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US3783412A
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Active band pass filter having continuously variable pass band
Assignee: MI Inc
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Filing: 1972-10-30
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Granted: 1974-01-01
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Expires: 1992-10-30
Abstract
Abstract A method and circuits are disclosed for permitting a pair of discrete circuit elements to operate as a continuously variable circuit element. The pair of elements, preferably resistances, are alternatively, periodically switched into connection and disconnection in a circuit at a rate substantially greater than the operative frequency of the circuit. The effective value of the switched elements depends upon their relative connection time. A continuously variable filter comprises an active filter in which the frequency determining resistance element is such a switched discrete pair of resistances. The addition of a regenerative feedback loop to such a filter provides a continuously variable oscillator. The further addition of a pulse width modulator to the oscillator, for alternatively switching the discrete resistances in response to an input signal provides a frequency modulator.
Inventors
- 👤 R Libby
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 15:43
CPC Classifications
H; H03; H03H; H03H19/00; H03H19/008; H03B; H03B5/00; H03B5/20; H03B5/24; H03G; H03G5/00; H03G5/16; H03G5/24
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
142 words
A continuously variable active filTer of the type having an amplifying device and an associated frequency determining feedback network, the frequency response of said active filter being a function of a resistive element of said network, wherein the improvement comprises: a. an effectively continuously variable resistive element comprising a pair of discrete resistors having a first electronic switch series connected to a first one of said discrete resistors and having the second resistor at least at times connected parallel to said series first resistor and first switch; and b. a switching means connected to control said electronic switch for alternately connecting and disconnecting said first resistor in said network at a rate substantially exceeding the operative frequency of said filter; wherein the operative frequency of said filter is a function of the relative time said first resistor is connected in said network.
Claim 2
Dependent Claim
142 words
A continuously variable active filTer of the type having an amplifying device and an associated frequency determining feedback network, the frequency response of said active filter being a function of a resistive element of said network, wherein the improvement comprises: a. an effectively continuously variable resistive element comprising a pair of discrete resistors having a first electronic switch series connected to a first one of said discrete resistors and having the second resistor at least at times connected parallel to said series first resistor and first switch; and b. a switching means connected to control said electronic switch for alternately connecting and disconnecting said first resistor in said network at a rate substantially exceeding the operative frequency of said filter; wherein the operative frequency of said filter is a function of the relative time said first resistor is connected in said network.
Claim 3
Dependent Claim
88 words
A filter according to claim 1 wherein a second electronic switch is interposed in series connection with said second resistance and is connected for control by said switching means and wherein said switching means alternatively periodically connects said resistors in said network wherein the operative frequency of said filter is continuously variable from the operative frequency determined by said first resistance alone to the operative frequency determined by said second resistance alone and is a function of the relative time each resistor is effectively connected in the circuit.
Claim 4
Dependent Claim
40 words
A filter according to claim 2 wherein said electronic switches comprise complementary transistors having their control inputs connected together and to the output of said switching means and wherein said switching means provides a rectangular output oscillating between opposite polarities.
Claim 5
Dependent Claim
24 words
A filter according to claim 3 wherein said switching means has a controlling input for selecting the relative time duration of each output polarity.
Claim 6
Dependent Claim
15 words
A filter according to claim 4 wherein said switching means comprises a pulse width modulator.
Claim 7
Dependent Claim
43 words
A band pass filter having a variable pass band and comprising a plurality of series connected filters according to claim 4 wherein each is operative at a different frequency and wherein the pass bands of each overlap to form a broader pass band.
References Cited (Backward Citations)
US3701059A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-12-31 | 1977-07-02 | 1978-01-01 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-12-31 | 1981-07-02 | 1982-01-01 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-12-31 | 1985-07-02 | 1986-01-01 | $7700.00 | Window Closed / Lapsed |