How to read a pulse out with an ADC?

[Gibson486]

How does one read a pulsed output with an ADC? Since most SPI ADCs capture on the finished transfer and the pulled up chip select, that would mean I would need to have the pulse be generated while I am doing a fake read and then time the next read and transfer correctly. I guess I could make a sample and hold circuit, but i would still need to generate a pulse during a fake read to ensure it reads what I want it to read. Do they make SPI ADCs that capture on the chips elect? I am guessing no, but i guess it was worth a shot

[tszaboo]

If you use fast SAR ADCs, then they start conversion typically on a start signal, and not on a command.
Depending on how long your signal is go for a few hundred ksps to a few msps ADC, get upset by it's price, redesign it to not use this method to capture the signal, figure out it doesn't work, buy the ADC anyway, realize it needs to be driven correctly, and so on and so on.

[dobsonr741]

Let me rephrase your question:

So you need a trigger signal to start data acquisition on an ADC, and measure parameters of a signal beginning with the trigger condition. Parameters can be a width of an impulse, perhaps the amplitude too.

Does it sound right?

[hubi]

I have a project using an ADS8586S that captures the data on a pulse to dedicated conversion start pins (CONVSTA/CONVSTB). The chip signals the completion of the conversion through a BUSY pin and you can read out the data via SPI after BUSY goes low. Not sure if this particular device is fast enough for your signals or if the phase delay from the built-in low-pass filter might be too high for your timing requirements, but it works really well for my relatively slow application. There are four and eight channel versions of the same device (ADS8584S/ADS8588S).

[BadeBhaiya]

How about using a peak detector to "store" the pulse and read it at your leisure? Of course that would not work if the timing characteristics of the pulse are important.