13-09-2013, 02:33 PM
VOLTAGE SHUNT FEEDBACK AMPLIFIER
Aim:
To design and test the voltage-shunt feedback amplifier and to calculate the
following parameters with and without feedback.
1. Mid band gain.
2. Bandwidth and cut-off frequencies.
3. Input and output impedance.
Theory:
In voltage shunt feedback amplifier, the feedback signal voltage is given to
the base of the transistor in shunt through the base resistor RB. This shunt connection
tends to decrease the input resistance and the voltage feedback tends to decrease the
output resistance. In the circuit RB appears directly across the input base terminal and
output collector terminal. A part of output is feedback to input through RB and increase in
IC decreases IB. Thus negative feedback exists in the circuit. So this circuit is also called
voltage feedback bias circuit. This feedback amplifier is known an transresistance
amplifier. It amplifies the input current to required voltage levels. The feedback path
consists of a resistor and a capacitor.
Procedure:
1. Connect the circuit as per the circuit diagram.
2. Keeping the input voltage constant, vary the frequency from 50Hz to 3MHz in
regular steps and note down the corresponding output voltage.
3. Plot the graph: Gain (dB) Vs Frequency
4. Calculate the bandwidth from the graph.
5. Calculate the input and output impedance.
6. Remove Emitter Capacitance, and follow the same procedures (1 to 5).
Result:
Thus the current series feedback amplifier is designed and constructed and the
following parameters are calculated.