# US 10,313,792 B2 · Digital microphones > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,313,792 B2 - Document ID: US10313792B2 - Status: Granted - Kind: B2 - Application number: 15/439,480 - Filed: 2017-02-22 - Published: 2017-08-31 - Granted: 2019-06-04 - Earliest claimed: 2016-02-26 - Assignees: Cirrus Logic, Inc. - Applicants: Cirrus Logic International Semiconductor Ltd. - Inventors: John Paul Lesso; John Laurence Melanson - Web page: https://patentgrep.com/patent/US10313792B2 ## CPC - H04R 3/06: of electrostatic transducers - H04R 3/00: Circuits for transducers (arrangements for producing a reverberation or echo sound G10K15/08; amplifiers H03F) - H04R 19/005: {using semiconductor materials} - H04R 19/04: Microphones (H04R19/01 takes precedence) - H04R 2201/003: Mems transducers or their use - H04R 2217/03: Parametric transducers where sound is generated or captured by the acoustic demodulation of amplitude modulated ultrasonic waves - H04R 2410/00: Microphones - H04R 2420/09: Applications of special connectors, e.g. USB, XLR, in loudspeakers, microphones or headphones - H04R 2430/03: Synergistic effects of band splitting and sub-band processing - H04R 2499/11: Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's - H04R: LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS (producing sounds with frequency not determined by supply frequency G10K) ## Abstract This application relates to methods and apparatus for digital microphones. Disclosed is a digital microphone apparatus (300) for outputting a digital output signal (DATA) at a sample rate defined by a received clock signal (CLK). The apparatus includes a band splitter (302) configured to receive a microphone signal (SMD) indicative of an output of a microphone transducer and split said microphone signal into first signal path (SP1) for frequencies in a first band and a second signal path (SP2) for frequencies in a second band, the frequencies of the second band being higher than the frequencies in the first band. A modulation block (304) is configured to operate on the second signal path to apply a selective gain modulation to signals in the second signal path. ## Claims ### Claim 1 A digital microphone apparatus for outputting a digital output signal at a sample rate defined by a received clock signal received by the digital microphone apparatus, the apparatus comprising: a band splitter configured to receive a microphone signal indicative of an output of a microphone transducer and split said microphone signal into first signal path for frequencies in a first band and a second signal path for frequencies in a second band, the frequencies of the second band being higher than the frequencies in the first band; and a modulation block configured to apply a selective gain modulation to signals in the second signal path. ### Claim 2 (depends on 1) A digital microphone apparatus as claimed in claim 1 wherein the modulation block comprise a gain element in the second signal path and a gain controller for controlling a gain setting of the gain element. ### Claim 3 (depends on 2) A digital microphone apparatus as claimed in claim 2 wherein the modulation block comprises a detector for detecting the power of any signal component in the second frequency band, wherein the gain controller is responsive to said power detector to control the gain setting. ### Claim 4 (depends on 3) A digital microphone apparatus as claimed in claim 3 wherein the controller is configured to control the gain setting according to a predetermined transfer function of gain setting versus an output signal of said power detector. ### Claim 5 (depends on 3) A digital microphone apparatus as claimed in claim 3 wherein the controller is configured to control the gain setting based on the detected power of any signal component in the second frequency band so as to achieve a predetermined signal-to-noise ratio for such signal component in the digital output signal. ### Claim 6 (depends on 3) A digital microphone apparatus as claimed in claim 3 wherein the controller is configured such that, for any signal components in the second frequency band where the detected power is above the threshold the gain setting is controlled to maintain a constant power output of the gain modulated signals in the second signal path. ### Claim 7 (depends on 2) A digital microphone apparatus as claimed in claim 2 wherein the second signal path comprises a band-pass filter upstream of the gain element with a pass-band corresponding to the second frequency band. ### Claim 8 A digital microphone apparatus as claimed in 7 wherein the band-pass filter in the second signal path is configured so that its pass-band is variable. ### Claim 9 (depends on 8) A digital microphone apparatus as claimed in claim 8 wherein the modulation block comprises a band controller for varying the pass band of the band-pass filter and detecting any activity above a defined threshold in the signal output from the band-pass filter. ### Claim 10 (depends on 1) A digital microphone apparatus as claimed in claim 1 comprising a coder block for receiving signals from said first and second signal paths and encoding the signals to provide said digital output signal. ### Claim 11 (depends on 10) A digital microphone apparatus as claimed in claim 10 where said coder block is operable so that the digital output signal is encoded in a 1 bit oversampled PDM format. ### Claim 12 (depends on 1) A digital microphone apparatus as claimed in claim 1 wherein said microphone signal is a digital microphone signal. ### Claim 13 (depends on 12) A digital microphone apparatus as claimed in claim 12 comprising an analogue-to-digital converter for receiving an analogue microphone signal and producing said digital microphone signal. ### Claim 14 (depends on 1) A digital microphone apparatus as claimed in claim 1 comprising a microphone transducer, the microphone signal being derived from the microphone transducer. ### Claim 15 (depends on 14) A digital microphone apparatus as claimed in claim 14 wherein said microphone transducer is a MEMS capacitive microphone. ### Claim 16 (depends on 1) An electronic device comprising a digital microphone apparatus as claimed in claim 1 and further comprising an audio codec, said audio codec being configured to, in use, receive said digital output signal. ### Claim 17 (depends on 1) An electronic device comprising a digital microphone apparatus as claimed in claim 1 wherein the electronic device comprises at least one of: a portable device, a battery powered device, a mobile telephone, an audio player, a video player, a computing device, a laptop, tablet or notebook computer, a games device, a wearable device and a voice activated device. ### Claim 18 A digital microphone apparatus for outputting a digital output signal at a sample rate defined by a received clock signal, the apparatus comprising: a band splitter configured to receive a microphone signal indicative of an output of a microphone transducer and split said microphone signal into first signal path for frequencies in a first band and a second signal path for frequencies in a second band, the frequencies of the second band being higher than the frequencies in the first band; and a modulation block comprising a detector for detecting the power of any signal component in the second frequency band, a gain element in the second signal path and a gain controller for controlling a gain setting of the gain element based on the detected power.