Low voltage techniques for high speed digital bipolar circuits

Abstract

This paper describes design techniques for multi-GHz digital bipolar circuits that operate with supply voltages as low as 1.5 V. Examples include a multiplexer (MUX), a latch, two exclusive OR (XOR) gates, and a buffer/level shifter, circuits that typically employ stacked differential pairs in conventional ECL and hence do not easily lend themselves to low voltage operation. When implemented in a 1.5 /spl mu/m, 12-GHz bipolar technology, these circuits exhibit a speed comparable with that of their 1.5 V CMOS counterparts designed in a 0.5 /spl mu/m process with a threshold voltage of 0.5 V. These results suggest that, although V/sub BE/ of bipolar transistors does not scale as easily as the threshold voltage of MOS devices, the large bipolar transconductance can be advantageous even in 1.5 V systems. In order to ensure reliable operation, the circuits described herein employ 400 mV single-ended swings and can also provide differential outputs.