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Internal Driver Circuit Using "Free" PNP Transistor

IP.com Disclosure Number: IPCOM000043406D
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Askin, HO: AUTHOR [+2]

Abstract

The above circuit can be used to drive high capacitance loads more rapidly than can a standard DTL (diode-transistor logic) circuit by improvements in open-collector driver performance. This is accomplished by providing the driver with a variable resistance load instead of the conventional constant resistance load, with the use of a "free" PNP transistor as an active resistor. The drawing shows a DTL circuit in which an output buffer has been formed. Transistor T1 with resistors R1, R2 and diodes D1, and D2 form a conventional DTL AND-invert gate. Resistor R3 is added to limit the current from the base of T2's. When at least one input is low, the base of T1 will be pulled low, turning off T1 . The bases of transistors T2 and T3 are then pulled high by R2, turning T2 off and T3 on, thereby forcing the output low.

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Internal Driver Circuit Using "Free" PNP Transistor

The above circuit can be used to drive high capacitance loads more rapidly than can a standard DTL (diode-transistor logic) circuit by improvements in open- collector driver performance. This is accomplished by providing the driver with a variable resistance load instead of the conventional constant resistance load, with the use of a "free" PNP transistor as an active resistor. The drawing shows a DTL circuit in which an output buffer has been formed. Transistor T1 with resistors R1, R2 and diodes D1, and D2 form a conventional DTL AND-invert gate. Resistor R3 is added to limit the current from the base of T2's. When at least one input is low, the base of T1 will be pulled low, turning off T1 . The bases of transistors T2 and T3 are then pulled high by R2, turning T2 off and T3 on, thereby forcing the output low. When all inputs are high, T1 is turned on by R1, causing the bases of T2 and T3 to be pulled low. T2 turns on, while T3 turns off, pulling the output high. Under these conditions R3 limits the base current drawn by T2 . Diodes DC1 and DC2 form antisaturation clamps for T2 and T3, respectively. The "free" PNP transistor, T2, obtained without additional process steps from the bipolar process by accepting a low beta, may be partially integrated with transistor T1 . The addition of the active pull-up device greatly improves driver circuit performance over standard DTL circuits with heavy loads.

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