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A switched resistor resonator for an active bandpass filter is disclos which minimizes the number of resistors required to achieve variable bandpass characteristics.
English (United States)
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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
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
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,...