WAVEFORM SHAPING Applications of Diodes: Clipper and Clamper Circuits
When a diode is connected with resistors, capacitors, and biasing voltage in either series or parallel, the resulting circuit performs wave-shaping operations on the input signal. Clipper and clamper are those wave-shaping circuits that provide the desired out voltage level. The article explores clippers, clampers, and their further classification.
Just as the name suggests, clipper circuits “clip” the input signal waveform. Clipper circuits are a combination of a diode, resistor, and a voltage source to prevent the output signal from exceeding a predetermined level by modifying the shape of the output waveform.
Clipper circuits do not distort the input signal to obtain the desired output. In simple words, clipper circuits remove only the unwanted part of the input signal.
Clipper circuits, also known as limiters, are used in various applications:
- Reducing high voltage spikes during overvoltage.
- Protection circuits.
- Noise reduction.
- Amplitude limiting.
The clipper circuit that clips (or removes) the positive part of the input waveform and provides output for the negative part of the waveform is known as the positive clipper circuit.
The clipper circuit that clips (or removes) the negative part of the input waveform and provides output for the positive part of the waveform is known as the negative clipper circuit.
Clippers based on connection configuration:
Clipper circuits are classified into series and parallel clipper circuits. However, both can be positive and negative with bias or no bias.
- Unbiased series clipper: The diode is connected to the resistor in series with no biasing voltage.
- Biased series clipper: The diode is connected in series to the resistor with a biasing voltage.
Parallel or shunt clippers
- Unbiased parallel clipper: The diode is connected to resistors in parallel with no biasing voltage.
- Biased shunt clipper: The diode is connected in series to resistors with a biasing voltage.
The main working principle of clippers is to keep the diode in forward or reverse bias for either portion of the cycle. The forward bias diode is “ON” to behave as a short circuit and provide an output waveform. On the other hand, a diode in reverse bias acts as an open circuit to clip or cut the output waveform.
The role of introducing a bias in the clipper circuit is to maintain a clipping voltage level. In simple words, it is not always desirable to clip off an entire half-cycle. The bias provides a reference voltage beyond which the signal is clipped.
Unlike clippers, clamper circuits use diodes mainly with capacitors (and resistors predominantly) to shift the voltage level of the input signal for providing the output. Clamper circuits add DC components to the output AC waveform without changing its shape. In simple words, a clamper circuit inserts a DC voltage level to an AC waveform that may have lost DC components passing through the amplifier. The “voltage-shifted” signal is termed as a “clamped waveform”.
In simple words, clampers do not clip the waveform from peak to peak but shift the entire reference level.
Also known as DC restorer circuits, clampers are used in:
- Voltage multipliers.
- Signal conditioning circuits.
The capacitor is connected in series with the diode and input voltage in a positive clamper circuit. It adds positive DC voltage to the output waveform. The resulting output waveform in the positive clamper “clamps”- shifts the negative peak of the signal above the reference level.
Positive clampers can be biased with a positive or negative reference voltage to increase the clamped level above the reference level.
The capacitor is connected in parallel with the diode and input voltage in the negative clamper circuit. It adds negative DC voltage to the output waveform. The resulting output waveform in the negative clamper “clamps”- shifts the positive peak of the signal below the reference level.
Negative clampers can be biased with a positive or negative reference voltage to increase the clamped level below the reference level.
The main working principle behind the clamper circuits is to charge the capacitor when the diode is in forward bias for storing the charge. But the capacitor stores the charge and maintains the same voltage level during the reverse operation of the diode. This operation adds a DC bias to the input waveform and shifts the signal above or below the reference level.
Positive clamper circuit
Usually, the first positive half cycle is ignored because the capacitor has no stored charge. This special circuit with a simple diode and capacitor is known as the Villard circuit. However, the Villard circuit is not limited to clamping but other applications.
During the first negative half cycle, the diode is forward-biased and acts as a closed switch. The diode conducts heavily to charge the capacitor to its peak value of the input waveform.
During the second positive half cycle, the diode is reverse-biased and open-circuited. The capacitor is disconnected from the circuit. However, the capacitor still has the stored charge from the previous cycle. Hence, the stored charge maintains the voltage level in the reverse-biased cycle- “clamps” the voltage level to a positive level above the reference line.
Negative clamper circuit
During the first positive half cycle, the diode is forward-biased and acts as a short circuit. The diode allows the current flow to gradually charge the capacitor to its peak value.
During the first negative half cycle, the diode is reverse-biased and open-circuited. The capacitor is disconnected and there is no current flow. However, the capacitor still has the stored charge. Hence, the voltage is “clamped” to a negative level below the reference line.
- Boylestad, R., & Nashelesky, L. (2012). Electronic Devices and Circuits Theory (11th ed.). Pearson Education.