[sdiy] square to sine

[Neil Johnson]

Hi David,

> I'm looking for a good way to convert square to sine.

There are various ways of doing it.  If you want the same frequency
out as you put in then the solutions generally split into
"resynthesis" (such as the PLL approach suggested by Noah and Scott),
or "subtractive", with various filter configurations.

If starting from a square wave there's not much shaping you can do, so
diode or FET shapers won't work, so it's going to be some technique
which tunes, tracks or locks onto your square wave in order to produce
the required sine wave.

> I need low-cost,
> stable, low-distortion sine wave generators with excellent 1V/octave
> tracking over the entire audio range.

Easier, much easier.  A decent quadrature or state variable oscillator
should easily achieve that with some care and attention to detail,
coupled with a good expo converter if necessary.

> One method I'm thinking of is a voltage-controlled clock with divider and
> switched capacitor filter.  Has anybody tried this?

The DDS or NCO approach as suggested by Richie.

> I'm not totally averse to digital solutions either, but I'd prefer analog.

Paul Schreiber has done well with his DSP-based modules.  Sine waves
with minuscule amounts of distortion.

Neil
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