Hi Thanks about the explanation on hysteresis and comparator. The PM6685(http://assets.fluke.com/manuals/PM6685__smeng0000.pdf ) is using 74ALS176 as the frontend for REF channel. So I tried that on the previous board. The performance is better with 74ALS176+74LVC2G14 than MC100LVELT22 at the sin wave input condition. Since the stdev has reached the spec of TDC chip, I need to do some more experiments with these chips next. There are some questions I want to ask: 1) Does the trigger interval need to be very accurate? Now I am using software scheduler to generate the interval, it might vary few ms. 2) Does any one have the test data of 12 digit/s counter when DUT=REF? I want to know the gap between mine and a commercial counter.
Thanks Li Ang 2015-02-27 4:30 GMT+08:00 Charles Steinmetz <csteinm...@yandex.com>: > Magnus wrote: > > A bit of hysteresis can help to avoid flipping back, but considering the >> type of signal, it passes the mid-point (0 V) at highest slew-rate, so >> there is very little risk of flipping back and fourth in the first >> place, so hysteresis may not even be needed. >> > > A 1 Vrms, 10MHz sine wave has a zero-cross slew rate of 88v/uS (88mV/nS). > One would think that would be enough to avoid indecision in a comparator > with 5-10nS of propagation delay. However, the LT1016 (10nS) is prone to > jitter problems when operating as a ZCD with such a signal, and external > hysteresis does not help much because it is delayed by 10nS. (The problem > appears to be that the front end has some indecision at this input slew > rate that happens faster than the propagation delay to the output -- but > this is just an inference because the internal nodes are not accessible for > measurement.) For this application, the small amount of internal > hysteresis of the LT1719 and LT1720 is very beneficial. > > Best regards, > > Charles > > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.