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Differential Signal Circuit With Current Mirror Transistors

IP.com Disclosure Number: IPCOM000059830D
Original Publication Date: 1986-Jan-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Beers, HR: AUTHOR

Abstract

The circuit of the drawing produces a binary valued voltage at a terminal Out according to the difference between the signals at its input terminals A and B. Terminals A and B are connected to a current source I1 through identical branches formed by transistors T1 to T4 that are connected as diodes. When the voltag terminal A is higher than the voltage at terminal B, the two diodes in the branch of terminal B are reverse biased, and all of the current from source I1 flows in the branch of terminal A. Conversely, when the voltage of terminal B is higher, no current flows in the branch of terminal A.

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Differential Signal Circuit With Current Mirror Transistors

The circuit of the drawing produces a binary valued voltage at a terminal Out according to the difference between the signals at its input terminals A and B. Terminals A and B are connected to a current source I1 through identical branches formed by transistors T1 to T4 that are connected as diodes. When the voltag terminal A is higher than the voltage at terminal B, the two diodes in the branch of terminal B are reverse biased, and all of the current from source I1 flows in the branch of terminal A. Conversely, when the voltage of terminal B is higher, no current flows in the branch of terminal A. Transistors T4 and T5 are connected in a current mirror configuration: the base-emitter junctions of transistors T4 and T5 have substantially identical characteristics so that the base-emitter current in T4 produces the appropriate voltage at the base terminal of T5 to cause T5 to have the same emitter current as T4. Thus, when the voltage at terminal B is higher than the voltage at terminal A, about half of the current of source I1 flows in the base-emitter circuit of transistor T5 and thereby turns on transistor T5. Additional diodes can be located in the branches of the input terminals to adapt the circuit to higher input voltage levels. Transistor T6 forms an output stage. The series combination of resistor R2 and current source I2 adjusts the range of the output voltage.

Disclosed anonymously.

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