Understood.
Regards.
Max. K 4 O D S.
Email: [email protected]
Transistor site http://www.funwithtransistors.net
Vacuum tube site: http://www.funwithtubes.net
Music site: http://www.maxsmusicplace.com
To subscribe to the fun with transistors group send an email to.
[email protected]
To subscribe to the fun with tubes group send an email to,
[email protected]
----- Original Message -----
From: "Neville Michie" <[email protected]>
To: "Discussion of precise time and frequency measurement"
<[email protected]>
Sent: Monday, July 26, 2010 5:48 PM
Subject: Re: [time-nuts] Basic question regarding comparing two frequencies
The reason to divide was that the signal from the phase detector "folds
back" as the phase shift gets to 360*.
At 10Mhz the fold back occurs every 100ns. At 100kHz it is every 10usec.
As the fold back (359.9 - 0.1degree) zone may have false triggering or
other noise
it made sense for it to be made a less frequent event. Also I did not
have faith in the CMOS output giving a true PWM average when clocking so
fast. Chip capacitance produces a more significant amount of current at
the higher clock rate.
It may well work OK at the 10MHz rate. I also needed to divide to
increase the full scale time to account for large time jitter of
mechanical clocks so I set it up to divide at any of a wide range of
frequencies.
Cheers, Neville Michie
On 27/07/2010, at 3:12 AM, Max Robinson wrote:
Hal Murray wrote:
There is another way to compare two frequencies, relevant when they
are
very close together. I divide a reference down to 100KHz and use it
to clock
a phase detector made of a pair of D flip flops. The unknown (divided
to
100KHz) is fed into the circuit and an output that is proportional
to the
phase difference appears on the output as a changing mark-space
ratio.
I'm wondering why divide the frequency at all. Seems to me you would
get much greater resolution if you did the phase comparison at the
native frequency.
Regards.
Max. K 4 O D S.
Email: [email protected]
Transistor site http://www.funwithtransistors.net
Vacuum tube site: http://www.funwithtubes.net
Music site: http://www.maxsmusicplace.com
To subscribe to the fun with transistors group send an email to.
[email protected]
To subscribe to the fun with tubes group send an email to,
[email protected]
----- Original Message ----- From: "Neville Michie" <[email protected]>
To: "Discussion of precise time and frequency measurement" <time-
[email protected]>
Sent: Monday, July 26, 2010 1:19 AM
Subject: Re: [time-nuts] Basic question regarding comparing two
frequencies
Hi,
the original was built using a HP10811 oscillator and a Garmin 17 GPS
that delivered PPS.
The HP10811 ran a divider by 10 by 10 by 10 down to 1 hz.
I was the servo that adjusted the EFC of the OCXO so that the PPS
matched the 1Hz.
The divider clocked a counter of three decades of BCD, with latches
driving a 3 decade DAC. (about 12 bits of modified R-2R chain)
The latches were triggered by a pendulum clock being observed, or the
PPS of the Garmin GPS receiver.
That delivered a DC signal that could be logged to observe phase drift
on a chart recorder or data logger.
For higher frequencies, I used the D FF phase detector, which could be
used at 1MHz, 100kHZ, 10kHz, 1kHz or 100Hz,
depending on how sensitive I wanted the frequency (phase) comparison.
The test was that the phase noise must be less than one tenth
of a period, so the automatic regeneration of the more significant
digits in XL afterwards did not have ambiguities.
For any oscillator under examination I used a 4046 PLL to generate a
high enough frequency to drive the phase detector.
My 1 Hz pendulum clock generated a 1kHz signal via the 4046 so the
phase detector gave 1ms full scale on the chart recorder,
with a resolution of 1 microsecond. The low pass filtering inherent in
the PLL was not a worry as I was concerned with longer term drift.
It all avoids using digital processing and other instruments, the main
reason for that was to be able to leave it running for weeks with only
low
battery backup power required.
cheers, Neville Michie
On 26/07/2010, at 3:12 PM, Hal Murray wrote:
There is another way to compare two frequencies, relevant when they
are
very close together. I divide a reference down to 100KHz and use it
to clock
a phase detector made of a pair of D flip flops. The unknown
(divided to
100KHz) is fed into the circuit and an output that is proportional
to the
phase difference appears on the output as a changing mark-space
ratio.
I like it. Thanks.
How did you pick 100 KHz?
Using CMOS and a precise power supply (because under no load, CMOS
output is precisely rail to rail), the averaged output (100ms RC
filter) is
fed to a strip chart recorder.
Has anybody checked the edge cases and/or linearity of a setup like
this?
The recorder shows the changing phase difference and folds back each
time
a whole cycle passes. A 12 bit analog data logger resolves 2.5ns of
phase
and gives data for further analysis.
Is 2.5 ns good enough? What would you gain by using a 16 bit DAC?
If 2.5 ns is good enough, I'll bet you can do the whole thing in
digital
logic. Just get a fast FPGA/CPLD. I haven't done a serious design,
but a
quick check at some old data sheets shows it's not silly. You could
probably
bump it up by another factor of 2 with some external (p)ECL chips.
--
These are my opinions, not necessarily my employer's. I hate spam.
_______________________________________________
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.
_______________________________________________
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.
