Vibration Sensor Readout Circuit With Integrated Self-Test Paths
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Solution Overview
Problem
Capacitive accelerometers suffer from reduced precision due to parasitic capacitance from self-test modules and the need for high-order high-pass filters, which occupy space and increase costs without effectively improving output precision.
Innovation Solution
A readout circuit incorporating an on-chip self-test circuit, low-noise charge amplifier, correlated double sampling circuit, PID feedback control circuit, and phase compensation circuit, along with Sigma-Delta conversion, to separate self-test and working paths and maintain precision without additional filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an independent self-test module is added to capacitive accelerometers, then the self-test function is achieved, but the device area increases and parasitic capacitance compromises output precision
Solution Approach 1:
The self-test function is merged into the existing readout circuit by integrating the self-test capacitor with the amplifier's feedback capacitor. This consolidation eliminates the need for separate self-test module components, reducing device area while maintaining the self-test capability through shared circuit resources.
Solution Approach 2:
The feedback capacitor in the readout circuit is designed to serve dual purposes: it functions as the feedback element for normal acceleration signal amplification and as the self-test capacitor when configured appropriately. This multi-functionality allows the same component to enable both measurement and self-test operations without requiring dedicated self-test hardware.
2Reliability
If an independent self-test module is added to capacitive accelerometers, then the self-test function is achieved, but parasitic capacitance leaks and couples to the output terminal, compromising output precision
Solution Approach 1:
By merging the self-test capacitor with the amplifier's feedback capacitor, the invention eliminates the parasitic capacitance issue. The integrated capacitor is part of the signal path and does not create additional leakage paths to the output terminal, thus maintaining measurement precision while enabling self-test functionality.
3Measurement precision
If a high-order high-pass filter is cascaded to the output terminal, then output precision is improved, but device cost increases and demodulation output errors occur due to parameter changes
Solution Approach 1:
The invention extracts and eliminates the need for external high-order high-pass filters by addressing the root cause of precision issues through circuit integration. The self-test capacitor is incorporated into the feedback path, removing the requirement for additional filtering components and their associated costs and potential errors.
4Measurement precision
If a high-order high-pass filter is cascaded to the output terminal, then output precision is improved, but demodulation output errors occur due to parameter changes
Solution Approach 1:
The invention removes the dependency on external high-order high-pass filters that cause demodulation errors. By integrating the self-test function into the feedback capacitor, the system eliminates the parameter variations and information loss associated with cascaded filters, maintaining accurate demodulation output.
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 high-precision output without the need for an independent self-test module and high-order filters, maintaining accuracy by filtering noise and separating signal paths, thus enhancing capacitive accelerometer performance.
Implementation Method 1
a low-noise charge amplifier, wherein a positive input terminal of the readout circuit is connected to a positive output terminal of the vibration sensor, and a negative input terminal of the readout circuit is connected to a negative output terminal of the vibration sensor
Implementation Method 2
a correlated double sampling circuit, wherein the output terminal of the low-noise charge amplifier is connected to an input terminal of the correlated double sampling circuit
Implementation Method 3
a proportional-integral-differential feedback control circuit, wherein an input terminal of the proportional-integral-differential feedback control circuit is connected to an output terminal of the correlated double sampling circuit
Data Source
AI summary
A readout circuit for a high-precision vibration sensor comprises an on-chip self-test circuit, a low-noise charge amplifier, a correlated double sampling circuit, a PID feedback control circuit, a phase compensation circuit and Sigma-Delta. A self-test signal is amplified by the low-noise charge amplifier, low-frequency noise and offsets are filtered out by the correlated double sampling circuit, then a self-test path and a working path of a vibration sensor are separated in the time domain by the PID feedback control circuit, the phase compensation circuit performs zero compensation and pole compensation on the signal, and Sigma-Delta converts an analog signal into a high-precision digital signal.