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

John Ackermann N8UR jra at febo.com
Fri Sep 16 08:41:32 EDT 2005

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.

Stephan, I don't know if this is the *best* answer, but I've stolen an 
idea used by Brooks Shera in his GPSDO controller.  He uses the input 
section (only) of a 74HCT4046 PLL chip to square the OCXO signal.  I 
implemented his idea using a 74AC4046 and it seems to work OK, though I 
don't know what its jitter/phase noise performance is.  A schematic of 
my circuit is at http://www.febo.com/time-freq/gps/z3801a/mods/index.html.


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