Aim
– Analysis of frequency response of
common source amplifiers.
Simulator
Used – Pspice
Simulator.
Theory – Of the possible three
configurations of JFET amplifiers, common source (CS) configuration is mostly
used. The advantage of using CS configuration is that it has very high input
impedance.
At the mid-frequency
range, there is no effect of input and output coupling capacitors. Therefore,
the voltage gain and phase angle are constant in this frequency range. The
amplifier shown in the circuit diagram has only two RC networks that influence
its low-frequency response. One network is formed by the output coupling
capacitors and the output impedance looking at the drain. Just as in the case
of BJT amplifier, the reactance of the input coupling capacitor, reactance
increases as the frequency decreases. The phase angle also changes with change
in frequency.
As the frequency is increased
beyond mid-frequency range the internal transistor capacitance effect is
predominant. For JFET it is the internal capacitance between gate and
source. This is also called input capacitance. The other internal capacitance,
which effects the performance acts as a feedback circuit, which couples both,
input and output. The effect of both these capacitances is that it reduces the
gain appreciably as in the case of BJT.
The major drawback in common source amplifiers is
its limited high-frequency response. Therefore, in practice the output often is
routed through either a voltage follower (common-drain or CD stage), or a current follower (common-gate or CG stage), to obtain more favorable output and
frequency characteristics. The CS–CG combination is called a cascode amplifier.
Circuit Diagram –
common source amplifier circuit
Result -
Here,
we observe that a very high gain is received which is constant over the
frequency range from approximately 40 Hz to 30 MHz.
Conclusion - Analysis of
frequency response of common source amplifiers has been performed.
No comments:
Post a Comment