Electronic Design

Serial Data Link Analysis (SDLA) Software Opens The Eyes Of Designers

The trend toward high-speed serial interfaces in computers, communications networks and other systems is well along, and we are now seeing a continuous ratcheting up in data speeds. In implementing serial data links with PCI Express, 10 Gigabit Ethernet, Serial ATA, Infiniband, RapidIO, XAUI, Fibre Channel, HDMI, Fully Buffered DIMM II and others, it has become increasingly more difficult to predict the performance of the data paths on PC board backplanes, through connectors and in cables. When traversing widely used FR4 PC board backplanes at multi-gigabit rates, you can expect significant attenuation and distortion of the signal, not to mention the occasional surprise you could not predict. Techniques such as pre-emphasis and de-emphasis as well as various forms of equalization have been developed to offset the signal degradation over the link. But how do you know beforehand what is needed, what will work and in what combination? With Tektronix's new Serial Data Link Analysis (SDLA) software you can measure, predict and test various solutions to optimize and finalize your design. The SDLA product is designated the 80SJNB Advanced Jitter, Noise, BER and Link Analysis software. It is designed to run on Tektronix's popular DSA8200 Digital Serial Analyzer, a modern sampling oscilloscope. Your entire design from transmitter through the physical link to the receiver comparator can be characterized and tested for compliance to the desired serial standard (Fig. 1). The software emulates the entire interconnect channel and enables testing the transmitter performance against multiple interconnects and corrective strategies. Virtual probing at inaccessible points is implemented to give you a complete view of the system. Here is basically how it works. You connect the sampling scope probe to the transmitter (Tx) output to capture the signal and display the eye diagram so you can see the jitter, noise and eye contour. The time domain reflectometry (TDR) feature of the scope is then enabled and the complete channel is tested. The TDR result is captured. This is then used by the iConnect software to generate the S-parameters of the channel. If you have a data file describing the channel (channel as in a "network" sense meaning like 2-port circuit analysis format) you can use that. If you have a vector network analyzer, it can be used to characterize the channel and create the file. Next, the 80SJNB advanced software is called up so that the channel is emulated from the S-parameter data. The output result is a view of what the receiver (Rx) will see. The received eye diagram is displayed. From there you can add various types of equalization to correct for the channel distortions. In this way, you can find any problems and then optimize the channel for best results. Software supports both feed forward equalization (FFE) and decision feedback equalization (DFE). With this arrangement, the waveform and the eye diagram at any point in the system are viewable so that a complete analysis of jitter, noise and BER can be made. This product also includes the capability to capture and analyze spread spectrum clocked (SSC) signals. The 80SJNB software sells for $15,800 when ordered with a new DSA8200 oscilloscope. Existing DSA8200 owners who already have 80SJNB or 80SJNB Essentials software from Tektronix can upgrade to the 80SJNB Advanced for $4900.

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