Capacitive Current Sensor Re-Referencing for High-Side Sensing
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Solution Overview
Problem
Current sensors face challenges in high-side current sensing due to high common mode voltages exceeding the voltage rating of operational amplifiers, leading to potential damage and inefficient signal processing.
Innovation Solution
The proposed solution involves a current sensor configuration that includes a resistive device and two capacitors, where the common mode voltage is reduced or re-referenced during operation by selectively coupling the capacitors with a common mode voltage source, allowing safe amplification and processing of the current sense voltage within the operational amplifier's voltage rating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-side current sensing is performed directly with operational amplifiers, then current monitoring capability is achieved, but the common mode voltage exceeds the voltage rating of operational amplifiers causing potential damage and unreliable operation
Solution Approach 1:
The patent introduces capacitors as intermediary components between the high common mode voltage environment and the operational amplifier. These capacitors couple the sense voltage to the amplifier inputs while blocking the harmful common mode voltage, thereby protecting the operational amplifier from voltage damage while still enabling current sensing functionality
Solution Approach 2:
The patent segments the voltage signal into differential components that can be safely processed. By using capacitive coupling, the sense voltage is separated into manageable voltage components that remain within the operational amplifier's voltage rating, allowing reliable operation without direct exposure to the full common mode voltage
2Reliability
If common mode voltage is reduced using traditional methods, then operational amplifier protection is achieved, but signal-to-noise ratio deteriorates
Solution Approach 1:
Capacitors are used as intermediary coupling elements that selectively transmit the differential sense voltage while blocking common mode voltage. This intermediary approach protects the operational amplifier without requiring traditional voltage reduction methods that would degrade the signal, thereby maintaining high signal-to-noise ratio
Solution Approach 2:
The patent changes the voltage reference parameter by re-referencing the sense voltage to a lower common mode voltage level using capacitive coupling. This parameter change allows the operational amplifier to operate within its voltage rating while preserving the integrity and amplitude of the differential sense signal, thus maintaining measurement precision
3Object-affected harmful factors
If capacitors are selectively coupled in parallel with resistive device, then common mode voltage is reduced, but device complexity increases
Solution Approach 1:
The capacitors in the patent serve multiple functions simultaneously: they block common mode voltage, couple differential sense voltage to the operational amplifier, and provide AC coupling without requiring additional complex voltage regulation circuitry. This multi-functionality reduces the need for separate components and simplifies the overall device complexity despite adding capacitive elements
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively reduces the common mode voltage, ensuring safe operation and enhancing the signal-to-noise ratio by up to 6 dB, enabling accurate and reliable high-side current sensing.
Implementation Method 1
transferring the first voltage including the first common mode voltage across first and second capacitors during a first phase of operation; and re-referencing the first voltage across the first and second capacitors with a second common mode voltage during a second phase of operation
Data Source
AI summary
An apparatus, including: a resistive device; a first capacitor selectively coupled in parallel with the resistive device; a second capacitor selectively coupled in parallel with the resistive device; and a common mode voltage source selectively coupled to respective first terminals of the first and second capacitors.