NOTE ON TRANSISTORS FOR AVALANCHE-MODE OPERATION

Abstract

We have found that selected Motorola transistors of the MM-486, MM-487, and MM-488 type are quite useful for avalanche-mode operation. Figure 1 shows a circuit used in conjunction with a traveling-wave oscilloscope for selecting avalanche units. The output of the line-type pulse generator is 40 to 60 volts (either polarity of output pulse is available), and the rise time is less than 0.5 nsec. Figure Z shows a plot of the static V-I characteristics of the collector-to-emitter junction for various units, avalanching and nonavalanching. A transistor that avalanches will do 80 over the entire flat portion of the V-I characteristic. One can expect that 10 to 30% of the transistors will avalanche. There is some indication that the low-beta type (MM-486) give the best yield. There is a time delay of a few nanoseconds between application of a trigger pulse and the rise of the main avalanche current. Figures 3 and 4 shows this delay, measured between the 50% point of the trigger-voltage waveform and the 50% point of the avalanche output waveform, as a function of trigger-voltage amplitude (Fig. 3) and static-collector current (Fig. 4). The negative-resistance region (such as that in Fig. 2) should be avoided if time and amplitude jitter of the output pulse are to be minimized. A temperature change from 70 to 150 F has negligible effect on time delay, but raises the breakdown knee (Fig. 2) to higher current (e. g., from 2 x 10{sup -3} to 8 x 10{sup -3} {micro}a).