Resonant Filter Self-Tuning for Stable Delta-Sigma ADCs
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Solution Overview
Problem
Delta-sigma analog-to-digital converters with RC active filters face instability and reduced signal-to-noise ratio due to manufacturing variations in resistor and capacitor values, requiring time-consuming measurement and adjustment processes that also introduce inaccuracies.
Innovation Solution
A small-scale additional circuit with a feedback path and switchable resonant filter allows for precise adjustment of resistor and capacitor values by controlling the feedback resistor and switch, enabling high-accuracy tuning without the need for an external RC oscillator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If RC active filter is used in delta-sigma A/D converter, then filtering function is achieved, but manufacturing variations cause instability and degraded signal-to-noise ratio
Solution Approach 1:
The patent introduces a feedback mechanism where the resonant filter operates as an oscillator to measure its own frequency characteristics. The measured frequency information is fed back to adjust the resistor and capacitor values, creating a closed-loop system that compensates for manufacturing variations and maintains stable filtering performance.
Solution Approach 2:
The resonant filter performs self-adjustment by using its own oscillation frequency as the measurement reference. The system automatically tunes its components without requiring external measurement instruments or manual calibration, achieving self-service calibration that eliminates the need for external RC oscillators.
2Measurement precision
If external RC oscillator is added for measurement, then frequency characteristics can be measured, but device complexity increases
Solution Approach 1:
The patent merges the measurement function with the filtering function by making the resonant filter itself capable of oscillation. This eliminates the need for a separate external RC oscillator, reducing device complexity while maintaining measurement precision through the unified oscillating structure.
Solution Approach 2:
The resonant filter is designed to serve multiple functions: it acts as both the filtering element and the oscillating source for measurement. This multi-functionality eliminates redundant components and simplifies the overall circuit architecture while enabling accurate frequency characteristics measurement.
3Measurement precision
If signal extraction and measurement are performed, then filter characteristics are obtained, but time is consumed and additional terminals are required
Solution Approach 1:
The resonant filter measures its own characteristics internally through self-oscillation, eliminating the need for external signal extraction and measurement processes. This self-service approach reduces measurement time and eliminates the requirement for additional input/output terminals for external measuring instruments.
4Object-generated harmful factors
If RC active filter is used, then filtering operation is achieved, but component value variations degrade signal-to-noise ratio
Solution Approach 1:
The patent employs feedback control where the oscillation frequency of the resonant filter is measured and used to adjust the resistor and capacitor values. This closed-loop feedback mechanism compensates for manufacturing variations, maintaining optimal signal-to-noise ratio despite component value deviations.
Solution Approach 2:
The system dynamically changes the resistance and capacitance parameters based on measured frequency characteristics. By adjusting these parameters in response to actual performance, the system optimizes the signal-to-noise ratio and compensates for manufacturing variations in the filter components.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves the stability and signal-to-noise ratio of delta-sigma A/D converters by allowing accurate adjustment of resonant filter components, reducing the need for external measurement tools and minimizing mismatches between filter and oscillator components.
Implementation Method 1
a feedback path configured to connect an output of the resonator to an input of the resonator, in a positive feedback fashion
Implementation Method 2
The resonant filter includes a resonator including a resistor and a capacitor and configured to receive a second input signal
Implementation Method 3
a feedback resistor configured to allow a resistance value thereof to be controlled based on a second external signal
Implementation Method 4
At least one of the resistor and the capacitor of the resonator is configured to allow a resistance value or a capacitance value thereof to be adjusted based on a third external signal
Data Source
AI summary
A delta-sigma A/D converter includes a loop filter including a resonant filter, a quantizer, and a feedback D/A converter. The resonant filter includes a resonator including a resistor and a capacitor, and a feedback path through which an output of the resonator is positively fed back to an input of the resonator. The resonant filter operates as an oscillator or a filter under the on/off control of a first switch. At least one of the resistor and the capacitor of the resonator is configured to allow a resistance value or a capacitance value thereof to be adjusted based on a third external signal.