Hi, I'm back. I have been testing my new borad for days. Compared to previous version, this board makes the PCB track of signals far from each other and replaces LDO for TDC with LP5907. CH_A: simple resistor bias and ac couple "front end", CH_B: CH_A+MC100LVELT22 LVPECL , CH_C: CH_A+74LVC2G14 . At first, the result is worse than previous board. Using CH_B as the REF and DUT source, the stdev of the phase measurement is about 160ps. The old board can reach about 70ps. CH_A and CH_C are way much better than CH_B. That bothers me for days. Today, I use the 74LVC2G14 to square the signal from MV89A, and do the same test. For all three channel, the stdevs are about 37ps. The spec of TDC_GP22 is 35ps. And now the performance looks a little bit better than the previous board. It looks like that the jitter of MC100LVELT22 is much bigger at slow slew rate. It seems that next step is to play with the front end.
The raw data is uploaded to http://www.qsl.net/b/bi7lnq/freqcntv4.1/test/20150222/ The pic of this version is uploaded to http://www.qsl.net/b/bi7lnq/freqcntv4.1/pic/ Regards Li Ang
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