On Aug 15, 2008, at 4:58 PM, Stuart Brorson wrote: >>> I noticed that on p. 3, the ST part (U300) has PVDD and PVSS >>> connections through 4.7 ohm resistors to PWR and GND, >>> respectively. I >>> can see using a small resistor + shunt cap to GND in series with the >>> power connection to attenuate power supply noise. However, why >>> is the >>> PVSS connection to GND also going through a resistor? >> >> There's noise on both power and ground lines. The P* pins are for >> the >> PLL's power supply, which need as clean a power source as you can >> provide. > > Did you use a ground plane? If so, then I'd expect that the plane is > quiet, and it would be better to connect directly. Or am I wrong?
You're right. I'm always amused by the "noise on ground" notion. It's the sound of one hand clapping. Noise relative to what? I'm not saying you can't have troublesome noise currents flowing on a ground connection, but that has to be analyzed from a transmission line, not a network theory, point of view. > > Of course, if you used tracks for ground on the same plane as other > signals, then you're right. Putting a cap between PVDD and PVSS, and > a resistor to PWR and GND makes sense. > > But anyway, thanks for the answer. It makes sense. > > Stuart > > > _______________________________________________ > geda-user mailing list > geda-user@moria.seul.org > http://www.seul.org/cgi-bin/mailman/listinfo/geda-user > John Doty Noqsi Aerospace, Ltd. http://www.noqsi.com/ [EMAIL PROTECTED] _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user