Current Sensor Gain Trim Circuit With Lower DAC Resolution
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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 of materials like copper, and the need for high-resolution digital-to-analog converters (DACs) for gain trimming, which increases cost and complexity.
Innovation Solution
The solution involves moving the gain trim term from the denominator to the numerator of the current sensor control loop, creating a linear gain trim relationship. This allows for the use of lower resolution DACs and simplifies the resistor network, reducing the dynamic range requirements and maintaining stability and accuracy.
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 simple copper PCB trace that has known, predictable properties. The copper trace is a standard, inexpensive material already present on the PCB, eliminating the need for special sense resistors while maintaining adequate measurement precision through compensation techniques.
Solution Approach 2:
The patent creates an electrical model that copies and simulates the behavior of the ideal low-TCR sense resistor using standard copper traces and compensation circuits. By modeling the temperature effects and compensating for them, the system achieves accurate current sensing without requiring physical exotic materials.
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 (3900 ppm/°C)
Solution Approach 1:
The patent implements a feedback mechanism using a temperature sensor positioned near the copper sense trace. The temperature sensor continuously monitors the trace temperature, and this information is fed back to a compensation circuit that adjusts the measured voltage to compensate for temperature-induced resistance changes, thereby maintaining measurement precision despite copper's large TCR.
Solution Approach 2:
The patent changes the measurement parameters by measuring not just the voltage across the sense trace but also the temperature near it. By introducing temperature as an additional measurement parameter and using it to compensate for resistance changes, the system overcomes the limitation of copper's large temperature coefficient.
3Measurement precision
If high-resolution DACs are used for gain trimming, then measurement precision is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent applies partial correction rather than requiring full precision through high-resolution DACs. By compensating for the dominant temperature effects and using a simplified trim approach, the system achieves adequate measurement precision without needing excessive DAC resolution, thereby reducing device complexity and power consumption.
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 approach reduces the required trim resolution, lowers the cost and power consumption of the current sensor system, and maintains accuracy and stability in current sensing across varying temperatures.
Implementation Method 1
an amplifier that is configured in a closed feedback loop to control the output current in a manner that tends to reduce or minimize a voltage difference across first and second inputs of the amplifier
Implementation Method 2
adjusting, using a trim circuit coupled across and in parallel with the first resistive element, a gain between the input node and the system current monitor node
Data Source
AI summary
Described are techniques to provide a gain trim term in the numerator for a current sensor control loop. In this manner, a linear gain trim relationship is created with respect to the trim code. This linear relationship reduces the dynamic range needed for the DAC, which allows the use of lower resolution DACs to smoothly adjust the gain while maintaining stability and accuracy.