Clipper (electronics)

The clippers are the combination of diodes and load resistor in the circuit, which are used to clip the output waveforms upwards or downwards at a certain level according to the requirements.

Or

The clippers are the circuits used to clip the waveform section without distorting the remaining part of the waveform. Clippers are also known as slicers.

Types of clippers

The types of clippers are classified based on the connection and orientation of the diode with the input voltage and the load. There are three types of clippers, series clippers, parallel clippers, and double clippers. The series and parallel clippers are further classified as positive clippers and negative clippers.

Series clipper

The clipper circuit connection of the diode in series with the load resistor is known as series clippers. It clips of the positive or negative half cycle of the input waveform. The connection of the series clipper is shown below:

The input waveform can be sinusoidal or non-sinusoidal. But, most of the circuits has sinusoidal input wave, as shown below:

Positive series clippers

The positive series clippers are used to clip-off the positive part of the input waveform. The positive series clipper circuit is shown below:

For the positive half cycle of the input sinusoidal waveform, the diode becomes reverse biased. It is because the positive input comes in contact with the negative terminal of the diode. Thus, there is no output for the positive half and it gets clipped-off. Similarly, for the negative half cycle of the input sinusoidal waveform, the diode becomes forward biased and conducts at the voltage proportional to the input voltage.

For the ideal diode, the equation becomes:

Vo = 0, Vin > 0

Vo = Vin, Vin < = 0

The waveforms are shown below:

Note: The region where diode is ON is known as transmitting region and when it is OFF is known as limiting region.

But, if the diode is not an ideal diode, the equation becomes:

Vo = 0, Vin > = -0.7V

Vo = Vin + 0.7, Vin < = - 0.7V

Where,

0.7 is the default cut-in voltage for silicon diodes. Here, it is negative because the diode is placed in the opposite orientation.

Both the positive and negative series clippers works on the same concept except the direction of the diode.

The transfer characteristics of an ideal diode are shown below:

The transfer characteristics of the non-ideal diode are shown below:

Negative series clippers

The negative series clippers are used to clip-off the negative part of the input waveform.

The negative series clipper circuit is shown below:

For the positive half cycle of the input sinusoidal waveform, the diode becomes forward biased and conducts. It is because the positive input comes in contact with the positive terminal of the diode. Thus the output for the positive half is proportional to the input voltage. Similarly, for the negative half cycle of the input sinusoidal waveform, the diode becomes forward reverse biased and do not conduct. Thus, there is no output for the negative half and it gets clipped off.

For the ideal diode, the equation becomes:

Vo = Vin, Vin > = 0

Vo = 0, Vin < 0

The output waveform is shown below:

But, if the diode is not an ideal diode, the equation becomes:

Vo = Vin - 0.7, Vin > 0.7V

Vo = 0, Vin < = 0.7V

Where,

0.7 is the default cut-in voltage for silicon diodes.

The above clippers are used to clip-off the positive or negative part of a waveform. But, it does not clip-off the input waveform at a certain level as per our requirements. It can be done by inserting a reference voltage in series with the load. Let's discuss this in detail.

Series clipper with the reference voltage

The series clippers can be used to clip above or below the reference voltage.

Clipping above the reference voltage

The circuit is shown below:

It is the same positive series clipper circuit except for the reference voltage connected with the load RL. The output can be controlled by adjusting the reference voltage or adding others in series with the load resistor. Let the reference voltage be VR, and the input voltage be Vin.

Working

When Vin is less than the V_R, the diode D becomes forward biased and acts as a short circuit. In such a case, the output voltage is equal to the input voltage (Vo = Vin).

The circuit will now appear as:

When Vin is greater than the V_R, the diode D becomes reverse biased and acts as an open circuit. In such a case, no current flows and the output voltage is equal to the reference voltage (Vo = V_R).

The circuit will now appear as:

The input and output waveforms of the series clipper above the reference voltage are shown below:

It shows that a portion of the input waveform is clipped off. We can adjust the clipped portion by adjusting the value of the reference voltage.

Clipping below the reference voltage

The difference in both the clippers with reference voltage is the orientation of the diode. The circuit is shown below:

It is the same negative series clipper circuit except for the reference voltage connected in series with the load RL.

Working

When Vin is less than the V_R, the diode D becomes reverse biased and acts as an open circuit. In such a case, no current flows and the output voltage is equal to the reference voltage (Vo = V_R).

The circuit will now appear as:

When Vin is greater than the V_R, the diode D becomes forward biased and acts as a short circuit. In such case, the output voltage is equal to the input voltage (Vo = Vin).

The circuit will now appear as:

The input and output waveforms of the series clipper above the reference voltage are shown below:

It shows that the portion below the reference voltage is clipped off. We can adjust the reference voltage as per our requirements.

Parallel clippers

The clipper circuit connection of the diode in parallel with the load is known as parallel clippers. It also clips of the positive or negative half cycle of the input waveform. There are two types of parallel clippers, positive and negative parallel clippers.

Positive parallel clippers

The positive parallel clippers are used to clip-off the positive half of the input waveforms. The parallel connection of the diode and the load resistor is shown below:

Working

During the positive half cycle of the input voltage, the diode becomes forward biased and acts like a short circuit. The single path created by the short circuit passes the entire current. It does not allow the current to pass through the load resistor. Hence, the output voltage is zero. The positive cycle of the output waveform of the positive parallel clipper gets clipped off, as shown below:

During the negative half cycle of the input voltage, the diode becomes reverse biased and acts like an open circuit. The open path created by the open circuit allows the current to pass through the load resistor. Hence, the output voltage is given by:

Vo = Vin R/ (RL + R1) for Vin < 0

Vo = 0 for Vin > 0

The negative cycle of the output waveform produces the desired output.

Negative parallel clippers

The negative parallel clippers are used to clip-off the negative half of the input waveforms.

The parallel connection of the diode and the load resistor is shown below:

Working

During the positive Vin, the diode becomes reverse biased and acts like an open circuit. The open path created by the open allows the current to pass through the load resistor. Hence, the output voltage is given by:

Vo = Vin R/ (RL + R1) for Vin < 0

During the negative Vin, the diode becomes forward biased and acts like a short circuit. The single path created by the short circuit passes the entire current, which does not allow the current to pass through the load resistor. Hence, the output voltage is zero.

Vo = 0 for Vin > 0

The negative cycle of the output waveform gets clipped-off, as shown below:

Double Clippers

The double clipper is a combination clipper where the two diodes and the load resistor are parallel to each other. It is used when the portion of both the positive and negative input cycle are required to be clipped off.

The circuit of the double clipper is shown below:

Working

During the positive half of the input voltage, the diode D1 becomes forward biased and diode D2 becomes reverse biased. Thus, voltage +V1 (reference voltage) will appear across the output of the clipper. The diode D1 remains in forward state till the input signal voltage is greater than +V1. During the negative half, the diode D1 becomes reverse biased and diode D2 becomes forward biased. The diode D2 remains in forward state till the input signal voltage is greater than +V1. Thus, voltage -V2 (reference voltage) will appear across the output of the clipper.

The output waveform is shown below:

Advantages of Clippers

The advantages of clippers are as follows:

• It is used to clip the required part of the input waveform.
• It removes the noise from the amplitude of the signal waveform.
• It is used as a protection device from the high voltage spikes.
• It clips the part of an input waveform without disturbing the rest part of the waveform.

The clippers are generally used to clip a part of the input waveform. For example, the clippers in Frequency Modulation transistors are used to remove the excess ripples and noise from the circuit.

Disadvantages of clippers

The disadvantages of clippers are as follows:

• The diode in both the series and parallel clippers work well in ON and OFF state. But in high frequency applications, the diode capacitance adversely impacts the working of the clippers.
• A potential drop across the diode can distort the signal.