Differential Anti-Aliasing Filter Calibration for Impedance Mismatch
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Solution Overview
Problem
Impedance mismatches in anti-aliasing filters within delta-sigma modulators lead to non-ideal operation, particularly the conversion of common-mode voltage AC components to the output of ADCs, increasing with frequency up to the corner frequency of the filter, necessitating a solution to reduce or eliminate these effects.
Innovation Solution
A method and system that apply a common-mode signal to the differential filter, measure the output signal to determine impedance mismatch errors, and use a PID controller to tune the impedance elements to minimize these errors, incorporating a signal generator, error extractor, and controller to adjust resistors and capacitors for optimal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If impedance elements in anti-aliasing filter are used, then filtering function is achieved, but impedance mismatch converts common-mode voltage AC components to differential output
Solution Approach 1:
The patent implements a calibration system that measures the common-mode to differential conversion error and uses this feedback to adjust the impedance elements. The system applies a common-mode test signal, measures the erroneous differential output, and uses PID controllers to tune the impedance elements until the error is minimized, thereby eliminating the harmful conversion effect while maintaining the filtering function.
Solution Approach 2:
The patent changes the impedance parameters of the filter elements dynamically through calibration. By adjusting the resistance and capacitance values of the impedance elements based on measured errors, the system optimizes the filter performance to minimize common-mode conversion while maintaining proper anti-aliasing functionality.
2Measurement precision
If impedance mismatch error is measured and tuning is applied, then common-mode conversion error is reduced, but system complexity increases due to calibration circuitry
Solution Approach 1:
The calibration system is self-service in that it automatically measures its own impedance mismatch errors and adjusts its own impedance elements without external intervention. The system uses its existing differential output nodes to measure common-mode conversion errors and employs on-chip tunable impedance elements that are automatically adjusted through the calibration process, eliminating the need for external calibration equipment.
Solution Approach 2:
The calibration circuitry serves multiple functions: it generates test signals, measures conversion errors, processes measurement data through PID controllers, and adjusts impedance elements. By integrating these multiple functions into a unified calibration system that operates during normal device operation, the patent reduces overall system complexity compared to having separate dedicated circuits for each function.
3Reliability
If continuous tuning of impedance elements is performed, then filter performance is optimized, but power consumption increases
Solution Approach 1:
The patent implements periodic calibration rather than continuous tuning. The calibration process is performed at specific intervals or under certain conditions (such as during startup or when performance degradation is detected), allowing the impedance elements to be tuned to optimal values without continuous power consumption. Between calibration events, the filter operates with fixed impedance settings, minimizing energy usage while maintaining optimized performance.
Data Source
AI summary
In accordance with embodiments of the present disclosure, a method may include, in a system comprising a differential filter comprising a plurality of impedance elements, applying a common-mode signal to the differential filter, measuring an output signal of the differential filter in response to the common-mode signal to determine an error due to impedance mismatch of the impedance elements, and tuning one or more of the plurality of impedance elements to minimize the error.