Tunable wideband active filter

Details Tunable wideband active filter Tunable wideband active filter

1992-02-28

1993-07-06

Mottola, Steven

Amplifiers

With semiconductor amplifying device

Including differential amplifier

330303, 330306, H03F 345, H03F 3191

Patent

active

052257908

ABSTRACT:
A wideband tunable (programmable) filter includes first-order and second-order filter circuits employing bipolar transistors. The bandwidth of the filter circuits are set by the product of the dynamic emitter resistance of the transistors and directly coupled on-chip capacitances. The filter bandwidth is inversely proportional to the time constant. To adjust the resonant frequency of the filter networks, emitter currents are varied, which in turn controls the emitter resistances. As the resonant frequency of the filter network is varied, the gain and normalized frequency response of the various output nodes remain constant. In the second-order configuration, the damping ratio of the filter is set using "positive" feedback, for a Q of greater than one-half, with a loop gain of less than one. Temperature compensation is accomplished by use of a temperature "dependent" voltage network. The output of this network provides the sum of the continuous temperature compensating voltage component and the externally controlled tuning voltage for the resonant frequency. This voltage is converted to currents that control the bandwidth of the filter so as to minimize dependence of the resonant frequency upon temperature.

REFERENCES:
patent: 4288754 (1981-09-01), Okada et al.
patent: 4381487 (1983-04-01), Erickson
patent: 4598256 (1986-07-01), Kinkel
patent: 5012201 (1991-04-01), Morita et al.

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