A PAM is generated from a pure sine wave modulating the signal and a square wave generator which produces the carrier pulse and a PAM modulator circuit.

A sine wave generator is used which is based on Wien Bridge Oscillator circuit. This can produce distortion less sine wave at the output. The circuit is designed such that the amplitude and the frequency of the oscillator can be adjusted using a potentiometer.

Sine Wave Generator

The frequency can be varied by varying the potentiometer R2 and the amplitude of the adjusted using the potentiometer R. The frequency of the sine wave generated is given by

F = 1/(2π√R1R2C1C2)

The square wave is generated using op-amp based astable circuit. The op-amp is used to reduce the complexity of generating the square wave. The ON time and the OFF time of the pulse can be made identical and the frequency can be adjusted without changing them.

Square Wave Generator

The time period of the pulses generated depends on the value of the resistance R and the capacitance C.The period of the op-amp astable circuit is given by T = 2.2RC

Types of PAM
Pulse amplitude modulation is categorized into two types

* Single Polarity PAM

* Double Polarity PAM

Single polarity PAM is a situation where a suitable fixed DC bias is added to the signal to ensure that all the pulses are positive.Double polarity PAM is a situation where the pulses are both positive and negative.

Applications of PAM
* It is used in Ethernet communication.
* It is used in many micro-controllers for generating the control signals.
* It is used in Photo-biology.

* It is used as an electronic driver for LED lighting

Advantages
* It is the simple process for both modulation and demodulation.
* Transmitter and receiver circuits are simple and easy to construct.

* PAM can generate other pulse modulation signals and can carry the message at the same time.

Disadvantages
* Bandwidth should be large for transmission PAM modulation.
* Noise will be great.

* Pulse amplitude signal varies so power required for transmission will be more.

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