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Voltage Difference Detector

IP.com Disclosure Number: IPCOM000045934D
Original Publication Date: 1983-May-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Murfet, PJ: AUTHOR

Abstract

A voltage difference detector with a transfer characteristic defining a voltage window provides an output signal in response to a differential input signal indicating whether or not the magnitude of the input signal lies within the upper and lower limits of the window.

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Voltage Difference Detector

A voltage difference detector with a transfer characteristic defining a voltage window provides an output signal in response to a differential input signal indicating whether or not the magnitude of the input signal lies within the upper and lower limits of the window.

The detector shown in Fig. 1 consists of two pairs of transistors T1, T2 and T3, T4 connected in long-tailed pair configuration to identical current sources each defining a combined emitter current I. Identical resistors R are provided in the emitter paths of transistors T1 and T3. The collectors of transistors T1 and T4 are connected to a common supply and the collectors of transistors T1 and T3 to a further current source defining a collector current of I/2. Input pads 1 and 2 are connected to the commoned bases of transistors T1, T4 and T2, T3 respectively. An output pad 3 is connected to the commoned collectors of transistors T1, T3.

In operation, the two halves of the circuit function as voltage comparators, with the comparator offset in each case being defined by the value of IR/2 caused by the presence of resistors R in the emitter paths of transistors T1, T3. The resulting transfer characteristic of the combined circuit forming the detector is shown in Fig. 2. Thus, with no input voltage across input pads l and 2, the voltage on output pad 3 is at an 'up' level. The output voltage remains at this level as the magnitude of the input voltage is differentially incre...