Dual-Loop ISI Cancellation for Data and Zero-Crossing Samples
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Solution Overview
Problem
Conventional CDR circuits fail to systematically address inter symbol interference (ISI) at zero crossings, leading to uncontrolled ISI effects that compromise bit error rates and eye margin stability.
Innovation Solution
An ISI cancellation circuit and detector circuit configuration that minimizes ISI at both data sampling and zero crossing points within a symbol interval, using shared or sequential architectures to generate data and crossing samples, thereby balancing vertical and horizontal eye margin optimization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional DFE equalization is used to minimize ISI at data samples, then vertical eye margin is maximized, but horizontal eye margin deteriorates due to uncontrolled ISI at zero crossings
Solution Approach 1:
The patent segments the ISI cancellation function into two distinct components: a data ISI canceler that operates at data sampling points and a crossing ISI canceler that operates at zero-crossing points. Each canceler is independently configured with its own feedback path and control logic, allowing separate optimization of vertical and horizontal eye margins without mutual interference.
Solution Approach 2:
The patent applies local quality by providing different equalization characteristics at different points in the symbol interval. The data ISI canceler provides strong cancellation at data sampling points to maximize vertical margin, while the crossing ISI canceler provides targeted cancellation at zero-crossing points to maximize horizontal margin, creating spatially varying equalization quality matched to local requirements.
2Measurement precision
If feedback waveform magnitude is optimized for data sampling points, then data ISI is minimized, but crossing ISI becomes uncontrolled and unpredictable
Solution Approach 1:
The patent implements feedback in two separate loops: one feedback path from data samples to the data ISI canceler, and another feedback path from crossing samples to the crossing ISI canceler. This dual feedback structure enables independent control and optimization of cancellation performance at both data points and zero-crossing points, making crossing ISI control as predictable and optimized as data ISI control.
Solution Approach 2:
The crossing ISI canceler uses crossing samples generated by the detector circuit to automatically adjust its own feedback waveform. The system self-regulates by using the detected crossing points and their associated ISI measurements to control the crossing canceler's operation, eliminating the need for external manual adjustment and making the system self-optimizing.
3Reliability
If equalization focuses on minimizing ISI at data samples, then bit error ratio performance improves, but jitter tolerance deteriorates due to residual zero-crossing ISI
Solution Approach 1:
The patent applies preliminary action by canceling ISI at zero-crossing points before the data sampling occurs. By removing crossing ISI in advance through the crossing ISI canceler operating on earlier crossing samples, the system prepares a cleaner signal environment for subsequent data sampling, thereby improving both BER performance and jitter tolerance without interfering with the primary data equalization function.
Data Source
AI summary
An apparatus comprising an inter symbol interference (ISI) cancellation circuit and a detector circuit. The inter symbol interference (ISI) cancellation circuit may be configured to minimize ISI at data sampling and crossing sampling points in a symbol interval of an input signal. The detector circuit may be configured to generate data samples and crossing samples at the data sampling and crossing sampling points in the symbol interval of the input signal.