Premature collection mode in IMPATT diodes

Experimental efficiencies of up to 35.5 percent have been reported for Read-type GaAs diodes, whereas realistic theoretical calculations have predicted an upper limit of approximately 30 percent for the conversion efficiency of IMPATT diodes. The concept of a premature collection mode is shown to resolve this discrepancy by predicting maximum efficiencies close to 40 percent. Premature collection refers to large-signal conditions where the modulation of the drift width is sufficiently large to result in collection of the avalanche current pulse at drift angles smaller than the small-signal angle. The onset of premature collection is accompanied by a substantial increase in power output because of a more favorable drift angle, and by high noise because of the high rf levels involved. The hysteresis in the tuning characteristic resulting from the discontinuous transition has been observed experimentally.