CDR Lock Control During USB4 Clock Switch Events
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Solution Overview
Problem
The challenge of maintaining clock and data recovery (CDR) locking during a clock switch event in USB4 links is complex due to rapidly changing frequencies and the stochastic nature of the clock switch, especially with the introduction of pulse amplitude modulation (PAM)-3, making it difficult to validate CDR ability and track incoming signals effectively.
Innovation Solution
A receiver is configured to control the CDR circuit to halt tracking during a detected clock switch event, allowing it to re-lock onto the incoming signal after the transition, using a recovered clock, thereby reducing complexity and ensuring robust operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If CDR tracking continues during clock switch events, then the receiver attempts to maintain locking, but the stochastic nature of clock switch events causes tracking failure and validation complexity
Solution Approach 1:
The receiver detects the clock switch event in advance and halts CDR tracking before the frequency change occurs. This preliminary action prevents the CDR from attempting to track the rapidly changing frequency, thereby avoiding tracking failure and reducing validation complexity while maintaining reliable locking during the transition.
2Ease of manufacture
If CDR tracking is halted during clock switch events, then CDR constraints are relaxed and validation is simplified, but the receiver must re-lock after the transition
Solution Approach 1:
The receiver rapidly re-locks onto the incoming signal immediately after halting CDR tracking during the clock switch event. This rushing through the re-locking process minimizes the time loss while still benefiting from the simplified CDR constraints and reduced validation complexity during the halt period.
3Productivity
If re-timer transmitters sequentially switch to forward incoming data, then data forwarding capability is improved, but the incoming signal frequency changes rapidly causing CDR tracking challenges
Solution Approach 1:
The receiver detects the upcoming clock switch event before it occurs and halts CDR tracking in advance. This preliminary action ensures that when the re-timer transmitter sequentially switches to forward incoming data, the CDR is already positioned to handle the frequency change, maintaining reliable locking while enabling improved data forwarding productivity.
Data Source
AI summary
In one embodiment, an apparatus comprises: a receiver to receive training data from a transmitter; a clock and data recovery (CDR) circuit coupled to the receiver, the CDR circuit to recover a recovered clock signal from the training data; and a media access control (MAC) circuit coupled to the CDR circuit, wherein the MAC circuit is to send a clock switch indicator to the CDR circuit to cause the CDR circuit to halt tracking operation of the CDR circuit. Other embodiments are described and claimed.