10 MHz reference switching
Hello Time Nuts,
I'm back again. I designed bandwidth-limited (30 MHz) ADA4899-1 opamp circuits to buffer the 10 MHz reference, with theoretical noise of less than 3 nV/rtHz. Oscillator noise is about -155 dBc/rtHz from 1 KHz to 10 KHz, and -160 dBc/rtHz from 10 KHz to 100 KHz. Unfortunately the rest of the design is holding up PCB manufacture, so results on these won't be available for awhile.
Which brings me to the other design-stopping considerations: Is anybody aware of low-noise analog switches that can be used to reconfigure the 10 MHz reference paths without significantly degrading the phase noise? As always, I believe 1/F noise would be the concern. Non-reflective is great, but I can accomplish that by using more switches and 50 ohm resistors if need be. Isolation is a key consideration as well. Mechanical relays are out of the question.
An alternative to switching is phase-locking the OCXO to an external reference. I have thoroughly looked into this possibility, and it is likely my preferred approach. But I need to understand how the switching approach compares, hence my question. I do not need help with phase-locking; this feature is readily available from OCXO vendors who have dedicated years of research to optimizing their products.
Any switch experience out there?
life speed wrote:
Hello Time Nuts,
I'm back again. I designed bandwidth-limited (30 MHz) ADA4899-1 opamp circuits to buffer the 10 MHz reference, with theoretical noise of less than 3 nV/rtHz. Oscillator noise is about -155 dBc/rtHz from 1 KHz to 10 KHz, and -160 dBc/rtHz from 10 KHz to 100 KHz. Unfortunately the rest of the design is holding up PCB manufacture, so results on these won't be available for awhile.
Which brings me to the other design-stopping considerations: Is anybody aware of low-noise analog switches that can be used to reconfigure the 10 MHz reference paths without significantly degrading the phase noise? As always, I believe 1/F noise would be the concern. Non-reflective is great, but I can accomplish that by using more switches and 50 ohm resistors if need be. Isolation is a key consideration as well. Mechanical relays are out of the question.
An alternative to switching is phase-locking the OCXO to an external reference. I have thoroughly looked into this possibility, and it is likely my preferred approach. But I need to understand how the switching approach compares, hence my question. I do not need help with phase-locking; this feature is readily available from OCXO vendors who have dedicated years of research to optimizing their products.
Any switch experience out there?
Why would flicker noise be a concern if there is no dc current flowing
in the switches?
Bruce
Hi
Or put another way:
If you have a structure that uses series resistors and shunt diodes:
The diodes are reverse biased when the switch is "on".
The diodes are forward biassed when the switch is "off".
No current when on = no noise.
Bob
On Mar 8, 2010, at 6:43 PM, Bruce Griffiths wrote:
life speed wrote:
Hello Time Nuts,
I'm back again. I designed bandwidth-limited (30 MHz) ADA4899-1 opamp circuits to buffer the 10 MHz reference, with theoretical noise of less than 3 nV/rtHz. Oscillator noise is about -155 dBc/rtHz from 1 KHz to 10 KHz, and -160 dBc/rtHz from 10 KHz to 100 KHz. Unfortunately the rest of the design is holding up PCB manufacture, so results on these won't be available for awhile.
Which brings me to the other design-stopping considerations: Is anybody aware of low-noise analog switches that can be used to reconfigure the 10 MHz reference paths without significantly degrading the phase noise? As always, I believe 1/F noise would be the concern. Non-reflective is great, but I can accomplish that by using more switches and 50 ohm resistors if need be. Isolation is a key consideration as well. Mechanical relays are out of the question.
An alternative to switching is phase-locking the OCXO to an external reference. I have thoroughly looked into this possibility, and it is likely my preferred approach. But I need to understand how the switching approach compares, hence my question. I do not need help with phase-locking; this feature is readily available from OCXO vendors who have dedicated years of research to optimizing their products.
Any switch experience out there?
Why would flicker noise be a concern if there is no dc current flowing in the switches?
Bruce
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rf relay would work
On Mon, Mar 8, 2010 at 6:51 PM, Bob Camp lists@rtty.us wrote:
Hi
Or put another way:
If you have a structure that uses series resistors and shunt diodes:
The diodes are reverse biased when the switch is "on".
The diodes are forward biassed when the switch is "off".
No current when on = no noise.
Bob
On Mar 8, 2010, at 6:43 PM, Bruce Griffiths wrote:
life speed wrote:
Hello Time Nuts,
I'm back again. I designed bandwidth-limited (30 MHz) ADA4899-1 opamp
circuits to buffer the 10 MHz reference, with theoretical noise of less than
3 nV/rtHz. Oscillator noise is about -155 dBc/rtHz from 1 KHz to 10 KHz,
and -160 dBc/rtHz from 10 KHz to 100 KHz. Unfortunately the rest of the
design is holding up PCB manufacture, so results on these won't be available
for awhile.
Which brings me to the other design-stopping considerations: Is anybody
aware of low-noise analog switches that can be used to reconfigure the 10
MHz reference paths without significantly degrading the phase noise? As
always, I believe 1/F noise would be the concern. Non-reflective is great,
but I can accomplish that by using more switches and 50 ohm resistors if
need be. Isolation is a key consideration as well. Mechanical relays are
out of the question.
An alternative to switching is phase-locking the OCXO to an external
reference. I have thoroughly looked into this possibility, and it is likely
my preferred approach. But I need to understand how the switching approach
compares, hence my question. I do not need help with phase-locking; this
feature is readily available from OCXO vendors who have dedicated years of
research to optimizing their products.
Any switch experience out there?
Why would flicker noise be a concern if there is no dc current flowing in
the switches?
and follow the instructions there.
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Hi
Assuming you are switching between an external reference and the internal OCXO:
The "bleed through" of the OCXO is going to show up as a discrete spur close to the external reference carrier. Unless you have a very unusual architecture, it will be inside the loop for everything you are doing. Attenuating it to a "suitable" level may be quite difficult.
Bob
On Mar 8, 2010, at 6:34 PM, life speed wrote:
Hello Time Nuts,
I'm back again. I designed bandwidth-limited (30 MHz) ADA4899-1 opamp circuits to buffer the 10 MHz reference, with theoretical noise of less than 3 nV/rtHz. Oscillator noise is about -155 dBc/rtHz from 1 KHz to 10 KHz, and -160 dBc/rtHz from 10 KHz to 100 KHz. Unfortunately the rest of the design is holding up PCB manufacture, so results on these won't be available for awhile.
Which brings me to the other design-stopping considerations: Is anybody aware of low-noise analog switches that can be used to reconfigure the 10 MHz reference paths without significantly degrading the phase noise? As always, I believe 1/F noise would be the concern. Non-reflective is great, but I can accomplish that by using more switches and 50 ohm resistors if need be. Isolation is a key consideration as well. Mechanical relays are out of the question.
An alternative to switching is phase-locking the OCXO to an external reference. I have thoroughly looked into this possibility, and it is likely my preferred approach. But I need to understand how the switching approach compares, hence my question. I do not need help with phase-locking; this feature is readily available from OCXO vendors who have dedicated years of research to optimizing their products.
Any switch experience out there?
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.