Digital Audio Clock Tracking with PLL Divide Ratio Control
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Solution Overview
Problem
Current digital audio CODECs face challenges in automatically detecting changes in data rates and re-establishing synchronization with new audio sources without a handover procedure, especially when switching between audio sources of unknown rates, which limits their ability to seamlessly switch between different audio streams.
Innovation Solution
A digital audio interface using an I2S protocol with a fractional-N phase-lock loop (PLL) that modifies the feedback divide ratio to minimize phase errors and automatically detect rate changes by computing an offset applied to the PLL's nominal feedback divide ratio, allowing for synchronization with unknown audio sources without a handover procedure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a fixed gear ratio is used in the phase-locked loop, then the system is simple to implement, but it cannot automatically adapt to different audio data rates from unknown sources
Solution Approach 1:
The system dynamically adjusts the gear ratio based on detected audio data rates. The controller monitors the phase error between the master clock and incoming audio clock, and automatically selects appropriate gear ratios from a set of predefined ratios, enabling the system to adapt to different audio sources without manual configuration
Solution Approach 2:
The system uses feedback from phase error detection to automatically adjust the gear ratio. The phase detector continuously monitors the synchronization status, and when rate changes are detected, the controller modifies the gear ratio accordingly, creating a closed-loop system that self-adjusts to maintain synchronization
2Ease of operation
If a handover protocol is required to switch between audio sources, then the gear ratio can be pre-configured, but switching between audio sources is not possible on the fly
Solution Approach 1:
The system pre-configures multiple gear ratios in advance, corresponding to different standard audio data rates. When rate changes are detected, the controller can immediately switch to the appropriate pre-configured ratio without requiring time-consuming calculations or manual intervention, enabling rapid switching between audio sources
Solution Approach 2:
The system performs automatic rate detection and gear ratio selection without requiring external handover protocols or manual intervention. The controller autonomously monitors the audio stream, detects rate changes, and re-synchronizes the phase-locked loop, enabling the system to service itself during source transitions
3Reliability
If the system waits for known audio sources with pre-configured rates, then synchronization is maintained, but switching to unknown audio sources is precluded
Solution Approach 1:
The system replaces manual configuration and handover protocols with an automatic electronic detection and adjustment mechanism. The phase detector and controller work together to automatically detect audio data rates and adjust the gear ratio, eliminating the need for pre-configuration of unknown sources while maintaining synchronization reliability
Data Source
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AI summary
Systems and methods to achieve a digital audio interface having automatic rate detection and tracking of digital audio streams have been achieved. The system comprises a digital controller working in conjunction with an analog phase-locked loop (PLL). It removes the need to know or communicate in advance the rate at which the interface will be operating, so allowing asynchronous switching between different audio streams. The digital controller acts as a phase-lock loop by modifying the feedback divide ratio of the PLL in order to minimize the phase error between the device clock and an arbitrary audio interface clock.