# US 10,375,475 B2 · Systems and methods for compressing a digital signal in a digital microphone system

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- Number: US 10,375,475 B2
- Document ID: US10375475B2
- Status: Granted
- Kind: B2
- Application number: 14/247,771
- Filed: 2014-04-08
- Published: 2014-10-09
- Granted: 2019-08-06
- Earliest claimed: 2013-04-09
- Assignees: Cirrus Logic, Inc.
- Applicants: Cirrus Logic, Inc.
- Inventors: John L. Melanson; John C. Tucker
- Web page: https://patentgrep.com/patent/US10375475B2

## CPC

- H04R 3/02: for preventing acoustic reaction {, i.e. acoustic oscillatory feedback (specially adapted for hearing aids H04R25/453)}
- H03F 1/26: Modifications of amplifiers to reduce influence of noise generated by amplifying elements
- H03F 3/16: with field-effect devices
- H03M 3/00: Conversion of analogue values to or from differential modulation
- H03M 3/39: {Structural details of delta-sigma modulators, e.g. incremental delta-sigma modulators (of digital delta-sigma modulators H03M7/3004)}
- H03M 3/424: {the quantiser being a multiple bit one}
- H03M 7/3026: {the quantiser being a multiple bit one}
- H03M 7/3028: {the quantiser being a single bit one}
- H04R 3/00: Circuits for transducers (arrangements for producing a reverberation or echo sound G10K15/08; amplifiers H03F)
- H04R 3/002: {Damping circuit arrangements for transducers, e.g. motional feedback circuits}
- H04R 3/007: {Protection circuits for transducers}
- H04R 29/001: {for loudspeakers (H04R29/007 takes precedence)}
- H03F 2200/372: Noise reduction and elimination in amplifier
- H03M 3/458: {Analogue/digital converters using delta-sigma modulation as an intermediate step}
- H03M 3/50: {Digital/analogue converters using delta-sigma modulation as an intermediate step (digital delta-sigma modulators per se H03M7/3004)}
- H04R 19/04: Microphones (H04R19/01 takes precedence)
- 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)
- H03F: AMPLIFIERS
- H03M: CODING; DECODING; CODE CONVERSION IN GENERAL (using fluidic means F15C4/00; optical analogue/digital converters G02F7/00; coding, decoding or code conversion, specially adapted for particular applications, see the relevant subclasses, e.g. G01D, G01R, G06F, G06T, G09G, G10L, G11B, G11C, H04B, H04L, H04M, H04N; ciphering or deciphering for cryptography or other purposes involving the need for secrecy G09C)

## Abstract

In accordance with embodiments of the present disclosure, a digital microphone system may include a microphone transducer and a digital processing system. The microphone transducer may be configured to generate an analog input signal indicative of audio sounds incident upon the microphone transducer. The digital processing system may be configured to convert the analog input signal into a first digital signal having a plurality (e.g., more than 3) of quantization levels, and in the digital domain, process the first digital signal to compress the first digital signal into a second digital signal having fewer quantization levels (e.g., +1, 0, −1) than that of the first digital signal.

## Claims

### Claim 1

A digital microphone system comprising:
a microphone transducer configured to generate an analog input signal indicative of audio sounds incident upon the microphone transducer;
a digital processing system configured to:
convert the analog input signal into a first digital signal having a plurality of quantization levels; and
in the digital domain, process the first digital signal to compress the first digital signal into a second digital signal having fewer quantization levels than that of the first digital signal, such that a third digital signal equivalent to the first digital signal can be reconstructed from the second digital signal;
wherein:
each quantization level of the second digital signal is represented by one of a plurality of possible digital codes;
the number of possible digital codes is more than the number of quantization levels of the second digital signal; and
one or more of the possible digital codes not corresponding to quantization levels represent a control signal associated with the digital microphone system.

### Claim 2 (depends on 1)

The system of claim 1, wherein the microphone transducer and the digital processing system are formed on a single substrate.

### Claim 3 (depends on 1)

The system of claim 1, wherein the microphone transducer and the digital processing system are formed on different substrates packaged within the same integrated circuit package.

### Claim 4 (depends on 1)

The system of claim 1, wherein the microphone transducer comprises a microelectromechanical systems microphone.

### Claim 5 (depends on 1)

The system of claim 1, wherein:
each quantization level of the first digital signal is represented by an N-bit digital code, wherein N is a positive integer; and
each quantization level of the second digital signal is represented by an M-bit digital code, wherein M is a positive integer less than N.

### Claim 6 (depends on 5)

The system of claim 5, wherein:
the second digital signal has three quantization levels, including:
a first quantization level that corresponds to an increase in the first digital signal equal to one quantization level of the first digital signal;
a second quantization level that corresponds to no change of the quantization level of the first digital signal; and
a third quantization level that corresponds to a decrease in the first digital signal equal to one quantization level of the first digital signal; and
the quantization level of the second digital signal is represented by a transition or lack of transition of the second digital signal.

### Claim 7 (depends on 6)

The system of claim 6, wherein the digital processing system is further configured to:
communicate the second digital signal on a bus interleaved with one or more control signals; and
suppress communication of control signals when the second digital signal is of the second quantization level.

### Claim 8 (depends on 1)

The system of claim 1, wherein the control signal represents a signal gain associated with the digital microphone system.

### Claim 9 (depends on 1)

The system of claim 1, wherein the control signal represents a direct current bias associated with the digital microphone system.

### Claim 10 (depends on 1)

The system of claim 1, wherein the third digital signal is reconstructed by integrating values of the second digital signal.

### Claim 11 (depends on 1)

The system of claim 1, wherein the second digital signal is indicative of a change, if any, between successive samples of the first digital signal.

### Claim 12

A system comprising:
a microphone transducer configured to generate an analog input signal indicative of audio sounds incident upon the microphone transducer; and
a digital processing system configured to convert the analog input signal into a digital signal having a plurality of quantization levels, such that each quantization level is uniquely obtained by a determined transition or of one or more bits of the digital signal during a sampling period of the digital signals;
wherein:
the digital signal has three quantization levels, including:
a first quantization level that corresponds to an increase in the analog input signal;
a second quantization level that corresponds to no change of the analog input signal; and
a third quantization level that corresponds to a decrease in the analog input signal;
the quantization level of the digital signal is represented by a transition or lack of transition of the digital signal; and
the digital processing system is further configured to:
communicate the digital signal on a bus interleaved with one or more control signals; and
suppress communication of control signals when the digital signal is of the second quantization level.

### Claim 13

A method comprising:
generating an analog input signal indicative of audio sounds incident upon a microphone transducer;
converting the analog input signal into a first digital signal having a plurality of quantization levels; and
in the digital domain, processing the first digital signal to compress the first digital signal into a second digital signal having fewer quantization levels than that of the first digital signal, such that a third digital signal equivalent to the first digital signal can be reconstructed from the second digital signal;
wherein:
each quantization level of the second digital signal is represented by one of a plurality of possible digital codes;
the number of possible digital codes is more than the number of quantization levels of the second digital signal; and
one or more of the possible digital codes not corresponding to quantization levels represent a control signal associated with the digital microphone system.

### Claim 14 (depends on 13)

The method of claim 13, wherein the control signal represents a signal gain associated with the digital microphone system.

### Claim 15 (depends on 13)

The method of claim 13, wherein the control signal represents a direct current bias associated with the digital microphone system.

### Claim 16 (depends on 13)

The method of claim 13, wherein:
each quantization level of the first digital signal is represented by an N-bit digital code, wherein N is a positive integer; and
each quantization level of the second digital signal is represented by an M-bit digital code, wherein M is a positive integer less than N.

### Claim 17 (depends on 16)

The method of claim 16, wherein:
the second digital signal has three quantization levels, including:
a first quantization level that corresponds to an increase in the first digital signal equal to one quantization level of the first digital signal;
a second quantization level that corresponds to no change of the quantization level of the first digital signal; and
a third quantization level that corresponds to a decrease in the first digital signal equal to one quantization level of the first digital signal; and
the quantization level of the second digital signal is represented by a transition or lack of transition of the second digital signal.

### Claim 18 (depends on 17)

The method of claim 17, further comprising:
communicating the second digital signal on a bus interleaved with one or more control signals; and
suppressing communication of control signals when the second digital signal is of the second quantization level.

### Claim 19 (depends on 13)

The method of claim 13, wherein the microphone transducer comprises a microelectromechanical systems microphone.

### Claim 20 (depends on 13)

The method of claim 13, wherein the third digital signal is reconstructed by integrating values of the second digital signal.

### Claim 21 (depends on 13)

The method of claim 13, wherein the second digital signal is indicative of a change, if any, between successive samples of the first digital signal.

### Claim 22

A method comprising:
generating an analog input signal indicative of audio sounds incident upon a microphone transducer;
converting the analog input signal into a digital signal having a plurality of quantization levels, such that each quantization level is uniquely obtained by a determined transition or of one or more bits of the digital signal during a sampling period of the digital signal, wherein:
the digital signal has three quantization levels, including:
a first quantization level that corresponds to an increase in the analog input signal;
a second quantization level that corresponds to no change of the analog input signal; and
a third quantization level that corresponds to a decrease in the analog input signal; and
the quantization level of the digital signal is represented by a transition or lack of transition of the digital signal;
communicating the digital signal on a bus interleaved with one or more control signals; and
suppressing communication of control signals when the digital signal is of the second quantization level.

### Claim 23

An integrated circuit comprising:
a microphone input configured to receive an analog input signal indicative of audio sounds incident upon a microphone transducer; and
a processing circuit configured to:
convert the analog input signal into a first digital signal having a plurality of quantization levels; and
in the digital domain, process the first digital signal to compress the first digital signal into a second digital signal having fewer quantization levels than that of the first digital signal, such that a third digital signal equivalent to the first digital signal can be reconstructed from the second digital signal;
wherein:
each quantization level of the second digital signal is represented by one of a plurality of possible digital codes;
the number of possible digital codes is more than the number of quantization levels of the second digital signal; and
one or more of the possible digital codes not corresponding to quantization levels represent a control signal associated with the digital microphone system.

### Claim 24 (depends on 23)

The integrated circuit of claim 23, wherein the microphone transducer comprises a microelectromechanical systems microphone.

### Claim 25 (depends on 23)

The integrated circuit of claim 23, wherein:
each quantization level of the first digital signal is represented by an N-bit digital code, wherein N is a positive integer; and
each quantization level of the second digital signal is represented by an M-bit digital code, wherein M is a positive integer less than N.

### Claim 26 (depends on 25)

The integrated circuit of claim 25, wherein:
the second digital signal has three quantization levels, including:
a first quantization level that corresponds to an increase in the first digital signal equal to one quantization level of the first digital signal;
a second quantization level that corresponds to no change of the quantization level of the first digital signal; and
a third quantization level that corresponds to a decrease in the first digital signal equal to one quantization level of the first digital signal; and
the quantization level of the second digital signal is represented by a transition or lack of transition of the second digital signal.

### Claim 27 (depends on 26)

The integrated circuit of claim 26, wherein the processing circuit is further configured to:
communicate the second digital signal on a bus interleaved with one or more control signals; and
suppress communication of control signals when the second digital signal is of the second quantization level.

### Claim 28 (depends on 23)

The integrated circuit of claim 23, wherein the control signal represents a signal gain associated with the digital microphone system.

### Claim 29 (depends on 23)

The integrated circuit of claim 23, wherein the control signal represents a direct current bias associated with the digital microphone system.

### Claim 30 (depends on 23)

The integrated circuit of claim 23, wherein the third digital signal is reconstructed by integrating values of the second digital signal.

### Claim 31 (depends on 23)

The integrated circuit of claim 23, wherein the second digital signal is indicative of a change, if any, between successive samples of the first digital signal.

### Claim 32

An integrated circuit comprising:
a microphone input configured to receive an analog input signal indicative of audio sounds incident upon a microphone transducer; and
a processing circuit configured to convert the analog input signal into a digital signal having a plurality of quantization levels, such that each quantization level is uniquely obtained by a determined transition or of one or more bits of the digital signal during a sampling period of the digital signal;
wherein:
the digital signal has three quantization levels, including:
a first quantization level that corresponds to an increase in the analog input signal;
a second quantization level that corresponds to no change of the analog input signal; and
a third quantization level that corresponds to a decrease in the analog input signal;
the quantization level of the digital signal is represented by a transition or lack of transition of the digital signal; and
the processing circuit is further configured to:
communicate the digital signal on a bus interleaved with one or more control signals; and
suppress communication of control signals when the digital signal is of the second quantization level.