Pulse Generator

A device that produces an electrical discharge at regular intervals, which can be modified as needed, as in an electronic pacemaker.

A pulse differs from a square wave in that it needs neither base line, nor left-right symmetry. Pulse generator consists of three parts called square wave generator (i.e. stable multivibrator). Monostable Multivibrator (i.e. one shot) and a attenuator.

Pulse Generator Block Diagram
Figure 1: Pulse Generator Block Diagram

Figure 1 shows the block diagram to contract a pulse generator. A Monostable multivibrator i.e. one shot follows a square wave oscillator. The pulse repetition rate is set by the square wave frequency. The one shot triggers on the leading edge of the square wave and produced me output pulse for each input cycle. The duration of each output pulse is set by the one time of the one shot, and may be either very short or may approach the period of the square wave.

Figure shows the circuit of pulse generator. The first part of the circuit consists of a operational amplifier stable multivibrator which produce square wave. The output of the stable multivibrator is provided to the input of the Monostable multivibrator i.e. it triggers the Monostable. Frequency range can be changed using anyone of the capacitor C1, C2 and C3 while frequency continuously changed with resistor R1. Monostable produced a desired width pulse when it is triggered. The width of the pulse can be changed using variable resistor R6.

At the output of the circuit, a inverting operational amplifier is used as a attenuator. A purpose of this attenuator is to adjust the amplitude of the output. Also a low impedance is obtained. The ratio of R11 / R2 is the voltage gain of the amplifier.

The amplifier of the pulse is less if value of R11 is less than the value of R7. It means that there is attenuation and hence we can have desired output amplitude to adjust variable resistor.