Variable Loop Filter PLL for OFDM Phase Noise Control
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Solution Overview
Problem
In OFDM systems with variable channel bands, the fixed phase noise characteristics of PLL modules lead to deteriorated orthogonality between subcarriers, resulting in reduced system performance due to phase noise operating as noise in adjacent subcarriers.
Innovation Solution
A PLL apparatus with a variable loop filter that adjusts its filtering band according to each channel band, comprising a frequency divider, phase detector, voltage control oscillator, and variable loop filter controller, enables different phase noise characteristics for each channel band, thereby maintaining orthogonality between subcarriers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a fixed loop filter is used in the PLL module, then the device complexity is reduced, but the phase noise characteristics cannot be adapted to different channel bands, causing orthogonality deterioration between subcarriers
Solution Approach 1:
The loop filter is made dynamically adjustable by introducing a loop filter controller that switches between different loop filter configurations based on the detected channel band. This allows the PLL module to adapt its phase noise characteristics to match the specific requirements of each channel band, resolving the contradiction between fixed structure and adaptive performance.
Solution Approach 2:
The invention changes the parameters of the loop filter (such as filtering bandwidth and cutoff frequencies) according to the channel band being used. By adjusting these parameters dynamically, the system achieves optimal phase noise performance for each channel band while maintaining a relatively simple overall structure through parameterization rather than structural complexity.
2Reliability
If the PLL module operates with constant phase noise characteristics, then the device complexity is minimized, but system performance deteriorates due to phase noise acting as interference in adjacent subcarriers
Solution Approach 1:
The PLL module transitions from a static configuration to a dynamic one where the loop filter characteristics are adjusted in real-time based on the operating channel band. This dynamic adaptation ensures that phase noise characteristics are optimized for each channel band, preventing phase noise from degrading orthogonality between subcarriers while avoiding excessive structural complexity.
Solution Approach 2:
The system implements a feedback mechanism where the channel band information is detected and used to control the loop filter configuration. This closed-loop approach ensures that the PLL module automatically adapts its phase noise characteristics to maintain optimal orthogonality between subcarriers across different channel bands without requiring complex manual configuration.
3Reliability
If a variable loop filter is implemented to adapt to different channel bands, then phase noise characteristics are optimized for each band, but the device complexity increases
Solution Approach 1:
Instead of implementing completely different loop filter structures for each channel band, the invention uses parameter changes within a unified loop filter structure. By adjusting filtering bandwidth and cutoff frequency parameters based on channel band detection, the system achieves optimized RF performance for each band while minimizing the increase in device complexity through parameterization rather than structural multiplication.
Data Source
AI summary
Provided are a PLL apparatus for an OFDM system having variable channel band and an operating method thereof. The PLL apparatus includes a frequency divider for dividing an oscillating signal; a phase detector for detecting a phase difference between a reference signal and the divided oscillating signal from the frequency divider and outputting the phase difference signal; a variable loop filter for filtering a phase difference signal outputted from the phase detector; a voltage control oscillator for outputting the oscillator signal to the frequency divider according to the voltage control signal filtered from the variable loop filter; and a variable loop filter controller for varying a filtering band of the variable loop filter according to each of the channel bands.