While developing electronic systems, engineers test the device by stimulating it with different types of signals they expect it to encounter in the field. The piece of test equipment that engineers use for generating the various test signals is the signal generator. A signal generator may be used as a stand-alone development system or in combination with other test instruments.
Depending on the requirement, signal generators may come in various forms and types, with each of them providing different forms of signals. For instance, some output only RF signals, others audio signals, while some provide a train of pulses, and still others offer different shapes of wave-forms. Although different signal generators offer a variety of facilities and performance levels, they may be broadly classified as:
Function Generators
This type of signal generators typically generates simple repetitive waveforms such as sine, sawtooth, square, and triangular waveforms. Early models of signal generators used analog circuits to generate the waveforms, but later models depend on digital circuitry to produce them. Users can set the frequency for the waveforms from the front panel of the instrument. Function generators operating at high frequencies are more expensive.
Arbitrary Waveform Generators
These signal generators can produce arbitrary waveforms that the user specifies. They are one of the most complex function generators and therefore expensive. Users can demand almost any shape of waveform for the instrument to generate, sometimes even by specifying points on the waveform. Some manufacturers compromise on the bandwidth because of the techniques they use to generate the signals.
RF Signal Generators
As the name suggests, these signal generators output radio frequency signals. Earlier analog models used free running oscillators with frequency locked loop techniques for improved stability. Nowadays, manufacturers use frequency synthesizers for achieving the stability and accuracy. Some also use direct digital synthesis along with phase locked loops for generating the required RF output.
Vector Signal Generators
These are a special type of RF signal generators for generating complex modulation formats such as QAM, QPSK, and similar.
Audio Signal Generators
These produce signals within the human audio range, typically from 20 Hz to 20 kHz. Suitable for audio and frequency response measurements, some versions offer repetitive and non-repetitive linear and logarithmic sweeps across the entire output. Some audio signal generators can synchronize with an oscilloscope to enable a visual display of the frequency response of the device under test. Usually with very flat response and extremely low levels of harmonic distortion, audio signal generators help in the measurement of distortion from the device under test.
Pulse Generators
This type of signal generators output pulses with variable height, width, and rise/fall times. Users can program them to output a single pulse after a defined time delay. The user may program all aspects of the pulse—its height, width, DC level, and its rise and fall times.
The large variety of signal generators producing different types of waveforms allows engineers to use them in various applications. They are useful for testing RF equipment, logic boards, and in hosts of other areas. Of course, for achieving the proper objective, the engineer has to determine the type of signal generator necessary for a given job.
