Digital Pre-Distorter for Beamforming 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 through polynomial coefficients or look-up-table coefficients.
Innovation Solution
A digital pre-distorter (DPD) is integrated into a radio frequency (RF) transceiver system, combining signals to apply digital predistortion, including a beamforming control signal, to compensate for nonlinearity, attenuation, and phase shifts in the transmit chain, using a nonlinear combiner and processing blocks like lookup tables to adjust supply voltage levels dynamically.
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 PA linearity deteriorates due to abrupt supply voltage changes
Solution Approach 1:
The system applies preliminary digital predistortion to the input signal before it reaches the power amplifier. The DPD pre-compensates for the distortion that will be introduced by the discrete supply modulation, so that the overall output remains linear despite the abrupt supply voltage changes.
Solution Approach 2:
The system dynamically changes the PA supply voltage parameter between discrete levels based on the signal amplitude. By switching between different supply voltage levels (e.g., high voltage for high power, low voltage for low power), the system improves efficiency while the DPD compensates for the resulting linearity degradation.
2Measurement precision
If high-order nonlinearity basis functions are used to model PA distortion, then distortion modeling accuracy is improved, but system complexity increases
Solution Approach 1:
The system changes the approach from using fixed high-order nonlinearity basis functions to using supply voltage level as a parameter to select appropriate polynomial coefficients. This reduces complexity by avoiding high-order nonlinearity modeling while maintaining accuracy through parameter-based coefficient selection.
Solution Approach 2:
The system uses different polynomial coefficients for different supply voltage levels. Each supply voltage level has its own optimized coefficients, allowing accurate distortion compensation for each specific operating condition without requiring a single complex high-order model for all conditions.
3Measurement precision
If polynomial coefficients are indexed to PA supply voltage level, then compensation accuracy for supply modulation is improved, but coefficient management complexity increases
Solution Approach 1:
The system uses the supply voltage level itself as an index parameter to select the appropriate polynomial coefficients. This creates a direct mapping between the physical supply voltage state and the compensation parameters, simplifying coefficient management by using the existing supply voltage control signal as the selection key.
Solution Approach 2:
The polynomial coefficients serve multiple functions: they compensate for PA nonlinearity and also adapt to different supply voltage levels. By making the coefficients universal across different operating conditions through indexing, the system reduces the need for separate compensation mechanisms for each supply voltage level.
Data Source
AI summary
According to some embodiments, in a radio frequency (RF) transceiver system having a transmit chain with a beamforming array, a digital pre-distorter (DPD) includes: a plurality of inputs including at least a first input to receive a first signal corresponding to a signal desired to be transmitted via the transmit chain or a modified version of the signal desired to be transmitted via the transmit chain, and a second input to receive a second signal corresponding to a signal associated with the beamforming array or a translated version of the signal associated with the beamforming array; circuitry configured to apply digital predistortion to the signal desired to be transmitted based at least in part on combining the first and second signals; and an output connected to provide a resulting pre-distorted signal to the transmit chain.