ADC Input Fault Detection Using High-Impedance Stimulus Injection
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Solution Overview
Problem
Existing analog measurement circuits, such as those using resistor divider circuits for voltage scaling, face challenges in distinguishing fault conditions from valid inputs due to loading effects, which can result in undetectable voltage changes at the ADC input.
Innovation Solution
Incorporating a high injection impedance between the analog measurement input and a stimulus generation circuit to provide a pulsed stimulus signal, with the injection impedance being greater than the source impedance, allowing for fault detection by analyzing the magnitude of the stimulus signal representation in the ADC output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a resistor divider circuit is used for voltage scaling, then the ADC input voltage range is extended to handle higher voltage signals, but fault detection capability deteriorates because fault conditions produce voltages indistinguishable from valid inputs
Solution Approach 1:
A stimulus generation circuit is introduced as an intermediary element between the ADC input and the measurement system. This circuit injects test signals through a high injection impedance to actively probe the signal path, enabling fault detection without interfering with normal high-voltage signal measurement. The intermediary stimulus circuit allows the system to distinguish between valid high-voltage inputs and fault conditions.
Solution Approach 2:
The stimulus generation circuit performs preliminary testing by injecting test signals before final measurement decisions are made. By proactively introducing known test patterns through the high injection impedance, the system can pre-identify fault conditions such as open circuits or short circuits in the signal path, separating fault detection from the main measurement function.
2Reliability
If a high injection impedance is used for stimulus injection, then fault detection capability is improved, but the complexity of the circuit increases due to additional stimulus generation circuitry
Solution Approach 1:
The stimulus generation circuit is designed to serve multiple functions: it generates test signals for fault detection, injects them through the high injection impedance, and allows the same circuit to handle both normal signal path testing and fault condition identification. This multi-functionality reduces the need for separate dedicated test equipment, thereby limiting the increase in overall circuit complexity while maintaining improved fault detection capability.
3Measurement precision
If the injection impedance is made larger than the source impedance, then the stimulus signal magnitude becomes distinguishable for fault detection, but the loading effect on the input signal increases
Solution Approach 1:
The stimulus generation circuit employs periodic or pulsed injection of test signals rather than continuous injection. This periodic action allows the high injection impedance to produce measurable voltage drops during test periods while minimizing continuous loading effects on the input signal path. The intermittent nature of the stimulus injection reduces the average loading effect while maintaining sufficient signal magnitude for fault detection during active test windows.
Data Source
AI summary
A fault detection scheme can include use of a relatively high injection impedance between an input port for analog measurements from a sensor and a stimulus generation circuit controlled in coordination with analog measurement. The stimulus generation circuit can provide a stimulus signal through the injection impedance. A magnitude of the injection impedance can be specified relative to a source impedance associated with a source (e.g., a sensor or other device) coupled to the input port. For example, a magnitude of the injection impedance can be specified to be larger than the source impedance or the injection impedance magnitude can be specified to be a multiple of the source impedance.