Adaptive PWM Driving Circuit for Piezo-Speaker Voltage Control
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Solution Overview
Problem
Conventional driving circuits, such as class-AB, -D, and -G amplifiers, are not suitable for piezoelectric-actuated speakers due to their highly capacitive loads, leading to inaccurate voltage increments and decrements, which degrade sound quality and output signal fidelity.
Innovation Solution
A method involving a PWM controller with a bidirectional circuit that adaptively adjusts pulse width control codes (PWCC) based on feedback signals to optimize PWM signal generation, using a table learning process to account for device variations and fluctuating battery voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional driving circuits (class-AB, -D, -G amplifiers) are used to drive piezoelectric-actuated speakers, then the circuit design is simple and follows traditional amplifier architecture, but the loading capability is insufficient due to highly capacitive loads causing inaccurate voltage increments and decrements
Solution Approach 1:
The patent changes the operating parameters of the amplifier by implementing a specialized control circuit that adjusts pulse width modulation (PWM) duty cycle based on feedback signals. This allows the amplifier to adapt its voltage increment/decrement characteristics to match the highly capacitive load of piezoelectric speakers, resolving the contradiction between maintaining simple circuit architecture and achieving accurate voltage control under capacitive loading conditions
2Use of energy by moving object
If DC-DC converter with energy recycling capability is used to drive capacitive piezo-speaker, then the energy efficiency is improved, but the performance becomes sensitive to PWM signal pulse width precision which varies with circuit parameters and battery voltage fluctuations
Solution Approach 1:
The patent implements a feedback mechanism where the control circuit receives feedback signals from the piezoelectric speaker and adjusts the PWM duty cycle accordingly. This closed-loop control compensates for variations in circuit parameters and battery voltage, maintaining precise voltage control despite the sensitivity of the DC-DC converter to PWM pulse width changes, thus preserving energy efficiency while ensuring measurement precision
Solution Approach 2:
The patent makes the PWM control dynamic by continuously adjusting the duty cycle based on real-time feedback signals. This dynamic adaptation allows the system to maintain optimal performance across varying operating conditions including battery voltage fluctuations and circuit parameter variations, resolving the contradiction between energy efficiency and pulse width precision
3Productivity
If fixed PWCC table is used in PWM controller, then the control logic is simple and fast, but the accuracy degrades when circuit operating conditions such as battery voltage level fluctuate or device parameters vary
Solution Approach 1:
The patent transforms the static PWCC table into a dynamic control system by implementing interpolation logic that adjusts control codes based on actual operating conditions. The control circuit calculates intermediate values between stored table entries according to real-time feedback signals and operating conditions, maintaining fast control response while adapting to battery voltage fluctuations and device parameter variations, thus resolving the contradiction between control speed and accuracy
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
This approach improves the accuracy of voltage control across piezo-speakers, reducing distortion and enhancing sound quality by dynamically updating PWCCs to match changing operating conditions.
Implementation Method 1
piezoelectric-actuated speakers (piezo-speakers) have emerged
Data Source
AI summary
A method is applied in a pulse width modulation (PWM) controller within a driving circuit including a bidirectional circuit coupled to a load. The method includes steps of: obtaining a pulse width control code (PWCC) from a table stored in a memory within the PWM controller according to a difference between a first feedback signal from the load and an input signal, wherein the PWCC is corresponding to an intended voltage difference, and the first feedback signal is corresponding to a first cycle; generating a plurality of PWM signals according to the PWCC, wherein during a second cycle the bidirectional circuit performs a charging or discharging operation on the load according to the PWM signals; receiving a second feedback signal from the load corresponding to the second cycle; and updating the PWCC according to the first and second feedback signals, and saving the updated PWCC back to the table.