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

Peterson, James F (jfpeterson@space.honeywell.com)
Tue, 20 Oct 1998 07:48:00 -0400

My $0.02 :
In regards to the grounding scheme, I guess it depends on how sensitive your
analog circuit is to the digital side. I have used some medium speed, noise
sensitive, 12-bit ADCs and have arrived at an approach that seems to be
effective for my applications. I connect both the AGND and DGND to the
analog ground. This seems to keep the digital noise at the DGND of the board
from capacitively coupling into the analog side of the chip. AGND and DGND
finally meet at a single point down-stream on the board. There is usually
enough noise margin on the digital side of the chip to handle this.
Again, it depends on your specific situation. The above applications have an
ADC, on the same board with a very noisy digital circuit.
Jim Peterson
jfpeterson@space.honeywell.com <mailto:jfpeterson@space.honeywell.com>
Honeywell, Space Systems Division, M/S 934-5
13350 US 19 N., Clearwater, FL, 34624
813-539-2719

----------
From: Elya B. Joffe [SMTP:ebj@netvision.net.il]
Sent: Monday, October 19, 1998 6:38 PM
To: 'Signal Integrity LIST'
Subject: [SI-LIST] : A/D and D/A Converters PWR/GND Connection

Dear Members,

D/A and A/D Converters process, as we all kknow, analog and digital
signals.

I could not find, neither in books, nor in application notes, a
general convention for power and ground connection to those devices. The
devices usually have VCC (Digital power) and VAA (Analog power) power
donnections, and DGND and AGND for ground connections. However, the method
of their connection is unclear. For instance, the following options were
observed by me:

1) Connect VCC pin to Digital power source
Connect VAA pin to Analog power source
Connect DGND pin to Digital power return
Connect AGND pin to Analog power return
Connect DGND to AGND in a single point ("Star") or a narrow
"Bridge" near the device

2) Connect BOTH VCC and VAA pins to Analog power source
Connect BOTH DGND and AGND pins to ANALOG power return
Connect DGND to AGND in a single point ("Star") or a narrow
"Bridge" near the device

I have also observed other connections too.

Note: If only a single power source is available, the VAA should be
filtered from the VCC. Any recommendations???

The Questions:

Are there any recommendations as to the correct manner of dealing
with the power supply and return (GND) connections of A/Ds and D/As? Any
experience that could be shared with us?

And - when there is only one such device in the system, the
condition could be quite controllable, since the interconnection between
the AGND and the DGND could be performed at a point close to the A/D or
D/A! However...

What should be done if there is more than 1 such device on the same
PCB? On several PCBs in the system? Should any decoupling or isolatioon
devices be placed between the devices (e.g. RF chokes, ferrite
beads?

Any recommendations?

Any contributions/inputs will be highly appreciated!

Thanks alot,

Elya B. Joffe - KTM

Every man is given the key to the gates of Heaven. The same key
opens the gates to Hell!

**** To unsubscribe from si-list: send e-mail to
majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE
si-list, for more help, put HELP. si-list archives are accessible at
http://www.qsl.net/wb6tpu/si-list ****

**** To unsubscribe from si-list: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list, for more help, put HELP. si-list archives are accessible at http://www.qsl.net/wb6tpu/si-list ****