A PWM divider was used in the excellent Datron 4910 voltage standard,
sub-ppm accuracy (and stability).
It included a multi-pole active LPF (5? 7? don't remember) to eliminate
switching noise in the output.
The reference/divider topology they used pretty much eliminated any temp
drift from any component other than the voltage ref itself (LTZ1000).
There are schematics online in various places.
I have two of them, I used to send them out alternatley for cal (by
Fluke) whenever the out-of-cal one had an average diff from the
calibrated one of more than 1uv. I haven't had to send either out for a
few years now. Going long distances down the aging curve is a wonderful
thing. Of course, they could both be aging at exactly the same rate now.
:) They're both on continuously, and have been for the 8 years I've had
them. I have no idea how many thousands of hours they had on them before
I got them.
--
Bill Ezell
----
They said 'Windows or better'
so I used Linux.
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