Hello,
Thanks for your answers.
I think that we where wrong with the capacitor resonant frequency.
I made the equivalent circuit of a real capacitor (R-L-C with parameters C=100nF, ESR=0.08ohm and fc=10MHz) and I put this circuit at the input of a 50 ohm impedance system (LNA or whatever) and the result is quite good: the upper cutoff frequency depends only of the series inductor and the input impedance (I found fcut =R/(2*pi*L)=+-3GHz). Nice, isn't it? No more small capacitor required! That confirms what I've seen also on some high-speed development kit. Sometimes they put such big capacitor (order of 100nF) on their transceiver lines (2Gb/s) and I was wondering how this stuff worked.
I've attached the schematics and bode plot + a matcad calculation.
What is very important for me is that I've to be sure that a given amplifier can do its job (as stated in the datasheet) with the low frequencies. Is someone has some references of good IC? (Gain: 20dB, 50kHz->2GHz)
:?: