US3789313A
Expired / Lapsed
US
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Active filter circuits
Assignee: INVENTRONICS
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Filing: 1972-05-23
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Granted: 1974-01-29
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Expires: 1992-05-23
Abstract
Abstract A family of active filter circuits. Each filter has two time constant networks with each network having an element in one loop of a multi-loop feedback circuit for an amplifier. A generalized transfer function EO/EIN AS2 + BS + C/(A+1)T1T2 s2 + ((A+1)T1 + T2)s + (A+1) describes the operation of each active filter. In this function, A is amplifier gain and T1 and T2 are time constants for the two time constant networks. Some specific circuits have a transfer function in which the coefficients ''''a'''' and ''''c'''' are 0 and operate as band-pass filters. In these circuits, amplifier gain variations do not affect the resonant frequency, while the resonant frequency can be changed by altering the time constant networks without affecting the quality factor or gain at resonance.
Inventors
- 👤 A Sanderson
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 00:26
CPC Classifications
H; H03; H03H; H03H11/00; H03H11/02; H03H11/04; H03H11/12; H03H11/1217
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
138 words
A filter circuit comprising: A. amplifier means with input and output connections B. first and second time constant networks, each network including a first and second impedance element in series and having first and second end connections, C. unity gain isolating means with an output coupled to said amplifier means input connection D. a first negative feedback path for said amplifier including said impedance element connected to the first end connection in said first time constant network and said isolating means and, E. a second negative feedback path for said amplifier including said impedance element connected to the first end connection in said second time constant network, said second feedback path being isolated from said first feedback path, said second end connections of said first and second time constant networks being terminated in zero impedance connection to ground.
Claim 2
Dependent Claim
138 words
A filter circuit comprising: A. amplifier means with input and output connections B. first and second time constant networks, each network including a first and second impedance element in series and having first and second end connections, C. unity gain isolating means with an output coupled to said amplifier means input connection D. a first negative feedback path for said amplifier including said impedance element connected to the first end connection in said first time constant network and said isolating means and, E. a second negative feedback path for said amplifier including said impedance element connected to the first end connection in said second time constant network, said second feedback path being isolated from said first feedback path, said second end connections of said first and second time constant networks being terminated in zero impedance connection to ground.
Claim 3
Dependent Claim
89 words
A filter circuit as recited in claim 1 wherein said first and second time constant networks have time constants TL and TH respectively, said filter having input and output terminal means and having the transfer function eout/ein f(s)/(A+1) TLTHS2+ ( (A+1)TH+TL)s + (A+1) wherein eout is the filter output voltage at said output terminal means,ein is the filter input voltage at said input terminal means, f(s) is a function of ''''s'''' and ''''s'''' is the operator j omega , omega being the operating angular frequency for said filter circuit.
Claim 4
Dependent Claim
36 words
A filter as recited in claim 2 wherein said input terminal means connect to said first time constant network and said output terminal means connect to said amplifier output connection, said filter constituting a band-pass filter.
Claim 5
Dependent Claim
14 words
A filter as recited in claim 3 wherein the filter connections provide f(S) -ATLs.
Claim 6
Dependent Claim
82 words
A filter as recited in claim 4 wherein said first and second time constant networks each comprise a resistor and capacitor, said first time constant network resistor being connected to said input terminal means and said capacitor being connected in said first feedback path, said second time constant network resistor being connected in said second feedback path and capacitor coupling a signal from said isolating means to said amplifier input connection, said amplifier output connection being connected to said output terminal means.
Claim 7
Dependent Claim
61 words
A filter as recited in claim 4 wherein said first time constant network comprises a capacitor coupled to said input terminal means and a resistor connected in said first feedback path and said second time constant network comprises a resistor for coupling signals from said isolating means to said amplifier input connection and a capacitor connect in said second feedback path.
Claim 8
Dependent Claim
17 words
A filter circuit as recited in claim 4 wherein said amplifier means additionally includes positive feedback means.
Claim 9
Dependent Claim
44 words
A filter as recited in claim 4 wherein said amplifier means includes first and second amplifiers having first and second gains, said amplifiers being cascaded and said utilization device being connected to an input terminal of said second amplifier, said amplifiers having opposite polarity.
Claim 10
Dependent Claim
31 words
A filter as recited in claim 4 additionally comprising a summing amplifier and means for summing the filter output with said signal, said summing amplifier combining the filter and non-filtered signals.
Claim 11
Dependent Claim
69 words
A filter system comprising first and second filters, each of said first and second filters including a filter as recited in claim 4, said filter system additionally comprising means for coupling said amplifier output connection in said second filter to said amplifier input connection in said first filter and means for coupling said amplifier output connection of said first filter to said amplifier input connection in said second filter.
Claim 12
Dependent Claim
27 words
A filter as recited in claim 2 wherein said input terminal means connects to said amplifier and said output terminal means connects to said amplifier output connector.
Claim 13
Dependent Claim
92 words
A filter as recited in claim 11 wherein said first time constant network comprises a resistor and capacitor connected in series to form a voltage divider, said resistor being in said first feedback path, and said second time constant network comprises a resistor connected to said isolating means for coupling the voltage across said first time constant network capacitor to said amplifier means and a capacitor connected in said second feedback path, said amplifier means additionally including a third negative feedback path, one of said input connections summing all the feedback signals.
Claim 14
Dependent Claim
41 words
A filter circuit as recited in claim 12 wherein said amplifier means has inverting and non-inverting input connections, said third feedback path connecting to said inverting input connection and another resistor connects said input terminal to said amplifier inverting input connection.
Claim 15
Dependent Claim
39 words
A filter circuit as recited in claim 11 wherein said amplifier means includes inverting and non-inverting input connections, said third negative feedback path connecting to said inverting input connection, said input terminal being connected to said non-inverting input connection.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-01-28 | 1977-07-30 | 1978-01-29 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-01-28 | 1981-07-30 | 1982-01-29 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-01-28 | 1985-07-30 | 1986-01-29 | $7700.00 | Window Closed / Lapsed |