Current Detecting Circuit Common Mode Noise Reduction
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Solution Overview
Problem
Current detecting circuits face challenges in accurately measuring currents due to noise interference, particularly common mode noise, caused by potential differences between ground terminals connected to bypass capacitors and power supply grounds, leading to inaccurate current detection.
Innovation Solution
A current detecting circuit design that positions one terminal of each bypass capacitor and the power supply ground on the same voltage node, eliminating impedance between them, and uses capacitors with matched or similar capacitance values to reduce noise, along with a shunt resistor on a high current path to measure current changes accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If bypass capacitors are connected between ground terminals and signal lines to remove common mode noise, then common mode noise is reduced, but impedance between different ground terminals causes common mode current and noise transfer
Solution Approach 1:
The patent connects both bypass capacitors to the same ground terminal, ensuring that both signal lines share a common reference potential. This eliminates the potential difference between ground terminals that causes common mode current, while still providing noise filtering through the capacitors to the shared ground.
2Measurement precision
If shunt resistor is placed on high current path for accurate measurement, then current measurement capability is provided, but resistance value is influenced by wire pattern resistance
Solution Approach 1:
The patent uses asymmetric wire routing where the wire patterns connecting to the shunt resistor terminals are deliberately designed to have different paths. This asymmetry, combined with the low resistance of the shunt resistor, ensures that the wire resistance becomes a negligible portion of the total measurement circuit resistance, improving measurement accuracy.
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 design improves current accuracy by effectively removing common mode noise and differential mode noise, enhancing the quality of output signals and reducing noise transfer, thereby improving the overall performance of current detection.
Implementation Method 1
there is a method of connecting bypass capacitors C21 and C22 between the ground terminals and each of two signal lines L221 and L22
Implementation Method 2
The noise which is an AC component flows to the path through the bypass capacitors C21 and C22. The differential mode noise may be removed by setting a current path through the bypass capacitors C21 and C22.
Data Source
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AI summary
A current detecting circuit includes: a shunt resistor (R1); an amplifier (30); a first signal line (L1) connecting a first terminal of the shunt resistor (R1) to a first input terminal of the amplifier (30); a second signal line (L2) connecting a second terminal of the shunt resistor (R1) to a second input terminal of the amplifier (30); and a third signal line (L3) connecting the second terminal of the shunt resistor (R1) to a first power supply terminal of the amplifier (30).