Sense Transistor Resistor Compensation for Power Transistors

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Solution Overview

Problem

In power circuits, indirect measurement of drain-source current of a power transistor using a sense transistor is affected by parasitic resistance and gate bias, leading to variable sense ratio due to temperature fluctuations and gate-to-source bias variations.

Innovation Solution

Integration of a resistor with polysilicon and metal sections coupled to the sense transistor, along with a controller providing a virtual connection and operational amplifier, to compensate for parasitic resistance and maintain a stable sense ratio by matching the resistance of the resistor to the ratio of sense transistor channel resistance to power transistor channel resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a sense transistor is used to indirectly measure the drain-source current of a power transistor, then the measurement capability is provided, but the measurement precision deteriorates due to parasitic resistance and temperature fluctuations causing variable sense ratio

Engineering Contradiction:

Improvesense ratio stabilityVSAvoidmeasurement accuracy under temperature variation

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

A dedicated resistor is introduced as an intermediary element between the sense transistor and the measurement circuit. This resistor has a value specifically designed to match the parasitic resistance, thereby serving as a compensating element that cancels out the harmful effects of parasitic resistance variations on the sense ratio, improving measurement precision across temperature ranges.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The resistor value is specifically selected to match the parasitic resistance value, creating a parameter relationship where the added resistor compensates for the parasitic effects. By changing the circuit configuration to include this matched resistor, the sense ratio becomes stable despite temperature-induced variations in parasitic resistance, resolving the contradiction between measurement precision and reliability.

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If parasitic resistance is present in the power transistor, then the transistor can function, but the sense ratio becomes variable due to gate-to-source bias variations and temperature fluctuations

Engineering Contradiction:

Improvetransistor functionalityVSAvoidsense ratio stability

Core Design Contradiction:

Ease of operationVSStability of the object's composition

Solution Approach 1:

The parasitic resistance, which normally degrades sense ratio stability, is converted into a benefit by introducing a compensating resistor with a matched value. The harmful parasitic resistance variations are counterbalanced by the deliberately added resistor, transforming the problem into a solution where the same parasitic effects are used to maintain stability through compensation.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

By introducing a resistor with a specific value that matches the parasitic resistance, the circuit parameters are changed to include this compensation element. This parameter matching creates a stable sense ratio despite variations in gate-to-source bias and temperature, as the added resistor compensates for the parasitic effects that would otherwise cause instability.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If the sense transistor drain-source current is used for indirect measurement, then current measurement capability is provided, but the measurement accuracy deteriorates due to the much smaller magnitude of sense current

Engineering Contradiction:

Improvecurrent measurement capabilityVSAvoidmeasurement signal magnitude

Core Design Contradiction:

Measurement precisionVSLoss of information

Solution Approach 1:

The resistor serves as an intermediary that converts the small sense current into a measurable voltage drop. By placing the matched resistor in series with the sense transistor, the small current generates a voltage signal that can be accurately measured, thereby recovering the measurement information that would be lost due to the small current magnitude while maintaining measurement precision.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS10422818B2Power transistors with a resistor coupled to a sense transistor

Publication Date: 2019.09.24 TEXAS INSTRUMENTS INC

AI summary

An electronic device comprises: a first semiconductor die; a power transistor integrated in the first semiconductor die, the power transistor comprising a gate, a first terminal, and a second terminal; a sense transistor integrated in the first semiconductor die, the sense transistor comprising a gate coupled to the gate of the power transistor, a first terminal, and a second terminal coupled to the second terminal of the power transistor; and a first resistor integrated in the first semiconductor die, the first resistor comprising a polysilicon section and a metal section coupled to the polysilicon section, the first resistor comprising a first terminal and a second terminal, wherein the first terminal of the first resistor is coupled to the first terminal of the sense transistor.