Sigma-Delta Integrator Cancellation Paths for Lower Output Swing
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Solution Overview
Problem
Conventional sigma-delta (ΣΔ) analog-to-digital converters face challenges in reducing integrator output swing without compromising noise performance, as scaling for smaller swing reduces AC gain and increases noise contribution, and existing techniques to mitigate this often alter the signal transfer function, making them unsuitable for designs with stringent requirements.
Innovation Solution
The implementation of a multi-stage loop filter with first and second cancellation paths, where cancellation signals are injected to reduce integrator output swing without significantly affecting the signal transfer function, using cancellation impedances and capacitors to balance currents and voltages, ensuring the net current into subsequent stages is minimized and the signal transfer function remains unchanged.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If integrators are scaled for smaller output swing, then amplifier distortion is reduced, but AC gain is reduced and noise contribution increases
Solution Approach 1:
The patent segments the feedback current cancellation into two independent paths: a first cancellation path that directly reduces integrator output swing, and a second cancellation path that compensates for the resulting signal transfer function changes. This segmentation allows each path to be optimized for its specific function without compromising the other.
Solution Approach 2:
The patent introduces cancellation signals as intermediary elements that mediate between the feedback DAC current and the integrator output. These cancellation signals are injected through specifically designed paths to counteract unwanted effects while preserving the desired signal transfer function.
2Object-generated harmful factors
If a feedforward path is added to reduce integrator output swing, then output swing is reduced, but signal transfer function is altered
Solution Approach 1:
The patent divides the cancellation mechanism into two distinct paths with different functions. The first cancellation path handles output swing reduction, while the second cancellation path handles signal transfer function compensation. This segmentation prevents the unwanted interaction that occurs in single-path approaches.
Solution Approach 2:
The patent adjusts the parameters of the cancellation paths (impedances, signal amplitudes, and phases) to achieve optimal cancellation of feedback current while maintaining the desired signal transfer function. The parameters are specifically tuned to counteract the effects of the feedforward path.
3Device complexity
If scaling is optimized to balance noise, distortion, and power, then trade-off is achieved, but integrator output swing cannot be reduced without compromising noise performance
Solution Approach 1:
The patent employs feedback mechanisms where cancellation signals are generated based on the feedback DAC output and injected back into the integrator stages. This feedback approach allows dynamic compensation that maintains noise performance while enabling reduced output swing.
Solution Approach 2:
The cancellation signals act as intermediary elements that mediate between the feedback loop and the integrator stages, allowing the system to achieve reduced output swing without directly compromising the noise performance of the integrators.
Data Source
AI summary
Embodiments of the present invention may include an apparatus and method to reduce an output swing in each stage of a multi-stage loop filter while also maintaining a desired signal transfer function for each respective stage. A given stage of the loop filter may include an integrator, a feedback path, a first cancellation path, and a second cancellation path. The first cancellation path may be coupled to the output of the integrator. The second cancellation path may be coupled to a feedback path provided about the input and output of the integrator. A first cancellation signal may be injected into the first cancellation path to reduce the output swing of the integrator. A second cancellation signal may be injected into the second cancellation path to minimize a change in the integrator's signal transfer function caused by the first cancellation signal.