Piezoelectric Driver Circuit for Mobile Haptics
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Solution Overview
Problem
Piezoelectric transducers used in mobile devices for speaker and haptics functionality are challenging to drive efficiently due to their high capacitive loads, requiring expensive components and high battery current, which increases costs and reduces robustness.
Innovation Solution
A driver apparatus comprising H-bridges and a control circuit that operates in buck, boost, and buck-boost modes to efficiently drive piezoelectric transducers within the audio band, reducing the need for multiple large inductors and minimizing battery current while maintaining performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a class G or class H boost stage with a class D amplifier is used to drive piezoelectric transducers, then the transducer can be driven with sufficient quality and power, but multiple large and expensive inductors are required, causing prohibitively high cost
Solution Approach 1:
The patent combines the boost converter and H-bridge amplifier into a single integrated circuit device, merging multiple discrete components (inductors, switches, control logic) into one unified chip. This integration eliminates the need for multiple large external inductors while maintaining the required transducer driving quality and power delivery capability
Solution Approach 2:
The integrated circuit performs multiple functions simultaneously: it provides voltage conversion (boost capability), voltage inversion (H-bridge capability), and transducer driving. This multi-functionality replaces what previously required separate discrete components, reducing overall device complexity and cost
2Power
If a class G or class H boost stage with a class D amplifier is used to drive piezoelectric transducers, then sufficient power can be delivered, but multiple large and expensive components are required, causing prohibitively high cost
Solution Approach 1:
The patent merges the power conversion and power delivery functions into a single integrated circuit, combining the boost converter stage and H-bridge amplifier stage that previously required multiple discrete components. This maintains full power delivery capability while dramatically reducing component count and overall system cost
3Reliability
If conventional driver circuits are used for piezoelectric transducers, then the transducer can be driven, but high battery current is required, reducing robustness
Solution Approach 1:
The patent implements adaptive voltage control that dynamically adjusts the output voltage parameters based on the transducer's operational state and signal requirements. By optimizing the voltage waveform parameters (amplitude, duty cycle, switching frequency) in real-time, the circuit achieves efficient power delivery with reduced average battery current draw, thereby improving robustness
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 efficiently drives piezoelectric transducers with reduced battery current and cost, enabling effective haptics and audio functionality while minimizing component expenses.
Implementation Method 1
a piezoelectric transducer can be secured to a screen so as to vibrate the screen
Implementation Method 2
a first H-bridge that is coupled to the supply terminal, the boost terminal, the first switching terminal, and the second switching terminal
Data Source
AI summary
A method for driving a piezoelectric transducer is provided. An input signal is received. At least one of a plurality of modes is selected for a buck-boost stage from a comparison of a desired voltage on a capacitor to a first threshold and a second threshold, where the desired voltage is determined from the input signal. The piezoelectric transducer is then driven substantially within the audio band using the desired voltage on the capacitor using an H-bridge that changes state with each zero-crossing.