IC Temperature Sensor Offset Cancellation Using Swapped Comparator Inputs
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Solution Overview
Problem
Integrated circuits face reliability and robustness issues due to localized high temperature 'hot spots' and existing temperature sensing methods, such as single slope ramp-based approaches, are prone to errors from offset voltages in buffers and comparators, which are not always available.
Innovation Solution
A temperature sensing circuit that uses twin 1st-order temperature-independent single slope ramp voltage references and counter circuitry, coupled with switch circuits to swap inputs and outputs of buffers and comparators during measurement operations, effectively canceling offset errors by performing measurements with both positive and negative offsets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single slope ramp based time-to-digital converter is used for temperature sensing, then temperature measurement can be achieved, but offset errors from voltage buffers and comparators cause significant measurement errors
Solution Approach 1:
The patent applies periodic action by performing two sequential measurements: a first measurement during a first time period and a second measurement during a second time period. The switch circuit alternates between connecting the first voltage buffer to the first input terminal and the second input terminal, enabling periodic swapping of connections to cancel offset errors through differential measurement.
Solution Approach 2:
The patent implements preliminary action by performing a first measurement before a second measurement. The switch circuit is configured to establish specific connections during the first time period, and then swaps connections for the second time period. This sequential preliminary measurement allows offset cancellation by comparing results from different connection states.
2Ease of operation
If voltage buffers and comparators are used in the temperature sensing circuit, then signal processing is enabled, but offset voltages introduce cumulative errors in the final temperature output
Solution Approach 1:
The patent converts the harmful offset voltages into a beneficial cancellation mechanism. By performing measurements with the switch circuit in different states (first connection state, then swapped connection state), the offset errors from voltage buffers and comparators are captured in both measurements. When the measurements are combined, the offset errors cancel each other out, transforming the previously harmful effect into a benefit.
Solution Approach 2:
The patent implements feedback by using the results from the first measurement to inform and correct the second measurement. The switch circuit swaps connections based on feedback from the first measurement phase, enabling the system to compensate for offset errors through iterative measurement and correction.
3Speed
If a fast clock is used in the single slope ramp method, then temperature sensing speed is improved, but the fast clock is not available on every integrated circuit
Solution Approach 1:
The patent achieves universality by designing a temperature sensing circuit that can operate with standard integrated circuit clocks rather than requiring specialized fast clocks. The dual measurement approach with switch circuitry enables the system to achieve accurate temperature sensing using readily available clock resources, making the circuit compatible with various integrated circuit platforms.
Data Source
AI summary
Performing a temperature measurement operation includes a first phase and a second phase. The first phase includes providing a voltage indicative of a measured temperature to a first input of a comparator, providing a ramp signal to a second input of the comparator, and generating at an output of the comparator, pulses based on a comparison of the first input to the second input of the comparator. The second phase includes providing the voltage indicative of a measured temperature to the second input of the comparator, providing the ramp signal to the first input of the comparator, and generating at an output of the comparator, pulses based on a comparison of the first input to the second input of the comparator. Performing the temperature measurement operation also includes utilizing the pulses generated during the first and second phases to provide a digital indication of the measured temperature.