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.