Single TCO Circuit for Three-Axis Accelerometer Chip Size Reduction
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Solution Overview
Problem
Conventional three-axis accelerometers require a large circuit area for temperature coefficient correction, leading to increased chip size and cost, which is undesirable for cost-effective fabrication.
Innovation Solution
A sensor unit with a single temperature coefficient of offset (TCO) circuit that sequentially generates correction values for X-axis, Y-axis, and Z-axis directions using switched capacitor circuits and operational amplifiers, reducing the need for multiple TCO circuits and minimizing chip size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If three separate TCO circuits are used to correct temperature dependency for X-axis, Y-axis, and Z-axis directions, then temperature compensation accuracy is improved, but circuit area increases significantly
Solution Approach 1:
The patent merges three separate TCO circuits into a single shared TCO circuit that sequentially serves all three axes. The correction values generated by this single circuit are stored in separate storage units for X-axis, Y-axis, and Z-axis respectively, allowing temperature compensation for all three directions while occupying minimal circuit area.
Solution Approach 2:
The single TCO circuit operates periodically to generate correction values for each axis in sequence. The circuit alternates between generating correction values for X-axis, Y-axis, and Z-axis directions, with each axis receiving its correction values at different time periods. This periodic operation enables one circuit to fulfill the function of three separate circuits.
2Reliability
If three separate TCO circuits with decoders and registers are used, then temperature coefficient correction is achieved, but chip size increases
Solution Approach 1:
The single TCO circuit is designed to perform multiple functions by sequentially generating correction values for all three axes. This universal circuit replaces three specialized circuits, reducing chip size while maintaining the necessary temperature coefficient correction capability for each axis through time-multiplexed operation.
Solution Approach 2:
The patent introduces a time dimension to resolve the spatial conflict. Instead of providing simultaneous correction for all three axes in the spatial domain (requiring three separate circuits), the system provides sequential correction in the time domain using a single circuit. Correction values for different axes are generated at different times but all are stored and applied as needed.
3Measurement precision
If multiple TCO circuits are used for each axis, then acceleration value correction accuracy is improved, but manufacturing cost increases
Solution Approach 1:
By merging three separate TCO circuits into one shared circuit, the patent reduces the total number of components that need to be manufactured and assembled. This consolidation maintains correction accuracy through dedicated storage units for each axis while significantly reducing manufacturing complexity and cost.
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 allows for accurate correction of acceleration values while significantly reducing the chip size and cost by using a single TCO circuit, maintaining high accuracy in temperature compensation.
Implementation Method 1
a first switched capacitor (SC) circuit for holding the first correction value TCx in response to a first pulse signal s1 from the TCO circuit when the input capacitor holds the acceleration value Ax
Implementation Method 2
The operational amplifier 131 calculates the difference between the input signal Vin (acceleration value Ax) and the temperature coefficient value TCx (reference voltage). Then, the operational amplifier 131 amplifies the difference to generate an acceleration signal Xout.
Data Source
AI summary
A sensor unit for a three-axis accelerometer enabling reduction in chip size. The sensor unit is connected to an accelerometer that detects a plurality of acceleration values for a plurality of axis directions. The sensor unit includes a correction value generation circuit that sequentially generates a plurality of correction values for correcting the plurality of acceleration values. A correction circuit is connected to the correction value generation circuit to sequentially correct the plurality of acceleration values with a plurality of correction values and generate a plurality of corrected acceleration values.