Delta-Sigma A/D Feedback Comb Filter for Blocker Immunity
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Solution Overview
Problem
Continuous-time delta-sigma modulators in radio transceivers face instability and distortion due to strong out-of-band blocker signals, and existing counter-measures increase circuit complexity and power consumption.
Innovation Solution
A delta-sigma A/D converter with a mixed-mode comb filter in the feedback loop and an analogue filter at the input to predistort and cancel feedback signal distortion, reducing operational amplifier slew rate requirements and channel filtering needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an analogue high pass filter is added to the feedback loop of a ΔΣ modulator to counter blocker signals, then immunity to interferers is improved, but circuit complexity increases and power consumption increases
Solution Approach 1:
The patent combines the high pass filtering function with the existing D/A converter in the feedback loop by implementing the filter directly in the digital domain using comb filter structures. This merging eliminates the need for separate analogue filter circuits while achieving the same blocker signal rejection, thereby reducing circuit complexity and power consumption while maintaining immunity to interferers
Solution Approach 2:
The patent replaces the analogue high pass filter (mechanical/electrical system) with a digital comb filter implementation. The digital filter uses simple delay elements and adders instead of analogue components like capacitors and resistors, significantly reducing circuit complexity and power consumption while achieving equivalent or superior blocker signal rejection
2Reliability
If an analogue high pass filter is added to the feedback loop of a ΔΣ modulator to counter blocker signals, then immunity to interferers is improved, but power consumption increases
Solution Approach 1:
The patent merges the high pass filtering function with the D/A converter, eliminating the need for separate analogue filter circuits that would consume additional power. The digital comb filter implementation uses minimal power-consuming components (delay elements and adders) compared to analogue filters requiring operational amplifiers and active components
Solution Approach 2:
The patent substitutes the power-hungry analogue high pass filter with a low-power digital comb filter implementation. The digital domain operation requires significantly less power than analogue filtering circuits, especially at the frequencies and bandwidths required for modern communication systems
3Device complexity
If a ΔΣ modulator is used to relax antialias filtering requirements, then channel filtering requirements are relaxed, but strong out-of-band signals may render the modulator unstable or create distortion
Solution Approach 1:
The patent applies preliminary anti-action by implementing a digital high pass filter (comb filter) in the feedback loop that proactively rejects blocker signals before they can reach the quantizer and cause distortion or instability. This preliminary filtering action prevents the harmful effects of strong out-of-band signals while maintaining the relaxed antialias filtering benefits of ΔΣ modulators
Data Source
AI summary
A delta-sigma A/D converter includes a D/A converter realized with a mixed-mode comb filter connected in a feedback loop from the output of the A/D converter to the input of the A/D converter. The D/A converter is configured to predistort a feedback signal. The converter further includes an analogue filter at the input of the A/D converter. The analogue filter is configured to cancel the predistortion of the feedback signal.