Comparator Calibration Circuit for Sub-mV Offset Cancellation
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Solution Overview
Problem
Current comparator circuits face challenges in achieving sub-millivolt offsets, particularly in CMOS technology, due to complex circuitries required for correlated double sampling and chopping techniques, which introduce fixed-pattern noise that needs filtering.
Innovation Solution
An adaptive calibration circuit with an up-down counter and switched capacitors is used to adjust offsets in spare cycles, allowing for arbitrarily small step sizes without filtering, enabling sub-mV resolution in comparator circuits suitable for power management and analog-to-digital converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If correlated double sampling or chopping techniques are used to achieve sub-mV offsets, then measurement precision is improved, but device complexity increases and fixed-pattern noise is introduced requiring filtering
Solution Approach 1:
The patent applies preliminary action by performing offset calibration in spare cycles before normal comparison operations. The calibration circuit pre-adjusts the offset using an up-down counter and switched capacitors during idle time, so that when the comparator is used for actual measurements, the offset has already been corrected without interfering with the main measurement function.
Solution Approach 2:
The calibration circuit uses the comparator's own output to drive the calibration process. The up-down counter automatically adjusts the offset based on the comparator output state, creating a self-regulating system that eliminates manual calibration needs and reduces external control complexity.
2Measurement precision
If chopping technique is used to cancel offset effects, then measurement precision is improved, but object-generated harmful factors increase due to fixed-pattern noise requiring filtering
Solution Approach 1:
The patent extracts the offset correction function into a separate calibration circuit that operates independently from the main comparison function. By using switched capacitors connected to the inverting input, the offset is extracted and adjusted separately, preventing the generation of fixed-pattern noise that would occur with chopping techniques.
Solution Approach 2:
The calibration is performed in advance during spare cycles before normal operation begins. This preliminary offset correction eliminates the need for continuous offset cancellation mechanisms like chopping, thereby avoiding the generation of fixed-pattern noise during the actual measurement period.
3Measurement precision
If complex circuitries like correlated double sampling are used, then measurement precision is improved, but ease of operation deteriorates due to sampling difficulty and filtering requirements
Solution Approach 1:
The calibration circuit automatically performs offset adjustment using the comparator's own output signal to control the up-down counter. This self-service mechanism eliminates the need for external sampling control logic and makes the system easier to operate without requiring complex external coordination for sampling operations.
Data Source
AI summary
A comparator has a first terminal, a second terminal, and an output terminal. A selection circuit is coupled to the first terminal. A calibration circuit is coupled to the output terminal and the second terminal. The comparator is configured to operate in a first mode when the selection circuit provides a first input signal to the first terminal and the calibration circuit provides a second input signal to the second terminal. The comparator is configured to operate in a second mode when the selection circuit provides a first calibration signal to the first terminal and the calibration circuit provides a second calibration signal to the second terminal based on an output signal at the output terminal. The comparator generates the output signal based on the first calibration signal and the second calibration signal.