Envelope Tracking Waveform Compression for Wideband RF Linearity
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Solution Overview
Problem
Envelope tracking systems in mobile communication devices face limitations in maintaining linearity and efficiency due to bandwidth constraints, particularly with the advent of 5G-NR technology, which requires higher bandwidth modulation, leading to reduced performance and spectral degradation.
Innovation Solution
An envelope tracking system that compresses the amplitude bandwidth of RF signals to match the voltage modulation bandwidth, using digital pre-distortion to correct signal distortions and ensure that modified voltage amplitudes are never less than the predefined amplitudes, thereby enhancing linearity and efficiency without degrading spectral performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If envelope tracking system uses higher bandwidth modulation to support 5G-NR technology, then data rate and communication capability are improved, but linearity and efficiency deteriorate due to inherent bandwidth limit
Solution Approach 1:
The system performs preliminary bandwidth compression on the amplitude envelope signal before it enters the envelope tracking amplifier. By pre-compressing the amplitude variations to match the voltage modulation bandwidth capability, the system prepares the signal in advance to avoid linearity degradation during amplification, thus maintaining both high data rates and good linearity
Solution Approach 2:
The system dynamically changes the amplitude parameter of the voltage waveform by compressing the amplitude bandwidth. The amplitude envelope is transformed to have a reduced bandwidth that matches the voltage modulation capability, allowing the system to operate within its inherent bandwidth limit while still supporting wider signal bandwidths through careful parameter management
2Power
If envelope tracking system increases output power to achieve higher data rates, then communication performance is improved, but power consumption and thermal dissipation increase
Solution Approach 1:
The system dynamically adjusts the supply voltage to the power amplifier in real-time according to the instantaneous output power requirements. By making the voltage supply dynamic rather than static, the system ensures the amplifier operates at high efficiency across varying power levels, reducing overall power consumption and thermal dissipation while maintaining the required output power for high data rates
3Reliability
If envelope tracking system operates at inherent bandwidth limit, then linearity and efficiency are maintained, but capability to support wide modulation bandwidth signals is reduced
Solution Approach 1:
The system segments the bandwidth handling into two parts: the amplitude envelope is compressed to match the voltage modulation bandwidth, while the phase information is preserved separately. This segmentation allows the voltage supply to operate within its bandwidth limits while the complete signal (including high-bandwidth phase components) is maintained, thus supporting wide modulation bandwidths without sacrificing efficiency
Data Source
AI summary
An envelope tracking (ET) system is provided. The ET amplifies a radio frequency (RF) signal correspond to an amplitude bandwidth exceeding a voltage modulation bandwidth limitation of the ET system. The ET system compresses the amplitude bandwidth to match the voltage modulation bandwidth of the ET system. More specifically, the ET system compresses a predefined voltage waveform, which tracks time-variant amplitudes of a digital form of the RF signal, to generate a modified voltage waveform at a reduced bandwidth. To ensure that signal distortion(s) resulted from the bandwidth compression can be corrected, the ET system nonlinearly modifies predefined amplitude(s) of the predefined voltage waveform to generate modified amplitude(s) of the modified voltage waveform that is never less than the predefined amplitude(s) of the predefined voltage waveform. As such, the ET system can amplify the RF signal with improved linearity and efficiency, without degrading spectral performance of the RF signal.