CMOS Sensor Array Offset Reduction via Segmentation
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Solution Overview
Problem
CMOS sensors face limitations in absolute accuracy due to sensitivity to packaging and fabrication processes, particularly non-uniform mechanical stress gradients, which current mitigation techniques struggle to address effectively without increasing costs.
Innovation Solution
A CMOS sensor system with a substrate featuring a sensor array and switches to establish different state conditions for each sensor element, allowing for the calculation of offsets and generation of a sensor system output, which includes a processor and memory to execute command instructions for data storage and offset calculation, thereby improving accuracy through adaptive calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional CMOS processes and packaging technologies are used, then manufacturing cost is reduced and ease of manufacture is improved, but measurement precision and manufacturing precision deteriorate due to non-uniform mechanical stress gradients
Solution Approach 1:
The sensor substrate is divided into multiple sensor elements arranged in an array, where each element experiences different mechanical stress due to non-uniform gradients. By segmenting the sensor into many individual elements, the patent enables statistical averaging and offset cancellation techniques that improve measurement precision while maintaining compatibility with conventional CMOS manufacturing processes
Solution Approach 2:
The patent performs offset characterization and calibration measurements before final sensor operation. By pre-measuring and storing offset values for each sensor element in a lookup table, the system eliminates the need for complex real-time compensation circuits, thereby maintaining manufacturing simplicity while improving measurement precision through preliminary calibration actions
2Measurement precision
If layout techniques with multiple devices and dummy devices are used, then measurement precision is improved through error cancellation, but device complexity increases
Solution Approach 1:
The patent employs sensor elements that are identical in structure and function, allowing each element to serve as both a measurement device and a reference for offset cancellation. The uniform design of all sensor elements enables them to mutually compensate for stress-induced offsets through statistical averaging, eliminating the need for complex dummy devices or asymmetric layouts while maintaining measurement precision
Solution Approach 2:
The patent combines multiple identical sensor elements into an array configuration where their outputs are processed together. By merging the measurements from multiple elements and applying offset cancellation algorithms, the system achieves improved precision without increasing individual device complexity, as all elements share the same simple CMOS structure
3Measurement precision
If spinning current technique is used to cancel offset errors, then measurement precision is improved, but device complexity and manufacturing cost increase due to additional front-end electronics
Solution Approach 1:
The patent replaces complex mechanical spinning current switching circuits with a simpler digital processing approach. Instead of physically spinning current through complex switch matrices, the system uses identical sensor elements with opposite polarity responses and applies digital offset cancellation through lookup tables and processing algorithms, thereby reducing device complexity while maintaining measurement precision
Solution Approach 2:
The patent creates multiple copies of identical sensor elements with opposite polarity characteristics. These copied elements respond oppositely to the same magnetic field, allowing their outputs to be combined and offset errors to be cancelled through digital processing. This copying approach eliminates the need for complex spinning current hardware while achieving the same precision benefits
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 reduces offset errors by four orders of magnitude, enhancing the accuracy of CMOS sensors without significant cost increases, as demonstrated by the comparison of traditional and proposed methods in sensor array outputs.
Implementation Method 1
the offset in Hall sensors is influenced by the piezoresistance effect. The piezoresistance effect results from the mechanical stress on the chip
Data Source
AI summary
A method and system for providing increased accuracy in a CMOS sensor system in one embodiment includes a plurality of sensor elements having a first terminal and a second terminal on a complementary metal oxide semiconductor substrate, a first plurality of switches configured to selectively connect the first terminal to a power source and to selectively connect the first terminal to a readout circuit, and a second plurality of switches configured to selectively connect the second terminal to the power source and to selectively connect the second terminal to the readout circuit.