Piezo Haptics Driver Amplifier With Feedback for Capacitive Loads
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Solution Overview
Problem
High-voltage amplifiers for Piezo haptics face challenges in efficiency, quiescent current, and stability due to the nearly pure capacitive load of Piezo elements, which results in significant heat dissipation and harmonic distortion, especially when boosting voltages from 3 to 4.2 volts to 200 volts differentially.
Innovation Solution
A high-voltage driver amplifier system incorporating a parallel amplifier pair with a feedback loop and shunt impedance to manage the capacitive load, allowing for efficient voltage and current management across the Piezo-capacitance, reducing stability concerns and harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-voltage amplifier drives a nearly pure capacitive load from Piezo elements, then the desired haptical information is delivered, but significant heat is dissipated in coupling lines and power efficiency deteriorates
Solution Approach 1:
The patent implements a feedback mechanism where the output of the first amplifier is fed back through a feedback impedance to the input of the input amplifier. This feedback loop allows the system to monitor and adjust its operation, improving power efficiency by optimizing the drive signal to the capacitive load and reducing unnecessary energy dissipation in coupling lines.
Solution Approach 2:
The patent changes the electrical parameters of the amplifier system by using an input amplifier with gain greater than one to boost the signal before it reaches the parallel amplifier pair. This parameter change allows the system to drive the capacitive load more efficiently, reducing the current required and thereby reducing I²R losses in the coupling lines.
2Power
If voltage is boosted from 3-4.2 volts to 200 volts differentially to drive Piezo elements, then the required drive voltage is achieved, but quiescent current increases significantly
Solution Approach 1:
The patent segments the high-voltage amplification function into multiple stages: an input amplifier stage with gain greater than one, followed by a parallel pair of amplifiers. This segmentation allows the voltage boosting to be distributed across stages, reducing the quiescent current requirement at each stage compared to a single high-gain stage, while still achieving the required 200V differential output.
Solution Approach 2:
The patent employs dynamic operation in the amplifier stages, where the parallel amplifier pair can be selectively activated based on the required output voltage. This dynamic operation allows the system to maintain low quiescent current when full power is not needed, while still being capable of delivering 200V differential when required.
3Productivity
If a high-voltage amplifier operates with a nearly pure capacitive load, then Piezo haptics are driven, but stability becomes problematic
Solution Approach 1:
The feedback impedance connected between the output of the first amplifier and the input of the input amplifier provides stabilizing feedback that compensates for the phase shifts introduced by the capacitive load. This feedback mechanism monitors the output and adjusts the input signal to maintain stability, allowing the amplifier to reliably drive the Piezo capacitive load.
Solution Approach 2:
The feedback impedance acts as an intermediary element that mediates between the amplifer output and input. This intermediary component helps to isolate the amplifier from the destabilizing effects of the pure capacitive load, providing a buffer that maintains system stability while still allowing effective driving of the Piezo elements.
4Ease of operation
If prior-art amplifiers are used to drive capacitive loads, then operation is possible, but harmonic distortion increases
Solution Approach 1:
The feedback loop in the patent's amplifier design monitors the output signal and corrects for nonlinearities and harmonic distortion. By comparing the actual output with the desired output and adjusting the input signal accordingly, the feedback mechanism reduces harmonic distortion and improves signal fidelity while maintaining ease of operation with capacitive loads.
Data Source
AI summary
A high-voltage driver amplifier for piezo haptics comprises an input amplifier having a gain greater than one, a first amplifier of an amplifier pair coupled to an output of the input amplifier, a second amplifier of the amplifier pair coupled to the output of the input amplifier, a first impedance coupled between an output of the first amplifier of the amplifier pair and an input of the input amplifier, and a second impedance coupled between the output of the first amplifier of the amplifier pair coupled to an output of the second amplifier of the amplifier pair. A substantially capacitive load is coupled to the output of the second amplifier. The substantially capacitive load is a piezo-capacitance, wherein the piezo-capacitance is employed in haptics. The second impedance, a shunt impedance, allows for a feedback of output variations between the first amplifier and the second amplifier over the first impedance.