Communications Device Envelope Extraction for Power Amplifier Linearity
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Solution Overview
Problem
Cellular devices face linearity issues and harmonic interference due to non-linearity in power amplifiers, particularly in Quadrature modulation, and complexity in polar modulation for broadband applications, affecting total radiated power and power efficiency.
Innovation Solution
A communications device with a processor that extracts envelope characteristics from digital baseband I and Q signals to generate near constant envelope signals, optimizing power amplifier operation and reducing complexity by selectively removing envelope data based on signal bandwidth, using I and Q circuits with DAC, low pass filters, and mixers to generate pre-amplification signals for power amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If Quadrature modulation is used, then broadband signal handling capability is improved, but power amplifier linearity and harmonic interference performance deteriorate
Solution Approach 1:
The signal processing is segmented into separate I (in-phase) and Q (quadrature) channels, each processed independently through dedicated circuits. This segmentation allows the power amplifier to handle constant envelope signals in each channel separately, reducing the overall non-linearity and harmonic interference while maintaining broadband capability
Solution Approach 2:
The system dynamically adjusts the modulation approach based on signal characteristics. By converting Quadrature modulation signals into polar coordinates and extracting envelope information, the system adapts the power amplifier operation to work with near-constant envelope signals, improving linearity and reducing harmonic distortion dynamically
2Loss of energy
If polar modulation is used, then power efficiency is improved, but device complexity increases for broadband applications
Solution Approach 1:
The envelope information is extracted and removed from the digital baseband I and Q signals before power amplification. By taking out the envelope characteristics and creating near-constant envelope signals, the system achieves power-efficient saturated amplifier operation without requiring complex polar modulation circuits, thereby reducing device complexity while maintaining power efficiency
Solution Approach 2:
The envelope extraction and signal conditioning is performed in advance before the signals reach the power amplifier. By preliminarily processing the I and Q signals to create near-constant envelope formats, the power amplifier can operate in a simple saturated mode without requiring complex real-time control circuits, reducing overall device complexity
3Loss of energy
If envelope extraction is performed on wideband signals, then power amplifier efficiency is improved, but processing complexity increases
Solution Approach 1:
Different processing approaches are applied to different parts of the signal spectrum. The system selectively extracts envelope characteristics from I and Q signals based on their specific bandwidth requirements, applying appropriate processing complexity only where needed rather than uniformly to all signals, thus optimizing power amplifier efficiency without unnecessarily increasing overall processing complexity
Data Source
AI summary
A communications device may include an encoder generating digital baseband In-phase (I) and Quadrature (Q) signals, a processor coupled to the encoder and extracting an envelope characteristic from the digital baseband I and Q signals based upon a bandwidth of the digital baseband I and Q signals. A power amplifier may be coupled downstream from the processor and may generate an amplified I and Q signal based upon the envelope characteristic.