DPD Envelope Shaping for RF Spectral Regrowth Control
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Solution Overview
Problem
Current RF transmitters face challenges in controlling spectral regrowth, particularly when using digital predistortion (DPD) techniques, which are inefficient and costly, especially for linear modulation schemes like 16-QAM that result in reduced power efficiency and linearity.
Innovation Solution
A transmitter architecture that includes a signal generator, a DPD circuit with first and second signal shaping circuits to apply envelope shaping to the digital baseband signal, and a multiplier to produce a digitally predistorted signal, allowing for control of spectral regrowth by adjusting DPD values and gain adjustments, using polynomial or non-polynomial shaping based on channel frequency, standard, modulation coding scheme, modulation bandwidth, or output power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If digital predistortion (DPD) techniques are used to linearise the transmit signal, then linearity is improved, but spectral regrowth control deteriorates at low output power levels
Solution Approach 1:
The patent divides the DPD signal into multiple components (original DPD signal and shaped DPD signal) that are combined through addition. The shaped DPD signal is generated by applying envelope shaping to the original DPD signal, creating a segmented approach to spectral regrowth control that works complementarily with the linearity correction.
Solution Approach 2:
The patent introduces an envelope shaping circuit as an intermediary component between the DPD circuit and the power amplifier. This intermediary applies polynomial or non-polynomial envelope shaping to the DPD signal, transforming it to control spectral regrowth while preserving the linearity correction function.
2Productivity
If linear modulation schemes with amplitude modulation component are used to increase bit rate, then data transmission capacity is improved, but power efficiency deteriorates
Solution Approach 1:
The patent applies parameter changes by modifying the envelope of the DPD signal through polynomial or non-polynomial shaping functions. By changing the envelope parameters of the predistortion signal, the system achieves spectral regrowth control that enables more aggressive modulation schemes while maintaining power efficiency.
3Device complexity
If conventional DPD circuits are used without envelope shaping, then circuit complexity is kept low, but spectral regrowth control is insufficient
Solution Approach 1:
The patent merges the envelope shaping function with the existing DPD circuit by adding an envelope shaping circuit that processes the DPD signal. This merging approach integrates spectral regrowth control into the conventional DPD architecture without requiring a complete redesign, thus maintaining reasonable complexity while improving performance.
Data Source
AI summary
A transmitter includes a signal generator arranged to generate a digital baseband signal representative of a signal for transmission; a digital predistortion, DPD, circuit configured to predistort the digital baseband signal; and a power amplifier is arranged to amplify the predistorted signal. The DPD circuit includes a first signal shaping circuit operably coupled to the signal generator and the DPD predistortion circuit and configured to receive the generated digital signal and apply first envelope shaping to shape the predistortion applied to at least the amplitude of the generated digital signal and produce a first DPD signal; a second signal shaping circuit operably coupled to the signal generator and an output of the DPD predistortion circuit and configured to receive and apply the second envelope shaped digital signal to the first DPD signal and produce a second envelope shaped DPD signal. A multiplier is configured to receive and multiply the digital signal and the second envelope shaped DPD signal and output a digitally predistorted signal for transmission.