TRAPATT oscillations in a p-i-n avalanche diode

The characteristics of TRAPATT oscillations in a p-in diode are discussed and an approximate semi-analytical solution for the diode voltage waveform is derived when the diode current is a square wave. It is shown that a traveling avalanche zone is not necessary to generate a dense "trapped" plasma and that the boundary conditions prevent the trapped plasma from completely filling the depletion layer. Typical voltage waveforms and corresponding diode power, efficiency, and impedance at the fundamental and higher harmonics are presented. When the diode current is a square wave the diode does not necessarily exhibit a negative resistance at all higher harmonics. A computer program for TRAPATT oscillations in a p-i-n diode is described. Its running time is two or three orders of magnitude less than more exact time domain computer analyses. Typical results of diode power, dc to RF conversion efficiency, and required circuit impedances are presented for several different current waveforms which are composed of up to the seventh harmonic of a square wave and the first two harmonics of a half-wave sine wave. It is shown that high-efficiency oscillations are possible with diode currents composed of only the fundamental and one harmonic.