Polar Transmitter Zero-Crossing Avoidance for Low-EVM PSK
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Solution Overview
Problem
Polar transmitters face challenges in avoiding zero-crossing events during PSK modulation, leading to high instantaneous FM modulation, which results in bit errors and EVM degradation, particularly in narrowband systems like Bluetooth, where precise time alignment is difficult and current zero-crossing avoidance schemes are unsuitable due to EVM degradation.
Innovation Solution
A polar transmitter design that generates a zero crossing avoidance signal with a frequency spectrum featuring first and second tones on opposite sides of a center-frequency valley, applied to the IQ waveform to prevent zero crossings, thereby reducing FM deviation and improving EVM performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If zero crossing avoidance schemes are implemented in polar transmitters, then FM deviation is reduced and power consumption is lowered, but EVM degradation occurs
Solution Approach 1:
The patent applies parameter changes by modifying the frequency spectrum characteristics of the zero crossing avoidance signal. Specifically, it uses a multi-tone signal with controlled peak frequencies and amplitude ratios to achieve effective zero crossing avoidance while minimizing EVM degradation. The signal parameters including frequency spacing, peak amplitude ratios, and spectral shaping are optimized to balance power efficiency and modulation accuracy.
Solution Approach 2:
The invention implements dynamic adjustment of the avoidance signal characteristics based on the instantaneous IQ trajectory. The system adaptively controls the amplitude and frequency content of the avoidance signal to match the specific zero crossing conditions, enabling optimal performance across different modulation scenarios while maintaining low power consumption and acceptable EVM.
2Object-affected harmful factors
If zero crossing avoidance is implemented, then instantaneous FM modulation is reduced, but EVM degradation occurs making it unsuitable for applications with EVM limits
Solution Approach 1:
The patent carefully controls the frequency spectrum parameters of the avoidance signal, using multiple tones with specific frequency spacing and amplitude ratios. This spectral parameter optimization reduces the instantaneous FM modulation effect on the VCO while minimizing the impact on EVM, achieving a balance between the two competing requirements.
Solution Approach 2:
The invention applies partial action by using a multi-tone signal structure where not all frequency components are active simultaneously. The signal applies avoidance action only when and where needed in the frequency domain, reducing overall FM deviation while maintaining sufficient avoidance effectiveness to prevent severe zero crossing issues without excessive EVM degradation.
3Use of energy by moving object
If current zero crossing avoidance schemes are used, then power consumption is reduced, but they exhibit EVM degradation and are difficult to implement in narrowband systems
Solution Approach 1:
The patent optimizes the frequency spectrum parameters including peak frequency spacing, amplitude ratios, and spectral shaping to achieve effective zero crossing avoidance with reduced power consumption. The carefully selected parameter set enables implementation in narrowband systems like Bluetooth while maintaining acceptable EVM performance.
Data Source
AI summary
A polar transmitter and method thereof generate a filtered IQ waveform in IQ space representing an input bit stream. The filtered IQ waveform is modified to avoid a zero crossing region by intermittently adding thereto a zero crossing avoidance signal with a frequency spectrum comprising at least first and second tones defining first and second peaks on opposite sides of a center-frequency valley. A polar signal comprising a polar amplitude and phase is generated based on the modified IQ waveform. An RF carrier is modulated using the polar signal.