Emitter-Induced Gain Effects on Dual-Emitter Phototransistor as an Electrooptical Switch

In this paper, an investigation of the static/dynamic performance of dual-emitter phototransistors (DEPTs) as an electrooptical switch was made. In the static case, the measured optical gains (the collector photocurrents) of DEPTs operated at a 12.5-muW optical power have been enhanced from 13.7 to 20.2 (88 to 129 muA) due to an emitter-induced gain high (EIGH) from photocurrent modulation. For DEPTs as an electrooptical switch, the EIGH from photocurrent modulation and the emitter-induced gain effect from junction-voltage modulation dominate the dynamic operation. In the case of continuous light input, good bistable-state output characteristics can be realized with an electrical clock signal. When the switch is operated with a 2-V supply voltage and a 10-kOmega load resistance, the stable electrical-logic swing (ELS) is 0.41 V for a 1-V/1-kHz clock signal. Electrical inputs of 5-, 10-, and 50-kHz clock signals are also employed to achieve outputs with increased ELSs of 1.18, 1.19, and 1.3 V, respectively. An optical inverter is realized. When two clock signals, an electrical input and an optical input, are employed, DEPTs are operated as a tristable-state switch.