ADC Comparator Offset Tracking Near Reference Thresholds
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Solution Overview
Problem
Existing analog-to-digital converter (ADC) technologies, particularly delay domain ADCs, face accuracy issues due to comparator flicker noise, which is not adequately addressed by conventional calibration methods, leading to noise degradation and increased comparator input offset errors.
Innovation Solution
The proposed solution involves an ADC system with calibration circuitry that estimates and corrects comparator input offset errors by applying pseudorandom binary sequence (PRBS) values to determine offset errors and provide calibration signals when the error exceeds a threshold, thereby reducing noise and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If chopper circuitry is used to reduce comparator flicker noise, then linearity error is reduced, but overall noise increases and comparator input offset increases
Solution Approach 1:
The patent applies different processing to different signal conditions by selectively tracking comparator offsets only when the analog signal is proximate to reference thresholds. This local approach addresses the specific problem area (threshold regions where offset errors are most impactful) without applying global dithering that increases overall noise.
Solution Approach 2:
The patent changes the operational parameters of comparators dynamically by adjusting comparator offsets based on detected threshold proximity and estimated offset errors. This allows the system to optimize comparator performance in specific operating conditions without degrading overall noise performance.
2Ease of manufacture
If conventional calibration is used, then manufacturing is simplified, but comparator flicker noise is not adequately accounted for resulting in lower accuracy
Solution Approach 1:
The patent performs preliminary detection of threshold proximity conditions and estimates comparator offset errors before final ADC conversion. This preliminary characterization of comparator behavior allows for accurate compensation without complicating the manufacturing process.
Solution Approach 2:
The patent implements a feedback mechanism where comparator output results are used to detect threshold proximity, estimate offset errors, and generate calibration signals that feed back to adjust comparator offsets. This closed-loop approach improves accuracy while maintaining manufacturing simplicity.
3Object-generated harmful factors
If selective offset tracking is implemented, then noise is reduced and SNR is enhanced, but device complexity increases
Solution Approach 1:
The patent implements partial offset tracking by only actively monitoring and correcting comparator offsets when the analog signal is proximate to reference thresholds. This partial action approach reduces the overall complexity compared to continuous tracking while still achieving noise reduction and SNR enhancement in the critical threshold regions.
4Measurement precision
If continuous comparator offset monitoring is performed, then accuracy is improved, but processing time increases
Solution Approach 1:
The patent performs comparator offset monitoring periodically based on threshold proximity detection rather than continuously. The calibration circuitry activates offset tracking only when needed (when analog signal is near thresholds) and remains inactive otherwise, creating a periodic action pattern that improves accuracy without excessive time loss.
Data Source
AI summary
An analog-to-digital converter (ADC) includes: a set of comparators configured to provide comparison results based on an analog signal and respective reference thresholds for comparators of the set of comparators; digitization circuitry configured to provide a digital output code based on the comparison results and a mapping; and calibration circuitry. The calibration circuitry is configured to: receive the comparison results; determine if the analog signal is proximate to one of the respective reference thresholds based on the comparison results; in response to determining the analog signal is proximate to one of the respective reference thresholds, receive ADC values based on different pseudorandom binary sequence (PRBS) values being applied to the analog signal; determine an offset error based on the ADC values; and provide a comparator input offset calibration signal at a calibration circuitry output if the estimated offset error is greater than an offset error threshold.