High-Side Current Sensing Circuit with Chopping and Ratio Measurement
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Solution Overview
Problem
Existing wireless power transmission systems face challenges in accurately measuring current across a sense resistor due to temperature variations, leakage currents, and offset issues, which affect efficiency and accuracy.
Innovation Solution
A wireless power system with a bridge, a coil, a tank capacitor, a regulator, and a sense resistor, utilizing a switching circuit, a gain stage, and an analog-to-digital converter (ADC) with temperature-independent reference voltages to accurately measure current, and a reference resistor that tracks the sense resistor's resistance across temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sense resistor is used to measure current in wireless power transmission, then power delivery measurement is enabled, but temperature variations cause drift and reduce measurement accuracy
Solution Approach 1:
The patent changes the measurement approach by using a ratio of two voltage measurements instead of directly measuring voltage across the sense resistor. This ratio-based measurement cancels out temperature-dependent parameters, including the sense resistor value drift, thereby maintaining measurement accuracy across temperature variations.
Solution Approach 2:
The patent introduces an intermediary measurement technique where two voltage dividers are used to create voltage ratios that indirectly represent the current measurement. This intermediary approach allows temperature-dependent parameters to cancel out in the final calculation, resolving the temperature drift issue.
2Reliability
If leakage currents and offset issues are present in the measurement circuit, then circuit operation continues, but measurement accuracy deteriorates
Solution Approach 1:
The patent converts the harmful effect of leakage currents and offsets into a beneficial cancellation effect. By measuring two voltages and taking their ratio, the common-mode leakage currents and offsets present in both measurement paths cancel each other out, transforming what would be measurement errors into a self-correcting mechanism.
Solution Approach 2:
The patent implements a feedback mechanism where the measured voltages are processed through a ratio calculation that automatically compensates for offset and leakage effects. This feedback-based ratio measurement ensures that even when leakage currents are present, the final measurement remains accurate.
3Device complexity
If traditional current sensing methods are used, then circuit simplicity is maintained, but measurement consistency over temperature is poor
Solution Approach 1:
The patent changes from direct voltage measurement to a ratio-based measurement approach. This parameter change in the measurement methodology enables temperature compensation without requiring complex additional circuitry, maintaining relative simplicity while dramatically improving measurement consistency over temperature.
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
The system achieves accurate and temperature-insensitive current measurement, reducing leakage and offset issues, thereby enhancing efficiency and accuracy of power delivery.
Implementation Method 1
a transmitter 11 including a transmission coil Lp and a serial capacitance Cp forming a serial resonant LC network, driven by electric power from a power source 12 (typically a wired connection, but in some cases a battery), that generates a time-varying electric field
Implementation Method 2
a receiver 15 including a receiver coil Ls and a serial capacitance Cs forming a similar serial resonant LC network in which the time-varying electric field induces an AC current
Implementation Method 3
The receiver 15 includes a bridge rectifier 16 (comprised of the illustrated diodes D1-D4) that rectifies the AC current to produce a DC current that charges a tank capacitor Ctank
Data Source
Figure 1~3
Figure 4
Figure 5
AI summary
A wireless-power-transmission-system includes a bridge (16) with a tank-capacitor (Ctank) coupled thereto, a sense-resistor (Rsense) coupled between the bridge (16) and an input of a regulator (17), a switching-circuit (32) having first and second inputs coupled across the sense-resistor (Rsense), and a gain-stage (33) having first and second inputs capacitively coupled to first and second outputs of the switching-circuit (32). An ADC (38) digitizes output of the gain-stage (33) by comparing the output to a reference voltage, and a temperature-independent current source (36) is coupled to a reference-resistor (R2) to generate the reference voltage. In a reset-phase, the switching-circuit (32) shorts the inputs of the gain-stage (33) to one another, and the gain-stage (33) shorts its inputs to its output. The switching-circuit (32), in a first-chopping-phase, couples the sense-resistor (Rsense) between the first and second inputs of the gain-stage (33), and in a second-chopping-phase, couples the sense-resistor (Rsense) in reverse between the second and first inputs of the gain-stage (33). The resistance of the reference-resistor (R2) tracks the sense-resistor (Rsense) across temperature.