Piezoelectric Driver Circuit with Charge Recycling for Low Distortion
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Solution Overview
Problem
Piezoelectric transducers exhibit hysteresis and creep when driven by voltage, leading to distortion in audio applications, and require high voltage boosts which are difficult to achieve efficiently, especially in battery-powered devices.
Innovation Solution
A circuitry system using a reservoir capacitance, switch network, and control circuitry to transfer charge efficiently between a power supply, reservoir capacitance, and piezoelectric transducer, with inductors for energy storage and feedback mechanisms to manage charge levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If voltage is used to drive the piezoelectric transducer, then the transducer can be easily controlled, but hysteresis and creep occur causing distortion
Solution Approach 1:
The patent changes the driving parameter from voltage to charge. By using charge drive circuitry that transfers charge to the piezoelectric transducer rather than applying voltage, the system eliminates hysteresis and creep effects while maintaining control capability. The charge transfer mechanism uses switching circuitry to move discrete charge packets, achieving both ease of control and signal accuracy.
2Reliability
If charge drive circuitry is used to improve signal accuracy, then hysteresis and creep are reduced, but power efficiency deteriorates due to continuous charging requirements
Solution Approach 1:
The patent implements charge recycling by capturing the discharge current from the piezoelectric transducer when it returns to ground potential and redirecting this current to recharge the reservoir capacitor. This recovery mechanism allows the system to maintain charge drive benefits while significantly improving power efficiency, as the recycled charge reduces the need for continuous power supply charging.
Solution Approach 2:
The reservoir capacitor continuously stores charge available for driving the piezoelectric transducer, eliminating interruptions in charge delivery. The capacitor maintains a steady charge level through continuous recycling from the transducer discharge current, ensuring uninterrupted charge drive operation and improving overall system efficiency.
3Force
If high voltage boost is applied to drive thin piezoelectric transducers, then transducer displacement is achieved, but device complexity increases due to multiple converters and inductors
Solution Approach 1:
The patent segments the charge transfer process into two distinct phases: charging the reservoir capacitor from the power supply, and transferring charge from the reservoir capacitor to the piezoelectric transducer. This segmentation allows each phase to be optimized independently and simplifies the overall circuit design compared to traditional multi-stage voltage boost converters.
Solution Approach 2:
The reservoir capacitor acts as an intermediary energy storage element between the power supply and the piezoelectric transducer. Instead of using complex voltage boost converters, the system uses the capacitor to store charge at an intermediate level and then transfer it to the transducer, simplifying the overall architecture while achieving the required displacement.
4Power
If duty cycle is increased to achieve high voltage gain, then voltage boost is achieved, but switching frequency requirements increase making practical implementation difficult
Solution Approach 1:
The reservoir capacitor is charged in advance from the power supply before charge transfer to the piezoelectric transducer begins. This preliminary charging action stores the necessary energy locally, eliminating the need for high-duty-cycle switching during the actual transducer drive operation. The capacitor maintains the voltage level needed for effective transducer operation without requiring continuous high-frequency switching.
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
Improves power efficiency by recycling charge between the piezoelectric transducer and reservoir capacitance, reducing power consumption and extending battery life while minimizing distortion.
Implementation Method 1
a reservoir capacitance; switch network circuitry; and control circuitry configured to control operation of the switch network circuitry so as to charge the reservoir capacitance from the power supply and to transfer charge between the reservoir capacitance and the piezoelectric transducer
Implementation Method 2
Piezoelectric transducers are increasingly being seen as a viable alternative to transducers such as speakers and resonant actuators for providing audio and/or haptic outputs
Data Source
AI summary
The present disclosure relates to driver circuitry for driving a piezoelectric transducer. The circuitry comprises: a power supply; a reservoir capacitance; switch network circuitry; and control circuitry. The control circuitry is configured to control operation of the switch network circuitry so as to charge the reservoir capacitance from the power supply and to transfer charge between the reservoir capacitance and the piezoelectric transducer.