Delta-Sigma Modulator Compensation Filter for Excess Loop Delay
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Solution Overview
Problem
Continuous-time delta-sigma modulators are sensitive to clock jitter and quantizer delay, which degrades their performance by reducing the maximum stable amplitude, increasing internal signal swings, and degrading the noise transfer function, thus limiting the signal-to-quantization noise ratio (SQNR).
Innovation Solution
A compensation filter is introduced between the output of the quantizer and the input of the inner portion of the analog loop filter, with a transfer function configured to correct for the effects of excess loop delay (ELD) in both the outer and inner feedback paths, allowing for improved stability and reduced power consumption by tolerating longer delays in the quantizer and feedback paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If continuous-time delta-sigma modulators are used to achieve power efficiency and inherent anti-alias filtering, then power consumption is reduced and anti-alias filtering is improved, but sensitivity to clock jitter and quantizer delay increases
Solution Approach 1:
A compensation filter is introduced as an intermediary component in the feedback path to counteract the harmful effects of excess loop delay. The filter has a transfer function specifically designed to compensate for the delay introduced by the quantizer and feedback path, thereby restoring the stability and performance of the continuous-time delta-sigma modulator while maintaining its power-efficient operation
2Use of energy by moving object
If longer delays are tolerated in the quantizer and feedback paths to reduce power consumption, then power efficiency is improved, but stability and noise transfer function degrade
Solution Approach 1:
The compensation filter applies preliminary anti-action by pre-compensating for the excess loop delay effects before they can degrade the system performance. The filter's transfer function is designed to counteract the phase shift and magnitude changes caused by the delay, allowing the system to tolerate longer delays while maintaining stability and noise transfer function characteristics
3Device complexity
If excess loop delay is present in the feedback path, then device complexity is reduced, but maximum stable amplitude is reduced and internal signal swings increase
Solution Approach 1:
The compensation filter serves as a mediator that allows the feedback path to maintain its simple structure with inherent delay while compensating for the negative effects of that delay. The filter restores the maximum stable amplitude and controls internal signal swings without adding significant complexity to the overall system
Data Source
AI summary
In accordance with an embodiment, a delta-sigma modulator includes: an analog loop filter comprising an outer portion and an inner portion having an input coupled to the outer portion; a quantizer coupled to an output of the inner portion of the analog loop filter; an outer feedback path coupled between an output of the quantizer and an input to the outer portion of the analog loop filter; and a compensation filter coupled between an output of the quantizer and an input of the inner portion of the analog loop filter. The compensation filter has a transfer function configured to correct for an effect of excess loop delay (ELD) on the delta-sigma modulator.