Hi Folks,
Got to conserve some energy in a micro-powered mote. One place to cut is a sensor that's a power hog. So we want to briefly power it, sample, hold, turn the sensor power off and then let a 22 bit delta-sigma ADC do its crunching. Can't find a micropower S&H that can live with a 3.3V single supply. Are there any?
I could roll my own mux - cap - buffer amp thing but that gets old and uses too much space.
-- Regards, Joerg http://www.analogconsultants.com/
ISTM that dedicated S&Hs went away when jellybean muxes got really good. 1 pC used to be really amazing, and it's now fairly run-of-the-mill.
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 hobbs at electrooptical dot net http://electrooptical.net
I wouldn't think it practical to make a s/h with anything like 22 bit accuracy. Well, maybe 18 bits with expensive parts and really slow acquisition time.
Can you just power up the sensor+ADC, measure, and shut down?
People don't make s/h chips much any more. Actually, never did.
You can't leave it on long enough for the number crunch? No S/H needed. (Is it a _really_slow_ ADC?) ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| 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.
True but it means that nowadays one must use a mux plus a cap plus a buffer amp while in the olden days a single IC was enough. I guess it's a pill I have to swallow, meaning some super tiny SON package to squeeze it all in. What I dread most is making the CAD models for those because there isn't much of a standard.
-- Regards, Joerg http://www.analogconsultants.com/
I really only remember the LF398, HA5351, and AD684. I don't think there ever were very many. Between improved MUXes and sampling ADCs, they sort of got squeezed out in the middle.
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 hobbs at electrooptical dot net http://electrooptical.net
??? Making a CAD model for a S/H should be downright trivial... at least for me... seems I have a building block for every occasion >:-} ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| 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.
Den torsdag den 13. august 2015 kl. 23.37.21 UTC+2 skrev Joerg:
how long do you intend to power the sensor?
-Lasse
It's the layout footprint that is sometimes a lot of work. Nothing can be copied from anywhere, all from scratch, everything must be down to a tenth of a millimeter, radiuses, and whatnot.
-- Regards, Joerg http://www.analogconsultants.com/
That's what I asked. If the ADC is fast enough, who needs a S/H? ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| 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.
No, because low cost ADCs >20 bits are generally slow delta sigma converters that need the input stable the whole time and spew out an incredible amount of spikes at the input.
22 bits will be a challenge for sure but we can employ some software tricks to compensate for imperfections due to droop.Oh, there are some good ones. But all in the twodigit Dollar range and they need half a nuclear power station to run.
-- Regards, Joerg http://www.analogconsultants.com/
Can't. It tops out at 60 samples per second and we need almost that many.
Yup, it's slow. Because of power consumption requirements.
-- Regards, Joerg http://www.analogconsultants.com/
As short as possible. It is a 1k strain gauge and ideally I'd like to push that to the low single-digit milliseconds. If I can achieve a 5% duty cycle that would cut the power consumption down by almost 95%.
Realistically we need around 20 bits of precision from a 22-bis delta sigma converter running at 60 samples/sec.
-- Regards, Joerg http://www.analogconsultants.com/
Is the sensor anything like 20 bits accurate? Actually, some load cells are.
-- John Larkin Highland Technology, Inc lunatic fringe electronics jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Run it at lower voltage! Save v-squared power.
-- John Larkin Highland Technology, Inc lunatic fringe electronics jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
It is a strain gauge and WRT dynamic loads it is more than 20 bits accurate but we can't squeeze more than 20 bits ENOB out of the converter. DC accuracy is the pits but we don't need much there.
-- Regards, Joerg http://www.analogconsultants.com/
Only if it's a switcher driving it. Could be done but we've already tried it with less than 1V and then there is a lot of in-band noise creeping up on us.
-- Regards, Joerg http://www.analogconsultants.com/
Next thing that you will be claiming is that there is no free lunch.
My experience with load cells is that they have enough vibration noise that you *have* to average them for a while. So a s/h may not work.
I can envision a power saving scheme, but it's awful.
We now use these pan balances (from china) that do 1 mg out of
200 g's. (Or something like that.) Pretty impressive for ~$200.George H.
I assume by "need half a nuclear" plant you mean they draw as much power as your sensor?
-- Rick
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