Current Detection Circuit Using Replica FETs for Accurate Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current semiconductor devices with normally-on-type switching elements face challenges in accurately detecting output currents due to manufacturing variations in on-resistance, which affects the reliability of current detection.
Innovation Solution
A current detection circuit is designed with a normally-on-type switching element and a pair of normally-off-type switching elements, where the gate voltage of one normally-off-type element is connected to the gate of another, and a division circuit processes the drain voltages of both to accurately detect output currents, mitigating the influence of manufacturing variations by using a common semiconductor substrate and adjusting the ratio of gate widths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a normally-on-type switching element is used to achieve high voltage resistance and low loss, then the switching element's performance is improved, but accurate detection of output current becomes difficult due to leakage current
Solution Approach 1:
The patent creates a replica circuit using normally-off switching elements that copies the electrical characteristics of the normally-on switching element. By measuring current in this replica circuit instead of directly in the normally-on switching element, the system can accurately detect output current without being affected by the leakage current inherent to normally-on devices.
2Productivity
If manufacturing processes are used to produce switching elements, then production is achieved, but manufacturing variations cause changes in on-resistance characteristics
Solution Approach 1:
The patent adjusts the gate width of the normally-off switching element in the replica circuit to match the electrical characteristics of the normally-on switching element. By changing the gate width parameter, the replica circuit's on-resistance is tuned to correspond to the actual on-resistance of the normally-on switching element, compensating for manufacturing variations.
3Measurement precision
If a replica circuit with normally-off switching elements is introduced to enable accurate current detection, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent creates a replica circuit using normally-off switching elements that copies the electrical characteristics of the normally-on switching element. By measuring current in this replica circuit instead of directly in the normally-on switching element, the system can accurately detect output current without being affected by the leakage current inherent to normally-on devices.
Solution Approach 2:
The patent applies different switching element types in different locations: normally-on switching elements are used in the main power circuit where high voltage resistance is needed, while normally-off switching elements are used in the replica circuit where accurate current measurement is required. Each location uses the most appropriate switching element type for its specific function.
Data Source
AI summary
A current detection circuit includes normally-on-type and a first normally-off-type switching elements with main current paths that are connected in series, and a second normally-off-type switching element that has a source and a gate that are connected to a source and a gate of the first normally-off-type switching element and a drain that is connected to a constant current source, and executes a division process by using drain voltages of the two normally-off-type switching elements.