Offset Corrected Bandgap Reference Using Switched Capacitors
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Solution Overview
Problem
Non-idealities in the operational amplifier bandgap reference circuit lead to voltage offset errors in CMOS bandgap temperature sensors, which are the dominant source of error in temperature sensing, especially during analog-to-digital conversion.
Innovation Solution
The use of switched capacitors to store and correct for operational amplifier offset voltage during a sample mode, allowing for accurate offset correction during a hold mode, thereby improving the accuracy of the digital temperature signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If operational amplifier is used in CMOS bandgap reference circuit, then temperature sensing function is achieved, but voltage offset error is introduced
Solution Approach 1:
The patent applies preliminary action by sampling and storing the operational amplifier offset voltage in a capacitor before the analog-to-digital conversion process. The offset is captured during a sample phase and then subtracted from the bandgap reference voltage during the measurement phase, preventing the offset error from affecting the final temperature reading.
Solution Approach 2:
The patent implements feedback by continuously monitoring the operational amplifier offset voltage and using this information to correct the bandgap reference voltage. The measured offset is fed back to the correction circuitry, which adjusts the output voltage to compensate for the offset, thereby maintaining measurement accuracy.
2Measurement precision
If offset correction is implemented, then measurement accuracy is improved, but circuit complexity increases
Solution Approach 1:
The patent introduces an intermediary capacitor to store the offset voltage and an intermediary correction circuit to process the offset compensation. These intermediate elements facilitate the offset correction process without requiring complete redesign of the entire bandgap reference circuit, thus managing complexity while improving accuracy.
Solution Approach 2:
The patent segments the bandgap reference circuit into distinct functional blocks: the offset sampling circuit, the offset storage capacitor, and the correction circuit. This segmentation allows each component to be optimized independently and simplifies the overall design by dividing the complex offset correction function into manageable subsystems.
Data Source
AI summary
An offset corrected bandgap reference and temperature sensor is disclosed. In a complementary metal-oxide-semiconductor (CMOS) bandgap reference, non-idealities in the operational amplifier (op-amp) bandgap reference circuit can lead to a voltage offset. This operational amplifier offset voltage is the dominant source of error in the bandgap reference. If the bandgap reference is used in a temperature sensor, it only needs to be accurate during the analog-to-digital conversion cycle. Embodiments of the present disclosure employ switched capacitors to store the operational amplifier offset during a sample mode in which the bandgap reference operates continuous-time. The operational amplifier offset is then corrected during a hold mode while the temperature sensor completes the analog-to-digital conversion.