Delta-Sigma ADC Dither Compensation for Stuck Code Prevention
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Solution Overview
Problem
Delta-sigma modulators in analog-to-digital converters face issues with stuck code sequences due to dither introduction, which generates errors and reduces precision, especially when the input and feedback signals are close in value.
Innovation Solution
A delta-sigma modulator design that injects dither into the noise-shaping filter and compensates for the resulting error by subtracting an offset from the quantizer output, using a dither compensation circuit to minimize the impact of dither on the conversion results, while also allowing for intermittent operation to reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dither is introduced to the noise-shaping filter to prevent stuck code sequences, then the quantizer output changes constantly and noise-shaping operation is provided, but error in the output increases and precision decreases
Solution Approach 1:
The patent applies preliminary anti-action by injecting dither into the noise-shaping filter to prevent stuck code sequences before they occur, then compensating for the resulting error by subtracting the dither value from the quantizer output. This preemptive approach ensures the quantizer remains active while correcting the introduced error in the output path.
Solution Approach 2:
The patent extracts the harmful effect of dither by separating the dither injection function from the main signal path. The dither is injected only into the noise-shaping filter to prevent stuck codes, while the compensating subtraction removes the dither's error contribution from the final output, effectively taking out the unwanted error while retaining the beneficial stuck-code prevention.
2Reliability
If dither is added to ensure sufficient signal level changes and constant quantizer output, then stuck code sequences are reduced, but the level of error due to dither increases
Solution Approach 1:
The patent implements feedback by monitoring the dither value injected into the noise-shaping filter and using this information to generate a compensating subtraction signal. The system feeds back the dither information through the dither compensation circuit to cancel its error effect, creating a closed-loop approach that maintains quantizer stability while eliminating dither-induced errors.
Solution Approach 2:
The dither compensation circuit acts as an intermediary between the dither injection point and the final output. It receives the dither signal, processes it to determine the appropriate compensation value, and subtracts the corrected dither from the quantizer output, serving as a mediator that allows dither to prevent stuck codes while removing its harmful error effects.
3Measurement precision
If the ADC operates continuously to maintain conversion accuracy, then measurement precision is maintained, but power consumption increases
Solution Approach 1:
The patent applies periodic action by enabling the ADC to operate in intermittent mode where the delta-sigma modulator can be reset and powered down between conversion cycles. The dither injection mechanism ensures that when conversions do occur, the quantizer is properly initialized and stuck code sequences are prevented, allowing accurate conversions at lower sample rates without continuous operation.
Solution Approach 2:
The patent uses preliminary action by resetting the delta-sigma modulator before intermittent operation periods. This preliminary reset ensures that when the converter is reactivated, the integrators are properly initialized and dither is injected to prevent stuck codes, allowing the ADC to maintain measurement precision even when operating intermittently to reduce power consumption.
Data Source
AI summary
An analog-to-digital converter (ADC) having integrator dither injection and quantizer output compensation reduces the probability of unchanging code sequences that occur when the input signal and feedback signal are equal and thus no quantizer output change occurs. In particular, in modulators that are periodically reset, the dither reduces the probability of a stuck code sequence at startup. The effect of the dither is removed from the output of the ADC, either by subtracting an offset value from the result of filtering the quantizer output, or directly from the quantizer output itself.