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09-19-2023, 12:33 PM
Hi Guys
In the past, analog signal generators fell into two categories: low-distortion oscillators (LDO), and function generators.
LDOs were sinewave generators intended for audio testing and more specifically , to be used along with a distortion analyser to test THD (total harmonic distortion). If you were lucky, the LDO distortion was around 0.002% (20ppm) and these would be fairly expensive and require some time to settle. More affordable sinewave generators exhibit 0.3% THD or so, maybe down to 0.1%.
Function generators produce sine, square and triangle wave outputs. THD for the sine is as described for affordable sinewave-only units.
In our digital age, test signals can be generated using computers using data tables and DACs to generate various wave shapes. The resolution of a sinewave depends upon the number of data points per cycle, similar to the sampling rate of an analog-to-digital conversion, just in the opposite direction. The DAC output is typically a current fed into an analog integrator stage (a virtual-earth stage with the virtual-earth node fed directly from the DAC). THD can potentially be quite low.
The digital version of a function generator is called an "arbitrary waveform generator" , or AWG. The AWG is a cheap and dirty signal generator that can produce, sine, square, triangle, pulse and other wave shapes. Those other shapes can be practically any shape you wish to program, limited only by the interface provided by the manufacturer.
For audio testing, the AWG should have a THD spec listed for its sinewave output. Generally, this will be in the 0.3% to 0.1% range. More expensive AWGs will offer sine THD down to 0.03% or 0.02% - the lowest I've seen for affordable AWGs. Cheapo AWGs are often around $60cdn where the units with the lowest-THD sine output are $5-600cdn.
DSOs (digital storage oscilloscope) can have AWGs built in, with sine THD listed (or not) down to 0.05% to 0.03%. It is certainly convenient to have both devices in one box as it makes frequency response tests easier to do.
In the past, analog signal generators fell into two categories: low-distortion oscillators (LDO), and function generators.
LDOs were sinewave generators intended for audio testing and more specifically , to be used along with a distortion analyser to test THD (total harmonic distortion). If you were lucky, the LDO distortion was around 0.002% (20ppm) and these would be fairly expensive and require some time to settle. More affordable sinewave generators exhibit 0.3% THD or so, maybe down to 0.1%.
Function generators produce sine, square and triangle wave outputs. THD for the sine is as described for affordable sinewave-only units.
In our digital age, test signals can be generated using computers using data tables and DACs to generate various wave shapes. The resolution of a sinewave depends upon the number of data points per cycle, similar to the sampling rate of an analog-to-digital conversion, just in the opposite direction. The DAC output is typically a current fed into an analog integrator stage (a virtual-earth stage with the virtual-earth node fed directly from the DAC). THD can potentially be quite low.
The digital version of a function generator is called an "arbitrary waveform generator" , or AWG. The AWG is a cheap and dirty signal generator that can produce, sine, square, triangle, pulse and other wave shapes. Those other shapes can be practically any shape you wish to program, limited only by the interface provided by the manufacturer.
For audio testing, the AWG should have a THD spec listed for its sinewave output. Generally, this will be in the 0.3% to 0.1% range. More expensive AWGs will offer sine THD down to 0.03% or 0.02% - the lowest I've seen for affordable AWGs. Cheapo AWGs are often around $60cdn where the units with the lowest-THD sine output are $5-600cdn.
DSOs (digital storage oscilloscope) can have AWGs built in, with sine THD listed (or not) down to 0.05% to 0.03%. It is certainly convenient to have both devices in one box as it makes frequency response tests easier to do.
