Fast Eye Diagram Algorithm and FIR Compensation Design for General Transmission Line Systems
Date Issued
2010
Date
2010
Author(s)
Lai, Yen-Cheng
Abstract
In the modern design of high-speed digital system, eye diagram is a beneficial metric of intuitively and quickly assessing the quality of digital signals through various interconnection structures. The tranditional way of eye-diagram acquisition by simulating the response of a long pseudo-random bit sequence (PRBS) consumes large amounts of time and memory and cannot obtain the worst-case eye diagram. In this thesis, a fast algorithm is first purposed to predict the worst-case eye diagram for the transmission line system with an arbitrary step response. Based on the property that the output waveform of a channel can be generated by time-shifted step responses multiplying corresponding transition polarities, eye-diagram waveform at a certain window time is formed by UI-separated voltage samples on the step response. With a proper manipulation of time-shifting, flipping and superposition, peak and valley values of these voltage samples can carry all ISI effects to the same time, producing a worst-case eye voltage. From the positions and transition polarities of voltage samples that are used, a substitution of PRBS, the input bit pattern is translated for simulating the worst-case eye diagram. Besides, this algorithm can be extended to handle signals with asymmetric rise/fall time if introducing two step responses that describe positive and negative transitions respectively. Furthermore, a probability model of that an n-bit specific pattern appears in an m-bit PRBS is developed to explain why it is not likely for a PRBS to carry the worst-case bit pattern that generates the worst-case eye diagram.
The second part of the thesis focuses on the compensation design for the imperfect effects of transmission line loss and multiple reflections due to mismatch loads by adding a pre-emphasis circuit at the transmitter side. Owing to the benefits of stability, linear phase, less area and low power comsumption, the finite impulse response (FIR) filter is adopted as the pre-emphasis circuit. With the aid of fast eye diagram algorithm, the optimal set of the tap coefficients can be extracted by applying the time domain optimization that is to maximize the reduction of voltage noise of the eye diagram within a range of window time. The simulation and experimental results of transmission line systems with matched, underdriven and overdriven impedance schemes that actually employ the pre-emphasis compensation technique are shown that the eye diagrams are reopened even if the compensated frequency responses do not become flat.
Subjects
eye diagram
step response
signal processing
FIR filter
pre-emphasis
Type
thesis
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