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# Logic Signal Level Shift Circuit

IP.com Disclosure Number: IPCOM000090814D
Original Publication Date: 1969-Jul-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 32K

IBM

## Related People

Taylor, DM: AUTHOR [+1]

## Abstract

This circuit enables interfacing of current switch logic with circuits operated at different voltage levels. By proper selection of resistor R1, transistor Q1 is maintained conducting at all times while transistors Q2 and Q3 supply a constant current through resistor R2. This establishes a fixed voltage drop across R2. Therefore any voltage change at the base of Q1 is shifted by an amount IR2 to the base of transistor Q5. The potential at the emitter of Q5 relative to the potential at the emitter of transistor Q10 controls which path the current takes through the current switch consisting of transistors Q6, Q7, and Q8. The level at the emitter of Q10 is a fixed reference level determined by reference source consisting of transistors Q9. Q10, Q11 resistor R13, and diodes CD2 and CD3.

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Logic Signal Level Shift Circuit

This circuit enables interfacing of current switch logic with circuits operated at different voltage levels. By proper selection of resistor R1, transistor Q1 is maintained conducting at all times while transistors Q2 and Q3 supply a constant current through resistor R2. This establishes a fixed voltage drop across R2. Therefore any voltage change at the base of Q1 is shifted by an amount IR2 to the base of transistor Q5. The potential at the emitter of Q5 relative to the potential at the emitter of transistor Q10 controls which path the current takes through the current switch consisting of transistors Q6, Q7, and Q8. The level at the emitter of Q10 is a fixed reference level determined by reference source consisting of transistors Q9. Q10, Q11 resistor R13, and diodes CD2 and CD3. This circuit shifts the voltage Vin supplied by the amount IR2 to a level compatible with the current switch logic. Transistors Q12 and Q13 provide an emitter-follower output for the circuit.

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