Constant-Envelope RF Power Amplification Using Baseband Delta-Sigma
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Solution Overview
Problem
Conventional mobile communication systems face difficulties in efficiently amplifying signals with high Peak-to-Average Power Ratio (PAPR) due to the need for high-speed and expensive bandpass Delta-Sigma Modulators (DSM) and switching mode power amplifiers, which are challenging to implement and costly, especially for frequencies above 800 MHz.
Innovation Solution
The implementation of a Low Pass Delta-Sigma Modulator (LPDSM) system that converts baseband signals into oversampled digital signals with a constant envelope, reducing the burden of oversampling and enabling efficient power amplification by using a power amplifier with a lower operating frequency, thereby improving the efficiency and linearity of the power amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a bandpass Delta-Sigma Modulator (DSM) is used for mobile communication frequencies above 800 MHz, then the system can achieve high-speed modulation, but the cost and implementation complexity increase significantly
Solution Approach 1:
The system separates the modulation function into two independent stages: baseband Delta-Sigma modulation at lower frequencies, followed by RF up-conversion. This segmentation allows each stage to operate at optimized frequencies, avoiding the need for a single high-frequency bandpass DSM
Solution Approach 2:
An intermediate baseband signal stage is introduced between the input signal and the final RF output. The baseband DSM operates at low frequencies to generate the modulated signal, which is then up-converted to the target RF frequency, serving as an intermediary that simplifies the overall system
2Use of energy by moving object
If a switching mode power amplifier is used to amplify RF pulse signals, then amplification efficiency reaches 100%, but the amplifier must operate at frequencies up to five times the input RF frequency requiring broadband characteristics
Solution Approach 1:
The frequency adaptation function is segmented from the power amplifier and assigned to the baseband DSM and up-converter stages. The power amplifier only needs to handle a fixed frequency determined by the up-conversion stage, simplifying its design while maintaining 100% efficiency through switching mode operation
Solution Approach 2:
The system changes the operating frequency parameter of the power amplifier from a broadband variable frequency (5x input RF) to a fixed frequency determined by the up-conversion stage, allowing the amplifier to be optimized for maximum efficiency at that specific frequency
3Measurement precision
If oversampling is applied to increase Signal-to-Noise Ratio (SNR), then the SNR improves, but the sampling speed must be four times faster than the minimum Nyquist rate which is difficult to realize at high frequencies
Solution Approach 1:
Instead of performing oversampling at high RF frequencies where it is difficult to implement, the system inverts the approach by performing baseband Delta-Sigma modulation at low frequencies where oversampling is easily achievable, then up-converting the result to the target frequency
Data Source
AI summary
An method and apparatus for power amplification in a mobile communication system, wherein a signal converter for receives signals from a baseband-side, modulates the received signals into oversampled baseband digital signals, and generates signals having a constant envelope with the oversampled base band digital signals, an up-converter up-converts the generated signals having the constant envelope to Radio Frequency (RF) signals for output, and a power amplifier amplifies the RF signals according to system setup levels and outputs envelope signals of a predetermined level.