The figure shows the circuit diagram of an RC COUPLED AMPLIFIER.
The circuit shown here using Voltage divider bias.
Rc coupled amplifier is commonly used to amplify the given input signal.
Here we considering the sinusoidal input signal and at output
terminals we get the amplified version of input signal.
ie; Amplitude increased by a factor equal to the gain of the amplifier.
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Of RC Coupled Amplifier
Consider the positive going wave of sinusoidal signal.
ie; Rising from zero to peak value and viceversa.
Due to transistor parameters, any variation in the input terminal(base) may
cause a large variations in the output terminal(collector) in common
This is the basic principle used for Rc coupled amplifier, to amplify
If the input signal rises from zero in the input, it cause a large
rise in voltage (amplitude)
at the output terminal.
And similarly for negetive going wave.
Inorder to achieve faithful amplification of input signal, the Q point
must be selected in the middle of DC Load Line.
To stabilize the Q point in the middle and make it independent of
temperature variations we are using voltage divider bias.
of Rc Coupled Amplifier
COMPONENTS AND THEIR USES
R1 and R2
- R1 and R2 provides necessary biasing to the Transistor Q.
- It will stabilize the Q point near the middle of DC Load line.
C in and C out
- It is called as Coupling Capacitor.
- It provides coupling to the input and output signals.
- It helps to achieve maximum power transform
Rc and Re
- It helps to control or drop the supply voltage Vcc.
- It gives a safer limit of vcc for collector and emitter terminals.
- Emitter capacitor, it also called as Bypass capacitor.
- It will bypass ac current and restricts dc,
- Due to this only dc voltage will drop across emitter resistor.
- If we neglecting the Bypass capacitor, ac voltage will drop across
Re, which may reduce the gain of amplifier.
ADVANTAGES OF RC COUPLED AMPLIFIER
- We can be able to amplify any signal in Audio frequency range.
- It provides faithful amplification of input signal.
- Simple circuit diagram
- By using the transistor BC107 it provides an amplification factor of nearly 50.
ie; it provides an output 50 times greater than the input.
DISADVANTAGES OF RC COUPLED AMPLIFIER
- Bjt Amplifier will oscillates on higher frequency range such as
- Band width is comparably narrow than JFET amplifier
DC BIASING CONDITIONS
- Voltage drop across collector resistor Rc
should be equal to 40% of Vcc.
- Voltage drop across emitter resistor Re
should be equal to 10% of Vcc.
- Voltage drop across Collector-Emitter terminal should be equal to 50% of Vcc.
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Note:: The dc biasing conditions should be check only after removing
all the capacitors.
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