Digital Pre-Distorter for RF Transceiver Linearity
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Solution Overview
Problem
Existing discrete supply modulation methods in power amplifiers (PAs) cause distortion due to abrupt changes in supply voltage, which existing systems fail to adequately address, leading to inefficiencies and nonlinearity in RF signal transmission.
Innovation Solution
A radio frequency (RF) transceiver system with a digital pre-distorter (DPD) and a control unit that generates a control signal to command the system state of PA cells, combining this signal with the input signal to apply digital predistortion, using a reconfigurable matching network (RMN) to adjust impedance and optimize supply voltage levels for improved linearity and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If discrete supply modulation is used to improve PA efficiency, then power efficiency is improved, but distortion increases due to abrupt supply voltage changes
Solution Approach 1:
The system applies digital pre-distortion to the input signal before it reaches the power amplifier. The DPD processes the input signal in advance to pre-compensate for the distortion that will be introduced by the abrupt supply voltage changes in discrete supply modulation, thereby canceling out the harmful distortion effects while maintaining the efficiency benefits
Solution Approach 2:
The system uses polynomial coefficients or look-up-table coefficients that are indexed to the PA supply voltage level. This feedback mechanism selects appropriate distortion compensation parameters based on the current supply voltage state, enabling dynamic compensation that adapts to the discrete supply modulation conditions and effectively reduces the generated distortion
2Measurement precision
If high-order nonlinearity basis functions and deep memory are used in DPD to accurately model PA distortion, then distortion modeling accuracy is improved, but device complexity increases
Solution Approach 1:
The system changes the parameters of the DPD by using polynomial coefficients or look-up-table coefficients that are indexed to the supply voltage level. This allows the DPD to adapt its characteristics based on the operating conditions, achieving accurate distortion modeling across different supply voltage states without requiring excessively complex fixed-structure models
3Measurement precision
If polynomial coefficients indexed to supply voltage level are used to compensate for distortion, then distortion compensation accuracy is improved, but device complexity increases due to multiple coefficient sets
Solution Approach 1:
The system implements dynamic coefficient selection where polynomial coefficients or look-up-table coefficients are indexed to the PA supply voltage level. The control unit dynamically selects the appropriate coefficient set based on the current supply voltage state, enabling accurate distortion compensation that adapts to changing operating conditions without requiring complex manual configuration
Data Source
AI summary
In some embodiments, in an RF transceiver system having a transmit chain and a digital pre-distorter (DPD), a control unit includes: one or more inputs, one of which is connected to receive a first signal corresponding to a transmit signal or a modified version thereof; circuitry configured to generate a control signal for commanding a system state of the transmit chain based in part on the first signal; and an output connected to provide the control signal to the DPD and to a plurality of power amplifier (PA) cells of the transmit chain, wherein the DPD is configured to apply digital predistortion to the signal to be transmitted based in part on combining the first signal with a second signal corresponding to the control signal or a translated version thereof, and to provide a resulting pre-distorted signal to the transmit chain operating at the system state.