<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">At least for the CDC, the most important measurement is the time, so I do not want to<div>compromise there. As for the pulse integral, the real issue is dynamic range. What is the</div><div>smallest meaningful amplitude that we want to measure, and what is the largest sensible</div><div>amplitude that we could measure.</div><div><br></div><div>curtis<br><div apple-content-edited="true">
<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>-------</div><div>Prof. Curtis A. Meyer<span class="Apple-tab-span" style="white-space: pre; "> </span> <span class="Apple-converted-space"> </span>Department of Physics</div><div>Phone: (412) 268-2745<span class="Apple-tab-span" style="white-space: pre; "> </span> <span class="Apple-converted-space"> </span>Carnegie Mellon University</div><div>Fax: (412) 681-0648<span class="Apple-tab-span" style="white-space: pre; "> </span> Pittsburgh, PA 15213</div><div><a href="mailto:curtis.meyer@cmu.edu">curtis.meyer@cmu.edu</a> <a href="http://www.curtismeyer.com/">http://www.curtismeyer.com/</a></div><div><br></div><div><br></div></div></span><br class="Apple-interchange-newline"></span><br class="Apple-interchange-newline">
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<br><div><div>On Jul 16, 2013, at 12:22 PM, Gerard Visser <<a href="mailto:gvisser@indiana.edu">gvisser@indiana.edu</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">hi all,<br><span class="Apple-tab-span" style="white-space:pre"> </span>Although I'm now not directly involved in the effort to define & design the <br>ADC125 algorithms and data format, I would like to comment here that in my <br>opinion there are too many bits devoted to pulse amplitude (19) and too few <br>devoted to time (11). You will never get an amplitude measurement with 19 <br>significant bits, I think. I would suggest flip a few more bits over to time, <br>for instance make it 16 bits amplitude and 14 bits time. In particular, it <br>should be possible to have time resolution down to 1/2 ns or 1/4ns, at least it <br>is less of a stretch to believe in the significance of those digits than in the <br>significance of an amplitude measurement to 2 ppm (19 bits).<br><span class="Apple-tab-span" style="white-space:pre"> </span>Sincerely,<br><br><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span>Gerard<br><br>On 7/16/2013 12:05 PM, David Lawrence wrote:<br><blockquote type="cite"><br>Hi Naomi,<br><br> Thanks for the feedback. I have some comments on your suggestions below:<br><br>On 7/15/13 4:27 PM, Naomi Jarvis wrote:<br><blockquote type="cite">Hello,<br><br>I prefer option 1, the coupled words with pedestal, as it packs more info into<br>the same space.<br><br>First word<br><br>Do we need the 2bits for 'pulse'? From looking through the spec it seems that<br>this is to label up to 4 pulses for which time data is to be sent. For the<br>CDC this would always be 1, just 1 pulse, so could we dispense with it?<br><br></blockquote>I think there should be enough room in the 64 bits to keep the 2 bits for this.<br>I would hate to give this up unless we really have to. Since we'll be using<br>these for the FDC cathodes which will have a much higher rate, it could be very<br>useful.<br><br><blockquote type="cite">We would like to increase the bits available for time data from 10 to 11 bits,<br>as an integer # of ns, that gives us 0-2047 ns. This allows some headroom for<br>slower drift times.<br><br></blockquote>This seems reasonable to me. If we move the 3 bits for the Q.F. down to the<br>second word as you suggested, we can use one of those.<br><br><blockquote type="cite"><br>Second word<br><br>Pedestal. I would indeed like to include this but it is not necessary to have<br>full range 0-4095 available in integer steps. We will set the pedestals to<br>something low, ~55-60. How about outputting pedestal/8 to cover the subrange<br>pedestal=0-504 as pedestal/8=0-63 in 6 bits. ?<br><br></blockquote>I'm not sure if I fully understand your notation of pedestal/8, but I think your<br>main point is that we can just limit the range of the pedestals to be within<br>that defined by 6 bits. Either by adjusting voltage offsets or applying an<br>offset parameter to the FPGA. Just to be clear though, the 6bits of pedestal<br>would have the same resolution as the integral right? (i.e. changing the<br>pedestal by 1 is equivalent to changing the pulse integral by 1)<br><br><blockquote type="cite">Integral. OK.<br></blockquote><br>Actually, I'm thinking we could reduce this by a couple of bits. With a 12bit<br>ADC, storing 19 bits for the integral means we could have up to 7bits=128<br>samples in saturation without overflowing. This would correspond to a pulse that<br>is over 1V high for more than 1 microsecond. That seems unlikely to provide<br>anything useful (correct me if I'm wrong here.) We could move 2 bits from this<br>to the Q.F. allowing use to keep 8 bits for the pedestal.<br><blockquote type="cite"><br>Integral quality factor.<br>I would like to include a count of the number of overflowed samples<br>contributing to the integral, this could count up to 63 samples (504ns) in the<br>6 bits freed up from the pedestal.<br></blockquote><br>OK<br><br><br>Here is a revised diagram which incorporates your suggestions and then my<br>modifications to those. Let me know what you think.<br><br><br>Regards,<br>-Dave<br><br><br><br>_______________________________________________<br>Halld-tracking-hw mailing list<br><a href="mailto:Halld-tracking-hw@jlab.org">Halld-tracking-hw@jlab.org</a><br>https://mailman.jlab.org/mailman/listinfo/halld-tracking-hw<br><br></blockquote>_______________________________________________<br>Halld-tracking-hw mailing list<br><a href="mailto:Halld-tracking-hw@jlab.org">Halld-tracking-hw@jlab.org</a><br>https://mailman.jlab.org/mailman/listinfo/halld-tracking-hw<br></blockquote></div><br></div></body></html>