Oscillation Circuit for Piezoelectric Resonator Stability
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Solution Overview
Problem
Piezoelectric resonators used in vibration devices for notification in cellular phones and wearable terminals face challenges in achieving stable oscillation near the mechanical resonance frequency due to variations in resonance frequency and low Q factor, leading to unreliable vibration performance.
Innovation Solution
An oscillation circuit with a first amplifier and a piezoelectric resonator connected between its input and output ends, featuring a feedback mechanism that applies an alternating-voltage waveform with sharper rising portions than a sine wave, and an optional filter to attenuate damped-capacitance currents, ensuring stable oscillation even with piezoelectric resonators having low Q factor and phase rotation variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a piezoelectric resonator with low Q factor is used to achieve vibration notification, then the device can be compact and energy-efficient, but stable oscillation near mechanical resonance frequency cannot be ensured due to phase rotation variations
Solution Approach 1:
The patent implements a feedback mechanism where the oscillation output is fed back to the input through a feedback circuit including a capacitor and resistor. This feedback loop compensates for phase rotation variations in the piezoelectric resonator, maintaining stable oscillation conditions even when the resonator's Q factor is low. The feedback ensures that oscillation continues reliably despite individual differences in resonator characteristics.
2Speed
If the resonance frequency is lowered to 100-300 Hz for effective vibration sensation, then the vibration notification becomes more effective, but the Q factor decreases making oscillation control more difficult
Solution Approach 1:
The patent employs dynamic adjustment of circuit parameters to maintain stable oscillation across different vibration frequencies. The oscillation circuit is designed with adjustable components that allow optimization of oscillation conditions for each specific resonator, enabling reliable operation at low frequencies (100-300 Hz) where vibration notification is most effective while compensating for the reduced Q factor.
Solution Approach 2:
The patent changes key circuit parameters including using a feedback capacitor with specific capacitance value (e.g., 100 pF to 1 nF) and adjusting feedback resistor values to optimize oscillation conditions. These parameter adjustments enable the circuit to maintain stable oscillation at low frequencies despite the inherently lower Q factor of piezoelectric resonators designed for vibration notification.
3Ease of manufacture
If individual piezoelectric resonators with varying resonance frequencies are used, then mass production and cost-effectiveness are improved, but consistent oscillation performance across all devices becomes difficult to achieve
Solution Approach 1:
The patent designs the oscillation circuit with adjustable parameters including feedback capacitor and resistor values that can be tuned to match each resonator's specific characteristics. This allows mass-produced resonators with varying resonance frequencies to be accommodated by adjusting circuit parameters rather than requiring tight resonance frequency control during manufacturing.
Solution Approach 2:
The oscillation circuit automatically adapts to each resonator's characteristics through its feedback mechanism, which self-adjusts to maintain stable oscillation conditions. This self-service capability eliminates the need for manual calibration or selection of resonators with tightly controlled resonance frequencies, enabling straightforward mass production.
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 enables stable oscillation near the mechanical resonance frequency, enhancing vibration performance by isolating and amplifying the primary resonance current, thus overcoming the limitations of piezoelectric resonators with low Q factor and phase rotation variations.
Implementation Method 1
a piezoelectric resonator connected between an input end and an output end of the first amplifier
Implementation Method 2
a filter that attenuates a damped-capacitance current flowing in a damped capacitance in an equivalent circuit of the piezoelectric resonator and that allows a resonance current to pass therethrough
Data Source
AI summary
An oscillation circuits that provides stable oscillations even when the amount of phase rotation of a piezoelectric resonator is small or fluctuates. The oscillation circuit includes a first amplifier having an input and an output, and a piezoelectric resonator connected between the input and the output of the first amplifier. Moreover, the oscillation circuit feeds, back to the input, a current flowing from the output of the first amplifier to the piezoelectric resonator. The oscillation circuit further includes an alternating-voltage waveform shaping circuit that applies, to the piezoelectric resonator, an alternating-voltage waveform having rising portions sharper than those of a sine wave.