Current Sense Circuit Topology for Wide-Range Low-Burden Measurement
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Solution Overview
Problem
Existing current measurement systems face challenges in accurately measuring a wide dynamic range of currents from sub-microamperes to hundreds of milliamps in battery-powered devices due to burden voltage issues, noise interference, and limitations in operational amplifiers and closed-loop power supplies, which affect battery life and system performance.
Innovation Solution
A current sense circuit with a series network of current sense resistors and diode voltage clamps, combined with a closed-loop regulated voltage supply and differential amplifiers, allows for precise current measurement across a wide range by minimizing burden voltage and noise, using overlapping measurement paths for high and low currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single current sense resistor is used to measure current over a wide dynamic range, then the measurement coverage is improved, but the burden voltage becomes too large for high current measurements
Solution Approach 1:
The patent divides the current measurement function into multiple segments by using a series network of current sense resistors with different values. Each resistor is optimized for a specific current range, allowing the system to measure both low currents (where a larger resistor provides sufficient voltage drop) and high currents (where a smaller resistor keeps burden voltage acceptable). This segmentation resolves the contradiction by making the measurement system adaptable across wide dynamic range while controlling burden voltage for each operating condition.
Solution Approach 2:
The patent implements dynamic switching between different current sense resistors based on the detected current magnitude. The controller selectively activates appropriate resistors from the series network, allowing the system to adapt its measurement configuration in real-time. This dynamic approach enables the system to maintain optimal performance across varying current conditions without being constrained by a single fixed resistor configuration.
2Measurement precision
If a differential operational amplifier is used to amplify the voltage drop across the current sense resistor, then the measurement precision is improved, but the noise amplification increases
Solution Approach 1:
The patent applies local quality by using differential amplification only where needed - specifically for the voltage drops across the current sense resistors that require amplification for precision measurement. The differential amplifier configuration provides high input impedance and controlled gain, amplifying the signal from the sense resistors while rejecting common-mode noise and providing isolation from the rest of the circuit. This localized application of amplification improves precision without unnecessarily amplifying noise throughout the entire system.
3Measurement precision
If the current sense resistor is placed at the battery to measure total current, then the measurement accuracy is improved, but the voltage drop affects device performance
Solution Approach 1:
The patent segments the current measurement function by placing different current sense resistors at different locations in the power delivery path. Larger resistors can be positioned where voltage drop is less critical (such as near the battery for total current measurement), while smaller resistors are used in later stages where precise measurement of high currents is needed but voltage drop must be minimized. This spatial segmentation allows optimization of both measurement accuracy and voltage drop characteristics for different measurement objectives.
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 solution enables accurate, low-noise current measurement over a dynamic range of 0.1 microamperes to 3.2 amps, supporting real-time monitoring and optimizing battery life in IoT devices with minimal voltage drop and reduced noise interference.
Implementation Method 1
A diode voltage clamp is connected in parallel with the current sense resistor to limit burden voltage across the current sense resistor
Implementation Method 2
The output of the operational amplifier is then applied to an analog to digital converter to convert the voltage into a digital value
Implementation Method 3
measure the voltage drop across this resistor, often with a differential operational amplifier (OPAMP) and using Ohm's Law (V=I×R), to determine the current (I)
Data Source
AI summary
A circuit topology for measuring current over a wide dynamic range using multiple series sense resistors and diode voltage clamping is described. A current sense network uses a diode clamping technique to reduce the voltage drop across the series network such that it can be used in a power supply circuit with minimal impact on output voltage regulation. The circuit topology allows for overlapping current measurement ranges that can be merged together to provide a wide dynamic range. The circuit topology does not dynamically switch current sense resistors (or capacitors) and avoids unintended noise injection caused by such switching, and is suitable for measuring a wide dynamic range of current in real time.