Multi-Channel LDO Current Sensing Across Wide IoT Load Ranges
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Solution Overview
Problem
Current measurement systems for low power IoT devices face challenges in accurately measuring a wide range of current consumption, especially when the same sense resistor is used across varying current levels, leading to reduced accuracy and signal-to-noise ratio, particularly at low currents.
Innovation Solution
A multiple-channel low dropout regulator with integrated I-V conversion and pass transistors that selectively choose the appropriate sense resistance path based on current consumption, reducing series elements and minimizing artifacts in current sensing, while maintaining high voltage headroom and accuracy across the entire current range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single sense resistor is used for current measurement across varying current levels, then the device complexity is reduced, but the measurement precision deteriorates particularly at low currents
Solution Approach 1:
The patent implements dynamic switching between multiple sense resistors based on the current being measured. The system automatically selects the appropriate resistor (R1 for high current, R2 for low current) to optimize measurement precision across different current ranges, transforming a static single-resistor system into a dynamic multi-resistor system.
Solution Approach 2:
The patent changes the resistance parameter by selecting different sense resistors (R1 with higher resistance, R2 with lower resistance) depending on the current magnitude. This parameter change allows the system to maintain optimal signal-to-noise ratio and measurement accuracy across a wide current range from nano- to microamperes.
2Measurement precision
If multiple sense resistors are multiplexed using analog switches, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The patent extracts the switching function from a complex analog multiplexer and implements it using simple pass transistors (M1, M2) controlled by basic logic signals. This extraction simplifies the overall circuit by removing the need for complex analog switch circuits while maintaining the ability to select between multiple sense resistors.
Solution Approach 2:
The patent replaces the mechanical/analog multiplexer system with a transistor-based electronic switching system. The pass transistors M1 and M2 act as electronic switches that can be controlled by logic signals, substituting the need for complex analog multiplexer circuits and reducing overall device complexity.
3Reliability
If series resistors are used for current measurement, then the reliability is improved, but the voltage headroom is reduced
Solution Approach 1:
The patent applies local quality by using different sense resistors with different resistance values for different current ranges. The higher resistance R1 is used for high current measurements where larger voltage drop is acceptable, while the lower resistance R2 is used for low current measurements to minimize voltage headroom consumption, thus optimizing both reliability and voltage efficiency locally.
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 provides high-performance current sensing with improved accuracy and reduced noise, enabling precise current measurements across a wide range of currents, from nano- to microamperes, by dynamically selecting the appropriate sense resistance path and minimizing voltage drop, thus maintaining stable load regulation.
Implementation Method 1
a first sense resistance to the load and a second pass transistor to couple a second sense resistance to the load
Implementation Method 2
An error amplifier determines a difference between a voltage being supplied to the load and a reference voltage
Data Source
AI summary
An apparatus for measuring a current being supplied to a load includes a first pass transistor to couple a first sense resistance to the load when the first pass transistor is enabled and a second pass transistor to couple a second sense resistance to the load when the second pass transistor is enabled. An error amplifier determines a difference between a voltage being supplied to the load and a reference voltage and to supplies an error amplifier output signal according to the difference. A switch couples the error amplifier output signal to a gate of the first pass transistor or to a gate of the second pass transistor. Control logic controls the switch according to a value of the current being supplied to the load. The voltage being supplied to the load is controlled using the error amplifier output signal that is selectively coupled to the gate of the first pass transistor or the gate of the second pass transistor.