Low Phase Noise buffer
T&F Nut question
Is the high frequency phase noise of a buffer important when the Oscillator
is used just as the Reference for taking ADEV data?
The current (2005) writings say that ADEV phase data should be bandpass
filtered which removes all the High freq edge jitter.
If that is the case, Does a buffer's added HIGH FREQUENCY phase noise and
jitter have any effect on the ADEV numbers when using modern, high
resolution, mixer type, Time interval counters? Of course the low frequency
type of buffer noise would still be important.
Previously there was some confusion and disagreement on the subject. What
are the latest opinions?
ws
I don't see any reason why the broadband noise should affect ADEV readings
outside the measurement bandwidth, any more than short-term stability
characteristics would influence ADEV at longer timescales. Shouldn't be an
issue.
-- john, KE5FX
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com]On
Behalf Of WarrenS
Sent: Friday, February 19, 2010 1:03 AM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Low Phase Noise buffer
T&F Nut question
Is the high frequency phase noise of a buffer important when the
Oscillator
is used just as the Reference for taking ADEV data?
The current (2005) writings say that ADEV phase data should be bandpass
filtered which removes all the High freq edge jitter.
If that is the case, Does a buffer's added HIGH FREQUENCY phase noise and
jitter have any effect on the ADEV numbers when using modern, high
resolution, mixer type, Time interval counters? Of course the low
frequency
type of buffer noise would still be important.
Previously there was some confusion and disagreement on the subject. What
are the latest opinions?
ws
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WarrenS wrote:
T&F Nut question
Is the high frequency phase noise of a buffer important when the
Oscillator is used just as the Reference for taking ADEV data?
The current (2005) writings say that ADEV phase data should be bandpass
filtered which removes all the High freq edge jitter.
If that is the case, Does a buffer's added HIGH FREQUENCY phase noise
and jitter have any effect on the ADEV numbers when using modern, high
resolution, mixer type, Time interval counters? Of course the low
frequency type of buffer noise would still be important.
Previously there was some confusion and disagreement on the subject.
What are the latest opinions?
The white noise which is the only dominant noise at higher frequencies
goes down into the lower range and do contribute to the ADEV measures
there, even if filtered. This filtering will affect lower-tau measures
more than mid or high tau measures. Telecom standards prescribe
filtering and tau0 for their reference measures for repeatable measures.
The filtering has been debated. The estimators will filter themselves
regardless when m has become a number of multiples, essentially when the
filter bandwidth becomes large compared to the inverse of the tau.
If the noise is benign white noise it should be kept at a low level, but
work on flicker noise is where most effort should be spent.
Cheers,
Magnus
Previously there was some confusion and disagreement on the subject.
What are the latest opinions?
The white noise which is the only dominant noise at higher frequencies
goes down into the lower range and do contribute to the ADEV measures
there, even if filtered.
Well, in which case it's part of the instability you're trying to measure,
right... noise is noise, regardless of its slope. You wouldn't want to
filter it if you could.
-- john, KE5FX
Magnus said
White noise goes down into the lower range and do contribute to the
ADEV....
Can you put some numbers to it to show how much effect there is.
If the 10 MHz had an incredible total of 10 ns (10%) white noise at say 100
MHz bandwidth, what would be the Phase noise for the 1 sec ADEV optimum BW
of 5 Hz?
ws
The white noise which is the only dominant noise at higher frequencies
goes down into the lower range and do contribute to the ADEV measures
there, even if filtered. This filtering will affect lower-tau measures
more than mid or high tau measures. Telecom standards prescribe
filtering and tau0 for their reference measures for repeatable measures.
The filtering has been debated. The estimators will filter themselves
regardless when m has become a number of multiples, essentially when the
filter bandwidth becomes large compared to the inverse of the tau.
If the noise is benign white noise it should be kept at a low level, but
work on flicker noise is where most effort should be spent.
Cheers,
Magnus
WarrenS wrote:
T&F Nut question
Is the high frequency phase noise of a buffer important when the
Oscillator is used just as the Reference for taking ADEV data?
The current (2005) writings say that ADEV phase data should be bandpass
filtered which removes all the High freq edge jitter.
If that is the case, Does a buffer's added HIGH FREQUENCY phase noise and
jitter have any effect on the ADEV numbers when using modern, high
resolution, mixer type, Time interval counters? Of course the low
frequency type of buffer noise would still be important.
Previously there was some confusion and disagreement on the subject. What
are the latest opinions?
I'll take a guess at the answer.
White noise is constant power over Frequency
If the Nose Bandwidth is reduced from 100MHZ to 10 Hz then power would be
reduced by 1e7 to 1
Voltage is square root of Power so 1e7 power ratio is = 3e3 to 1 (1/3162)
The 10 ns noise would be reduced to 3ps
Or put another way, if you want under 1ps ADEV nose,
Need to keep the Buffer's wide bandwidth phase noise down around 1 ns or 1%.
From: "WarrenS"
Magnus said
White noise goes down into the lower range and do contribute to the
ADEV....
Can you put some numbers to it to show how much effect there is.
If the 10 MHz had an incredible total of 10 ns (10%) white noise at say
100 MHz bandwidth, what would be the Phase noise for the 1 sec ADEV
optimum BW of 5 Hz?
ws
The white noise which is the only dominant noise at higher frequencies
goes down into the lower range and do contribute to the ADEV measures
there, even if filtered. This filtering will affect lower-tau measures
more than mid or high tau measures. Telecom standards prescribe
filtering and tau0 for their reference measures for repeatable measures.
The filtering has been debated. The estimators will filter themselves
regardless when m has become a number of multiples, essentially when the
filter bandwidth becomes large compared to the inverse of the tau.
If the noise is benign white noise it should be kept at a low level, but
work on flicker noise is where most effort should be spent.
Cheers,
Magnus
WarrenS wrote:
T&F Nut question
Is the high frequency phase noise of a buffer important when the
Oscillator is used just as the Reference for taking ADEV data?
The current (2005) writings say that ADEV phase data should be bandpass
filtered which removes all the High freq edge jitter.
If that is the case, Does a buffer's added HIGH FREQUENCY phase noise and
jitter have any effect on the ADEV numbers when using modern, high
resolution, mixer type, Time interval counters? Of course the low
frequency type of buffer noise would still be important.
Previously there was some confusion and disagreement on the subject. What
are the latest opinions?