[SI-LIST] Re: AC Blocking capacitor relative positions and reference plane voids
- From: steve weir <weirsi@xxxxxxxxxx>
- To: jean-francois hasson <jfhasson@xxxxxxxxxxxxxxxx>
- Date: Wed, 18 Nov 2009 13:25:28 -0800
A good design voids in order to compensate as much as possible the
impedance discontinuities otherwise imposed by the pads and the
capacitor themselves. Designing the structures is a good application
for a 3D solver like Simbeor.
Steve
jean-francois hasson wrote:
> Hi,
>
> When looking at AC coupling capacitors on high speed serial links it is
> often recommended to void the reference plane under these capacitors to
> minimize capacitance variations. Most of the times, in the designs I
> have seen, the void is exactly underneath each AC blocking capacitor
> including landing pads. If ever the capacitors were quite close, would
> there be any reason why a single void below both capacitors would be an
> issue ? I have also noticed that most of the times AC blocking
> capacitors are not as close as possible to a transmitter or receiver
> where I thought it was beneficial to do so to remove the number of
> impedance disruptions ? Could anyone provide me with some explanation ?
>
> Best regards,
>
> JF
>
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