Adaptive SAR ADC Bit Control for Low-Power Medical Sensing
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Solution Overview
Problem
Implantable medical devices face challenges in reducing power consumption of analog-to-digital converters, which is crucial for device size reduction and battery longevity, as they require continuous monitoring of physiological signals using a fixed number of bits for conversion.
Innovation Solution
A self-adjusting analog-to-digital converter with an adaptive successive approximation register (ASAR) and conversion control module that dynamically adjusts the number of bits used for conversion cycles, allowing for a reduced bit number during periods when the signal remains within a smaller range, thereby conserving power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed number of bits is used for A/D conversion to ensure full scale range coverage, then measurement precision is maintained, but power consumption increases
Solution Approach 1:
The patent applies dynamics by making the number of bits used for conversion variable rather than fixed. The ASAR dynamically adjusts the bit depth based on the signal's actual range, using fewer bits when the signal occupies a limited range and full bits when the full scale range is needed, thus reducing average power consumption while maintaining precision when required
Solution Approach 2:
The patent changes the parameter of bit depth from a constant to a variable parameter. By monitoring the signal range and adjusting the number of bits accordingly, the system optimizes the balance between measurement precision and power consumption, using only the necessary resolution for each conversion cycle
2Reliability
If continuous monitoring of physiological signals is performed with high resolution, then reliability of physiological data is improved, but device power consumption increases
Solution Approach 1:
The system dynamically adjusts conversion resolution based on physiological signal characteristics. During stable physiological states, fewer bits are used maintaining reliability while reducing power. During rapid changes or critical events, full resolution is restored to ensure data reliability, creating an adaptive monitoring system
Solution Approach 2:
The patent applies partial action by using only the necessary portion of available bit resolution for each conversion cycle. When physiological signals remain within a limited range, partial bit depth (fewer bits) suffices for reliable monitoring, avoiding the excessive power consumption of always using full resolution
3Measurement precision
If A/D converter operates at full resolution continuously, then signal processing accuracy is maintained, but average conversion cycle time increases
Solution Approach 1:
The ASAR dynamically adjusts the conversion process by reducing bit depth when signals are stable and within a limited range, thereby shortening conversion cycle time. When signals exhibit large variations requiring full scale range, the system restores full bit depth to maintain accuracy, optimizing the time-accuracy tradeoff dynamically
Data Source
AI summary
A medical device and associated method convert an analog signal using an adaptable bit number. The medical device includes an analog-to-digital (A/D) converter for receiving an analog signal. The A/D converter has a full scale range and a total number of bits spanning the full scale range. The A/D converter converts the analog signal to a digital signal over conversion cycles using an adaptable bit number so that on at least a portion of the conversion cycles an adapted number of bits spanning a portion of the full scale range less than the total number of bits is used by the A/D converter to convert the analog signal.