Patent US3886469A successfully refreshed from Google Patents.
US3886469A
Expired / Lapsed
US
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Filter networks
Assignee: Post Office
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Filing: 1974-01-10
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Granted: 1975-05-27
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Expires: 1994-01-10
Abstract
Abstract Filter networks have generally been constructed from passive components in the form of resistor, capacitor and inductors. This invention uses active devices in a subnetwork to simulate inductors and combines the subnetworks to provide the desired filter characteristic such as a Butterworth, Tchebychev or pseudo-elliptic filters which are particularly useful in telephone circuitry for handling the audio tones uses in dialling.
Inventors
- 👤 John Mortimer Rollett
- 👤 David Richard Wise
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 22:35
CPC Classifications
H; H03; H03H; H03H11/00; H03H11/02; H03H11/04; H03H11/12
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
166 words
An insensitive low-pass filter network comprising an input port including a first and a second input terminal, said first input terminal being connected by way of a first resistor and a first capacitor in series to a first stage of the filter network, said second input terminal being earthed, said first stage being coupled by way of a resistive impedance to one of a plurality of further stages, having a final stage which is coupled by way of a second resistor in series with an input to an output amplifier, and which final stage is coupled to a second capacitor between said input to the output amplifier and the second input terminal, and wherein Each stage of the filter network includes a single stage amplifier, having substantially unity gain, and a third resistor connected between an output of the stage amplifier and a junction between a third and a fourth capacitor coupled in series between an input of the stage amplifier and the second input terminal.
Claim 2
Dependent Claim
166 words
An insensitive low-pass filter network comprising an input port including a first and a second input terminal, said first input terminal being connected by way of a first resistor and a first capacitor in series to a first stage of the filter network, said second input terminal being earthed, said first stage being coupled by way of a resistive impedance to one of a plurality of further stages, having a final stage which is coupled by way of a second resistor in series with an input to an output amplifier, and which final stage is coupled to a second capacitor between said input to the output amplifier and the second input terminal, and wherein Each stage of the filter network includes a single stage amplifier, having substantially unity gain, and a third resistor connected between an output of the stage amplifier and a junction between a third and a fourth capacitor coupled in series between an input of the stage amplifier and the second input terminal.
Claim 3
Dependent Claim
43 words
An insensitive low-pass filter network as claimed in claim 1 in which each stage amplifier consists of an operational amplifier having a high resistive input impedance and having a feed-back path providing a voltage feed-back to maintain the amplifier gain at substantially unity.
Claim 4
Dependent Claim
51 words
An insensitive low-pass filter network as claimed in claim 1 in which the output amplifier consists of a differential input operational amplifier having an inverting input terminal which is directly connected to an output of the amplifier, and having a non-inverting input terminal which forms said input to the output amplifier.
Claim 5
Dependent Claim
169 words
An insensitive low-pass filter network comprising a number of stages the first stage of which is coupled by way of a first resistor and a first capacitor in series to a first input terminal of an input port formed by said first input terminal and a second input terminal which is earthed and the last of said stages being coupled to an input of an output amplifier by way of a second resistor in series, and a second capacitor in parallel between said output amplifier input and said second input terminal, each of said stages including a single stage amplifier having substantially infinite gain, and having an input which is capacitively coupled by way of a third capacitor to the input of the stage which said input of the stage is directly coupled by way of a fourth capacitor to the output of said stage amplifier which output of the stage amplifier is also directly coupled to the input of said stage amplifier by way of a third resistor.
Claim 6
Dependent Claim
169 words
An insensitive low-pass filter network comprising a number of stages the first stage of which is coupled by way of a first resistor and a first capacitor in series to a first input terminal of an input port formed by said first input terminal and a second input terminal which is earthed and the last of said stages being coupled to an input of an output amplifier by way of a second resistor in series, and a second capacitor in parallel between said output amplifier input and said second input terminal, each of said stages including a single stage amplifier having substantially infinite gain, and having an input which is capacitively coupled by way of a third capacitor to the input of the stage which said input of the stage is directly coupled by way of a fourth capacitor to the output of said stage amplifier which output of the stage amplifier is also directly coupled to the input of said stage amplifier by way of a third resistor.
References Cited (Backward Citations)
US3564441A
Cited
US3501709A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-05-26 | 1978-11-25 | 1979-05-27 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-05-26 | 1982-11-25 | 1983-05-27 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-05-26 | 1986-11-25 | 1987-05-27 | $7700.00 | Window Closed / Lapsed |