> > 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. 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. 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, it's only the matter of math. I prefer to enhance the resolution and reduce noise. I'm using Trimble GPSDO(NTPX26AB) as the signal source and FE5650 Rb as the ref. I've tried Rb+MV89A 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? > 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 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.
