----- Original Message -----
From: Ernie Murphy <ernie@SURFREE.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Saturday, June 12, 1999 12:10 PM
Subject: Re: Osc cap return


> Remember small signal analysis? Power rails are both ground. What do you
> think the impedance of the power supply decoupling cap is at 4 MHz?


Yes I do, Perhaps you better make such a measurement, at fundamental and
harmonics through 1GHz, and consider lead lengths and trace impedance.
VCC is always some impedance away from GND, and it may be quite significant.
That osc current through the caps needs to return to the chip's ground, and
it will, if it has to run all over your system, and radiate on all your
attached cables to do so.