Voltage-Based Current Sensing with PVT-Tolerant Offset Calibration
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Solution Overview
Problem
Current sensing in microelectronic applications, particularly with mirror-based current sensors, faces inaccuracies due to current mirror mismatches and resistive losses, as well as susceptibility to voltage offsets, which affect the accuracy of current measurement in CPU or GPU power gating scenarios.
Innovation Solution
A method and apparatus for voltage-based current sensing that involves coarse calibration to determine a coarse offset, fine calibration to determine a fine offset, and transfer function calibration to determine a sensor transfer function, using frequency calibration to improve accuracy and account for voltage offsets, employing oscillators and a calibration module to generate ADC codes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If mirror-based current sensing is used to monitor current in microelectronic applications, then current sensing capability is provided, but measurement precision deteriorates due to current mirror mismatches and resistive losses
Solution Approach 1:
The patent replaces the traditional current mirror-based sensing mechanism with a voltage-based sensing approach. Instead of using current mirrors that are susceptible to mismatches and resistive losses, the invention measures voltage directly and converts it to current readings, thereby eliminating the harmful effects of current mirror inaccuracies while maintaining current sensing capability
Solution Approach 2:
The patent changes the fundamental measurement parameter from current to voltage. By measuring voltage across the load and using a transfer function to convert voltage readings to current values, the system avoids the precision degradation inherent in current mirror architectures while achieving more reliable and accurate current sensing
2Measurement precision
If voltage-based current sensing is implemented without calibration, then device complexity is reduced, but measurement precision deteriorates due to voltage offsets and frequency inaccuracies
Solution Approach 1:
The patent performs calibration operations in advance during manufacturing or initialization. The coarse calibration determines offset values and the fine calibration determines frequency correction factors before the device enters normal operation. This preliminary action ensures high measurement precision during actual use without requiring complex real-time calibration mechanisms
Solution Approach 2:
The calibration module uses the device's own internal oscillators and voltage references to perform self-calibration. By comparing the actual oscillator frequencies and voltage levels against expected values, the system automatically determines correction factors without requiring external calibration equipment, thereby reducing overall system complexity while maintaining high precision
3Measurement precision
If frequency calibration is performed to improve accuracy, then measurement precision is improved, but loss of time increases due to multiple calibration steps
Solution Approach 1:
The patent divides the calibration process into two distinct segments: coarse calibration and fine calibration. The coarse calibration performs the bulk of the correction by determining offset values, while the fine calibration provides additional precision by adjusting frequency factors. This segmentation allows each calibration stage to be optimized independently and enables the calibration to be completed more efficiently than a single comprehensive calibration would require
Data Source
AI summary
Aspects of the disclosure are directed to voltage-based current sensing. In accordance with one aspect, voltage-based current sensing may include performing a coarse calibration of a voltage based current sensor to determine a coarse offset; performing a fine calibration of the voltage based current sensor to determine a fine offset; performing a frequency calibration of the voltage based current sensor to determine a frequency offset; and performing a transfer function calibration of the voltage based current sensor to determine a sensor transfer function using one or more of the coarse offset, the fine offset and the frequency offset; and measuring a load current using the sensor transfer function.