[time-nuts] Question about AD9832 "I out Full Scale" (what does it mean?)

Tim Shoppa tshoppa at gmail.com
Fri Nov 18 10:46:02 EST 2016


Bruce, I assume you are talking about Figure 12 of UG-313.

If an LCD scope is not in single shot mode it will show a composite of many
cycles which will hide the stairsteps (especially if the frequency control
word is not a nice round binary number) in the fuzz.

I think the 0.1uF capacitor on IOUT on the evaluation board also helps roll
off the stairsteps.

Tim N3QE

On Thu, Nov 17, 2016 at 11:49 PM, Bruce Griffiths <
bruce.griffiths at xtra.co.nz> wrote:

> With no internal PLL to generate a higher internal frequency than the
> 25MHz MCLK, that 1MHz waveform looks a bit too smooth for an unfiltered
> 1MHz output.
> Bruce
>
>     On Friday, 18 November 2016 5:12 PM, Richard (Rick) Karlquist <
> richard at karlquist.com> wrote:
>
>
>  Trying to figure out what "Iout Full Scale" means on the AD9832.
> Some time nuts may have used this one.
>
> On page 7 of this doc:
>
> http://www.analog.com/media/en/technical-documentation/
> user-guides/UG-313.pdf
>
> It shows the AD9832 output as 572 mV peak to peak
> across 300 ohms.  This works out to 1.9 mA peak to
> peak current through the resistor.  But Rset on the
> board is 3.9K, which is supposed to give a value
> for so-called "Iout Full Scale" of 3.878 mA.
>
> I would have thought (just guessing) that peak to
> peak output current would be equal to Iout Full
> Scale, but it appears to be only half of that.
>
> Can anyone clarify this?
>
> Rick
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