Re: [time-nuts] 10 MHz reference switching (Clay)
Yes, high frequency AC current doesn't usually result in flicker noise. Bruce life speed wrote: Why would flicker noise be a concern if there is no dc current flowing in the switches? Bruce Hi Bruce, Does it matter if the current is DC or AC? I expect to see +/-20 mA current due to the signal level. Clay From: Bob Camp Subject: Re: [time-nuts] 10 MHz reference switching 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 Hi Bob, I had not considered pin diode switches. I guess in my mind they are "RF", and 10 MHz is not. No reason not to think about them. However, I think to get any sort of useable isolation at 10 MHz series-shunt or pi configuration is required, which will have current flowing in one of the paths at all times. Clay From: paul swed Subject: Re: [time-nuts] 10 MHz reference switching rf relay would work Hi Paul, Sorry, no relays for a high-reliability application. Not enough room or current either. Clay From: Bob Camp Subject: Re: [time-nuts] 10 MHz reference switching 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 Good point. I could power down the internal oscillator based on a detected external reference. Just more circuits to add . . . Thanks to all who replied, you raised some good points. Locking the internal to external sounds better all the time, it's just kind of expensive. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 10 MHz reference switching (Clay)
Hi Can you simply turn off the "oscillator" part of the OCXO? In other words, leave the oven on and kill the RF at the source. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of life speed Sent: Tuesday, March 09, 2010 12:22 PM To: time-nuts@febo.com Subject: Re: [time-nuts] 10 MHz reference switching (Clay) > Why would flicker noise be a concern if there is no dc current flowing > in the switches? > Bruce Hi Bruce, Does it matter if the current is DC or AC? I expect to see +/-20 mA current due to the signal level. Clay From: Bob Camp Subject: Re: [time-nuts] 10 MHz reference switching > 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 Hi Bob, I had not considered pin diode switches. I guess in my mind they are "RF", and 10 MHz is not. No reason not to think about them. However, I think to get any sort of useable isolation at 10 MHz series-shunt or pi configuration is required, which will have current flowing in one of the paths at all times. Clay From: paul swed Subject: Re: [time-nuts] 10 MHz reference switching > rf relay would work Hi Paul, Sorry, no relays for a high-reliability application. Not enough room or current either. Clay From: Bob Camp Subject: Re: [time-nuts] 10 MHz reference switching > 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 Good point. I could power down the internal oscillator based on a detected external reference. Just more circuits to add . . . Thanks to all who replied, you raised some good points. Locking the internal to external sounds better all the time, it's just kind of expensive. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 10 MHz reference switching (Clay)
> Why would flicker noise be a concern if there is no dc current flowing > in the switches? > Bruce Hi Bruce, Does it matter if the current is DC or AC? I expect to see +/-20 mA current due to the signal level. Clay From: Bob Camp Subject: Re: [time-nuts] 10 MHz reference switching > 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 Hi Bob, I had not considered pin diode switches. I guess in my mind they are "RF", and 10 MHz is not. No reason not to think about them. However, I think to get any sort of useable isolation at 10 MHz series-shunt or pi configuration is required, which will have current flowing in one of the paths at all times. Clay From: paul swed Subject: Re: [time-nuts] 10 MHz reference switching > rf relay would work Hi Paul, Sorry, no relays for a high-reliability application. Not enough room or current either. Clay From: Bob Camp Subject: Re: [time-nuts] 10 MHz reference switching > 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 Good point. I could power down the internal oscillator based on a detected external reference. Just more circuits to add . . . Thanks to all who replied, you raised some good points. Locking the internal to external sounds better all the time, it's just kind of expensive. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 10 MHz reference switching
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? > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 10 MHz reference switching
rf relay would work On Mon, Mar 8, 2010 at 6:51 PM, Bob Camp 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? > > > > Bruce > > > > > > ___ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 10 MHz reference switching
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 > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 10 MHz reference switching
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 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] 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? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
