IQ Mismatch Estimation Circuit with DPD Bin Pruning
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Solution Overview
Problem
Zero-intermediate frequency (IF) transmitters face challenges in maintaining the amplitude and phase relationship between in-phase (I) and quadrature (Q) signals due to IQ gain/phase imbalance and local oscillator (LO) leakage, which are exacerbated by direct current (DC) offsets and digital predistortion (DPD) expansion signals, leading to inaccurate signal transmission and performance limitations.
Innovation Solution
The implementation of an IQ mismatch estimation circuit with a raw channel estimation circuit, reference channel estimation circuit, DPD bin identification circuit, channel estimate pruning circuit, and IQ correction coefficient generation circuit, which generates and applies IQ mismatch correction coefficients to compensate for IQ mismatch and LO leakage, while also utilizing a DPD circuit to pre-compensate for power amplifier non-linearity and correct for DPD expansion signal effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If digital predistortion (DPD) is applied to compensate for power amplifier non-linearity, then power amplifier performance is improved, but IQ mismatch and LO leakage are exacerbated due to DPD expansion signals
Solution Approach 1:
The patent applies preliminary action by estimating and compensating for IQ mismatch and LO leakage before the DPD expansion signals fully distort the signal. The system performs channel estimation, identifies DPD expansion signal components, and applies correction coefficients to pre-compensate for the expected distortion, thereby reducing the harmful effects before they fully manifest in the transmitted signal
Solution Approach 2:
The patent extracts and removes the harmful DPD expansion signal components from the channel estimates. By identifying frequency bins dominated by DPD expansion signals and excluding them from the channel estimation process, the system separates the useful signal information from the harmful distortion components, enabling accurate IQ mismatch and LO leakage compensation
2Area of stationary object
If channel estimation is performed using all frequency bins including those dominated by DPD expansion signals, then channel estimation coverage is improved, but measurement precision deteriorates due to DPD-induced distortions
Solution Approach 1:
The patent applies local quality by treating different frequency bins differently based on their characteristics. Frequency bins dominated by DPD expansion signals are identified and excluded from channel estimation, while other frequency bins are used for accurate estimation. This localized approach ensures high measurement precision in regions where DPD expansion signals do not dominate, while maintaining overall system performance
3Measurement precision
If IQ mismatch correction is applied to compensate for gain/phase imbalance, then signal transmission accuracy is improved, but system complexity increases due to additional correction circuits and processing
Solution Approach 1:
The patent merges the IQ mismatch compensation function with the existing DPD and channel estimation processes. By integrating the IQ correction coefficient generation into the existing signal processing chain and utilizing the same feedback path, the system achieves accurate IQ mismatch compensation without requiring completely separate correction circuits, thereby limiting the increase in system complexity
Data Source
AI summary
An IQ mismatch estimation circuit includes a raw channel estimation circuit, a reference channel estimation circuit, a digital predistortion (DPD) bin identification circuit, a channel estimate pruning circuit, and an IQ correction coefficient generation circuit. The raw channel estimation circuit generates raw channel estimates for a plurality of frequency bins of a baseband signal. The reference channel estimation circuit identifies a reference channel estimate based on the raw channel estimates. The DPD bin identification circuit identifies, based on the reference channel estimate, the frequency bins for which the raw channel estimates are based on a DPD expansion signal. The channel estimate pruning circuit generates pruned raw channel estimates by discarding the raw channel estimates of the frequency bins identified by the DPD bin identification circuit. The IQ correction coefficient generation circuit generates IQ mismatch correction coefficients based on the pruned raw channel estimates.