Radio Receiver Equalization for Analog Filter Cutoff Mismatch
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Solution Overview
Problem
Analog filters in direct conversion receivers introduce distortion due to manufacturing tolerances and temperature variations, which are difficult to correct accurately, especially in strict telecommunication standards like LTE and WCDMA, where signal quality errors must be kept below 1%.
Innovation Solution
A method that estimates the cutoff frequency of the analog filter by analyzing test tones and modifies the filter tuning word to determine residual mismatches, allowing for selection of an appropriate digital equalizer configuration to correct for inaccuracies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If analog filter components are manufactured with standard tolerances, then manufacturing cost and complexity are reduced, but signal quality deteriorates due to cutoff frequency mismatch exceeding 1% error limits
Solution Approach 1:
The patent applies preliminary action by measuring the actual cutoff frequency of the analog filter during manufacturing or initialization, and pre-calculating the compensation parameters for the digital equalizer before the filter is put into service. This allows the system to compensate for manufacturing tolerances in advance, ensuring signal quality compliance without requiring ultra-precise component manufacturing.
Solution Approach 2:
The patent changes the parameters of the digital equalizer (filter coefficients, cutoff frequency settings) based on the measured analog filter characteristics. By dynamically adjusting these parameters to match the actual analog filter performance, the system compensates for manufacturing variations and maintains signal quality within the 1% error limit required by telecommunication standards.
2Measurement precision
If high-precision calibration methods are implemented to characterize analog component mismatch, then signal quality improves, but device complexity and implementation difficulty increase
Solution Approach 1:
The patent implements self-service by using the analog filter itself to generate test signals that are used to measure its own characteristics. The filter processes known test tones, and the output is analyzed to determine the actual cutoff frequency and mismatch parameters. This self-measurement approach eliminates the need for external complex calibration equipment, reducing device complexity while maintaining high measurement precision.
Solution Approach 2:
The patent employs feedback by measuring the actual performance of the analog filter and using this information to adjust the digital equalizer parameters. The system continuously monitors the cutoff frequency mismatch and dynamically compensates for it, creating a closed-loop calibration process that achieves high precision without requiring overly complex open-loop measurement systems.
3Reliability
If calibration is performed frequently (e.g., on every device startup or channel switch), then signal quality is maintained, but processing time and power consumption increase
Solution Approach 1:
The patent applies partial action by performing a full calibration only when necessary (e.g., on device startup or when temperature thresholds are exceeded), and using lighter-weight compensation adjustments for routine operations. This selective calibration approach maintains signal quality consistency while minimizing the time and processing resources spent on calibration activities.
Solution Approach 2:
The patent implements dynamic calibration by adapting the calibration frequency and depth based on operating conditions such as temperature changes, device startup state, and channel switching events. The system performs comprehensive calibration when conditions warrant it, and uses faster, simplified compensation methods during stable operation, thereby balancing reliability with time efficiency.
Data Source
AI summary
A method, apparatus and computer program product are configured to provide calibration accuracy in an analog filter. In this regard, a method is provided that includes estimating a cutoff frequency for an analog filter. The method further includes causing a filter tuning word to be modified based on the estimated cutoff frequency for the analog filter. The method also includes determining a residual cutoff frequency mismatch for the analog filter. The method also includes causing an equalizer configuration to be selected for a digital filter based on the determined residual cutoff frequency mismatch.