CTLE Equalizer Control Using Threshold Crossings Before CDR Lock
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Solution Overview
Problem
Existing equalizer control systems face challenges in adjusting the frequency characteristic of continuous time linear equalizers (CTLEs) when the clock and data recovery (CDR) circuit is not locked, particularly due to unknown or varying transmission line lengths, leading to issues of over or under equalization.
Innovation Solution
An equalizer control device that includes a first circuit to count the number of times a data signal crosses a threshold or differential signals intersect within a specific time period, allowing for the selection of appropriate equalization parameters for the CTLE, even before the CDR circuit is locked, using a control signal to adjust the frequency characteristic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the CTLE is over-equalized to compensate for unknown transmission line loss, then the frequency characteristic compensation is sufficient for long lines, but the CDR circuit may not be locked due to excessive emphasis causing jitter
Solution Approach 1:
The patent applies preliminary action by performing equalization parameter adjustment before CDR locking. The control circuit adjusts CTLE parameters based on threshold crossing counts measured during a calibration period before formal communication starts, enabling the system to prepare optimal equalization settings in advance without requiring CDR to be locked first
Solution Approach 2:
The system applies self-service by using the data signal itself to determine equalization parameters. The control circuit counts threshold crossings of the received data signal and uses this information to automatically select appropriate CTLE settings, eliminating the need for external measurement equipment or manual adjustment
2Measurement precision
If the eye opening measurement method is used to adjust CTLE parameters, then accurate equalization can be achieved, but the CDR circuit must be locked first which prevents parameter adjustment before locking
Solution Approach 1:
The patent performs equalization parameter determination as a preliminary action before CDR locking. By measuring threshold crossings during an initial calibration period and selecting parameters before formal communication begins, the system eliminates the time loss associated with post-locking parameter adjustment while maintaining measurement accuracy
Solution Approach 2:
The patent extracts the equalization parameter measurement function from the CDR locking process. Instead of requiring CDR locking as a prerequisite for measurement, the system separates parameter determination into an independent preliminary step that uses simplified threshold crossing counting rather than full eye diagram analysis
3Adaptability or versatility
If communication is started with equalization parameters for over-equalization, then the system can operate with unknown transmission line characteristics, but the parameters need to be readjusted which disrupts communication
Solution Approach 1:
The patent applies preliminary action by determining optimal equalization parameters before communication starts. The control circuit measures threshold crossings during an initial calibration period and configures the CTLE accordingly, eliminating the need for parameter readjustment during active communication and maintaining continuous productivity
Solution Approach 2:
The system applies dynamics by making equalization parameters adjustable and adaptable. The control circuit can modify CTLE parameters based on measured threshold crossing patterns, allowing the system to adapt to different transmission line characteristics while maintaining communication efficiency
Data Source
AI summary
An equalizer control device includes a first circuit configured to, upon receipt of a data signal that has been equalized by a continuous time linear equalizer (CTLE) circuit, output a first signal related to a first number of times a waveform of the data signal crosses a threshold value or differential signals of the data signal cross each other. A second circuit is configured to count the first number during a particular time period based on the output first signal, and select one of equalization parameters to be set to the CTLE circuit based on the counted first number.