Integrated Current Sensing Circuit With Switch Matrix Offset Calibration
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Solution Overview
Problem
Current sensing in wireless power systems faces inaccuracies due to process variations and pressure-induced stress in resistor arrays, affecting the accuracy of power measurement and foreign object detection.
Innovation Solution
An integrated circuit with a current sense circuit that includes a switch matrix and polysilicon resistors arranged to minimize stress differential, allowing for accurate offset measurement and compensation, thereby improving current sensing accuracy across a wide range of currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional resistor arrays are used in current sensing circuits, then the circuit structure is simple, but measurement precision deteriorates due to process variations and pressure-induced stress
Solution Approach 1:
The current sensing circuit is divided into multiple segments: a differential pair stage with transistors, a resistor array with specific stress compensation layout, and a readout circuit. This segmentation allows each part to be optimized independently - the differential pair provides signal differentiation while the resistor array compensates for stress effects, achieving high measurement precision without excessive overall complexity
Solution Approach 2:
The resistor array is designed with non-uniform stress distribution compensation where specific resistors are positioned to experience different stress levels. By locally optimizing the resistor layout and selecting specific resistors for differential measurement, the circuit compensates for pressure-induced stress effects in critical measurement regions while maintaining overall circuit simplicity
2Measurement precision
If resistor arrays are designed to compensate for stress differential, then measurement precision improves, but manufacturing precision requirements increase
Solution Approach 1:
The circuit implements automatic offset compensation by measuring the stress-induced voltage differential in the resistor array and using feedback mechanisms to cancel this offset. The differential pair configuration inherently provides feedback by comparing voltages across different resistor paths, automatically compensating for manufacturing variations and stress effects without requiring external calibration
Solution Approach 2:
The resistor array and differential pair configuration enable the circuit to self-compensate for stress effects and manufacturing variations. The symmetric layout and differential measurement approach allow the circuit to automatically reject common-mode errors from process variations, eliminating the need for external precision matching or manual calibration procedures
3Measurement precision
If a switch matrix is added for offset measurement, then measurement precision improves through compensation, but device complexity increases
Solution Approach 1:
The switch matrix is designed to perform multiple functions: it enables offset measurement, facilitates resistor selection for differential pairs, and supports various sensing configurations. By using the same switching network for multiple purposes, the circuit achieves high measurement precision through offset compensation without proportionally increasing complexity - the switches serve universal roles in the measurement architecture
Solution Approach 2:
The switch matrix enables dynamic reconfiguration of the measurement circuit for different operating conditions. Switches can be controlled to select different resistor combinations and measurement modes based on the specific sensing requirements, allowing the circuit to adapt its configuration for optimal precision while maintaining a relatively simple base structure that only becomes complex when dynamically reconfigured
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 achieves current sense accuracy within 0.5% of the actual current, enhancing power measurement precision and foreign object detection in wireless power systems.
Implementation Method 1
the first resistor is configured to carry a first current (Isns) across the first resistor when the first node includes a first voltage (Vrect) and the second node includes a second voltage (Vmid)
Implementation Method 2
an amplifier configured to output a third voltage (Vo)
Data Source
AI summary
An integrated circuit for measuring current while receiving wireless power is described. The integrated circuit measures a current across a resistor by an amplifier. A gain of the amplifier is based on a pair of matched upstairs resistors and a pair of matched downstairs resistors. The pair of matched upstairs resistors may include an offset in resistance. The integrated circuit includes a switch matrix with switches coupled between the integrated resistor and the pair of matched upstairs resistors. The offset for the pair of matched upstairs resistors may be measured by selectively controlling the switches.