PLL Circuit Weighting Control for Multipath Phase Alignment
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Solution Overview
Problem
Radio receivers, especially in car radios, face performance degradation due to the multipath reception phenomenon, where signals from direct and indirect paths interfere, causing destructive addition and reducing audio quality, which existing phase diversity algorithms struggle to mitigate effectively when using separate crystals for each antenna.
Innovation Solution
A phase locked loop circuit that compares the phase of input and feedback signals to generate up-phase and down-phase signals, applies unequal weighting values to these signals, and adjusts the frequency of a variable-frequency oscillator to minimize phase differences, allowing for constructive signal addition without the need for separate crystals, using a common timing reference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate crystals are used for each antenna path, then frequency stability is improved, but phase offset cannot be distinguished from time of arrival differences, making phase diversity algorithms ineffective
Solution Approach 1:
The patent merges the frequency reference function into a single shared crystal oscillator that provides timing references to both antenna paths. This eliminates the phase offset problem caused by separate crystals while maintaining frequency stability through the common reference. The shared crystal ensures that both paths operate with the same frequency基准, allowing phase diversity algorithms to correctly distinguish phase differences from time of arrival differences.
Solution Approach 2:
The patent introduces a shared crystal oscillator as an intermediary that mediates the timing reference provision to both antenna paths. This intermediary component ensures consistent frequency reference while enabling accurate phase measurement by eliminating the phase offset that would otherwise be introduced by separate crystal oscillators.
2Measurement precision
If unequal weighting values are applied to up-phase and down-phase signals, then phase alignment accuracy is improved, but loop stability may deteriorate when operating signal reaches limit values
Solution Approach 1:
The patent implements dynamic adjustment of weighting values in the oscillator driver circuit. The weighting values are not fixed but are adjusted based on the operating conditions of the phase locked loop. When the operating signal approaches limit values, the weighting values are modified to prevent loop instability, thereby maintaining both phase alignment accuracy and loop stability under varying operating conditions.
Solution Approach 2:
The patent changes the weighting values as adjustable parameters in the oscillator driver to optimize phase alignment accuracy. By making these parameters variable rather than fixed, the system can adapt to different operating conditions and maintain stability even when unequal weighting is applied for improved phase measurement precision.
Data Source
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AI summary
A phase locked loop circuit comprising: a phase detector configured to compare the phase of an input signal with the phase of a feedback signal in order to provide an up-phase signal and a down-phase-signal; an oscillator-driver configured to: apply an up-weighting-value to the up-phase signal in order to provide a weighted-up-phase signal; apply a down-weighting-value to the down-phase signal in order to provide a weighted-down-phase signal; and combine the weighted-up-phase signal with the weighted-down-phase signal in order to provide an oscillator-driver-output-signal; and a controller configured to: set the up-weighting-value and the down-phase-weighting as a first-set-of-unequal-weighting-values, and replace the first-set-of-unequal-weighting-values with a second-set-of-unequal-weighting-values if an operating signal of the phase locked loop circuit reaches a limit-value without satisfying a threshold value.