[time-nuts] V standards
Bruce Griffiths
bruce.griffiths at xtra.co.nz
Tue Dec 2 09:09:13 UTC 2008
Poul-Henning Kamp wrote:
> In message <58C70987-017E-44ED-BF07-D578679C03C2 at hughes.net>, Richard Moore wri
> tes:
>
>
>>> If you are controlling this with a microcontroller, there is an
>>> alternative
>>> you should consider:
>>>
>>> Use only a single DAC and then PWM modulate its output, followed
>>> by a low-pass filter.
>>>
>> Poul, how do I PWM a DAC that is itself a PWM device? This question
>> is prompted by the DAC I'm using in Bert Zauhar's FLL GPSDO, which is
>> a dithered 10-bit DAC in a PIC chip that results in 14-bit
>> resolution. I'd like to have a simple way to get 2 to 4 extra bits of
>> resolution out of this. Can you recommend some design resources to do
>> this?
>>
>
> I would simply cummutate the DAC output with a PWM controlled fet or
> CMOS switch.
>
>
You can either do this with the filtered DAC output and filter the
result, or with some ingenuity just combine the unfiltered PWM outputs
and then filter the result with a single low pass filter.
Bruce
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