An InAlAs/InGaAs heterojunction bipolar transistor clocked latch on InP

A clocked latch functioning as a simple comparator with InAlAs/InGaAs heterojunction bipolar transistors (HBTs) on an InP substrate is discussed. Typical comparator offset voltages of 2 mV, and as low as 0.2 mV, along with differential pair measurements indicate good V/sub be/ matching of the HBTs in the circuit. A thermal hysteresis of approximately 1 mV was measured. These results are comparable to those for the best GaAs HBT-based comparators, despite the unoptimized device fabrication procedure. Additionally, these comparators are able to operate at low power levels and with a 2-V input common-mode voltage range. Despite remaining materials problems, these results indicate that InP-based HBTs have great potential for high-speed, low-power digital and linear small- and medium-scale ICs due to the ease of good ohmic contact formation, the low base-emitter diode turn-on voltage, and the intrinsically high speed and scalability of InP-based HBTs.<
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