Two-Wire Sensor Current Modulator for EMC Slew Rate
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Solution Overview
Problem
The use of a capacitor in two-wire speed sensors to meet the RI 130 EMC test degrades the slew rates of current pulses beyond the allowed tolerance windows for automotive applications, leading to incorrect detection by microcontrollers.
Innovation Solution
A sensor device with a current modulator that toggles the output current between multiple levels, increasing the current level during the initial phase and decreasing it during the terminal phase of the pulse to improve slew rates, allowing faster charging and discharging of the capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capacitor is used in parallel to the sensor to meet the RI 130 EMC test, then electromagnetic compatibility is improved, but the slew rates of current pulses are degraded beyond allowed tolerance windows
Solution Approach 1:
The current modulator performs preliminary action by pre-charging the capacitor during an initial phase before the main current pulse transition. This is achieved by switching a first current source to charge the capacitor in advance, so that when the main pulse occurs, the capacitor is already partially charged, reducing the required charge transfer time and improving the slew rate during the actual pulse transition.
Solution Approach 2:
The solution employs periodic action by dividing the current pulse into multiple phases: an initial charging phase, a main pulse phase, and a final discharge phase. Each phase uses different current sources switched at specific times, creating a multi-stage periodic waveform that ensures both EMC compliance and acceptable slew rates by controlling the charge/discharge timing of the capacitor.
2Speed
If the output current is increased at the initial phase and decreased at the terminal phase, then the slew rate is improved, but the current pulse waveform becomes more complex
Solution Approach 1:
The current pulse waveform is segmented into distinct phases with different current levels. The initial phase uses a first current source to charge the capacitor, the main pulse phase uses a second current source for the primary current transfer, and the final phase adjusts the current to ensure proper discharge. This segmentation allows each phase to be optimized independently for slew rate while managing overall waveform complexity through structured timing control.
Data Source
AI summary
A sensor device includes a two-pin current interface including an input pin configured to draw an input current and an output pin configured to output an output current, a sensor configured to generate a measurement signal, and a current modulator configured to generate a current pulse as the output current such that the output current toggles between at least two main current states based on the measurement signal. The current modulator is configured to modulate the output current such that the output current is increased, to a first current level greater than the at least two main current states, at an initial phase of the current pulse for a first duration, and to modulate the output current such that the output current is decreased, to a second level less than the at least two main current states, at a terminal phase of the current pulse for a second duration.