Multi-Channel ADC Redundancy for ASIL-D Temperature Sensing
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Solution Overview
Problem
Current thermal sensor implementations in automotive applications, such as transmission and braking control units, face complexity and increased die size due to the need for redundant analog-to-digital converters (ADCs) to achieve high safety integrity levels like ASIL-D, which is inefficient and costly in terms of resources and testing time.
Innovation Solution
A multi-channel valve drive system that associates a main temperature sensor with each channel and redundant temperature sensors to a single shared ADC using a multiplexer, reducing the number of ADCs required from 2N to N+1 by providing redundant temperature measurements within the same time frame, thus maintaining safety integrity while minimizing hardware redundancy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If redundant ADCs are implemented for each channel to achieve high safety integrity levels, then safety and reliability are improved, but device complexity and die size increase
Solution Approach 1:
Multiple redundant temperature sensors from different channels are merged and connected to a single shared ADC through a multiplexer. This allows the system to maintain safety integrity through redundant sensing while reducing the number of ADCs from 2N to N+1, thereby decreasing device complexity and die size.
Solution Approach 2:
A single ADC is designed to serve multiple functions by sequentially converting temperature signals from both main and redundant sensors across different channels. The ADC acts as a universal converter that handles multiple sensor inputs, eliminating the need for dedicated ADCs for each sensor while maintaining measurement capabilities.
2Reliability
If redundant ADCs are implemented for each channel to achieve high safety integrity levels, then safety and reliability are improved, but die size increases
Solution Approach 1:
Multiple redundant temperature sensors from different channels are merged and connected to a single shared ADC through a multiplexer. This allows the system to maintain safety integrity through redundant sensing while reducing the number of ADCs from 2N to N+1, thereby decreasing device complexity and die size.
Solution Approach 2:
Instead of implementing physical redundant ADCs for each channel, the patent uses a single ADC that is time-multiplexed to read both main and redundant sensors. This virtual copying approach maintains the functional redundancy needed for safety while dramatically reducing the physical area required on the die.
3Device complexity
If a single shared ADC is used for multiple sensors, then device complexity and die size are reduced, but measurement precision and real-time accuracy may be compromised
Solution Approach 1:
The system implements periodic measurement cycles where the single ADC sequentially converts temperature signals from main and redundant sensors in a time-multiplexed manner. This periodic action ensures that both main and redundant measurements are taken within the same thermal transient event, maintaining measurement precision while using fewer ADCs.
Solution Approach 2:
The multiplexer is configured to switch between main and redundant sensors in a predetermined sequence, ensuring that redundant measurements are taken before thermal conditions change significantly. This preliminary action approach maintains measurement accuracy by capturing temperature data within the same thermal event window.
Data Source
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AI summary
A circuit (100) for use in transmission control units and braking control units for motor vehicles comprises of plurality of N sensing channels such as BJT-based temperature sensing channels. Each channel includes a first main sensing node (S_CH_1 to S_CH_N) and a second redundancy sensing node (S_CH_1R to S_CH_NR) paired therewith. A plurality of N analog-to-digital converters (ADC_1 to ADC_N) are coupled to the first sensing nodes (S_CF_1 to S_CH_N), with digital processing circuitry (101, 102) coupled to the converters (ADC 1 to ADC N) and configured to perform, e.g. interpolator processing of the N first digital signals. A pair of multiplexers (MUX1, MUX2) are coupled to the second sensing nodes (S_CF_1R to S_CF_NR) and to the N analog-to-digital converters (ADC_1 to ADC_N), with a further analog-to-digital converter (ADC_R) coupled to the output of the second multiplexer (MUX2). Error checking circuitry (103) is coupled to the outputs of the second multiplexer (MUX2) and the further analog-to-digital converter (ADC_R) to compare, at each time window in the sequence of N time windows, a first digital value (TEMP _CODE) and a second digital value (TEMP_CODE_RED) resulting from conversion to digital of: an analog sensing signal at one of the first sensing nodes (S_CF_1 to S_CH_N), and an analog sensing signal at the second sensing paired with the selected one of the first sensing nodes (S_CF_1 to S_CH_N).