High-Speed, High-Accuracy Voltage Comparators Implemented with GaAs/(GaAl)As Heterojunction Bipolar Transistors

The first voltage comparators implemented with GaAs/(GaAl)As heterojunction bipolar transistors (HBTs) are reported. On a quasi-static basis, the offset voltage was found to be generally below 4 mV, and hysteresis about 1 mV. The HBT comparators could be clocked at frequencies above 2.5 GHz. They operated over a range of reference voltage of 2 V. The preliminary yield was high. These results indicate that the HBT comparators are suitable for flash analog-to-digital converters with up to 8 bit accuracy, and sampling rates well above 1 GHz.