Differential Current Sensor with Transconductor and Emitter Degeneration
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Solution Overview
Problem
Traditional current sensing techniques in power supplies, which use a sense resistor to monitor current, are undesirable due to the power consumption caused by the resistor, leading to inefficiencies and potential errors from process and temperature variations.
Innovation Solution
A current sensor using a pair of sense transistors with associated series-connected sense resistors and a transconductor, where the transistors and resistors are fabricated as a monolithic device to reduce errors and power consumption, providing a differential voltage proportional to the sensed current with a scaling factor, and emitter degeneration to minimize power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sense resistor is used to monitor current, then current sensing is achieved, but power consumption increases
Solution Approach 1:
The patent replaces the traditional resistive current sensing mechanism with a transconductor-based electronic sensing system. The transconductor converts the voltage drop across a small sense resistor directly into a proportional output current, eliminating the need for a large power-consuming sense resistor while maintaining accurate current measurement capability
Solution Approach 2:
The patent changes the operating parameters by using a transconductor with high transconductance to amplify the small voltage signal from a minimal sense resistor. This allows the use of a much smaller sense resistor value compared to traditional methods, thereby reducing power consumption while preserving measurement accuracy through the transconductor's signal amplification
2Measurement precision
If a sense resistor is used to monitor current, then current sensing is achieved, but errors from process and temperature variations occur
Solution Approach 1:
The patent replaces the vulnerable resistive sensing system with a transconductor-based system that is inherently more stable against process and temperature variations. The transconductor's current output is less sensitive to parameter drift, and the differential sensing architecture further rejects common-mode variations, improving reliability
Solution Approach 2:
The patent employs a feedback mechanism where the transconductor's output current is fed back through a feedback resistor to generate a voltage that compensates for sense resistor variations. This feedback loop actively corrects for process and temperature-induced errors, maintaining high measurement accuracy and reliability under varying conditions
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 effectively reduces power consumption and minimizes errors in current sensing by matching transistors and resistors, improving the accuracy and efficiency of current monitoring in power supplies, while maintaining a proportional output current.
Implementation Method 1
Each sense transistor has an associated series connected sense resistor. The two sense resistors are unbalanced and provide a differential voltage based on the sensed current at the sense transistor
Data Source
AI summary
A current sensor having a pair of sense transistors is disclosed. The sense transistors sense a current conducted by a power transistor of a voltage regulator. The ratio in size between the power transistor and the sense transistors corresponds to a scaling factor M. Each sense transistor has an associated series connected sense resistor. The two sense resistors are unbalanced and provide a differential voltage based on the sensed current at the sense transistor to a transconductor. The transconductor has heavy emitter degeneration to provide an output current substantially proportional to the current conducted by the primary power transistor, the proportion determined by the scaling factor M and a ratio of the emitter degeneration and sense resistors.