Computing stuff tied to the physical world

Arbitrary Waveform Generator

In Hardware on Mar 23, 2012 at 00:01

Earlier this week, I described how a fixed frequency can be used to stabilize others.

Well… as part of my continuing drive to set up a more complete workbench here at JeeLabs, I’ve decided to get another piece of equipment which relies on this mechanism, called an “Arbitrary Waveform Generator” (AWG) or “function generator” or “signal generator” – three names for essentially the same instrument, as far as I can tell.

An AWG produces a repetitive electrical signal, such as a sine wave or a square wave. Very roughly speaking, you can think of sine waves as “pure analog” and square waves as “pure digital” frequencies.

The unit I picked is a fairly advanced one, the TG2511 from TTi (´┐╝Thurlby Thandar Instruments), in the UK:

DSC 2966

(Check out that box underneath – as a reference it now makes a lot more sense, eh?)

It produces sine waves and square waves up to 25 MHz, and has tons of other waveforms built in, including ramp, triangle, pulse, noise, and more. In fact, since it’s an AWG, you can load any waveform shape into it, and it’ll reproduce it at up to 125 Mega-samples per second and 14-bit resolution (it goes up to 6 MHz in this mode).

Two other major capabilities of such a unit are: the ability to “sweep” across a range of frequencies and being able to “modulate” the generated signal with another one in numerous ways: AM, FM, PM, PWM, and FSK.

As with the Hameg HMO2024 oscilloscope and the GW-Instek GPD-2303S power supply, this thing can be remotely controlled over USB. So it can be driven from a computer to perform complex and/or lengthy tests.

This model does more than I need, but there was a good “price burner” offer at Distrelec, so I decided to go for it. Function generators are not the most important instruments for an electronics lab, but they are extremely useful to learn about all sorts of analog electronics, and to illustrate various concepts and effects “for real”. Note that for lower frequencies, you can generate rough arbitrary waveforms with simply an ATmega and a few resistors.

Here’s the FFT spectrum of its 25 MHz sine wave – a few spikes at 25 MHz multiples, as expected, plus a bunch of 90..105 MHz spikes which also appear when the AWG output is off (more about those tomorrow):

SCR32

Such an AWG is not limited to strictly analog uses, by the way. This unit should also be able to generate a serial bit-stream, like an RS232 message, for example. Such patterns can be loaded via USB on the front panel.

I intend to put this instrument to good use here at JeeLabs, not in the least to create good examples for future weblog posts and to illustrate relevant electronics concepts in that huge playground called Physical Computing.

  1. As I used to call it: ‘lopik’ is in the way. Had a similar problem between 88-105 with testing sonic test probes. The higher freq ones were very adapt on picking up sky radio somehow…

  2. That’s a fancy signal generator! I look forward to seeing what you do with it.

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