[[RF.Spice A/D]] uses the same Berkeley SPICE and XSPICE simulation engines of its forerunner [[B2.Spice A/D]]. In other words, the high frequency AC analysis is carried out by the same analog and mixed-mode SPICE simulation engines based on nodal admittance analysis, which have been enhanced with additional RF simulation capabilities. As a result, you can mix the RF devices in your circuits with all the other analog and mixed-mode devices of [[B2.Spice A/D]]. You can also mix transmission-line-type RF devices with digital parts and perform mixed-mode time domain simulations.
At the heart of [[RF.Spice]] lie the The concepts of RF [[Transmission Lines|transmission lines]] and [[Multiport Networks|multiport networks]]are integral to any RF simulation. All the RF devices of [[RF. Spice A/D]] can be divided into two groups: devices based on transmission line models, and devices based on multiple networks. As you will see in the later sections of this manual, [[RF.Spice]]'s transmission line models are based on enhanced versions of SPICE's standard LTRA model. [[Multiport Networks|Multiport networks]] are characterized and modeled based on their frequency-domain scattering (S) [[parameters]].
The S-[[parameters]] are tabulated as a function of frequency and interpolated in between the frequency samples. [[RF.Spice]] performs an AC analysis of these RF devices by converting their S-[[parameters]] to Y-[[parameters]] and using them in conjunction with SPICEâs nodal admittance matrix formalism.