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 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu