# US 12,009,791 B2 · Increasing power efficiency in a digital feedback class D driver

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- Number: US 12,009,791 B2
- Document ID: US12009791B2
- Status: Granted
- Kind: B2
- Application number: 17/702,312
- Filed: 2022-03-23
- Published: 2022-07-07
- Granted: 2024-06-11
- Earliest claimed: 2019-09-24
- Assignees: Analog Devices, Inc.
- Applicants: Analog Devices, Inc.
- Inventors: Abhishek Bandyopadhyay
- Web page: https://patentgrep.com/patent/US12009791B2

## CPC

- H03F 3/2175: {using analogue-digital or digital-analogue conversion (H03F3/2173 takes precedence)}
- H03F 3/187: in integrated circuits
- H03M 3/412: {characterised by the number of quantisers and their type and resolution}
- H03M 3/464: {Details of the digital/analogue conversion in the feedback path}
- H04R 3/02: for preventing acoustic reaction {, i.e. acoustic oscillatory feedback (specially adapted for hearing aids H04R25/453)}
- H03F 2200/03: the amplifier being designed for audio applications
- H03F 2200/331: Sigma delta modulation being used in an amplifying circuit
- H03F 2200/351: Pulse width modulation being used in an amplifying circuit
- 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)
- 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

Systems and methods are provided for architectures for a digital class D driver that increase the power efficiency of the class D driver. In particular, systems and methods are provided for a digital class D driver having a feedback analog-to-digital converter (ADC) that can have a latency of 1 cycle or more than 1 cycle. A feedback ADC with a latency of 1 cycle or more is significantly lower power than a low latency feedback ADC. Systems and methods are disclosed for a power efficient digital class D driver architecture that allows for a latency of one or more cycles in the feedback ADC.

## Claims

### Claim 1

An architecture for a class D driver, comprising:
a first summer configured to receive a digital input signal;
a digital modulator configured to receive a summer output from the first summer and further configured to produce an output; and
an analog feedback loop from a driver output line to the first summer, the analog feedback loop including:
an analog-to-digital converter comprising a loop filter and a first quantizer, and
a second summer configured to add an analog-to-digital converter output and a second digital input signal, wherein a second summer output is input to the first summer.

### Claim 2 (depends on 1)

The architecture of claim 1, further comprising a second quantizer coupled to the digital modulator, configured to quantize a digital modulator signal, wherein a second quantizer output is the second digital input signal to the second summer.

### Claim 3 (depends on 2)

The architecture of claim 2, wherein the second quantizer is one of a single-hit quantizer and a multi-hit quantizer.

### Claim 4 (depends on 1)

The architecture of claim 1, further comprising a transfer function module configured to receive and filter the digital input signal, wherein a transfer function module output is the second digital input signal that is input to the second summer.

### Claim 5 (depends on 1)

The architecture of claim 1, further comprising a digital-to-analog converter, wherein the digital-to-analog converter is coupled to the second summer output, wherein the digital-to-analog converter converts the second summer output to a feedback loop analog signal, and wherein the feedback loop analog signal is fed back to an analog feedback loop input.

### Claim 6 (depends on 5)

The architecture of claim 5, further comprising a third summer coupled to the digital-to-analog converter and the driver output line, wherein the feedback loop analog signal is input to the third summer.

### Claim 7 (depends on 6)

The architecture of claim 6, wherein the third summer is configured to subtract the feedback loop analog signal from a driver output signal resulting in an error content signal, and the error content signal is output from the third summer to the loop filter.

### Claim 8 (depends on 1)

The architecture of claim 1, further comprising a power stage configured to receive a digital modulator output and generate a driver output signal for the driver output line.

### Claim 9 (depends on 1)

The architecture of claim 1, fluffier comprising a filter configured to filter the output from the digital modulator, wherein the driver output line is an output from the filter.

### Claim 10 (depends on 1)

The architecture of claim 1, further comprising a speaker configured to receive the output from the digital modulator, wherein the driver output line is an output from the speaker.

### Claim 11 (depends on 1)

The architecture of claim 1, wherein the analog-to-digital converter output is a digital output signal from the first quantizer.

### Claim 12 (depends on 1)

The architecture of claim 1, wherein the analog-to-digital converter output is an output from the loop filter.

### Claim 13

A method for a digital class D driver, comprising:
receiving a digital input signal at a first summer;
performing digital modulation on a first summer output from the first summer, at a digital modulator;
amplifying a digital modulator output at a power stage and generating a driver output signal;
filtering an error signal from the driver output signal through an analog feedback loop from a driver output line to the first summer, resulting in a filtered signal;
quantizing the filtered signal at a first quantizer in the analog feedback loop, resulting in a quantized filtered signal;
adding the quantized filtered signal and a second digital input signal at a second summer to generate a second summer summed signal; and
subtracting, at the first summer, the second summer summed signal from the digital input signal.

### Claim 14 (depends on 13)

The method of claim 13, further comprising quantizing a digital modulator signal at a second quantizer, wherein a second quantizer output is the second digital input signal that is input to the second summer.

### Claim 15 (depends on 13)

The method of claim 13, further comprising receiving the digital input signal at a transfer function module, and adding a delay to the digital input signal at the transfer function module, wherein a transfer function module output is the second digital input signal that is input to the second summer.

### Claim 16 (depends on 13)

The method of claim 13, further comprising adding a delay to the analog feedback loop from a driver output line to the first summer.

### Claim 17 (depends on 13)

The method of claim 13, further comprising converting the quantized filtered signal to a feedback loop analog signal and, at a third summer, subtracting the feedback loop analog signal from the driver output signal to generate the error signal.

### Claim 18

A circuit for a digital class D driver, the circuit comprising:
a first summer configured to receive a digital input signal;
a digital modulator configured to receive a summer output from the first summer and is further configured to produce a digital modulator output;
means for amplifying the digital modulator output and generating a driver output signal; and
an analog feedback loop from a driver output line to the first summer, the analog feedback loop including:
means for filtering an error signal from the driver output signal through the analog feedback loop from the driver output line to the first summer, wherein the analog feedback loop includes an analog-to-digital converter; and
means for adding an analog-to-digital converter output and a second digital input signal to generate a summed feedback signal, wherein the summed feedback signal is input to the first summer.

### Claim 19 (depends on 18)

The circuit of claim 18, further comprising means for quantizing a digital modulator signal to generate the second digital input signal.

### Claim 20 (depends on 18)

The circuit of claim 18, further comprising means for filtering the digital input signal to generate the second digital, input signal.