Patent US3883727A successfully refreshed from Google Patents.
US3883727A
Expired / Lapsed
US
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Multilevel digital filter
Assignee: DOWTY COMMUNICATIONS Inc A CORP OF
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Filing: 1972-07-05
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Granted: 1975-05-13
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Expires: 1992-07-05
Abstract
Abstract A multi-level digital filter system applicable to modems is provided. The incoming data is read serially into M shift registers and read out in parallel by M further shift registers under the control of an M-bit clock, where M log2N and N is the number of levels. After appropriate conditioning by a logic control circuit, the parallel outputs are filtered separately by M digital shaping filters. The shaping filters each comprise a chain of shift registers the outputs of which are weighted by a resistor network and summed to produce a desired time response, which in an exemplary embodiment is the inverse Fourier transform of an ideal low-pass filter. Summing of the filter outputs produces an N-level signal.
Inventors
- 👤 Richard L Stuart
- 👤 Arvind M Bhopale
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 09:04
CPC Classifications
H; H03; H03H; H03H17/00; H03H17/02; H03H17/0283; H03H17/0286; H03H17/0289; H03H2218/00; H03H2218/12
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
120 words
A four-level digital filter system for data modems comprising means for converting the incoming data input into first and second parallel inputs, logic control means connected to said inputs for converting said inputs into a sign bit output and an amplitude bit output, first and second digital shaping filters connected to the said outputs for shaping each said output into the inverse Fourier transform of the time response of a substantially ideal low-pass filter, means for adding a bias term to the outputs of one of said digital shaping filters so as to produce a modified output, and summing means for summing said modified output with the output of the other of said digital filters to produce a four-level signal.
Claim 2
Dependent Claim
120 words
A four-level digital filter system for data modems comprising means for converting the incoming data input into first and second parallel inputs, logic control means connected to said inputs for converting said inputs into a sign bit output and an amplitude bit output, first and second digital shaping filters connected to the said outputs for shaping each said output into the inverse Fourier transform of the time response of a substantially ideal low-pass filter, means for adding a bias term to the outputs of one of said digital shaping filters so as to produce a modified output, and summing means for summing said modified output with the output of the other of said digital filters to produce a four-level signal.
Claim 3
Dependent Claim
56 words
A system as claimed in claim 1 wherein said summing means comprises an operational amplifier having a first input connected to said modified output through a first resistor and a econd input connected to the output of said other digital filter through a second resistor having a value equal to twice that of said firstt resistor.
Claim 4
Dependent Claim
61 words
A system as claimed in claim 1 wherein said logic control means comprises means for directly connecting said first parallel input to the input of said first digital filter and an exclusive-Or gate having a first input connected to said first parallel input, a second input connected to said second parallel input and an output connected to said second digital filter.
Claim 5
Dependent Claim
42 words
A system as claimed in claim 1 wherein one oF the digital filters produces a truncated sinx/x waveform shaped in accordance with the window function Ko and K1 are constants and the function exists for the truncated period t 0 to 2T1.
Claim 6
Dependent Claim
13 words
A system as claimed in claim 4 wherein Ko 0.538 and K1 0.462.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-05-12 | 1978-11-11 | 1979-05-13 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-05-12 | 1982-11-11 | 1983-05-13 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-05-12 | 1986-11-11 | 1987-05-13 | $7700.00 | Window Closed / Lapsed |