Ratiometric Sensor Output Topology With Distinct Fault Voltage States
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Solution Overview
Problem
Conventional sensor configurations, particularly in safety-critical applications like automobile control systems, fail to effectively communicate failure information, as they lack a distinct state to indicate faults, limiting their ability to convey failure conditions beyond normal high or low output states.
Innovation Solution
The implementation of ratiometric sensor output configurations that utilize a resistor divider, operational amplifier, and pass element to generate output signals at different percentages of the supply voltage, allowing for fault indication by outputting the supply voltage or ground, thereby providing a distinct fault state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If conventional sensor output configurations are used, then the device complexity is low, but the ability to communicate failure information is insufficient
Solution Approach 1:
The output signal is segmented into multiple distinct voltage levels (first percentage, second percentage, and supply voltage level) to encode different operational states. This segmentation allows the sensor to communicate both normal operational data and fault conditions through a single output channel, resolving the contradiction by encoding more information without adding multiple physical output channels.
Solution Approach 2:
The sensor output configuration is designed to perform multiple functions: indicating normal operational states through ratiometric voltage levels and indicating fault conditions through the supply voltage level. This multi-functionality allows a single output circuit to convey both measurement data and diagnostic information, eliminating the need for separate fault indication circuits.
2Reliability
If ratiometric output configurations are implemented to indicate faults, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The operational amplifier is configured in a feedback arrangement where the output signal is fed back to the inverting input. This feedback mechanism automatically maintains the output at the desired ratiometric voltage levels (first or second percentage of supply voltage) based on the input signal state, and automatically indicates faults by allowing the output to reach the supply voltage level when a fault condition is detected, improving reliability through automatic fault detection.
Solution Approach 2:
The fault indication function is merged with the normal output signal generation. The same output circuit and pass element used to generate ratiometric output levels are also used to indicate faults by allowing the output to reach the supply voltage level. This merging eliminates the need for separate fault indication circuitry while maintaining functional safety.
3Loss of information
If distinct fault states are introduced, then the loss of information is reduced, but the ease of operation becomes more complex
Solution Approach 1:
The output signal uses different voltage level parameters to distinguish between operational states and fault conditions. Normal states are indicated by ratiometric voltage levels (first or second percentage of supply voltage), while fault conditions are indicated by the output reaching the supply voltage level. This parameter-based distinction maintains ease of operation by using a single voltage parameter that can naturally represent multiple states without requiring additional signal lines or complex encoding schemes.
Data Source
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.