US4496859A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Notch filter system
Assignee: BARCUS-BERRY ELECTRONICS Inc
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Filing: 1982-09-30
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Granted: 1985-01-29
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Expires: 2002-09-30
Abstract
Abstract A notch filter system for eliminating a specific "stop" frequency from an AC electrical input signal, such as 60 Hz "hum" from an audio program signal. An L/C tuned circuit that is tuned to the stop frequency is used to develop a modified input signal that is in phase with the input signal only at the stop frequency. The two signals are amplitude-balanced and fed to the respective inputs of a balanced differential amplifier which is responsive to both input signal phase and amplitude differences so as to cancel the signals at the stop frequency where they have the same phase and amplitude but not at frequencies above and below the stop frequency where they differ in phase and amplitude.
Inventors
- 👤 Robert C. Crooks
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 00:25
CPC Classifications
H; H03; H03H; H03H11/00; H03H11/02; H03H11/04; H03H11/12; H03H11/1217
Claims Analysis
Total Claims: 30
Claim 1
Independent Claim
138 words
A method of substantially eliminating a specific frequency from a first AC electrical signal, which comprises: applying said first signal to a tuned circuit that is tuned to said specific frequency and is phase-responsive to frequency variations above and below said specific frequency so as to develop a second AC electrical signal that is in phase with said first signal only at substantially said specific frequency; balancing the amplitudes of said first and second signals at said specific frequency; and applying said first and second signals as so balanced to the respective inputs of a differential amplifier that is responsive to input signal phase differences so as to substantially cancel said signals at substantially said specific frequency where they are in phase but not at frequencies above and below said specific frequency where they are not in phase.
Claim 2
Independent Claim
138 words
A method of substantially eliminating a specific frequency from a first AC electrical signal, which comprises: applying said first signal to a tuned circuit that is tuned to said specific frequency and is phase-responsive to frequency variations above and below said specific frequency so as to develop a second AC electrical signal that is in phase with said first signal only at substantially said specific frequency; balancing the amplitudes of said first and second signals at said specific frequency; and applying said first and second signals as so balanced to the respective inputs of a differential amplifier that is responsive to input signal phase differences so as to substantially cancel said signals at substantially said specific frequency where they are in phase but not at frequencies above and below said specific frequency where they are not in phase.
Claim 3
Dependent Claim
16 words
The method of claim 1, wherein said specific frequency is 60 Hz or a harmonic thereof.
Claim 4
Dependent Claim
47 words
The method of claim 1, wherein said tuned circuit to which said first signal is applied is also amplitude-responsive to frequency variations above and below said specific frequency, and said differential amplifier to which said balanced signals are applied is also responsive to input signal amplitude differences.
Claim 5
Dependent Claim
22 words
The method of claim 3, wherein said tuned circuit to which said first signal is applied is an L/C parallel tuned circuit.
Claim 6
Dependent Claim
17 words
The method of claim 4, wherein the inductor component of said tuned circuit is a passive inductor.
Claim 7
Dependent Claim
17 words
The method of claim 4, wherein the inductor component of said tuned circuit is an active inductor.
Claim 8
Dependent Claim
30 words
The method of claim 1, wherein said amplitude balancing is accomplished by adjusting the amplitude of one of said signals to be equal to the amplitude of the other signal.
Claim 9
Dependent Claim
17 words
The method of claim 7, wherein it is the amplitude of said second signal that is adjusted.
Claim 10
Dependent Claim
16 words
The method of claim 8, wherein said amplitude adjustment is accomplished by means of a potentiometer.
Claim 11
Dependent Claim
30 words
The method of claim 9, which comprises isolating said tuned circuit from said potentiometer by means of a voltage follower to avoid loading of the tuned circuit by the potentiometer.
Claim 12
Independent Claim
50 words
The method of claims 1 or 4, wherein said first signal is applied to said tuned circuit by applying said first signal across a voltage divider comprising a resistor and said tuned circuit, said second signal being developed at a voltage divider junction between said resistor and said tuned circuit.
Claim 13
Dependent Claim
24 words
The method of claim 1, wherein said specific frequency is substantially eliminated within a bandwidth of less than about 7% of said specific frequency.
Claim 14
Dependent Claim
17 words
The method of claim 1, wherein said specific frequency is attenuated to at least about 50 db.
Claim 15
Dependent Claim
24 words
The method of claim 1, wherein said specific frequency is attenuated within a response curve having slopes at least about 1,000 db per octave.
Claim 16
Dependent Claim
254 words
A notch filter system for substantially eliminating a specific frequency from a first AC electrical signal, which comprises: an input terminal to which said first signal is applied, and an output terminal; phase-responsive circuit means comprising a tuned circuit that is tuned to said specific frequency and is phase-responsive to frequency variations above and below said specific frequency, said phase-responsive circuit means having an output junction and being electrically connected to said input terminal for application of said first signal to said phase-responsive circuit means to develop a second AC electrical signal at said junction that is in phase with said first signal only at substantially said specific frequency; a differential amplifier having first and second inputs and having an output that is connected to said output terminal, said differential amplifier being responsive to input signal phase differences; first connection circuit means from said input terminal to said first amplifier input to deliver said first signal to said first amplifier input, and second connection circuit means from said junction to said second amplifier input to deliver said second signal to said second amplifier input; and balancing circuit means electrically connected to at least one of said connection circuit means for balancing the amplitudes of said first and second signals at said amplifier inputs at said specific frequency; said differential amplifier substantially cancelling said signals at said output terminal at substantially said specific frequency where they are in phase but not at frequencies above and below said specific frequency where they are not in phase.
Claim 17
Dependent Claim
254 words
A notch filter system for substantially eliminating a specific frequency from a first AC electrical signal, which comprises: an input terminal to which said first signal is applied, and an output terminal; phase-responsive circuit means comprising a tuned circuit that is tuned to said specific frequency and is phase-responsive to frequency variations above and below said specific frequency, said phase-responsive circuit means having an output junction and being electrically connected to said input terminal for application of said first signal to said phase-responsive circuit means to develop a second AC electrical signal at said junction that is in phase with said first signal only at substantially said specific frequency; a differential amplifier having first and second inputs and having an output that is connected to said output terminal, said differential amplifier being responsive to input signal phase differences; first connection circuit means from said input terminal to said first amplifier input to deliver said first signal to said first amplifier input, and second connection circuit means from said junction to said second amplifier input to deliver said second signal to said second amplifier input; and balancing circuit means electrically connected to at least one of said connection circuit means for balancing the amplitudes of said first and second signals at said amplifier inputs at said specific frequency; said differential amplifier substantially cancelling said signals at said output terminal at substantially said specific frequency where they are in phase but not at frequencies above and below said specific frequency where they are not in phase.
Claim 18
Dependent Claim
16 words
The system of claim 15, wherein said specific frequency is 60 Hz or a harmonic thereof.
Claim 19
Dependent Claim
34 words
The system of claim 15, wherein said phase-responsive circuit means is also amplitude-responsive to frequency variations above and below said specific frequency, and said differential amplifier is also responsive to input signal amplitude differences.
Claim 20
Dependent Claim
15 words
The system of claim 17, wherein said tuned circuit is an L/C parallel tuned circuit.
Claim 21
Dependent Claim
16 words
The system of claim 18, wherein the inductor-component of said tuned circuit is a passive inductor.
Claim 22
Dependent Claim
17 words
The system of claim 18, wherein the inductor component of said tuned circuit is an active inductor.
Claim 23
Dependent Claim
12 words
The system of claim 15, wherein said balancing circuit means is adjustable.
Claim 24
Dependent Claim
19 words
The system of claim 21, wherein said balancing circuit means is electrically connected to said second connection circuit means.
Claim 25
Dependent Claim
13 words
The system of claim 22, wherein said balancing circuit means comprises a potentiometer.
Claim 26
Dependent Claim
32 words
The system of claim 23, which comprises voltage follower means in said second connection circuit means between said phase-responsive circuit means and said potentiometer for isolating said tuned circuit from said potentiometer.
Claim 27
Independent Claim
38 words
The system of claims 15 or 18, wherein said phase-responsive circuit means comprises a voltage divider comprising a resistor and said tuned circuit, said junction being located in said voltage divider between said resistor and said tuned circuit.
Claim 28
Dependent Claim
20 words
The notch filter system of claim 15 which has a bandwidth of less than about 7% of said specific frequency.
Claim 29
Dependent Claim
21 words
The notch filter system of claim 15 which has an attenuation at said specific frequency of at least about 50 db.
Claim 30
Dependent Claim
21 words
The notch filter system of claim 15 which has a response curve with slopes at least about 1,000 db per octave.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1988-01-29 | 1988-07-30 | 1989-01-29 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1992-01-29 | 1992-07-30 | 1993-01-29 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1996-01-29 | 1996-07-30 | 1997-01-29 | $7700.00 | Window Closed / Lapsed |