[time-nuts] PLL performance?

Bill Byrom time at radio.sent.com
Mon Mar 20 23:36:05 EDT 2017

Hi, Scott. I rarely post here, but just noticed your post. I can open
the "PLL0.pdf" file, but the other files appears to be corrupted. Adobe
Acrobat Reader thinks it's not really a PDF file or it's corrupted. I'm
not ready to comment on the expected results yet, and would like to see
the histogram. 

Are you using phase detector 1 or 2? What are the details for your loop

Bill Byrom N5BB

----- Original message -----
From: David Scott Coburn <scotttt at optonline.net>
To: time-nuts at febo.com
Subject: [time-nuts] PLL performance?
Date: Mon, 20 Mar 2017 21:07:03 -0400

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

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....


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