Patent US4317092A successfully refreshed from Google Patents.
US4317092A
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Recursive low pass digital filter
Assignee: HP Inc
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Filing: 1980-06-30
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Granted: 1982-02-23
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Expires: 2000-06-30
Abstract
Abstract A recursive digital low-pass filter processes an input signal with essentially unity gain and sharp frequency cutoff without using multipliers to provide an output signal with an information bandwidth substantially one-half that of the input signal.
Inventors
- 👤 Ronald W. Potter
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 21:52
CPC Classifications
H; H03; H03H; H03H17/00; H03H17/02; H03H17/04; H03H17/0202
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
184 words
An apparatus for filtering a digital input signal representative of a sequence of substantially equally-spaced samples of a signal x(t) comprising: first combining means for providing a first signal in response to the combining of a feedback signal and said digital input signal; feedback means coupled to said first combining means for providing said feedback signal in response to said first signal; feedforward means coupled to said first combining means for delaying and scaling by selected values said first signal to provide a plurality of feedforward signals; and second combining means coupled to said feedforward means for producing a filtered digital output signal representative of a signal y(t) having an information bandwidth substantially one-half that of the signal x(t) in response to selected combinations of said feedforward signals and having a transfer function H(z) as the combination of signals from said first and second combining means, feedback means, and feedforward means, where: ##EQU12## z=e s Δt, which represents a time advance of Δt seconds; s is the complex variable of the LaPlace transform; B is a selected scaling; and n is a selected integer.
Claim 2
Independent Claim
184 words
An apparatus for filtering a digital input signal representative of a sequence of substantially equally-spaced samples of a signal x(t) comprising: first combining means for providing a first signal in response to the combining of a feedback signal and said digital input signal; feedback means coupled to said first combining means for providing said feedback signal in response to said first signal; feedforward means coupled to said first combining means for delaying and scaling by selected values said first signal to provide a plurality of feedforward signals; and second combining means coupled to said feedforward means for producing a filtered digital output signal representative of a signal y(t) having an information bandwidth substantially one-half that of the signal x(t) in response to selected combinations of said feedforward signals and having a transfer function H(z) as the combination of signals from said first and second combining means, feedback means, and feedforward means, where: ##EQU12## z=e s Δt, which represents a time advance of Δt seconds; s is the complex variable of the LaPlace transform; B is a selected scaling; and n is a selected integer.
Claim 3
Dependent Claim
232 words
The apparatus as in claim 1 wherein: (a) said feedback means comprises a first delay-scaler means for providing said feedback signal and said feedback signal is a representation of the complement of said first signal delayed and scaled one-half; (b) said feedforward means comprises: second delay-scaler means for providing a first feedforward signal in response to said first signal, said first feedforward signal being a representation of said first signal delayed and scaled one-half; first delay means for providing a second feedforward signal in response to said first signal; and third delay-scale means for providing a third feedforward signal in response to said first signal, said third feedforward signal being representative of said first signal delayed and scaled one-quarter; and (c) said second combining means comprises: first summer means for summing said first and second feedforward signals to provide a second signal; second delay means coupled to the output of said first summer for delaying said second signal; second summer means coupled to said second delay means for summing said delayed second signal and said second feedback signal to provide a third signal; fourth delay-scale means coupled to said second summer for providing a fourth signal representative of said third signal delayed and scaled one-half; and third summer means coupled to said fourth delay-scale means for summing said fourth signal and said third feedforward signal to provide said filter digital output signal.
Claim 4
Independent Claim
155 words
An apparatus for filtering a digital input signal comprising: feedback circuit means having a transfer function of H 0 (z)=z r /(z 2 +0.5) for providing an output signal in response to an input signal, wherein r is a selected integer; first feedforward circuit means having a transfer function of H 1 (z)=(z+1)/z 2 for providing an output signal in response to an input signal, wherein s is a selected integer; second feedforward circuit means having a transfer function of H 2 (z)=(z 2 +z+1)/z t for providing an output signal in response to an input signal, wherein t is a selected integer; scaling circuit means for providing an output signal representative of an input signal scaled by a selected factor B; and combination of said feedback, feedforward, and scaling circuit means coupled in series in a selected order to provide a circuit for a recursive digital filter having the transfer function: ##EQU13## wherein n=(s+t)-r.
Claim 5
Independent Claim
155 words
An apparatus for filtering a digital input signal comprising: feedback circuit means having a transfer function of H 0 (z)=z r /(z 2 +0.5) for providing an output signal in response to an input signal, wherein r is a selected integer; first feedforward circuit means having a transfer function of H 1 (z)=(z+1)/z 2 for providing an output signal in response to an input signal, wherein s is a selected integer; second feedforward circuit means having a transfer function of H 2 (z)=(z 2 +z+1)/z t for providing an output signal in response to an input signal, wherein t is a selected integer; scaling circuit means for providing an output signal representative of an input signal scaled by a selected factor B; and combination of said feedback, feedforward, and scaling circuit means coupled in series in a selected order to provide a circuit for a recursive digital filter having the transfer function: ##EQU13## wherein n=(s+t)-r.
Claim 6
Independent Claim
127 words
An apparatus for filtering a digital input signal comprising: feedback circuit means having a transfer function of H 0 (z)=z r /(z 2 +0.5) for providing an output signal in response to an input signal, wherein r is a selected integer; third feedforward circuit means having a transfer function of H 3 (z)=(z 3 +2z 2 +2z+1)/z s for providing an output signal in response to an input signal, wherein s is a selected integer; scaling circuit means for providing an output signal representative of an input signal scaled by a selected factor B; and combination of said feedback, feedforward, and scaling circuit means coupled in series in a selected order to provide a circuit for a recursive digital filter having the transfer function: ##EQU14## wherein n=s-r.
Claim 7
Independent Claim
127 words
An apparatus for filtering a digital input signal comprising: feedback circuit means having a transfer function of H 0 (z)=z r /(z 2 +0.5) for providing an output signal in response to an input signal, wherein r is a selected integer; third feedforward circuit means having a transfer function of H 3 (z)=(z 3 +2z 2 +2z+1)/z s for providing an output signal in response to an input signal, wherein s is a selected integer; scaling circuit means for providing an output signal representative of an input signal scaled by a selected factor B; and combination of said feedback, feedforward, and scaling circuit means coupled in series in a selected order to provide a circuit for a recursive digital filter having the transfer function: ##EQU14## wherein n=s-r.
Claim 8
Independent Claim
128 words
An apparatus for filtering a digital input signal comprising: first feedforward circuit means having a transfer function of H 1 (z)=(z+1)/z s for providing an output signal in response to an input signal, wherein s is a selected integer; fourth feedback-feedforward circuit means having a transfer function of H 4 (z)=z r (z 2 +z+1)/(z 2 +0.5) for providing an output signal in response to an input signal, wherein r is a selected integer; scaling circuit means for providing an output signal representative of an input signal scaled by a selected factor B; and combination of said first feedforward and said fourth feedback-feedforward circuit means coupled in series in a selected order to provide a circuit for a recursive digital filter having the transfer function: ##EQU15## wherein n=s-r.
Claim 9
Independent Claim
128 words
An apparatus for filtering a digital input signal comprising: first feedforward circuit means having a transfer function of H 1 (z)=(z+1)/z s for providing an output signal in response to an input signal, wherein s is a selected integer; fourth feedback-feedforward circuit means having a transfer function of H 4 (z)=z r (z 2 +z+1)/(z 2 +0.5) for providing an output signal in response to an input signal, wherein r is a selected integer; scaling circuit means for providing an output signal representative of an input signal scaled by a selected factor B; and combination of said first feedforward and said fourth feedback-feedforward circuit means coupled in series in a selected order to provide a circuit for a recursive digital filter having the transfer function: ##EQU15## wherein n=s-r.
References Cited (Backward Citations)
US3622916A
Cited
US3599108A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1985-02-22 | 1985-08-24 | 1986-02-23 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1989-02-22 | 1989-08-24 | 1990-02-23 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1993-02-22 | 1993-08-24 | 1994-02-23 | $7700.00 | Window Closed / Lapsed |