The Techniques Of Crosstalk Cancellation In High-Speed, High-Density Bus System

With the progress in integrated circuit technology and increasing of customer demand, electronic products are developing toward higher processing speed and smaller physical size, which makes the frequency, scale and pin number of integrated circuits to be increased and the circuit density of the printed circuit board also to be raised. So signal integrity problems have been the enormous challenge that pin-interconnection of chip-to-chip has to face, and the key point of signal integrity is how to reduce crosstalk in high-speed, high-density bus system.Crosstalk is formed with electromagnetic coupling between the transmission lines and it is one of the main problems in signal integrity. When the signals in one network are transferred to the adjacent network as noise, crosstalk appears and it always exists between any pair of the network. Crosstalk will cause two serious results:firstly, noise will be generated in the adjacent transmission line, which will reduce the noise tolerance of the system and damage signal integrity of the system; secondly, different step directions of signals on adjacent transmission lines will cause different time delay, which will deteriorate system timing. Therefore, for high speed and high density bus system, reducing crosstalk can increase noise tolerance of system, improve the timing of system, ensure the integrity of signal and avoid mis-triggering or wrong judgments in circuit operation.Usually, crosstalk can be divided into two kinds according to the location where crosstalk has occurred, one is chip-level (intra-chip) and the other is board-level (inter-chip). Methods for board-level crosstalk cancellation in high-speed, high-density bus system are studied in this paper. From the view of signal detection, four methods are proposed to eliminate the far-end crosstalk. The main work and innovations are as follows.1. A crosstalk reduction method applying RC derivative circuit on output of transmission line is proposed. Based on the property of the far-end crosstalk at a victim, RC derivative circuits are applied to the receiver ends of the aggressor and victim line, then the crosstalk signals are rebuilt to offset those output from victim. The proposed method is easy in circuit implement. The results of both software simulation and circuit experiment show its effect of crosstalk cancellation is petty good.2. A method that can reduce crosstalk by using the inverted signal at the middle of aggressor line is presented. In a bus system with n lines, phase inversions are set at the middle of the odd (or even) number line, then the amplitudes of far-end crosstalk, which come from the front and the back half coupling length, are numerically equal and the phases are opposite. The far-end crosstalk on transmission line would be set-off when these two parts of crosstalk signals are added automatically. Simulation results show that crosstalk can be eliminated mostly by this method, which is better than the method using the RC derivative circuit.3. A method based on the sample-decision (SD) to suppress crosstalk and other noise is presented. In this method, SD circuits are applied on outputs to rebuild sending signals and then crosstalk and other noise are suppressed. The way of computing the times of SD for different length transmission line is given and the bit error rates (BERs) formula is studied by SD method. The simulation results and numerical calculation show that when the length of transmission line is less than the defined one, single SD can recover the distortion signal into sending one; when the length of transmission line is longer than the defined one, multiple SD circuits could improve the performance of BERs.4. The conception of Coupled Transmission Lines-Channel Transmission Matrix (CTL-CTM) is present and the mathmetics model is built. According to the form of sigular value decomposition (SVD) of CTL-CTM, a crosstalk cancellation method is proposed. In this method, unitary transformation processings are used at the input and the output terminal of CTL respectively and then the bus system with crosstalk would be converted into a parallel transmission without crosstalk which means crosstalk would be eliminated.Four solutions of crosstalk cancellation are proposed in the dissertation and their scope of application and effects are analysed and compared. Diverse technology options and technique reference are provided to solve SI problems in high speed, high density bus system.