[time-nuts] Correcting jitter on the 1 PPS signalfrom a GPS receiver.

Hal Murray hmurray at megapathdsl.net
Mon Sep 15 15:38:25 EDT 2014

dave.martindale at gmail.com said:
> Is there any reason (other than cost) not to both series-terminate the
> source and parallel-terminate the sink? 

With both series and parallel termination, the signal at the receiver is 1/2 
the output level of the output driver.  That doesn't work well if you use 
typical CMOS logic chips at both ends.

I don't remember ever seeing an app-note describing how to do that cleanly 
with readily available chips or data sheets for chips designed to solve that 

An HCT type receiver might work well.  Driver is 5V.  Half that is 2.5V.  
Receiver switches at 1.4 (nominal) which is close to half the signal.   I 
don't think anybody makes a similar chip using modern high-speed CMOS 

> When I was dealing with analog video, the standard distribution method was :
> 3. A single video signal could be looped through multiple high impedance
> loads.
> 4. 75 ohm parallel termination at the far end of the signal path  (usually
> on the last device).

That "looped through" is important.  Most video boxes have 2 connectors per 
signal.  The idea is that the signal gets routed through the box rather than 
using a T connector.  That lets them minimize the stub length.

These are my opinions.  I hate spam.

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