Hi Looks like something came loose when you swapped around the parts. That or the regulator is very noisy.
Bob > On Dec 1, 2014, at 11:39 AM, Li Ang <[email protected]> wrote: > > New tests today. It's strange that the data is not so stable as before. > > I've already add a 22uF Ceramic Cap and a 100nF. 10ohm resistor is removed. > > > > > First: > reg [15:0] shift; > always @(posedge refclk10M) begin > shift <= {shift[14:0], sw_gate}; > end > assign tdc_start = shift[3]; > assign tdc_stop1 = shift[4]; > assign tdc_stop2 = shift[5]; > > stop1-start= 935, stop2-stop1= 1049 > stop1-start= 957, stop2-stop1= 1047 > stop1-start= 961, stop2-stop1= 1046 > stop1-start= 1005, stop2-stop1= 1049 > stop1-start= 930, stop2-stop1= 1048 > stop1-start= 911, stop2-stop1= 1046 > stop1-start= 1005, stop2-stop1= 1049 > stop1-start= 936, stop2-stop1= 1048 > stop1-start= 930, stop2-stop1= 1047 > stop1-start= 1006, stop2-stop1= 1048 > stop1-start= 955, stop2-stop1= 1047 > stop1-start= 976, stop2-stop1= 1047 > stop1-start= 932, stop2-stop1= 1047 > stop1-start= 965, stop2-stop1= 1048 > stop1-start= 913, stop2-stop1= 1048 > stop1-start= 955, stop2-stop1= 1048 > stop1-start= 953, stop2-stop1= 1049 > stop1-start= 993, stop2-stop1= 1049 > stop1-start= 993, stop2-stop1= 1049 > stop1-start= 982, stop2-stop1= 1048 > stop1-start= 918, stop2-stop1= 1047 > stop1-start= 961, stop2-stop1= 1046 > stop1-start= 1007, stop2-stop1= 1047 > stop1-start= 912, stop2-stop1= 1046 > stop1-start= 928, stop2-stop1= 1049 > stop1-start= 995, stop2-stop1= 1048 > stop1-start= 1003, stop2-stop1= 1047 > stop1-start= 966, stop2-stop1= 1046 > stop1-start= 953, stop2-stop1= 1050 > stop1-start= 971, stop2-stop1= 1047 > stop1-start= 995, stop2-stop1= 1045 > stop1-start= 959, stop2-stop1= 1048 > stop1-start= 914, stop2-stop1= 1047 > stop1-start= 1002, stop2-stop1= 1047 > stop1-start= 1004, stop2-stop1= 1047 > > > ========================================= > Second: > assign tdc_start = shift[3]; > assign tdc_stop1 = shift[5]; > assign tdc_stop2 = shift[7]; > > //stop2-stop1 is not exact 2 times as test 1. > stop1-start= 2024, stop2-stop1= 2104 > stop1-start= 2034, stop2-stop1= 2106 > stop1-start= 1991, stop2-stop1= 2104 > stop1-start= 2016, stop2-stop1= 2105 > stop1-start= 2019, stop2-stop1= 2105 > stop1-start= 2005, stop2-stop1= 2106 > stop1-start= 2006, stop2-stop1= 2104 > stop1-start= 1962, stop2-stop1= 2104 > stop1-start= 2056, stop2-stop1= 2106 > stop1-start= 2020, stop2-stop1= 2105 > stop1-start= 1961, stop2-stop1= 2107 > stop1-start= 2011, stop2-stop1= 2105 > stop1-start= 2005, stop2-stop1= 2106 > stop1-start= 2035, stop2-stop1= 2106 > stop1-start= 2011, stop2-stop1= 2105 > stop1-start= 2006, stop2-stop1= 2104 > stop1-start= 2013, stop2-stop1= 2104 > stop1-start= 1964, stop2-stop1= 2104 > stop1-start= 2054, stop2-stop1= 2105 > stop1-start= 2056, stop2-stop1= 2106 > stop1-start= 2019, stop2-stop1= 2106 > stop1-start= 1982, stop2-stop1= 2105 > stop1-start= 2010, stop2-stop1= 2105 > stop1-start= 1964, stop2-stop1= 2106 > stop1-start= 1989, stop2-stop1= 2106 > stop1-start= 2008, stop2-stop1= 2107 > stop1-start= 2059, stop2-stop1= 2106 > stop1-start= 1985, stop2-stop1= 2104 > stop1-start= 2011, stop2-stop1= 2105 > stop1-start= 1962, stop2-stop1= 2105 > stop1-start= 2012, stop2-stop1= 2104 > stop1-start= 2008, stop2-stop1= 2105 > stop1-start= 2048, stop2-stop1= 2104 > stop1-start= 2009, stop2-stop1= 2106 > stop1-start= 2009, stop2-stop1= 2105 > stop1-start= 2006, stop2-stop1= 2105 > stop1-start= 2009, stop2-stop1= 2105 > stop1-start= 2009, stop2-stop1= 2104 > stop1-start= 2005, stop2-stop1= 2105 > stop1-start= 2049, stop2-stop1= 2105 > stop1-start= 2023, stop2-stop1= 2106 > > ++++++++++++++++++++++++++++++++++++++++++++++++++ > Third: > //This test shows that stop2 path is shorter than stop1 path. I need to > consider it when doing the calc. > assign tdc_start = shift[3]; > assign tdc_stop1 = shift[5]; > assign tdc_stop2 = shift[5]; > > stop1-start= 2059, stop2-stop1= -5 > stop1-start= 2065, stop2-stop1= -6 > stop1-start= 1989, stop2-stop1= -2 > stop1-start= 2013, stop2-stop1= -2 > stop1-start= 2011, stop2-stop1= -5 > stop1-start= 2019, stop2-stop1= -6 > stop1-start= 1987, stop2-stop1= -6 > stop1-start= 2065, stop2-stop1= -2 > stop1-start= 1974, stop2-stop1= -6 > stop1-start= 1968, stop2-stop1= -2 > stop1-start= 2055, stop2-stop1= -5 > stop1-start= 2065, stop2-stop1= -5 > stop1-start= 2012, stop2-stop1= -2 > stop1-start= 2035, stop2-stop1= -2 > stop1-start= 2014, stop2-stop1= -2 > stop1-start= 2014, stop2-stop1= -6 > stop1-start= 2028, stop2-stop1= -1 > stop1-start= 2034, stop2-stop1= -6 > stop1-start= 2013, stop2-stop1= -2 > stop1-start= 1974, stop2-stop1= -5 > stop1-start= 2014, stop2-stop1= -2 > stop1-start= 2009, stop2-stop1= -1 > stop1-start= 2029, stop2-stop1= -5 > stop1-start= 2053, stop2-stop1= -2 > stop1-start= 2017, stop2-stop1= -5 > stop1-start= 2013, stop2-stop1= -2 > stop1-start= 1992, stop2-stop1= -1 > stop1-start= 2016, stop2-stop1= -2 > stop1-start= 1970, stop2-stop1= -2 > stop1-start= 1973, stop2-stop1= -2 > stop1-start= 2065, stop2-stop1= -5 > stop1-start= 1975, stop2-stop1= -5 > stop1-start= 2017, stop2-stop1= -6 > stop1-start= 2013, stop2-stop1= -6 > stop1-start= 2016, stop2-stop1= -2 > stop1-start= 1987, stop2-stop1= -2 > stop1-start= 2062, stop2-stop1= -6 > stop1-start= 2021, stop2-stop1= -5 > > > > > 2014-11-29 1:41 GMT+08:00 Bob Camp <[email protected]>: > >> Hi >> >>> On Nov 28, 2014, at 10:14 AM, Li Ang <[email protected]> wrote: >>> >>>> >>>> 1) What frequency is the crystal at? (can you drive the chip from an >> OCXO?) >>> >>> I'm clking this chip with the refclk/2=5Mhz, which is done by cpld. >>> something like always @(posedge refclk) tdc_clk <= ~tdc_clk; Not sure if >>> it's noisy. >> >> If the clock source into the CPLD is clean, the output should not be to >> bad. >> >>> >>> 2) Is there more bypassing on the circuit than shown? (If not, add some >>>> more). >>> >>> Since there is only few power supply pins, I just put 100uF + 100nF >> there. >>> I can try put more to see if helps. And I'm going to use dedicated LDO >> for >>> digital part and analog part next time to make a new pcb. >> >> I suspect that a few more 100nF caps might be a good idea. They may not >> help, but it would rule out the supply as an issue. >> >>> >>> 3) How confident are you of your input signal? (can you check it with a >>>> “known good” counter?) >>> >>> The best counter I get is the RACAL DANA 1992. That is not good enough. >> I >>> think the accurarcy is not a problem, as if the reference is good enough, >> >> That’s correct. I was hoping you might be able to borrow a SR620 or 53132 >> for a few minutes to check your input signal. >> >>> it's only the matter of math. I prefer to enhance the resolution and >> reduce >>> noise. >> >> If the noise is on your test signal, it can be very frustrating to chase >> it with a lot of software work. >> >>> I'm using Trimble GPSDO(NTPX26AB) as the signal source >> >> The GPSDO should be fairly quiet, but it has an ADEV that’s a bit high. >> The outputs also can have noise on them. >> >>> and FE5650 Rb >> >> The FE Rb’s tend to have a lot of spurs on the output. In some cases that >> can get you in trouble. >> >>> as the ref. I've tried Rb+MV89A >> >> If the MV89A is working properly, it should be a pretty good source. Based >> on some of the prices I’ve seen on the internal China market, you might get >> a couple of them as sources. >> >>> and Rb + SMY01 signal generator, same >>> performance. The 2nd-hand 53132A,PM6690,SR620 about 600~800$ here in >> China. >>> I'm trying not to get one unless necessary. If I have get one to compare >>> the performance, what's your suggested model? >> >> The SR620 is a good counter, so is the 53132. They both can have problems. >> The 53132 display wears out and it’s power supply can fail. The 620 can run >> a bit hot, which kills a variety of parts in it. It’s better to pay a bit >> more for one you can actually check out before you buy than to get one >> shipped in. >> >>> >>> >>>> 4) Have you tried jumping the 10 ohm resistor on the regulator output? >> (it >>>> may not be helping things …) >>> >>> I'll try to remove that tomorrow >> >> It may be allowing the supply to drop a bit when the chip goes into some >> sort of computation. Often these things happen at just the wrong time … >> >> >> ———————— >> >> If you have a CPLD and a MV89: >> >> 1) With a 10 MHz sine wave out of the OCXO, you need to convert it to >> logic first. A biased input is a pretty good way to do this. >> >> 2) Generate 200 or 400 ns wide pulses out of the CPLD for testing. That >> will eliminate any issues from the 5 MHz crystal in the MV-89. >> >> 3) Keep the PCB as simple as you can. You need at least a double sided >> board (one side ground plane). If you can get a cheap 4 layer board, go for >> it. A full internal ground plane is a good thing. >> >> 4) Route the high speed signals (like the OCXO output) through solid >> connections. Flying wire leads are not a good idea. Mounting a MV89 direct >> to the PCB is a good way to do things. SMA connectors are also good. >> >> 5) If you have an oscilloscope or can borrow one, take a look at the >> signals on your board. Even a quick check can tell you a lot about signals >> that are not what they should be. >> >> 6) Be careful of ground loops and power supply issues. I’ve spent a *lot* >> of time on breadboards that didn’t work because I had power line noise >> running around. >> >> Good luck !! >> >> Bob >> >> >>> >>> >>> All of which is *plenty* good enough to make a decent counter. That >>>> assumes that they are talking about accuracy (even 1 sigma) rather than >>>> just the resolution of the LSB. Specs are often confusing on parts like >>>> this. >>> >>> I guess the accuracy is not important in the interpolator scenario. It >> has >>> a feature to output the result of delta_time / ref_cycle_time(it will >>> measure the 2cycle_time - 1cycle_time after the delta_time measurement >> and >>> do the float calculation). All I need is this part(it's the fraction >> part >>> of refcnt). So if I can reach 90ps resolution they claim, the counter can >>> tell 1/1000 of one reference cycle. That's 3 digits. >>> >>> >>> >>> Thanks. >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
