RF-DAC Power Amplifier Linearization With Multiphase Drive
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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-bandwidth applications.
Innovation Solution
A digitally-controlled power amplifier (DPA) is designed with nonlinearly weighted power amplifier segments and a multiphase RF drive signal generator, which intrinsically 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 are used to achieve high efficiency, then power consumption is reduced, but significant AM-AM and AM-PM distortion occurs due to nonlinear output impedance
Solution Approach 1:
The power amplifier is divided into multiple parallel PA segments (first PA segment, second PA segment, third PA segment, fourth PA segment) with different output impedances. Each segment processes a portion of the amplitude code word, and their combined output achieves linearized amplitude and phase characteristics while maintaining high efficiency operation.
Solution Approach 2:
Each PA segment is designed with specific nonlinear weighting factors (first weighting factor, second weighting factor, third weighting factor, fourth weighting factor) that compensate for the nonlinear output impedance. This local customization of segment characteristics enables intrinsic compensation for ACW-dependent amplitude and phase distortions without requiring digital predistortion.
2Manufacturing precision
If digital predistortion is applied to correct AM-AM and AM-PM distortion, then linearity is improved, but device complexity and power dissipation increase
Solution Approach 1:
The system performs self-linearization through intrinsic compensation mechanisms built into the PA segments themselves. The nonlinear weighting factors and multiphase drive signals enable the amplifier to automatically correct its own AM-AM and PM-PM distortions without external predistortion circuitry, thereby reducing complexity and power consumption.
3Device complexity
If traditional single-phase drive is used, then device simplicity is maintained, but phase errors increase and efficiency decreases
Solution Approach 1:
The system employs multiphase drive signals (first multiphase RF drive signal, second multiphase RF drive signal, third multiphase RF drive signal, fourth multiphase RF drive signal) with different phase relationships. This periodic, phase-diversified drive approach reduces phase errors and improves efficiency by ensuring that not all PA segments switch simultaneously, thereby reducing peak current demands and improving overall power utilization.
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.