Polar Phase Modulation Circuit for Zero-Crossing Without Phase Jumps
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Solution Overview
Problem
Polar modulation systems face challenges in accommodating zero crossings, which require phase modulators to handle nearly infinite frequencies, leading to distortions due to limited bandwidth in existing implementations.
Innovation Solution
The implementation includes a phase shifter that selectively shifts the phase of a baseband phase signal 180 degrees during zero crossings, combined with an inverter to manage phase modulation, allowing for continuous phase input to the phase modulator and reducing distortion, along with a phase-lock loop and variable controlled oscillator to enhance bandwidth and fidelity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a phase modulator is used to accommodate zero crossings in polar modulation, then the system can handle phase transitions, but the modulator requires nearly infinite bandwidth which is impossible to realize without distortions
Solution Approach 1:
The phase modulation process is segmented into two independent parts: amplitude modulation handling the envelope variations and phase modulation handling only the phase information. This segmentation allows each modulator to operate within realistic bandwidth constraints while collectively achieving the desired polar modulation with zero crossing capability.
Solution Approach 2:
The problematic infinite frequency component is extracted and removed from the phase modulator input by using amplitude modulation to handle the zero crossing envelope transitions. This leaves only the essential phase information for the phase modulator, enabling it to operate within practical bandwidth limits without distortions.
2Loss of information
If the baseband phase signal instantaneously shifts 180 degrees during zero crossing, then the digital information can be accurately transmitted, but the phase modulator cannot accommodate such rapid transitions due to limited bandwidth
Solution Approach 1:
The amplitude modulation is performed in advance to handle the zero crossing envelope transitions before the phase modulation occurs. This preliminary action prepares the signal by removing the problematic rapid amplitude variations, allowing the phase modulator to subsequently handle only the phase transitions at manageable speeds without information loss.
3Ease of manufacture
If real-world phase modulators are used with limited bandwidth, then the system is practically implementable, but distortions occur during zero crossing scenarios
Solution Approach 1:
An amplitude modulator is introduced as an intermediary component between the baseband signal and the phase modulator. This intermediary handles the zero crossing envelope transitions, protecting the phase modulator from problematic input conditions and ensuring both practical implementability and signal fidelity are maintained.
Data Source
AI summary
A circuit includes a phase shifter configured to selectively shift a phase of a baseband phase signal in accordance with a zero crossing signal to output a selectively phase-shifted signal, a phase modulator configured to provide a phase modulated carrier signal in accordance with the selectively phase-shifted signal, and an inverter configured to selectively invert the phase modulated carrier signal in accordance with the zero crossing signal.