Fractional-N PLL Frequency Switching With Repeatable Phase Coherence
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Solution Overview
Problem
Fractional-N phase-locked loops face challenges in maintaining phase coherence when switching between frequencies, leading to unpredictable phase relationships with the reference clock signal, which is critical for applications like radar and Bluetooth Low Energy High Accuracy Distance Measurements.
Innovation Solution
The implementation of a fractional-N phase-locked loop with a multi-modulus divider and a pattern generator that supplies drive patterns at specific boundary times, resetting the state variables of the sigma-delta modulator to zero, ensures repeatable phase coherence by initiating the drive pattern at a time equivalent to t=0, thereby maintaining phase coherence across frequency changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If frequency switching is implemented in a fractional-N PLL, then frequency versatility is improved, but phase coherence is degraded
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing optimal drive patterns for the multi-modulus divider in a lookup table before operation. When frequency switching is required, the pre-computed patterns are retrieved and applied immediately, eliminating the need for real-time calculation and ensuring phase coherence is maintained during transitions between different output frequencies.
Solution Approach 2:
The patent implements periodic action by using periodic drive patterns from the lookup table that are synchronized to the reference clock frequency. These periodic patterns ensure that the multi-modulus divider transitions between division ratios in a rhythm that maintains phase coherence, with each pattern corresponding to a specific frequency transition scenario.
2Measurement precision
If phase coherence is maintained during frequency switching, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent applies copying by creating a lookup table that stores pre-computed drive patterns representing ideal phase-coherent transitions. Instead of implementing complex real-time calculation circuits, the system copies the appropriate pre-stored pattern from the lookup table based on the desired frequency transition, thereby maintaining measurement precision while avoiding excessive circuit complexity.
Solution Approach 2:
The patent uses preliminary action by pre-calculating all necessary drive patterns during the design phase and storing them in the lookup table. This eliminates the need for complex real-time computation circuits during operation, achieving phase coherence through simple table lookup and pattern application rather than through complex active circuitry.
Data Source
AI summary
A fractional-N phase-locked loop (PLL) that maintains phase coherence for an output signal with a plurality of possible output frequencies. The fractional-N PLL includes an oscillator, a phase detector to receive a reference clock signal and a feedback signal, and a multi-modulus divider coupled in a feedback path between the oscillator and the phase detector. A multi-modulus pattern generator supplies a drive pattern to the multi-modulus divider to achieve a desired change in frequency of the output signal. The multi-modulus pattern generator initiates the drive pattern at a boundary time to cause the output signal to have a substantially repeatable phase when restarting switching from any one of the output frequencies to any other of the output frequencies.