Hi > On Jun 10, 2017, at 4:10 PM, Chris Albertson <[email protected]> > wrote: > > On Sat, Jun 10, 2017 at 12:59 PM, Poul-Henning Kamp <[email protected]> > wrote: > >> -------- >> >> Delta-Sigma strategies for spreading the noise-spectrum are >> interesting, but will not save you if the required heater power >> ends up being a small rational fraction (1/2, 1/3, 1/4 ...) of the >> full scale. >> > > How many output bits are required? Most uPs have quite a few digital > output pins. Each pin could drive a heater resister. Values of the > resisters organized by power of two. Again note the title (poor mans...) > resisters cost almost zero. Even of driver transistors are needed you'd > get change back from a dollar bill.
If you believe that you have a “background” TC of 1x10^-8 / C (for a variety of reasons), that will drive a few things. For right now simply take it as another arbitrary parameter, just like the +/- 0.1C we started with. If you want the controller noise to *not* be the limiting factor at an ADEV floor of 1x10^-12, that drives you to a noise floor of < 0.1 mK. You can then work through the various thermal gains to come up with a level of DAC bits that you need. You could equally as well decide on a 1x10^-13 floor and / or might have a 1x10^-9 sensitivity. Bob > > The reason I ask "how many bits" is because the above is reasonable with 4 > to 6 effective bits but not reasonable with 24 > > I say "effective" because we can dither the low order bits to gain maybe 6 > effective bits form 4 real bits (we can filter the switching noise from a > low frequency dither) > > -- > > Chris Albertson > Redondo Beach, California > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
