Sigma-Delta Converter Calibration by Injected Signal Correlation
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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, affecting quantization noise performance.
Innovation Solution
A calibration system using injected signal correlation, where a pseudo-random or dual-tone signal is injected into the sigma-delta converter, filtered, and correlated with the output to adjust the resonator frequencies of the loop filter, ensuring optimal notch frequency alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If passive devices (resistors and capacitors) are used to set resonator frequencies, then the converter structure is simple and easy to manufacture, but the resonator frequencies drift due to manufacturing variation and temperature dependency
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the resonator frequencies through active calibration. The system modifies the frequency parameters of the loop filter using digital correction codes to compensate for manufacturing variations and temperature drift, thereby maintaining precise resonator frequencies despite using simple passive devices
Solution Approach 2:
The patent implements feedback through an automatic calibration mechanism that measures the actual resonator frequencies and adjusts them accordingly. The system uses feedback from frequency measurements to generate correction codes that are applied to the loop filter, creating a closed-loop control system that maintains frequency accuracy
2Reliability
If resonator frequencies are calibrated to minimize quantization noise, then the signal-to-quantization noise ratio improves, but the device complexity increases due to additional calibration circuitry
Solution Approach 1:
The patent applies self-service by designing an automatic calibration system that performs frequency adjustment without external intervention. The calibration circuitry autonomously measures resonator frequencies, generates correction codes, and applies adjustments, enabling the system to self-correct frequency drift and maintain optimal performance
Solution Approach 2:
The patent implements preliminary action by performing calibration during the manufacturing process or initial setup phase. The system pre-adjusts the resonator frequencies to account for manufacturing variations, so that the converter starts operation with optimized frequency settings, reducing the need for complex real-time calibration circuitry
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
The calibration method effectively converges quickly, even offline, and can be used for start-up or periodic calibration, improving signal-to-quantization noise ratio by adjusting resonator frequencies to minimize noise contributions.
Implementation Method 1
a correlator having a first input coupled to the output of the first bandpass filter, having a second input coupled to the output of the second bandpass filter, and having an output configured to provide an error signal
Data Source
Figure 1
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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.