John With a slow slew rate input signal like a 10MHz sinewave the Wavecrest jitter due to the noise of its wideband input amplifiers may be quite high.
So it may be better to measure the relative jitter of 2 dividers. Bruce John Ackermann N8UR wrote: > Hi Brian -- > > It's good to collect this data; thanks. It's interesting that your std > dev in the first test seems to increase significantly with the number of > samples; I haven't seen that kind of scaling here (1K sample and 10k > sample turned in very similar std dev). From what Poul-Henning said > earlier, your first run may suffer the same distortion as my data at the > bottom of this thread. > > I just finished rerunning the TADD-2 test using a Wavecrest DTS-2075 > (the first real use I've had for that box!) and with 1 PPS input on the > start channel, 10 MHz from the same source on the stop channel, and 10K > samples, I got 22.0 ps of jitter, and a 92 ps min/max range. (As far as > I can determine, the Wavecrest doesn't allow you to use an external > reference, and its internal reference runs at 100 MHz so it probably > wouldn't be useful in this measurement.) > > That's consistent with what I measured earlier with the 5370B when I > didn't have the reference and the inputs in coherence. It appears that > the test below, where I used the same reference for *everything* > triggered the problem that Poul-Henning warned about, so those results > should be disregarded. > > While I haven't done any testing to validate this, I think the complaint > about the 74HC390 dividers isn't so much their jitter in normal use, but > the tempco problems the cascaded stages can cause. If you can do it, it > would be interesting to measure the phase change over temperature -- > I've done a preliminary experiment on that for the TADD-2, but plan to > rerun it with much better measurement technique. > > I'm also hoping to do a jitter and tempco test of the Wenzel input > conditioning circuit by itself. I really like that circuit for its wide > input amplitude range. > > John > ---- > Brian Kirby said the following on 04/04/2009 04:18 PM: > >> I will report some results on a asynchronous divider, which I basically >> copied from Dr. Thomas Clark's designs, which everybody likes to report >> as a bad design. >> >> The 10 MHz input signal is coupled thru a resistor and capacitor. On >> the other side of the capacitor is the resistive divider that is tied to >> Vcc and ground - it biases the signal to 2.5 volts, which is feed to the >> input of the 74HC132. The output of the 74HC132 feeds several 74HC390s >> until it becomes a buffered 1 pulse per second signal. I also have >> buffered 5 MHz and 1 MHz outputs. The other 3/4 of the 74HC132 are used >> to externally synchronize the 74HC390s. >> >> I used the Thunderbolt as the source of 10 MHz and it was feed to the >> divider, and the stop input on the HP5370B. The 5370B was run on >> internal clock. The 1 PPS from the divider feed the start input on the >> 5370B. >> >> 100 seconds TI 79.865 nS MIN 79.80 nS MAX 79.98 nS STD 36.4 pS. >> 1000 seconds TI 79.831 nS MIN 79.71 nS MAX 80.00 nS STD 49.9 pS >> 10K seconds TI 80.1552 nS MIN 79.79 nS MAX 80.88 nS STD 271 pS >> 100K planned >> >> Also a second test, using the Thunderbolt as a source of 10 MHz and it >> was feed to the divider, the stop input on the 5370B and the external >> clock of the 5370B. The 1 PPS from the divider feed the start input on >> the 5370B. >> >> 100 seconds TI 75.002 nS MIN 74.96 nS MAX 75.04 nS STD 22.5 pS >> 1000 seconds TI 74.931 nS MIN 74.80 nS MAX 75.04 nS STD 56.8 pS >> 10K seconds TI 77.5135 nS MIN 77.40 nS MAX 77.62 nS STD 35.9 pS >> 100K measurement in progress. >> >> I believe having STD in parts of 10-14th is fairly respectable for >> amateur designs.. >> >> Brian KD4FM >> >> John Ackermann N8UR wrote: >> >>> I just finished a jitter test of the first TADD-2 built on the >>> production circuit board. >>> >>> The configuration was somewhat optimized from what I used for the >>> earlier tests. >>> >>> A single 10 MHz source was daisy-chained to the TADD-2 input, to the >>> 5370B external reference input, and to the 5370B STOP channel. The 1 >>> PPS output from the TADD-2 was connected to the 5370B START channel. >>> Thus any reference jitter shouldn't be common-mode, and using the >>> reference clock on the STOP channel avoids the need for a second >>> divider, and ensures that the time interval is small (always less than >>> 100 ns; in this case, about 90 ns). >>> >>> For a 10,000 sample run, the standard deviation was 12.1 picoseconds, >>> and the peak-to-peak variation was 70 picoseconds. Based on experiments >>> I ran a few years ago, I think this is pretty much the noise floor of >>> the 5370B and the divider could be better than this. >>> >>> John >>> >>> _______________________________________________ >>> 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.
