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

Elya B. Joffe (ebj@netvision.net.il)
Mon, 19 Oct 1998 22:38:28 +2

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.

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

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!

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