[SI-LIST] Re: Capacitors at high frequency
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 25 Oct 2010 19:08:37 -0400
A question to the list, now that we understand the difference between
signal capacitors and power capacitors.
Assuming an 0402 X5R capacitor that is 40 mil long and 40 mil tall:
Where exactly does signal field travel through the capacitor at the
Nyquist frequency of 1.5625 GHz for a 3.125 Gbps data stream?
Does a signal at 1.5625 GHz experience the full capacitance directly?
Scott McMorrow
Teraspeed Consulting Group LLC
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(401) 284-1827 Business
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On 10/25/2010 5:40 PM, Alvaro alkschbirs wrote:
> Thank you guys! I understand the diferences between signal coupling and
> power decoupling.
> Rgds for all,
> Álvaro
>
>
> On Sun, Oct 24, 2010 at 12:58 PM, Ken Cantrell<
> Ken.Cantrell@xxxxxxxxxxxxxxxx> wrote:
>
>> Alvaro,
>> One is a low pass filter (power bypassing), the other is a bandbass filter
>> (AC coupling). The series cap and the inductance of the receiver form the
>> bandpass. The BP is tolerant of larger variations w.r.t. to inductance (or
>> capacitance), and L dI/dt noise is a second or third order effect (don't
>> care). Apples and oranges.
>>
>> Thanks,
>>
>> Ken
>>
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx
>> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Alvaro alkschbirs
>> Sent: Saturday, October 23, 2010 8:33 AM
>> To: si-list@xxxxxxxxxxxxx
>> 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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