Application Note 1389 Setting Pre-Emphasis Level for DS40MB200 Dual 4Gb/s Mux/Buffer

The DS40MB200 is a dual 2:1 multiplexer and 1:2 fan-out repeater designed to support redundancy and extending copper backplane to data rates up to 4 Gb/s. With input equalization and output pre-emphasis, the DS40MB200 is capable of compensating attenuation distortion and reducing deterministic jitter caused by bandwidth-limited transmission lines. This application note outlines the methods to set the proper amount of equalization to achieve optimum jitter performance. Each output driver of the DS40MB200 has pre-emphasis for compensating the transmission loss disparity of the transmission medium that it is driving. Figure 1 shows the preemphasized waveforms before and after a transmission medium. Whenever there is a transition of logic state, the driver sends the first data bit with its full amplitude. In anticipation of lower transmission loss from the transmission medium, the driver sends the subsequent data bits of the same logic state with reduced amplitude. Effectively, the driver conditions the output signal amplitude such that the lower and higher frequency pulses reach approximately the same amplitude at the receiving end of the transmission medium.