CHAPTER 15: TRANSISTOR TUNED AMPLIFIERS

Example 15.1 : Page number 394

In [2]:
from math import sqrt
from math import pi

#Variable declaration
C=250.0*10**-12;                       #Capacitor of parallel resonant circuit, F
L=1.25*10**-3;                         #Inductor of the parallel resonant circuit, H
R=10.0;                                #Resistor of the parallel resonant circuit, ohm

#Calculation
#(i) Resonant frequency
fr=((1/(2*pi))*sqrt((1/(L*C))-(R/L)**2))/1000;                         #Resonant frequecy, kHz

#(ii)  Impedance of the circuit at resonance
Zr=(L/(C*R))/1000;                          #Impedance of the circuit at resonance, kilo ohm

#(iii) Quality factor of the circuit
Q=2*pi*(fr*10**3)*L/R;                          #Quality factor of the circuit

#Result
print("(i) The resonant frequency=%.1fkHz."%fr);
print("(ii) The impedance of the circuit at resonance=%d kilo ohm."%Zr);
print("(iii) The quality factor of the circuit=%.1f."%Q);

(i) The resonant frequency=284.7kHz.
(ii) The impedance of the circuit at resonance=500 kilo ohm.
(iii) The quality factor of the circuit=223.6.

Example 15.2 : Page number 394-395

In [1]:
from math import sqrt
from math import pi

#Variable declaration
C=100.0*10**-12;                        #Capacitor of parallel resonant circuit, F
L=100.0*10**-6;                         #Inductor of the parallel resonant circuit, H
R=10.0;                                 #Resistor of the parallel resonant circuit, ohm
V=10.0;                                 #Supply voltage, V

#Calculation
#(i) Resonant frequency
fr=((1/(2*pi))*sqrt((1/(L*C))-(R/L)**2))/1000;                         #Resonant frequecy, kHz

#(ii)  Impedance of the circuit at resonance
Zr=(L/(C*R))/10**6;                          #Impedance of the circuit at resonance, mega ohm

I=V/Zr;                                     #Line current at resonance, microampere

#Result
print("(i) The resonant frequency=%.2fkHz."%fr);
print("(ii) The impedance of the circuit at resonance=%.1f mega ohm."%Zr);
print("The line current at resonance=%d micro ampere."%I);

#Note : The resonant frequency in the text has been calculated as 1592.28 kHz, but here it gets approximated to 1591.47 kHz.

(i) The resonant frequency=1591.47kHz.
(ii) The impedance of the circuit at resonance=0.1 mega ohm.
The line current at resonance=100 micro ampere.

Example 15.3 : Page number 395

In [3]:
from math import sqrt
from math import pi

#Variable declaration
C=250.0*10**-12;                              #Capacitor of parallel resonant circuit, F
Zr=500.0*10**3;                               #Dynamic impedance, ohm
R=10.0;                                       #Resistance of the coil, ohm


#Calculation
#(i)
#Since,Zr=L/CR,
L=(Zr*C*R)*10**3;                           #Inductance of the coil, mH

#(ii) Resonant frequency
fr=((1/(2*pi))*sqrt((1/(L*10**-3*C))-(R/(L*10**-3))**2))/1000;                         #Resonant frequecy, kHz

#(iii) Quality factor of the circuit
Q=2*pi*(fr*10**3)*(L*10**-3)/R;                          #Quality factor of the circuit

#Result
print("(i) The inductance of the coil=%.2fmH."%L);
print("(ii) The resonant frequency=%.1fkHz."%fr);
print("(iii) The quality factor of the circuit=%.1f."%Q);

(i) The inductance of the coil=1.25mH.
(ii) The resonant frequency=284.7kHz.
(iii) The quality factor of the circuit=223.6.

Example 15.4 : Page number 397

In [4]:
#Variable declaration
Q=60.0;                     #Quality factor of the tuned amplifier
fr=1200.0;                  #Resonant frequency, kHz

#Calculation
#(i)
BW=fr/Q;                    #Bandwidth, kHz

#(ii)
f1=fr-(BW/2);                       #Lower cut-off frequency, kHz
f2=fr+(BW/2);                       #Upper cut-off frequency, kHz

#Result
print("(i)  The bandwidth=%dkHz"%BW);
print("(ii) The lower and upper cut-off frequencies are=%dkHz and %dkHz."%(f1,f2));

(i)  The bandwidth=20kHz
(ii) The lower and upper cut-off frequencies are=1190kHz and 1210kHz.

Example 15.5 : Page number 397

In [5]:
#Variable declaration
fr=2.0;                     #Resonant frequency, MHz
BW=50.0;                    #Bandwidth, kHz

#Calculation
#Since, bandwidth=resonant_frequency/quality_factor
Q=(fr*10**6)/(BW*10**3);                            #Quality factor

#Result
print("The quality factor=%d"%Q);

The quality factor=40

Example 15.7 : Page number 400

In [6]:
from math import sqrt
from math import pi

#Variable declaration
C=0.1*10**-6;                          #Capacitor of parallel resonant circuit, F
L=33.0*10**-3;                         #Inductor of the parallel resonant circuit, H
R=25.0;                                #Resistor of the parallel resonant circuit, ohm


#Calculation
#(i)
fr=(1/(2*pi*sqrt(L*C)))/1000;                  #Resonant frequency, kHz

#(ii)
XL=2*pi*(fr*10**3)*L;                           #Inductive reactance, ohm
Q=round(XL/R,0);                                #Quality factor

#(iii)
BW=(fr*10**3)/Q;                                #Bandwidth

#Result
print("(i)   The resonant frequency=%.2fkHz"%fr);
print("(ii)  The quality factor= %d."%Q);
print("(iii) The bandwidth=%dHz."%BW);

(i)   The resonant frequency=2.77kHz
(ii)  The quality factor= 23.
(iii) The bandwidth=120Hz.

Example 15.8 : Page number 401-402

In [7]:
#Variable declaration
BW_dt=200.0;                       #Bandwidth, kHz
fr=10.0;                        #Operating frequency, MHz

#Calculation
#Since, BW_dt=k*fr (i.e.,co-efficient_of_coupling * operating_frequency)
k=BW_dt/(fr*10**3);                     #co-efficient of coupling

#Result
print("The co-efficient of coupling=%.2f."%k);

The co-efficient of coupling=0.02.

Example 15.9 : Page number 405

In [11]:
from math import sqrt
from math import pi

#Variable declaration
C=500.0*10**-12;                          #Capacitor of parallel resonant circuit, F
L=50.7*10**-6;                            #Inductor of the parallel resonant circuit, H
R=10.0;                                   #Resistor of the parallel resonant circuit, ohm
RL=1.0;                                   #Load resistance, mega ohm

#Calculation
#(i)
fr=round((1/(2*pi*sqrt(L*C)))/1000);                  #Resonant frequency, Hz

#(ii)
R_dc=R;                                             #d.c load, ohm
XL=2*pi*(fr*1000)*L;                                       #Inductive reactance, ohm
Q_coil=round(XL/R,1);                               #Quality factor
R_P=(Q_coil*XL)/1000   ;                            #Equivalent parallel resistance, kilo ohm
R_AC=(R_P*RL*10**3)/(R_P+RL*10**3);                 #A.C load,kilo ohm


#Result
print("(i)   The resonant frequency=%dkHz"%fr);
print("(ii)  d.c load=%d ohm and a.c load=%d kilo ohm."%(R_dc,R_AC));

#Note: In the text resonant frequency has been wrongly calculated to 106kHz but its actual value is approximately 1000kHz

(i)   The resonant frequency=1000kHz
(ii)  d.c load=10 ohm and a.c load=10 kilo ohm.

Example 15.10 : Page number 406-407

In [9]:
#Variable declaration
RL=50.0;                #Load resistance, ohm
n=5;                    #Turns ratio of the transformer
VCC=50.0;               #Supply voltage, V

#Calculation
#(i)
R_ac=n**2*RL;               #A.C load, ohm

#(ii)
P_o_max=VCC**2/(2*R_ac);                #Maximum load power, W

#Result
print("(i)  The a.c load=%d ohm"%R_ac);
print("(ii) Maximum load power=%dW"%P_o_max);

(i)  The a.c load=1250 ohm
(ii) Maximum load power=1W

Example 15.11 : Page number 407

In [10]:
#Variable declaration
P_D=4.0;                    #Maximum power dissipation, mW
P_o_max=1.0;                #Maximum load power, W


#Calculation
max_collector_eff=(P_o_max/(P_o_max+(P_D/1000)))*100;         #Maximum collector efficiency

#Result
print("The maximum collector efficiency=%.1f%%"%max_collector_eff);

The maximum collector efficiency=99.6%
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