US 8,553,909 B2Granted

Low-power class D amplifier using multistate analog feedback loops

AssigneeSMSC Holdings S.A.R.L.

InventorsJustin L. Fortier, Ralph D. Mason, Renyuan Li, Christopher A. DeVries, Peter H. R. Popplewell, William Kung

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Abstract

An audio amplifier system may include an audio CODEC/output (AOP) path featuring analog class-D amplifiers, and using Natural Sampling Pulse Width Modulation (PWM) to convert an analog input into a series of Rail-to-Rail pulses. The audio signal may be encoded in the average value of the PWM pulse train and may be recovered from the PWM signal by analog low pass filtering. The Class-D amplifiers may be designed with a negative feedback loop/network to compare the output signal with the input signal and suppress non-idealities introduced by the Class-D switching stage. Furthermore, operation of the AOP may be designed according to a separate signal transfer function and a separate noise transfer function, and 2nd order noise shaping may be performed at low power, with an optimized filter included in the feedback loop to achieve the best noise reduction at low power. Operation of the amplifier feedback network may be similar to that of a continuous time, low-pass delta-sigma modulator, but with a PWM loop wrapped around the class-D power amplifier.

Claims26

Dependent claims

An audio processing system comprising:

a dynamic element matching (DEM) component having an output comprising a first number of bits, and further having an input comprising a second number of bits configured to receive a digital audio signal in a first format, wherein the DEM component is configured to:
convert the digital audio signal into a second format;
while converting the digital audio signal into the second format, randomize an ordering of the output bits of the DEM component with respect to the input bits of the DEM component;
and
provide the converted digital audio signal through the output bits of the DEM component according to the randomized ordering of the output bits of the DEM component;
a digital-to-analog converter (DAC) having an input comprising a first number of bits configured to receive the converted digital audio signal from the DEM component, wherein the DAC is configured to convert the converted digital audio signal into a corresponding analog signal;
and
an amplifier network having an input configured to receive the analog signal and generate a modulated digital signal based on the analog signal, wherein the amplifier network comprises a negative feedback loop between an output of the amplifier network and the input of the amplifier network, implementing a transfer function configured to reconstruct the analog signal from the modulated digital signal while attenuating quantization noise to produce an amplified driving signal at the output of the amplifier network.

5 more elements

A method for reducing noise at low power operation of a class-D amplifier amplifying an audio signal, the method comprising:

receiving a digital audio signal in a first format at an input of a dynamic element matching (DEM) component, wherein the DEM component has an output comprising a first number of bits, and wherein the input of the DEM comprises a second number of bits;
the DEM component converting the digital audio signal into a second format, comprising randomizing an ordering of the output bits of the DEM component with respect to the input bits of the DEM component;
the DEM component providing the converted digital audio signal through the output bits of the DEM component according to the randomized ordering of the output bits of the DEM component;
receiving the converted digital audio signal at the input of a digital-to-analog converter (DAC), wherein the input of the DAC comprises a first number of bits;
the DAC converting the converted digital audio signal into a corresponding analog signal;
generating a modulated digital signal based on the analog signal;
producing an amplified driving signal by reconstructing the analog signal from the modulated digital signal and attenuating quantization noise.

4 more elements

A system comprising:

an audio source configured to generate a digital audio signal in a first format having a resolution of a first number of bits;
and
an audio path comprising:
a dynamic element matching (DEM) component configured to:
receive the digital audio signal and convert the digital audio signal into a second format having a resolution of a second number of bits;
randomize an ordering of output bits of the DEM component with respect to input bits of the DEM component;
and
provide the converted digital audio signal through the output bits of the DEM component according to the randomized ordering of the output bits of the DEM component;
a digital-to-analog converter (DAC) configured to receive the converted digital audio signal, and further configured to convert the converted digital audio signal into a corresponding analog signal;
and
an amplifier network configured to receive the analog signal at an input of the amplifier network, and further configured to generate a modulated digital signal based on the analog signal, wherein the amplifier network comprises a negative feedback loop between an output of the amplifier network and the input of the amplifier network to reconstruct the analog signal from the modulated digital signal while attenuating quantization noise, to produce an amplified driving signal at the output of the amplifier network.

8 more elements

Dependencies are inferred from the claim text.