Circuit models for both long-base and short-base p-n junction diodes which are valid for non-linear high-speed and high-frequency operations are presented. The diode model consists of a parallel connection of higher-order dynamic elements and includes the conventional diffusion model as a special case. The new dynamic model can be used for simulating arbitrary p-n junction diode circuits under all operating conditions. In particular, it is capable of simulating realistically the diode's reverse transient behaviour and providing an increasingly accurate approximation to the diffusion equation as the order of the model gets higher. The model is also shown to be capable of reproducing the frequency-dependent small-signal characteristics of p-n junction diodes.The model is based mainly upon the device's physical operating principles. Perhaps the most significant implication of the model is the fact that it illustrates the important roles played by higher-order and dynamic elements in highspeed and high-frequency non-linear device modelling.
. INTRODUCTIONFrequency-dependent behaviour' is observed in many different materials and devices and is one of the main inspirations leading t o the investigations of higher-order and dynamic elements. * t Among devices exhibiting frequency-dependent characteristics, the p-n junction diode is a particularly familiar one and its physics is simple enough t o illustrate the usefulness of higher-order and/or dynamic elements in device modelling. p-n junctions are of great importance both in circuit applications and in understanding other semiconductor devices, and have played a major role in the characterization and the development of modern I C technology. Simple as the structure of p-n junction may be, it does serve as the foundation of the physics of many semiconductor devices.The traditional p-n junction diode model4 consists of a n ideal junction-law diffusion resistor in parallel with a non-linear diffusion capacitor and a non-linear depletion capacitor as shown in Figure 1. Several modifications have been made upon this basic model t o improve the simulation accuracy under different operating conditions. These include the modelling of depletion generation-recombination current under reverse and low forward bias, and the memristor for simulating conductivity modulation effect.Although the traditional two-capacitor model sometimes predicts switching times three orders of magnitude smaller than actually measured during reverse transients, the sophisticated multi-lumped diffuson model' proposed by Linvill is capable of providing as accurate a n approximation t o the diode diffusion equation as possible. However, the number of lumped sections needed for accurate prediction is usually so high that the actual circuit simulation becomes impractical.Furthermore, the two elements responsible for the diffusion mechanism within the diode, the diffusion resistor and capacitor, are valid only under low-frequency operations and can not reproduce the diode's frequency-dependent charact...
