Aim – Analysis of
frequency response of cascade amplifiers.
Simulator Used – PSpice .
Theory –
The cascode is a two-stage amplifier that consists of
a common-emitter stage
feeding into a common-base stage.
In modern circuits, the cascode is often constructed from two transistors (BJTs or FETs), with one operating as a common emitter or common source and the
other as a common base or common gate.
This circuit has a lot of advantages over the
single stage amplifier like, better input output isolation, better gain,
improved bandwidth, higher input impedance, higher output impedance, better
stability, higher slew rate etc. The reason behind the increase in
bandwidth is the reduction of Miller effect.
Miller effect is the multiplication of
drain to source stray capacitance by the voltage gain. The drain to source
stray capacitance always reduces the bandwidth and when it gets multiplied by
the voltage gain the situation is made further worse. Multiplication of stray
capacitance increases the effective input capacitance and for an amplifier, the increase in input
capacitance increases the lower cut of frequency and that means reduced
bandwidth. Miller effect can be reduced by adding a current buffer stage at the
output of the amplifier or by adding a voltage buffer stage before the input.
Circuit
Diagram –
Result
–
Here, we receive that the gain is high
over a much larger frequency band as compared to common source amplifiers.
Thus, we see that the bandwidth has increased.
Conclusion - Analysis of
frequency response of cascade amplifiers has been performed.
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