Capacitive Accelerometer Excitation Circuit for Flicker Noise Cancellation
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Solution Overview
Problem
Existing MEMS capacitive transducers face challenges in achieving an optimal noise versus power trade-off, particularly in battery-powered consumer devices, where existing solutions do not effectively cancel offsets and flicker noise, limiting the signal-to-noise ratio (SNR) performance.
Innovation Solution
A high voltage excitation circuit is implemented to produce a double differential excitation signal by applying two consecutive stimuli with opposite polarities, using a charge pump to generate an excitation voltage greater than the supply voltage, which cancels offsets and flicker noise while increasing sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional excitation circuits are used, then power consumption is low, but signal-to-noise ratio performance is limited due to inability to cancel offsets and flicker noise
Solution Approach 1:
The patent applies periodic action by using alternating excitation signals that switch between different voltage levels (including negative voltages) in a time-varying manner. This periodic excitation enables the cancellation of offsets and flicker noise through differential measurement techniques, significantly improving signal-to-noise ratio while the duty-cycled operation manages power consumption in battery-powered devices.
Solution Approach 2:
The patent changes the voltage parameter of the excitation signal by generating signals with negative voltage levels and varying amplitude. By modulating the excitation voltage parameters (including applying reverse polarity voltages during specific time periods), the system achieves offset cancellation and noise reduction, improving measurement precision without proportionally increasing power consumption.
2Measurement precision
If simple excitation circuits are used, then device complexity is low, but sensitivity of the capacitive transducer is insufficient
Solution Approach 1:
The patent introduces an intermediary excitation circuit that generates complex voltage sequences (including negative voltages and multiple amplitude levels) to drive the capacitive transducer. This intermediary circuit acts as a mediator between the power supply and the transducer, enabling sensitivity enhancement through sophisticated excitation patterns without requiring complex modifications to the transducer structure itself.
Solution Approach 2:
By implementing periodic excitation sequences with specific timing patterns (including periods with negative voltages and periods with different amplitude levels), the system enhances transducer sensitivity through resonant effects and differential measurement, achieving high sensitivity while keeping the circuit architecture relatively manageable through systematic timing control.
3Measurement precision
If high voltage excitation is applied continuously, then signal-to-noise ratio is improved, but power consumption increases
Solution Approach 1:
The patent implements periodic action by applying high voltage excitation only during specific time periods rather than continuously. The excitation signal alternates between active high-voltage periods (for measurement) and low-power periods (including periods with negative or zero voltage), achieving high signal-to-noise ratio during measurement while reducing average power consumption through duty cycling.
Solution Approach 2:
The patent discards and recovers energy by using bidirectional voltage excitation (including negative voltages). During certain phases, energy is stored in capacitive elements during high-voltage excitation, then recovered during voltage reversal phases. This energy recycling approach reduces net power consumption while maintaining high signal-to-noise ratio performance during active measurement periods.
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
This approach significantly improves the signal-to-noise ratio (SNR) performance at a modest cost in terms of die size and power consumption, enhancing the sensitivity and reliability of MEMS capacitive transducers.
Implementation Method 1
at least one charge pump for producing an excitation signal that is greater than a supply voltage
Implementation Method 2
a capacitive transducer, such as a microelectromechanical systems (MEMS) capacitive accelerometer
Data Source
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AI summary
A system includes a capacitive transducer, an excitation circuit, and a measuring circuit. The excitation circuit is configured to excite the capacitive transducer and the measuring circuit measures an output signal from the capacitive transducer responsive to the excitation voltage. The excitation circuit includes a voltage source for providing a first voltage in response to receipt of a supply voltage, a voltage generator coupled to the voltage source for receiving the first voltage and generating a second voltage that is greater than the supply voltage, and a control circuit coupled to the voltage source and the voltage generator. The control circuit is configured to provide any of a system ground, the first voltage, and the second voltage to first and second terminals of the capacitive transducer, and particularly, being configured to apply the system ground and the second voltage in the form of two consecutive stimuli with opposite polarities.