Multi-Range Current Sensor Circuit With Leakage Compensation
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Solution Overview
Problem
Current monitoring circuits face accuracy issues due to offset errors caused by finite open loop-gain and device mismatch, particularly at low current ranges, and leakage current from series switches affects measurement accuracy across a wide current range.
Innovation Solution
A multi-ranging current monitor circuit using multiple shunt resistors of varying values and back-to-back connected NMOS devices to nullify leakage current, with a drive amplifier to manage drain-source voltage and minimize leakage, ensuring accurate current measurement across a wide range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a current sensor circuit uses finite open loop-gain and mismatched devices, then the circuit complexity is reduced, but offset error increases causing poor measurement precision
Solution Approach 1:
The patent changes the electrical parameters of circuit elements by providing multiple resistive circuit elements with different resistance values and multiple transistor pairs with different current gains. This allows selection of optimal parameter combinations to minimize offset errors while maintaining circuit simplicity, directly resolving the contradiction between device complexity and measurement precision.
Solution Approach 2:
The patent implements dynamic switching between different resistive circuit elements and transistor pairs based on the current measurement range. The circuit transitions from static to dynamic operation, selecting the most appropriate component combination for each measurement condition, thereby maintaining high precision across varying current levels without requiring a overly complex fixed circuit design.
2Adaptability or versatility
If series switching circuits are used to select resistive elements, then the circuit adaptability across wide current range is improved, but leakage current increases affecting measurement precision
Solution Approach 1:
The patent converts the harmful leakage current effect into a beneficial compensation mechanism. By providing multiple transistor pairs with different current gains and selecting appropriate pairs based on measurement conditions, the circuit compensates for leakage currents that would otherwise degrade precision. This transforms the inherent limitation of series switching into an advantage for maintaining precision across wide current ranges.
Solution Approach 2:
The patent changes the electrical parameters by providing multiple transistor pairs with different current gains (beta values) and multiple resistive elements with different resistance values. This allows the circuit to adapt to different current ranges and compensate for leakage effects by selecting the optimal transistor-resistor combination, thereby maintaining measurement precision while achieving wide current range adaptability.
3Measurement precision
If multiple resistive circuit elements with different resistance values are used, then the measurement precision across wide current range is improved, but the device complexity increases
Solution Approach 1:
The patent implements multi-functionality by designing transistor pairs that serve dual purposes: both as switching elements for selecting resistive circuit elements and as active components for current amplification and leakage compensation. This universal design allows the same transistor pairs to perform multiple functions, reducing the need for additional dedicated components and thereby limiting the increase in device complexity while maintaining high measurement precision across wide current ranges.
Solution Approach 2:
The patent merges the switching function and the amplification function into a unified circuit architecture. The transistor pairs are used both to select among multiple resistive circuit elements and to provide current gain and offset compensation. This merging of functions reduces the total component count and circuit complexity while maintaining the ability to achieve high precision measurements across multiple decades of current 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
The solution maintains a good signal-to-noise ratio and minimizes offset errors, providing accurate current monitoring across multiple decades of current range with reduced impact from leakage currents.
Implementation Method 1
a drive amplifier to manage drain-source voltage and minimize leakage
Implementation Method 2
The current through the sense resistor is measured by observing the voltage developed across the sense resistor through the current sense amplifier's inputs. Due to Ohm's law, the voltage across the resistor terminals is proportional to the current though the resistor.
Data Source
AI summary
A current sensor circuit comprises multiple resistive circuit elements of different values of electrical resistance arranged between at least one input terminal of the current sensor circuit and an output terminal; a first plurality of switching circuits coupled between the input terminal and the resistive circuit elements, wherein each switching circuit of the first plurality of switching circuits includes a pair of transistors connected in series; at least one drive amplifier including an output and an input connected to the output terminal; and a second plurality of switching circuits, each switching circuit including a first switch terminal coupled to the at least one drive amplifier output and a second switch terminal coupled to a common connection of a pair of transistors of the first plurality of switching circuits.