Zero-IF Transmitter Calibration via FFT Feedback
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Solution Overview
Problem
Zero-IF transmitter circuits face RF impairments such as IQ imbalance and LO leakage due to differences in in-phase and quadrature-phase channel responses and residual local oscillation interference, requiring efficient calibration methods to optimize compensation values for effective signal processing.
Innovation Solution
A method involving a compensation device and a digital signal processor that performs calibration using Fast Fourier Transform (FFT) on feedback signals to determine optimal compensation values by minimizing energy at specific frequencies, thereby addressing IQ imbalance and LO leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a Zero-IF transmitter circuit uses direct-up conversion technology, then the circuit complexity is reduced and the conversion efficiency is improved, but RF impairments such as IQ imbalance and LO leakage occur due to differences in channel responses and residual local oscillation interference
Solution Approach 1:
The patent implements a feedback mechanism where the transmitter circuit outputs signals are fed back to a calibration device that measures IQ imbalance and LO leakage levels. Based on these measurements, the calibration device adjusts compensation parameters and feeds them back to the transmitter circuit to iteratively reduce RF impairments, thus resolving the contradiction between simplified circuit design and RF performance.
Solution Approach 2:
The patent changes key parameters including compensation values for IQ imbalance (amplitude and phase compensation parameters), LO leakage suppression parameters, and calibration frequencies. By dynamically adjusting these parameters based on measured impairments, the system optimizes performance while maintaining the simple direct-up conversion architecture.
2Measurement precision
If different compensation methods are used for IQ imbalance and LO leakage, then the compensation accuracy is improved, but the calibration process complexity and time consumption increase
Solution Approach 1:
The patent designs a universal calibration device that can handle both IQ imbalance compensation and LO leakage suppression through a single integrated platform. The device uses a unified feedback mechanism and parameter adjustment process that works for both types of impairments, eliminating the need for separate calibration procedures while maintaining high compensation accuracy for both issues.
Solution Approach 2:
The patent merges the calibration processes for IQ imbalance and LO leakage into a single unified calibration routine. The calibration device simultaneously measures both types of impairments and adjusts all compensation parameters in one coordinated process, reducing overall calibration complexity and time while achieving accurate compensation for both impairment types.
3Reliability
If multiple pairs of compensation values are tested to find optimal parameters, then the compensation effectiveness is improved, but the calibration time and processing complexity increase
Solution Approach 1:
The patent implements preliminary action by pre-calculating and storing multiple pairs of compensation values (lookup tables) that cover a range of expected impairment conditions. During calibration, the system quickly searches through these pre-prepared compensation pairs rather than performing exhaustive real-time optimization, significantly reducing calibration time while still finding effective compensation parameters for the specific impairment conditions encountered.
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
This approach enables efficient calibration of compensation values to reduce RF impairments, enhancing image rejection capability and minimizing unwanted signal energy, thus optimizing transmitter circuit performance.
Implementation Method 1
The power spectrum density calculation device is configured to perform Fast Fourier Transform (FFT) on a plurality of feedback signals received from the transmitter to generate corresponding frequency domain feedback signals
Data Source
AI summary
A method for calibrating one or more compensation values utilized by a compensation device of a transmitter includes: obtaining a plurality of output signals which were sequentially generated by the transmitter by processing a pair of input signals according to multiple pairs of compensation values as a plurality of feedback signals, where each feedback signal corresponds to one of the multiple pairs of compensation values, determining a plurality of coefficients of a cost function according to the multiple pairs of compensation values and the feedback signals in an operation of calibration; and determining a pair of calibrated compensation values according to the coefficients and providing the pair of calibrated compensation values to the compensation device.