Mason is designed to simplify the process of moving from design (schematic) to simulation to layout. Sometimes the number of pins on a physical part do not line up with the number of ports in a simulation. For example, a part may have power or ground pins that are not part of the S-Parameter model. The part may also have digital control pins that are not part of the RF simulation. Mason has a special "Nodes" parameter to map the pin terminals to the S-Parameter ports.
Consider the amplifier below. Pin 1 corresponds with Port 1 of the S-Parameter model, and Pin 3 corresponds with Port 2 of the S-Parameter model. The RF simulation wants to treat this as a two port device. The layout wants to treat this as a four terminal device.
Figure 1: Schematic view
We need to identify how to map the schematic pins to the simulation ports: we use the “Nodes” parameter (Figure 2) to set that. From the data sheet, we see that Pin 1 goes to Port 1, Pin 2 is grounded (not part of our simulation's S-Parameters), Pin 3 goes to Port 2, and Pin 4 is grounded (not part of our simulation's S-Parameters). The “Nodes” parameter uses “0” to mean “not part of the simulation, and so our Nodes are described as “1 0 2 0” (pin 1→ Port 1, pin 2 → not used, pin 3 → Port 2, pin 4 → not used).
Figure 2: Amplifier's properties