RF Signal Generation with Digital Predistortion Correction
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Solution Overview
Problem
Current RF vector modulation generators suffer from variable channel response as a function of frequency, making it difficult to generate wideband signals with consistent amplitude and linear phase, which is particularly problematic for applications like RADAR pulses, leading to the need for custom 'golden radios' for system qualification.
Innovation Solution
A RF microwave signal generation system that applies digital modulation correction through predistortion to compensate for channel amplitude and phase nonlinearities using complex finite impulse response filters, with automatic level control loops to correct for variability across a wide modulation bandwidth, and recalculates correction filters in real-time to adapt to changing analog parameters such as frequency, gain, and temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional RF vector modulation generators are used, then basic signal generation is achieved, but channel response varies with frequency causing amplitude non-flatness and phase non-linearity
Solution Approach 1:
The system performs preliminary calibration to measure the actual channel response characteristics (amplitude and phase vs frequency) before signal generation. These measurements are stored and used to pre-calculate correction factors that are applied during operation, eliminating the need for real-time measurement and correction during signal generation.
Solution Approach 2:
The system creates a digital model (copy) of the channel response characteristics through calibration measurements. This digital representation is then used to generate correction signals that compensate for the physical channel imperfections, allowing the system to replicate ideal signal characteristics despite hardware imperfections.
2Adaptability or versatility
If wideband signals are generated without correction, then bandwidth coverage is achieved, but amplitude flatness and phase linearity deteriorate across the bandwidth
Solution Approach 1:
The system applies different correction characteristics to different frequency regions within the bandwidth. The calibration process measures and stores amplitude and phase corrections specific to each frequency point, allowing the system to maintain consistent signal quality across the entire wideband range by applying locally-optimized corrections.
Solution Approach 2:
The system dynamically adjusts the correction applied to signals based on the operating frequency and bandwidth settings. When the signal parameters change, the system selects or calculates appropriate correction factors from the calibration data, ensuring optimal performance across varying wideband conditions.
3Ease of operation
If analog parameters change due to temperature or aging, then operational flexibility is maintained, but channel response variability increases
Solution Approach 1:
The system performs self-calibration by automatically measuring its own channel response characteristics and generating appropriate correction factors. This self-service capability allows the system to compensate for drift due to temperature or aging without external intervention, maintaining reliable performance while preserving operational flexibility.
Solution Approach 2:
The system uses feedback from calibration measurements to continuously update and refine the correction characteristics. By monitoring actual channel response and adjusting corrections accordingly, the system compensates for parameter drift caused by environmental changes or component aging.
Data Source
Figure 1
Figure 2A~2B
Figure 2C~2D
AI summary
A signal generation system can include an input source configured to provide an input radio frequency (RF) signal, a correction filter calculation (CFC) block configured to determine correction filter parameters, and an automatic level control (ALC) loop configured to provide ALC loop information to the CFC block. The correction filter parameters may be determined based at least in part on the ALC information. The system can also include a predistortion field programmable gate array (FPGA) configured to apply a correction filter to the input RF signal, wherein the correction filter is based at least in part on the correction filter parameters, and an RF output configured to provide an RF output signal.