Piezoelectric Loudspeaker PWM Control With Audible Noise Shaping
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Solution Overview
Problem
The sound quality of piezoelectric loudspeakers is inadequate due to non-linear behavior and temperature-related nonlinearities, leading to quantization noise in the audible frequency range, which affects the accuracy of sound wave generation.
Innovation Solution
A device with a digital correction unit, digital PWM generator, and power stage that corrects non-linearities and converts audio signals into pulse width modulated switching signals to charge the piezoelectric actuator, combined with a noise shaping unit that shifts noise energy outside the audible frequency range to improve sound quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a digital correction unit is used to correct nonlinearity of the loudspeaker, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent combines the digital correction unit, PWM generator, and power stage into a single integrated audio signal processing device. This merging approach maintains the functional benefits of nonlinearity correction while reducing overall device complexity by eliminating the need for separate control circuits and reducing the number of discrete components required.
Solution Approach 2:
The audio signal processing device performs multiple functions simultaneously: it corrects nonlinearity, generates PWM signals, and drives the piezoelectric actuator through the power stage. This multi-functionality eliminates the need for separate dedicated circuits for each function, thereby improving sound quality while maintaining manageable device complexity.
2Productivity
If pulse width modulation is used to convert corrected signals, then productivity is improved, but object-generated harmful factors increase
Solution Approach 1:
The patent applies noise shaping to the PWM quantization noise, intentionally shaping the noise spectrum to push quantization noise out of the audible frequency range and into ultrasonic frequencies. This converts the harmful audible quantization noise into inaudible ultrasonic noise, thereby maintaining the fast response benefits of PWM while eliminating its harmful auditory effects.
3Manufacturing precision
If noise shaping is applied to shift noise energy outside audible range, then sound quality is improved, but use of energy increases
Solution Approach 1:
The noise shaping filter modifies the frequency distribution parameter of the quantization noise, shifting energy from audible to ultrasonic frequencies. This parameter change in the noise spectrum achieves improved sound quality without requiring additional power-consuming hardware, as the noise shaping is implemented through digital signal processing within the existing PWM control architecture.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances sound quality by reducing nonlinearities and quantization noise, ensuring accurate sound wave generation and improved signal-to-noise ratio, thereby improving the overall performance of the piezoelectric loudspeaker.
Implementation Method 1
a piezoelectric actuator of the loudspeaker can be charged with a voltage to deflect a diaphragm
Data Source
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AI summary
The invention relates to a device (1) and method for audio signal processing for a piezoelectric loudspeaker (2) for generating sound waves in the audible wavelength spectrum, comprising a signal input (3) for a digital audio signal (Vin), a digital correction unit (4) for correcting non-linearity of the loudspeaker (2), a digital PWM generator (5) with which the signal corrected by the correction unit (4) can be converted into a pulse-width modulated switching signal, a power stage (6) which can be controlled with the switching signal converted by the PWM generator (5) such that a piezoelectric actuator of the loudspeaker (2) can be charged with a voltage (X) for deflecting a diaphragm, and a feedback loop forming a control circuit with which the voltage can be fed back as a feedback signal (Y(z), Ydig), wherein the feedback signal (Y(z),Ydig) in its intended use exhibits a first signal noise (Qz) in the audible frequency range caused by the correction unit (4), the PWM generator (5), the power stage (6) and/or the piezoelectric loudspeaker (2). According to the invention, the device (1) has a noise shaping unit (16) which is designed and/or implemented in the control loop in such a way that a noise energy of the first signal noise (Qz) can be shifted outside the audible frequency range by means of this unit.