# US 11,444,587 B2 · Multiple feedback filter

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- Number: US 11,444,587 B2
- Document ID: US11444587B2
- Status: Granted
- Kind: B2
- Application number: 17/124,785
- Filed: 2020-12-17
- Published: 2022-06-23
- Granted: 2022-09-13
- Earliest claimed: 2020-12-17
- Assignees: Texas Instruments Incorporated
- Applicants: Texas Instruments Incorporated
- Inventors: Yang Xu; William Bright; Hasibur Rahman
- Web page: https://patentgrep.com/patent/US11444587B2

## CPC

- H03F 3/04: with semiconductor devices only
- H03F 3/45475: {using IC blocks as the active amplifying circuit}
- H03H 11/12: using amplifiers with feedback ({H03H11/0422} , H03H11/08, H03H11/10 take precedence)
- H03H 11/126: {using a single operational amplifier (H03H11/1204 takes precedence; parallel-T filters H03H11/1295)}
- H03F 2200/129: there being a feedback over the complete amplifier
- H03F 2200/165: A filter circuit coupled to the input of an amplifier
- H03F 2203/45526: the FBC comprising a resistor-capacitor combination and being coupled between the LC and the IC
- H03H 11/1286: {Sallen-Key biquad}
- H03F: AMPLIFIERS
- H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P)

## Abstract

A circuit having an input and an output, the circuit comprising: a first amplifier having a first input, a second input and an output coupled to the output of the circuit; a first capacitor having a first terminal coupled to the first input of the first amplifier and a second terminal coupled to the output of the first amplifier; a first resistor having a first terminal coupled to the first input of the first amplifier and a second terminal; a buffer having an output coupled to the second terminal of the first resistor and an input; a second resistor having a first terminal coupled to the output of the first amplifier and a second terminal coupled to the input of the buffer; a second capacitor coupled between the input of the buffer and ground; and a third resistor coupled between the input of the buffer and the input of the circuit.

## Claims

### Claim 1

A circuit having an input and an output, the circuit comprising:
a first amplifier having a first input, a second input and an output coupled to the output of the circuit;
a first capacitor having a first terminal coupled to the first input of the first amplifier and a second terminal coupled to the output of the first amplifier;
a first resistor having a first terminal coupled to the first input of the first amplifier and a second terminal;
a buffer having an output coupled to the second terminal of the first resistor and an input;
a second resistor having a first terminal coupled to the output of the first amplifier and a second terminal coupled to the input of the buffer;
a second capacitor coupled between the input of the buffer and ground; and
a third resistor coupled between the input of the buffer and the input of the circuit.

### Claim 2 (depends on 1)

The circuit of claim 1, wherein the circuit is a low-pass filter.

### Claim 3 (depends on 1)

The circuit of claim 1, wherein the second input of the first amplifier is coupled to a reference voltage.

### Claim 4 (depends on 1)

The circuit of claim 1, wherein the first capacitor has a first capacitance value and the second capacitor has a second capacitance value that is substantially equal to the first capacitance value.

### Claim 5 (depends on 1)

The circuit of claim 1, wherein the buffer includes a second amplifier having a first input connected to the second terminal of the second resistor, a second input and an output connected to the second input and to the second terminal of the first resistor.