One common piece of test equipment in any RF laboratory is the signal generator. The purpose of these devices is in the name itself “signal generator,” in that it generates signals with tunable properties such as amplitude, frequency, and wave shape. Signal generators are also called function generators, although, function generators often have more advanced features.
Signal generators are most commonly used to test the response of circuits using known and controllable input signal. In order to validate the output signal coming from the function generator it is common to validate that signal with an oscilloscope (but that’s the topic of a future post).
In terms of the the types of signals these devices can generate, they can range from simple sine waves to complex waveforms and digital signals. Simple waveforms like sine waves, square waves, and triangle wave are useful for testing transfer functions of simple analog circuits. These signals can be tuned and adjusted in various ways such as frequency, amplitude, DC bias, etc.
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More advanced function generators have the ability to generate very complex signals for testing complex circuit responses. These software defined function generators can output signals mobile phone waveforms, wi-fi, Bluetooth, zigbee, satcom signals, or aviation signals. The signal generators are able to cover very large frequency ranges from very low frequencies of only a few hertz to many GHz.
5 Common Types of Signal Generators
1. Oscillators
Oscillators generate sinewaves, clipped-sinewaves, and squarewaves. Oscillators can vary widely in terms of price, functionality and complexity. Many oscillators have tunable output power and frequency. Many oscillators are quartz based due to the high stability and spectral purity of quartz oscillator circuits. Silicon MEMS oscillators from companies like SiTime are quickly improving performance to go head-to-head with quartz based devices. In cases where extreme frequency stability is required, oscillators can be phase-locked to GPS to provide excellent long-term stability.
2. Arbitrary Waveform Generators (AWG)
Arbitrary Waveform Generators are complex and highly functional signal generators. They can produce the most complex types of waveforms and signals. They can generate periodic signals or single-shot signals to be used as a triggering source.
Many of the most advanced arbitrary waveform generators have the ability to define or load new waveforms using software.
3. Frequency Synthesizers
Frequency synthesizers generate output signals as a multiple or fractional multiples of a single reference signal. Frequency synthesizers are most commonly used in an RF chain as up and down converters. The most advanced frequency synthesizers are direct digital synthesizers or DDS generators. These advanced IC allow for wide frequency tuning and very low noise. DDS chipsets are also extremely common in modern software defined radios.
4. Pulse Generators
There are very few single purpose Pulse Generators available. Most signal generators, even the very basic ones, offer pulse output functions. The more advanced arbitrary waveform generators can control pulse width, duty cycle, rise and fall time and other nuances of the pulse waveform.
5. Random-Noise Generators
Random-noise generators are used in many different applications from mechanical system testing, electronics, audio testing, and even psychological testing! Random-noise generators create wideband noise or colors noise (white, brown, pink noise).
