[sdiy] square to sine

[David G Dixon]

Tim Parkhurst sez:

> I'd say the 4151 could be an excellent solution. It's still 
> in production by Exar, and looks to be a great replacement 
> for the 2206. It has very good specs, and the data sheet even 
> shows the trick used by Thomas Henry and others of putting 
> the CV input in the feedback loop of an op-amp to further 
> improve the linearity. Actually, I'm surprised someone hasn't 
> taken that data sheet schematic, hung an expo converter off 
> the front end, and made a nifty triangle core VCO. An 
> under-utilized chip, IMHO. 

In fact, Ian Fritz has used the LM331 (a nearly identical, pin-compatible
alternative) in his "Double Deka" 10-step wave generator, and attests to its
excellent linearity with the opamp in the feedback loop (more or less
exactly as per the "precision V/F converter" schematic in the datasheet).