Switched Transistor Current Sensing Under Matched Aging Stress
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Solution Overview
Problem
Current current sensing in inductive loads of switched converter circuits faces accuracy issues due to aging of power transistors, which is not mirrored in associated sense transistors, leading to on-resistance and threshold voltage mismatches, especially under environmental stress conditions like temperature and vibration, affecting automotive applications.
Innovation Solution
A circuit design that applies electrical stress to both power and sense transistors, using coupling circuitry with switches and diodes to maintain a stable on-resistance ratio and reduce the impact of high-temperature reverse bias and hot carrier injection, ensuring accurate current sensing over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sense transistor is used as a down-sized replica of a power transistor for current sensing, then current sensing accuracy is improved through precise parameter relationships, but accuracy is degraded over time due to aging phenomena such as HTRB and HCI causing mismatch between power and sense transistors
Solution Approach 1:
The patent creates a replica power transistor that copies the physical and electrical characteristics of the actual power transistor. This replica transistor experiences the same aging phenomena (HTRB, HCI) and parameter drifts, allowing the sensing circuit to compensate for these changes by comparing the replica's behavior against the actual power transistor's behavior, thereby maintaining accurate current sensing throughout the device lifetime
Solution Approach 2:
The replica power transistor acts as an intermediary that mediates between the actual power transistor and the sensing circuit. By introducing this intermediate element that experiences identical stress conditions, the system can indirectly measure and compensate for aging effects without directly exposing the sense transistor to harsh operating conditions
2Reliability
If the sense transistor is exposed to the same electrical stress as the power transistor, then aging mismatch is reduced, but the sense transistor may suffer from degraded performance due to direct exposure to high voltage and current stress
Solution Approach 1:
The patent segments the function of experiencing electrical stress from the function of performing sensing. The replica power transistor is dedicated to experiencing stress and aging, while the sense transistor remains protected and dedicated to accurate measurement. This functional segmentation allows each component to optimize its specific role without compromising the other
Solution Approach 2:
Instead of exposing the sense transistor directly to stress, the patent creates a copy (replica power transistor) that experiences the stress on behalf of the sensing system. The replica serves as a surrogate that undergoes HTRB and HCI phenomena, providing aging information to the sensing circuit without degrading the sense transistor's measurement capabilities
3Measurement precision
If additional coupling circuitry is added to apply electrical stress to the sense transistor, then circuit complexity increases, but current sensing accuracy is maintained over time
Solution Approach 1:
The replica power transistor serves multiple functions: it acts as a stress-experience element, an aging reference, and a compensation source simultaneously. This multi-functionality reduces the need for separate dedicated components for each function, thereby limiting the increase in overall circuit complexity while achieving accurate long-term current sensing
Solution Approach 2:
The patent utilizes parameter changes in the replica power transistor (such as threshold voltage drift, on-resistance changes) caused by controlled electrical stress as useful information. By monitoring these parameter changes in the replica, the system can compensate for similar changes in the actual power transistor, converting what would be degradation into a useful sensing mechanism
Data Source
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AI summary
A circuit, comprising at least one switching transistor (QLS, QHS) having a control terminal configured to receive a control signal (X) as well as a current flow path therethrough, the at least one switching transistor (QLS, QHS) configured to be switched towards a conductive, resp. non-conductive, state in response to the control signal (X) having a first, resp. second, value wherein the current flow path through the at least one switching transistor (QLS, QHS) provides a current flow line (IQLS, IQHS) between a switching circuit node (VO) and a reference node (VI, PGND), wherein, in the non-conductive state, a voltage drop stress is applied across the at least one switching transistor (QLS, QHS). The circuit comprises a sense transistor (MLS) coupled to the least one switching transistor (QLS, QHS) and being a scaled replica thereof, the sense transistor (MLS) having a current sense flow path therethrough wherein the intensity of the current (IMS) flowing therein is indicative of the intensity of the current (IQLS, IQHS) flowing in the current flow path through the at least one switching transistor (QLS, QHS), and coupling circuitry (13, SB, S1, S2, S3, S4) configured to apply the voltage drop stress across the sense transistor (MLS) in response to the at least one switching transistor (QLS, QHS) being switched towards the non-conductive state, wherein, in response to the at least one switching transistor (QLS, QHS) being switched towards the non-conductive state, the voltage drop stress is replicated across both the at least one switching transistor (QLS, QHS) and across the sense transistor (MLS, MSH).