RF-DAC Power Amplifier Linearization Without Digital Predistortion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Digitally-modulated polar power amplifiers suffer from significant amplitude-to-amplitude modulation (AM-AM) and amplitude-to-phase modulation (AM-PM) distortion due to their nonlinear output impedance, which complicates linearization and reduces efficiency, especially in high-speed, wide dynamic range applications.
Innovation Solution
A digitally-controlled power amplifier (DPA) is designed with a radio frequency digital-to-analog converter (RF-DAC) constructed from nonlinearly weighted power amplifier segments and a multiphase RF drive signal generator, which compensates for ACW-dependent amplitude and phase distortions, eliminating the need for digital predistortion and enhancing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If digitally-modulated polar power amplifiers use nonlinear output impedance operation, then power efficiency is improved, but amplitude-to-amplitude and amplitude-to-phase modulation distortion increases
Solution Approach 1:
The patent applies digital predistortion technology to pre-compensate for the nonlinear distortion characteristics of the power amplifier. By introducing a predistorter before the PA that applies the inverse of the expected nonlinear transformation, the overall system achieves linearized output. This preliminary action counteracts the distortion before it affects the signal, allowing the PA to operate in its efficient nonlinear region while maintaining signal fidelity.
Solution Approach 2:
The patent implements feedback mechanisms to monitor and correct the output signal characteristics. By continuously measuring the actual output and comparing it with the desired linear response, the system can dynamically adjust the predistortion parameters or apply corrective transformations, thereby maintaining low distortion levels while the PA operates at high efficiency points.
2Manufacturing precision
If digital predistortion is implemented to correct distortion, then linearity is improved, but device complexity increases
Solution Approach 1:
The patent replaces complex analog linearization circuits with digital signal processing techniques. By implementing predistortion and correction algorithms in the digital domain using software or programmable logic, the system achieves precise linearization control without requiring complex analog components. This substitution of digital for analog approaches reduces hardware complexity while maintaining or improving linearity performance.
3Manufacturing precision
If output power is backed off to avoid signal peak clipping, then signal fidelity is improved, but power efficiency deteriorates
Solution Approach 1:
The patent applies predistortion to pre-expand the signal amplitude characteristics before amplification. By intentionally shaping the input signal to anticipate the PA's nonlinear compression behavior, the system ensures that even when operating at high output power levels close to peak envelope power, the output signal remains free of clipping and maintains high fidelity without requiring power backoff.
Data Source
AI summary
A digitally-controlled power amplifier (DPA) includes a radio frequency digital-to-analog converter (RF-DAC) constructed from nonlinearly weighted PA segments, a multiphase RF drive signal generator that drives the PA segments, and overdrive voltage control circuitry. The nonlinear weighting of the PA segments intrinsically compensates for amplitude-code-word dependent amplitude distortion (ACW-AM distortion) involved in the operation of the RF-DAC and the multiphase RF drive signal generator facilitates ACW-dependent phase distortion (ACW-PM distortion) reduction, thus obviating the need for complicated and efficiency-degrading digital predistortion. The overdrive voltage control circuitry is used to fine tune the RF output of the DPA and compensate for other non-idealities and external influences such as process, voltage, temperature (PVT), frequency and/or load impedance variations.