Most of the electronic devices work on a single positive power supply except few like op-amps,
oscillators etc. Majority of the amplifiers circuits or amplifiers ICs
are also works on positive power supply. Such kind of devices can
operate only with input signals having only positive voltages. Devices
like amplifiers, modulators, demodulators etc. are supposed to work with
natural signals as input. Since the natural signals like sine wave,
audio signals etc. has both positive and negative cycles they have to be
modified in such a way the single supply electronic circuits can
operate them.
Clamping
is the common technique that is applied on the input signals to modify
them so that the circuits can process the entire signal without losing
either positive or negative half. In this method the entire waveform is
shifted to positive of negative voltage side hence making them single
polarity varying voltage. This article discusses the details of the
clamping and the practical positive and negative clamping circuits.
DESCRIPTION:
The
waveforms having both positive and negative half cycles can be clamped
to either positive or negative voltage side. When the entire waveform is
shifted to the positive side it is called positive clamping of a
waveform. The negative clamping is the method in which the entire
waveform is shifted to the negative voltage side.
The following represents the clamping of a sine wave using both the positive and negative clamping devices.
The
positive or negative clamping of a sine wave can be achieved by using a
single diode and a capacitor. Here the positive and negative clamping
of a sine wave is demonstrated with the help of a Wien Bridge oscillator
circuit which can generate a sine wave. The Wien Bridge is a circuit
which can generate the pure sine wave with minimum distortion.
The circuit used here to generate the sine wave based on Wien Bridge has both the frequency and amplitude adjustments. The circuit diagram of the variable frequency sine wave oscillator is shown in the following:
The
frequency of the above circuit can be varied by simply varying the
potentiometer R2 and the amplitude of the wave form can be adjusted by
varying the potentiometer R. The frequency of the sine wave generated by
the above circuit depends on the components R1, R2, C1 and C2 and the
equation for the frequency is given below:
For
the ease of adjusting the amplitude of the wave to obtain proper
sinusoidal sweep, a coarse and fine adjustment has been implemented
using potentiometers. A low value (1K) potentiometer is connected in
series with the high value (100K) potentiometer so that the coarse
adjustment can be done with the high value resistor and the fine
adjustment with the low value resistor.
POSITIVE CLAMPING
The
clamping circuit requires only a diode and a capacitor and in the case
of positive clamping the positive end of the diode is grounded and the
wave is received at the other end through a capacitor. The circuit of the positive clamper is shown below:
The
above circuit forms the simplest positive waveform clamper, but it
cannot be directly used in most of the circuits since it cannot be
loaded. When a load of very small resistance is applied at the output
end of the circuit it may not work properly. Hence a buffer (current
amplifier) must be added at the output end of the circuit as shown in
the following diagram Sign up here with your email
ConversionConversion EmoticonEmoticon