I/Q Conversion Calibration Using Offset Local Oscillators
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Electronic receiving and transmission devices are vulnerable to I/Q mismatch, resulting in spurious signal components due to mismatched mixing operations, which complicates self-calibration processes.
Innovation Solution
A digital signal processor configures a signal processing circuit to switch to a calibration mode using first and second local oscillator frequencies with a frequency offset, measuring amplitudes of frequency components to determine compensation parameters for I/Q mismatch during up-conversion and down-conversion, allowing for precise calibration without adjusting anti-aliasing bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If self-calibration is performed using traditional methods (single tone test signal with complex processing), then I/Q mismatch can be eliminated, but the device complexity and calibration process complexity increase significantly
Solution Approach 1:
The patent changes the frequency parameter relationship between transmission and reception paths by introducing a frequency offset between the first local oscillator frequency (f_LO1) and the second local oscillator frequency (f_LO2). This parameter change enables the separation of I/Q mismatch error components in the frequency domain, allowing for simplified calibration without complex processing algorithms.
Solution Approach 2:
The patent introduces a frequency offset as an intermediary parameter between the transmission and reception local oscillator signals. This intermediary enables the distinction and separate measurement of I/Q mismatch errors from the transmission path and reception path, respectively, simplifying the calibration process by allowing independent error characterization.
2Ease of operation
If I/Q mismatch compensation is performed without frequency offset, then the calibration process is simpler, but spurious signal components cannot be distinguished and eliminated effectively
Solution Approach 1:
The patent segments the I/Q mismatch errors from the transmission and reception paths by exploiting the frequency offset. The error components appear at distinct frequency locations (f_offset ± f_signal), allowing separate identification and compensation of transmission path errors and reception path errors, thereby improving signal fidelity while maintaining calibration simplicity.
3Measurement precision
If frequency offset is introduced for calibration, then I/Q mismatch errors can be distinguished and compensated, but the local oscillator frequency configuration becomes more complex
Solution Approach 1:
The patent implements dynamic frequency configuration where the local oscillators are set to different frequencies (f_LO1 and f_LO2 with offset Δf) during calibration mode, and can be switched to matched frequencies during normal operation. This dynamic adjustment enables precise error distinction during calibration while allowing simplified operation during normal signal processing.
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 effectively reduces I/Q mismatch errors by determining and compensating for mismatch parameters, eliminating spurious components and improving signal fidelity in both transmission and reception modes.
Implementation Method 1
a signal is mixed down with versions of a local oscillator signal that are ninety degrees out of phase with each other. This results in an in-phase signal and a quadrature signal
Data Source
Figure 1~2b
Figure 3a~4c
Figure 4d~5
AI summary
A signal processing circuit comprises a frequency up-conversion circuit (14, 60) for performing up-conversion with a first local oscillator frequency and a frequency down-conversion circuit (16) for performing down-conversion with a second local oscillator frequency. A digital signal processor (10) controls supply first signals representing a first complex signal to the up-conversion circuit, and receives second signals representing a second complex signal. The digital signal processor controls a compensation of I/Q mismatch of results of up-conversion and/or down-conversion. The digital signal processor (10) switches to a calibration mode for selecting a parameter of said compensation. In the calibration mode the first and second local oscillator frequencies have a frequency offset with respect to each other. The digital signal processor (10) measures an amplitude of a frequency component at a frequency corresponding to mismatch in one and not more than one of the results of up-conversion and/or down-conversion, and selects the parameter dependent on the amplitude.