[time-nuts] PLL performance?

[Daniel Mendes]

Hi. I did a 15728640Hz signal locked to a 7680Hz reference using a 
74hct9046. It was ugly (I mean, individual trimming of the resistors... 
I assembled 20 boards). Circuit behaves more like a FLL than a PLL (if 
you look at both with an scope they never quite locks to each other), 
but it works for the mean values (so long averages are ok, and that´s 
what I was looking for). I didn´t measure stability, just tested each 
board to see if they kept locked between (60,1*128)Hz and (59,9*128)Hz. 
That was a pain. I think these 4046 and 9046 don´t work well when the 
frequencies are too apart, but I can´t tell for sure. Not enough 
experience with that.

Daniel


Em 20/03/2017 22:07, David Scott Coburn escreveu:
> Hi All,
>
> I have built and tested a PLL circuit that will be used to generate a 1 MHz signal locked to a 0.5 HZ signal from a pendulum.  (Details available upon request.)
>
> The circuit is a classic 4046 generating the 1 MHz signal which is fed into a 2e6 digital divider which outputs 0.5 Hz which is fed back to the 4046 phase comparator (PC).
>
> I take a 1 MHz signal from an HP 107A run through another 2e6 divider to generate a reference 0.5 Hz signal for the other 4046 PC input.
>
> I tested this by feeding the 0.5 Hz output of the PLL into a "time-stamp counter" board which I built to go into an HP 3582A Data Acquisition unit.  The TSC uses the 5 MHz signal from the HP 107A to feed a free-running 32-bit binary counter.  The 0.5 Hz input latches the count value (on the rising edge of the signal), which is then logged.
>
> See the attached diagram.  The PLL under test is in the red box.  (Not sure what the policy is here for attachments?)
>
> If all was perfect I would get a string of values of 10,000,000 counts each, one every 2 seconds.
>
> Over the course of one day the average reading is, in fact, 10e6, so the PLL looks to be working over "long" time scales.
>
> The attached histogram plot shows the actual data for the 0.5 Hz signal, showing the distribution of deviations from 10e6 counts.  This is almost a full day of data, about 40,000 readings.
>
> The standard deviation for the data is about 55 counts.
>
> The plot looks to my eye to be a nice Gaussian shape, so I assume that the deviations are caused mainly by (white?) noise.  There does not look to be much other structure in the shape of the data.  (Comments welcome.)
>
> Sorry for the long introduction, there are some questions coming!
>
> I have looked for information on the web about others who may have done this kind of PLL, but did not find much.
>
> Does anyone know of any articles related to this?
>
> If so, do you know what kind of performance they got?
>
> What kind of statement could I make about the 'stability' of this circuit?  Simplistically: a 'stability' of ~50 counts in 10e6 is ~5e-7?
>
> By the way, this performance is WAY WAY beyond what I was expecting....
>
> Cheers,
>
> Scott
>
>
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