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

Alberto di Bene dibene at usa.net
Tue Jun 29 12:52:10 EDT 2010


On 6/29/2010 11:10 AM, Attila Kinali wrote:

> Yes, 16bit D/A seems to
> be the maximum that is currently available. It crossed my mind
> to build a 24bit R-2R D/A using discrete components, but this might
> have actually a worse performance than a off the shelf 16bit D/A.
> (temperature drifft, resistor values missmatch, EMI, etc)

A few years ago (circa 2004) I built a GPSDO that used the PWM feature of
an Atmel uC to generate the EFC. The PWM in that uC has only 10 bits of granularity,
but then I applied another 10 bits of dithering to the two register values
that defined the limits of the PWM. Of course, I had to low pass the generated
signal with a filter with almost 120 dB of rejection at 3.9 Hz, but this
contraption worked, and was really inexpensive, costing only a few lines of code.

Alberto  I2PHD





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