RF Receiver I/Q Filter Calibration via Digital Tuning
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Solution Overview
Problem
RF receivers face interference issues due to mismatch between I-path and Q-path analog filters, leading to frequency-dependent I/Q imbalance, which is not effectively addressed by existing methods, especially under process variability, random mismatch, and systematic mismatch variations.
Innovation Solution
A digitally-assisted calibration method is employed using a digital tuning engine to adjust the I-path and Q-path analog filters, incorporating RC time constant calibration, I/Q filter mismatch calibration, and filter residual mismatch calibration to align the cut-off frequencies and reduce systematic and random mismatch variations, thereby minimizing I/Q imbalance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the cut-off frequency of the filter is shifted toward in-band due to filter variations, then interference attenuation is improved, but in-band signal is hurt
Solution Approach 1:
The patent applies preliminary calibration action during the manufacturing process to set the filter cut-off frequency and I/Q balance before the receiver operates. A calibration circuit measures and adjusts the analog filter parameters in advance, storing calibration data that compensates for process variations. This preliminary adjustment ensures the filter operates at the correct frequency without hurting in-band signals during normal operation.
Solution Approach 2:
The patent changes the parameters of the analog filter dynamically through calibration. By measuring actual filter characteristics and adjusting parameters such as cut-off frequency and I/Q balance using calibration circuits and stored data, the system compensates for process variations. This parameter adjustment allows the filter to maintain proper attenuation while preserving in-band signal quality despite manufacturing variations.
2Reliability
If the cut-off frequency of the filter is shifted toward out-band due to filter variations, then in-band signal is preserved, but interference attenuation decreases
Solution Approach 1:
The calibration circuit performs preliminary measurement and adjustment of the filter cut-off frequency before operation. By detecting the actual frequency characteristics and storing calibration data, the system proactively compensates for variations that would otherwise shift the cut-off frequency toward out-band. This ensures proper interference attenuation is established in advance.
Solution Approach 2:
The system adjusts the filter parameters through calibration to counteract frequency shifts. By changing parameters such as cut-off frequency based on measured variations and stored calibration data, the filter maintains its designed characteristics despite process variations, ensuring both signal preservation and interference attenuation.
3Manufacturing precision
If component area is enlarged to limit random mismatch variation, then I/Q filter mismatch is reduced, but area cost increases
Solution Approach 1:
The patent replaces the mechanical/physical approach of enlarging component area with a digital calibration approach. Instead of increasing physical size to reduce mismatch, the system uses calibration circuits to measure and compensate for random mismatch variations. Calibration data is stored and used to adjust I/Q balance digitally, achieving the same precision goal without the area penalty.
Solution Approach 2:
The system compensates for random mismatch variations by changing parameters through calibration rather than through physical size. The calibration circuit measures actual I/Q filter mismatches and adjusts parameters using stored calibration data, achieving precise matching without requiring larger component areas. This parameter-based compensation is more area-efficient than physical enlargement.
4Measurement precision
If RC calibration is used to compensate process variation, then cut-off frequency shift is corrected, but I/Q imbalance remains
Solution Approach 1:
The patent segments the calibration process into two distinct parts: RC calibration for cut-off frequency correction and I/Q calibration for balance correction. The RC calibration circuit handles frequency accuracy by adjusting resistor-capacitor time constants, while a separate I/Q calibration circuit handles balance by adjusting I/Q path matching. This segmentation allows each circuit to specialize in one aspect, achieving both frequency accuracy and I/Q balance independently.
Solution Approach 2:
The patent introduces calibration data as an intermediary that bridges the gap between RC calibration and I/Q balance. The calibration circuit measures both cut-off frequency and I/Q characteristics, stores this data separately, and uses it to independently adjust each parameter. This intermediary calibration data allows the system to correct frequency shifts and I/Q imbalance through separate adjustment mechanisms without interference between the two functions.
Data Source
AI summary
A radio frequency (RF) receiver includes a digital tuning engine; and I-path and Q-path analog filters, tuned by the digital tuning engine. The digital tuning engine gets an I/Q imbalance difference, and the digital tuning engines tunes the I-path analog filter and/or the Q-path analog filter based on the I/O imbalance difference.