High sampling ADC's selection-help needed

[krishnakumard]

My requirement is to digitize completely the incoming pulse (Gaussian nuclear pulse from the preamplifier/delay line amplifier of about 2 micro second width and 0.5 - 5 V height ) and carry out the further signal analysis in the DSP. To be more precise, I need to digitize each pulse into many samples. I need to analyze these samples individually. For example, first sample of the pulse at time t1, second sample of the pulse at t2 etc.. Last sample of the same pulse at time Tn. This will lead voltage samples of the incoming pulse with respect to time. I need to get this information for all incoming pulses to deduce rise time characteristics of the incoming pulses. In short, pulses are to be segregated out with respect to its rise time characteristics as I would use a phoswitch detector as the sensor.

For this purpose I need an ADC with high sampling rate for this requirement (is 100MHzall right) and a DSP for signal analysis ( to exclude noises and segregate signals) and store it in the memory.
Most of the ADC's comes with the DSP evaluation kits are SAR type for example AD7266(2MSPS) for Analogue devices. But I was told that all SAR type ADC's are peak detection ADC's. it will only detect the peak voltage and convert it into digital value. Whether SAR of high speed of the order of 10-100MHz will chop the incoming pulses into many as I described earlier and my problem would be solved. Please throw light into it as I was stuck up due to ADC selection.
Thanks

with regards
Krishnakumar

 

[barry]

. I need to get this information for all incoming pulses to deduce rise time characteristics of the incoming pulses.

If you need to measure rise time, you need to tell us what the expected rise time is; it has nothing to do with the pulse width. You can have a 2uS pulse with 1ns rise time, or a 1000nS rise time; that's a big difference. Also, how accurate do you need to measure?

You're a little misinformed about SAR ADCs. They have an 'aperture delay' which determines how long a time they look at the incoming signal. If that aperture is too long with respect to the slew rate of the signal, then you'll get a bad reading. But if you have a fast enough ADC, you'll capture (essentially) a single point of your signal. It does not 'peak detect'.

Barry

 

[krishnakumard]

Thank you Barry for the information and sorry for missing the rise time information. I need to separate the incoming pulses with respect to its rise time. The first type pulse is of 250 nanoseconds and second type of pulses are of one microsecond rise time approximately. Hence I need high accuracy of conversion.. Hence, i want to digitize first the incoming pulses and then analyze in DSP further.
thanking you
Krishnakumar

 

[barry]

Ok, so I think an ADC with at least 10MHz sample rate would do (100MHz would, obviously, be better), assuming you're just looking to discriminate between 250nS and 1000nS pulses. Texas Instruments(among others) has lots and lots of ADCs that would meet your requirements. You need to consider what other features you need. I think that 8-bits would be fine if you're only looking to determine which one of two pulses you have. If you need a more accurate representation of the pulse, then get more bits.

Barry

 

[krishnakumard]

Thank you Barry. It solved my problem. As you suggested, I had been little mislead about the SAR ADC's. Thanks for your kind help
with regards
krishnakumar