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From: Don Pearce
Subject: Re: High frequency PCB layout techniques.
Date: Mon, 13 Jan 2003 22:30:50 +0000
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On Mon, 13 Jan 2003 22:24:24 +0000, Joseph Casey
>At approximately what frequency does the need for special PCB design
>techniques start? By special I mean where board capacitance and track
>inductance has significant influence, signals are significangly
>attenuated, intercoupling is significant and RFI is a real problem.
>I realise that on a LF board there is always some RFI from digital
>signal transitions; rise/fall times are increased and analog signals
>need to be routed to avoid intercoupling. I can manage those effects.
>What I want to know is at what stage do I need to call in the
If the application demands great accuracy, about 1/50th of a
wavelength. Generally speaking 1/20th wavelength should be the maximum
you hit without starting to take care over track dimensions.
If the board is digital, use the rise times of the pulses to decide
the maximum frequency, and hence wavelength. (Roughly speaking, the
rise time takes one quarter of a cycle at the highest frequency of
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