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Synchronizing two crystal oscillators - RF Cafe Forums

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Post subject: Synchronizing two crystal oscillators Posted: Sat Nov 24, 2007 3:26 am


Joined: Fri Nov 23, 2007 11:59 am

Posts: 4

Location: Israel

Hi Guys,

I have xo for my VSAT tuner, and I'm currently designing the LO for my burst receiver (direct conversion).

Problem: I have to use the tuner crystal oscillator, (synchronous LO's) but the main xo is located "miles" away from my LO, and it passes through LVDS.

The phase noise performance is awful: (-105dBc/Hz @1KHz) and I must use a local reference oscillator!!!(I need -35dBc integrated noise, with settling time of roughly 100us. I use a broad band VCO so it includes an active loop filter)

I was thinking to use a close by VCXO, and synchronize it with the main xo.

Question: What is the simple, cost effective way to implement such a synchronization loop (pll, costas)?

Your help will be highly appreciated,





Post subject: Posted: Sun Nov 25, 2007 3:07 am


Joined: Sun Mar 19, 2006 5:25 pm

Posts: 21

Location: Burnaby

Hi Eran,

You may think about using GPS modules to synchronize them. A general GPS module can provide quite precise clock signal. Working with a VCXO, both the short term stability and long term stability can be achieved at the same time.

Hope it is little helpful.



Post subject: GPS module is overkillPosted: Mon Nov 26, 2007 3:31 am


Joined: Fri Nov 23, 2007 11:59 am

Posts: 4

Location: Israel

I was thinking using a phase detector and vcxo at the same xo refference frequebcy(no prescaler is needed) and simply close a loop on the vcxo.

I only need to check the influance of the delay time, but as for the phase lock i think it will work.don't you think?



Post subject: Has anyone done it before?Posted: Sun Dec 02, 2007 3:32 am


Joined: Fri Nov 23, 2007 11:59 am

Posts: 4

Location: Israel

did anyone implemented a sync. of two oscillators,and have comments?



Post subject: Posted: Mon Dec 03, 2007 8:04 am


Joined: Fri Feb 17, 2006 12:07 pm

Posts: 218

Location: London UK

Hi Eran

This is a comment requirement for the design of SONET/SDH multiplexers, where the synch clock is extracted from the data stream. If that should become corrupted or the link broken, the mux is required to free-run on its own internal TCXO, then re-synch when the stream is re-established. For that function the TXCO is continuously synched to the stream if it is there.

I have not seen the circuits that achieve this, but I guess there must be refs on the web to how it is done. Try a search engine with some key words like SONET, SDH and "clock".

Posted  11/12/2012

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