US3919658A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Active RC filter circuit
Assignee: AT&T Inc
•
Filing: 1972-05-09
•
Granted: 1975-11-11
•
Expires: 1992-05-09
Abstract
Abstract A filter circuit is disclosed which uses an operational amplifier and a plurality of resistors and capacitors to obtain a variety of filter transfer functions. By modification of a basic circuit structure, bandpass, high-pass, low-pass notch, high-pass notch, and all-pass filter transfer functions are obtained.
Inventors
- 👤 Joseph John Friend
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 19:04
CPC Classifications
H; H03; H03H; H03H11/00; H03H11/02; H03H11/04; H03H11/12; H03H11/126; H03G; H03G5/00
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
256 words
An RC filter circuit (FIG. 1) which utilizes a single amplifier to provide an output siGnal, between an output terminal and a reference terminal having fixed potential, which is a second order transformation of an input signal applied between an input terminal and said reference terminal, said filter circuit comprising: a single amplifier having first and second input terminals and having a single output terminal, said single output terminal common with said filter output terminal; a first resistor connected to said amplifier first input terminal and to said filter output terminal; a second resistor connected to said amplifier second input terminal and to said filter output terminal; a circuit branch comprising the serial connection of a third resistor and a first capacitor, the resistor terminal of said circuit branch connected to said filter input terminal and the capacitor terminal of said circuit branch connected to said amplifier first input terminal; a second capacitor connected to said circuit branch, intermediate said third resistor and said first capacitor, and to said filter output terminal; a fourth resistor connected to said filter input terminal and to said amplifier first input terminal; a fifth resistor connected to said filter input terminal and to said amplifier second input terminal; a sixth resistor connected to said amplifier first input terminal and to said reference terminal; a seventh resistor connected to said amplifier second input terminal and to said reference terminal; and an eighth resistor connected to said circuit branch, intermediate said third resistor and said first capacitor, and to said reference terminal.
Claim 2
Dependent Claim
256 words
An RC filter circuit (FIG. 1) which utilizes a single amplifier to provide an output siGnal, between an output terminal and a reference terminal having fixed potential, which is a second order transformation of an input signal applied between an input terminal and said reference terminal, said filter circuit comprising: a single amplifier having first and second input terminals and having a single output terminal, said single output terminal common with said filter output terminal; a first resistor connected to said amplifier first input terminal and to said filter output terminal; a second resistor connected to said amplifier second input terminal and to said filter output terminal; a circuit branch comprising the serial connection of a third resistor and a first capacitor, the resistor terminal of said circuit branch connected to said filter input terminal and the capacitor terminal of said circuit branch connected to said amplifier first input terminal; a second capacitor connected to said circuit branch, intermediate said third resistor and said first capacitor, and to said filter output terminal; a fourth resistor connected to said filter input terminal and to said amplifier first input terminal; a fifth resistor connected to said filter input terminal and to said amplifier second input terminal; a sixth resistor connected to said amplifier first input terminal and to said reference terminal; a seventh resistor connected to said amplifier second input terminal and to said reference terminal; and an eighth resistor connected to said circuit branch, intermediate said third resistor and said first capacitor, and to said reference terminal.
Claim 3
Dependent Claim
241 words
An RC filter circuit (FIG. 4) which utilizes a single amplifier to provide an output signal, between an output terminal and a reference terminal having fixed potential, which is a second order transformation of an input signal applied between an input terminal and said reference terminal, said filter circuit comprising: a single amplifier having first and second input terminals and having a single output terminal, said single output terminal common with said filter output terminal; a first resistor connected to said amplifier first input terminal and to said filter output terminal; a second resistor connected to said amplifier second input terminal and to said filter output terminal; a circuit branch comprising the serial connection of a third resistor and a first capacitor, the resistor terminal of said circuit branch connected to said filter input terminal and the capacitor terminal of said circuit branch connected to said amplifier first input terminal; a second capacitor connected to said circuit branch, intermediate said third resistor and said first capacitor, and to said filter output terminal; a fourth resistor connected to said filter input terminal and to said amplifier first input terminal; a fifth resistor connected to said filter input terminal and to said amplifier second input terminal; a sixth resistor connected to said amplifier second input terminal and to said reference terminal; and a seventh resistor connected to said circuit branch, intermediate said third resistor and said first capacitor, and to said reference terminal.
Claim 4
Dependent Claim
241 words
An RC filter circuit (FIG. 4) which utilizes a single amplifier to provide an output signal, between an output terminal and a reference terminal having fixed potential, which is a second order transformation of an input signal applied between an input terminal and said reference terminal, said filter circuit comprising: a single amplifier having first and second input terminals and having a single output terminal, said single output terminal common with said filter output terminal; a first resistor connected to said amplifier first input terminal and to said filter output terminal; a second resistor connected to said amplifier second input terminal and to said filter output terminal; a circuit branch comprising the serial connection of a third resistor and a first capacitor, the resistor terminal of said circuit branch connected to said filter input terminal and the capacitor terminal of said circuit branch connected to said amplifier first input terminal; a second capacitor connected to said circuit branch, intermediate said third resistor and said first capacitor, and to said filter output terminal; a fourth resistor connected to said filter input terminal and to said amplifier first input terminal; a fifth resistor connected to said filter input terminal and to said amplifier second input terminal; a sixth resistor connected to said amplifier second input terminal and to said reference terminal; and a seventh resistor connected to said circuit branch, intermediate said third resistor and said first capacitor, and to said reference terminal.
Claim 5
Dependent Claim
240 words
An RC filter circuit (FIG. 5) which utilizes a single amplifier to provide an output signal, between an output terminal and a reference terminal having fixed potential, which is a second order transformation of an input signal applied between an input terminal and said reference terminal, said filter circuit comprising: a single amplifier having first and second input terminals and having a single output terminal, said single output terminal common with said filter output terminal; a first resistor connected to said amplifier first input terminal and to said filter output terminal; a second resistor connected to said amplifier second input terminal and to said filter output terminal; a circuit branch comprising the serial connection of a third resistoR and a first capacitor, the resistor terminal of said circuit branch connected to said filter input terminal and the capacitor terminal of said circuit branch connected to said amplifier first input terminal; a second capacitor connected to said circuit branch, intermediate said third resistor and said first capacitor, and to said filter output terminal; a fourth resistor connected to said filter input terminal and to said amplifier second input terminal; a fifth resistor connected to said amplifier first input terminal and to said reference terminal; a sixth resistor connected to said amplifier second input terminal and to said reference terminal; and a seventh resistor connected to said circuit branch, intermediate said third resistor and said first capacitor, and to said reference terminal.
Claim 6
Dependent Claim
240 words
An RC filter circuit (FIG. 5) which utilizes a single amplifier to provide an output signal, between an output terminal and a reference terminal having fixed potential, which is a second order transformation of an input signal applied between an input terminal and said reference terminal, said filter circuit comprising: a single amplifier having first and second input terminals and having a single output terminal, said single output terminal common with said filter output terminal; a first resistor connected to said amplifier first input terminal and to said filter output terminal; a second resistor connected to said amplifier second input terminal and to said filter output terminal; a circuit branch comprising the serial connection of a third resistoR and a first capacitor, the resistor terminal of said circuit branch connected to said filter input terminal and the capacitor terminal of said circuit branch connected to said amplifier first input terminal; a second capacitor connected to said circuit branch, intermediate said third resistor and said first capacitor, and to said filter output terminal; a fourth resistor connected to said filter input terminal and to said amplifier second input terminal; a fifth resistor connected to said amplifier first input terminal and to said reference terminal; a sixth resistor connected to said amplifier second input terminal and to said reference terminal; and a seventh resistor connected to said circuit branch, intermediate said third resistor and said first capacitor, and to said reference terminal.
Claim 7
Dependent Claim
225 words
An RC filter circuit (FIG. 7) which utilizes a single amplifier to provide an output signal, between an output terminal and a reference terminal having fixed potential, which is a second order transformation of an input signal applied between an input terminal and said reference terminal, said filter circuit comprising: a single amplifier having a first and second input terminals and having a single output terminal, said single output terminal common with said filter output terminal; a first resistor connected to said amplifier first input terminal and to said filter output terminal; a circuit branch comprising the serial connection of a second resistor and a first capacitor, the resistor terminal of said circuit branch connected to said filter input terminal and the capacitor terminal of said circuit branch connected to said amplifier first input terminal; a second capacitor connected to said circuit branch, intermediate said second resistor and said first capacitor, and to said filter output terminal; a third resistor connected to said filter input terminal and to said amplifier second input terminal; a fourth resistor connected to said amplifier first input terminal and to said reference terminal; a fifth resistor connected to said amplifier second input terminal and to said reference terminal; and a third capacitor connected to said circuit branch, intermediate said second resistor and said first capacitor, and to said reference terminal.
Claim 8
Dependent Claim
225 words
An RC filter circuit (FIG. 7) which utilizes a single amplifier to provide an output signal, between an output terminal and a reference terminal having fixed potential, which is a second order transformation of an input signal applied between an input terminal and said reference terminal, said filter circuit comprising: a single amplifier having a first and second input terminals and having a single output terminal, said single output terminal common with said filter output terminal; a first resistor connected to said amplifier first input terminal and to said filter output terminal; a circuit branch comprising the serial connection of a second resistor and a first capacitor, the resistor terminal of said circuit branch connected to said filter input terminal and the capacitor terminal of said circuit branch connected to said amplifier first input terminal; a second capacitor connected to said circuit branch, intermediate said second resistor and said first capacitor, and to said filter output terminal; a third resistor connected to said filter input terminal and to said amplifier second input terminal; a fourth resistor connected to said amplifier first input terminal and to said reference terminal; a fifth resistor connected to said amplifier second input terminal and to said reference terminal; and a third capacitor connected to said circuit branch, intermediate said second resistor and said first capacitor, and to said reference terminal.
Claim 9
Dependent Claim
181 words
An RC filter circuit (FIG. 9) which utilizes a single amplifier to provide an output signal, between an output terminal and a reference terminal having fixed potential, which is a second order transformation of an input signal applied between an input terminal and said reference terminal, said filter circuit comprising: a single amplifier having first and second input terminals and having a single output terminal, said single output terminal common with said filter output terminal; a first resistor connected to said amplifier first input terminal and to said filter output terminal; a circuit branch comprising the serial connection of a second resistor and a first capacitor, the resistor terminal of said circuit branch connected to said filter input terminal and the capacitor terminal of said circuit branch connected to said amplifier first input terminal; a third resistor connected to said filter input terminal and to said amplifier second input terminal; a fourth resistor connected to said amplifier first input terminal and to said reference terminal; and a fifth resistor connected to said amplifier second input terminal and to said reference terminal.
Claim 10
Dependent Claim
181 words
An RC filter circuit (FIG. 9) which utilizes a single amplifier to provide an output signal, between an output terminal and a reference terminal having fixed potential, which is a second order transformation of an input signal applied between an input terminal and said reference terminal, said filter circuit comprising: a single amplifier having first and second input terminals and having a single output terminal, said single output terminal common with said filter output terminal; a first resistor connected to said amplifier first input terminal and to said filter output terminal; a circuit branch comprising the serial connection of a second resistor and a first capacitor, the resistor terminal of said circuit branch connected to said filter input terminal and the capacitor terminal of said circuit branch connected to said amplifier first input terminal; a third resistor connected to said filter input terminal and to said amplifier second input terminal; a fourth resistor connected to said amplifier first input terminal and to said reference terminal; and a fifth resistor connected to said amplifier second input terminal and to said reference terminal.
Claim 11
Dependent Claim
171 words
In an RC filter circuit (FIG. 8) having an input port including an input terminal and a reference terminal of fixed potential and an output port including an output terminal and said reference terminal, a single amplifier having a first and second input terminals and a single output terminal, said single output terminal common with said filter output terminal, a first circuit branch including a first resistor and a first capacitor serially connected, the resistor termInal of said first circuit branch connected to said filter input terminal and the capacitor terminal of said first circuit branch connected to said amplifier first input terminal, a second resistor connected to said filter input terminal and to said amplifier second input terminal, a third resistor connected to said amplifier second input terminal and to said reference terminal of fixed potential, the improvement comprising: a single feedback path connected to said amplifier output terminal consisting solely of a resistive device connected between said amplifier output terminal and said first input terminal of said single amplifier.
Claim 12
Dependent Claim
171 words
In an RC filter circuit (FIG. 8) having an input port including an input terminal and a reference terminal of fixed potential and an output port including an output terminal and said reference terminal, a single amplifier having a first and second input terminals and a single output terminal, said single output terminal common with said filter output terminal, a first circuit branch including a first resistor and a first capacitor serially connected, the resistor termInal of said first circuit branch connected to said filter input terminal and the capacitor terminal of said first circuit branch connected to said amplifier first input terminal, a second resistor connected to said filter input terminal and to said amplifier second input terminal, a third resistor connected to said amplifier second input terminal and to said reference terminal of fixed potential, the improvement comprising: a single feedback path connected to said amplifier output terminal consisting solely of a resistive device connected between said amplifier output terminal and said first input terminal of said single amplifier.
Claim 13
Dependent Claim
82 words
A filter circuit (FIG. 1) as defined in claim 5 further comprising: a sixth resistor connected to said amplifier second input terminal and to said filter output terminal; a second capacitor connected to said second resistor and said first capacitor and to said filter output terminal; a seventh resistor connected to said filter input terminal and to said amplifier first input terminal; and an eighth resistor connected to said second resistor and said first capacitor and to said terminal of fixed potential.
Claim 14
Dependent Claim
66 words
A filter circuit (FIG. 5) as defined in claim 5 further comprising: a sixth resistor connected to said amplifier second input terminal and to said filter output terminal; a second capacitor connected to said second resistor and said first capacitor and to said filter output terminal; and a seventh resistor connected to said second resistor and said first capacitor and to said terminal of fixed potential.
Claim 15
Dependent Claim
51 words
A filter circuit (FIG. 7) as defined by claim 5 further comprising: a second capacitor connected to said second resistor and said first capacitor and to said filter output terminal; and a third capacitor connected to said second resistor and to said first capacitor and to said terminal of fixed potential.
Claim 16
Dependent Claim
29 words
A filter circuit (FIG. 9) as defined by claim 6 further comprising: a fourth resistor connected to said amplifier first input terminal and to said terminal of fixed potential.
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) | 1978-11-10 | 1979-05-12 | 1979-11-11 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-11-10 | 1983-05-12 | 1983-11-11 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-11-10 | 1987-05-12 | 1987-11-11 | $7700.00 | Window Closed / Lapsed |