Receiver-Feedback Transmitter Equalization for Cable Length Variation
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Solution Overview
Problem
Existing techniques for transmitting signals at high speeds over copper cables, such as 40 Gbps, face challenges due to frequency-dependent loss and varying cable lengths, leading to suboptimal eye opening characteristics and increased error rates, with existing solutions like fixed transmit equalization being inadequate and high-power digital signal processing being complex.
Innovation Solution
The system employs adaptive transmit equalization, where receivers can adjust transmitter settings across multiple lanes, using a control channel to optimize equalizer settings, allowing for independent operation of each lane and supporting a range of cable lengths, and can use copper or other metal cables, including optical cables, to maintain acceptable bit error rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fixed transmit equalization is used, then transmitter side eye opening is optimized, but receiver side eye opening varies with cable length leading to errors
Solution Approach 1:
The patent implements dynamic transmit equalization where the transmitter equalizer settings are continuously adjusted based on feedback from the receiver. The receiver measures the actual eye opening and cable length, then sends control signals back to the transmitter to optimize the equalizer coefficients, transforming the static fixed equalization into a dynamic adaptive system that maintains optimal performance across varying cable lengths.
Solution Approach 2:
The patent establishes a feedback loop where the receiver measures signal quality metrics (eye opening, cable length) and communicates these measurements back to the transmitter via a control channel. The transmitter uses this feedback information to adjust its equalizer settings, creating a closed-loop control system that resolves the contradiction between fixed transmitter optimization and variable receiver performance.
2Reliability
If analog filter at receiver is used, then received signals are reproduced, but eye opening characteristics are suboptimal
Solution Approach 1:
The patent inverts the traditional approach by moving the equalization function from the receiver side to the transmitter side. Instead of using analog filters at the receiver to compensate for channel loss, the system uses adaptive equalizers at the transmitter that are controlled by receiver feedback, thereby achieving both good signal reproduction and optimal eye opening characteristics.
Solution Approach 2:
The patent replaces the mechanical/analog filter approach at the receiver with a digital control system. The equalization is performed through digital signal processing at the transmitter, controlled by digital feedback from the receiver, substituting the analog filter mechanism with a more flexible digital adaptation system that achieves superior eye opening characteristics.
3Measurement precision
If A/D converter and digital signal processor at receiver are used, then signal processing is improved, but power consumption increases and implementation becomes complicated
Solution Approach 1:
The patent extracts the heavy digital signal processing requirements from the receiver side and relocates them to the transmitter side. The receiver only performs minimal analog-to-digital conversion and measurement functions, while the computationally intensive equalization and signal processing are performed at the transmitter using feedback-controlled digital signal processing, thereby reducing receiver power consumption and complexity.
Solution Approach 2:
The patent introduces a control channel as an intermediary that carries measurement and adjustment information between the receiver and transmitter. This intermediary mechanism allows the system to achieve sophisticated digital signal processing performance without requiring the receiver to continuously perform heavy computations, as the control channel enables the transmitter to pre-compute and apply appropriate equalization settings.
4Device complexity
If fixed transmit equalization is used, then transmitter circuit is simplified, but cable length tolerance is limited
Solution Approach 1:
The patent transforms the static fixed equalization circuit into a dynamic adaptive equalization system. The equalizer coefficients are no longer fixed but are dynamically adjusted based on real-time feedback about cable length and signal quality, enabling the circuit to adapt to various cable lengths while maintaining optimal performance without significantly increasing base circuit complexity.
Solution Approach 2:
The patent changes the parameters of the equalizer circuit based on feedback information. The equalizer coefficients and settings are modified as parameters in response to varying cable lengths and signal conditions, allowing the same physical circuit to operate optimally across a wide range of cable lengths by dynamically changing its electrical parameters rather than requiring different hardware configurations.
Data Source
AI summary
Techniques are described to adaptively adjust the equalizer settings of each transmitter in a transmitter-receiver pair. The transmitter-receiver pair can be used at least with implementations that comply with 40GBASE-CR4 or 100GBASE-CR10. For implementations that comply with 40GBASE-CR4, equalizer settings of four transmitters may be independently established.