Eye Opening Measurement Circuit for High-Speed Serial Receiver
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Solution Overview
Problem
In high-speed serial link systems, it is challenging to measure the eye diagram of a signal equalized by the receiver's equalizer, as the equalized signal is internally processed and cannot be probed, necessitating a technology to assess the eye opening and equalization quality within the receiver.
Innovation Solution
An eye opening measurement circuit that tracks minimum and maximum sigma levels, calculates their difference, and adjusts the equalizer coefficients to improve signal quality, enabling effective compensation for channel losses and noise within the receiver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the equalized signal is internally processed in the receiver, then the signal quality is improved through equalization, but the ability to measure the eye diagram is lost
Solution Approach 1:
The patent introduces an eye opening measurement circuit as an intermediary component that receives the equalized signal from the equalizer and performs measurement without disrupting the internal processing. This mediator enables eye diagram measurement while the signal continues to be processed internally for communication, resolving the contradiction between signal quality improvement and measurement capability
Solution Approach 2:
The measurement function is segmented from the main signal processing path. The eye opening measurement circuit operates as a separate functional block that samples and measures the equalized signal independently, allowing both the equalization process and measurement process to occur simultaneously without interfering with each other
2Measurement precision
If the eye opening measurement circuit tracks sigma levels step-by-step, then the measurement precision is improved, but the circuit complexity increases
Solution Approach 1:
The patent employs dynamic tracking of sigma levels where the measurement circuit adaptively adjusts its operation based on the incoming signal characteristics. The circuit dynamically updates the eye opening measurement by comparing current signal levels with reference levels, enabling precise measurement without requiring a fixed, complex structure
Solution Approach 2:
The eye opening measurement circuit uses the signal itself to perform the measurement by comparing voltage levels against reference levels derived from the signal distribution. The circuit self-calibrates by identifying the voltage levels corresponding to different logical values and calculating the eye opening based on these self-determined reference points, reducing the need for external calibration equipment
Data Source
AI summary
A receiver includes a sampler that samples first voltage levels corresponding to a first logical value of data and second voltage levels corresponding to a second logical value of the data, based on a sampling clock. An equalizer receives and adjusts the first and second voltage levels. A clock and data recovery circuit recovers the sampling clock, based on the first and second voltage levels from the equalizer. An eye opening measurement circuit: (1) tracks a first sigma level by a first step unit depending on upper voltage levels greater than a first reference voltage level among the first voltage levels, (2) tracks a second sigma level by a second step unit depending on lower voltage levels less than a second reference voltage level among the second voltage levels, and (3) calculates a difference between the first sigma level and the second sigma level.