Chapter4-Diode Characteristics and Applications

Ex1-pg141

In [2]:
##Ex4_1
import math
Irs = 0.2*10**-6
Vf = 0.1
VT = 26.*10**-3
eta = 1.##for germanium
I = Irs*(math.exp(Vf/eta/VT)-1.)
print'%s %.2e %s'%("Irs = ",(Irs),"A")##reverse saturation current
print'%s %.2f %s'%("Vf = ",(Vf),"V")##applied voltage
print'%s %.2f %s'%("VT = ",(VT),"V")##voltage at room temperature
print'%s %.2f %s'%("eta = ",(eta),"")
print("I = Irs*(math.exp(Vf/eta/VT)-1)")##current at room temperature
print'%s %.2e %s'%("I = ",(I),"A")

##current in silicon:
eta = 2.##for silicon
print'%s %.2f %s'%("eta = ",(eta),"")
I = Irs*(math.exp(Vf/eta/VT)-1.)
print'%s %.2e %s'%("I = ",(I),"A")




## note: incomplete solution in textbook for above question.

Irs =  2.00e-07 A
Vf =  0.10 V
VT =  0.03 V
eta =  1.00 
I = Irs*(math.exp(Vf/eta/VT)-1)
I =  9.16e-06 A
eta =  2.00 
I =  1.17e-06 A

Ex2-pg141

In [3]:
##Ex4_2
import math
Irs = 2.0*10**-6
I = 10.*10**-3
VT = 26.*10**-3
eta = 2##for silicon
print'%s %.2e %s'%("Irs = ",(Irs),"A")##reverse saturation current
print'%s %.2f %s'%("I = ",(I),"A")##forward current
print'%s %.2f %s'%("VT = ",(VT),"V")##voltage at room temperature
print'%s %.2f %s'%("eta = ",(eta),"")
Vf = eta*VT*math.log((I/Irs)+1)##voltage produced
print'%s %.2f %s'%("Vf = eta*VT*log((I/Irs)+1) = ",(Vf),"V")

Irs =  2.00e-06 A
I =  0.01 A
VT =  0.03 V
eta =  2.00 
Vf = eta*VT*log((I/Irs)+1) =  0.44 V

Ex3-pg142

In [4]:
##Ex4_3
import math
If = 3.*10**-3##forward current
eta = 1.##for germanium
T = 300.##room temperature
VT = T/11600.##voltage at room temperature
print'%s %.2e %s'%("If = ",(If),"A")
print'%s %.2f %s'%("eta = ",(eta),"")
print'%s %.2f %s'%("T = ",(T),"degreeK")
print'%s %.2f %s'%("VT = ",(VT),"V")
Rdf = (eta*VT/If)##dynamic resistance at room temprature
print'%s %.2f %s'%("Rdf = (eta*VT/If) = ",(Rdf),"ohm")

If =  3.00e-03 A
eta =  1.00 
T =  300.00 degreeK
VT =  0.03 V
Rdf = (eta*VT/If) =  8.62 ohm

Ex4-pg142

In [5]:
##Ex4_4
import math
A = 4*10**-6
W = 1.5*10**-6
apsilent_r = 16.##for germanium
apsilent_not = 8.85*10**-12##permitivity in vaccum
print'%s %.2e %s'%("A = ",(A),"m_sq")##cross sectional are
print'%s %.2e %s'%("W = ",(W),"m")##width of depletion layer
print'%s %.2e %s'%("apsient_r = ",(apsilent_r),"")##relative permittivity
print("CT = apsilent*A/W")##transition capacitance
print'%s %.2e %s'%("   = ",(apsilent_r*apsilent_not*A/W),"F")


## note: units given in textbook in the solution for cross sectional area and width are misprinted.

A =  4.00e-06 m_sq
W =  1.50e-06 m
apsient_r =  1.60e+01 
CT = apsilent*A/W
   =  3.78e-10 F

Ex5-pg142

In [6]:
##Ex4_5
import math
I = 10.*10**-3
eta = 1##for germanium
VT = 26.*10**-3
tawo = 6.*10**-3
CD = I*tawo/eta/VT
print'%s %.2f %s'%("I = ",(I),"A")##forward current
print'%s %.2f %s'%("eta = ",(eta),"")
print'%s %.2f %s'%("VT = ",(VT),"V")##voltagr at room temperature
print'%s %.2f %s'%("tawo = ",(tawo),"sec")##mean lifetime
print'%s %.2e %s'%("CD = I*tao/eta/VT = ",(CD),"F")##

I =  0.01 A
eta =  1.00 
VT =  0.03 V
tawo =  0.01 sec
CD = I*tao/eta/VT =  2.31e-03 F