Diode-Connected Transistor Circuit for Fast MOSFET Current Sensing
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Solution Overview
Problem
Existing current sensing circuits for MOSFET circuits face challenges in achieving high-speed, low-latency, and high-precision current detection, with limitations in size, noise susceptibility, power loss, and increased cost due to resistor and operational amplifier usage.
Innovation Solution
A current sensing circuit utilizing a diode-connected transistor configuration and a series connection of transistors, along with an optional analog-to-digital converter or DC-to-DC converter, to measure current without a resistor series structure and operational amplification, ensuring high-speed and low-latency operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If Hall effect sensors are used for current sensing, then both AC and DC currents can be measured, but the sensor size becomes large and noise susceptibility increases
Solution Approach 1:
The patent extracts the current sensing function from traditional bulky Hall effect sensors and implements it using a compact transistor-based circuit. The sensing function is separated from the need for large magnetic field detection components, achieving the same measurement capability in a much smaller footprint.
Solution Approach 2:
The patent replaces the mechanical/magnetic field-based Hall effect sensing mechanism with an electrical transistor-based sensing mechanism. Instead of measuring magnetic field effects, the circuit uses transistor current characteristics to detect and measure current, eliminating the need for large magnetic sensors.
2Measurement precision
If shunt resistors are used for current sensing, then current can be converted to voltage signal, but additional power loss occurs and voltage drop is required
Solution Approach 1:
The patent changes the sensing parameter from voltage drop measurement (shunt resistor method) to direct current measurement using transistor characteristics. By utilizing the transistor's current transfer ratio and gate voltage relationships, the circuit measures current without requiring a voltage drop across a resistor, thereby eliminating the associated power loss.
Solution Approach 2:
The patent introduces a transistor as an intermediary element between the current to be measured and the measurement circuit. The transistor acts as a current-controlled device that allows measurement of the main current through its gate-source voltage or drain current characteristics, avoiding the need for a shunt resistor that would create power loss.
3Measurement precision
If operational amplifier feedback current detection circuit is used, then current detection can be achieved, but operating bandwidth is limited and static current consumption increases
Solution Approach 1:
The patent extracts the current detection function from the operational amplifier-based feedback circuit and implements it using a simpler transistor configuration. By removing the operational amplifier and its associated feedback network, the circuit achieves current detection without the bandwidth limitations and high static current consumption inherent to op-amp-based solutions.
Solution Approach 2:
The patent replaces the expensive and power-hungry operational amplifier with simpler, lower-cost transistor components. The transistor-based solution provides adequate current detection capability without the high static current consumption and bandwidth limitations of operational amplifiers, effectively using simpler components to achieve the required function.
4Measurement precision
If operational amplifier circuits are added for current detection, then current measurement capability is improved, but overall circuit cost increases
Solution Approach 1:
The patent replaces expensive operational amplifier circuits with simpler and cheaper transistor-based current sensing components. The transistor configuration provides the necessary current measurement capability without requiring costly operational amplifiers, feedback networks, and associated precision components, thereby reducing overall circuit cost.
Solution Approach 2:
The patent extracts the current measurement function from complex operational amplifier circuits and implements it using basic transistor elements. By separating the essential sensing function from the expensive op-amp infrastructure, the design achieves current measurement at a fraction of the cost.
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 proposed circuit achieves high-speed, low-latency, and high-precision current detection suitable for over-current protection and power IC current feedback, reducing size, noise, and cost while maintaining precise current measurement.
Implementation Method 1
a diode-connected first transistor connected between the output node and a current circuit
Data Source
AI summary
A current sensing circuit includes an output driving transistor with an output node that provides an output voltage; a diode-connected first transistor connected between the output node and a current circuit; a second transistor and a third transistor connected in series, the second transistor having a gate connected to a gate of the output driving transistor, and the third transistor having a gate connected to a gate of the first transistor; and a current measuring circuit connected in series with the second transistor and the third transistor to measure a current flowing through the second transistor and the third transistor.