[SI-LIST] Re: A/D grounding
- From: Alan Hilton-Nickel <ahilton@xxxxxxxxxxxxx>
- To: steeve.gaudreault@xxxxxxxxxxxx
- Date: Wed, 10 Oct 2001 17:59:58 -0700
Steeve,
It's been awhile since I last did a design with an A/D on board, and
that was a 10 MHz device. However, it would not advise "separate" Analog
and Digital/Common grounds. The issues are more complex than I would
care to get into without more understanding of your design. However,
perhaps I could suggest the following as a starting point:
1. Use one ground. Perhaps multiple planes depending on your
requirements, but they are all the same ground.
2. Although you are using one ground, you should still *partition* your
design into analog and digital sections. That is, assign regions where
you only allow analog signals and components, and exclude digital
components. A good practice is often to put digital components and
signals on one side of the board and analog on the other.
3. Try to avoid the sharing of return paths for analog and digital
circuits. Analog circuitry can be very sensitive to noise on the ground
and power planes, and this is primarily caused within the system by
digital circuitry using the same return path as the analog circuitry.
Especially do not situate an analog region between two digital ones, and
be careful if you plan to place an analog section between a power supply
and a digital section.
Alan Hilton-Nickel
Transmeta Corporation
Steeve Gaudreault wrote:
>
> I have A/D devices on a board with High Speed components (2.4Gbps). From
> your experience, do you suggest to use an "analog ground" for the AGND
> connection or it is preferable to use the common ground plane and just
> try to locate the A/D to a quiet portion of the board. As for the VCC,
> does a pi-filter is a good idea?
>
> Thanks,
> -Steeve
>
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