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Maximum and Minimum Voltage Detection

IP.com Disclosure Number: IPCOM000043933D
Original Publication Date: 1984-Oct-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Bhansali, M: AUTHOR [+2]

Abstract

Circuits for selecting either the largest or smallest of a group of analog voltages have many applications. This article describes integrated circuit implementations for these functions which provide accurate voltage outputs without temperature or process dependencies characteristic of comparable contemporary circuits. Figs. 1 and 2, respectively, illustrate circuit configurations for maximum voltage and minimum voltage detection, as presently contemplated. In Fig. 1, transistors Q1, Q2, Q2b and Q3 act as balanced current sources relative to node 1. Transistors Q4 - Q7 have common emitter connections to node 1, and separate base couplings to respective sources of input or "argument" voltages Ain, Bin, Cin and Din.

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Maximum and Minimum Voltage Detection

Circuits for selecting either the largest or smallest of a group of analog voltages have many applications. This article describes integrated circuit implementations for these functions which provide accurate voltage outputs without temperature or process dependencies characteristic of comparable contemporary circuits. Figs. 1 and 2, respectively, illustrate circuit configurations for maximum voltage and minimum voltage detection, as presently contemplated. In Fig. 1, transistors Q1, Q2, Q2b and Q3 act as balanced current sources relative to node 1. Transistors Q4 - Q7 have common emitter connections to node 1, and separate base couplings to respective sources of input or "argument" voltages Ain, Bin, Cin and Din. The voltage at node 1 is one VBE (base-to-emitter voltage) drop less than the largest of the inputs to Q4 - Q7, since the largest input at a base pulls up the emitter node (node 1) shutting off all other input devices. Since the current in all devices is the same (a reference current mirrored from Q1), transistors Q8 and Q9 translate the voltage at node 1 to a voltage precisely two VBE's higher than that at node 1, which transistor Q10 translates to a voltage reduced by one VBE (i.e., corresponding exactly to the maximum input voltage). In Fig. 2, transistors Q1, Q2, Q2b and Q3 act as current sources relative to node 2 which connects in common to emitters of transistors Q4 - Q7. Voltage inputs Ain - Din, the smalles...