[hpsdr] [OZY] Schematic update May 16, 2006

[Philip Covington]

On 5/16/06, Ray Anderson <ray.anderson at xilinx.com> wrote:
>
>
>
> -----Original Message-----
>
> >PDF Schematic at:
>
> ><http://www.philcovington.com/HPSDR/OZY/REVXA.3/>
>
> >Added Panasonic RC filter networks to the local IO on OZY.
>
> >Good news is that I will probably be able to add the 20 pin logic
> >analyzer/debug port back into the design because of the space savings
> >from using resistor networks and moving some of the passive components
> >to the backside of the PCB.
>
> >73 de Phil N8VB
>
>
> Phil-
>
> While reviewing your latest schematic changes I noticed the LC filters
> (L2/C21 and L4/C22) feeding +1.2VA1 and +1.2VA2. Quick question for you:
> What is the anticipated current draw on those outputs (and what sort of
> things will they power))? The reason I ask is that I've seen a good
> number of designs have issues with noise peaking when utilizing simple
> LC filters like that, especially if they power sensitive circuitry like
> PLLs or other noise sensitive loads. You can easily have more noise on
> the output than you have on the input in the couple hundred kHz range.
> This is a function of a low input impedance from the regulator and a
> moderate load impedance. Large ratios of Zout/Zin can cause problem if
> you don't manage the filter design correctly.
>
> Lots of app notes from IC vendors specify these kinds of filters (and
> whoever wrote the app notes usually wasn't aware of the issues
> involved....)
>
>
> -Ray    WB6TPU

Hi Ray,

They are there to power the 2 PLL analog supply pins on the Cyclone II
only.  I will look ASAP to see exactly what kind of current they will
pull... I expect very low...

73 de Phil N8VB

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