Diode-Based Temperature Measuring Circuit with Switched Capacitor
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Solution Overview
Problem
Conventional temperature measuring circuits using parasitic PNP transistors in integrated circuits face degradation due to manufacturing defects, leading to significant errors in temperature sensing, which are costly to correct through trimming processes and may not be feasible in all fabrication technologies.
Innovation Solution
A switched capacitor temperature sensor circuit that charges and discharges a capacitor through a diode at different times, using the voltage measurements to calculate temperature, effectively canceling out errors from manufacturing tolerances and noise sources by taking and subtracting multiple measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If parasitic PNP transistors are used as temperature sensing elements, then temperature measurement can be implemented in integrated circuits, but manufacturing defects cause significant errors in temperature sensing
Solution Approach 1:
The patent changes the sensing element from parasitic PNP transistors to diodes, and changes the measurement approach from direct voltage measurement to measuring the time constant of RC circuits. This parameter change eliminates sensitivity to manufacturing defects in transistor junctions while maintaining temperature sensing capability.
Solution Approach 2:
The patent creates multiple copies of RC circuits with different resistance values but identical capacitance values. By measuring and comparing the time constants of these copied circuits, the system can cancel out common-mode errors and achieve higher measurement precision without requiring perfect manufacturing tolerances.
2Measurement precision
If single- or multi-point circuit trimming is used to compensate for temperature sensing errors, then measurement precision improves, but the process becomes time consuming and increases manufacturing cost
Solution Approach 1:
The patent implements self-calibration by having the circuit automatically perform multiple measurements with different RC time constants and compute the temperature mathematically. The system uses internal references and computational algorithms to self-correct for manufacturing variations without requiring external trimming processes, thereby maintaining high precision while improving manufacturing efficiency.
3Adaptability or versatility
If parasitic PNP transistors are used for temperature sensing, then temperature measurement is available, but some fabrication processes do not offer suitable transistors
Solution Approach 1:
The patent uses diodes and resistors as universal building blocks that can be fabricated in virtually any CMOS process. These components serve multiple functions: diodes provide the temperature-dependent voltage characteristic, resistors provide the time constant variation, and together they enable temperature sensing without requiring specialized transistor structures. This universal approach enhances fabrication process compatibility while maintaining measurement precision.
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 accurate absolute temperature measurements by minimizing errors due to manufacturing variations and noise, reducing the need for costly trimming processes and overcoming limitations in fabrication technologies that lack high-quality PNP transistors.
Implementation Method 1
the voltage across the capacitor will decay faster at higher temperatures and slower at lower temperatures
Data Source
AI summary
A temperature measuring circuit uses a diode to drain a switched capacitor at two different lengths of time. The capacitor's voltage is amplified, measured, and compared for each length of time to calculate a temperature. The circuitry may cancel out errors due to manufacturing tolerances and variations, as well as offset voltages, supply noise, substrate noise, and other issues. The process may charge a capacitor, then drain the capacitor with a diode for a first period of time, at which point, the diode is switched out of the circuit. The remaining charge in the diode may be amplified, then analyzed using an analog to digital converter. A second measurement may be taken with a different period of time, and the two measurements may be subtracted to yield an absolute temperature.