[sdiy] square to sine

[nvawter at media.mit.edu]

Quoting Tom Wiltshire <tom at electricdruid.net>:

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

I'm not sure about the details, but I would also consider using a PLL.
You could use the VCO output of the PLL to drive a sine oscillator.
That's 100% analog.  Although iiuc, PLLs have a tracking tag, but I don't
know how severe it is, or how severely your signals will be changing.

Also, does anyone have experiencing tracking square waves with PLLs?  How well
do they handle it?  To improve the edges, perhaps you could also  
estimate frequency through counting zero-crossings, drive the Fc of an  
LPF with that.