# US 2016/0365084 A1 · Hybrid finite impulse response filter > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2016/0365084 A1 - Document ID: US20160365084A1 - Status: Published application - Kind: A1 - Application number: 14/734,418 - Filed: 2015-06-09 - Published: 2016-12-15 - Earliest claimed: 2015-06-09 - Assignees: Cirrus Logic International Semiconductor Ltd. - Applicants: Cirrus Logic International Semiconductor Ltd. - Inventors: Jeffrey D. Alderson; John L. Melanson; Nitin Kwatra; Ryan A. Hellman - Web page: https://patentgrep.com/patent/US20160365084A1 ## CPC - H03H 17/0223: {Computation saving measures; Accelerating measures (computations per se G06F)} - G10K 11/17817: {between the output signals and the error signals, i.e. secondary path} - G10K 11/17854: {the filter being an adaptive filter} - G10K 11/17855: {for improving speed or power requirements} - G10K 11/17857: {Geometric disposition, e.g. placement of microphones} - G10K 11/17881: {the reference signal being an acoustic signal, e.g. recorded with a microphone} - G10K 11/17885: {additionally using a desired external signal, e.g. pass-through audio such as music or speech} - H03H 17/0291: {Digital and sampled data filters} - H03H 17/06: Non-recursive filters - G10K 2210/3012: Algorithms - G10K 2210/3014: Adaptive noise equalizers [ANE], i.e. where part of the unwanted sound is retained - G10K 2210/3028: Filtering, e.g. Kalman filters or special analogue or digital filters - G10K 2210/3051: Sampling, e.g. variable rate, synchronous, decimated or interpolated - G10K 2210/3053: Speeding up computation or convergence, or decreasing the computational load - G10K 2210/509: Hybrid, i.e. combining different technologies, e.g. passive and active - H03H 2017/0245: {Measures to reduce power consumption} - H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P) - G10K: SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR ## Abstract In accordance with embodiments of the present disclosure, a hybrid finite impulse response filter having a plurality of delay stages comprising a first filter portion and a second filter portion. In some embodiments, the first filter portion may be a high-rate filter portion associated with a first portion of the plurality of delay stages and configured to filter an input signal having a first sampling rate to generate a first intermediate output signal and the second portion may be a low-rate filter portion associated with a second portion of the plurality of delay stages and configured to filter a downsampled version of the input signal at a second sampling rate to generate a second intermediate output signal. In other embodiments, the first filter portion may include an analog filter portion associated with a first portion of the plurality of delay stages and configured to filter an input signal to generate a first intermediate output signal and the second filter portion may be a digital filter portion associated with a second portion of the plurality of delay stages and configured to filter the input signal. ## Claims ### Claim 1 A hybrid finite impulse response filter having a plurality of delay stages, comprising: a high-rate filter portion associated with a first portion of the plurality of delay stages and configured to filter an input signal having a first sampling rate to generate a first intermediate output signal; a decimator for downsampling the input signal to a downsampled input signal having a second sampling rate smaller than the first sampling rate; a low-rate filter portion associated with a second portion of the plurality of delay stages and configured to filter the downsampled input signal; an interpolator for upsampling the downsampled input signal as filtered by the low-rate filter portion to generate a second intermediate output signal having a sampling rate larger than the second sampling rate; and a summer for summing the first intermediate output signal and the second intermediate output signal to generate an output signal of the hybrid impulse response filter. ### Claim 2 (depends on 1) The hybrid finite impulse response filter of claim 1, wherein the second intermediate output signal has the first sampling rate. ### Claim 3 (depends on 1) The hybrid finite impulse response filter of claim 1, wherein: each of the plurality of delay stages is associated with a respective delay; and an aggregate delay of the decimator and the interpolator is approximately equal to an aggregate delay of all of the first portion of delay stages. ### Claim 4 (depends on 1) The hybrid finite impulse response filter of claim 1, further comprising a delay element associated with the low-rate filter portion and wherein: each of the plurality of delay stages is associated with a respective delay; and an aggregate delay of the delay element, the decimator, and the interpolator is approximately equal to an aggregate delay of all of the first portion of delay stages. ### Claim 5 (depends on 1) The hybrid finite impulse response filter of claim 1, wherein, for each sample of the input signal, a corresponding sample of the output signal is generated before receipt by the hybrid finite impulse response filter of a subsequent sample of the input signal. ### Claim 6 (depends on 1) The hybrid finite impulse response filter of claim 1, wherein, for each sample of the input signal, a corresponding sample of the output signal is generated before receipt by the hybrid finite impulse response filter of ten subsequent samples of the input signal. ### Claim 7 (depends on 1) The hybrid finite impulse response filter of claim 1, wherein, for each sample of the input signal, a corresponding sample of the output signal is generated within 50 microseconds of receipt by the hybrid finite impulse response filter of the sample of the input signal. ### Claim 8 (depends on 1) The hybrid finite impulse response filter of claim 1, wherein each of the plurality of delay stages has associated therewith a respective gain, and at least one of the respective gains is adaptively responsive to at least one of the input signal and the output signal. ### Claim 9 (depends on 1) The hybrid finite impulse response filter of claim 1, wherein the hybrid finite impulse response filter is configured to adapt its response to minimize an error signal. ### Claim 10 (depends on 9) The hybrid finite impulse response filter of claim 9, wherein both of the high-rate filter portion and the low-rate filter portion are configured to adapt their responses to minimize the error signal. ### Claim 11 A method comprising: filtering with a high-rate filter portion of a hybrid finite impulse response filter having a plurality of delay stages and an input signal having a first sampling rate to generate a first intermediate output signal; downsampling the input signal to a downsampled input signal having a second sampling rate smaller than the first sampling rate; filtering with a low-rate filter portion the downsampled input signal; upsampling the downsampled input signal as filtered by the low-rate filter portion to generate a second intermediate output signal having a sampling rate larger than the second sampling rate; and summing the first intermediate output signal and the second intermediate output signal to generate an output signal of the hybrid impulse response filter. ### Claim 12 (depends on 11) The method of claim 11, wherein the second intermediate output signal has the first sampling rate. ### Claim 13 (depends on 11) The method of claim 11, wherein: each of the plurality of delay stages is associated with a respective delay; an aggregate delay of the downsampling and the upsampling is approximately equal to an aggregate delay of all of the first portion of delay stages. ### Claim 14 (depends on 11) The method of claim 11, further comprising delaying at least one of the downsampled input signal, the downsampled input signal as filtered by the low-rate filter portion, and the downsampled input signal as filtered by the low-rate filter portion after upsampling and wherein: each of the plurality of delay stages is associated with a respective delay; an aggregate delay of the downsampling, the upsampling, and the delaying is approximately equal to an aggregate delay of all of the first portion of delay stages. ### Claim 15 (depends on 11) The method of claim 11, further comprising, for each sample of the input signal, generating a corresponding sample of the output signal before receipt by the hybrid finite impulse response filter of a subsequent sample of the input signal. ### Claim 16 (depends on 11) The method of claim 11, further comprising, for each sample of the input signal, generating a corresponding sample of the output signal before receipt by the hybrid finite impulse response filter of ten subsequent samples of the input signal. ### Claim 17 (depends on 11) The method of claim 11, further comprising, for each sample of the input signal, generating of the output signal within 50 microseconds of receipt by the hybrid finite impulse response filter of the sample of the input signal. ### Claim 18 (depends on 11) The method of claim 11, wherein each of the plurality of delay stages has associated therewith a respective gain, and at least one of the respective gains is adaptively responsive to at least one of the input signal and the output signal. ### Claim 19 (depends on 11) The method of claim 11, further comprising adapting a response of at least one of the high-rate filter portion and the low-rate filter to minimize an error signal. ### Claim 20 (depends on 11) The method of claim 11, further comprising adapting responses of both of the high-rate filter portion and the low-rate filter to minimize an error signal. ### Claim 21 An integrated circuit for implementing at least a portion of a personal audio device, comprising: an output for providing an output signal to a transducer including both a source audio signal for playback to a listener and an anti-noise signal for countering the effect of ambient audio sounds in an acoustic output of the transducer; a microphone input for receiving a microphone signal; and a processing circuit that implements: a hybrid filter that generates the anti-noise signal to reduce the presence of the ambient audio sounds at the acoustic output of the transducer based at least on the microphone signal, the hybrid filter comprising: a high-rate filter portion configured to filter an input signal having a first sampling rate to generate a first intermediate anti-noise signal; a low-rate filter portion configured to filter the input signal downsampled to a second sampling rate to generate a second intermediate anti-noise signal; and a summer to sum the intermediate anti-noise signal and the second intermediate anti-noise signal to generate the anti-noise signal. ### Claim 22 (depends on 21) The integrated circuit of claim 21, further comprising a coefficient control block that shapes the response of at least one of the high-rate filter portion and the low-rate filter portion to counter the effect of ambient audio sounds in an acoustic output of the transducer. ### Claim 23 (depends on 21) The integrated circuit of claim 21, wherein: the microphone signal comprises a reference microphone signal indicative of the ambient audio sounds at the acoustic output of the first transducer; and the hybrid filter comprises a feedforward filter configured to generate the anti-noise signal from the reference microphone signal. ### Claim 24 (depends on 21) The integrated circuit of claim 21, wherein: the microphone signal comprises an error microphone signal indicative of the output of the transducer and the ambient audio sounds at the transducer; and the hybrid filter comprises a secondary path estimate adaptive filter for modeling an electro-acoustic path of the first source audio signal through the transducer and having a response that generates a secondary path estimate signal. ### Claim 25 A hybrid finite impulse response filter having a plurality of delay stages, comprising: an analog filter portion associated with a first portion of the plurality of delay stages and configured to filter an input signal to generate a first intermediate output signal; a digital filter portion associated with a second portion of the plurality of delay stages and configured to filter the input signal to generate a second intermediate output signal; and a summer for summing the first intermediate output signal and the second intermediate output signal to generate an output signal of the hybrid impulse response filter. ### Claim 26 (depends on 25) The hybrid finite impulse response filter of claim 25, wherein: each of the plurality of delay stages is associated with a respective delay; and each of the respective delays of the first portion of the plurality of delay stages are lower than each of the respective delays of the second portion of the plurality of delay stages. ### Claim 27 (depends on 25) The hybrid finite impulse response filter of claim 25, wherein, for each sample of the input signal, a corresponding sample of the output signal is generated before receipt by the hybrid finite impulse response filter of a subsequent sample of the input signal. ### Claim 28 (depends on 25) The hybrid finite impulse response filter of claim 25, wherein, for each sample of the input signal, a corresponding sample of the output signal is generated before receipt by the hybrid finite impulse response filter of ten subsequent samples of the input signal. ### Claim 29 (depends on 25) The hybrid finite impulse response filter of claim 25, wherein, for each sample of the input signal, a corresponding sample of the output signal is generated within 50 microseconds of receipt by the hybrid finite impulse response filter of the sample. ### Claim 30 (depends on 25) The hybrid finite impulse response filter of claim 25, wherein each of the plurality of delay stages has associated therewith a respective gain, and at least one of the respective gains is adaptively responsive to at least one of the input signal and the output signal. ### Claim 31 A method comprising: filtering with an analog filter portion associated with a first portion of a plurality of delay stages of a hybrid finite impulse response filter an input signal to generate a first intermediate output signal; filtering with a digital filter portion associated with a second portion of the plurality of delay stages the input signal to generate a second intermediate output signal; and summing the first intermediate output signal and the second intermediate output signal to generate an output signal of the hybrid impulse response filter. ### Claim 32 (depends on 31) The method of claim 31, wherein: each of the plurality of delay stages is associated with a respective delay; and each of the respective delays of the first portion of the plurality of delay stages are lower than each of the respective delays of the second portion of the plurality of delay stages. ### Claim 33 (depends on 31) The method of claim 31, further comprising, for each sample of the input signal, generating a corresponding sample of the output signal before receipt by the hybrid finite impulse response filter of a subsequent sample of the input signal. ### Claim 34 (depends on 31) The method of claim 31, further comprising, for each sample of the input signal, generating a corresponding sample of the output signal before receipt by the hybrid finite impulse response filter of ten subsequent samples of the input signal. ### Claim 35 (depends on 31) The method of claim 31, further comprising, for each sample of the input signal, generating of the output signal within 50 microseconds of receipt by the hybrid finite impulse response filter of the sample. ### Claim 36 (depends on 31) The method of claim 31, wherein each of the plurality of delay stages has associated therewith a respective gain, and at least one of the respective gains is adaptively responsive to at least one of the input signal and the output signal.