Re: [SI-LIST] : RF & Digital

Adrian Shiner (adrian.shiner@virgin.net)
Wed, 11 Aug 1999 19:18:21 +0100

Yes, it is called using a star point earth with segregation of circuits to avoid capacitive and radiative coupling. the clever & difficult bit is too minimise the loops (good radiators and receivers).

Adrian

"THOMPSON, Martin" wrote:

> Would routing carefully not steer the ground.power currents as effectively?
>
> Martin Thompson.
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> -----Original Message-----
> From: Mark Sauerwald [SMTP:Mark.Sauerwald@nsc.com]
> Sent: Wednesday, August 11, 1999 4:25 PM
> To: si-list
> Subject: Re: [SI-LIST] : RF & Digital
>
> 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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