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Tristate Driver Utilizing Bipolar Complementary Metal Oxide Semiconductor Technology

IP.com Disclosure Number: IPCOM000080651D
Original Publication Date: 1974-Jan-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Kraft, WR: AUTHOR [+3]

Abstract

This driver circuit features a small signal swing and good transient performance, without the use of any DC power in the base drive bias network of the bipolar output transistor.

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Tristate Driver Utilizing Bipolar Complementary Metal Oxide Semiconductor Technology

This driver circuit features a small signal swing and good transient performance, without the use of any DC power in the base drive bias network of the bipolar output transistor.

Referring to the figure, with the complementary metal-oxide semiconductor (CMOS) input at 8.5 volts, device N2 is ON and N4 is OFF. Base drive for bipolar transistor T1 is supplied through the series path of N2 and N3; and the output of T1 rises to one Vbe drop below the 3.0 v. supply.

With the CMOS input at the ground level, N2 is OFF, N4 is ON and, device T1 turns OFF. Concurrently N6 turns ON, supplying base current to bipolar transistor T2, thereby initiating a pulldown of the output line toward ground. At the same time, device N9 is conducting in parallel with T2. Device N7 serves as a large resistor so that the base of T2 does not float when N6 is turned OFF. Because the base drive for T2 is supplied by output capacitance, no DC biasing path exists. Device N9 serves to keep the output impedance of the driver at a reasonably low value after T2 ceases to conduct. In a practical circuit, device N9 may not be necessary.

For a normal bistate operation, the gates of N3 and N8 are biased at +8.5 volts, while device N5 is biased at ground. However, when a floating output is desired, N3 and N8 are turned OFF and N5 is turned ON, thereby turning OFF both bipolar devices T1 and T2 and causing the output to fl...