I/Q DC Offset Correction for Local Oscillator Feedthrough
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Solution Overview
Problem
Local oscillator feedthrough in communication systems causes errors in signal transmission, including increased error vector magnitude, transmit power inaccuracies, and spurious emissions, which are difficult to filter, especially in microwave applications and direct up-conversion systems.
Innovation Solution
A local oscillator feedthrough signal correction apparatus and method that adjusts direct current components of quadrature signals in real time using a microprocessor control unit, digital-to-analog converters, and a signal splitter to reduce local oscillator feedthrough, with a closed loop system for accurate detection and correction in the receive timeslot.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a local oscillator filter is disposed at an output end of a mixer to filter out local oscillator feedthrough, then local oscillator feedthrough is reduced, but in microwave applications and direct up-conversion systems, the filter cannot effectively reject the local oscillator signal because it falls within the signal band
Solution Approach 1:
The patent extracts the local oscillator feedthrough signal from the mixed signal using a signal splitter, separating it for dedicated processing. This allows the feedthrough component to be identified and corrected without requiring the entire signal path to be modified, solving the limitation of conventional filters that cannot distinguish the feedthrough from the desired signal in microwave and direct up-conversion systems
Solution Approach 2:
The patent implements a feedback mechanism where the detected local oscillator feedthrough signal is fed back to adjust the direct current components of the quadrature signals in real time. This closed-loop correction continuously compensates for feedthrough effects, providing adaptability across different system types including microwave and direct up-conversion systems where fixed filters are ineffective
2Object-affected harmful factors
If direct current components of quadrature signals I/Q are adjusted in real time to reduce local oscillator feedthrough, then feedthrough is reduced, but system service may be affected during correction
Solution Approach 1:
The patent employs periodic action by performing local oscillator feedthrough correction during receive timeslots when transmit timeslots are inactive. This timing-based approach allows correction operations to occur periodically without interfering with continuous system service, as the correction is confined to periods when the system is not actively transmitting
Solution Approach 2:
The patent introduces an intermediary mechanism using a signal splitter to separate the local oscillator feedthrough signal from the main signal path before correction. This intermediary structure enables independent detection and correction of feedthrough without disrupting the primary signal flow, maintaining system service continuity while effecting correction
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
Effectively reduces local oscillator feedthrough by accurately detecting and correcting direct current components, improving signal quality and system performance without affecting system service, with a dynamic detection range of more than 50 dB and efficient correction in both TDD systems and systems with enabled or disabled power amplifiers.
Implementation Method 1
a radio-frequency signal and an oscillator signal are processed to a combined signal by at least one mixer
Implementation Method 2
first and second digital-to-analog converters, respectively connected to the mixer; the first digital-to-analog converter and the second digital-to-analog converter are configured to provide quadrature direct current components
Data Source
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AI summary
The present invention discloses a local oscillator feedthrough signal correction apparatus, including a microprocessor control unit, a first digital-to-analog converter, a second digital-to-analog converter, a mixer, a local oscillator, a signal output line, a signal splitter, and a detector tube. The signal splitter is disposed in the signal output line, and the first digital-to-analog converter and the second digital-to-analog converter are configured to provide the mixer with quadrature direct current components VI and VQ used for local oscillator feedthrough signal correction. The local oscillator provides the mixer with a local oscillator signal, and the mixer outputs a local oscillator feedthrough signal to the signal output line. The signal splitter obtains the local oscillator feedthrough signal by means of splitting, and the detector tube detects the local oscillator feedthrough signal. When a detection value of the local oscillator feedthrough signal exceeds a preset target value, the microprocessor control unit controls and adjusts output values of the VI and the VQ. According to the apparatus provided in embodiments of the present invention, direct current components of quadrature signals I/Q at an input end of the mixer can be adjusted in real time, thereby reducing local oscillator feedthrough.