Sigma-Delta Feed-Forward Filtering for STF Peaking Control
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Solution Overview
Problem
Sigma-delta modulators with distributed feed-forward architectures exhibit out-of-band peaking close to the signal bandwidth, which increases the requirements for pre-filters and limits the achievable resolution.
Innovation Solution
Incorporating a filter in the feed-forward path of a sigma-delta modulator to reduce peaking behavior of the signal transfer function (STF), allowing the peaking to be moved to higher frequencies and potentially eliminating the need for a pre-filter, by implementing poles, zeros, or phase shifts in the feed-forward path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a distributed feed-forward architecture is used in a sigma-delta modulator, then the signal transfer function achieves high gain in the signal band, but out-of-band peaking occurs close to the signal bandwidth
Solution Approach 1:
A pre-filter is introduced as an intermediary component between the input signal and the sigma-delta modulator. This pre-filter attenuates out-of-band signals before they enter the modulator, preventing the peaking phenomenon from occurring in the final output. The pre-filter acts as a mediator that removes harmful out-of-band components while allowing the beneficial in-band signal to pass through to the distributed feed-forward architecture.
2Object-generated harmful factors
If out-of-band peaking is reduced by adding a pre-filter, then the harmful peaking is suppressed, but the device complexity increases
Solution Approach 1:
The coefficients of the loop filter are optimized and adjusted to achieve the desired signal transfer function characteristics with minimal out-of-band peaking. By carefully selecting and tuning the loop filter parameters, the system achieves high in-band gain while suppressing out-of-band peaking inherently, without requiring additional pre-filter components. This parameter optimization allows the existing distributed feed-forward architecture to self-regulate the peaking issue.
Data Source
AI summary
Proposed is a sigma-delta modulator circuit. The circuit comprises a loopfilter having at least one integrator or resonator section; and a feed-forward path adapted to provide a feed-forward signal to the output of the at least one integrator or resonator section via a filter.