Semiconductor Current-Limit Circuit Using a Scaled Reference Transistor
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Solution Overview
Problem
Existing semiconductor integrated circuits face challenges in accurately controlling current flow to prevent overcurrent, which can lead to ineffective overcurrent protection and potential damage due to fluctuations in resistance ratios and temperature variations, and require additional trimming elements increasing cost and area.
Innovation Solution
Incorporating a reference transistor with dimensions smaller than the switch transistor in the reference current path, allowing for precise current determination and overcurrent protection without trimming elements, and using a differential amplifier circuit to control the gate voltage of the switch transistor based on the ratio of resistances between the main and reference current paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a switch transistor is used to control current flow between power supply and output, then current control function is achieved, but overcurrent protection accuracy deteriorates due to resistance ratio fluctuations and temperature variations
Solution Approach 1:
The patent introduces a reference transistor as an intermediary element that provides a stable reference current path. This reference transistor, having different dimensions than the switch transistor, creates a predictable resistance ratio that serves as a mediator between the power supply and output, enabling accurate overcurrent detection without being affected by temperature variations or resistance fluctuations in the main current path
Solution Approach 2:
The patent changes the physical parameters (dimensions) of the reference transistor relative to the switch transistor to establish a fixed resistance ratio. By carefully selecting the dimension ratio between the reference transistor and switch transistor, the circuit achieves temperature-compensated current detection, where the parameter change in one transistor is compensated by the corresponding change in the other, maintaining detection accuracy
2Measurement precision
If trimming elements are added to improve current control accuracy, then measurement precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent implements a self-service mechanism where the reference transistor automatically provides the necessary reference current with the correct resistance ratio built into its structure. The circuit self-regulates the current detection accuracy through the inherent dimensional relationship between the reference and switch transistors, eliminating the need for external trimming elements or calibration circuits
Solution Approach 2:
The patent extracts the trimming function entirely from the circuit by using the reference transistor's fixed dimensional ratio to provide stable current detection. Instead of including adjustable trimming elements that would add complexity, the design takes out the need for trimming by relying on the predictable physical relationship between transistors of different sizes
3Device complexity
If the reference transistor has the same dimensions as the switch transistor, then circuit simplicity is maintained, but temperature stability deteriorates
Solution Approach 1:
The patent deliberately introduces asymmetry by making the reference transistor have different dimensions than the switch transistor. This asymmetric design creates a stable resistance ratio that compensates for temperature effects, where the different dimensional characteristics of the two transistors work together to maintain detection accuracy across temperature variations
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
This configuration enhances the accuracy of overcurrent detection and protection, reduces the risk of damage from overcurrent, and minimizes temperature fluctuations, achieving effective current control without the need for additional trimming elements, thus ensuring reliable operation and lower power consumption.
Implementation Method 1
a differential amplifier circuit having a first input terminal electrically connected to the second node, a second input terminal electrically connected to the third node, and an output terminal electrically connected to a gate of the first switch transistor and a gate of the first reference transistor
Data Source
AI summary
According to one embodiment, there is provided a semiconductor integrated circuit including a first switch transistor, a first reference transistor, a differential amplifier circuit, and a current source. The first switch transistor is electrically connected between a first node on an input terminal side and a second node on an output terminal side. The first reference transistor is electrically connected between the first node and a third node. The differential amplifier circuit has a first input terminal electrically connected to the second node, a second input terminal electrically connected to the third node, and an output terminal electrically connected to a gate of the first switch transistor and a gate of the first reference transistor. The current source is electrically connected between the third node and a reference potential. The first reference transistor has dimensions smaller than dimensions of the first switch transistor.