# Chapter 08 : BJT specifications and performance¶

## Example 8.2, Page No 313¶

In [1]:
import math
#initialisation of variables
P2=25.0*10**-3#when frequency increase to 20KHz
P1=50.0*10**-3#when signal frequency is 5KHz

#Calculations
Po=10*math.log((P2/P1),10)

#Results
print(" output power change in decibels is %.2f dB " %Po)

 output power change in decibels is -3.01 dB


## Example 8.3, Page No 314¶

In [2]:
import math

#initialisation of variables
v1=1# output voltage measured at 5KHz
v2=.707# output voltage measure at 20kHz

#Calculations
Po=20*math.log((v2/v1),10)

#Results
print(" output power change is %.2f dB " %Po)

 output power change is -3.01 dB


## Example 8.4 Page No 317¶

In [3]:
import math

#initialisation of variables
Ic=1.0*10**-3
hfe=50.0
hie=1.3*10**3
fT=250.0*10**6
Cbc=5.0*10**-12
Rc=8.2*10**3
Rl=100.0*10**3

#Calculations
Ie=Ic
Av=(hfe*((Rc*Rl)/(Rc+Rl)))/hie
Cbe=(6.1*Ie)/fT
Cin=(Cbe+(1+Av)*Cbc)*10**9

#Results
print(" input capacitance when the circuit operated as CE is %.2fnF "%Cin)

 input capacitance when the circuit operated as CE is 1.49nF


## Example 8.5, Page No 319¶

In [4]:
import math
#initialisation of variables
R1=100*10**3
R2=47.0*10**3
Re=4.7*10**3
Cbc=5.0*10**-12
Cbe=24.4*10**-12
hfe=50
hie=1.3*10**3
hib=24.5
rs=hib
rs=600.0

#Calculations
print(" common emitter circuit")
Rb=(R1*R2)/(R1+R2)
Zi=(Rb*hie)/(Rb+hie)
Cin=1.48*10**-9
f2=1/(2*3.14*Cin*((rs*Zi)/(rs+Zi)))
print("input-capacitance upper cutoff frequency is %dHz " %f2)
print("common base circuit")
Zi=(Re*hib)/(Re+hib)
Cin=(Cbe+Cbc)
f2=(1/(2*3.14*Cin*((rs*Zi)/(rs+Zi))))*10**-6

#Results
print(" input capacitance upper cutoff when operating as CB circuit with base bypassed to ground is %.2f MHz " %f2)

 common emitter circuit
input-capacitance upper cutoff frequency is 265447Hz
common base circuit
input capacitance upper cutoff when operating as CB circuit with base bypassed to ground is 231.25 MHz


## Example 8.6 Page No 322¶

In [5]:
import math
#initialisation of variables
fT=50.0*10**6
hfe=50.0
f2o=60.0*10**3
Rc=10.0*10**3

#Calculations
fae=fT/hfe
C4=(1.0/(2*3.14*f2o*Rc))*10**12

#Results
print("capacitance required for C4 to give 60kHz upper cutoff frequency is %.2f pF " %C4)

capacitance required for C4 to give 60kHz upper cutoff frequency is 265.39 pF


## Example 8.8 Page No 326¶

In [6]:
import math

#initialisation of variables
ton=100.0*10**-9
Rs=600.0
Rb=4.7*10**3

#Calculations
C1=(ton/Rs)*10**12
print(" suitable speed up capacitor is %dpF " %C1)
C1=160*10**-12#standard value
PWmin=(5*Rs*C1)
SWmin=5*Rb*C1
fmax=1/(PWmin+SWmin)

#Results
print("maximum signal frequency is %.2f Hz " %(fmax/1000))

 suitable speed up capacitor is 166pF
maximum signal frequency is 235.85 Hz


## Example 8.9, Page No 330¶

In [7]:
import math
#initialisation of variables
R1=30.0*10**3
R2=30.0*10**3
rs=30.0*10**3
f2=40.0*10**3
f1=100.0
k=1.37*10**-23
R=10.0*10**3
Av=600.0
Ri=3.0*10**3

#Calculations
Rb=(R1*R2)/(R1+R2)
Rg=(rs*Rb)/(rs+Rb)
T=(273+25)
B=f2-f1
en=math.sqrt(4*k*T*B*R)
eni=en*((Ri/(Ri+Rg)))
eno=(Av*eni)*10**6

#Results
print("noise output voltage is %.2f uV " %eno)

noise output voltage is 353.44 uV


## Example 8.10 Page No 331¶

In [8]:
import math

#initialisation of variables
Ic=30.0*10**-6
Vce=5.0
eno=354.0*10**-6
NF=10.0
F=2.51#F=antilog(NF/10)

#Calculations
Vn=((math.sqrt(F))*eno)*10**6

#Results
print("total noise output volateg for amplifier is %.2f uV " %Vn)

total noise output volateg for amplifier is 560.84 uV


## Example 8.11 Page No 333¶

In [9]:
import math
#initialisation of variables
Pd25=625.0*10**-3
D=5.0*10**-3
Vce=10.0
T2=55.0

#Calculations
Pdt2=Pd25-D*(T2-25)
Pd=Pdt2
Ic=Pd/Vce

#Results
print(" maximum Ic level is %.2fA " %(Ic*1000))

 maximum Ic level is 47.50A


## Example 8.13 Page No 335¶

In [10]:
import math

#initialisation of variables
Pd=80.0
Vce=60.0

#Calculations
Ic=Pd/Vce
print("point 1 Vce=60 and Ic= %.2f A" %Ic)
Vce=40.0
Ic=Pd/Vce
print("point 2 Vce=40 and  Ic= %.2f A" %Ic)
Vce=20.0
Ic=Pd/Vce
print(" point 3 Vce=20 and  Ic= %.2f A" %Ic)
Vce=10.0
Ic=Pd/Vce

#Results
print(" point 4 Vce=10 and  Ic= %.2f A" %Ic)

point 1 Vce=60 and Ic= 1.33 A
point 2 Vce=40 and  Ic= 2.00 A
point 3 Vce=20 and  Ic= 4.00 A
point 4 Vce=10 and  Ic= 8.00 A


## Example 8.14, Page No 339¶

In [11]:
import math

#initialisation of variables
Vce=20.0
Ic=1.0
T2=90.0
T1=25.0

#Calculations
Q=Vce*Ic
Qcs=.4
Qjc=1#from table
Qsa=((T2-T1)/Q)-(Qjc+Qcs)

#Results
print("Qsa= %.2f " %Qsa)

Qsa= 1.85