Flash ADC Background Calibration Without Spare Comparators
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Solution Overview
Problem
Analog-to-digital converters (ADCs), particularly FLASH ADCs, face challenges in size and power constraints due to small technology nodes, leading to mismatches in the receive path that require calibration to compensate for aging, voltage, and temperature variations, often necessitating complex and power-intensive switching networks.
Innovation Solution
The implementation of an ADC with a calibration control circuit that takes one comparator offline for continuous recalibration without a substitute, using neighboring comparators' values or random inference to maintain operation, thereby avoiding large switching networks and ensuring reliable calibration with reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a substitute comparator is used during calibration, then calibration reliability is improved, but device complexity and power consumption increase due to large switching networks
Solution Approach 1:
The patent extracts the substitute comparator from the system entirely. Instead of including a spare comparator that would require complex switching networks to integrate, the invention takes one of the existing comparators offline for calibration and uses inference algorithms based on neighboring comparator values and random guessing to estimate its output. This eliminates the need for additional hardware components and their associated switching networks.
Solution Approach 2:
The patent creates a virtual copy of the offline comparator's output through inference algorithms. By analyzing the thermometer code values from neighboring comparators and using random guessing when necessary, the system reconstructs what the offline comparator would have outputted without physically replicating the comparator itself. This virtual copying approach avoids the hardware overhead of a physical substitute.
2Reliability
If a substitute comparator is used during calibration, then calibration reliability is improved, but power consumption increases
Solution Approach 1:
The patent removes the power-intensive substitute comparator and its associated switching network from the system. By using inference algorithms that process existing comparator data, the calibration process consumes significantly less power while maintaining reliability through statistical estimation rather than physical replication.
3Measurement precision
If comparators are calibrated in foreground calibration routines, then initial calibration accuracy is improved, but continuous recalibration requires system interruption
Solution Approach 1:
The patent enables continuous recalibration by taking one comparator offline for calibration while the remaining comparators continue to operate and provide thermometer code values. The inference algorithm processes these values to estimate the offline comparator's output, allowing calibration to proceed without interrupting the overall ADC operation. This maintains continuous useful action in the form of ongoing signal conversion while performing calibration in the background.
4Area of moving object
If small technology nodes are used to meet size constraints, then device size is reduced, but mismatch errors increase due to manufacturing variations
Solution Approach 1:
The patent implements a feedback mechanism through continuous background calibration. By periodically taking comparators offline for recalibration and using inference algorithms to maintain accurate thermometer codes, the system compensates for manufacturing mismatches that become more significant at smaller technology nodes. This feedback loop continuously corrects for variations without requiring larger, more precise manufacturing.
Data Source
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AI summary
Analog-to-digital converters (ADCs) with background calibration processes are disclosed. In one aspect, an ADC with a plurality of comparators that each compare an input voltage to voltages that are generated at taps across a plurality of references (e.g., a reference resistor ladder). The comparators are initially calibrated with foreground calibration routines and continuously recalibrated to compensate for aging, voltage, and temperature variations without interrupting operation of the ADC by randomly taking one comparator of the plurality of comparators off-line to run calibration processes without replacing that comparator. The value for the off-line comparator may be reliably inferred from values from neighboring comparators or, in some cases, guessed randomly. While possible errors may be introduced, such errors may be driven to a mean square quantization noise level through example aspects of the present disclosure.