Multiplexed ADC Redundancy for ASIL-D Thermal Sensing
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Solution Overview
Problem
Current thermal sensor implementations in automotive applications, particularly in transmission and braking systems, face complexity and size issues due to the need for redundant analog-to-digital converters (ADCs) to achieve high safety integrity levels like ASIL-D, which doubles the number of ADCs required for each channel.
Innovation Solution
A multi-channel valve drive system where each channel is associated with a main temperature sensor and a redundant temperature sensor, with both sharing a single ADC via a multiplexer, reducing the total number of ADCs needed from 2N to N+1 by using a redundant measurement scheme that alternates between channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If redundant ADCs are implemented for each channel to achieve ASIL-D safety integrity, then measurement reliability is improved, but device complexity and die area increase
Solution Approach 1:
The patent merges multiple redundant temperature sensor measurements into a single ADC by implementing a multiplexer that sequentially connects different sensor channels to the same ADC. This combining approach maintains the redundancy needed for ASIL-D safety integrity while eliminating the need for separate ADCs for each channel, thereby reducing overall device complexity.
Solution Approach 2:
The single ADC is designed to serve multiple functions by sequentially measuring temperature from different sensor channels through the multiplexer. This multi-functional ADC replaces what would traditionally require multiple dedicated ADCs, reducing complexity while maintaining the ability to perform redundant measurements across multiple channels for safety-critical applications.
2Reliability
If redundant ADCs are implemented for each channel to achieve ASIL-D safety integrity, then measurement reliability is improved, but die area increases
Solution Approach 1:
The patent merges multiple redundant temperature sensor measurements into a single ADC by implementing a multiplexer that sequentially connects different sensor channels to the same ADC. This combining approach maintains the redundancy needed for ASIL-D safety integrity while eliminating the need for separate ADCs for each channel, thereby reducing overall device complexity.
Solution Approach 2:
The patent transitions from a spatial arrangement where each sensor channel would require its own dedicated ADC (increasing die area), to a temporal arrangement where a single ADC sequentially serves multiple channels through time-division multiplexing. This dimensional change from space to time allows redundancy to be maintained without proportionally increasing die area.
3Device complexity
If a single shared ADC is used for redundant sensors, then device complexity is reduced, but measurement speed may be affected
Solution Approach 1:
The patent implements periodic sequential measurement of different temperature sensor channels through the multiplexer, where each channel is measured in a predetermined sequence at regular intervals. This periodic action allows the single ADC to efficiently service multiple channels without requiring simultaneous conversion, maintaining measurement speed adequacy while reducing complexity.
Solution Approach 2:
The multiplexer dynamically switches between different sensor channels based on measurement requirements, allowing the system to adaptively allocate the single ADC's resources to different channels as needed. This dynamic switching optimizes measurement throughput and maintains adequate measurement speed despite using a shared ADC resource.
Data Source
AI summary
In an embodiment, a circuit includes N sensing channels. Each channel includes a first main sensing node and a second redundancy sensing node paired therewith. N analog-to-digital converters (ADCs) are coupled to the first sensing nodes, with digital processing circuits coupled to the N ADCs. A pair of multiplexers are coupled to the second sensing nodes and to the N ADCs with a further ADC coupled to the output of the second multiplexer. An error checking circuit is coupled to the outputs of the second multiplexer and the further ADC to compare, at each time window in a sequence of N time windows, a first digital value and a second digital value resulting from conversion to digital of: an analog sensing signal at one of the first sensing nodes, and an analog sensing signal at the second sensing node paired with the selected one of the first sensing nodes.