Bidirectional integrated low temperature coefficient current sensor
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Solution Overview
Problem
Existing current sensors face challenges in accurately sensing large currents on printed circuit boards (PCBs) due to high temperature coefficients and process variations, leading to inaccuracies and increased complexity in temperature compensation and trim techniques.
Innovation Solution
A bidirectional system current sensor module utilizing a matched thermal substrate, such as copper, in conjunction with the front two amplifiers of a three amplifier instrumentation amplifier, which cancels out temperature coefficient dependency and supports factory gain trim and voltage or current mode type outputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a discrete sense resistor with low temperature coefficient is used, then measurement precision is improved, but device complexity and cost increase due to exotic materials and Kelvin-sense requirements
Solution Approach 1:
The patent replaces expensive exotic material sense resistors with a standard copper PCB trace that achieves comparable temperature coefficient performance through the operational amplification circuitry. The copper trace is a inexpensive, readily available material that eliminates the need for costly iron-chrome or manganese-copper alloys while maintaining measurement accuracy through the T1 and T2 amplifier stages that compensate for temperature drift.
Solution Approach 2:
The patent substitutes the physical property-based temperature compensation (inherent in exotic materials) with an electronic compensation system using operational amplifiers. Instead of relying on the material's intrinsic low TCR, the system uses active electronic circuits to measure and compensate for resistance changes, replacing passive material properties with active electronic control.
2Ease of manufacture
If a copper PCB trace is used as the sense element, then ease of manufacture is improved, but measurement precision deteriorates due to large temperature coefficient
Solution Approach 1:
The patent implements feedback circuits using operational amplifiers T1 and T2 that continuously monitor the voltage across the copper sense trace and compensate for temperature-induced resistance changes. The amplifiers measure the sense voltage and adjust the output to counteract temperature drift, creating a closed-loop system that maintains accuracy despite copper's high intrinsic temperature coefficient.
Solution Approach 2:
The patent changes the operating parameters of the sense system by using operational amplification to overcome the limiting parameter (temperature coefficient). Instead of selecting a material based on its static TCR property, the system dynamically compensates for TCR variations through electronic control, effectively changing how temperature stability is achieved from a material property to a controlled system parameter.
3Measurement precision
If temperature compensation techniques are applied to copper trace sensing, then measurement precision is improved, but device complexity increases due to additional temperature sensors and signal conditioning
Solution Approach 1:
The patent merges the temperature compensation function with the existing sense amplification circuitry. The operational amplifiers T1 and T2 perform both the voltage measurement and temperature compensation functions in a unified circuit architecture, eliminating the need for separate temperature sensors and independent compensation circuits. The compensation is integrated into the signal path rather than being an add-on system.
Solution Approach 2:
The operational amplifiers in the patent serve multiple functions: they amplify the small sense voltage, compensate for temperature drift, and provide bidirectional current measurement capability. This multi-functionality reduces overall system complexity compared to dedicated temperature compensation circuits, as the same components handle multiple tasks rather than requiring separate specialized circuits for each function.
4Measurement precision
If trim techniques are applied to achieve desired accuracy, then measurement precision is improved, but manufacturing precision requirements increase and test cost increases
Solution Approach 1:
The patent implements a self-calibrating system where the operational amplifiers automatically compensate for variations in PCB trace dimensions and temperature coefficients during normal operation. The circuit measures the actual sense voltage and adjusts its output accordingly, making the system self-correcting rather than requiring external trimming or calibration procedures. This eliminates the need for manual trim adjustments and reduces dependency on tight manufacturing tolerances.
Data Source
AI summary
This disclosure describes various bidirectional current sensing techniques. The solution described utilizes a matched thermal substrate, e.g., copper, in conjunction with the front two amplifiers of a three amplifier instrumentation amplifier. The bidirectional system current sensor module described utilizes the matched thermal substrate approach to cancel out temperature coefficient dependency in the sensor. Behind the lead two amplifiers, the circuits can be varied to support factory gain trim and voltage or current mode type outputs.