CIF Mixer Calibration for Image Rejection and IQ Leakage Control
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Solution Overview
Problem
Conventional radio receivers suffer from image interference and IQ leakage due to gain and phase imbalance in RF and IF mixers, which degrade the performance and lead to crosstalk between signals.
Innovation Solution
A Complex Intermediate Frequency (CIF) mixer stage is designed with multiple branches of mixers driven by IF clock signals with predefined phase relationships and tuneable phase skews, along with adders to combine outputs and correct for imbalances, and an IQ leakage correction unit to remove in-band leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional RF and IF mixers are used for signal down-conversion, then the receiver can perform basic frequency conversion, but gain and phase imbalance causes image interference and IQ leakage that degrade signal quality
Solution Approach 1:
The receiver is divided into multiple functional segments including RF mixer stage, CIF mixer stage with multiple branches, and calibration units. Each segment handles specific signal processing tasks independently, allowing precise control and correction of imbalances in each stage without affecting the entire system.
Solution Approach 2:
The system dynamically adjusts mixer parameters including conversion gain and clock signal phase relationships through calibration units. By changing these parameters based on measured imbalances, the system compensates for gain and phase errors, reducing image interference and IQ leakage while maintaining signal quality.
2Measurement precision
If multiple mixer branches with tuneable phase skews are added to correct imbalances, then image rejection and signal quality improve, but device complexity increases
Solution Approach 1:
The mixer branches incorporate tuneable phase skews and variable conversion gains that can be dynamically adjusted during calibration and operation. This dynamic capability allows the system to adapt to different imbalance conditions without requiring a completely different hardware architecture, balancing performance improvement with manageable complexity.
Solution Approach 2:
Calibration units measure the actual gain and phase imbalances in the mixer stages and feed this information back to adjust the mixer parameters. This closed-loop feedback mechanism enables automatic correction of imbalances, improving image rejection ratio while keeping the complexity increase limited to the calibration measurement and control circuitry.
Data Source
AI summary
The invention relates to a complex intermediate frequency (CIF) mixer stage, methods of operation thereof, and methods of calibration thereof. The CIF mixer stage comprises numerous individual mixers driven by IF clock signals to down-convert received IF signals into a set of signals at baseband frequency which are further combined to form a lower side band signal and an upper side band signal. The IF clock signals used have a predefined phase relationship among them, which involves tuneable phase skews. By calibration of the conversion gains and the phases of the IF clock signals the gain and phase imbalance introduced in a preceding radio frequency mixer stage and/or the CIF mixer stage can be cancelled. Further, in-channel IQ leakage control can be applied to the lower side band signal and/or the upper side band signal. The CIF mixer stage can thus effectively suppress image interference and IQ leakage.