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# Differential Threshold Detector Circuit

IP.com Disclosure Number: IPCOM000074952D
Original Publication Date: 1971-Jul-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 32K

IBM

## Related People

Chaloupka, JA: AUTHOR [+2]

## Abstract

The circuit shown will have an output at terminal 10 when the absolute difference between I/1/ and I/2/ exceeds the threshold of the circuit. When I/1/ = I/2/, the circuit is biased such that transistors 12 and 14 are off, and transistor 16 is on.

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Differential Threshold Detector Circuit

The circuit shown will have an output at terminal 10 when the absolute difference between I/1/ and I/2/ exceeds the threshold of the circuit. When I/1/ = I/2/, the circuit is biased such that transistors 12 and 14 are off, and transistor 16 is on.

The emitter of transistor 12 is back-biased to the extent of the V(BE) voltage of transistor 16, plus the voltage drop across resistor 18. Similarly, transistor 14 is back-biased to the extent of the VBE voltage of transistor 16 and the voltage drop across resistor 20. The voltage drop across resistor 18 is a function of the current I/1/,the voltage bias (+V), and accordingly, the current through bias resistors 22 and 24. Similarly, the current through resistor 20 and thus its voltage drop is a function of the current I/2/, the bias voltage (+V), and resistors 22 and
26. Resistor 28, attached to the collector of transistor 16, is a load resistor. The voltage output of the circuit at terminal 10 is at a low level when transistor 16 is on, and rises to +V bias level when transistor 16 turns off.

As an example of operation, assume that current I1 decreases and current I/2/increases. As the input currents I1 and 12 are differential, -- equal in magnitude and opposite in direction -- the voltage at node 30 will remain unchanged. The voltage at node 32 will increase while the voltage at node 34 will decrease. If the differential current difference exceeds the level predetermined for the...