RC COUPLING

RC coupling is an interstage coupling mechanism that consists of two transistor stages in which the first stage output is coupled with the second stage using a special capacitor(also known as a blocking capacitor) between the two stages. The purpose of RC coupling is to provide fruitful voltage gain, frequency response, and stability. The elements in both stages are identical to each other and perform similar operations which sets the operation point unchanged with the help of a resistor at the coupling. The coupling capacitor helps in maintaining the quiescent point unchanged as it blocks DC currents.

TWO STAGE RC COUPLED AMPLIFIER CIRCUIT

The above circuit diagram represents two stage RC coupling transistor circuit . The Transistors are voltage divider biased with C_E in parallel to re(emitter resistance) . +Vcc and Vs are the AC and DC voltage supplies for the circuit .Each stage in this circuit acts as CE amplifier.

Working and Operation

At the input stage an AC signal is applied to the base of first transistor through a capacitor(C₁). The applied input is amplified and that output is taken at collector this is used to drive the second stage transistor with a cc between them. The output of second transistor is connected to the load resistor R_L which converts the collector current variations into voltage output. To understand this concept more clearly let’s take some cases.

Case 1: Vs value increases (Vs>0)

AT STAGE-1

• when Vs value is increasing the base current(Ib1) also increases since in CE amplifier the base current is proportional to collector currrent (I_c) the voltage across collector and emitter (Vce) decreases. Therefore for first stage output is low if input value is increases. This is a 180 degree phase shifted output .Now, this voltage acts as input to the second transistor.

AT STAGE-2

• As the input for the base transistor at second stage is low the base current is low and therefore collector current will be low thus the emitter collector voltage is increased. The final output is amplified and in phase with the input signal.

Case 2: Vs value Decreases (Vs<0)

AT STAGE-1

• when Vs value is decreasing the base current(Ib1)also decreases since CE amplifier the base current is proportional to collector currrent (I_c) the voltage across collector and emitter (V_ce) decreases. Therefore for first stage output is high, if input value is decreases. This is a 180 degree phase shifted output .Now, this voltage acts as input to the second transistor.

AT STAGE-2

• As the input for the base transistor at second stage is high the base current is high and therefore collector current will be high thus the emitter collector voltage is decreased. The final output will be in phase with the input signal.

Applications of RC Coupling Amplifier

• RC Coupling amplifiers are used in Audio amplifiers as it has stable frequency response at lower frequencies.
• RC couplers are used in transmitters and receivers signal amplification.
• RC couplers are used in modulators and demodulators in communication systems
• RC couplers are used in oscillators and signal generators

Advantages

• It is cheap, compactable and light weighted.
• It offers good gain and works efficiently at Mid frequency range.

Disadvantages

• RC coupling amplifier is sensitive to component tolerance any changes in values of resistance or capacitance effects the overall performance of the system.
• RC coupling amplifier produces distortions at higher frequencies .
• RC coupling amplifiers has narrow frequency bandwidth which limits it to smaller applications only.
• The gain of amplifier changes with frequency as the capacitance is changed with frequency.

FAQs on RC Coupling

Q.1: what is RC coupling?

Answer:

RC coupling is a interstage coupling mechanism which consists of two transistor stages in which the first stage output is coupled with the second stage using a special capacitor(also known as blocking capacitor) between the two stages. The purpose of RC coupling is to provide fruitful voltage gain, frequency response and stability

Q.2: what is phase shift in RC coupling ?

Answer:

RC coupling provides 0 (or)360 degree phase shift in which the output is a exact replica of input with significant amplification.

Q.3: What is need of coupling capacitor in RC coupling?

Answer:

The coupling capacitor also known as blocking capacitor helps in maintaining quiescent point unchanged as it blocks DC currents.

Q.4: How does RC coupling works?

Answer:

In RC coupling at the input stage an AC signal is applied to the base of first transistor through a capacitor(C1). The applied input is amplified and that output is taken at collector this is used to drive the second stage transistor with a cc between them. The output of second transistor is connected to the load resistor RL which converts the collector current variations into voltage output.

Q.5: Applications of RC Coupling?

Answer:

1. RC Coupling amplifiers are used in Audio amplifiers as it has stable frequency response at lower frequencies.

2. RC couplers are used in transmitters and receivers signal amplification.

3. RC couplers are used in modulators and demodulators in communication systems

4. RC couplers are used in oscillators and signal generators