Re: Timing Info

[Matthew Shepherd <mashephe@indiana.edu>]

Hi Fernando,

I should first say that I only read the note myself and did not do the  
study, but I think I can address your point:

On Jan 25, 2008, at 1:57 PM, Fernando J. Barbosa wrote:

> This is a very interesting note but it does not serve as "proof of  
> principle" that this technique will work with a real fADC, in my  
> opinion. I think, in this context, there is a flaw in the  
> application of the technique. The technique relies primarily on  
> having a sample (peak) that represents the actual peak value of the  
> input signal and then using two samples to determine the crossing  
> point. Obtaining a sample at the actual peak of a signal is not  
> guaranteed by a sampling ADC. Please note that no ADC was employed  
> at the time this note was written.

I don't think the technique requires having a sample at the peak, but  
rather just a peak sample.  Every fADC digitized buffer of a  
reasonably-shaped PMT pulse will have a peak.  Sure, it won't happen  
right in time with the actual analog peak necessarily, but there will  
be a peak.  True the study does not use a real fADC, but it does use  
real phototube pulses.  I trust relatively well a computer's ability  
to sample at 4 ns and digitize to n-bits.  A fit to the high  
resolution digitized pulse is used to determine the true 50% crossing  
point, this is compared with what  is obtained after the sample is  
digitized and processed by the algorithm.

> As we discussed before, I suggest you perform the tests with 8-bit  
> ADC from Paul and compare the results to the note. This is easier  
> than getting the fADC, CODA....

Of course we plan to do this, but I still don't see any obvious flaw  
in this note as a proof of principle.  Thanks for the other reference  
-- I'll take a look at it.

Cheers,

-Matt