Dual-Shunt Current Measurement Circuit for Wide Dynamic Range
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Solution Overview
Problem
Existing Source and Measure Units (SMU) struggle to measure current consumption across a wide dynamic range without changing the shunt resistor, particularly for applications involving active loads that experience rapid current fluctuations, and they suffer from poor signal-to-noise ratios when measuring low currents.
Innovation Solution
A device using shunt resistors with different resistive values and differential amplifiers coupled to analog-to-digital converters, along with power amplifiers and control loops, dynamically switches between amplifiers to maintain measurement accuracy and bandwidth across varying current levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single shunt resistor is used for current measurement, then the device structure is simple, but the measurement precision deteriorates when measuring currents across a wide dynamic range from nanoamperes to amperes
Solution Approach 1:
The current measurement function is segmented across multiple shunt resistors with different resistance values. Each shunt resistor is optimized for a specific current range (e.g., high resistance for low currents, low resistance for high currents), allowing precise measurement across the entire dynamic range from nanoamperes to amperes without requiring a single complex resistor
Solution Approach 2:
The system achieves multi-functionality by enabling a single measurement device to accurately measure currents across vastly different magnitudes (nanoamperes to amperes) using multiple shunt resistors. The processing circuit unit dynamically selects the appropriate shunt resistor based on the current level, making the device universally capable of measuring any current within the extended range
2Measurement precision
If the shunt resistor value is changed to measure different current levels, then the measurement precision improves, but the acquisition bandwidth is reduced and brief current events are lost
Solution Approach 1:
The system dynamically switches between different shunt resistors based on the current level being measured. The processing circuit unit monitors the current and selects the appropriate shunt resistor in real-time, allowing the measurement precision to adapt to the current magnitude while maintaining high acquisition bandwidth to capture brief current events without loss
3Measurement precision
If a high resistance shunt resistor is used to measure low currents, then the measurement precision for low currents improves, but the signal-to-noise ratio deteriorates
Solution Approach 1:
Different shunt resistors with optimized resistance values are used for different current ranges. For low current measurements, a high resistance shunt resistor is selected to achieve sufficient voltage signal, while for high current measurements, a low resistance shunt resistor is used to minimize power loss and heating. This local optimization of resistance value for each measurement context improves both precision and signal-to-noise ratio across the entire dynamic range
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
Enables precise measurement of current consumption from nanoamperes to amperes with high frequency and low noise, maintaining measurement quality without altering the shunt resistor configuration.
Implementation Method 1
using shunt resistors in series to measure the current consumption of the load with a first resistor having a high resistive value and a second resistor having a low resistive value
Data Source
AI summary
Load current consumption measured using a first resistor having a high resistive value and a second resistor having a low resistive value. Differential amplifiers, the outputs of which are coupled to analog-to-digital converters and to a processing circuit unit, are connected to each of the nodes of the resistors. Depending on the current level, the processing circuit unit advantageously selects one of the analog-to-digital converters to estimate the present consumption of current in the load. Each input terminal of a resistor is advantageously power supplied from a power amplifier and each power amplifier is advantageously driven by a control loop. For low load currents, the first amplifier associated with the first resistor power supplies the load through the resistors while, for high load currents, when this first amplifier saturates, the second amplifier associated with the second resistor, takes over from the first amplifier to continue to power supply the load.