Use appropriate band-limiting filters to reject unwanted frequencies in the input signal path.

A 1:2 balun transformer is needed to convert the 50-Ω, single-ended signal to 100-Ω differential for input to the ADC. The balun outputs can be either AC-coupled, or directly connected to the ADC differential inputs, which are terminated internally to GND.

Drivers must be selected to provide any needed signal gain and that have the necessary bandwidth capabilities.

In general, baluns must be selected to cover the needed frequency range, have a 1:2 impedance ratio, and have acceptable gain and phase balance over the frequency range of interest. Mount baluns with poor differential output return loss as close to the ADC inputs as possible to avoid ripples in the frequency response at high input frequencies. Resistive attenuators (Pi- or T-type) can also help dampen ripples caused by poor return loss. Table 8-1 lists a number of recommended baluns for different frequency ranges.