Die Temperature Measurement Using Bipolar Transistor Sensing
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Solution Overview
Problem
Existing methods for measuring die temperature in integrated circuits, such as those in System-on-Chip (SoC) products, face challenges due to poor accuracy from external temperature sensors and limitations in fully integrated sensors, including thermal gradient errors and signal leakage issues, which complicate high-precision temperature validation and calibration.
Innovation Solution
An integrated temperature sensing structure using bipolar transistors, where the sensing element is placed at the silicon junction and relies on external test instrumentation for signal conditioning, eliminating complex internal processing circuitry and leveraging external instrumentation for high accuracy, while employing techniques to cancel parasitic resistances and pad leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If external temperature sensors (thermocouples) are used to measure die temperature, then the measurement point can be positioned outside the package, but the measurement accuracy deteriorates to worse than ±7° C. due to thermal gradient between the silicon junction and sensor locus
Solution Approach 1:
The patent extracts the temperature sensing function from external sensors and integrates it directly into the silicon junction through a bipolar transistor. The emitter-base junction of the transistor serves as the temperature sensor, eliminating the thermal gradient problem by positioning the sensing element exactly where the temperature measurement is needed - at the silicon junction itself.
Solution Approach 2:
The bipolar transistor acts as an intermediary between the silicon junction and the external measurement system. It converts the temperature information at the junction into an electrical signal (emitter-base voltage) that can be measured externally, while maintaining high accuracy because the sensing element remains at the junction rather than being positioned externally.
2Measurement precision
If fully integrated temperature sensors are used, then thermal gradient errors are eliminated, but device complexity increases due to complex measurement and signal-conditioning circuitry
Solution Approach 1:
The patent extracts the complex signal conditioning and measurement circuitry from the integrated circuit and relocates it to external test instrumentation. Only the essential temperature sensing element (bipolar transistor) remains integrated in the silicon, while all the complex processing is performed externally, thus maintaining measurement accuracy without increasing internal device complexity.
Solution Approach 2:
The bipolar transistor serves as a simple intermediary that converts temperature to voltage without requiring complex internal circuitry. The external instrumentation performs the signal conditioning and measurement, acting as an intermediary between the simple sensor and the final temperature reading, thereby avoiding the need for complex integrated signal processing.
3Ease of operation
If temperature measurement is performed through pads, then external access is enabled, but measurement precision deteriorates due to leakage currents creating signal offsets
Solution Approach 1:
The patent acknowledges that pad leakage currents are inevitable but converts this harmful effect into a benefit by using it as a diagnostic signal. The measurement system intentionally applies a reverse bias voltage to the pad and measures the leakage current, then uses this information to compensate for and eliminate the leakage-induced offsets in the temperature measurement, thereby turning the harmful leakage into a useful correction mechanism.
Solution Approach 2:
The system implements feedback by measuring the pad leakage current and using this information to adjust and compensate the temperature measurement. The leakage current measurement provides feedback about the offset conditions, which is then used to correct the final temperature reading, eliminating the precision degradation caused by leakage.
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 enables highly precise die temperature measurement, improving accuracy and allowing for better validation and calibration of temperature-related specifications, reducing errors associated with thermal gradients and signal leakage.
Implementation Method 1
Die temperature is sensed using an integrated temperature sensing structure... Die temperature is extracted during factory-test with higher accuracy
Data Source
AI summary
A die temperature measurement system (300) includes an external test environment setup (352) and an integrated circuit (302). The external test environment setup (352) includes means to force and accurately measure electrical variables. The integrated circuit (302) includes a bipolar transistor (325); a selectable switch (340) for selecting from plurality of integrated resistances (342, 344) to be coupled in series between a base (322) of the bipolar transistor and a first input (362); and a selectable-gain current mirror (310) with a gain, a programmable current-mirror output coupled to the collector (326) of the bipolar transistor. The bipolar transistor and optional diodes (335) are sequentially biased with a set of proportional collector current levels. For each bias condition, the temperature-dependent voltage produced by the structure is extracted and stored. Die temperature is obtained through algebraic manipulation (450) of this data. Parasitic resistance and I/O pad leakage effects are canceled.