US3725799A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Pole frequency stabilized active rc filter
Assignee: AT&T Inc
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Filing: 1972-01-12
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Granted: 1973-04-03
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Expires: 1992-01-12
Abstract
Abstract In an active RC filter exhibiting a predetermined signal transfer characteristic, a reference signal is applied to the input of the filter and examined for phase shift at the low-pass signal output of the filter. A signal proportional to the variation in phase of the reference signal is used to alter a voltage controlled resistor, which in turn varies the pole frequency of the filter. The reference signal is cancelled from the signal appearing at the bandpass output of the filter to remove it from the final desired output of the filter.
Inventors
- 👤 R Cubbison
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 22:26
CPC Classifications
H; H03; H03H; H03H11/00; H03H11/02; H03H11/04; H03H11/12; H03H11/1217; H03H11/1252
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
94 words
In an active RC filter circuit, having a low-pass signal output terminal, a bandpass signal output terminal, and a signal transfer pole frequency determining voltage controlled resistor, the improvement comprising: means for applying a first predetermined reference signal to the filter circuit input terminal; means for multiplying the signal appearing at the low-pass output terminal of the filter circuit with a second predetermined reference signal to develop an error signal; and means responsive to said error signal for altering the resistance of the voltage controlled resistor to change the pole frequency of said filter.
Claim 2
Dependent Claim
94 words
In an active RC filter circuit, having a low-pass signal output terminal, a bandpass signal output terminal, and a signal transfer pole frequency determining voltage controlled resistor, the improvement comprising: means for applying a first predetermined reference signal to the filter circuit input terminal; means for multiplying the signal appearing at the low-pass output terminal of the filter circuit with a second predetermined reference signal to develop an error signal; and means responsive to said error signal for altering the resistance of the voltage controlled resistor to change the pole frequency of said filter.
Claim 3
Dependent Claim
91 words
The active RC filter circuit of claim 1 wherein said means for multiplying the signal appearing at the low-pass output terminal of said filter circuit with a second predetermined reference signal to develop an error signal further comprises: first transistor circuit means responsive to said first reference signal for developing a signal pulse during each alternate half-cycle of said first reference signal; and second transistor circuit means for selectively multiplying the signal appearing at the low-pass output terminal of said filter circuit with said pulses developed by said first transistor circuit.
Claim 4
Dependent Claim
52 words
The active RC filter circuit of claim 1 further comprising means for removing from said signal appearing at the low-pass output terminal of said filter circuit signal frequency components, substantially near the signal frequency of said first reference signal, resulting from an input signal applied to the input terminal of said filter.
Claim 5
Dependent Claim
148 words
In an active RC filter circuit, exhibiting a predetermined signal transfer response in response to an applied input signal, having a low-pass signal output terminal, a bandpass signal output terminal, and a signal transfer pole frequency determining voltage controlled resistor connecting said low-pass output terminal and the input terminal of said filter circuit, the improvement comprising: means for applying a first predetermined reference signal to said filter circuit input terminal; means for multiplying the signal appearing at the low-pass output terminal of said filter circuit with a second predetermined reference signal to develop an error signal; means responsive to said error signal for altering the resistance of said voltage controlled resistor to change the pole frequency of said filter transfer response; and means for cancelling said first reference signal from the signal appearing at said bandpass output terminal to develop a filtered version of said applied input signal.
Claim 6
Dependent Claim
148 words
In an active RC filter circuit, exhibiting a predetermined signal transfer response in response to an applied input signal, having a low-pass signal output terminal, a bandpass signal output terminal, and a signal transfer pole frequency determining voltage controlled resistor connecting said low-pass output terminal and the input terminal of said filter circuit, the improvement comprising: means for applying a first predetermined reference signal to said filter circuit input terminal; means for multiplying the signal appearing at the low-pass output terminal of said filter circuit with a second predetermined reference signal to develop an error signal; means responsive to said error signal for altering the resistance of said voltage controlled resistor to change the pole frequency of said filter transfer response; and means for cancelling said first reference signal from the signal appearing at said bandpass output terminal to develop a filtered version of said applied input signal.
Claim 7
Dependent Claim
91 words
The active RC filter circuit of claim 4 wherein said means for multiplying the signal appearing at the low-pass output terminal of said filter circuit with a second predetermined reference signal to develop an error signal further comprises: first transistor circuit means responsive to said first reference signal for developing a signal pulse during each alternate half-cycle of said first reference signal; and second transistor circuit means for selectively multiplying the signal appearing at the low-pass output terminal of said filter circuit with said pulses developed by said first transistor circuit.
Claim 8
Dependent Claim
45 words
The active RC filter circuit of claim 4 further comprising means for removing from said signal appearing at the low-pass output terminal of said filter circuit signal frequency components, substantially near the signal frequency of said first reference signal, due to said applied input signal.
Claim 9
Dependent Claim
114 words
In an active RC filter circuit, having a first filtered signal output terminal, a second filtered signal output terminal, and a signal transfer pole frequencY determining voltage controlled resistor, the improvement comprising: means for applying a first predetermined reference signal to the filter circuit input terminal; means for multiplying the signal appearing at said first filtered signal output terminal with a second predetermined reference signal to develop an error signal; means responsive to said error signal for altering the resistance of said voltage controlled resistor to change the pole frequency of the filter transfer response; and means for cancelling said first reference signal from the signal appearing at said second filtered signal output terminal.
Claim 10
Dependent Claim
114 words
In an active RC filter circuit, having a first filtered signal output terminal, a second filtered signal output terminal, and a signal transfer pole frequencY determining voltage controlled resistor, the improvement comprising: means for applying a first predetermined reference signal to the filter circuit input terminal; means for multiplying the signal appearing at said first filtered signal output terminal with a second predetermined reference signal to develop an error signal; means responsive to said error signal for altering the resistance of said voltage controlled resistor to change the pole frequency of the filter transfer response; and means for cancelling said first reference signal from the signal appearing at said second filtered signal output terminal.
Claim 11
Dependent Claim
65 words
The active RC filter circuit of claim 7 wherein said means for multiplying further comprises: first transistor circuit means responsive to said first reference signal for developing a signal pulse during predetermined intervals of said first reference signal; and second transistor circuit means for selectively multiplying the signal appearing at said first filtered signal output terminal with said pulses developed by said first transistor circuit.
Claim 12
Dependent Claim
41 words
The active RC filter circuit of claim 7 further comprising means for removing from said signal appearing at said first filtered signal output terminal of said filter circuit signal frequency components substantially near the signal frequency of said first reference signal.
Claim 13
Dependent Claim
156 words
In an active RC filter circuit, exhibiting a predetermined signal transfer response in response to an applied input signal, having a low-pass signal output terminal, a bandpass signal output terminal, and a signal transfer pole frequency determining voltage controlled resistor connecting said low-pass output terminal and the input terminal of said filter circuit, the improvement comprising: means for applying a first predetermined reference signal to said filter circuit input terminal; means for multiplying the signal appearing at the low-pass output terminal of said filter circuit with a second reference signal, having a predetermined phase relationship to said first reference signal, to develop an error signal; means for filtering said error signal; means responsive to said filtered error signal for altering the resistance of said voltage controlled resistor to change the pole frequency of said filter transfer response; and means for selectively combining said first reference signal and the signal appearing at said bandpass signal output terminal.
Claim 14
Dependent Claim
156 words
In an active RC filter circuit, exhibiting a predetermined signal transfer response in response to an applied input signal, having a low-pass signal output terminal, a bandpass signal output terminal, and a signal transfer pole frequency determining voltage controlled resistor connecting said low-pass output terminal and the input terminal of said filter circuit, the improvement comprising: means for applying a first predetermined reference signal to said filter circuit input terminal; means for multiplying the signal appearing at the low-pass output terminal of said filter circuit with a second reference signal, having a predetermined phase relationship to said first reference signal, to develop an error signal; means for filtering said error signal; means responsive to said filtered error signal for altering the resistance of said voltage controlled resistor to change the pole frequency of said filter transfer response; and means for selectively combining said first reference signal and the signal appearing at said bandpass signal output terminal.
Claim 15
Dependent Claim
91 words
The active RC filter circuit of claim 10 wherein said means for multiplying the signal appearing at the low-pass output terminal of said filter circuit with a second predetermined reference signal to develop an error signal further comprises: first transistor circuit means responsive to said first reference signal for developing a signal pulse during each alternate half-cycle of said first reference signal; and second transistor circuit means for selectively multiplying the signal appearing at the low-pass output terminal of said filter circuit with said pulses developed by said first transistor circuit.
Claim 16
Dependent Claim
45 words
The active RC filter circuit of claim 10 further comprising means for removing from said signal appearing at the low-pass output terminal of said filter circuit signal frequency components caused by said applied input signal substantially near the signal frequency of said first reference signal.
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) | 1976-04-02 | 1976-10-02 | 1977-04-03 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-04-02 | 1980-10-02 | 1981-04-03 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-04-02 | 1984-10-02 | 1985-04-03 | $7700.00 | Window Closed / Lapsed |