Digital Audio Clock Tracking for Asynchronous Source Switching
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Solution Overview
Problem
Current digital audio CODECs face challenges in automatically detecting changes in data-rate and re-establishing synchronization with new audio sources without a handover protocol, especially when switching between audio sources of unknown rates, leading to potential loss of audio signal samples.
Innovation Solution
A digital audio interface using a fractional-N loop PLL and a digital tracking controller that modifies the feedback divide ratio based on phase error and its derivative to synchronize clocks and automatically detect I2S rates, eliminating the need for a handover procedure and enabling asynchronous switching between audio sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a handover protocol is used to switch between audio sources, then synchronization can be maintained with known rates, but switching between audio sources on the fly or to unknown sources is precluded
Solution Approach 1:
The system performs self-detection of the incoming audio data rate automatically without requiring external handover protocols. The digital controller continuously monitors and detects rate changes, enabling the system to adapt to unknown sources autonomously
Solution Approach 2:
The system pre-establishes multiple gearing ratios in advance that correspond to different audio data rates. When a rate change is detected, the system can quickly switch to the appropriate pre-configured ratio, enabling rapid adaptation without lengthy reconfiguration
2Adaptability or versatility
If automatic rate detection is implemented, then switching between unknown audio sources is enabled, but complex detection and rate change handling is required
Solution Approach 1:
The system uses feedback from the phase detector to continuously monitor synchronization status. When phase errors indicate a rate change, the feedback loop triggers automatic detection and adjustment of the gearing ratio, creating a self-correcting system that reduces the need for complex external control logic
Solution Approach 2:
The digital controller is designed to handle multiple functions including rate detection, gearing ratio selection, and synchronization maintenance within a single integrated unit. This multi-functionality reduces overall system complexity by consolidating what could be separate components into one versatile controller
3Adaptability or versatility
If multiple gearing ratios are supported, then tracking of different data rates is enabled, but selection of the correct ratio requires precise rate knowledge
Solution Approach 1:
The system dynamically adjusts the gearing ratio based on real-time detection of phase errors and rate changes. Rather than requiring precise pre-knowledge of the target rate, the system continuously adapts its configuration in response to observed signal characteristics, making the selection process dynamic rather than static
4Duration of action of stationary object
If synchronization is maintained with drifting clocks, then audio signal continuity is preserved, but phase errors accumulate over time
Solution Approach 1:
The system periodically recalibrates the phase relationship between clocks using the detected rate information to adjust the gearing ratio. This periodic correction prevents long-term phase accumulation while maintaining continuous synchronization, balancing duration and precision
Data Source
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.