Delta-Sigma Modulator Chopping Error Cancellation for Wideband Purity
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Solution Overview
Problem
High-speed delta-sigma modulators face challenges in mitigating quantization noise downfolding due to non-ideal chopping effects, which degrade modulator noise and spectral purity, especially in wideband applications, as conventional techniques like FIRDACs and RTZ switching are ineffective or impractical at GHz rates.
Innovation Solution
A system and method that replicates and cancels chopping folding errors in delta-sigma modulators through digital post-cancellation, utilizing a replica of the folding error extracted from the modulator output and subtracted to suppress in-band noise and spurs, employing digital choppers and filters to model and correct for chopping imperfections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional techniques like FIRDACs and RTZ switching are used to mitigate quantization noise downfolding, then noise suppression is improved, but device complexity and impracticality increase at GHz rates
Solution Approach 1:
The patent replaces complex analog chopping mechanisms with digital signal processing techniques. Specifically, it uses digital filtering and spectral inversion methods to cancel quantization noise downfolding artifacts, substituting the mechanical/analog chopping approach with digital signal manipulation that is more suitable for high-speed operation
Solution Approach 2:
The patent introduces digital filters as intermediary components between the quantizer and the output stage. These filters act as mediators that selectively remove downfolded quantization noise components without affecting the desired signal, providing a controlled transition that resolves the noise suppression problem without requiring complex direct intervention in the chopping mechanism
2Speed
If chopping frequency is increased to meet wideband application requirements, then bandwidth is improved, but spectral purity deteriorates due to non-ideal chopping effects
Solution Approach 1:
The patent converts the harmful effect of non-ideal chopping (which creates downfolded quantization noise) into a beneficial cancellation mechanism. By modeling the exact spectral characteristics of the downfolded noise and applying spectral inversion, the patent transforms the chopping imperfections from a source of degradation into a predictable artifact that can be systematically eliminated through digital processing
Solution Approach 2:
The patent employs feedback mechanisms where the quantizer output is fed back through digital filters that model the chopping transfer function. This feedback path allows the system to continuously monitor and cancel downfolded noise components, maintaining spectral purity even as chopping frequency increases to meet wideband requirements
3Productivity
If device dimensions are scaled down to increase speed capability, then productivity is improved, but flicker noise increases and dominates thermal noise
Solution Approach 1:
The patent extracts and separates the flicker noise component from the overall noise spectrum by utilizing the chopping mechanism's frequency translation property. The chopping process upconverts low-frequency flicker noise to higher frequencies where it can be filtered out, effectively extracting the harmful flicker noise component from the signal band and removing it through spectral separation and filtering
Data Source
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AI summary
A system and method of replicating and cancelling chopping folding error in delta-sigma modulators. The modulator may include a loop filter coupled to a quantizer providing a digital signal, chopper circuitry that chops analog signals of the loop filter at a chopping frequency, and chopping folding error cancellation circuitry that replicates and cancels a chopping folding error of the chopper circuitry to provide a corrected digital signal. A digital chopper or multiplier chops the digital signal to provide a chopped digital signal, and the chopped digital signal is either amplified or multiplied by a gain value or digitally filtered to replicate the chopping folding error, which is then subtracted from the digital signal for correction. The timing and duty cycle of the chopping frequency may be adjusted. Timing and duty cycle adjustment may be calibrated along with the filtering.