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