Low Distortion Sine Wave Oscillator

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diffuse371
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Low Distortion Sine Wave Oscillator

Post by diffuse371 » Thu Mar 10, 2016 1:19 pm

Hi all.

I'm designing modular music synthesizers. I've made available for non commercial purposes a sub circuit of one of my designs.

After considering some of the options available for low distortion sine, I preferred the idea of a real time compensation system that uses the trigonometric nature of a sine wave to advantage. As it turns out this idea has been explored before.

On my production model I have substituted the 2 main gain cells in the state variable loop with THAT2180 which have much higher dynamic range.

Offsets are the main problem to contend with. Though once tackled this design is very simple and very high performance (distortion was measured at -100dBC with output offset trims only). If you can find good deals on higher performance multipliers such as AD534/734 these can be used without much concern for trimming.

Feel free to use in your own personal projects! :)

http://aether-machine.com/research/

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JR.
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Re: Low Distortion Sine Wave Oscillator

Post by JR. » Thu Mar 10, 2016 4:33 pm

I recall having some conversations with Brad maybe 10 years ago about using that trig identity (sin^2+cos^2=1) to make a SVF based sine wave generator with no ripple in the level control loop.

IIRC Brad came up with schematic from when someone else had done it before (maybe using OTAs for the multipliers?). That was on another forum and I'm not sure the old stuff from back then is still around. (it was at least one hard drive ago).


JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

diffuse371
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Re: Low Distortion Sine Wave Oscillator

Post by diffuse371 » Thu Mar 10, 2016 4:49 pm

There's a Barrie Gilbert patent called the Pythagorator that slims down the concept into a single IC.

http://www.patents.com/us-5714911.html

I tried quite a few variations on this topology and this one just works very well without any mess.

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JR.
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Re: Low Distortion Sine Wave Oscillator

Post by JR. » Fri Mar 11, 2016 10:19 am

diffuse371 wrote:There's a Barrie Gilbert patent called the Pythagorator that slims down the concept into a single IC.

http://www.patents.com/us-5714911.html

I tried quite a few variations on this topology and this one just works very well without any mess.
Sweet,,,, I recognize Mr Gilbert for his work linearizing OTA front ends (Gilbert cell).

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

diffuse371
Posts: 10
Joined: Thu Mar 10, 2016 7:48 am

Re: Low Distortion Sine Wave Oscillator

Post by diffuse371 » Fri Mar 11, 2016 11:57 am

The AD534 is Gilbert's design, I would suspect he had a hand in it's revised version the AD734.

I *think* the AD633 is based on the AD534 as well, but without much concern for laser trimming at the factory.

I require heavy use of linear multiplication in my designs, and the above 4 quadrants multipliers are my bread and butter devices.

The OTA can be linearized by alternative means, e.g. http://www.teaser.fr/~amajorel/sims/ , The Gilbert cell is much easier to apply on the board though.

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JR.
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Re: Low Distortion Sine Wave Oscillator

Post by JR. » Fri Mar 11, 2016 2:38 pm

I'm an old analog dog and even have one VCA patent (no big deal, a class A VCA with servo to trim out device Vbe). Modern IC VCAs are better, so I abandoned mine a long time ago. It was only used in one commercial product.

But around the turn of this century I went over to the dark (digital) side, and find it much more powerful for product design.

Multiplies take one clock tick... :lol:

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

diffuse371
Posts: 10
Joined: Thu Mar 10, 2016 7:48 am

Re: Low Distortion Sine Wave Oscillator

Post by diffuse371 » Fri Mar 11, 2016 5:31 pm

Multiple similar products have reduced the component count by many factors using FPGAs and PICs.

There are several technical reasons for generating sound in the analogue domain, but the one that I like the most is subatomic particle behaviour. An oscillator in a loop is very interesting when observed under this praxis.

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