Low IF Mixer Selectivity via Dynamic LO Frequency Selection
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Solution Overview
Problem
Low-IF receivers in wireless communication systems suffer from poor adjacent channel rejection due to adjacent channel interference, which causes distortion in adjacent channels, despite offering superior sensitivity by filtering out unwanted DC content and IQ imbalance distortion.
Innovation Solution
A low IF mixer that evaluates the energy of sidebands and selects a local oscillator frequency based on the sideband with lower energy to down-convert signals, improving selectivity performance by placing the receiver image in the adjacent channel with lower energy levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Low-IF receiver uses down-conversion to intermediate frequency, then sensitivity is improved by filtering out DC content and IQ imbalance distortion, but adjacent channel rejection deteriorates due to adjacent channel interference causing distortion in adjacent channels
Solution Approach 1:
The patent applies dynamics by making the local oscillator frequency selectable between two options (first frequency and second frequency) based on operating conditions. The system dynamically switches between different LO frequencies to place the receiver image in the adjacent channel with lower energy, thereby adapting to varying interference conditions and resolving the contradiction between sensitivity and adjacent channel rejection
Solution Approach 2:
The patent changes the local oscillator frequency parameter between two distinct values (first LO frequency and second LO frequency) depending on which adjacent channel has lower energy. This parameter change allows the receiver image to be positioned in the less interfered adjacent channel, improving selectivity performance while maintaining the sensitivity benefits of Low-IF architecture
2Reliability
If the desired frequency is down-converted to intermediate frequency, then DC content is filtered out improving signal quality, but adjacent channel interference causes distortion in adjacent channels
Solution Approach 1:
The system dynamically selects between two local oscillator frequencies based on real-time assessment of adjacent channel energy levels. By switching LO frequencies, the receiver image is placed in the adjacent channel with lower energy, dynamically reducing distortion in adjacent channels while preserving signal quality improvements from DC filtering
Solution Approach 2:
The patent implements feedback by evaluating the energy of adjacent channels and using this information to select the appropriate local oscillator frequency. This feedback mechanism allows the system to adapt to changing interference conditions, placing the receiver image in the less interfered channel to minimize distortion while maintaining reliable signal reception
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances the selectivity performance of low-IF receivers by effectively reducing adjacent channel interference, thereby improving signal quality and handling of adjacent signals.
Implementation Method 1
The desired frequency may have a frequency of RF and the signal at the desired frequency may be multiplied by the selected local oscillator frequency to down-convert the signal
Data Source
AI summary
A low IF mixer and method for down-converting a signal at a desired frequency are disclosed with improved selectivity performance. The energy of sidebands on each side of the desired frequency is evaluated; and a local oscillator frequency is selected based on the evaluation of the energy. Generally, the local oscillator frequency associated with the sideband having a lower energy is selected. The desired frequency may have a frequency of RF and the sidebands have a frequency of the desired frequency plus or minus an offset frequency (RF+IF or RF−IF). The signal at the desired frequency may be multiplied by the selected local oscillator frequency to down-convert the signal.