[SI-LIST] : A/D and D/A Converters PWR/GND Connection

Jay Diepenbrock (jaydiep@us.ibm.com)
Tue, 20 Oct 1998 17:57:24 -0400

To whomever sent this item (name wasn't listed),

I would recommend using the most solid Ground possible. You may want to use
"islands" for the analog and digital regions, connecting them together back at
the power supply point ("single point grounding"). That way you don't have
digital noise causing problems in the analog circuitry. However, if you also
have high-speed signals routed across the plane boundary you can have other
problems (like EMI) due to the lack of a continuous return path. As for power,
on a previous design we had good results by isolating the analog power from
digital power using high frequency ferrite beads and ceramic capacitors (on the
analog side of the bead) for A/D converters. For more sensitive circuitry, a
separate ANALOG (no, not a switcher) was necessary to provide clean power to
the analog circuitry. It depends on what you're doing with the analog power,
but I would not think that would be necessary for an A/D converter. Your
mileage may vary.

For what it's worth, Analog Devices in their applications seminars and notes
recommends common connections for both power and Ground for A/D converters.
Their reasoning is that they provide separate pins on the devices so the
package parasitics (mainly inductance) don't share noise in getting to the
outside world.

Jay Diepenbrock

Advisory Engineer
Interconnect Technology & Qualification
IBM Global Procurement, B8UA/061, RTP, NC
Phone: 919-543-8804 Fax: 919-543-3642
Email: jaydiep@us.ibm.com

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