Patent US4721870A successfully refreshed from Google Patents.
US4721870A
Expired / Lapsed
US
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Filtering of electromagnetic interference from a digital signal
Assignee: Caterpillar Inc
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Filing: 1986-10-03
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Granted: 1988-01-26
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Expires: 2006-10-03
Abstract
Abstract An apparatus for filtering radio frequency interference from digital signals. The filter uses a resistor, an inductor and a capacitor to provide a filter with a broad bandwidth capable of passing high frequency digital signals, while severely attenuating radio frequencies coupled to the digital signals. The filter is used primarily in conjunction with an electronic control to filter input signals to the control from remote sensors.
Inventors
- 👤 Stephen W. Rector
- 👤 Gwenne A. E. Henricks
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 16:31
CPC Classifications
H; H03; H03H; H03H1/00; H03H1/0007; H03H7/00; H03H7/01
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
92 words
An apparatus for filtering a digital input signal, comprising: a current limiting resistor having first and second terminals, said first terminal for receiving said digital signal; an inductor having first and second terminals, said first terminal being connected to the second terminal of said resistor and forming a junction; a capacitor having a first terminal connected to the junction of said resistor and inductor, and having a second terminal connected to a circuit ground; and a metal oxide semiconductor gate having an input connected only to the second terminal of said inductor.
Claim 2
Independent Claim
92 words
An apparatus for filtering a digital input signal, comprising: a current limiting resistor having first and second terminals, said first terminal for receiving said digital signal; an inductor having first and second terminals, said first terminal being connected to the second terminal of said resistor and forming a junction; a capacitor having a first terminal connected to the junction of said resistor and inductor, and having a second terminal connected to a circuit ground; and a metal oxide semiconductor gate having an input connected only to the second terminal of said inductor.
Claim 3
Dependent Claim
23 words
The apparatus, as set forth in claim 1, wherein digital input signals are receivable on the first terminal of said current limiting resistor.
Claim 4
Dependent Claim
16 words
The apparatus as set forth in claim 1, wherein said inductor inhibits radio frequency radiation transmission.
Claim 5
Dependent Claim
37 words
The apparatus, as set forth in claim 3, wherein said inductor, upon reception of radio frequency radiation, attains a sufficiently high impedance to inhibit transmission of the radio frequency radiation to said metal oxide semiconductor gate input.
Claim 6
Dependent Claim
19 words
The apparatus, as set forth in claim 1, wherein said capacitor transmits radio frequency radiation to the circuit ground.
Claim 7
Dependent Claim
32 words
The apparatus, as set forth in claim 5, wherein said capacitor, upon reception of radio frequency radiation, attains a sufficiently low impedance to transmit the radio frequency radiation to the circuit ground.
Claim 8
Dependent Claim
44 words
The apparatus, as set forth in claim 1, wherein said capacitor, upon the reception of radio frequency radiation, attains an impedance sufficiently lower than the impedance of said inductor so that said capacitor transmits substantially all of the radio frequency radiation to circuit ground.
Claim 9
Dependent Claim
26 words
The apparatus, as set forth in claim 1, wherein said metal oxide semiconductor gate input includes a capacitance between the gate input and the circuit ground.
Claim 10
Dependent Claim
16 words
The apparatus, as set forth in claim 8, wherein said capacitance further attenuates radio frequency radiation.
Claim 11
Dependent Claim
29 words
The apparatus, as set forth in claim 1, wherein said capacitor prevents a phase shift between the first terminal of said resistor and the metal oxide semiconductor gate input.
Claim 12
Dependent Claim
35 words
The apparatus, as set forth in claim 8, wherein said capacitor and said capacitance, upon recepton of radio frequency radiation, attain a sufficiently low impedance to transmit the radio frequency radiation to the circuit ground.
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) | 1991-01-25 | 1991-07-27 | 1992-01-26 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1995-01-25 | 1995-07-27 | 1996-01-26 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1999-01-25 | 1999-07-27 | 2000-01-26 | $7700.00 | Window Closed / Lapsed |