DIY Circuit Design: Waveform Clamping
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.
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.
Negative Clamping 
Negative Clamping 
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:
Waveform Clamping 
Waveform Clamping Circuit 
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.
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:

Positive ClamperThe 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

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