On 11/14/2016 6:36 PM, Ivor Bowden wrote:
Various industry specifications call out separate
"circuit" and "chassis" (sometimes called "frame" or
"safety") grounds, along with voltage isolation, bleed
resistors, bridging capacitance etc. requirements. Some
examples include IEEE 1101.1-1998 (Base 3U/6U/9U),
VITA1.1-1997r2003 (VME), ANSI/VITA 46.0-2007 (Base VPX),
PICMG 2.0r3 (Base CPCI), IEEE 802.3 (Ethernet), EIA-644-A
(LVDS), etc. I understand there are similar specifications
for some types of consumer products. Also, while not part
of specification sometimes designers (or app notes they
work from) will call out separate "digital" and "analog"
grounds, connected at single point with zero ohm resistor
or ferrite bead. While there may be use case for such
topology, it frequently causes problems. Regards, Ivor
On 11/14/2016 2:00 PM, Loyer, Jeff (Redacted sender
jwloyer for DMARC) wrote:
I was looking at some designs and found different ground
symbols connected by capacitors. Can anyone explain why
this might be done? Everything I've seen or heard says
this is a bad thing (I would connect them directly), but
I want to be sure I'm not missing something. I think
there are some A/D devices which have specific guidelines
for separating digital and analog grounds, but I don't
think they'd be connected by caps.
Thanks,
Jeff Loyer
