freq to v convertor

[Paul Perry]

I was looking at a f to v ckt, the usual 'convert to a square then
trigger a uniform narrow pulse then integrate and filter' when
it occured to me that if you had even just a very basic filter
(like a RC) and used the pulse to run a sample and hold from 
the RC output, you would be able to get the ripple out completely.

For all I know, this is in fact done already in commercial f to v chips..
anyone know?
I need this for a theremin driven f to v.... at the bottom end, NO filter
is really good enough, if you are going to drive say a VCO from it..

paul perry FrostwaveP/L Melbourne Australia