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
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
Is the idea to use an opposite going pulse on the second gate to compensate for the capacitive coupling?
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?
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I just sample-and-hold between clocks, but I can roll my own charge-compensated switches :-) ...Jim Thompson
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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
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
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.
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
So it's effectively a cascode?
Could you possibly digitally limit the amount of code change, essentially digitally slew limit? I have an idea for a deglitcher but it could only tolerate a half volt or so of voltage step.
-- 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
Yes, that's certainly possible, but the update rate might have to be juiced up.
Yes, that's right. The cascode device is on-chip, though, so it works better.
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
That's just the problem with DACs, on chip things get worse because the miniscule remnants of digital control pulses find their way into everything. Almost like spilled oil.
The best de-glitcher would be off chip and, most importantly, differential. Compensating charge injection via a "counter charge" is one of the tricks to muffle any newly induced spikes. I have always done it in discretes but maybe the ADG12xx series switches is good enough for Spehro's project.
-- Regards, Joerg http://www.analogconsultants.com/
Would they be useful for a digitally controlled power supply?
Rather than return them to their owners. That's not surprising.
This thread reminds of a tube of serial DACs that were ship to us by mistake. We kept them for prosperity.
Jamie
Sure, if you don't mind the occasional 10 PPM bump.
-- 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
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One clever idea is the so-called re-glitching technique used by National In= struments for the past 15 years or so. Less is more, no T/H is used. The id= ea there is to uniformize the glitch energy, or make it code independent, a= nd shift its spectrum to the sampling frequency where the so-called anti-im= aging LPF can eliminate it. This can't be done with code-dependent glitch e= nergy since quite a lot of it remains withing the signal band. See US564662=
0...guess it's still protected though.ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.