Piezoelectric Transformer Modulation for Acoustic Noise
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Solution Overview
Problem
Piezoelectric transformers used in LCD backlighting produce audible noise due to intermodulation products from mixing resonant and modulation frequencies, affecting user experience and requiring a method to reduce sound without compromising amplification.
Innovation Solution
A power-supply circuit with a modulation mechanism that applies both duty-cycle and additional frequency, pulse-time, or phase modulation to spread harmonic energy over a range of frequencies, reducing the perception of sound associated with the power-supply signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If duty-cycle modulation is applied to control display brightness, then brightness control is achieved, but audible noise is generated due to intermodulation products
Solution Approach 1:
The patent applies dynamic modulation by combining duty-cycle modulation with additional frequency modulation. The modulation frequency is dynamically adjusted to spread harmonic energy across a broader frequency spectrum, transforming the fixed-frequency audible noise into distributed frequency components that are less perceptible as discrete tones while maintaining brightness control functionality
Solution Approach 2:
The patent changes the frequency parameter of the modulation signal by introducing frequency modulation on top of the duty-cycle modulation. This parameter change spreads the harmonic energy from a narrow frequency range to a broader spectrum, reducing the concentration of energy at specific audible frequencies while preserving the average power for brightness control
2Object-generated harmful factors
If mechanical constraints are applied to reduce sound, then audible noise is reduced, but amplification capability is reduced
Solution Approach 1:
The patent replaces mechanical constraint approaches with an electronic signal processing approach. Instead of physically constraining the piezoelectric transformer to reduce sound, the system applies additional frequency modulation to the electrical signal, which spreads harmonic energy across a broader spectrum and reduces audible noise without affecting the mechanical amplification process
3Object-generated harmful factors
If additional frequency modulation is applied to spread harmonic energy, then sound perception is reduced, but device complexity increases
Solution Approach 1:
The patent merges the duty-cycle modulation and frequency modulation into a unified modulation mechanism. By combining these two modulation techniques in a coordinated manner, the system achieves sound reduction through frequency spreading while avoiding the need for separate independent modulation circuits, thus managing complexity through integration
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 effectively reduces the perception of sound generated by the piezoelectric transformer while maintaining the brightness control and amplification efficiency, by spreading harmonic energy over a broader frequency range, thus enhancing the user experience.
Implementation Method 1
This is accomplished by applying an AC-input voltage to the piezoelectric transformer. This applied voltage has a frequency near a resonant frequency of the piezoelectric transformer (around 50 kHz) and causes mechanical oscillations in the piezoelectric transformer which amplify the input voltage.
Implementation Method 2
the second modulation includes frequency modulation, pulse-time modulation, and/or phase modulation
Data Source
AI summary
A power-supply circuit is described. In particular, the power-supply circuit includes an input node configured to receive a power-supply signal, an output node configured to output a modulated power-supply signal, and a modulation mechanism coupled between the input node and the output node. This modulation mechanism is configured to modulate the power-supply signal to produce the modulated power-supply signal. Furthermore, the modulation mechanism may be configured to modulate the power-supply signal using both a first modulation and a second modulation. This first modulation is a duty-cycle modulation which controls the power output of the piezoelectric transformer signal, and the second modulation spreads harmonic energy associated with the first modulation over a range of frequencies. By spreading the harmonic energy, the perceived acoustical noise generated by the piezoelectric transformer is reduced.