Cascode Current Sensing Circuit for Leakage-Accurate Detection

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Solution Overview

Problem

Conventional current detecting circuits for semiconductor devices with normally-ON type switching elements, such as those made from GaN or SiC, face challenges in precisely detecting output current due to leakage currents, leading to unreliable current measurement.

Innovation Solution

A current detecting circuit is designed with a normally-ON type switching element and a normally-OFF type switching element in cascode connection, along with a differential amplification circuit that outputs a voltage proportional to the drain-source voltage of the normally-OFF type switching element, allowing precise detection of output current by operating the normally-OFF type switching element in a linear region and using an adjustment circuit to prevent overvoltage and improve reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If a normally-ON type switching element is used to achieve high withstand voltage and low energy loss, then the device performance is improved, but the output current cannot be precisely detected due to leakage current

Engineering Contradiction:

Improveenergy lossVSAvoidoutput current detection precision

Core Design Contradiction:

Loss of energyVSMeasurement precision

Solution Approach 1:

A normally-OFF type switching element is introduced as an intermediary between the normally-ON type switching element and the current detection circuit. This intermediary element blocks leakage current from reaching the detection circuit while allowing controlled current flow during normal operation, thereby enabling precise current measurement without sacrificing the low energy loss characteristics of the normally-ON type device

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The switching function is segmented into two distinct elements: a normally-ON type switching element for high withstand voltage and low energy loss, and a normally-OFF type switching element for precise current detection. This segmentation allows each element to specialize in its respective function, resolving the contradiction between energy efficiency and measurement precision

Inventive Principle:

Principle #1Segmentation

2Measurement precision

If a normally-OFF type switching element is added in cascode connection to enable precise current detection, then the measurement precision is improved, but the device complexity increases

Engineering Contradiction:

Improveoutput current detection precisionVSAvoidcircuit structure complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The normally-OFF type switching element serves multiple functions simultaneously: it acts as a switch for current control, a block for leakage current prevention, and a sense element for current detection through its drain-source voltage. This multi-functionality reduces the need for additional dedicated components, thereby limiting the increase in device complexity while achieving precise measurement

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Measurement precision

If the normally-OFF type switching element is operated in linear region for precise detection, then the measurement precision is improved, but the power consumption increases

Engineering Contradiction:

Improvecurrent detection precisionVSAvoidpower consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The normally-OFF type switching element operates in the linear region only during the detection phase of the switching cycle, rather than continuously. During the main switching operation, it returns to a high-impedance state with minimal current flow. This periodic operation in the linear region allows precise measurement while limiting overall power consumption

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The element operates in the linear region (excessive action) only when measurement is required, rather than maintaining continuous linear operation. This partial application of the linear region operation achieves sufficient measurement precision while avoiding the continuous power consumption that would result from sustained linear mode operation

Inventive Principle:

Principle #16Partial or excessive action

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 solution enables precise detection of output current while reducing power consumption and preventing erroneous overcurrent detection, enhancing the reliability and efficiency of current measurement in semiconductor devices.

Implementation Method 1

a differential amplification circuit that outputs a voltage according to a voltage between the drain and the source of the second switching element

Methodology Applied

Scientific EffectDifferential amplification:

Data Source

PatentUS11680964B2Current detecting circuit

Publication Date: 2023.06.20 KK TOSHIBA

AI summary

According to one embodiment, a current detecting circuit includes: a normally-ON type first switching element that includes a drain, a source, and a gate; a normally-OFF type second switching element including a drain that is connected to the source of the first switching element, a source that is connected to the gate of the first switching element, and a gate; and a differential amplification circuit that outputs a voltage according to a voltage between the drain and the source of the second switching element.