Switched-Capacitor MOSFET Current Sensing Without Sense Resistors
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Solution Overview
Problem
Existing integrated circuits that utilize isolated transistors as control elements face challenges in measuring current independently of the common-mode voltage, leading to inefficiencies and power dissipation due to the need for current sense resistors.
Innovation Solution
The implementation of a switched capacitor circuitry that isolates the current measurement from the common-mode voltage, using a field effect transistor (FET) and a reference transistor in a precise ratio, allows for current measurement without a series sense resistor, thereby eliminating voltage drop and power dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current sense resistor is used to measure current in an isolated transistor circuit, then current measurement capability is provided, but voltage drop and power dissipation occur
Solution Approach 1:
The patent replaces the passive mechanical/resistive current sensing method with an active electronic measurement system using MOSFET devices. The current scaling circuit uses transistors to sense and amplify current signals without the continuous power dissipation of a sense resistor, achieving current measurement through electronic amplification rather than resistive voltage drop.
Solution Approach 2:
The patent introduces a current scaling circuit as an intermediary between the isolated transistor and the measurement system. This circuit includes MOSFET devices that act as intermediate elements to transfer and amplify the current signal, allowing accurate measurement without directly inserting a sense resistor into the main current path.
2Measurement precision
If a current sense resistor is used for current measurement, then current sensing is enabled, but voltage drop occurs
Solution Approach 1:
The patent substitutes the resistive voltage-based sensing method with a transistor-based current scaling approach. The MOSFET devices in the current scaling circuit provide current amplification and sensing functionality without relying on resistive voltage drops, thereby eliminating the associated power loss and voltage drop issues.
3Measurement precision
If conventional current measurement techniques are used in isolated transistor circuits, then measurement is possible, but the measurement depends on common-mode voltage
Solution Approach 1:
The patent replaces conventional voltage-based current measurement techniques with a current scaling circuit using MOSFET devices. This electronic approach measures current through transistor characteristics and scaling ratios rather than voltage drops, making the measurement independent of common-mode voltage variations and enabling operation across different voltage domains.
Data Source
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AI summary
A current monitor circuit comprises a sense transistor disposed in a first voltage domain; a reference transistor disposed in a second voltage domain isolated from the first voltage domain; and sensing circuitry configured to determine if a current in the sense transistor is greater than or less than a specified current using a current in the reference transistor.