Ch-11 : Frequency Response of Amplifiers

Page No. 380 Example 11.2.

In [1]:
tr=10*10**-9
BW=0.35/tr
x1=BW*10**-6
print "BW = 0.35 / tr =%0.2f MHz"%x1

BW = 0.35 / tr =35.00 MHz

Page No. 382 Example 11.3.

In [3]:
from math import pi
hfe=400.
hie=10*10**3
Rs=600.
RL=5*10**3
RE=1*10**3
VCC=12.
R1=15*10**3
R2=2.2*10**3
CE=50*10**-6
RB=(R1*R2)/(R1+R2)
Av=(-hfe*RL)/(Rs+hie+((hie*Rs)/RB))
print "AV = (-hfe*RL) / (RS + hie + ((hie*RS)/RB)) =%0.2f MF"%Av
print "Lower 3-dB point,"
f1=(1.+hfe)/((Rs+hie)*2*pi*CE)
print "f1 = (1+hfe) / ((RS+hie)*2*pi*CE) =%0.2f"%f1

AV = (-hfe*RL) / (RS + hie + ((hie*RS)/RB)) =-145.70 MF
Lower 3-dB point,
f1 = (1+hfe) / ((RS+hie)*2*pi*CE) =120.42

Page No. 386 Example 11.4

In [4]:
from math import pi
RS=600.
hie=1*10**3
hfe=60.
R1=5*10**3
R2=1.25*10**3
RCE=25.
f1=125.
print "The lower 3 dB frequency, f1 = 1 / (2*pi*(RS+R1dash)*CC)"
R1dash=(R1*R2*hie)/((R2*hie)+(R1*hie)+(R1*R2))
CC=1 / (2*pi*f1*(RS+R1dash))
x1=CC*10**6
print "(a)    R1'' = R1 || R2 || hie =%0.2f ohm "%R1dash
print "       CC = 1 / (2*pi*f1*(RS+R1'')) =%0.2f uF"%x1
x2=hie+((1.+hfe)*RCE)
R1dash=(R1*R2*x2)/((R2*x2)+(R1*x2)+(R1*R2))
CC=1 / (2*pi*f1*(RS+R1dash))
x3=CC*10**6
print "(b)    R1''(ohm) = R1 || R2 || [hie+((1+hfe)*RCE)] =%0.2f ohm"%R1dash
print "       CC = 1 / (2*pi*f1*(RS+R1'')) =%0.2f uF"%x3

The lower 3 dB frequency, f1 = 1 / (2*pi*(RS+R1dash)*CC)
(a)    R1'' = R1 || R2 || hie =500.00 ohm 
       CC = 1 / (2*pi*f1*(RS+R1'')) =1.16 uF
(b)    R1''(ohm) = R1 || R2 || [hie+((1+hfe)*RCE)] =716.31 ohm
       CC = 1 / (2*pi*f1*(RS+R1'')) =0.97 uF

Page No. 390 Example 11.5

In [5]:
from math import pi
gm=1./26 #mho
x1=gm*10**3  #m-mho
print "  gm = IC(mA)/26mV = 1/26 =%0.2f m-mho"%x1
rbe=224./(38.46*10**-3)
x2=rbe*10**-3 #k-ohm
print "  rb''e = hfe / gm =%0.2f kohm"%x2
rbb=6000.-5824. #ohm
print "  rbb'' = hie - rb''e = 6000-5824 =%0.2f ohm"%rbb
cbe=((38.46*10**-3)/(2*pi*(80*10**6)))-(12*10**-12) # farad
x3=cbe*10**12 #pF
print "  cb''e(pF) = gm/2*pi*fT - Cb''c =%0.2f pF"%x3

  gm = IC(mA)/26mV = 1/26 =38.46 m-mho
  rb''e = hfe / gm =5.82 kohm
  rbb'' = hie - rb''e = 6000-5824 =176.00 ohm
  cb''e(pF) = gm/2*pi*fT - Cb''c =64.51 pF

Page No. 392 Example 11.6.

In [9]:
from math import pi
alpha=224./(2*pi*(5.9*10**3)*(63*10**-12)) #Hz
x1=alpha*10**-6 #MHz
print "  f_alpha = hfe / 2*pi*rb''e*Cb''e =%0.2f MHz"%x1
beta=1/(2*pi*(5.9*10**3)*((63*10**-12)+(12*10**-12)))
x2=beta*10**-6
print "  f_beta = 1 / 2*pi*rb''e*(Cb''e+Cb''c) =%0.2f MHz"%x2
fT=(38*10**-3)/(2*pi*((63*10**-12)+(12*10**-12)))
x3=fT*10**-6
print "  fT = gm / 2*pi*(Cb''e+Cb''c) =%0.2f MHz"%x3

  f_alpha = hfe / 2*pi*rb''e*Cb''e =95.91 MHz
  f_beta = 1 / 2*pi*rb''e*(Cb''e+Cb''c) =0.36 MHz
  fT = gm / 2*pi*(Cb''e+Cb''c) =80.64 MHz