# US 11,909,362 B2 · Amplifier circuitry > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,909,362 B2 - Document ID: US11909362B2 - Status: Granted - Kind: B2 - Application number: 17/835,326 - Filed: 2022-06-08 - Published: 2022-10-13 - Granted: 2024-02-20 - Earliest claimed: 2019-10-04 - Assignees: Cirrus Logic, Inc. - Applicants: Cirrus Logic International Semiconductor Ltd. - Inventors: John Paul Lesso - Web page: https://patentgrep.com/patent/US11909362B2 ## CPC - H03F 3/217: Class D power amplifiers; Switching amplifiers - H03F 3/2173: {of the bridge type} - H03F 1/26: Modifications of amplifiers to reduce influence of noise generated by amplifying elements - H03F 1/3223: {using feed-forward (H03F1/3211 takes precedence)} - H03F 3/183: with semiconductor devices only - H03F 2200/03: the amplifier being designed for audio applications - 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: AMPLIFIERS ## Abstract This application relates to amplifier circuitry, in particular class-D amplifiers, operable in open-loop and closed-loop modes. An amplifier (300) has a forward signal path for receiving an input signal (SIN) and outputting an output signal (SOUT) and a feedback path operable to provide a feedback signal (SFB) from the output. A feedforward path provide a feedforward signal (SFF) from the input and a combiner (105) is operable to determine an error signal (ε) based on a difference between the feedback signal and the feedforward signal. The feedforward comprises a compensation module (201) configured to apply a controlled transfer function to the feedforward signal in the closed-loop mode of operation, such that an overall transfer function for the amplifier is substantially the same in the closed-loop mode of operation and the open-loop mode of operation. ## Claims ### Claim 1 Amplifier circuitry comprising: a forward signal path for receiving an input signal and outputting an output signal; a feedback path operable to provide a feedback signal derived from the output signal; a feedforward path operable to provide a feedforward signal derived from the input signal; a combiner operable to determine an error signal based on a difference between the feedback signal and the feedforward signal; and a controller for selectively controlling a loop gain factor; wherein the amplifier circuit is selectively operable to vary the loop gain factor so as to vary an extent to which the error signal contributes to the forward signal path; and wherein the feedforward path comprises a compensation module configured to apply a controlled transfer function to the feedforward signal such that an overall transfer function for the amplifier circuit is substantially the same for different values of the loop gain factor. ### Claim 2 (depends on 1) The amplifier circuitry of claim 1 wherein the compensation module comprises a filter having a controlled transfer function. ### Claim 3 (depends on 2) The amplifier circuitry of claim 2 wherein the filter is an adaptive filter. ### Claim 4 (depends on 1) The amplifier circuitry of claim 1 wherein the compensation module is an adaptive module configured to monitor the error signal to adapt its transfer function in response to the error signal so that the error signal exhibits a desired characteristic over a signal band of interest. ### Claim 5 (depends on 1) The amplifier circuitry of claim 1 wherein the compensation module is configured to have a transfer function which is matched to a transfer function for the feedback path. ### Claim 6 (depends on 1) The amplifier circuitry of claim 1 wherein the controller is configured to selectively control the loop gain factor such that the loop gain factor can adopt any of at least two different non-zero values. ### Claim 7 (depends on 1) The amplifier circuitry of claim 1 wherein the controller is configured to control the loop gain factor based on an indication of power supply noise. ### Claim 8 (depends on 1) The amplifier circuitry of claim 1 wherein the controller is configured to control the loop gain factor based on the error signal. ### Claim 9 (depends on 1) The amplifier circuitry of claim 1 wherein the controller is further configured to control a bias applied to a component in the feedback path to have different levels for different values of the loop gain factor. ### Claim 10 (depends on 1) The amplifier circuitry of claim 1 wherein the controller is configured to selectively control the loop gain factor such that the loop gain factor can adopt at least one non-zero value and also so that the loop gain factor can be zero to enable an open-loop mode of operation. ### Claim 11 (depends on 1) The amplifier circuitry of claim 1 comprising a class-D modulator and a class-D output stage in the forward signal path. ### Claim 12 (depends on 1) The amplifier circuitry of claim 1 comprising a feedback filter in the feedback path. ### Claim 13 (depends on 12) The amplifier circuitry of claim 12 wherein said feedback filter comprises a low-pass filter. ### Claim 14 (depends on 1) The amplifier circuitry of claim 1 comprising a loop-filter in an error path for the error signal. ### Claim 15 (depends on 1) The amplifier circuitry of claim 1 implemented as an integrated circuit. ### Claim 16 (depends on 1) An electronic device comprising the amplifier circuitry of claim 1.