[time-nuts] 32768 Hz from 10 MHz

Chris Albertson albertson.chris at gmail.com
Thu Feb 2 21:09:49 UTC 2012

On Thu, Feb 2, 2012 at 12:21 PM, Tom Van Baak <tvb at leapsecond.com> wrote:

> I'm curious how a 10 MHz-driven high-end DDS would generate
> 32 kHz with the lowest possible jitter?

I wonder if your 32K diver could be improved if it used interpolation.
  In other words use an analog output.   So at each cycle you decide
what value to put out, either one or zero or some voltage between.

The next question is why use a PIC divider?  Why not a DDS?  For
low-end DDS the cost is not much different.  Maybe $1 vs. $10 or about
that. (don't say "10X" say "$9 more")

The DDS does about the same thing is a PIC except that at each cycle
it picks an entry from a sine wave table.  I don't know if they
interpolate or just use the nearest value.   Your algorithm in the
PIC, I think is the same as that but you use nearest value in your
"square wave look up table".  Try interpolating. and filtering.   This
can move to zero crossing to someplace unrelated to the 10MHz

Chris Albertson
Redondo Beach, California

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