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Old 6th November 2005, 06:06 PM   #1
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Default Need AC voltage reference

I need to find or build an ac voltage reference. It only needs to read +/- 3 or 4 volts max peak-to-peak. I need to be able to measure from 10 Hz to 20kHz. I have a couple of DC voltage reference chips from Maxim that seem to work well for DC but I don't see any for AC.
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Old 6th November 2005, 06:50 PM   #2
bogicp is offline bogicp  Yugoslavia
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Default Re: Need AC voltage reference

Quote:
Originally posted by johngalt47
I need to find or build an ac voltage reference. It only needs to read +/- 3 or 4 volts max peak-to-peak. I need to be able to measure from 10 Hz to 20kHz. I have a couple of DC voltage reference chips from Maxim that seem to work well for DC but I don't see any for AC.
Sorry I dont remember good...
Try at google "function generator ICs"
I think that Maxim do some of this chips...
Old manufacturers are Exar and Intersil.


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-boggy
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Old 6th November 2005, 07:13 PM   #3
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Yes, try " 8038" or try this:

http://www.apogeekits.com/function_g..._kit_k8016.htm .

or this:

http://wiredworld.tripod.com/tronics/signal_source.html


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Old 6th November 2005, 07:18 PM   #4
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I think you misunderstand what he is asking for (or is it me getting it wrong?). I think he asks for a signal source that has a very precisely defined amplitude. I hardly think they are any chips or similar simple solutions to buy though. Maybe one could build an oscillator where that amplitude is somehow compared (peak value? rectified LP-filtered value?) to a DC level from a voltage reference, and feedback used to adjust the amplitude?
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Old 6th November 2005, 07:31 PM   #5
bogicp is offline bogicp  Yugoslavia
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Quote:
Originally posted by Christer
I think you misunderstand what he is asking for (or is it me getting it wrong?). I think he asks for a signal source that has a very precisely defined amplitude. I hardly think they are any chips or similar simple solutions to buy though. Maybe one could build an oscillator where that amplitude is somehow compared (peak value? rectified LP-filtered value?) to a DC level from a voltage reference, and feedback used to adjust the amplitude?
Wow!

If this IS true, then forget about "AC reference voltages" in that range of stability (couple of ppm). Oscillators don't have this range of precision and stability. Feedback regulated is only (if I remember) Wien bridge topology, but you can obtain better results with Maxim function generator than with Wien bridge (Maxim/Exar/Intersil chips don't have feedback, and generate sine wave with precise nonlinear network)

In this case, best available solution for this is to build signal/waveform generator with precise and stable D/A converter and lookup table in EPROM, but this solution is much more expensive than precise DC references. You must have precise and gain-stable amplifier for this etc.

----
I remember something! Long ago Micro Linear do some 8pin chips, working with lookup tables and digital clock. I don't know what is happen with Micro Linear and their small chips. I remember also that this chips are very rare and only obtainable from Micro Linear (single manufacturer). This is something like digital controlled sine wave generator.
----


Best regards,

-boggy
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Old 7th November 2005, 12:44 AM   #6
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Christer, you are right. I want some circuit or chip that has a precise amplitude.
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Old 7th November 2005, 05:00 AM   #7
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Yes, but how exact? Remember that you are interested in dB's I'll suppose? What are you going to use it for?

An ICL8038 or similar has pretty stable amplitude.
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Old 7th November 2005, 05:53 AM   #8
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A 8038 amplitude is intimately depending on the supply voltage. Use a regulated supply and you get good stability. Would square wave be OK for you, or does it need to be sine?
What do you need in terms of dB or PPM?

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Old 7th November 2005, 10:04 PM   #9
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I want to verify the accuracy of the ac scale on my Fluke 8800A multimeter. I have already checked the resistance and dc voltage scale to my satisfaction.
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Old 7th November 2005, 10:14 PM   #10
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What exactly are you going to do?

You could try some FFT software like Rightmark Audio Analyzer, very good russian freeware together with your soundcard. An example of the report is here.

http://audio.rightmark.org
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