Mixer Cell Logic for Zero-Crossing Polar Modulator Accuracy
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Solution Overview
Problem
Modern polar modulators face modulation errors at zero crossings in the constellation diagram due to the inability to process 180° phase jumps and the limitation of high-frequency DACs providing only positive signals.
Innovation Solution
A mixer cell is implemented to logically combine data signals with oscillator and sign signals, allowing for polarity reversal without phase jumps by using digital signals and XOR operations, ensuring high synchronism and accuracy in modulator output signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DPLL is used to modulate the phase of the RF signal, then phase modulation is achieved, but modulation errors occur at zero crossings due to inability to process 180° phase jumps
Solution Approach 1:
The modulator is divided into multiple parallel mixer cells, each handling a portion of the modulation task. This segmentation allows the system to process zero crossings locally without requiring the DPLL to handle 180° phase jumps globally, thereby maintaining modulation accuracy while avoiding the complexity of phase jump processing in the DPLL.
Solution Approach 2:
Instead of using the DPLL to directly handle phase jumps, the invention inverts the approach by using mixer cells with sign bits to represent polarity changes. The phase information is extracted from the oscillator signal while the sign bit handles the polarity reversal, effectively inverting the traditional phase modulation approach to avoid 180° phase jumps in the DPLL.
2Reliability
If a high-frequency DAC is used to modulate the amplitude, then amplitude modulation is achieved, but the DAC can only provide positive signals limiting negative half-wave processing
Solution Approach 1:
The invention adds a sign bit dimension to the modulation process. Instead of relying solely on the DAC output polarity, a separate sign bit is introduced that can independently control the polarity of the mixer cell output. This dimensional addition allows the system to process negative half-waves without requiring the DAC to provide negative signals, thereby maintaining signal accuracy while extending polarity handling capability.
Solution Approach 2:
The mixer cell acts as an intermediary between the positive-only DAC output and the final modulated signal. The mixer cell combines the DAC output with the oscillator signal and the sign bit, effectively mediating the polarity issue by allowing the sign bit to control the final output polarity regardless of the DAC's positive-only constraint.
3Measurement precision
If multiple mixer cells are used to process positive and negative half-waves, then signal accuracy is improved, but device complexity increases
Solution Approach 1:
Each mixer cell is designed to be universal and multi-functional, capable of handling both positive and negative half-waves through the sign bit mechanism. This universality means that the same mixer cell design can be replicated multiple times without increasing the complexity of individual cells, as each cell performs the same function with different sign bit values, thereby improving output accuracy through parallel processing without proportionally increasing device complexity.
Data Source
AI summary
Embodiments provide a mixer cell, which is implemented to logically combine a data signal with an oscillator signal and a sign signal to obtain a mixer cell output signal based on the logical combination. Further embodiments provide a modulator with a plurality of mixer cells.