Patent US4509019A successfully refreshed from Google Patents.
US4509019A
Expired / Lapsed
US
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Tunable active filter
Assignee: Nokia Bell Labs
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Filing: 1983-01-27
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Granted: 1985-04-02
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Expires: 2003-01-27
Abstract
Abstract A tunable high-pass or low-pass filter employs a balanced amplifier having electronically controlled elements in either the two input or the two feedback paths (or both). A reactive element is placed in the other of the paths. Especially low distortion results from this arrangement, allowing convenient integrated circuit implementation with a nonlinear device (e.g., MOS transistor) as a voltage-controllable element. Multiple stages can be cascaded and controlled from a reference clock or other precision source for high accuracy.
Inventors
- 👤 Mihai Banu
- 👤 Yannis Tsividis
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 12:34
CPC Classifications
H; H03; H03H; H03H11/00; H03H11/02; H03H11/04; H03H11/12; H03G; H03G5/00; H03H11/1291
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
128 words
A filter comprising a balanced amplifier having an inverting input and a noninverting input, and an inverted output and a noninverted output, wherein a pair of first and second input paths are connected to said inverting input and said noninverting input, respectively, and wherein a pair of first and second feedback paths are connected between said noninverted output and said inverting input, and between said inverted output and said noninverting input, respectively, and wherein at least one of said pair of paths comprises an electronically controlled resistance in the form of a field effect transistor in each of said first and second paths therein, and wherein at least the other of said pair of paths comprises a reactive element in each of said first and second paths therein.
Claim 2
Dependent Claim
128 words
A filter comprising a balanced amplifier having an inverting input and a noninverting input, and an inverted output and a noninverted output, wherein a pair of first and second input paths are connected to said inverting input and said noninverting input, respectively, and wherein a pair of first and second feedback paths are connected between said noninverted output and said inverting input, and between said inverted output and said noninverting input, respectively, and wherein at least one of said pair of paths comprises an electronically controlled resistance in the form of a field effect transistor in each of said first and second paths therein, and wherein at least the other of said pair of paths comprises a reactive element in each of said first and second paths therein.
Claim 3
Dependent Claim
12 words
The filter of claim 1 wherein said reactive element is a capacitor.
Claim 4
Dependent Claim
28 words
The filter of claim 1 wherein said input paths each comprise said controlled resistance, and said feedback paths each comprises a capacitor, whereby a low-pass filter is obtained.
Claim 5
Dependent Claim
30 words
The filter of claim 1 wherein each of said input paths comprises a capacitor, and each of said feedback paths comprises said controlled resistance, whereby a high-pass filter is obtained.
Claim 6
Dependent Claim
22 words
The filter of claim 1 wherein the electronically controlled resistances therein are adapted to being controlled by reference to a precision source.
Claim 7
Dependent Claim
17 words
The filter of claim 1 wherein all of said elements are included on a single semiconductor chip.
Claim 8
Dependent Claim
50 words
The filter of claim 1 wherein the nonlinearity of said controlled resistances is sufficiently cancelled so that the total harmonic distortion introduced by said filter is at least 20 decibels less than if said controlled resistance and said reactance are located in only one of said first and second paths.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1988-04-01 | 1988-10-01 | 1989-04-02 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1992-04-01 | 1992-10-01 | 1993-04-02 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1996-04-01 | 1996-10-01 | 1997-04-02 | $7700.00 | Window Closed / Lapsed |