[time-nuts] Interfacing a 8dBm sine output of an OCXO to a digital logic standard

David Forbes dforbes at dakotacom.net
Fri Sep 16 10:19:11 EDT 2005


At 12:49 PM +0200 9/16/05, Stephan Sandenbergh wrote:
>I wondered if anyone could help me with an interfacing problem? I guess
>that it is a trivial question to those that know, but I am rather
>puzzled by it.
>
>My very stable OCXO output a 8dBm (50ohm) sine wave. How is this signal
>converted/interfaced to a logic standard (e.g. LVDS)? I can imagine that
>the sine wave must be squared off using a fast comparator and then fed
>through to a logic driver. Are there any integrated IC's out there that
>does this? It would be rather sad to sustain substantial phase noise
>degradation due to a floating comparator threshold and limited slew
>rate.
>
>Regards,
>
>Stephan Sandenbergh

Stephan,

Hi.  I had to build such a circuit a couple years ago, and used a bit 
of overkill...

First, I sent the 10 MHz signal through a two-section LC bandpass 
filter to remove any externally-generated noise. Then I detected the 
zero crossing with an AD8561 fast comparator chip. This circuit is 
tuned to 10 MHz.

Schematic here:
http://www.nixiebunny.com/FBEPP-A.pdf


-- 

--David Forbes, Tucson, AZ
http://www.cathodecorner.com/



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