Single-Transistor Temperature Sensor With Beta Compensation Feedback
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Solution Overview
Problem
Existing temperature measurement circuits in integrated circuits face significant errors due to low and variable current gain beta (β) values of transistors, especially in modern manufacturing processes with line widths and spacings less than 90 nanometers, as they typically control emitter current rather than collector current, leading to inaccurate temperature readings.
Innovation Solution
A circuit and method that use current mirrors to precisely control the collector current of a temperature sensing transistor by mirroring the base current back to the emitter, ensuring the collector current is equal to the excitation current, thereby compensating for variations in β and reducing measurement errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If emitter current is controlled in temperature measurement circuits, then the circuit operation is simple, but temperature measurement accuracy deteriorates due to low and variable beta values
Solution Approach 1:
The patent introduces a feedback mechanism where the controlled current from the current mirror circuit is fed back to the emitter of the sensing transistor. This feedback loop automatically adjusts the emitter current to maintain the desired collector current despite variations in beta, thereby resolving the contradiction between operational simplicity and measurement accuracy.
Solution Approach 2:
The patent introduces a current mirror circuit as an intermediary between the excitation current source and the sensing transistor. This intermediary device precisely controls the collector current by mirroring the excitation current, eliminating the direct dependence on beta variations and improving temperature measurement accuracy while maintaining circuit simplicity.
2Productivity
If modern manufacturing processes with line widths less than 90 nanometers are used, then device scaling and integration are improved, but transistor beta becomes low and widely variable causing measurement errors
Solution Approach 1:
The feedback mechanism in the current mirror circuit continuously monitors and adjusts the collector current to compensate for beta variations caused by modern manufacturing processes. This allows the circuit to maintain accurate temperature measurements despite the low and variable beta values inherent in scaled transistors.
Solution Approach 2:
The patent changes the controlling parameter from emitter current to collector current through the current mirror mechanism. By controlling the collector current directly rather than relying on emitter current control, the system becomes insensitive to beta variations, enabling accurate measurements in modern scaled manufacturing processes.
3Device complexity
If beta is assumed to be independent of collector current, then calculations are simplified, but temperature measurement accuracy deteriorates
Solution Approach 1:
The feedback mechanism automatically compensates for the dependence of beta on collector current without requiring complex calculations. The current mirror circuit adjusts the emitter current in real-time to maintain the desired collector current, eliminating the need for complex beta correction calculations while preserving measurement accuracy.
Solution Approach 2:
The current mirror circuit performs self-adjustment to maintain accurate collector current control despite beta variations. The circuit automatically compensates for the non-independent relationship between beta and collector current through its inherent feedback mechanism, without requiring external correction calculations or complex processing.
Data Source
AI summary
A circuit (1-2) for compensating for variations in the current gain β of a sensing transistor (Q1) having a collector coupled to a reference voltage (GND) includes a first current mirror (20) having an input coupled to a base of the sensing transistor. A second current mirror (21) has an input coupled to an output of the first current mirror. A current source (13) is coupled to provide emitter current for the sensing transistor. An output of the second current mirror circuit (21) feeds base current of the sensing transistor back to its emitter to cause the collector current of the sensing transistor to be precisely equal to the current (I1) provided by the current source.