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Switched Resistor Resonator for an Active Bandpass Filter

IP.com Disclosure Number: IPCOM000051612D
Original Publication Date: 1981-Feb-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Zumbado, JA: AUTHOR

Abstract

A switched resistor resonator for an active bandpass filter is disclos which minimizes the number of resistors required to achieve variable bandpass characteristics.

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Switched Resistor Resonator for an Active Bandpass Filter

A switched resistor resonator for an active bandpass filter is disclos which minimizes the number of resistors required to achieve variable bandpass characteristics.

High-order active filters are implemented using combinations of second-order resonators. This article presents a method of modifying a second-order biquad bandpass resonator to achieve variable filter frequencies, for the filter case having constant resonator quality, Q, by switching only one resistor.

Using known design techniques, resonators are designed for each desired frequency, to a required gain and Q, resulting in different resistor values for each resonator. As an example, for the resonator in the figure, R9, R10, R11 and R12, connected to the four type HA4602 amplifiers, as shown, would have three different values for three frequency bands. During the design, it was noticed that the variations on resistors R9, R10, R11 and R12 were minimal, most of the frequency changes being governed by R9. By forcing all resistors, except R9 to have the same value for all three frequencies, a new value was calculated for R9. The value of R9 is given by the relationship: R9 = 1 over (2 pi f) R10 (1). where f is the desired bandpass center frequency. For this resonator, R10 = R11 = R12 (2). and can be calculated by the relationships given on page 141 of Johnson and Hilburn, Rapid Practical Designs of Active Filters, John Wiley & Sons, Inc., New York,...