Browse Prior Art Database

Filter Circuit

IP.com Disclosure Number: IPCOM000098773D
Original Publication Date: 1959-Dec-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 61K

Publishing Venue

IBM

Related People

Dersch, WC: AUTHOR

Abstract

An amplifier having input terminals 1 and output terminals 2, shown at the top, is arranged to pass selective bands of frequencies in response to a control voltage which acts to change the parameters of a parallel T band rejection filter 3 connected in the negative feedback path of the amplifier.

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 71% of the total text.

Page 1 of 2

Filter Circuit

An amplifier having input terminals 1 and output terminals 2, shown at the top, is arranged to pass selective bands of frequencies in response to a control voltage which acts to change the parameters of a parallel T band rejection filter 3 connected in the negative feedback path of the amplifier.

The band rejection characteristics of the filter 3 are varied by changing the impedance values of three resistors 4, 5 and 6.

As shown at the bottom, each of the three resistors 4, 5, and 6 comprises a plurality of resistors 4', 5' and 6' which may be selectively connected in parallel by a sequence of relays 7, 8, 9 and 10 which are responsive to a control voltage appearing at an input terminal 11 and operable by voltage comparator units 12, 13, 14 and 15 which respond variously to the voltage differential between terminals 11 and 16.

The twin-T filter 3 comprises a high pass T section including a pair of serially connected capacitors 17 and 18 and the resistor 6 and a low pass T section including the two resistors 4 and 5 and a capacitor 19.

By varying the values of resistors 4, 5 and 6, the band of frequencies which are rejected by the filter 3 may be shifted, and correspondingly those same frequencies become the new pass bands of the amplifier. If the values of the capacitors 17, 18 and 19 and the resistors 4, 5, and 6 are judiciously chosen, the various rejection bands and pass bands may be maintained at very closely the same width measured in cycles a...