This may seem a strange question for someone who’s made their living out of signal integrity for so long, but things have changed. There was a period in the 80s and 90s that I call the SI Deficit: the period when signal integrity issues took engineers by surprise and my specialty was even called “Black Magic”. The design landscape has changed radically since then – the main reason for this being standardization…
S-Parameters are Scattering Parameters: they describe how derivatives of a wave arriving at a circuit network port are scattered to all of the ports, including the one at which the wave arrived. Each S-Parameter names the port to which the wave is scattered first, followed by the port from which it has been scattered. S21, therefore, is the S-Parameter for the wave scattered to Port 2 from Port 1, representing the transformation in terms of both magnitude and phase.
Last week I introduced you to the concept of S-Parameters, and now I’m going to explain a bit more about measuring them and simulating with S-Parameter models.
So here goes. Mainstream high-speed PCB design has generally followed in the slipstream of RF and microwave engineering. This is often out of necessity, as techniques have been simplified and made applicable to wider use. For example IBIS models that describe input/output behaviour without revealing internal design details are published for most high-speed integrated circuits.