Single Transistor Thermal Diode for Accurate SoC Temperature Sensing
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Solution Overview
Problem
Conventional thermal sensing systems in modern system-on-a-chip (SoC) applications face challenges with temperature monitoring due to voltage drops associated with routing transistors to digital ground, leading to inaccurate readings and increased costs and die area, especially when using single or paired transistors.
Innovation Solution
A thermal sensing system employing dynamic, two-phase current switching with a single transistor, utilizing a DPST or SPDT configuration, where a single BJT acts as a thermal diode, selectively coupled to either of two current sources, eliminating voltage uncertainty by generating distinct temperature-dependent signals that are subtracted to provide accurate readings without requiring an analog ground reference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a single transistor is used to sense temperature at a given location, then component cost and die area are reduced, but voltage drop due to routing resistance degrades performance and provides incorrect temperature readings
Solution Approach 1:
The patent introduces an intermediary mechanism (current source switching system) between the single transistor sensor and the ground reference. By switching between multiple current sources with different known voltage characteristics, the system mediates the voltage drop issue, allowing the single transistor to provide accurate temperature readings without requiring direct connection to a distant analog ground.
Solution Approach 2:
The patent changes the electrical parameters (current levels) by switching between multiple current sources with different known voltage drops. This parameter variation allows the system to compensate for routing resistance effects mathematically, maintaining measurement precision while using a single transistor located close to the measurement point.
2Measurement precision
If a differential approach with a pair of transistors is used to monitor temperature, then the voltage drop problem is addressed, but component cost and die area increase due to doubled transistor count
Solution Approach 1:
The patent merges the functions of two transistors into a single transistor by combining the temperature sensing function with a switching function. The single transistor serves dual purposes: sensing temperature and being selectively switched between different current sources, eliminating the need for a second transistor while maintaining differential measurement capabilities.
Solution Approach 2:
The single transistor in the patent performs multiple functions: it acts as both the temperature sensing element and the switching element that can be coupled to different current sources. This multi-functionality replaces the need for separate transistors for sensing and reference, reducing component count and die area while maintaining measurement accuracy.
3Stability of the object's composition
If transistors are routed to an analog ground located far from the transistor, then a common reference voltage is provided, but routing length, die area, and overall cost increase
Solution Approach 1:
The patent introduces a local digital ground with known voltage characteristics as an intermediary, eliminating the need for long routing to distant analog ground. The switching system mediates between this local ground and the transistor, providing reference voltage stability through computational compensation rather than physical proximity.
Solution Approach 2:
The patent replaces the mechanical/physical solution (long routing to analog ground) with an electrical/computational solution (current source switching with known voltage characteristics). Instead of physically connecting to a stable reference through long traces, the system uses electronic switching and mathematical compensation to achieve the same reference stability.
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 reduces hardware requirements, eliminates device mismatch errors, decreases die area and cost, and improves thermal diode performance by eliminating routing-related voltage variations, while maintaining accurate temperature sensing without the need for dual transistors at each location.
Implementation Method 1
a single BJT acts as a thermal diode, selectively coupled to either of two current sources, eliminating voltage uncertainty by generating distinct temperature-dependent signals
Data Source
AI summary
A thermal sensing system includes a circuit having a layout including standard cells arranged in rows and columns. First and second current sources provide first and second currents, respectively. The thermal sensing system includes thermal sensing units, first and second switching modules, and an analog to digital converter (ADC). Each thermal sensing unit is configured to provide a voltage drop dependent on a temperature at that thermal sensing unit. The first switching module is configured to select one of the thermal sensing units. The second switching module includes at least one switch controllable by a control signal. The at least one switch is configured to selectively couple the thermal sensing units, based on the control signal, to one of the first and second current sources, via the first switching module. The ADC is configured to convert an analog voltage, provided by the selected thermal sensing unit, to a digital value.