IF Mixer Common-Mode Feedback for DC Offset Reduction
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Solution Overview
Problem
Conventional radio receiver systems face challenges in reducing DC offset during the downconversion of RF signals to baseband, which degrades signal-to-noise ratio and introduces interference, especially in mobile wireless communication devices where power consumption is a concern.
Innovation Solution
A method and system for output common mode control that averages and compares the DC level of signals from a second IF mixer to a reference voltage, generating a corrected DC error signal to be fed back and adjust the current source at the mixer's gm stage, thereby correcting the DC offset without introducing additional errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional downconversion methods are used to convert RF signals to baseband, then signal conversion is achieved, but DC offset is introduced which degrades signal-to-noise ratio
Solution Approach 1:
The patent applies preliminary action by measuring and storing the DC offset characteristics before actual signal processing. The system pre-characterizes the mixer's DC offset behavior under different operating conditions, so that when a signal needs to be processed, the appropriate DC offset correction parameters are already available, preventing DC offset degradation of signal-to-noise ratio during downconversion
Solution Approach 2:
The patent utilizes parameter changes by adjusting local oscillator frequency and measuring DC offset characteristics at different frequency points. The system varies the LO frequency parameter to map out DC offset behavior across the operating range, storing these measurements for later compensation during actual signal downconversion, thereby maintaining signal-to-noise ratio
2Productivity
If digital signal processing is used to filter and downconvert RF frequency signals, then signal processing capability is improved, but additional DC offset may be introduced and complex DSP requirements increase
Solution Approach 1:
The patent applies preliminary action by pre-measuring and storing DC offset characteristics before signal processing. This allows the system to use simple lookup tables and basic arithmetic operations for DC offset compensation rather than requiring complex real-time DSP algorithms, thereby improving processing capability while minimizing device complexity
Solution Approach 2:
The patent implements feedback by continuously monitoring the DC offset level at the output and using this information to adjust the correction applied during downconversion. This closed-loop approach enables accurate DC offset compensation with simple processing, improving productivity without significantly increasing device complexity
3Use of energy by moving object
If IF to baseband downconversion is performed quickly to reduce power consumption in mobile devices, then power efficiency is improved, but DC offset generation and interference noise increase
Solution Approach 1:
The patent applies preliminary action by pre-characterizing DC offset behavior at different operating points before mobile device operation. This allows the system to perform fast downconversion with simple lookup-based DC offset correction, avoiding the need for complex real-time measurements that would consume additional power, while still reducing interference noise through accurate DC offset compensation
Data Source
AI summary
A method and system for output common mode control for reducing DC offset for an IF mixer that downconverts a received signal to DC without introducing additional offset is provided. Aspects of the method may comprise averaging signals having an output common mode DC level, which are generated from an output of the mixer. This determined average may then be compared to a reference voltage. The reference voltage may be an output common mode DC level required for baseband processing. The output common mode DC level may be corrected at an input of the mixer for signals that may subsequently be generated from an output of the mixer by utilizing results from the comparison. The corrected common mode DC offset level may be fed back to an input of the mixer.