Polar Modulator Extended AM Mapping for Peak FM Deviation
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Solution Overview
Problem
Polar transmitters face challenges in reducing peak FM deviation and bandwidth of FM signals, which leads to distortion, elevated noise floors, and spectrum corruption due to strong FM impulses and wide bandwidth, limiting the performance of VCO and PLL.
Innovation Solution
The implementation of an extended AM signal approach that inverts the AM signal when it exceeds a predetermined threshold, effectively reducing FM deviation by folding strong FM impulses and reshaping the FM spectrum, thereby reducing the peak FM requirement and simplifying VCO design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the FM signal bandwidth is reduced to limit peak FM deviation, then the VCO and PLL performance is improved, but the FM signal becomes distorted and the noise floor is elevated
Solution Approach 1:
The patent applies preliminary action by pre-shaping the FM signal before it is applied to the VCO. The FM signal is differentiated and shaped in advance to control its bandwidth and impulse characteristics, preventing distortion and noise floor elevation while maintaining reliable VCO and PLL operation.
Solution Approach 2:
The patent changes the parameters of the FM signal by controlling its bandwidth and impulse strength through differentiation and shaping circuits. By adjusting these parameters before the signal reaches the VCO, the system maintains optimal performance without distortion or excessive noise.
2Power
If the FM signal bandwidth is limited by practical circuits, then the peak FM deviation is reduced, but the transmit output spectrum is corrupted
Solution Approach 1:
The patent applies preliminary action by pre-shaping the FM signal before it is applied to the VCO. The FM signal is differentiated and shaped in advance to control its bandwidth and impulse characteristics, preventing distortion and noise floor elevation while maintaining reliable VCO and PLL operation.
Solution Approach 2:
The patent changes the parameters of the FM signal by controlling its bandwidth and impulse strength through differentiation and shaping circuits. By adjusting these parameters before the signal reaches the VCO, the system maintains optimal performance without distortion or excessive noise.
3Manufacturing precision
If strong FM impulses are present in the modulation signal, then the phase modulation is achieved, but the FM signal bandwidth is widened and impulses are generated
Solution Approach 1:
The patent segments the modulation process into separate AM and FM components. By processing the in-phase and quadrature components separately and combining them through polar modulation, the system achieves accurate phase modulation while controlling FM bandwidth and impulse generation.
Solution Approach 2:
The patent changes the parameters of the FM signal by controlling its bandwidth and impulse strength through differentiation and shaping circuits. By adjusting these parameters before the signal reaches the VCO, the system maintains optimal performance without distortion or excessive noise.
Data Source
AI summary
Apparatus and methods for adjusting spectral characteristics of a polar modulation signal in a polar modulator are described. A detection circuit is configured to determine when an FM signal component of the modulation signal exceeds a threshold value. The output of the detection circuit is coupled with FM and AM mapping circuits to selectively map the FM signal component and an AM signal component of the modulation signal to mapped signals, thereby reducing FM deviation.