Clock Recovery Using Autonegotiation Frequency Offset Alignment
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Solution Overview
Problem
High-speed Ethernet systems face challenges in clock recovery due to the difficulty in accurately sampling high-frequency data signals, where frequency offsets can lead to substantial ISI, requiring extensive scanning of clock frequencies, which is time-consuming and resource-intensive.
Innovation Solution
Implementing an autonegotiation mechanism to perform initial clock recovery at low speeds, determining frequency offsets during low-speed information exchanges, and using these offsets to align high-speed clock signals without full clock recovery techniques, thereby reducing the need for extensive frequency scanning during high-speed data transmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If clock recovery circuit scans through entire range of possible frequencies to ensure proper equalizer operation, then frequency alignment accuracy is improved, but time consumption and resource usage increase substantially
Solution Approach 1:
The patent applies preliminary action by performing initial frequency alignment during the autonegotiation phase before high-speed data transmission begins. The receiving device determines a frequency offset value from low-speed autonegotiation signals and uses this to pre-align its clock signal frequency, avoiding the need to scan the entire frequency range during actual data transmission. This preliminary frequency alignment significantly reduces the time and resources required while maintaining accurate frequency synchronization.
2Reliability
If clock recovery circuit scans through entire range of possible frequencies, then reliability of equalizer operation is improved, but device complexity and resource consumption increase
Solution Approach 1:
The patent performs frequency offset determination during the autonegotiation phase, establishing accurate frequency alignment before high-speed transmission begins. This preliminary action ensures reliable equalizer operation during data transmission without requiring complex real-time frequency scanning mechanisms, thereby reducing device complexity while maintaining reliability.
Solution Approach 2:
The patent uses low-speed autonegotiation signals as an intermediary to transfer frequency offset information from transmitting to receiving devices. This intermediary mechanism allows the receiving device to determine the frequency offset without directly scanning high-frequency ranges, simplifying the clock recovery process while ensuring reliable equalizer operation during subsequent high-speed data transmission.
3Speed
If high-speed data transmission is performed without preliminary frequency alignment, then data transmission speed is maximized, but intersymbol interference increases substantially
Solution Approach 1:
The patent performs preliminary frequency alignment during the autonegotiation phase by determining the frequency offset value from low-speed signals and applying it to align the receiving clock frequency with the transmitting clock frequency. This preliminary alignment ensures that when high-speed data transmission begins, the clock signals are already synchronized, allowing maximum transmission speed without substantial intersymbol interference.
Solution Approach 2:
The patent applies preliminary anti-action by determining and compensating for frequency offset during autonegotiation before high-speed transmission. By identifying and correcting the frequency difference in advance, the system prevents intersymbol interference from occurring during high-speed data transmission, allowing the system to operate at maximum speed without harmful interference effects.
Data Source
AI summary
A method and apparatus of clock recovery is disclosed. A communications device matches the frequency of a local clock signal with the frequency of a transmit clock signal of a transmitting device based on a first set of signals received from the transmitting device during a low-speed information exchange. The low-speed information exchange may correspond to an autonegotiation operation, wherein each of the transmitting device and the communications device declares its communication capabilities to the other device. The communications device then determines a frequency offset to be applied to the local clock signal during a high-speed data communication with the transmitting device. During the high-speed communication, the communications device may apply the frequency offset to the local clock signal and match the phase of the receive clock signal with the phase of the transmit clock signal based on a second set of signals received from the transmitting device.