Browse Prior Art Database

Analog Signal Selector Circuits

IP.com Disclosure Number: IPCOM000074065D
Original Publication Date: 1971-Mar-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 3 page(s) / 43K

Publishing Venue

IBM

Related People

Schultz, RA: AUTHOR

Abstract

A network of identical voltage comparator circuits selects, from the plural analog DC unipolar input signals being applied to its various inputs, the input signal having the maximum level and passes it to their commonly connected outputs.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 52% of the total text.

Page 1 of 3

Analog Signal Selector Circuits

A network of identical voltage comparator circuits selects, from the plural analog DC unipolar input signals being applied to its various inputs, the input signal having the maximum level and passes it to their commonly connected outputs.

For purposes of explanation, the illustrated circuit is adopted to select the most positive analog signal. With switch I closed and switches IIa - IIn open, assume that e1>e2, e1>e3, ... e1>en. Under these circumstances, only the operational amplifier 11 of the first comparator 10a passes the input signal e1 as signal -e1' to its output 13 and hence at output 12, signal e0=-e1. For each of the operational amplifiers of the other comparators 10b-10m, the feedback signal to its respective inverting input terminal (-) is far too negative. Therefore, each of the other operational amplifiers will have its output 13 driven as far positive as possible in an attempt to null its summing point 14. As the other operational amplifiers' outputs go positive, they are isolated from the selected output signal e0 by their respective reverse biased diode D2. As the diodes D1 of the other amplifiers 11 become turned on, the particular operational amplifier becomes balanced with each of the amplifier output signals e2', e3', ---en' being substantially equal to one diode drop above ground, i.e., drop across its respective associated diode D1. Thus, all the output signals of the unselected amplifiers are isolated from the output signal e0, which is being supplied exclusively by the output signal -e1' of amplifier 11 of the first comparator 10a, since the input signal e1 is the most positive in the given example. None of the diode drops of diodes D1 of the unselected amplifiers have an effect on the signal transmission due to the location of the feedback resistors R. Diode drops of the selected amplifier actually do represent an offset, but this offset is negligible since it is effectively reduced by a factor equal to the open-loop gain of the particular selected operational amplifier.

Resistor RB is provided to insure that even with an open-circuit load, there is enough current available to forward bias the particular selected amplifier's output diode D2.

To implement a circuit which selects the most negative input signal, each of the circuits 10a-10n is modified so that the diodes D1 and D2 are oppositely poled and the positive polarity of the bias voltage +Vb is changed to a negative one.

With switches IIa - IIn closed, identical logic/detector circuits 15a-15n are connected to the respective outputs 13 of the particular amplifiers 11 of comparators 10a-10n, respectively. This provides the circuit with the ability to detect which most positive input signal has been chosen, and supply an appropriate digital logic signal at standard logic level voltages. When...