Simulating RF circuits using PSpice

PSpice as a simulator has no upper frequency limit; the difficulty is in getting models that are accurate at high frequencies. High-frequency models are provided with PSpice and include RF diodes and transistors from major European, American and Japanese manufacturers. Other manufacturers also provide high-frequency models and where these are not included with PSpice they are often available free of charge with their data books or from their Internet sites. Points to note for RF applications: 1) passive devices (R, L, C) are ideal, i.e. they include no parasitics and have infinite Q. For high frequency simulation, users often have to specify the parasitic components explicitly; 2) there are no geometry based transmission line models, e.g. a microstrip line can not be defined by its dimensions. Transmission lines must be modeled in R, L, G, C per unit length format. PSpice transmission line models are fully distributed, not lumped, and allow frequency dependence in R and G to simulate skin effect and dielectric loss; 3) two-port S-parameters can be used indirectly to model linear devices. If such models are to be used for time-domain simulation, then the frequency range of the data must include very low and very high frequencies, and the phase information must be unwrapped to include the delay information.