Piezoelectric Charge-Drive Circuit With Charge Recirculation
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Solution Overview
Problem
Piezoelectric transducers driven by voltage exhibit hysteresis and creep, leading to distortion in audio applications, which can be mitigated by driving them with charge instead of voltage, but existing charge drive circuitry faces inefficiencies due to high switching losses and complexity.
Innovation Solution
A drive circuitry comprising an inductor, reservoir capacitors, and a switch network controlled by circuitry to selectively couple these components for unipolar or bipolar drive of piezoelectric transducers, operating in a discontinuous mode to transfer charge efficiently and recycle it between the transducer and capacitors, reducing switching losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If piezoelectric transducers are driven by voltage, then the transducer can operate, but hysteresis and creep occur causing distortion
Solution Approach 1:
The patent changes the driving parameter from voltage to charge. By controlling the charge applied to the piezoelectric transducer through a charge pump circuit, the system eliminates hysteresis and creep effects while maintaining reliable transducer operation. The charge-driven approach directly controls the electric displacement field, avoiding the nonlinear voltage-displacement relationship that causes distortion.
2Object-affected harmful factors
If charge drive circuitry is used to reduce hysteresis and creep, then distortion is reduced, but switching losses and circuit complexity increase
Solution Approach 1:
The patent implements a charge recirculation mechanism where charge is transferred from the piezoelectric transducer back to the reservoir capacitor during the return phase. This recovering of charge reduces the net charge that needs to be supplied from the power source, thereby reducing switching losses and improving overall energy efficiency while maintaining the benefits of charge-driven operation.
Solution Approach 2:
The patent employs a discontinuous charge transfer mode alternating with charge recirculation phases. During the charge transfer phase, charge is pumped from the reservoir capacitor to the transducer; during the recirculation phase, charge flows back from the transducer to the capacitor. This continuous cycle maintains useful action while minimizing energy loss through efficient charge management.
3Object-affected harmful factors
If charge drive circuitry is used to reduce hysteresis and creep, then distortion is reduced, but circuit complexity increases
Solution Approach 1:
The patent designs a switch network where the same switching components perform multiple functions: charging the reservoir capacitor from the power source, transferring charge from the reservoir capacitor to the piezoelectric transducer, and recirculating charge back from the transducer to the capacitor. This multi-functionality reduces the need for separate dedicated circuits for each operation, thereby managing circuit complexity while achieving charge-driven operation.
4Loss of energy
If discontinuous charge transfer mode is used, then power efficiency is improved, but continuous drive capability may be affected
Solution Approach 1:
The patent implements a periodic charge transfer and recirculation cycle that operates at frequencies sufficient to maintain continuous drive capability. The discontinuous charge transfer mode transfers charge in periodic pulses from the reservoir capacitor to the piezoelectric transducer, while the recirculation phase replenishes the capacitor. When operated at appropriate frequencies, this periodic action provides effectively continuous drive while maintaining the power efficiency benefits of discontinuous operation.
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 hysteresis and creep in piezoelectric transducers, improving power efficiency and reducing distortion by recirculating charge between the transducer and capacitors, while minimizing switching losses and circuit complexity.
Implementation Method 1
an inductor; a first reservoir capacitor; a switch network; and control circuitry configured to control operation of the switch network to selectively couple the inductor to one of a power supply, the first reservoir capacitor and the piezoelectric transducer
Implementation Method 2
drive a piezoelectric transducer to cause the piezoelectric transducer to produce an audible or haptic output based on the electrical input signal
Data Source
AI summary
Drive circuitry for driving a piezoelectric transducer, the circuitry comprising: an inductor; a first reservoir capacitor; a switch network; and control circuitry configured to control operation of the switch network to selectively couple the inductor to one of a power supply, the first reservoir capacitor and the piezoelectric transducer, wherein the circuitry is operative in a discontinuous mode to transfer charge between the reservoir capacitor and the piezoelectric transducer, and wherein a polarity of the first reservoir capacitor is opposite to a polarity of the power supply.