Sense Current Generation Apparatus for Low-Current Measurement Accuracy
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Solution Overview
Problem
Current sensing techniques using current sensing transistors are limited by input offset voltage errors in operational amplifiers, leading to inaccuracies in measuring load currents, especially when the load current is small and the on-resistance of the main switch is low, resulting in significant percentage errors in sense current measurements.
Innovation Solution
A sense current generation apparatus that includes a voltage matching circuit and a voltage governor to adjust the gate voltage of the main electronically controlled switch, ensuring the voltage across its terminals remains above a predetermined threshold, thereby minimizing the impact of offset voltage errors and maintaining accurate current measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current sensing techniques using operational amplifiers are used, then current measurement capability is provided, but input offset voltage errors cause measurement inaccuracies especially at low load currents
Solution Approach 1:
The patent changes the operating parameters of the main switch by dynamically adjusting its on-resistance through gate voltage control. By modifying the switch's resistance parameter, the voltage drop across the switch is optimized to be sufficiently large for accurate sensing while remaining small enough not to significantly impact the load. This parameter adjustment resolves the contradiction between achieving measurable voltage drops and maintaining measurement accuracy at low currents.
Solution Approach 2:
The patent implements a feedback mechanism where the sensed current is used to control the main switch's gate voltage. The sensing circuit continuously monitors the current and adjusts the switch operating point accordingly, ensuring that the voltage drop remains in the optimal range for accurate measurement. This closed-loop feedback system maintains measurement reliability across varying load conditions, particularly at low currents where offset errors would otherwise dominate.
2Loss of energy
If the on-resistance of the main switch is kept low, then power loss is reduced, but the voltage drop becomes too small for accurate sensing
Solution Approach 1:
The patent makes the main switch's on-resistance dynamic rather than fixed. The switch resistance is continuously adjusted based on the sensed current magnitude and other operating conditions. At low load currents, the resistance is increased to generate sufficient voltage drop for accurate sensing. At higher currents, the resistance is decreased to minimize power losses. This dynamic adaptation resolves the contradiction between power efficiency and measurement accuracy.
Solution Approach 2:
The patent changes the electrical parameter (on-resistance) of the main switch to optimize both power loss and measurement accuracy. By controlling the gate voltage, the switch's effective resistance is modulated to achieve the desired voltage drop for sensing while keeping power dissipation acceptable. This parameter transformation allows the system to operate in different resistance states depending on the required measurement precision and power efficiency.
3Measurement precision
If the voltage across the main switch is increased to improve sensing accuracy, then measurement precision improves, but power loss increases
Solution Approach 1:
The patent employs dynamic control of the voltage across the main switch rather than maintaining a fixed voltage level. The voltage is adjusted in real-time based on the sensing requirements and power loss considerations. At low measurement precision requirements or high current levels, the voltage is kept low to minimize power loss. At high measurement precision requirements or low current levels, the voltage is increased to improve sensing accuracy. This dynamic voltage control resolves the contradiction between measurement precision and power dissipation.
Data Source
AI summary
A sense current generation apparatus constituted of: a main electronically controlled switch arranged to provide a current path for an input current; a sense electronically controlled switch arranged to generate a sense current; a voltage matching circuit arranged to adjust the voltage across the first and second terminals of the sense switch to equal the voltage across the first and second terminals of the main switch, within a predetermined maximum error voltage, such that the sense current is representative of the input current; and a voltage governor arranged to: receive an indication of the voltage across the first and second terminals of the main switch; and responsive to the received voltage indication, adjust the control voltage of the main switch such that the absolute value of the voltage across the terminals thereof is maintained above a predetermined voltage threshold greater than a boundary of the error range.