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Combination Cmos/Bipolar Driver for High Capacitance

IP.com Disclosure Number: IPCOM000043509D
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Pricer, WD: AUTHOR

Abstract

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.

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Combination Cmos/Bipolar Driver for High Capacitance

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. Active drive recovers the weakly saturated bipolar drivers during the opposite transient. It is assumed that true and complement input drive exists for both circuits. This may be generated by a simple CMOS inverter or may already exist as in the case of a cascode voltage switch (CVS). For the first circuit (Fig. 1), when the true line (T) is held negative and the complement line (C) is held positive, only transistor T1 is conductive. T1 holds T3 nonconductive. When the true input line goes positive, T1 turns off and T2 turns on, allowing charge to flow from the true line (T) to the base of T3, turning on T3 . T2 remains conductive until the output approaches one threshold below...