Browse Prior Art Database

Second Order Active Filter

IP.com Disclosure Number: IPCOM000053192D
Original Publication Date: 1981-Sep-01
Included in the Prior Art Database: 2005-Feb-12
Document File: 3 page(s) / 75K

Publishing Venue

IBM

Related People

Lewkowitz, J: AUTHOR [+2]

Abstract

Active filters which make use of resistor-capacitor networks and operational amplifiers are well known. The active filter concept was developed to eliminate the need for inductors, which are the most troublesome element in passive filters, especially in low frequency applications.

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 64% of the total text.

Page 1 of 3

Second Order Active Filter

Active filters which make use of resistor-capacitor networks and operational amplifiers are well known. The active filter concept was developed to eliminate the need for inductors, which are the most troublesome element in passive filters, especially in low frequency applications.

High frequency applications of active filters are limited by the gain bandwidth product of operational amplifiers. A new class of active filters is described which makes use of high frequency amplifiers with a predetermined transfer function. This type of filter is suitable for high frequency applications and a high level of circuit integration.

Previously, operational amplifiers used in active filters had a fixed frequency response characterized by one pole roll-off, while the RC network was of second order (two poles). Consequently, when the limited gain bandwidth product of an operational amplifier is taken into account, the ideal second-order active filter becomes a third-order system. In other words, the transfer function of the second-order filter is modified by one pole roll-off of an amplifier. This effect is more pronounced when the operation of the active filter is closer to the gain bandwidth product limit of an operational amplifier.

The present technique solves this problem by making the transfer function of the amplifier selectable and part of the second order system. Therefore, the RC network contributes one pole and the amplifier the second pol...