Analog Pre-Distorter for I/Q Distortion in Quadrature Transmitters
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Solution Overview
Problem
Quadrature transmitters face issues with in-phase/quadrature (I/Q) distortion due to gain and phase mismatches, leading to undesired frequencies, images, and sidebands in the output signal, which can cause receiver errors and violate emission masks, and existing digital correction methods require access to digital transmit signals not always available.
Innovation Solution
Incorporating a pre-distorter in the quadrature transmitter that couples portions of the in-phase and quadrature components to reduce signal power of error signals, implemented using resistors and amplifiers, and controlled by a controller that adjusts resistance values to minimize I/Q distortion, allowing for calibration and adjustment even without digital access to transmit signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If digital correction is used to correct I/Q mismatch, then I/Q distortion is reduced, but access to digital transmit signals is required which may not be available
Solution Approach 1:
The patent introduces an analog pre-distorter circuit as an intermediary component that operates in the analog domain before the signal enters the digital correction path. This pre-distorter uses resistors and amplifiers to pre-compensate for I/Q mismatch, allowing the system to achieve correction without requiring access to digital transmit signals that may not be available in all configurations.
2Productivity
If analog portions of quadrature transmitter are used, then signal generation is achieved, but I/Q mismatch is introduced due to gain and phase differences
Solution Approach 1:
The patent applies preliminary action by implementing an analog pre-distorter circuit that pre-compensates for I/Q mismatch before the signal is processed further. This pre-distortion approach anticipates and corrects the gain and phase differences that will occur in the analog portions of the transmitter, thereby maintaining signal generation capability while reducing I/Q distortion.
Solution Approach 2:
The pre-distorter circuit performs preliminary anti-action by introducing opposite gain and phase adjustments to counteract the expected I/Q mismatch. The circuit uses resistors coupled to in-phase and quadrature components with amplifiers to create compensating signals that cancel out the harmful I/Q distortion effects before they manifest in the final output.
3Manufacturing precision
If pre-distortion is applied to reduce I/Q distortion, then undesired frequencies are reduced, but additional analog components are required
Solution Approach 1:
The patent segments the I/Q correction function into a dedicated pre-distorter module with specific resistors and amplifiers, separating this function from the main signal path. This segmentation allows the pre-distortion to be implemented as a modular analog component that can be designed and tuned independently, managing complexity through functional separation while achieving undesired frequencies reduction.
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 I/Q distortion by attenuating undesired frequencies and sidebands, ensuring compliance with emission masks and improving signal quality without requiring digital access to transmit signals, enabling efficient calibration and adjustment of the pre-distorter.
Implementation Method 1
implemented using resistors and amplifiers
Implementation Method 2
implemented using resistors and amplifiers
Data Source
AI summary
Methods and apparatus to pre-compensate for in-phase/quadrature (I/Q) distortion in quadrature transmitters are disclosed. A disclosed example method comprises coupling a portion of an analog baseband in-phase signal to an analog baseband quadrature signal through an impedance, and selecting a resistance value for the impedance to pre-distort the analog baseband quadrature signal to compensate for an error introduced by modulation of the analog baseband in-phase signal and the analog baseband quadrature signal.