Sigma-Delta Resonator Calibration for Notch Frequency Alignment

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Solution Overview

Problem

Higher order sigma-delta converters face challenges in maintaining optimal resonator frequencies due to manufacturing variations and temperature dependencies, which affect the signal to quantization noise ratio (SQNR) in the band of interest.

Innovation Solution

A calibration system and method that uses injected signal correlation, specifically a pseudo-random bit stream (PRBS) or dual tone signal, to adjust the resonator frequencies of the loop filter in sigma-delta converters, ensuring optimal notch frequency alignment through bandpass filtering and correlation-based feedback.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If resonator frequencies are set by passive devices (resistors and capacitors), then the converter achieves basic frequency determination, but manufacturing variation and temperature dependency cause frequency drift and performance degradation

Engineering Contradiction:

Improveresonator frequency accuracyVSAvoidfrequency stability over temperature

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent changes the resonator frequency parameter dynamically by adjusting the loop filter coefficients based on temperature measurements and calibration data, allowing the system to adapt to temperature variations and manufacturing variations rather than relying solely on fixed passive components

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements a feedback mechanism where the actual resonator frequency is measured and compared against target frequencies, and the loop filter coefficients are adjusted accordingly to correct frequency drift caused by temperature and manufacturing variations

Inventive Principle:

Principle #23Feedback

2Measurement precision

If resonator frequencies are calibrated to optimize SQNR, then noise performance in the band of interest is improved, but additional calibration circuitry and complexity are required

Engineering Contradiction:

Improvesignal to quantization noise ratioVSAvoidcalibration circuitry

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent makes the loop filter serve multiple functions: it not only shapes the noise spectrum but also acts as the calibration mechanism itself by adjusting its coefficients to tune the resonator frequencies, eliminating the need for separate calibration circuitry

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The system performs self-calibration by using its own output spectrum as feedback to automatically adjust the loop filter coefficients and optimize the resonator frequencies, without requiring external calibration equipment or complex additional circuitry

Inventive Principle:

Principle #25Self-service

3Measurement precision

If offline calibration is performed to adjust resonator frequencies, then optimal SQNR is achieved, but calibration time and productivity are reduced

Engineering Contradiction:

Improveresonator frequency accuracyVSAvoidcalibration time

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The patent performs preliminary calibration during the manufacturing process to establish initial loop filter coefficients, so that when the device is deployed, the resonator frequencies are already optimized and require minimal or no additional calibration time

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements periodic calibration at scheduled intervals or when temperature thresholds are exceeded, rather than continuous calibration, allowing the system to maintain optimal performance while minimizing the time spent in calibration mode and maximizing productivity during normal operation

Inventive Principle:

Principle #19Periodic action

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 effectively calibrates the resonator frequencies quickly, even offline, and maintains optimal SQNR performance across temperature variations, enhancing the converter's noise performance.

Implementation Method 1

a correlator to compute a correlation between the injected signal and the output signal

Methodology Applied

Scientific EffectSignal correlation:

Implementation Method 2

a bandpass filter to filter the output signal

Methodology Applied

Scientific EffectBandpass filtering: Filter (electronic)

Data Source

PatentUS11502699B1System and method of calibration of sigma-delta converter using injected signal correlation

Publication Date: 2022.11.15 NXP BV

AI summary

A digital conversion system including a sigma-delta converter, a signal generator providing a substantially symmetrical injection signal that is injected into the sigma-delta converter conversion path, bandpass filters for filtering the injection signal and the output of the sigma-delta converter, a correlator that correlates the filtered signals for providing an error signal, and a loop controller that uses the error signal to adjust a resonant frequency of the sigma-delta converter to output a target notch frequency. The loop controller may adjust a resonant frequency of a loop filter of the sigma-delta converter, in which the bandpass filters may each be centered at the target notch frequency at the output of the sigma-delta converter. The correlator may include a complex conjugate block, a multiplier and a mean calculator. The loop controller may include a converter and an amplifier and an integrator or a least-mean square block.