multi input multi output analog to digital converter

Yup, you need an analog switch and it has to be switched via uC line or what ever.. It switches, then a reading is taken. etc..

If you're trying to work with a high resolution ADC and expect accurate readings you need to have a way to calibrate between the two sources. Some use a table of values in the uC others, use pots on the board etc..

Jamie

Put an analog multiplexer ahead of the ADC,, like an HC4051 or a DG408 sort of thing. Some ADCs have built-in multiplexers, AD7699 for instance. uPs that have an internal ADC often include a mux to digitize multiple inputs.

--

John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

i cant use a mux, i need those signals to be synchronized in order to obtain synchronized samples. Is there another way to do that?

Best Regards, Tareq Matar

If you expect a single converter to measure 2 or more signals simultaneously, I don't think you can.

If by 'synchronized' you mean sampled within a few tens of microseconds of each other, a mux solution should be adequate.

If you mean to synchronize multiple samples with adc's on a single chip, digikey lists devices with up to 32 adc's on a simgle chip (DDC264).

HTH

--- news://freenews.netfront.net/ - complaints: snipped-for-privacy@netfront.net ---

You can have multiple sample-and-holds, one for each input, that you strobe all at once to acquire one multi-sample. The separate input samples are held (on charged capacitors) for subsequent reading via a MUX and ADC.

Another approach would be to have multiple ADCs that share the same clock and are strobed at the same time. Then you could use a *digital* MUX to read them one at a time into your processor.

However, I suspect that you can get away with a normal MUX-ADC system if you take the inter-sample delays into account when computing relative phase between channels. Obviously, the sample rate will need to be high enough such that there is much less than one cycle's-worth of delay between channels at the highest frequency of interest, to prevent phase ambiguity. But you pretty much need to do that anyway for ordinary anti-aliasing.

Best regards,

Bob Masta DAQARTA v7.60 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, Pitch Track, Pitch-to-MIDI FREE Signal Generator, DaqMusiq generator Science with your sound card!

see if you can get a schematic for a 'good' soundcard. they do two channels, useable 10Hz to 85kHz at 24bits with one ADC, and even 8 channels at slower rates up to 20kHz.

If you're developing a product, you can license a working design from a manufacturer. Someone like Creative Labs will negotiate to license you their design, but at the volume pricing they offer for the OEM soundcards, may not be worthwhile.

But aren't those muxed also?

Jamie

The classic way to do this is to have multiple analog sample-and-hold circuits, followed by a multiplexed ADC. That could be hard or easy, depending on your unstated speed and accuracy requirements.

There are some simultaneous-sampling multi-channel ADC chips that do this.

I've done electric meters where I wanted to "simultaneously" sample voltage and current waveforms. One trick is to just mux and digitize, which gives a time sampling error, but tweak the phase shift of the input amplifiers to correct for the time error. That only works at one frequency, of course. A proper delay line could do this wideband.

You can also in some cases alternate sampling

AB...BA....AB....BA

which statistically removes the sampling skew error. I've done that in electric meters too.

If you oversample, you can do math on the samples to emulate simultaneous sampling.

Or, since ADCs are cheap these days, use lots of them.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation

[snip]

Yes, each of the 32 adc's has a 2:1 mux, but if the OP needs 32 channels or less, he can leave the mux on one channel.

Sure it gives up 1/2 the functionality of the chip, but it gives him his simultaneous sampling.

I'd expect the same would hold true of the smaller (