          = 1;                #current in A
ID2          = 2.1;              # current in A
VGS1         = 3.0;              #pinch off voltage in V
VGS2         = 3.5;              #pinch off voltage in V

#calculation
dID         = ID2-ID1;
dVGS        = VGS2-VGS1;
gm          = (dID*10**-3)/float(dVGS);   #transconductance in mho

#result
print'transconductance =%3.2e '%gm,'ohm';

transconductance =2.20e-03  ohm


## Example 7.15,Page No:7.25¶

In [13]:
import math

#variable declaration
ID1         = 8;                    #drain current in mA
ID2         = 8.3;                  #drain current in mA
VDS1        = 5;                    #drainn source voltage in V
VDS2        = 14;                   #drain source voltage in V
ID3         = 7.1;                  #drain current when VDS constant VGS change
ID4         = 8.3;                  #drain current when VDS constant VGS change
VGS1         = 0.1;                 #drain source voltage in V
VGS2         = 0.4;                 #drain source voltage in V

#calculation
dID1        = ID2-ID1;
dVDS        = VDS2-VDS1;
rd          = dVDS/float(dID1);                #ac drain resistance
dID2        = ID4-ID3;
dVGS        = VGS2-VGS1;
gm          = dID2/float(dVGS);               #transconductance mhos
u           = rd*gm;                          #amplification factor

#result
print'ac drain resistnce =%3.2f'%rd,'k-ohms';
print'transconductance =%3.2d'%(gm/10**-3),'u mhos';
print'amplification factor=%3.2f'%u;

ac drain resistnce =30.00 k-ohms
transconductance =4000 u mhos
amplification factor=120.00


## Example 7.16,Page No:7.26¶

In [14]:
import math

#variable declaration
u          = 100;              #amplification factor
rd         = 33*10**3;         #drain resistance  in ohms

#calculation
gm          = u/float(rd);         #transconductance in mhos

#result
print'transconductance =%3.2f'%(gm*10**3),' mmhos';
print'Note:transconductance value is wrongly printed in terms of umhos';

transconductance =3.03  mmhos
Note:transconductance value is wrongly printed in terms of umhos