Measure amplitude of nanoseconde, short pulse.

[L._Andrzejewski]

Hi,

I am looking for a simple solution "cheap" to replace our 500Mhz scope we use to measure a short pulse of a few nanoseconds (~6ns with 80% amplitude decay, maybe 20ns total) in our laser chain at a frequency of 100Hz. The pulse is not square or TTL, it s a signal decade with fast rising sloop and slow discharge, more like an rounded exponential ramp. Amplitude is around 1.5V peak.

I don t need an absolute value of the voltage or the waveform, I am more interested in the maximum amplitude jitter between shot to shot “pulse to pulse” at 100Hz. I was thinking about using some M series board that I would trigger it s analog input with an delayed TTL that corresponds to the diode maximum (as measured by the scope) and then output a single point 100 times per second and compare them. Problem is, I assume, that there isn’t a card that has a settling time of a few nanoseconds, or a sufficient  trigger response delay, am I right?

I also heard about sample and hold signal conditioners put I am confused  on which one would suite my application without over killing and over billing, are they fast enough?

Thanks for any help

Lukasz

[jaced]

Hi Lukasz,

It is my understanding that you wish to take one sample every trigger edge, and the sample must capture the largest amplitude. such as shown in the picture below.

If I am correct in my understanding I do not believe that an M-series card will be capable of capturing the data that you wish to. An M-series card can capture, at best, samples that are 357 ns apart. So any jitter in either the sample clock or signal would cause you to miss your entire signal. I recommend a scope which has a much higher sampling rate. For example the PCI-5152 is capable of 2Gs/s which equates to .5ns between samples.  I believe that the best solution for you application would be to use the PCI-5152 and an advance trigger, The Advance trigger initiates the acquisition of the additional records in a multirecord acquisition.  You can define the number of samples that you want in your record, and then the advance trigger will allow you to capture a record on each trigger pulse. This will allow you to capture the section of interest and use post processing to compare the highest points of each record. I hope this helps!!

Message Edited by jaced on 11-02-2007 03:40 PM