Second the comments on implementing a 16 bit DAC. You need separate analogue/digital grounds, superb voltage references, and lots of attempts to get a good design that actually uses the L.S. bit (rather than losing it in the noise). What you can do is use a second DAC to offset the 16 bit DAC. The offset DAC need only be 8 bit, as long as it is stable. I used this to autozero the output of a photomultiplier amplifier, and I needed about 20 bits to get the correct resolution. However, it can be tricky to adjust the offset DAC without jumps in the output. Incidentally superb experimental design, circuit boards taped to an odd piece of cardboard, with jumpers leads to tie everything together :). I use a dab of hot melt glue to do similar, and it can be used to secure wiring as well. On 15 September 2012 07:01, Don Latham <djl@montana.com> wrote: > Michael: Actually implementing a 16 bit DAC to its 1-bit minimum > resolution will be headache enough. You will gain a real education in > good grounding practice, shielding, power supply stability and noise, > and other Murphy intrusion. A 32 bit DAC IMHO, is impossible, and that's > the name of that tune. > Don > > Chris Albertson > > On Fri, Sep 14, 2012 at 11:21 AM, Michael Tharp > > <gxti@partiallystapled.com> wrote: > > > >> Finally, do people think a 16 bit DAC is adequate or should I consider > >> building a 32-bit one? I looked at a few designs when putting this > >> together > >> but decided to keep it simple until things were up and running. > > > > Having a 32-bit DAC would give you enough range so that you could drop > > in any OCXO you might have. But if you can have trimmer resisters to > > selected for your specif OCXO then 16-bits should be enough. If it > > were me, I'd want the DAC steps to be smaller than what the phase > > detector can measure. Said another way a 32-bit DAC might > > eliminate the need for scale and offset trimmer resistors. > > > > Chris Albertson > > Redondo Beach, California > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > > > -- > "Neither the voice of authority nor the weight of reason and argument > are as significant as experiment, for thence comes quiet to the mind." > De Erroribus Medicorum, R. Bacon, 13th century. > "If you don't know what it is, don't poke it." > Ghost in the Shell > > > Dr. Don Latham AJ7LL > Six Mile Systems LLP > 17850 Six Mile Road > POB 134 > Huson, MT, 59846 > VOX 406-626-4304 > www.lightningforensics.com > www.sixmilesystems.com > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > -- Tom Harris <celephicus@gmail.com>

The PWM DAC should have perfect differential linearity, which I believe is all that matters in this application. (That and no missing codes.) Not so when you try to combine two DACs to make one higher resolution DAC. -----Original Message----- From: Tom Harris <celephicus@gmail.com> Sender: time-nuts-bounces@febo.com Date: Sun, 16 Sep 2012 12:00:55 To: Discussion of precise time and frequency measurement<time-nuts@febo.com> Reply-To: Discussion of precise time and frequency measurement <time-nuts@febo.com> Subject: Re: [time-nuts] GPSDO control loops and correcting quantization error Second the comments on implementing a 16 bit DAC. You need separate analogue/digital grounds, superb voltage references, and lots of attempts to get a good design that actually uses the L.S. bit (rather than losing it in the noise). What you can do is use a second DAC to offset the 16 bit DAC. The offset DAC need only be 8 bit, as long as it is stable. I used this to autozero the output of a photomultiplier amplifier, and I needed about 20 bits to get the correct resolution. However, it can be tricky to adjust the offset DAC without jumps in the output. Incidentally superb experimental design, circuit boards taped to an odd piece of cardboard, with jumpers leads to tie everything together :). I use a dab of hot melt glue to do similar, and it can be used to secure wiring as well. On 15 September 2012 07:01, Don Latham <djl@montana.com> wrote: > Michael: Actually implementing a 16 bit DAC to its 1-bit minimum > resolution will be headache enough. You will gain a real education in > good grounding practice, shielding, power supply stability and noise, > and other Murphy intrusion. A 32 bit DAC IMHO, is impossible, and that's > the name of that tune. > Don > > Chris Albertson > > On Fri, Sep 14, 2012 at 11:21 AM, Michael Tharp > > <gxti@partiallystapled.com> wrote: > > > >> Finally, do people think a 16 bit DAC is adequate or should I consider > >> building a 32-bit one? I looked at a few designs when putting this > >> together > >> but decided to keep it simple until things were up and running. > > > > Having a 32-bit DAC would give you enough range so that you could drop > > in any OCXO you might have. But if you can have trimmer resisters to > > selected for your specif OCXO then 16-bits should be enough. If it > > were me, I'd want the DAC steps to be smaller than what the phase > > detector can measure. Said another way a 32-bit DAC might > > eliminate the need for scale and offset trimmer resistors. > > > > Chris Albertson > > Redondo Beach, California > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > > > -- > "Neither the voice of authority nor the weight of reason and argument > are as significant as experiment, for thence comes quiet to the mind." > De Erroribus Medicorum, R. Bacon, 13th century. > "If you don't know what it is, don't poke it." > Ghost in the Shell > > > Dr. Don Latham AJ7LL > Six Mile Systems LLP > 17850 Six Mile Road > POB 134 > Huson, MT, 59846 > VOX 406-626-4304 > www.lightningforensics.com > www.sixmilesystems.com > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > -- Tom Harris <celephicus@gmail.com> _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.

In message <1225454799-1347767280-cardhu_decombobulator_blackberry.rim.net-1901 834519-@b27.c1.bise6.blackberry>, lists@lazygranch.com writes: >The PWM DAC should have perfect differential linearity, which I >believe is all that matters in this application. (That and no missing >codes.) Not so when you try to combine two DACs to make one higher >resolution DAC. The main problem with two staggered DAC's is actually that all OCXO's drift and eventually you will have to step the major DAC which will give a glitch in the lower bits, almost no matter how much you calibrate beforehand. The PRS10 uses a staggered DAC internally and the steps on the major DAC are measurable in the output signal. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.