Looking for an IC with the Ability to Output Many Sine Wave Oscillations - diyAudio
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Old 25th February 2013, 04:52 PM   #1
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Default Looking for an IC with the Ability to Output Many Sine Wave Oscillations

Hi everyone,

I'm searching for a way to cheaply build an array of possibly hundreds of low amplitude sine wave oscillators. Since their outputs will be summed up to produce a line level signal, I currently believe that a 20mV output would be sufficient per oscillator, provided that it is not too close to the noise floor. For example, if there were 150 oscillators outputting 20mV each, that would leave you with a 3V output to work with summed up - plenty sufficient for a line signal (it could be attenuated if it is too high for the input stage of the amplifier, for example).

So, because of these requirements, it seems to me that an IC chip could fit the bill because of the sheer number of oscillators I need, and the fact that they don't need to produce a very strong signal.

The grand purpose of this is an esoteric piece of test equipment. I am open to alternatives to an array of sine wave oscillators, but I am for the most part convinced that this is the only way to do what I need to do.

What do you guys think, does an IC like this exist? Advice?
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Old 25th February 2013, 05:02 PM   #2
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As the outputs will be summed, is it not possible to calculate what the summed output should be, and synthesise it using a DAC?
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Old 25th February 2013, 05:06 PM   #3
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Digital "stepped" output would be a problem for this application. I need the outputs to be actual sums of analog sine wave oscillations.
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Old 25th February 2013, 05:10 PM   #4
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Quote:
Originally Posted by Deepsatchel View Post
Digital "stepped" output would be a problem for this application. I need the outputs to be actual sums of analog sine wave oscillations.
Correctly filtered, the output would not be stepped, however. What is the bandwidth requirement?
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Old 25th February 2013, 05:23 PM   #5
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Yes, filtering could turn a digital signal into an "analog" sort of thing. However, it does not completely fulfill my design requirements.

The bandwidth would be simply the audio band, with each oscillator tuned to some increment, logarithmic, within the 20 - 20k range. For example something like this

1 - 20 Hz
2 - 40 Hz
3 - 100 Hz
4 - 200 Hz
5 - 400 Hz
6 - 1 kHz
...
x - 20 khz

But the increments would be smaller for more precision... I haven't worked out the actual numbers. But no less than 20 and no more than 20k.
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Old 25th February 2013, 05:23 PM   #6
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If it really could only be achieved with analogue means, could the oscillators free-run with frequencies derived from RC networks, for example, or would the frequency & phase need to be accurately derived? What frequencies are required?

It could be expensive, but 'the gold standard' of generating an individual sine wave at an accurate but adjustable frequency is a sine wave VCO locked to an incoming clock signal using a frequency divider and PLL i.e. a frequency synthesiser with a sine wave output. You could look at ICL8038 (probably fairly obsolete these days) and a 4046 PLL for example. It could cost you a few hundred GBP to build what you want, however, and consume a fair bit of power...

An intermediate solution could be analogue low pass filtering of accurate square waves with op amps or you might be able to shape triangle waveforms using diodes (what THD is required?)

Free running oscillators include Wien bridge, for example,
http://en.wikipedia.org/wiki/Wien_bridge_oscillator
http://www.4qdtec.com/singen.html

or Colpitts
http://arxiv.org/pdf/physics/0507133.pdf

You can use Operational Transconductance Amplifiers:
http://technologyinterface.nmsu.edu/.../griseota.html

Maybe there's a way of using a couple of CMOS gates in a 4000 series IC to generate a sine wave - that would be cheap.
http://www.edn.com/design/power-mana...ion-sine-waves

It's all a bit nasty though...

Last edited by CopperTop; 25th February 2013 at 05:38 PM.
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Old 25th February 2013, 05:55 PM   #7
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Analogue multiplier chips might be used to generate sine waves, and then another stage can double that frequency.

http://www.analog.com/static/importe...eets/AD633.pdf
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Old 25th February 2013, 06:11 PM   #8
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Any mileage in ripping apart a vintage electronic organ..? I should think there are various types, but some with drawbars may effectively give you a large number of harmonically-locked sine wave generators. Modern ones will synthesise the output from a DAC of course (very sensibly! :-) )
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Old 25th February 2013, 06:19 PM   #9
oshifis is offline oshifis  Hungary
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A "programmable function generator" or "arbitrary waveform generator" is what you need. As I remember, Wavetek used to produce one, perhaps others too (HP/Agilent?).
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Old 25th February 2013, 06:42 PM   #10
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a long time ago a friend of mine built an electronic keyboard from scratch. He built 12 oscilators for the top octave and then divided each ouput by two to get each lower octave and so on. He then passed the square waves through a LC filter to get his sine waves. You could do the same, start at the top 10khz, 12khz, 15khz, 20khz, 40khz divide each output by 10 and then 10 and then 10 again to get your frequencies. LC filter your outputs and voila. Another aproach is to use quad op amps, 1 op amp per frequency. Depending on the number of frequencies you need will determine the number of opamps. Getting all the frequemcies to be in phase is another matter. Remember a square wave is nothing but odd sine waves added up. A 10hz square wave will give you 10, 30, 50, 70 90 etc hz after proper LC filtering. A tringle wave is even harmonics added up. The obvious as mentioned before is to use some software to generate the sine waves and output via sound card.
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