[time-nuts] yet another GPSDO design, or so

Hal Murray hmurray at megapathdsl.net
Tue Jun 29 19:55:10 UTC 2010

> Another approach is to distribute the individual bits rather than clump them
>  together.  If you want 1/2, send 10101010 rather than 11110000.  You would
> have to do something like build a bit pattern in memory and use a serial
> port  to send it out. 

> I can't determine if that's good enough.  I think the math is similar to the
>  spurs you get from a DDS. 

I'm getting slow in my old age...  

You can also generate the bit pattern on the fly.  It's the same logic as a 
DDS: just an adder.  If you want the D/A to output X (as a fraction) just add 
X to your register each clock cycle.  (I think of the register as having the 
decimal point on the left.)

With a DDS, you would feed the top bits to a D/A.  For the distributed PWM 
(Pulse Density Modulation?) use the carry out of the top bit.

These are my opinions, not necessarily my employer's.  I hate spam.

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