A computer simulation of Trapatt circuits†

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Abstract
A computer simulation of Evans-type Trapatt circuits is presented. The diode is approximated by a depletion capacitance and a current generator. The latter represents the current induced by the avalanche generated charge carriers. By examining the response to a periodic impulse of current in this circuit, suitable triggering conditions are found which are dependent on the package parameters and circuit impedance. Useful operation should result if the effective electrical length of the circuit is n(π —δ) radians at the nth harmonic, provided that δ⋍(½π)2ω0C1Z0 [C1, package capacitance, Za the line impedance]. The circuit then places across the terminals of the diode a capacitive impedance that increases with harmonic number (a negative inductance). This concept leads to a technique for circuit design that allows for the diode structure. The required ' negative inductance ' to match a diode must not be too low compared to the package lead inductance. Similarly, the diode capacitance must not be too high if the rate of rise of voltage is to create a travelling avalanche. A simulation with approximately 55% efficiency is given. This work shows that the key features in obtaining or improving on this efficiency are low circuit and diode losses and a low overshoot of the voltage above the breakdown value, but still sufficient generation of charge to give good trapping of the plasma.

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