Electronic Circuit Analysis

222 Electronic Circuit Analysis
6.5.1 Shunt Compensation
One simple method of shortening the rise time in the response of an amplifier circuit and thus enhancing
the high frequency response of the amplifier. (pulse having, sudden change in the input is considered
as high frequency variation) is to add an inductor in series with, V cc and collector.
Fig. 6.12 Shunt compensation circuit
In the a.c equivalent circuit, this 'Inductance' will be in parallel with capacitor. Thus 'Inductance
Capacitor' combinations changes the output response. Since in shunt in the output stage, this is
called shunt compensated amplifier. The collector circuit Z = Rc + jwL.
This increases with frequency. So Vo increases and gain increases. So if 'Inductance' is not
present, the gain will be less. When 'capacitor' is present in the output circuit, Xc decreases as!
increases. Thus L will compensate for capacitor.
So for compensated amplifier, when L is introduced, the damping factor K is defined as,
K=Rc.~
1
fi=21tRC
c
Where fi is the upper 3 db point of the uncompensated amplifier.
~f
Fig. 6.13 Frequency response
So the frequency response changes, when 'L' is added:
The bandwidth of an amplifier circuit can be increased by decreasingfi and increasingfi.