FreeLists / si-list / [SI-LIST] LVPECL AC COUPLING - CAPACITOR VALUE for 1.25G Ethernet

[salvador JR <sa_jr@xxxxxxxxx>]

Hello All,

If I want to size the value of the AC coupling
capacitor used for DC blocking in a differential
LVPECL  link should my input frequency range be the
same as the resonat frequency of the capacitor?

For example:

For a ceramic SMT capacitor of NPO dielectric

if the capacitance is 18 pF

The resonant frequency is 1250.44 MHz
The impedance (vs frequency) is 0.593 ohms  
ESR = 0.59 ohms  and 
ESL = 0.9 nH

Where the impedance over frequency is calculated
using:
Z = sqrt[Rs^2 + (X_C -X_L)^2]

Where Rs = ESR

is 18pF the value of the capacitor for my DC blocking
in LVPECL differential link used for 1.25Gbps serial
data?

Thank you.

-- Sal 

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