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

[Philip Covington]

On 5/18/06, Ray Anderson <ray.anderson at xilinx.com> wrote:
>
>
>
> >Note that the inductors are 0805 SMT so a 0805 resistor can be
> >substituted if the inductors are a problem.  Each PLL analog supply
> >looks like it pulls < 7 mA worst case...
>
> >73 de Phil N8VB
>
>
> Phil-
>
> Do you a particular part in mind for the inductors? All the schematic
> presently says is 'IND_0805'. If you can identify a candidate part I can
> run a quick simulation to determine if there may be a problem lurking.
> If so, the solution on the simple side may entail the addition of a
> single resistor per filter and on the complex side, the addition of an
> extra resistor & capacitor per filter. Replacing the ferrite bead with a
> resistor can indeed provide a RC filter, but the size of the resistor
> required to provide the desired rolloff may induce intolerable DC drop
> in the supply. When you only have 1.2 volts to start with, the IR drop
> can be significant percentagewise.
>
> In the 12 years I was at Sun Microsystems consulting with various
> hardware design teams I witnessed  numerous  simple  LC filter designs
> that caused up to 20dB increase in noise in the 50kHz to 200kHz range on
> the PLL power pins of various ASICS. In all cases we were able to tame
> them with just a few additional parts.
>
> -Ray   WB6TPU


Ray,

It actually will be a ferrite per Altera's recommendation in the
Cyclone II Device Handbook, Chapter 7.  I planned on using an 0805 SMT
ferrite chip like the Steward HZ0805C202R-00, impedance 2000 ohm @ 100
MHz, 300 mA max.

73 de Phil N8VB

 1147973491.0