Auxiliary Receiver IQ Imbalance Compensation for Multi-Transmitter Systems
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Solution Overview
Problem
Mobile transceivers face performance degradation due to initial IQ imbalances, which increase Bit Error Rate (BER) and are challenging to correct over process and temperature variations, especially in multi-band systems.
Innovation Solution
A communications device with a plurality of wireless transmitters and an auxiliary receiver, where a controller applies predistortion to each transmitter to reduce initial IQ imbalances, utilizing a phase locked loop and digital signal processing blocks to generate and apply predistortion signals, and a non-directional coupler for wideband operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If mixers are designed to be precisely 90 degrees in phase delay to reduce IQ imbalance, then IQ imbalance is reduced, but manufacturing precision becomes difficult to maintain over process and temperature variations
Solution Approach 1:
The patent applies preliminary action by measuring the actual IQ imbalance characteristics of the transmitter before normal operation, and using this measurement information to pre-calculate compensation parameters. The controller then applies these pre-calculated parameters to adjust the mixers or signal processing paths, effectively compensating for the inherent phase delays without requiring precise manufacturing tolerances.
Solution Approach 2:
The patent implements feedback by using the auxiliary receiver to continuously monitor the actual IQ imbalance in the transmitted signal, feeding this information back to the controller. The controller then adjusts the mixer phase delays or signal processing parameters based on this feedback, creating a closed-loop system that maintains IQ balance despite manufacturing variations and environmental changes.
2Ease of operation
If I and Q paths traverse different lengths in layout, then practical implementation is achieved, but IQ imbalance increases
Solution Approach 1:
The patent introduces an intermediary approach by inserting a signal processing stage between the physical I and Q paths and the final mixer. This intermediary processing block (controlled by the controller) compensates for the phase differences introduced by the different path lengths, allowing practical layout designs while maintaining the required 90-degree phase relationship at the mixer inputs.
3Power
If DC offset is amplified by amplifiers in the signal path, then signal strength is increased, but baseband circuit saturation occurs
Solution Approach 1:
The patent extracts and removes the DC offset component from the signal path before it can cause saturation. The auxiliary receiver measures the DC offset and IQ imbalance, and the controller applies compensation that effectively subtracts or neutralizes these unwanted components, allowing the signal to be amplified without causing baseband circuit saturation.
Data Source
AI summary
A communications device includes a plurality of wireless transmitters operable at different respective frequencies and each configured to generate respective IQ signals having an initial IQ imbalance. An auxiliary receiver is coupled to a given wireless transmitter. In addition, a controller is configured to apply predistortion to the each wireless transmitter of the plurality thereof based upon the initial IQ imbalance generated by the given wireless transmitter to reduce the initial IQ imbalance in each wireless transmitter.