Dual CORDIC Down-Conversion for I/Q Mismatch Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing digital complex rotator modules in digital radios face challenges in accommodating phase and gain mismatches between I and Q channels, which complicates image rejection and coherent demodulation, especially when dealing with varying intermediate frequencies.
Innovation Solution
Employing two Coordinate Rotation Digital Computer (CORDIC) modules, one for each quadrature channel, with a phase offset signal applied to one CORDIC and a compensatory gain applied to the input of one CORDIC, allowing for dynamic or fixed compensation of phase and gain mismatches, respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single CORDIC module is used for complex rotation, then the device complexity is reduced, but phase and gain mismatch compensation becomes difficult and less flexible
Solution Approach 1:
The patent divides the complex rotation function into two separate CORDIC modules, each handling one quadrature channel (I and Q). This segmentation allows independent phase and gain adjustment for each channel, enabling flexible mismatch compensation while maintaining relatively simple device architecture.
Solution Approach 2:
The patent applies different phase offset signals and gain factors to the I and Q channels respectively, allowing local optimization of each channel's characteristics. This local quality adjustment enables precise compensation for channel-specific mismatches without affecting the overall system complexity significantly.
2Measurement precision
If complex multiplications are used for mismatch compensation, then compensation accuracy is improved, but the ease of operation and flexibility deteriorate
Solution Approach 1:
The patent replaces complex multiplicative compensation operations with additive phase offset signals and simple gain adjustments in the CORDIC modules. This substitution maintains compensation accuracy while dramatically improving ease of operation and flexibility for different intermediate frequencies.
Solution Approach 2:
The patent changes the compensation approach from modifying multiplication factors to adjusting phase offset parameters and gain factors in the CORDIC modules. This parameter change enables accurate mismatch compensation while maintaining operational simplicity and flexibility across different frequency configurations.
3Device complexity
If phase offset compensation is applied to both CORDICs equally, then the system remains symmetric and simple, but mismatch compensation effectiveness is reduced
Solution Approach 1:
The patent introduces asymmetry by applying different phase offset signals to the two CORDIC modules handling the I and Q channels. This asymmetric configuration is necessary to compensate for the inherent asymmetries in analog RF to digital conversion paths, thereby improving image rejection performance while maintaining overall system manageability.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A digital radio receiver is disclosed comprising: • a first section arranged to receive an analogue radio signal and to generate therefrom digital intermediate frequency I and Q channel samples, • a second section arranged to convert said I and Q channel samples to a lower, baseband frequency, said second section comprising: • a first coordinate rotation digital computer, CORDIC, module arranged to perform a complex rotation of the I channel samples; • a second coordinate rotation digital computer, CORDIC, module arranged to perform a complex rotation of the Q channel samples; • a phase accumulator arranged to provide an output signal representing a complex rotation to be applied to each of the I and Q channel samples, • wherein the second section is arranged such that the phase accumulator output signal is modified by a phase offset signal prior to being supplied to one of the first and second coordinate rotation digital computers, CORDICs.