Bob Camp wrote:
Hi
Are you referring to something like this:
http://www.electronicsweekly.com/Articles/2008/05/01/43680/fast-settling-syn
chronous-pwm-dac-filter-has-almost-no.htm
as a synchronous filter for the PWM?
Bob
Yes, that is the original article.
There's a later one (the link is in the archives) which shows how to use
a pair of 16 bit PWM signals in conjunction with such a filter.
However there is an error in one of the resistor values.
Ulrich built and tested a 24 bit version using a pair of 16 bit PWM signals.
Bruce
-----Original Message-----
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
Behalf Of Bruce Griffiths
Sent: Tuesday, June 29, 2010 4:07 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] yet another GPSDO design, or so
Attila Kinali wrote:
On Tue, 29 Jun 2010 21:32:10 +1200
Bruce Griffiths<bruce.griffi...@xtra.co.nz> wrote:
Its possible to build a 24 bit resolution D/A using a synchronously
filtered PWM circuit.
A pair of PWM outputs and a few relatively low precision resistors and
capacitors together with a low noise low drift reference are required.
The technique takes advantage of the fact that the required EFC voltage
changes slowly and isnt updated at a highg rate.
The synchronous filter technique eliminates the very long time constant
RC filters required with an asynchronously filtered PWM waveform.
I've thought about that, but i'm afraid that this will add too
much phase noise trough EFC noise. Though, i have not calculated
how much noise this would generate.
Attila Kinali
How do you conclude that?
You don't know what the circuit is and you've never tested it.
Ulrich has, and the output noise is very low.
Bruce
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