Re: [SI-LIST] : RF & Digital

Adrian Shiner (adrian.shiner@virgin.net)
Wed, 11 Aug 1999 19:15:24 +0100

You would be wise to have a digital ground and an RF ground, joined only at one point. Segregate the areas of board into the two functions as well.

Any way you look at it, digital and analogue circuits are like oil and water, they don't mix too well.

Adrian

Mark Sauerwald wrote:

> Lum
>
> In addition to the stack up changes that have been mentioned, I would cut
> isolation rings in the ground and power planes to separate the RF and Digital
> sections of the board. Noise induced in the ground plane in one part of the
> circuit can capacitively couple into components in the RF section if you are
> not careful. By cutting a slot in the plane, you can steer ground and power
> currents around the more sensitive portions of your circuit. Another thing
> that will help isolate the digital signals from the RF is to use small-swing
> differential logic levels, such as LVDS, rather than fast CMOS wherever
> possible.
>
> Mark Sauerwald
> National Semiconductor
>
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