Improve return loss performance by adding capacitor in parallel with return loss network at 3G SDI

Satoshi

If there is a parasitic inductance on the trace between the LMH0303 and the BNC connector, then this can be compensated for by the additional capacitor.    To determine if it is required, use a network analyzer to examine the impedance of the output vs frequency - in most circuits you will see the impedance be close to 75Ohms at low frequencies, and when the frequency gets very high, then the parasitic capacitance at the output of the LMH0303 causes the impedance to drop - the 6.8nH inductor in the circuit compensates for this.   If you see a rise in the impedance at very high frequencies, that may be due to parasitic inductance and this can be compensated for with the capacitor, set the pole frequency of the capacitor at about the frequency where you see the parasitic inductance having an impact.