Baseband Predistortion for PWM-PPM Slewing Correction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
PWM-PPM modulation methods are sensitive to slewing distortions, especially at high power levels and small duty cycles, leading to amplitude and phase distortions in RF carrier signals, which degrade performance.
Innovation Solution
Applying predistortion to the baseband signal using envelope information to adjust the pulse width and phase, with a control loop for symmetrical slewing, reduces or removes slewing distortions by determining the duty cycle and phase modulation based on the envelope's normalized level and slew rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If PWM-PPM modulation is used for high power RF transmission, then power amplifier efficiency is improved, but slewing distortions occur especially at small duty cycles causing amplitude and phase distortions
Solution Approach 1:
The patent applies predistortion to the baseband signal before modulation, using envelope information to pre-correct the signal characteristics. This preliminary action compensates for the slewing distortions that will occur during PWM-PPM modulation, allowing the system to maintain both high power amplifier efficiency and low signal distortion
Solution Approach 2:
The patent changes the parameters of the baseband signal based on envelope information, specifically adjusting the signal characteristics in response to detected envelope levels. This parameter adaptation allows the system to optimize performance across different duty cycles while maintaining accuracy and reducing distortion
2Productivity
If pulse shaping is applied to generate PWM-PPM modulated signal, then modulation efficiency is improved, but waveform changes from trapezium to triangle at small duty cycles resulting in RF carrier distortions
Solution Approach 1:
The predistortion is applied to the baseband signal before pulse shaping occurs, preparing the signal in advance to compensate for the waveform transformation that will happen during modulation. This ensures that even when the waveform changes from trapezium to triangle at small duty cycles, the RF carrier remains distortion-free
Solution Approach 2:
The system uses envelope detection to monitor the signal characteristics and applies predistortion based on this feedback. The envelope information drives the predistortion process, creating a closed-loop system that automatically adjusts to maintain RF carrier integrity across varying duty cycles
Data Source
AI summary
The present invention relates to a circuit arrangement and method of applying predistortion to a baseband signal used for modulating a pulse-shaped signal, wherein an envelope information of the baseband signal is detected and slewing distortions of the pulse-shaped signal are reduced by applying at least one of a phase modulation and a duty cycle 5 modulation to the baseband signal as additional predistortion in response to the detected envelope information. Thereby, slewing distortions in the pulse-shaped signal are removed or at least reduced.