Ratiometric Sensor Output Circuit for Fault-Indicating Logic States
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Solution Overview
Problem
Conventional sensor configurations, particularly in safety-critical applications like automotive systems, fail to effectively communicate fault conditions beyond the traditional high or low output states, lacking a third state to indicate sensor failures, which is essential for ensuring functional safety and compliance with specifications like ASIL requirements.
Innovation Solution
The implementation of a ratiometric sensor output configuration that utilizes different percentages of the supply voltage to represent logic high and low states, allowing the output to indicate a fault by reaching the supply voltage or ground levels, achieved through a closed-loop feedback arrangement or multiple selectable parallel paths, including the use of a pass element like an NMOS transistor and a chopper circuit for offset removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional sensor output configurations are used, then the circuit structure is simple, but the sensor cannot effectively communicate fault conditions beyond traditional high or low output states
Solution Approach 1:
The patent segments the output signal range into multiple distinct zones: valid logic high range, valid logic low range, and fault indication ranges (supply voltage level and ground level). This segmentation allows the sensor to communicate both normal operation states and fault conditions through the same output pin, improving reliability without adding external fault indication circuits.
Solution Approach 2:
The output pin of the sensor is given multiple functions: it can indicate valid logic high states, valid logic low states, and various fault conditions (open circuit, short circuit, out-of-range). This multi-functionality eliminates the need for separate fault indication pins or additional external circuits, maintaining circuit simplicity while enhancing fault detection capability.
2Reliability
If a third state is added to indicate sensor failures, then fault detection capability is improved, but the device complexity increases
Solution Approach 1:
The patent changes the voltage parameter of the output signal to encode different states. Instead of adding more output pins, it utilizes different voltage levels within the existing output range: valid states are represented by voltages within specific percentages of the supply voltage (e.g., 20-80%), while fault states are indicated by voltages at or near the extremes (0% or 100% of supply voltage). This parameter-based encoding provides multiple states without increasing physical device complexity.
Data Source
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AI summary
A sensor includes an output circuit configured to generate a sensor output signal based on an input signal having a logic high or low level, as may be provided by a Schmitt trigger circuit. During normal operation, the output switches between a first percentage of the supply voltage for logic high and a second percentage of the supply voltage for logic low. To convey a failure at the output, an output signal is output as either ground or the supply voltage when a fault is detected. As such, a fault can be communicated any time the output voltage is not equal to the first percentage or the second percentage of the supply voltage.