Clipper (electronics)

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Voltage clipping limits the voltage to a device without affecting the rest of the waveform

In electronics, a clipper is a device designed to prevent the output of a circuit from exceeding a predetermined voltage level without distorting the remaining part of the applied waveform.

A clipping circuit consists of linear elements like resistors and non-linear elements like junction diodes or transistors, but it does not contain energy-storage elements like capacitors. Clipping circuits are used to select for purposes of transmission, that part of a signal wave form which lies above or below a certain reference voltage level.

Thus a clipper circuit can remove certain portions of an arbitrary waveform near the positive or negative peaks. Clipping may be achieved either at one level or two levels. Usually under the section of clipping, there is a change brought about in the wave shape of the signal.

Clipping circuits are also called slicers, amplitude selectors or limiters.

Types[edit]

Diode clipper[edit]

Positive peak clipper circuit

A simple diode clipper can be made with a diode and a resistor. This will remove either the positive, or the negative half of the waveform depending on the direction the diode is connected. The simple circuit clips at zero voltage (or to be more precise, at the small forward voltage of the forward biased diode) but the clipping voltage can be set to any desired value with the addition of a reference voltage. The diagram illustrates a positive reference voltage but the reference can be positive or negative for both positive and negative clipping giving four possible configurations in all.

The simplest circuit for the voltage reference is a resistor potential divider connected between the voltage rails. This can be improved by replacing the lower resistor with a zener diode with a breakdown voltage equal to the required reference voltage. The zener acts as a voltage regulator stabilising the reference voltage against supply and load variations.

Zener diode[edit]

Two shunt diode clipper circuits
Two shunt diode clipper circuits

In the example circuits above, two zener diodes are used to clip the voltage VIN. The voltage in either direction is limited to the reverse breakdown voltage plus the voltage drop across one zener diode.

Op-amp precision clipper[edit]

For very small values of clipping voltage on low-level signals the I-V curve of the diode can result in clipping onset that is not very sharp. Precision clippers can be made by placing the clipping device in the feedback circuit of an operational amplifier in a similar way to precision rectifiers.

Classification[edit]

Clippers may be classified into two types based on the positioning of the diode. [1]

  • Series Clippers, where the diode is in series with the load resistance, and
  • Shunt Clippers, where the diode is shunted across the load resistance.

The diode capacitance affects the operation of the clipper at high frequency and influences the choice between the above two types. High frequency signals are attenuated in the shunt clipper as the diode capacitance provides an alternative path to output current. In the series clipper, clipping effectiveness is reduced for the same reason as the high frequency current passes through without being sufficiently blocked.

Clippers may be classified based on the orientation(s) of the diode. The orientation decides which half cycle is affected by the clipping action.

The clipping action can be made to happen at an arbitrary level by using a biasing elements (potential sources) in series with the diode.

  • Positively Biased Diode Clipper
  • Negatively Biased Diode Clipper

The signal can be clipped to between two levels by using both types of diode clippers in combination. [2] This clipper is referred to as

  • Combinational Diode Clipper or Two-Level Clippers

The clamping network is the one that will "clamp" a signal to a different dc level. The network must have capacitor, a diode, and a resistive element, but it also employs an independent dc supply to introduce an additional shift.

References[edit]

  1. ^ Salivahanan, Electronic devices and circuits. 2nd Edition. Tata McGraw Hill, 2008, Page 555, ISBN 0-07-066049-2
  2. ^ Rao K Venkata, Pulse And Digital Circuits, Pearson, 2010, page 163, ISBN 978-81-317-2135-3

See also[edit]