RC COUPLED AMPLIFIER
AIM: To calculate voltage gain, to observe frequency response.
Transistors - BC 107 -2Nos,
Resistors - 3.3K -2Nos,
Capacitors - 100uF -3Nos,
Regulated power supply,
Cathode ray oscilloscope,
This is most popular type of coupling as it provides excellent audio fidelity.
A coupling capacitor is used to connect output of first stage to input of second stage. Resistances R1, R2,Re form biasing and stabilization network. Emitter bypass capacitor offers low reactance paths to signal coupling Capacitor transmits ac signal, blocks DC. Cascade stages amplify signal and overall gain is increased total gain is less than product of gains of individual stages. Thus for more gain coupling is done and overall gain of two stages equals to A=A1*A2
A1=voltage gain of first stage
A2=voltage gain of second stage.
When ac signal is applied to the base of the transistor, its amplified output appears across the collector resistor Rc.It is given to the second stage for further amplification and signal appears with more strength. Frequency response curve is obtained by plotting a graph between frequency and gain in db .The gain is constant in mid frequency range and gain decreases on both sides of the mid frequency range. The gain decreases in the low frequency range due to coupling capacitor Cc and at high frequencies due to junction capacitance Cbe.
1. Apply input by using function generator to the circuit.
2. Observe the output waveform on CRO.
3. Measure the voltage at
a. Output of first stage
b. Output of second stage.
4. From the readings calculate voltage gain of first stage, second stage and overall gain of two stages. Disconnect second stage and then measure output voltage of first stage calculate voltage gain.
5. Compare it with voltage gain obtained when second stage was connected.
6. Note down various values of gain for different frequencies.
7. A graph is plotted between frequency and voltage gain.
in dB (20 log10Vo/Vi)
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INPUT WAVE FORM:
FIRST STAGE OUTPUT:
SECOND STAGE OUTPUT:
1) All connections should be tight.
2) Transistor terminals must be identifying properly.
should be taken with out any parallax error. Reading
RESULT: Thus voltage gain is calculated and frequency response is observed along with loading affect.