US3714588A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Self tuning bandpass filter
Assignee: National Aeronautics and Space Administration
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Filing: 1970-10-13
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Granted: 1973-01-30
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Expires: 1990-10-13
Abstract
Abstract An electronic filter which simultaneously maintains a constant bandwidth and a constant center frequency gain as the input signal frequency varies, and remains self-tuning to that center frequency over a decade range. The filter utilizes a field effect transistor (FET) as a voltage variable resistance in the bandpass frequency determining circuit. The FET is responsive to a phase detector to achieve self-tuning.
Inventors
- 👤 G Deboo
- 👤 R Hedlund
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 11:30
CPC Classifications
H; H03; H03J; H03J7/00; H03J7/02; H03J7/04; H03J7/08; H03H; H03H11/00; H03H11/02; H03H11/04; H03H11/12; H03H11/1291
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
177 words
A self-tuning, constant-bandwidth, constant-gain filter device comprising: a filter circuit for receiving an input signal and operative to provide an output signal, said filter circuit having a passband of a constant bandwidth and a constant gain and including a variable impedance means responsive to a control signal for determining the center frequency of said passband; a phase detector responsive to said input signal and said output signal for developing said control signal in response to the phase relationship between said input and output signals; said filter means including an operational amplifier having first and second input terminals and an output terminal, an input circuit including a first resistor and a first capacitor connected in series for coupling said input signal to said first input terminal, the connection between said first resistor and said first capacitor forming a junction, a capacitive feedback circuit coupling said output terminal and said junction, a resistive feedback circuit coupling said output terminal and said first input terminal, and said variable impedance means being coupled between said junction and Said second input terminal.
Claim 2
Dependent Claim
177 words
A self-tuning, constant-bandwidth, constant-gain filter device comprising: a filter circuit for receiving an input signal and operative to provide an output signal, said filter circuit having a passband of a constant bandwidth and a constant gain and including a variable impedance means responsive to a control signal for determining the center frequency of said passband; a phase detector responsive to said input signal and said output signal for developing said control signal in response to the phase relationship between said input and output signals; said filter means including an operational amplifier having first and second input terminals and an output terminal, an input circuit including a first resistor and a first capacitor connected in series for coupling said input signal to said first input terminal, the connection between said first resistor and said first capacitor forming a junction, a capacitive feedback circuit coupling said output terminal and said junction, a resistive feedback circuit coupling said output terminal and said first input terminal, and said variable impedance means being coupled between said junction and Said second input terminal.
Claim 3
Dependent Claim
177 words
A self-tuning, constant-bandwidth, constant-gain filter device comprising: a filter circuit for receiving an input signal and operative to provide an output signal, said filter circuit having a passband of a constant bandwidth and a constant gain and including a variable impedance means responsive to a control signal for determining the center frequency of said passband; a phase detector responsive to said input signal and said output signal for developing said control signal in response to the phase relationship between said input and output signals; said filter means including an operational amplifier having first and second input terminals and an output terminal, an input circuit including a first resistor and a first capacitor connected in series for coupling said input signal to said first input terminal, the connection between said first resistor and said first capacitor forming a junction, a capacitive feedback circuit coupling said output terminal and said junction, a resistive feedback circuit coupling said output terminal and said first input terminal, and said variable impedance means being coupled between said junction and Said second input terminal.
Claim 4
Dependent Claim
177 words
A self-tuning, constant-bandwidth, constant-gain filter device comprising: a filter circuit for receiving an input signal and operative to provide an output signal, said filter circuit having a passband of a constant bandwidth and a constant gain and including a variable impedance means responsive to a control signal for determining the center frequency of said passband; a phase detector responsive to said input signal and said output signal for developing said control signal in response to the phase relationship between said input and output signals; said filter means including an operational amplifier having first and second input terminals and an output terminal, an input circuit including a first resistor and a first capacitor connected in series for coupling said input signal to said first input terminal, the connection between said first resistor and said first capacitor forming a junction, a capacitive feedback circuit coupling said output terminal and said junction, a resistive feedback circuit coupling said output terminal and said first input terminal, and said variable impedance means being coupled between said junction and Said second input terminal.
Claim 5
Dependent Claim
112 words
A self-tuning, constant-bandwidth, constant-gain filter device as recited in claim 1 wherein said phase detector includes a differentiator for differentiating the signal appearing at said output terminal, comparator means responsive to the output of said differentiator and the signal appearing at said first input terminal for generating a square-wave signal, logic circuit means coupled to said comparator means for rectifying said square-wave signal and producing a d-c output voltage, means coupled to said logic circuit means for offsetting the average of said d-c voltage, an integrator having an input and an output, said logic circuit means being coupled to said integrator input, and said control signal being produced at said integrator output.
Claim 6
Dependent Claim
29 words
A self-tuning, constant-bandwidth, constant-gain filter device as recited in claim 1 wherein said variable impedance means is a variable resistance means coupled between said junction and second input terminal.
Claim 7
Dependent Claim
61 words
A self-tuning, constant-bandwidth, constant-gain filter device as recited in claim 3 wherein said variable resistance means is a field-effect transistor having a gate electrode, a source electrode, and a drain electrode, said drain electrode being coupled to said junction, said source electrode being coupled to said second input terminal, and said gate being coupled to the output of said phase detector.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-01-30 | 1976-07-31 | 1977-01-30 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-01-30 | 1980-07-31 | 1981-01-30 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-01-30 | 1984-07-31 | 1985-01-30 | $7700.00 | Window Closed / Lapsed |