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Bidirectional Bipolar Electronic Switch

IP.com Disclosure Number: IPCOM000047515D
Original Publication Date: 1983-Nov-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Bhansali, MM: AUTHOR [+3]

Abstract

Electronic switching of bidirectional signals is achieved in bipolar technology. Switching of a bidirectional signal from point A to point B is achieved in bipolar technology (Fig. 1A). This capability is identical to that of a field-effect transistor (FET) switch (Fig. 1B) but may not be accomplished identically in bipolar technology. A typical bipolar switch is unidirectional (Fig. 1C). The FET switch of Fig. 1B will switch a signal of any voltage from node A to node B or vice versa as will the switch of Fig. 1A. The typical bipolar open collector switch of Fig. 1C, however, will only switch a signal from node A to -V. This constraint places an artificial limit on circuits designed in bipolar technology. In the bidirectional bipolar switch of Fig. 2, transistor T1 or T2 forms the signal path.

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Bidirectional Bipolar Electronic Switch

Electronic switching of bidirectional signals is achieved in bipolar technology. Switching of a bidirectional signal from point A to point B is achieved in bipolar technology (Fig. 1A). This capability is identical to that of a field-effect transistor (FET) switch (Fig. 1B) but may not be accomplished identically in bipolar technology. A typical bipolar switch is unidirectional (Fig. 1C). The FET switch of Fig. 1B will switch a signal of any voltage from node A to node B or vice versa as will the switch of Fig. 1A. The typical bipolar open collector switch of Fig. 1C, however, will only switch a signal from node A to -V. This constraint places an artificial limit on circuits designed in bipolar technology. In the bidirectional bipolar switch of Fig. 2, transistor T1 or T2 forms the signal path. When current enters node J from transistor T6, T1 or T2 will turn on dependent on input polarity. Transistors T3 and T4 form the high impedance current mirror source. Transistor T5 is the current shunt path to route the drive current (I drive) away from node J, leaving T1 and T2 off (open switch condition). The circuit functions bidirectionally since the collectors of T4 and T6 are in high impedance states, allowing their voltages to be set by the greater of the voltages at nodes A and B. Thus, as in the FET switch of Fig. 1B, the voltages at A or B may be any value between +V and -V.

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