# Chapter - 21 : MULTISTAGE BJT AMPLIFIERS¶

## Ex 21.1 Pg 565¶

In [1]:
from __future__ import division
from math import log10
Av1=10#
Av2=20#
Av3=40#
Av=Av1*Av2*Av3#
print "Av=%0.2f"%Av
GV1=20*log10(Av1)#
GV2=20*log10(Av2)#
GV3=20*log10(Av3)#
GV=GV1+GV2+GV3##CORRECTION
print 'GV=%0.2f dB'%GV

Av=8000.00
GV=78.06 dB


## Ex 21.2 Pg 565¶

In [4]:
from __future__ import division
vin1=0.05#
vout3=150#
Av1=20#
vin3=15#
Av=vout3/vin1#
print "Av=%0.2f"%Av
Av3=vout3/vin3#
print "Av3=%0.2f"%Av3
Av2=Av/(Av3*Av1)#
print "Av2=%0.2f"%Av2
vin2=Av2/vin3#
print 'vin2=%0.2f V'%vin2

Av=3000.00
Av3=10.00
Av2=15.00
vin2=1.00 V


## Ex 21.3 Pg 566¶

In [6]:
from __future__ import division
from math import log10
VCC=10#
Rc=5*10**3#
RB=1*10**6#
RE=1*10**3#
RL=10*10**3#
B1=100#
B2=100#
B=B1#
IE=VCC/(RE+(RB/B1))#
re=25/(IE*10**3)#
Ri1=B*re#
print 'Ri1=%0.2f ohm'%Ri1
Ri2=B*re#
print 'Ri2=%0.2f ohm'%Ri2
Ro1=(Rc*Ri2)/(Rc+Ri2)#
print 'Ro1=%0.2f ohm'%Ro1
Ro2=(Rc*RL)/(Rc+RL)#
print 'Ro2=%0.2f ohm'%Ro2
Av1=Ro1/re#
print "Av1=%0.2f"%Av1
Av2=Ro2/re#
print "Av2=%0.2f"%Av2
Av=Av1*Av2#
print "Av=%0.2f"%Av
Gv=20*log10(Av)#
print 'Gv=%0.2f dB'%Gv

Ri1=2750.00 ohm
Ri2=2750.00 ohm
Ro1=1774.19 ohm
Ro2=3333.33 ohm
Av1=64.52
Av2=121.21
Av=7820.14
Gv=77.86 dB


## Ex 21.4 Pg 567¶

In [7]:
from __future__ import division
from math import log10
VCC=15#
Rc=3.3*10**3#
RE=1000#
R1=33*10**3#
R2=8.2*10**3#
RL=10*10**3#
B=100#
VBE=0.7#
VTH=VCC*(R2/(R1+R2))#
RTH=(R1*R2)/(R1+R2)#
IE=(VTH-VBE)/(RE+(RTH/B))#
re=25/(IE*10**3)#
Ri2=B*re#
print 'Ri1=%0.2f ohm'%Ri2 #the answer of Ri2 varies from the answer printed in the book with slight difference(11.7 in book & 11.65 here),but this affects some answers further.
Ro1=(Rc*Ri2)/(Rc+Ri2)#
print 'Ro1=%0.2f ohm'%Ro1
Ro2=(Rc*RL)/(Rc+RL)#
print 'Ro2=%0.2f ohm'%Ro2
Av1=Ro1/re#
print "Av1=%0.2f"%Av1
Av2=Ro2/re#
print "Av2=%0.2f"%Av2
Av=Av1*Av2#
print "Av=%0.2f"%Av
Gv=20*log10(Av)#
print 'Gv=%0.2f dB'%Gv

Ri1=1165.73 ohm
Ro1=861.43 ohm
Ro2=2481.20 ohm
Av1=73.90
Av2=212.85
Av=15728.47
Gv=83.93 dB


## Ex 21.5 Pg 568¶

In [8]:
from __future__ import division
from math import sqrt
bw=500*10**3#
Avmax=120#
f1=25#
f2=bw+f1#
print 'f2=%0.2f kHZ'%(f2*10**-3)
Av=Avmax/(sqrt(2))
print "Av=%0.2f"%Av #ans printed in the book is  wrong

f2=500.03 kHZ
Av=84.85


## Ex 21.6 Pg 569¶

In [1]:
from __future__ import division
from math import log10
VCC=10#
RB=470*10**3#
RE=1*10**3#
RL=1*10**3#
a=4#
B=50#
IE=VCC/(RE+(RB/B))#
re=25/(IE*10**3)#
Ri1=(RB*(B*re))/(RB+(B*re))#
print 'Ri1=%0.2f ohm'%Ri1
Ri2=(RB*(B*re))/(RB+(B*re))#
print 'Ri2=%0.2f ohm'%Ri2
RI2=(a**2)*Ri2#
RO1=RI2#
RI2=(a**2)*RL#
Av1=RO1/re#
print "Av1=%0.2f"%Av1
RO2=RI2#
Av2=RO2/re#
print "Av2=%0.2f"%Av2
Av=Av1*Av2#
print "Av=%0.2f"%Av
Gv=20*log10(Av)#
print 'Gv=%0.2f dB'%Gv

Ri1=1296.41 ohm
Ri2=1296.41 ohm
Av1=797.79
Av2=615.38
Av=490949.75
Gv=113.82 dB


## Ex 21.7 Pg 570¶

In [2]:
from __future__ import division

VCC=12#
R1=100*10**3#
R2=20*10**3#
R3=10*10**3#
R4=2*10**3#
R5=10*10**3#
R6=2*10**3#
B=100#
B2=100#
VTH=VCC*(R2/(R1+R2))#
IE1=VTH/R4#
re1=25/IE1*10**-3#
VR6=VCC-IE1*R3#
IE2=VR6/R6#
re2=25/IE2*10**-3#
Ri2=B2*(re2+R6)#
R01=(R3*Ri2)/(R3+Ri2)#
RO2=R5#
Av1=R01/(re1+R4)#
print "Av1=%0.2f"%Av1
Av2=RO2/(re2+R6)#
print "Av2=%0.2f"%Av2
Av=Av1*Av2#
print "Av=%0.2f"%Av

Av1=4.71
Av2=4.94
Av=23.24


## Ex 21.8 Pg 571¶

In [3]:
from __future__ import division

VCC=10#
R1=800#
R2=200#
R3=600#
R4=200#
R5=100#
R6=1*10**3#
B=100#
B2=B#
VBE=0.7#
RE=200#
VR2=VCC*(R2/(R1+R2))#
IE1=(VR2-VBE)/RE#
IC1=IE1#
print 'IC1=%02.f mA'%(IC1*10**3)
VC1=VCC-IC1*R3#
VE1=IE1*R4#
VCE1=VC1-VE1#
print 'VCE1=%0.2f V'%VCE1
VE2=VC1-(-VBE)#
IE2=(VCC-VE2)/R6#
IC2=IE2#
VC2=IC2*R5#
VCE2=VC2-VE2#
print 'VCE2=%0.2f V'%VCE2
re1=25/IE1*10**-3#
re2=25/IE2*10**-3#
Ri2=B2*(re2+R6)#
R01=(R3*Ri2)/(R3+Ri2)#
Av1=R01/(re1+R4)#
print "Av1=%0.2f "%Av1
Av2=1#
print "Av2=%0.2f "%Av2
Av=Av1*Av2#
print "Av=%0.2f "%Av

IC1=07 mA
VCE1=4.80 V
VCE2=-6.48 V
Av1=2.93
Av2=1.00
Av=2.93


## Ex 21.9 Pg 572¶

In [5]:
from __future__ import division

VCC=10#
R1=30*10**3#
R2=20*10**3#
RE=1.5*10**3#
B1=150#
B2=100#
VBE=0.7#
Ai=B1*B2#
print "Ai=%0.2f"%Ai
VR2=VCC*(R2/(R1+R2))#
VB2=VR2-VBE#
VE2=VB2-VBE#
IE2=VE2/RE#
re2=25/(IE2*10**3)#
print 're2=%0.2f ohm'%re2
Ib2=IE2/B2#
IE1=Ib2#
re1=25/(IE1*10**3)#
print 're1=%0.2f ohm'%re1
Ri1=(R1*R2)/(R1+R2)#
print 'Ri1=%0.2f kohm'%(Ri1*10**-3)
Av=RE/((re1/B2)+(re2+RE))#
print "Av=%0.2f "%Av

Ai=15000.00
re2=14.42 ohm
re1=1442.31 ohm
Ri1=12.00 kohm
Av=0.98