On-Chip Current Sensing Using OTA for Accuracy
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Solution Overview
Problem
Existing switching regulator ICs face challenges in accurately monitoring current due to the inaccuracy of current-mirroring techniques and the additional cost and space required for external sense resistors and sensing circuitry.
Innovation Solution
An on-chip current-sense system using identical sense transistors and an operational transconductance amplifier to generate a sense current linearly related to the output current, with a sense circuit comparing this current to a predetermined magnitude to indicate over-current conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current-mirror transistors are used to monitor current magnitude, then current sensing is achieved, but measurement precision deteriorates due to non-linearity of the mirrored current
Solution Approach 1:
The patent introduces an operational transconductance amplifier (OTA) as an intermediary device between the power transistor and the sensing circuit. The OTA receives the output current and generates a sense current that is linearly proportional to the output current magnitude, eliminating the non-linearity issues of direct current-mirroring techniques. This intermediary transformation enables accurate current monitoring while maintaining reliability.
2Measurement precision
If external sense resistors and sensing circuitry are incorporated, then current monitoring capability is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent merges the current sensing function directly into the integrated circuit by incorporating sense transistors and an operational transconductance amplifier within the IC. This integration eliminates the need for external sense resistors and separate sensing circuitry, reducing device complexity and manufacturing cost while maintaining accurate current monitoring capability.
Solution Approach 2:
The sense transistors and OTA are designed to perform multiple functions: they monitor current magnitude, detect over-current conditions, and provide linear sensing across a wide range of output current magnitudes. This multi-functionality reduces the need for additional dedicated components, simplifying the overall circuit configuration.
3Manufacturing precision
If sense transistors are made substantially identical and proportionally matched with the power transistor, then manufacturing precision is improved, but device area increases
Solution Approach 1:
The patent applies local quality by making sense transistors substantially identical and proportionally matched with the power transistor in specific regions of the IC. This localized matching approach ensures high manufacturing precision for current sensing while minimizing the overall chip area by only replicating transistor structures where needed for sensing purposes.
Data Source
AI summary
One embodiment of the invention includes an on-chip current-sense system for measuring a magnitude of an output current through a power transistor. The system includes a first sense transistor that conducts a first reference current to or from a phase node and a second sense transistor configured to conduct a second reference current to or from a power rail. The first and second sense transistors can be substantially identical and can be proportionally matched to the power transistor. An OTA receives the first and second reference currents and a third reference current that flows to or from the phase node and generates a sense current that is proportional to the output current in response to the first, second, and third reference currents. A sense circuit compares the sense current with a predetermined magnitude and generates an over-current signal in response to the sense current being greater than the predetermined magnitude to indicate an over-current condition of the output current.