Forums

Deglitching a DAC

Started by Spehro Pefhany July 17, 2012
Any clever ideas on getting rid of glitches in a high precision DAC
output? Update rate is a fixed rate, probably in the 10-100kHz range,
and I'd like to keep the glitches (especially variation in glitches)
to << 25ppm, preferably < 5ppm. A S&H with a low charge injection
switch? 

On 07/17/2012 03:43 PM, Spehro Pefhany wrote:
> Any clever ideas on getting rid of glitches in a high precision DAC > output? Update rate is a fixed rate, probably in the 10-100kHz range, > and I'd like to keep the glitches (especially variation in glitches) > to<< 25ppm, preferably< 5ppm. A S&H with a low charge injection > switch? >
I'm a fan of dual-gate MOSFETs for that sort of job, because the charge injection is so low. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
On Tue, 17 Jul 2012 15:46:35 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 07/17/2012 03:43 PM, Spehro Pefhany wrote: >> Any clever ideas on getting rid of glitches in a high precision DAC >> output? Update rate is a fixed rate, probably in the 10-100kHz range, >> and I'd like to keep the glitches (especially variation in glitches) >> to<< 25ppm, preferably< 5ppm. A S&H with a low charge injection >> switch? >> > >I'm a fan of dual-gate MOSFETs for that sort of job, because the charge >injection is so low. > >Cheers > >Phil Hobbs
Is the idea to use an opposite going pulse on the second gate to compensate for the capacitive coupling?
Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> wrote:

>Any clever ideas on getting rid of glitches in a high precision DAC >output? Update rate is a fixed rate, probably in the 10-100kHz range, >and I'd like to keep the glitches (especially variation in glitches) >to << 25ppm, preferably < 5ppm. A S&H with a low charge injection >switch?
What kind of DAC is it? IIRC the better DACs have a latch enable pin which sets the new value for a bits in 1 go. Or does the DAC have that and is still misbehaving? -- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico@nctdevpuntnl (punt=.) --------------------------------------------------------------
On Tue, 17 Jul 2012 15:43:21 -0400, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

>Any clever ideas on getting rid of glitches in a high precision DAC >output? Update rate is a fixed rate, probably in the 10-100kHz range, >and I'd like to keep the glitches (especially variation in glitches) >to << 25ppm, preferably < 5ppm. A S&H with a low charge injection >switch?
I just sample-and-hold between clocks, but I can roll my own charge-compensated switches :-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Tue, 17 Jul 2012 15:43:21 -0400, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

>Any clever ideas on getting rid of glitches in a high precision DAC >output? Update rate is a fixed rate, probably in the 10-100kHz range, >and I'd like to keep the glitches (especially variation in glitches) >to << 25ppm, preferably < 5ppm. A S&H with a low charge injection >switch?
LTC makes some 16-bit internally-deglitched DACs. Or use a fast dac and lowpass filter it. That will help kill digital clock+data feedthrough, which can be as big a problem as pure glitches. A delta-sigma dac will have low glitch energy, but maybe not enough bandwidth. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Spehro Pefhany wrote:
> > On Tue, 17 Jul 2012 15:46:35 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > > >On 07/17/2012 03:43 PM, Spehro Pefhany wrote: > >> Any clever ideas on getting rid of glitches in a high precision DAC > >> output? Update rate is a fixed rate, probably in the 10-100kHz range, > >> and I'd like to keep the glitches (especially variation in glitches) > >> to<< 25ppm, preferably< 5ppm. A S&H with a low charge injection > >> switch? > >> > > > >I'm a fan of dual-gate MOSFETs for that sort of job, because the charge > >injection is so low. > > > >Cheers > > > >Phil Hobbs > > Is the idea to use an opposite going pulse on the second gate to > compensate for the capacitive coupling?
No, you bypass the second gate, or connect it to the source via an RC. The effective output capacitance then is about 0.02 pF or less, a good factor of 10 less than you can get in other discrete parts. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
On Tue, 17 Jul 2012 20:11:32 GMT, nico@puntnl.niks (Nico Coesel)
wrote:

>Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> wrote: > >>Any clever ideas on getting rid of glitches in a high precision DAC >>output? Update rate is a fixed rate, probably in the 10-100kHz range, >>and I'd like to keep the glitches (especially variation in glitches) >>to << 25ppm, preferably < 5ppm. A S&H with a low charge injection >>switch? > >What kind of DAC is it? IIRC the better DACs have a latch enable pin >which sets the new value for a bits in 1 go. Or does the DAC have that >and is still misbehaving?
It's not a digital thing. There's an output glitch whenever the code is updated. The size depends on the number of switches changing, so it's almost independent of the output value (eg. 0x3F..F changing to 0x40..0 is only one LSB but most of the switches change, while 0x40..00 to 0x40..01 is the same change single LSB but only a single switch changes.
On Tue, 17 Jul 2012 13:23:37 -0700, John Larkin
<jlarkin@highlandtechnology.com> wrote:

>On Tue, 17 Jul 2012 15:43:21 -0400, Spehro Pefhany ><speffSNIP@interlogDOTyou.knowwhat> wrote: > >>Any clever ideas on getting rid of glitches in a high precision DAC >>output? Update rate is a fixed rate, probably in the 10-100kHz range, >>and I'd like to keep the glitches (especially variation in glitches) >>to << 25ppm, preferably < 5ppm. A S&H with a low charge injection >>switch? > > >LTC makes some 16-bit internally-deglitched DACs. > >Or use a fast dac and lowpass filter it. That will help kill digital >clock+data feedthrough, which can be as big a problem as pure >glitches. > >A delta-sigma dac will have low glitch energy, but maybe not enough >bandwidth.
It's an Analog '5791- pretty much a real 20 bits.
On Tue, 17 Jul 2012 16:47:29 -0400, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

>On Tue, 17 Jul 2012 13:23:37 -0700, John Larkin ><jlarkin@highlandtechnology.com> wrote: > >>On Tue, 17 Jul 2012 15:43:21 -0400, Spehro Pefhany >><speffSNIP@interlogDOTyou.knowwhat> wrote: >> >>>Any clever ideas on getting rid of glitches in a high precision DAC >>>output? Update rate is a fixed rate, probably in the 10-100kHz range, >>>and I'd like to keep the glitches (especially variation in glitches) >>>to << 25ppm, preferably < 5ppm. A S&H with a low charge injection >>>switch? >> >> >>LTC makes some 16-bit internally-deglitched DACs. >> >>Or use a fast dac and lowpass filter it. That will help kill digital >>clock+data feedthrough, which can be as big a problem as pure >>glitches. >> >>A delta-sigma dac will have low glitch energy, but maybe not enough >>bandwidth. > >It's an Analog '5791- pretty much a real 20 bits.
We used to use AD1862 (20 bit parallel) DACs, but we had bad popcorn noise problems, and AD eventually discontinued them. We have 140 in stock, popcorn fallouts. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation