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.
There are different types of clippers e.g. series clipper, parallel clipper etc. but the method for solving all
the type of circuits are same. Now let us discuss the procedure with the help of a problem. For a clipping
circuit at least two components—an ideal diode and resistor are required and sometimes a dc battery is
also employed for fixing the clipping level. The diode acts as a closed switch when forward biased and an
open switch when reverse biased. The input waveform can be clipped at different levels by simply
changing the voltage of the battery and by interchanging the positions of the various elements.
Depending on the orientation of the diode, the positive or negative region of the input signal is “clipped”
off and accordingly the diode clippers may be positive or negative clippers.
There are two general categories of clippers: series and parallel (or shunt). The series configuration is
defined as one where diode is in series with the load, while the shunt clipper has the diode in a branch
parallel to the load.
1. Positive Clipper
The clipper which removes the positive half cycles
of the input voltage is called the positive clipper.
The circuit arrangements for a positive clipper are
illustrated in the figure given below.
The figure illustrates the positive series clipper
circuit (that is, diode in series with the load). From
the figure (a) it is seen that while the input is posi tive, diode D is reverse biased and so the out put
remains at zero that is, positive half cycle is clipped off. Dur ing the negative half cycle of the input, the
diode is forward biased and so the nega tive half cycle appears across the output.
Figure (b) illustrates the positive shunt clipper circuit (that is, diode in parallel with the load). From the
figure (b) it is seen that while input side is positive, the diode D is forward biased and conducts heavily
(that is, diode acts as a closed switch). So the voltage drop across the diode or across the load resistance
RL is zero. Thus output voltage during the positive
half cycles is zero, as shown in the output
waveform. During the negative half cycles of the
input signal voltage, the diode D is reverse biased and behaves as an open switch. Consequently the
entire input voltage appears across the diode or across the load resistance R L if R is much smaller than RL
Actually the circuit behaves as a voltage divider with an output voltage of [R L / R+ RL] Vmax = -Vmax when
RL >> R
Note: If the diode in figures (a) and (b) is reconnected with reversed polarity, the cir cuits will become
for a negative series clipper and negative shunt clipper respec tively. The negative series and nega tive
shunt clip pers are shown in figures (a) and (b) as
given below.
In the above discussion, the diode is considered to
be ideal one. If second approximation for diode is
considered the barrier potential (0.7 V for silicon
and 0.3 V for Germanium) of diode, will be taken
into account. Then the output wave forms for
positive and negative clippers will be of the shape
shown in the figure below.
2. Biased Clipper
Sometimes it is desired to remove a small portion of positive or negative half cycles of the signal voltage.
Biased clippers are employed for this purpose. The circuit diagram for a biased negative clipper (that is
for removing a small portion of each negative half cycle) is illustrated in figure (a).
The action of the circuit is explained below. When
the input signal voltage is positive, the diode D is reverse-biased and behaves as an open-switch, the
entire positive half cycle appears across the load, as illustrated by output wave form [figure (a)]. When
the input signal volt age is negative but does not exceed battery voltage V, the di ode D remains reverse-
biased and most of the input voltage ap pears across the output. When during the nega tive half cycle of
input signal, the signal voltage exceeds the battery voltage V, the diode D is forward biased i.e conducts
heavily. The output voltage is equal to – V and stays at – V as long as the input signal voltage is greater
than battery voltage V in magnitude. Thus a biased negative clipper removes input voltage when the
input signal voltage exceeds the battery voltage. Clipping can be changed by reversing the battery and
diode connections, as illustrated in figure (b).
Some of other biased clipper circuits are given below in the figure. While drawing the wave-shape of the
output basic principle discussed above are followed. The diode has been considered as an ideal one.
Different Clipping Circuits
3. Combination Clipper
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. The circuit for such a clipper is given in the figure below.
The action of the circuit is summarized below. 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 + V 1 stays as long as. the input signal voltage exceeds +
V1. On the other hand for the negative input voltage signal, the diode D 1remains reverse biased and
diode D2 conducts heavily only when input voltage exceeds battery voltage V 2 in magnitude. Thus during
the negative half cycle the output stays at – V 2 so long as the input signal voltage is greater than -V 2.
