Diode-Based Temperature Sensor for Discrete Power Semiconductors
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Solution Overview
Problem
Existing temperature sensors in discrete semiconductor devices, such as polysilicon diodes, suffer from low accuracy due to production variations, trace resistances, and current source variations, leading to measurement errors in temperature readings.
Innovation Solution
A method involving a semiconductor die with a diode-based temperature sensor that measures a first and second forward voltage drop under different test conditions, using a difference-based approach to estimate temperature, which is less susceptible to errors from production variations and trace resistances, and utilizes separate test currents with the same magnitude to improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a polysilicon diode is used as a temperature sensor with a fixed current, then the temperature can be measured based on the forward voltage drop, but production variation causes wide variation in forward voltage behavior leading to low measurement accuracy
Solution Approach 1:
The patent measures the change in forward voltage drop (ΔVF) of the diode when the test current changes from a first value to a second value, rather than relying on the absolute forward voltage at a fixed current. This parameter change approach eliminates the need for precise manufacturing control of the diode's forward voltage characteristics, as the measurement depends only on the change in voltage with respect to change in current, which is determined by the diode's physical properties rather than manufacturing variations.
2Measurement precision
If current is driven through the diode to measure forward voltage drop, then temperature sensing is enabled, but trace resistance inside the semiconductor die introduces additional voltage drop and measurement error
Solution Approach 1:
The patent converts the harmful effect of trace resistance into a beneficial measurement approach. By measuring the change in forward voltage drop (ΔVF) corresponding to a change in test current (ΔI), the method inherently compensates for trace resistance effects. The relationship ΔVF/ΔI equals the dynamic resistance of the diode junction itself, excluding the trace resistance, because the trace resistance remains constant and its effect cancels out in the differential measurement.
3Measurement precision
If the test current through the diode varies due to temperature changes or lot-to-lot changes, then the forward voltage changes, but this is erroneously interpreted as temperature change introducing measurement error
Solution Approach 1:
The patent measures the ratio or relationship between the change in forward voltage (ΔVF) and the change in test current (ΔI), rather than relying on the absolute forward voltage at a fixed current. This differential measurement approach makes the temperature sensing independent of the absolute test current value, thereby eliminating errors caused by test current variations due to temperature drift or manufacturing lot-to-lot changes. The measurement depends only on the diode's dynamic resistance characteristics, which are stable and predictable.
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 approach provides high accuracy in temperature measurement for discrete power semiconductor devices, reducing errors and improving sensitivity, with a signal magnitude of 0.2 to 0.4 mV/Kelvin, compared to conventional sensors which have a gain of 1.4 to 1.6 mV/Kelvin, and allows for real-time temperature monitoring with minimal additional circuitry.
Implementation Method 1
A known fixed current is driven through the polysilicon diode and the absolute forward voltage drop of the diode is measured. Ideally, the absolute forward voltage drop of the diode decreases linearly with temperature.
Data Source
AI summary
A semiconductor die includes a single power transistor or power diode, a temperature sense diode formed close enough to the single power transistor or power diode to measure an accurate temperature. The temperature sense diode comprises first and second diodes or strings of diodes. A separate integrated circuit is operable to measure first and second voltage drops of both the first and second diodes or strings of diodes using same magnitude currents, and estimate the temperature of the single power transistor or power diode based on the difference between the first and second forward voltage drop measurements. An overall pn junction area of the first diode or string of first diodes is different from an overall pn junction area of the second diode or string of second diodes.