Low Distortion Sine Wave Oscillator

Construction information for DIY projects, including the MS Mid Side Matrix, Elliptic Equalizer, Mastering Console, Phono Transfer System, Insert Switcher and the Dual Class-A Amplifier. You can post your baby pictures here.
Post Reply
diffuse371
Posts: 10
Joined: Thu Mar 10, 2016 6:48 am

Low Distortion Sine Wave Oscillator

Post by diffuse371 »

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/
User avatar
JR.
Posts: 3700
Joined: Sat May 24, 2008 7:21 pm
Contact:

Re: Low Distortion Sine Wave Oscillator

Post by JR. »

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
Cancel the "cancel culture", do not support mob hatred.
diffuse371
Posts: 10
Joined: Thu Mar 10, 2016 6:48 am

Re: Low Distortion Sine Wave Oscillator

Post by diffuse371 »

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.
User avatar
JR.
Posts: 3700
Joined: Sat May 24, 2008 7:21 pm
Contact:

Re: Low Distortion Sine Wave Oscillator

Post by JR. »

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
Cancel the "cancel culture", do not support mob hatred.
diffuse371
Posts: 10
Joined: Thu Mar 10, 2016 6:48 am

Re: Low Distortion Sine Wave Oscillator

Post by diffuse371 »

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.
User avatar
JR.
Posts: 3700
Joined: Sat May 24, 2008 7:21 pm
Contact:

Re: Low Distortion Sine Wave Oscillator

Post by JR. »

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
Cancel the "cancel culture", do not support mob hatred.
diffuse371
Posts: 10
Joined: Thu Mar 10, 2016 6:48 am

Re: Low Distortion Sine Wave Oscillator

Post by diffuse371 »

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.
Post Reply