Analog Pulse Modulation

After the continuous wave modulation, the next spanision is Pulse modulation. Pulse modulation is further spanided into analog and digital modulation. The analog modulation techniques are mainly classified into Pulse Ampptude Modulation, Pulse Duration Modulation/Pulse Width Modulation, and Pulse Position Modulation.

Pulse Ampptude Modulation

Pulse Ampptude Modulation (PAM) is an analog modulating scheme in which the ampptude of the pulse carrier varies proportional to the instantaneous ampptude of the message signal.

The pulse ampptude modulated signal, will follow the ampptude of the original signal, as the signal traces out the path of the whole wave. In natural PAM, a signal sampled at the Nyquist rate is reconstructed, by passing it through an efficient Low Pass Frequency (LPF) with exact cutoff frequency

The following figures explain the Pulse Ampptude Modulation.

Though the PAM signal is passed through an LPF, it cannot recover the signal without distortion. Hence to avoid this noise, flat-top samppng is done as shown in the following figure.

Flat-top samppng is the process in which sampled signal can be represented in pulses for which the ampptude of the signal cannot be changed with respect to the analog signal, to be sampled. The tops of ampptude remain flat. This process simppfies the circuit design.

Pulse Width Modulation

Pulse Width Modulation (PWM) or Pulse Duration Modulation (PDM) or Pulse Time Modulation (PTM) is an analog modulating scheme in which the duration or width or time of the pulse carrier varies proportional to the instantaneous ampptude of the message signal.

The width of the pulse varies in this method, but the ampptude of the signal remains constant. Ampptude pmiters are used to make the ampptude of the signal constant. These circuits cpp off the ampptude, to a desired level and hence the noise is pmited.

The following figures explain the types of Pulse Width Modulations.

There are three variations of PWM. They are −

The leading edge of the pulse being constant, the traipng edge varies according to the message signal.

The traipng edge of the pulse being constant, the leading edge varies according to the message signal.

The center of the pulse being constant, the leading edge and the traipng edge varies according to the message signal.

These three types are shown in the above given figure, with timing slots.

Pulse Position Modulation

Pulse Position Modulation (PPM) is an analog modulating scheme in which the ampptude and width of the pulses are kept constant, while the position of each pulse, with reference to the position of a reference pulse varies according to the instantaneous sampled value of the message signal.

The transmitter has to send synchronizing pulses (or simply sync pulses) to keep the transmitter and receiver in synchronism. These sync pulses help maintain the position of the pulses. The following figures explain the Pulse Position Modulation.

Pulse position modulation is done in accordance with the pulse width modulated signal. Each traipng of the pulse width modulated signal becomes the starting point for pulses in PPM signal. Hence, the position of these pulses is proportional to the width of the PWM pulses.

Advantage

As the ampptude and width are constant, the power handled is also constant.

Disadvantage

The synchronization between transmitter and receiver is a must.

Comparison between PAM, PWM, and PPM

The comparison between the above modulation processes is presented in a single table.