[sdiy] An Improved Sine Shaper Circuit

Donald Tillman don at till.com
Sat Apr 18 21:51:24 CEST 2020

> On Apr 17, 2020, at 2:12 PM, David G Dixon <dixon at mail.ubc.ca> wrote:
> I've used Thomas Henry's version of the two-transistor sine shaper in all my
> VCO designs for years (and did a bit of an optimization study to confirm
> that his resistor values were indeed optimum).  Simulation suggests that I
> can get as low as 0.57% THD with that shaper, and there is no visual
> evidence of the triangle apex leaking through.  At that level, there is
> virtually no aural evidence that it isn't a pure sine wave.
> How much better is this new shaper in terms of THD?  (If no one answers, I
> guess I could simulate it myself.)

The spectrum plots in my article show this.  

For the mathematical tsin() curve, the third and fifth harmonics are down 76dB.  So that should be below 0.05% distortion.  

For the Spice simulated example circuit with two transistors and fixed EIA resistor values, the harmonics are well below 60dB down, so that would be about 0.12% distortion.

Gettin' tough to measure.  

  -- Don
Donald Tillman, Palo Alto, California

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