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  #1  
Old 07-09-2009, 07:28 PM
someonesdad someonesdad is offline
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Default Function Generator Applications

I am working on a document that discusses function generators and arbitrary waveform generators. It is aimed roughly at folks in technician and beginning engineering/science positions. It acknowledges the usefulness of function generators for a variety of tasks, looks at the DDS method of waveform generation (probably used in most modern equipment), and shows some typical applications.

I'd like to ask this group of experts for some suggestions about interesting uses of these instruments. My goal is to make the examples interesting, practical, and accessible to the average reader. Here are the example applications I have either worked on so far or am considering (they generally assume the use of a scope):
  1. Troubleshooting: identifying a bad subsystem in a system by injecting a signal into the first subsystem and checking its output, moving to the next subsystem and repeating.
  2. Same as previous, but starting from the last subsystem and working backwards.
  3. Measuring the ESR of a capacitor in circuit (can use an AC voltmeter instead of the scope).
  4. Time domain reflectometry: I show scope traces of reflected pulses in a network cable.
  5. Response testing by sweeping.
  6. Response testing using square waves, pulses, and noise.
  7. How to use a power supply to change the DC offset of a function generator.
The examples are practical and, where possible, show the results of building the indicated circuit and making the measurements shown.

I'm aware of B&K's old function generator guidebook and I've looked at a few Agilent and Tek app notes.

I look forward to your creative ideas!
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Old 07-09-2009, 08:36 PM
Mass Mass is offline
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This is more frequency related, but I used to work with a laser that could only read frequencies up to 20kHz. We were tuning oscillators in MHz, so we would need to use a generator to output the nominal frequency of the oscillator and subtract the actual oscillator frequency. We would then take the mixed frequency, now in kHz, and supply it to the laser so it could trim it to its target frequency.
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Old 07-09-2009, 09:11 PM
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Bill_Marsden Bill_Marsden is offline
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Triangle waves are the basis of linear PWM modulation, especially class D audio amps. This is very similar to the system computers use on their audio output, I believe.

I have an ongoing thread that has been temporarly shelved, until I try some new experiments...

http://forum.allaboutcircuits.com/sh...ad.php?t=12405
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Old 07-09-2009, 10:48 PM
someonesdad someonesdad is offline
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Originally Posted by Mass View Post
we would need to use a generator to output the nominal frequency of the oscillator and subtract the actual oscillator frequency.
I've never heard of a laser "reading" a frequency; does this mean you could modify its output by inputting a signal?

Do I understand you to mean you used the function generator to generate some waveform which you then mixed with another signal, then used the difference between the oscillator's signal and the function generator's signal to tell the laser how it should be tuned? This implies your mixing circuit had some kind of nonlinear behavior to get the difference, right?

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Originally Posted by Bill_Marsden View Post
Triangle waves are the basis of linear PWM modulation, especially class D audio amps. This is very similar to the system computers use on their audio output, I believe.
Bill, you'll have to educate me some more. What function generator application are you recommending -- using triangle waves for doing PWM?

I'm gonna be away from the computer for a few days beginning tomorrow, but I'll be interested in others' inputs.
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Old 07-09-2009, 10:49 PM
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Your applications list is biased heavily towards servicing/fault finding activities.

Function generators are just the modern development of signal generators and can be (and are) used whereever these may have been used in the past.

One field you have overlooked is development. Of mechanical systems, electronic sytems, etc.

So they can provide the driving signal for the development of loudspeakers, radar, navigation systems, vibration analysers and counteracters...........

They are particulary useful when combined with a gating system so that a train of a fixed sequence of pulses may be produced. This includes one shot mode. You should also mention trigger modes.

Finally I am sure that AAC would be interested in at least part of your document if you were prepared to publish here as well.
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Old 07-09-2009, 11:59 PM
someonesdad someonesdad is offline
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Quote:
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Your applications list is biased heavily towards servicing/fault finding activities.
I agree; this tends to be a common activity of the target audience.

Quote:
Originally Posted by studiot View Post
One field you have overlooked is development. Of mechanical systems, electronic sytems, etc.
Actually, I haven't, although one wouldn't know that from the post I made above. I do point out there are many uses in the development and research worlds. But I find it difficult to give meaningful examples because I have to leave out most of the technically interesting stuff to focus on the application of the function generator.

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Finally I am sure that AAC would be interested in at least part of your document if you were prepared to publish here as well.
The document will eventually be published by the company that contracted with me to write it and it will be freely available to anyone on the web. I'll try to remember to post a link to it when it is published.
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Old 07-10-2009, 02:05 AM
KL7AJ KL7AJ is offline
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Quote:
Originally Posted by Bill_Marsden View Post
Triangle waves are the basis of linear PWM modulation, especially class D audio amps. This is very similar to the system computers use on their audio output, I believe.

I have an ongoing thread that has been temporarly shelved, until I try some new experiments...

http://forum.allaboutcircuits.com/sh...ad.php?t=12405
IN fact, they're useful for checking the linearity AND PHASE SHIFT of ANY amplifier.

Eric
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Old 07-10-2009, 02:10 AM
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Yep, square waves in particular can tell you a lot, looking at the specific distortions. It is a quick and dirty method of looking at frequency response, both low and high ends.
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Old 07-10-2009, 01:42 PM
Mass Mass is offline
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Quote:
Originally Posted by someonesdad View Post
I've never heard of a laser "reading" a frequency; does this mean you could modify its output by inputting a signal?
The laser had a frequency card. The actual laser beam would vaporize some of the electrode off of a laser trimmable capacitor to modify the oscillator frequency.

Quote:
Originally Posted by someonesdad View Post
Do I understand you to mean you used the function generator to generate some waveform which you then mixed with another signal, then used the difference between the oscillator's signal and the function generator's signal to tell the laser how it should be tuned? This implies your mixing circuit had some kind of nonlinear behavior to get the difference, right?
Correct. But I'm not sure whether the mixer was nonlinear. As far as I know, the mixer simply subtracted the frequency of signal A from signal B.
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Old 07-11-2009, 01:50 AM
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Here is a super simple PWM using a sawtooth, instead of the classic triangle wave.



As far as I know it has never been built. I'm going to have to try it out someday.

If you were to feed audio on the + input it would be the basis for a decent class D audio, if the sawtooth distortion wasn't too extreme.
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