Chapter 5 - Basic Transistor Amplifiers

Example 5_1 Page No. 136

In [3]:
from __future__ import division  
RL=5*10**(3)
print "RL= %0.2f"%(RL)," ohm"  #Load resistance
R1=100*10**(3)
print "R1= %0.2f"%(R1)," ohm"  # resistance
R2=10*10**(3)
print "R2= %0.2f"%(R2)," ohm"  # resistance
rc=50*10**(3)
print "rc= %0.2f"%(rc)," ohm"  #collector resistance
rd=rc # Drain and collector  resistance are equal
rbe=1*10**(3)
print "rbe= %0.2f"%(rbe)," ohm"  #Load resistance
gm=50*10**(-3)
print "gm = %0.2f"%(gm)," A/V"#  transconductance for BJT 
Av=(-gm*RL)
print "For BJT,Av=(-gm*RL)= %0.2f"%(Av) #Voltage gain for BJT
AI=gm*rbe
print "AI=(gm*rbe)= %0.2f"%(AI) # current gain for BJT
gm=5*10**(-3)
print "gm = %0.2f"%(gm)," A/V"#  transconductance for FET 
Av=(-gm*RL)
print "For FET,Av=(-gm*RL)= %0.2f"%(Av)," " # gain for FET
R0=rd
print "R0= %0.2f"%(R0)," ohm"  #output resistance for FET and BJT
Ri=rbe
print "Ri= %0.2f"%(Ri)," ohm"  #BJT input resistance 
RB=(R1*R2)/(R1+R2)
print "RB=(R1*R2)/(R1+R2)= %0.2f"%(RB)," ohm"  # eqivalent Base resistance for  BJT
Ri=(RB*rbe)/(RB+rbe)
print "Ri= (RB*rbe)/(RB+rbe)=%0.2f"%(Ri)," ohm"  #New value of BJT input resistance 

RL= 5000.00  ohm
R1= 100000.00  ohm
R2= 10000.00  ohm
rc= 50000.00  ohm
rbe= 1000.00  ohm
gm = 0.05  A/V
For BJT,Av=(-gm*RL)= -250.00
AI=(gm*rbe)= 50.00
gm = 0.01  A/V
For FET,Av=(-gm*RL)= -25.00  
R0= 50000.00  ohm
Ri= 1000.00  ohm
RB=(R1*R2)/(R1+R2)= 9090.91  ohm
Ri= (RB*rbe)/(RB+rbe)=900.90  ohm

Example 5_2 Page No. 137

In [7]:
from __future__ import division  
RL=5*10**(3)
print "RL= %0.2f"%(RL)," ohm"  #Load resistance
R1=100*10**(3)
print "R1= %0.2f"%(R1)," ohm"  # resistance
R2=100*10**(3)
print "R2= %0.2f"%(R2)," ohm"  # resistance
Rs=5*10**(3)
print "Rs= %0.2f"%(Rs)," ohm"  # Source resistance
Beta_o=50
print "Beta_o = %0.2f"%(Beta_o) #BJT gain
rbe=1*10**(3)
print "rbe= %0.2f"%(rbe)," ohm"  #Base-emitter resistance
gm=50*10**(-3)
print "gm = %0.2f"%(gm)," A/V"#  transconductance for BJT 
rc=50*10**(3)
print "rc= %0.2f"%(rc)," ohm"  #collector resistance
Av=RL/(RL+1/gm) # Gain formulae
print "Av=RL/(RL+1/gm)= %0.2f"%(Av) # voltage gain for BJT
Avs=RL/((Rs/Beta_o)+(1/gm)+(RL))
print "Avs=RL/((Rs/Beta_o)+(1/gm)+(RL))= %0.2f"%(Avs) # Overall voltage gain for BJT
AI=-(Beta_o+1)
print "AI=-(Beta_o+1)= %0.2f"%(AI) # current gain for BJT
R0=(Rs+rbe)/Beta_o
print "R0= (Rs+rbe)/Beta_o=%0.2f"%(R0)," ohm"  #output resistance for  BJT
Ri=rbe+Beta_o*RL # formulae
print "Ri= rbe+Beta_o*RL=%0.2f"%(Ri)," ohm"  # value of BJT input resistance 
RB=(R1*R2)/(R1+R2)
print "RB=(R1*R2)/(R1+R2)= %0.2f"%(RB)," ohm"  # eqivalent Base resistance for  BJT
Rieff=(Ri*RB)/(RB+Ri)
print "Rieff= (Ri*RB)/(RB+Ri)=%0.2f"%(Rieff)," ohm"  #Effective value of BJT input resistance 

RL= 5000.00  ohm
R1= 100000.00  ohm
R2= 100000.00  ohm
Rs= 5000.00  ohm
Beta_o = 50.00
rbe= 1000.00  ohm
gm = 0.05  A/V
rc= 50000.00  ohm
Av=RL/(RL+1/gm)= 1.00
Avs=RL/[(Rs/Beta_o)+(1/gm)+(RL)]= 0.98
AI=-(Beta_o+1)= -51.00
R0= (Rs+rbe)/Beta_o=120.00  ohm
Ri= rbe+Beta_o*RL=251000.00  ohm
RB=(R1*R2)/(R1+R2)= 50000.00  ohm
Rieff= (Ri*RB)/(RB+Ri)=41694.35  ohm

Example 5_3 Page No. 142

In [8]:
from __future__ import division  
RL=5*10**(3)
print "RL= %0.2f"%(RL)," ohm"  #Load resistance
RF=5*10**(3)
print "RF= %0.2f"%(RF)," ohm"  # resistance
Beta_o=50
print "Beta_o = %0.2f"%(Beta_o) #BJT gain
rbe=1*10**(3)
print "rbe= %0.2f"%(rbe)," ohm"  #Base-emitter resistance
gm=50*10**(-3)
print "gm = %0.2f"%(gm)," A/V"#  transconductance for BJT 
rc=50*10**(3)
print "rc= %0.2f"%(rc)," ohm"  #collector resistance
Ri=rbe+RF*(1+gm*rbe) # formulae
print "Ri= rbe+RF*(1+gm*rbe)=%0.2f"%(Ri)," ohm"  #  BJT input resistance 
Av=(-gm*RL)/(1+gm*RF)# formulae
print "Av=(-gm*RL)/(1+gm*RF)= %0.2f"%(Av) # voltage gain for BJT
AI=Beta_o
print "AI=(Beta_o)= %0.2f"%(AI) # current gain for BJT
R0=Beta_o*rc
print "R0= Beta_o*rc=%0.2f"%(R0)," ohm"  #output resistance for  BJT

RL= 5000.00  ohm
RF= 5000.00  ohm
Beta_o = 50.00
rbe= 1000.00  ohm
gm = 0.05  A/V
rc= 50000.00  ohm
Ri= rbe+RF*(1+gm*rbe)=256000.00  ohm
Av=(-gm*RL)/(1+gm*RF)= -1.00
AI=(Beta_o)= 50.00
R0= Beta_o*rc=2500000.00  ohm

Example 5_4 Page No. 148

In [1]:
from __future__ import division  
RL=5*10**(3)
print "RL= %0.2f"%(RL)," ohm"  #Load resistance
RF=2.5*10**(3)
print "RF= %0.2f"%(RF)," ohm"  # resistance
Rs=50
print "Rs= %0.2f"%(Rs)," ohm"  # resistance
ro=50*10**(3)
print "ro= %0.2f"%(ro)," ohm"  # output resistance
rd=ro # drain resistance
rc=ro# Collector resistance
print "rc= %0.2f"%(rc)," ohm"  # Collector resistance
rbe=1*10**(3)
print "rbe= %0.2f"%(rbe)," ohm"  #base -emitter resistance
print "For CG Amplifier"
gm=5*10**(-3)
print "gm = %0.2f"%(gm)," A/V"#  transconductance for FET 
Ri=1/gm # formulae
print "Ri= 1/gm=%0.2f"%(Ri)," ohm"  # value of CGA (common gate amplifier)input resistance for FET
Avs=gm*RL/(1+gm*Rs)
print "Avs=gm*RL/(1+gm*Rs)= %0.2f"%(Avs) # Overall voltage gain for FET (CGA)
Ro=rd*(1+gm*Rs)
print "Ro=rd*(1+gm*Rs)=%0.2f"%(Ro)," ohm"  #output resistance for  FET (CGA)
print "For CB Amplifier"
gm=50*10**(-3)
print "gm = %0.2f"%(gm)," A/V"#  transconductance for BJT
Ri=1/gm # formulae
print "Ri= 1/gm=%0.2f"%(Ri)," ohm"  # value of CBA (common base amplifier)input resistance for BJT
Avs=gm*RL/(1+gm*Rs)
print "Avs=gm*RL/(1+gm*Rs)= %0.2f"%(Avs) # Overall voltage gain for BJT (CBA)
Ro=gm*(rbe*rc)
print "Ro=gm*(rbe*rc)=%0.2e"%(Ro)," ohm"  #output resistance for  BJT (CBA)

#NOTE: I have calculated first all the parameters for CG amplifier and then for CB amplifier but in book parameters have been calculated alternatingly for CG and CB amplifiers.

RL= 5000.00  ohm
RF= 2500.00  ohm
Rs= 50.00  ohm
ro= 50000.00  ohm
rc= 50000.00  ohm
rbe= 1000.00  ohm
For CG Amplifier
gm = 0.01  A/V
Ri= 1/gm=200.00  ohm
Avs=gm*RL/(1+gm*Rs)= 20.00
Ro=rd*(1+gm*Rs)=62500.00  ohm
For CB Amplifier
gm = 0.05  A/V
Ri= 1/gm=20.00  ohm
Avs=gm*RL/(1+gm*Rs)= 71.43
Ro=gm*(rbe*rc)=2.50e+06  ohm

Example 5_5 Page No. 152

In [4]:
from math import pi
from __future__ import division  
RL=5*10**(3)
print "RL= %0.2f"%(RL)," ohm"  #Load resistance
Cc=0.1*10**(-6)
print "Cc= %0.2e"%(Cc)," farad"  #capacitance
Ri=100*10**(3)
print "Ri= %0.2f"%(Ri)," ohm"  #  input resistance for Amplifier
CSH=100*10**(-12)
print "CSH= %0.2f"%(CSH)," farad"  #shunt load capacitance
Avm=100
print "Avm=%0.2f"%(Avm) # Mid-frequency gain 
fL=1/(2*(pi)*(Ri)*(Cc))
print "fL=1/(2*(pi)*(Ri)*(Cc))= %0.2f"%(fL),"Hz " # Lower cutoff-frequency 
fH=1/(2*(pi)*(RL)*(CSH))
print "fH=1/(2*(pi)*(RL)*(CSH))= %0.2e"%(fH)," Hz" # Higher cutoff-frequency 
BW=fH-fL
print "BW=fH-fL= %0.2f"%(BW)," Hz" # Bandwidth
fT=Avm*fH
print "fT=Avm*fH= %0.2e"%(fT)," Hz" # Unity gain bandwidth
# ERROR NOTE: calculated value of lower cutoff frequency, fL= 15.915494 Hz but in book given as 15.0 Hz   

RL= 5000.00  ohm
Cc= 1.00e-07  farad
Ri= 100000.00  ohm
CSH= 0.00  farad
Avm=100.00
fL=1/(2*(pi)*(Ri)*(Cc))= 15.92 Hz 
fH=1/(2*(pi)*(RL)*(CSH))= 3.18e+05  Hz
BW=fH-fL= 318293.97  Hz
fT=Avm*fH= 3.18e+07  Hz

Example 5_6 Page No. 152

In [1]:
from __future__ import division  
IDSS=16*10**(-3)
print "IDSS = %0.2f"%(IDSS)," ampere" #  maximum drain current JFET 
VP=(-4)
print "VP= %0.2f"%(VP)," volts" # pinch off voltage for JFET 
VGSQ=(-2)
print "VGSQ= %0.2f"%(VGSQ)," volts" # Gate  operating point voltage 
Vsm=(0.2)
print "Vsm= %0.2f"%(Vsm)," volts" #  sinusoidal input voltage for JFET 
D=(((0.5)*(Vsm)**2)/(4*Vsm))*100 # derived from ID=IDSS(1-VGS/VP)**2 and putting value of VGS=VGSQ+Vs, where Vs=Vsm sinwt
print "D=(((0.5)*(Vsm)**2)/(4*Vsm))*100  =%0.2f"%(D),"% " #  Percentage second harmonic distortion calculation

IDSS = 0.02  ampere
VP= -4.00  volts
VGSQ= -2.00  volts
Vsm= 0.20  volts
D=(((0.5)*(Vsm)**2)/(4*Vsm))*100  =2.50 %

Example 5_7 Page No. 153

In [3]:
from math import pi
from __future__ import division  
Ic=1*10**(-3)
print "Ic = %0.2e"%(Ic)," ampere" #  collector current BJT
rbe=2*10**(3)
print "rbe= %0.2f"%(rbe)," ohm"  #base -emitter resistance
gm=50*10**(-3)
print "gm = %0.2f"%(gm)," A/V"#  transconductance for BJT
Beta_o=100
print "Beta_o = %0.2f"%(Beta_o)," " #BJT gain
rc=50*10**(3)
print "rc= %0.2f"%(rc)," ohm"  #collector resistance
Cbe=10*10**(-12)
print "Cbe= %0.2e"%(Cbe)," farad"  #base -emitter capacitance
Ctc=1*10**(-12)
print "Ctc= %0.2e"%(Ctc)," farad"  #input device capacitance
print "part(i)"# part(i)of question
RL=10*10**(3)
print "RL= %0.2f"%(RL)," ohm"  #Load resistance
Rs=500
print "Rs= %0.2f"%(Rs)," ohm"  #input source resistance
Rth=(Rs*rbe)/(Rs+rbe)
print "Rth=(Rs*rbe)/(Rs+rbe)=%0.2f"%(Rth)," ohm"  # eqivalent resistance
Avm=(-gm*RL)
print "Avm=(-gm*RL)=%0.2f"%(Avm) # Mid-frequency gain for CE amplifier
CM=Ctc*(1-Avm)
print "CM=Ctc*(1-Avm)= %0.2f"%(CM)," farad"  #calculated capacitance
Ci=Cbe
print "Ci=Cbe= %0.2f"%(Ci)," farad"  #calculated input capacitance
fHi=1/(2*(pi)*(Rth)*(Cbe+CM))
print "fHi=1/(2*(pi)*(Rth)*(Cbe+CM))= %0.2f"%(fHi)," Hz" # Higher-frequency cutoff for CE amplifier
Ri=rbe
print "Ri=rbe =%0.2f"%(Ri)," ohm"  #input resistance CE amplifier
Ro=rc
print "R0= rc=%0.2f"%(Ro)," ohm"  #output  resistance for CE amplifier
fB=1/(2*(pi)*(rbe)*(Cbe))
print "fB=1/(2*(pi)*(rbe)*(Cbe))= %0.2e"%(fB)," Hz" # base terminal frequency cutoff
fT=Beta_o*fB
print "fT=Beta_o*fB= %0.2e"%(fT)," Hz" # Unity gain bandwidth for CE amplifier
print "part(ii)"# part(ii)of question
Rs=50*10**(3)
print "Rs= %0.2f"%(Rs)," ohm"  #input source resistance for CC amplifier
RL=1*10**(3)
print "RL= %0.2f"%(RL)," ohm"  #Load resistance  for CC amplifier
fhi=1/(2*(pi)*(Rs)*(Ctc))
print "fhi=1/(2*(pi)*(Rs)*(Ctc))= %0.2e"%(fhi)," Hz" # Higher-frequency cutoff for CC amplifier
Avm=(gm*RL)/(1+gm*RL)
print "Avm=(gm*RL)/(1+gm*RL)=%0.2f"%(Avm) # Mid-frequency gain for CC amplifier
Ro=1/gm
print "Ro= 1/gm=%0.2f"%(Ro)," ohm"  #output  resistance for CC amplifier
Ri=Beta_o*RL
print "Ri=Beta_o*RL =%0.2f"%(Ri)," ohm"  #input resistance CE amplifier
print "part(iii)"# part(iii)of question
RL=10*10**(3)
print "RL= %0.2f"%(RL)," ohm" #Load resistance  for CB amplifier
Rs=50
print "Rs= %0.2f"%(Rs)," ohm"  #input source resistance for CB amplifier
fHi=gm/(2*(pi)*(Cbe))
print "fHi=gm/(2*(pi)*(Cbe))= %0.2e"%(fHi)," Hz" # Higher-frequency cutoff for CB amplifier
fHo=1/(2*(pi)*(Ctc)*(RL))
print "fHo=gm/(2*(pi)*(Ctc)*(RL))= %0.2e"%(fHo)," Hz" # Higher-frequency cutoff for CB amplifier
Avs=(gm*RL)/(1+gm*Rs)
print "Avs=(gm*RL)/(1+gm*Rs)=%0.2f"%(Avs) # Mid-frequency gain for CB amplifier
Ri=1/gm
print "Ri= 1/gm=%0.2f"%(Ri)," ohm"  #output  resistance for CB amplifier
Ro=Beta_o*rc
print "Ro=Beta_o*rc =%0.2e"%(Ro)," ohm"  #input resistance CB amplifier
#ERROR NOTE:some parameters in the book have been calculated using gm=40 mA/V while given value is gm=50 mA/V. So ,for part(ii) CC amplifier correct value of R0=20 ohm,Ri=100000 ohm,and for part(iii)CB amplifier over all voltage gain Avs=142.85714 ,Ri=20 ohm all calculated for gm=50 mA/V.

Ic = 1.00e-03  ampere
rbe= 2000.00  ohm
gm = 0.05  A/V
Beta_o = 100.00  
rc= 50000.00  ohm
Cbe= 1.00e-11  farad
Ctc= 1.00e-12  farad
part(i)
RL= 10000.00  ohm
Rs= 500.00  ohm
Rth=(Rs*rbe)/(Rs+rbe)=400.00  ohm
Avm=(-gm*RL)=-500.00
CM=Ctc*(1-Avm)= 0.00  farad
Ci=Cbe= 0.00  farad
fHi=1/(2*(pi)*(Rth)*(Cbe+CM))= 778644.54  Hz
Ri=rbe =2000.00  ohm
R0= rc=50000.00  ohm
fB=1/(2*(pi)*(rbe)*(Cbe))= 7.96e+06  Hz
fT=Beta_o*fB= 7.96e+08  Hz
part(ii)
Rs= 50000.00  ohm
RL= 1000.00  ohm
fhi=1/(2*(pi)*(Rs)*(Ctc))= 3.18e+06  Hz
Avm=(gm*RL)/(1+gm*RL)=0.98
Ro= 1/gm=20.00  ohm
Ri=Beta_o*RL =100000.00  ohm
part(iii)
RL= 10000.00  ohm
Rs= 50.00  ohm
fHi=gm/(2*(pi)*(Cbe))= 7.96e+08  Hz
fHo=gm/(2*(pi)*(Ctc)*(RL))= 1.59e+07  Hz
Avs=(gm*RL)/(1+gm*Rs)=142.86
Ri= 1/gm=20.00  ohm
Ro=Beta_o*rc =5.00e+06  ohm

Example 5_8 Page No. 154

In [1]:
from __future__ import division  
tp=10*10**(-3)
print "tp= %0.2f"%(tp)," s" # Time period of pulse
tr=0.05*10**(-6)
print "tr= %0.2e"%(tr)," s" # Rise-Time of pulse
CSH=50*10**(-12)
print "CSH= %0.2e"%(CSH)," farad"  #output capacitor
tilt=5
print "percentage tilt= %0.2f"%(tilt),"%"  #Sag or percentage tilt of output 
Ri=100*10**(3)
print "Ri= %0.2f"%(Ri)," ohm"  # source resistance
RL=tr/(2.2*CSH)
print "RL=tr/(2.2*CSH)= %0.2f"%(RL)," ohm"  #Load resistance calculation
Cc=(tp*100)/(tilt*Ri)
print "Cc= (tp*100)/( tilt*Ri)=%0.2e"%(Cc)," farad"  #capacitance
#ERROR NOTE: calculated value of RL=454.54545 ohm but in book given as 455 ohm  

tp= 0.01  s
tr= 5.00e-08  s
CSH= 5.00e-11  farad
percentage tilt= 5.00 %
Ri= 100000.00  ohm
RL=tr/(2.2*CSH)= 454.55  ohm
Cc= (tp*100)/( tilt*Ri)=2.00e-06  farad