Modern high-speed analogue-to-digital converters (ADCs) have enabled the direct sampling of radio frequency (RF) signals, which in many cases eliminates the need for mixing stages while increasing system flexibility and capability. Traditionally, ADC signal and clock inputs have been represented by lumped element models.
However, for RF sampling converters, this approach is inadequate, since operating frequencies have increased to the point where a distributed representation is required.
In this three-part series, David Guidry of Texas Instruments explains how to use scattering parameters, also known as S-parameters, in the design of direct RF sampling architectures.
S-parameters provide a framework for describing networks based on the ratio of incident and reflected microwaves. This is useful for circuit design, because you can use these ratios to calculate properties such as input impedance, frequency response and isolation. It’s not necessary to know the details of the network, since it’s possible to directly measure S-parameters with a vector network analyser (VNA).
To read the full article from Texas Instruments, click here.