Envelope Tracking Transmitter With Bandwidth-Reduced PA Supply
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Solution Overview
Problem
Conventional Envelope Tracking (ET) techniques have limited bandwidth capability due to high accuracy requirements for time alignment, leading to spectral degradation and reduced efficiency in power amplifiers, especially for high bandwidth signals.
Innovation Solution
The proposed solution involves a bandwidth reduction circuit that modifies the envelope signal by replacing signal transients with linear interpolation, allowing for efficient operation of DC-to-DC converters and predistortion circuits to adapt to the reduced bandwidth, enabling ET for higher bandwidths while maintaining system efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional ET is used with high bandwidth signals, then bandwidth capability is improved, but time alignment accuracy deteriorates leading to spectral degradation
Solution Approach 1:
The system performs preliminary time alignment compensation by predicting the time misalignment based on the envelope signal bandwidth and pre-calibrated delay characteristics. The delay compensation value is calculated in advance and applied to the envelope signal before it reaches the PA, preventing spectral degradation without requiring real-time measurement adjustments.
Solution Approach 2:
The system implements a feedback mechanism where the actual time alignment between envelope signal and main signal path is continuously monitored. Based on measured time misalignment and spectral degradation levels, the system dynamically adjusts the delay compensation parameters to maintain optimal alignment accuracy for high bandwidth signals.
2Reliability
If constant supply voltage is used for PA, then time alignment requirements are relaxed, but system efficiency deteriorates
Solution Approach 1:
The system dynamically changes the supply voltage parameter to the PA based on the envelope signal characteristics. By adjusting the voltage level in real-time according to the signal envelope, the system maintains high efficiency while the delay compensation mechanism ensures time alignment tolerance is preserved even with voltage variations.
3Speed
If DC-DC tracker operates at high bandwidth, then envelope tracking capability is improved, but conversion efficiency deteriorates
Solution Approach 1:
The DC-DC tracker performs preliminary conversion of the high-bandwidth envelope signal to an intermediate frequency or format that is more suitable for efficient power conversion. By pre-processing the envelope signal and separating high-frequency components, the main power conversion operates at lower frequencies with higher efficiency while still supporting high-bandwidth envelope tracking.
Data Source
AI summary
A transmitter is provided. The transmitter includes an envelope tracking circuit, wherein the envelope tracking circuit includes an envelope circuit configured to generate, based on a baseband signal, an envelope signal indicating a temporal course of the baseband signal's envelope. Further, the envelope tracking circuit includes a bandwidth reduction circuit configured to generate a bandwidth reduced envelope signal based on the envelope signal, and a DC-to-DC converter configured to generate a supply voltage for a power amplifier of the transmitter based on the bandwidth reduced envelope signal. The transmitter additionally includes a predistortion circuit configured to generate a predistorted baseband signal based on the baseband signal and an adjustable predistortion configuration. The predistortion circuit is further configured to adjust the predistortion configuration based on the bandwidth reduced envelope signal.