ADC Error Signal Normalization for Runaway Loop Recovery
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Solution Overview
Problem
Sigma-delta ADCs can enter a 'runaway' state when the supply voltage dominates the feedback loop, causing oscillation and rendering the converter non-functional, requiring a time-consuming reset to resume normal operation.
Innovation Solution
Incorporating auxiliary comparators and an auxiliary DAC to digitize and correct error signals with wider reference ranges, allowing for quick normalization of the feedback loop and removal from a runaway state without reset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the supply voltage range substantially exceeds the analog input signal range, then the ADC can handle larger voltage variations, but the feedback loop becomes dominated by supply voltage causing runaway state and oscillation
Solution Approach 1:
The comparator set is divided into main comparators for normal operation and auxiliary comparators for runaway state detection. The auxiliary comparators monitor when the error signal exceeds predetermined thresholds, enabling segmented handling of different operational states to prevent feedback loop domination by supply voltage
Solution Approach 2:
An auxiliary digital-to-analog converter (DAC) is introduced as an intermediary component that activates during runaway states to generate corrective feedback signals. This auxiliary DAC mediates between the auxiliary comparators and the main feedback loop, providing intermediate correction action to restore stability without requiring full system reset
2Measurement precision
If the ADC enters a runaway state, then the error signal exceeds the predetermined range, but the main comparators cannot digitize the error signal accurately
Solution Approach 1:
The comparator functionality is segmented into main comparators with narrow reference ranges for precise normal operation and auxiliary comparators with wide reference ranges for runaway state detection. This segmentation allows each comparator set to operate within its optimal range, maintaining measurement precision while expanding overall adaptability
Solution Approach 2:
The system transitions from a single comparator set operating in one dimension (normal range) to a two-dimensional architecture where auxiliary comparators provide coverage in extended voltage dimensions. This dimensional expansion enables accurate error signal digitization across both normal and runaway states without compromising precision in either regime
3Reliability
If the ADC is reset to resume normal operation from a runaway state, then the ADC can return to functional operation, but the reset process is time-consuming
Solution Approach 1:
The auxiliary comparators and auxiliary DAC are pre-configured and continuously monitoring, ready to activate immediately upon detecting runaway conditions. This preliminary preparation enables instantaneous corrective action without waiting for system reset sequences, dramatically reducing the time to restore functionality
Solution Approach 2:
A fast-acting feedback mechanism is implemented where auxiliary comparators detect runaway states and immediately trigger the auxiliary DAC to generate corrective feedback signals. This closed-loop feedback operates independently of the main ADC reset sequence, enabling rapid self-correction that eliminates time-consuming reset delays
Data Source
AI summary
In some embodiments, an analog-to-digital converter (ADC) comprises a loop filter configured to produce an error signal based on a difference between an analog input signal and a feedback signal. The ADC also comprises a main comparator set comprising one or more main comparators, the main comparator set configured to digitize the error signal and further configured to drive a main digital-to-analog converter (DAC). The ADC further comprises an auxiliary comparator set comprising a plurality of auxiliary comparators, the auxiliary comparator set configured to digitize the error signal when the ADC is in a runaway state and further configured to drive an auxiliary DAC to bring the error signal into a predetermined range.