DIODE CLIPPER

A device which removes the peak of a waveform is known as a Clipper

Voltage clipping diagram

• Clipping circuit is a wave-shaping circuit, and is used to either remove or clip a portion of the applied wave in order to control the shape of the output waveform

• Clipping Circuits are also called as Slicers, amplitude selectors or limiter

Clipping circuit

A clipping circuit consists of

• Resistor

• Junction diode

• A battery

• Load resistance

• According to level of clipping the clippers may be

Positive clippers

Negative clippers

Biased clippers

Combination clippers

• There are two general categories of clippers: series parallel (shunt)

Types of clippers

• The positive half cycles of the input voltage will be removed

• During the positive half cycle of the input waveform, the diode ‘D’ is reverse biased, Thus causes the positive half cycle to be clipped off.

• During the negative half cycle of the input, the diode is forward biased and so the negative half cycle appears across the output.

Positive Diode Clipper

Negative Diode Clipper

The negative clipping circuit is almost same as the positive

clipping circuit, If the diode is reconnected with reversed

polarity, the circuits will become for a negative series

clipper and negative shunt clipper respectively figure (a)

and (b).

In a practical diode, the breakdown voltage will exist (0.7 V for silicon and

0.3 V for Germanium). When this is taken into account, the output wave-

forms for positive and negative clippers will be of the shape shown in the

figure below.

Practical diode Clipper

Biased Positive Clipper and Biased Negative Clipper

• When a small portion of positive or negative half cycles of the signal voltage is to be removed.

• When a small portion of the negative half cycle is to be removed, clipper is called biased negative clipper

• When a small portion of the positive half cycle is to be removed,

clipper is called biased negative clipper

a

b

Working of Biasing Clipper

In a biased clipper, when the input signal voltage is positive, the diode ‘D’ is reverse-

biased. Thus the entire positive half cycle appears across the load, as illustrated by

output waveform [figure (a)]. When the input signal voltage is negative but does not

exceed battery the voltage ‘V’, the diode ‘D’ remains reverse-biased and most of the

input voltage appears across the output. When during the negative half cycle of input

signal, the signal voltage becomes more than the battery voltage V, the diode D is

forward biased and so conducts heavily. The output voltage is equal to ‘- V’ and stays at ‘-

V’ as long as the magnitude of the input signal voltage is greater than the magnitude of

the battery voltage, ‘V’. Thus a biased negative clipper removes input voltage when the

input signal voltage becomes greater than the battery voltage. Clipping can be changed

by reversing the battery and diode connections, as illustrated in figure (b).

When a portion of both positive and negative of each half cycle of the input

voltage is to be clipped (or removed), combination clipper is employed

combination clipper

For positive input voltage signal when input voltage exceeds battery voltage ‘+

V1‘ diode D1 conducts heavily while diode ‘D2‘ is reversed biased and so voltage

‘+ V1‘ appears across the output. This output voltage ‘+ V1‘ stays as long as. the

input signal voltage exceeds ‘+ V1‘. On the other hand for the negative input

voltage signal, the diode ‘D1‘ remains reverse biased and diode ‘D2‘ conducts

heavily only when input voltage exceeds battery voltage ‘V2‘ in magnitude.

Thus during the negative half cycle the output stays at ‘- V2‘ so long as the

input signal voltage is greater than ‘-V2‘.

Working of combination clipper

CLAMPERS

COMPONETS OF CLAMPING CIRCUIT

• Capacitor

• Junction diode

• Resistance

CLAMPING CIRCUIT

• A clamping circuit is used to place either the positive or

negative peak of a signal at a desired level

• A clamp circuit adds the positive or negative dc component to

the input signal so as to push it either on the positive side, as

illustrated in figure (a) or on the negative side, as illustrated in

figure (b)

CLAMPING CIRCUIT

POSITIVE CLAMPER

• The signal is pushed upward by the circuit

NEGATIVE CLAMPER

• The signal is pushed downward by the circuit

A circuit that shifts the original signal in a vertical downward direction, as shown

in the figure above. The diode D will be forward biased and the capacitor C is

charged with the polarity shown, when an input signal is applied. During the

positive half cycle of input, the output voltage will be equal to the barrier

potential of the diode, V0 and the capacitor is charged to (V – VQ). During the

negative half cycle, the diode becomes reverse-biased and acts as an open-

circuit. Thus, there will be no effect on the capacitor voltage. The resistance R,

being of very high value, cannot discharge C a lot during the negative portion of

the input waveform. Thus during negative input, the output voltage will be the

sum of the input voltage and the capacitor voltage and is equal to – V – (V — V0)

or – (2 V – V0). The value of the peak-to-peak output will be the difference of the

negative and positive peak voltage levels is equal to V0-[-(2V-V0)] or 2 V.

Negative clamper circuit

The figure shown below can me modified into a positive clamping

circuit by reconnecting the diode with reversed polarity. The positive

clamping circuit moves the original signal in a vertical upward

direction. A positive clamping circuit is shown in the figure below. It

contains a diode D and a capacitor C as are contained in a negative

clamper. The only difference in the circuit is that the polarity of the

diode is reversed. The remaining explanation regarding the working of

the circuit is the same as it is explained for the negative clamper.

Positive clamper circuit

• The shape of the waveform will be the same, but its level is

shifted either upward or downward

• There will be a change in the peak and average values of the

waveform

• The values of the resistor R and capacitor C affect the

waveform.

• We have a positive dc clamper and when the diode points

downward, the circuit is a negative dc clamper.

IMPORTANT POINTS