[SI-LIST] Re: Capacitors at high frequency
- From: Jory McKinley <jory_mckinley@xxxxxxxxx>
- To: Alvaro alkschbirs <alvaro.alkschbirs@xxxxxxxxx>, si-list@xxxxxxxxxxxxx
- Date: Sat, 23 Oct 2010 12:53:23 -0700 (PDT)
Hello Alvaro,
Different applications. PDN very low impedance targets more than likely in the
milli-ohms if shared plane from daylight to dawn so series inductance often
reduce the effectiveness of decoupling caps which is usually dominated not by
the ESL of the cap but the Via/routing in the path of the decoupling cap. AC
coupling caps are in a much higher impedance environment for PCIE gen3 85 ohms
differential the ESL does not come into play until say 20Ghz-50Ghz range.
-Jory
________________________________
From: Alvaro alkschbirs <alvaro.alkschbirs@xxxxxxxxx>
To: si-list@xxxxxxxxxxxxx
Sent: Sat, October 23, 2010 10:33:01 AM
Subject: [SI-LIST] Capacitors at high frequency
Hi all,
I have a question about power (de)coupling and ac coupling capacitors;
Situation 1:
Thinking about capacitors at high frequency, According to what I've read,
the power supply (de)coupling discrete capacitors works until some hundred
of MHz. Above this, the inductance goes dominant and the power charge
capacity goes down.
Situation 2:
Now, thinking about this same discrete capacitor working as AC coupling on
1Gb/s or 3,125Gbp/s signals. I have done this in my projects (using 0402
capacitors) and no error have been reported at this signals.
Q1. What do you think about it ?
Q2. Why the dominant inductance is a problem in situation 1, and not for 2 ?
Thank you very much,
Álvaro Alkschbirs
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