Pulse Generator

- key points about pulse generators: what they are; how they work; an how they can be used.

Pulse generators are items of electronic test equipment that are used to generate pulses - normally rectangular pulses.

These pulse generators are used for a wide variety of applications, but most commonly as bench test equipment when developing logic circuits of various forms.

The pulse generators can be used to generate pulses that can stimulate logic circuit.

In order to be able to provide the right kinds of pulses a considerable degree of adjustment is required for the pulses in terms of length, delay, repetition rate and the like.

Many of the functions of a pulse generator are similar to those of a function generator or arbitrary waveform generator. As a result, many function or arbitrary waveform generators include function generator capabilities, making them multi-purpose test instruments.

TTi TGP 110 Pulse Generator

Pulse generator basics

Pulse generators are used to provide pulses for use in a variety of electronic applications. Typically pulse generators will provide a number of functions and capabilities:

  • Rectangular wave generation   As the name implies a pulse generator is designed to produce pulses that are rectangular in nature, often capable of driving logic circuitry, although they are not necessarily confined to just this type of application.
  • Pulse width:   In order to produce a variety of waveforms, the pulse width can be varied.
  • Repetition rate :   The repetition rate is a key parameter. When used in a "free run" mode, the repetition rate can be varied.
  • Pulse trigger:   Using an external waveform, it is possible to trigger the pulse generator. Pulse triggering can normally occur on either the negative or positive edge via a selection switch.
  • Pulse delay:   When a pulse is triggered it is normal to be able to select a delay for the pulse from the pulse generator. This delay is adjustable.
  • Pulse amplitude:   Although the pulse amplitude will normally be required to drive logic circuits, the amplitude is normally adjustable. If nothing else this is required because there are many standard logic levels in use today.
  • Pulse rise and fall times:   For some applications it may be necessary to be able to adjust the rise and fall times of the logic outputs. This facility is available on many pulse generators.

Pulse generators may use either digital or analogue techniques, or a mixture of both. Elements such as triggering and the pulse generation will almost certainly utilise digital technology, but aspects such as the rise and fall time control on the pulse generator are likely to use analogue techniques.

TTL pulse generator

Often pulse generators are required to produce TTL logic outputs. These generators may be referred to as TTL pulse generators. Their output levels will conform to the standard TTL levels of 0 and 5V.

Although TTL levels are widely used and there are many different families of TTL circuits that have been used including standard TTL, low power, low power Schottky and many more versions of TTL. However the standard definitions of the TTL levels have been accepted.

TTL "Definition" Low (Volts) High (Volts)
TTL input signal definition   0 - 0.8   2.2 - 5
Often TTL limits are restricted to a narrower limit to improve immunity, etc   0 - 0.4   2.6 - 5

For an item of test equipment such as the TTL pulse generator, the narrower TTL limits are bound to be adopted.

Multichannel pulse generators

Some of the later pulse generators are what are termed multichannel pulse generators. These multichannel pulse generators can produce several channels of pulses with independent pulse widths and delays with independent outputs and even independent polarities.

These pulse generators are often used for synchronizing, delaying, gating and triggering multiple devices often with respect to a single event. This means that even though the outputs are independent, they are all linked to the same source in one way or another. This allows for far more sophisticated systems to be linked from a single source, although having different delays, etc..

It is also possible to multiplex the timing of several channels onto one channel in order to trigger or gate the same device multiple times.

By Ian Poole

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