Patent US3876951A successfully refreshed from Google Patents.
US3876951A
Expired / Lapsed
US
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Digital filter circuits
Assignee: Johnson Service Co
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Filing: 1973-11-19
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Granted: 1975-04-08
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Expires: 1993-11-19
Abstract
Abstract An intrusion alarm system for providing an alarm indication in response to the detection of an intruder within a protected area includes Doppler radar apparatus having a transmitter for radiating energy into the protected area, a receiver for receiving Doppler signals provided whenever radiated energy is reflected off a moving body within the protected area and a signal detecting and filter circuit having a level detector circuit and a low pass digital filter circuit responsive to Doppler signals in excess of a predetermined amplitude and frequency to provide a logic level output indicative of the detection of an intruder within the protected area. In addition to the low pass digital filter circuit, there are described a high pass digital filter circuit and a digital band pass filter circuit.
Inventors
- 👤 Michael B Mclean
- 👤 Allen Rasmussen
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-02 16:40
CPC Classifications
H; H03; H03D; H03D3/00; H03D3/02; G; G01; G01S; G01S13/00; G01S13/02; G01S13/50; G01S13/52; G01S13/56
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
185 words
A low pass digital filter for providing a logic level output signal whenever the frequency of an input signal supplied to said digital filter over an input means is less than a predetermined cutoff frequency for said digital filter, said digital filter comprising reference means connected to an output of said input means and enabled by said input signal to provide a reference signal of a preselected duration representing the cutoff frequency for said digital filter, exclusive OR means connected to said output of said input means and to an output of said reference means for comparing the duration of said input signal with the duration of the reference signal to provide an enabling signal whenever the duration of one of the signals is greater than the duration of the other signal, and output means connected to said output of said input means and to an output of said exclusive OR means and controlled by said enabling signal and said input signal to provide said logic level output signal whenever the duration of said input signal is greater than the duration of said reference signal.
Claim 2
Dependent Claim
185 words
A low pass digital filter for providing a logic level output signal whenever the frequency of an input signal supplied to said digital filter over an input means is less than a predetermined cutoff frequency for said digital filter, said digital filter comprising reference means connected to an output of said input means and enabled by said input signal to provide a reference signal of a preselected duration representing the cutoff frequency for said digital filter, exclusive OR means connected to said output of said input means and to an output of said reference means for comparing the duration of said input signal with the duration of the reference signal to provide an enabling signal whenever the duration of one of the signals is greater than the duration of the other signal, and output means connected to said output of said input means and to an output of said exclusive OR means and controlled by said enabling signal and said input signal to provide said logic level output signal whenever the duration of said input signal is greater than the duration of said reference signal.
Claim 3
Dependent Claim
116 words
A low pass digital filter as set forth in claim 1 wherein said reference means includes monostable circuit means having an input connected to said output of said input means for receiving said input signal, said exclusive OR means having a first input connected to said output of said input means for receiving said input signal and a second input connected to an output of said monostable circuit means for receiving said reference signal, and said output means includes gating means having a first input connected to said output of said input means for receiving said input signal and a second input connected to the output of said exclusive OR means for receiving said enabling signal.
Claim 4
Dependent Claim
44 words
A low pass digital filter as set forth in claim 2 wherein said monostable circuit means includes an adjustable timing network for enabling the duration of said reference signal to be varied to thereby alter the cutoff frequency for said low pass filter circuit.
Claim 5
Dependent Claim
184 words
A high pass digital filter for providing a logic level output signal whenever the frequency of an input signal supplied to said digital filter over an input means is greater than a predetermined cutoff frequency for said digital filter, said digital filter comprising reference means connected to an output of said input means and enabled by said input signal to provide a reference signal of a preselected duration representing the cutoff frequency for said digital filter, exclusive OR means connected to said output of said input means and an output of said reference means for comparing the duration of said input signal with the duration of the reference signal to provide an enabling signal whenever the duration of one of the signals is greater than the duration of the other signal, and output means connected to said output of said reference means and to an output of said exclusive OR means and controlled by said enabling signal and said reference signal to provide said logic level output signal whenever the duration of said input signal is less than the duration of said reference signal.
Claim 6
Dependent Claim
184 words
A high pass digital filter for providing a logic level output signal whenever the frequency of an input signal supplied to said digital filter over an input means is greater than a predetermined cutoff frequency for said digital filter, said digital filter comprising reference means connected to an output of said input means and enabled by said input signal to provide a reference signal of a preselected duration representing the cutoff frequency for said digital filter, exclusive OR means connected to said output of said input means and an output of said reference means for comparing the duration of said input signal with the duration of the reference signal to provide an enabling signal whenever the duration of one of the signals is greater than the duration of the other signal, and output means connected to said output of said reference means and to an output of said exclusive OR means and controlled by said enabling signal and said reference signal to provide said logic level output signal whenever the duration of said input signal is less than the duration of said reference signal.
Claim 7
Dependent Claim
116 words
A high pass digital filter as set forth in claim 4 wherein said reference means includes monostable circuit means having an input connected to said output of said input means for receiving said input signal, said exclusive OR means having a first input connected to said output of said input means for receiving said signal and a second input connected to an output of said monostable circuit means for receiving said reference signal, and said output means includes gating means having a first input connected to said output of said monostable circuit means for receiving said reference signal and a second input connected to the output of said exclusive OR means for receiving said enabling signal.
Claim 8
Dependent Claim
43 words
A high pass digital filter as set forth in claim 5 wherein said monostable circuit means includes an adjustable timing network for enabling the duration of said reference signal to be varied to thereby alter the cutoff frequency for said high pass filter.
Claim 9
Dependent Claim
248 words
A digital bandpass filter for providing a logic level output signal whenever the frequency of an input signal supplied to said digital filter over an input means is within the pass band of said digital filter, said digital filter comprising first reference means connected to an output of said input means and enabled by said input signal to provide a first reference signal of a preselected duration representing the upper cutoff frequency for the pass band of said digital filter, first means connected to the pass output of said input means and to an output of said first reference means, said first means being controlled by said first reference signal and said input signal to provide a control signal having a duration related to the frequency of the input signal whenever the duration of said input signal is greater than the duration of said first reference signal, second reference means connected to an output of said first means and responsive to the control signal provided by said first means to provide a second reference signal of a preselected duration representing the lower cutoff frequency for thepass band of the digital filter, and second means connected to said output of said first means and an output of said second reference means, said second means being controlled by said second reference signal and said control signal to provide said logic level output signal whenever the duration of said control signal is less than the duration of said second reference signal.
Claim 10
Dependent Claim
248 words
A digital bandpass filter for providing a logic level output signal whenever the frequency of an input signal supplied to said digital filter over an input means is within the pass band of said digital filter, said digital filter comprising first reference means connected to an output of said input means and enabled by said input signal to provide a first reference signal of a preselected duration representing the upper cutoff frequency for the pass band of said digital filter, first means connected to the pass output of said input means and to an output of said first reference means, said first means being controlled by said first reference signal and said input signal to provide a control signal having a duration related to the frequency of the input signal whenever the duration of said input signal is greater than the duration of said first reference signal, second reference means connected to an output of said first means and responsive to the control signal provided by said first means to provide a second reference signal of a preselected duration representing the lower cutoff frequency for thepass band of the digital filter, and second means connected to said output of said first means and an output of said second reference means, said second means being controlled by said second reference signal and said control signal to provide said logic level output signal whenever the duration of said control signal is less than the duration of said second reference signal.
Claim 11
Dependent Claim
163 words
A digital bandpass filter as set forth in claim 7 wherein said first means includes exclusive OR means having a first input connected to said output of said input means for receiving said input signal, a second input connected to said output of said first reference means and an output, and gating means having a first input connected to said output of said input means for receiving said input signal and a second input connected to the output of said exclusive OR means and an output connected to an input of said second reference means, and wherein said second means includes further exclusive OR means having a first input connected to the output of said gating means, a second input connected to the output of said second reference means and an output, and further gating means having a first input connected to the output of said second reference means and a second input connected to the output of said further exclusive OR means.
Claim 12
Dependent Claim
91 words
A digital bandpass filter as set forth in claim 7 wherein said first reference means comprises a monostable circuit having an associated adjustable timing network for enabling the duration of said first reference signal to be varied to thereby alter the high frequency cutoff for said digital band pass filter, and wherein said second reference means comprises a further monostable circuit having an associated adjustable timing network for enabling the duration of said second reference signal to be varied to thereby alter the low frequency cutoff for said digital bandpass filter.
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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) | 1978-04-07 | 1978-10-07 | 1979-04-08 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-04-07 | 1982-10-07 | 1983-04-08 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-04-07 | 1986-10-07 | 1987-04-08 | $7700.00 | Window Closed / Lapsed |