ADPLL Loop Bandwidth Switching for Fast Lock and Low Phase Noise
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Solution Overview
Problem
Digital PLLs, such as ADPLLs, face challenges in reducing lock-up time and minimizing frequency fluctuations during transitions from wideband to narrowband loop bandwidth settings, which can lead to prolonged convergence times and potential transmission errors in wireless communication devices like Bluetooth 5.0 devices.
Innovation Solution
The transmission device employs a stepwise switching mechanism for the loop bandwidth of the ADPLL, transitioning from a wideband to intermediate and then narrowband settings, allowing for reduced frequency fluctuations and phase noise, thereby shortening the lock-up time and stabilizing the operating frequency before transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the loop bandwidth is switched from wideband to narrowband, then the phase noise is reduced, but the lock-up time is prolonged
Solution Approach 1:
The loop bandwidth switching is divided into multiple stages: first switching from wideband to intermediate bandwidth, then from intermediate to narrowband. This segmentation allows the system to gradually reduce phase noise while maintaining reasonable lock-up time, avoiding the extreme trade-off of direct wideband-to-narrowband switching.
Solution Approach 2:
The system performs preliminary switching to intermediate bandwidth before final switching to narrowband. This preliminary action prepares the system by reducing the bandwidth gap, allowing for smoother transition and reduced frequency fluctuations during the final narrowband engagement.
2Reliability
If the loop bandwidth is switched directly from wideband to narrowband, then the phase noise is reduced, but frequency fluctuations increase
Solution Approach 1:
The direct wideband-to-narrowband switching is segmented into wideband-to-intermediate and intermediate-to-narrowband transitions. This reduces the magnitude of each individual switching event, thereby minimizing frequency fluctuations and improving frequency stability during the transition period.
Solution Approach 2:
The intermediate bandwidth setting acts as an intermediary state between wideband and narrowband configurations. This intermediary allows for gradual adaptation of the loop filter and DCO, reducing abrupt frequency fluctuations and improving overall frequency stability during the transition.
3Loss of time
If the loop bandwidth is kept wideband, then the lock-up time is reduced, but the phase noise increases
Solution Approach 1:
The loop bandwidth is made dynamic by implementing time-dependent switching from wideband to intermediate and then to narrowband. This dynamic adjustment allows the system to optimize between lock-up time and phase noise at different stages of operation, achieving both fast initial acquisition and low steady-state phase noise.
Solution Approach 2:
The bandwidth switching follows a periodic sequence: wideband during initial startup for fast lock-up, then transitioning to intermediate and narrowband for reduced phase noise. This periodic action pattern allows the system to achieve both fast response and low noise performance at appropriate times.
Data Source
AI summary
According to one embodiment, there is provided a transmission device including a digital PLL and a power amplifier. The power amplifier is connected to the digital PLL. The digital PLL includes a digital oscillator and a controller. The controller operates the digital oscillator with a first loop bandwidth in a first period corresponding to startup of the power amplifier, operates the digital oscillator with a second loop bandwidth narrower than the first loop bandwidth in a second period being after the first period, and operates the digital oscillator with a third loop bandwidth narrower than the second loop bandwidth in a third period being after the second period.