I.sub.cct leakage current interrupter

Abstract

An electronic switch to be used in BiCMOS circuitry when CMOS stages are controlled by logic output from (bipolar) TTL stages. Its purpose is to avoid the static leakage current I.sub.cct which can occur in a CMOS stage when the pulldown transistor is turned on while the pullup transistor is not completely turned off. This is a problem which arises when CMOS and TTL stages are coupled; the logic-high output from a TTL stage is sufficient in magnitude to turn on the CMOS pulldown transistor but not to turn off the CMOS pullup transistor. The present invention introduces an ancillary input to the subcircuit encompassing the CMOS input stage and also an ancillary output from one of the CMOS stages of the subcircuit (typically an output buffer) encompassing the TTL output stage. The ancillary output is chosen so as to provide a CMOS logic-high signal whenever the TTL stage is outputting a TTL logic-high signal. The ancillary input is connected to the control node of a switching transistor interposed between V.sub.cc and the CMOS input stage's pullup transistor. In this manner, the source of I.sub.cct is interrupted immediately after the CMOS stage is switched from pull-up mode to pull-down mode. The invention has particular applicability to latched transceivers, where the CMOS input stage is located in the latch circuit and the TTL in the tristate output buffer circuit.