Combination Cmos/Bipolar Driver for High Capacitance
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-04
Bipolar transistors are frequently mentioned as supplements to complementary metal oxide semiconductor (CMOS) technology for applications like off-chip drivers where very heavy capacitance loading may be encountered. In some CMOS processes, a vertical bipolar transistor can be fabricated with little or no additional process complexity. The trick is to use the bipolar technology without encountering the power dissipation usually associated with bipolar techniques. Two circuits are proposed that use active drive to the bipolar transistors only during transients. Feedback techniques are employed to turn off the base drive and trap the base charge just prior to saturation. The bipolar transistors thus saturate but are not driven into deep saturation. CMOS technology maintains the drive levels in the steady state.