DESIGNING DIFFERENTIAL SIGNALS IN PCBs FOR REDUCED NOISE, LOWER VOLTAGE

摘要

Designers in the network and telecommunica-tions industry are adopting differential signal technology, enamored with its ability to reliably drive high-speed signals over relatively large distances. Differential technology offers important advantages over single line technology including reduced noise susceptibility, faster circuit speed, and lower supply voltage. To realize these benefits, and correctly design the interconnect for differential data transfer, PCB engineers need to consider signal quality across the entire interconnect from the silicon to the package to the board. In this article we will suggest a new design method that can make the process faster, easier and more reliable. In differential technology the same signal ― in both inverted and non-inverted form ― is sent from driver to receiver over two traces. In digital differential design both receiver outputs are sending out signals of opposite polarity. While the non-inverted output sends out a low-to-high transmission, the inverted output sends out a high-to-low transmission. The differential waveform is seen as an artificial signal formed by Vdiff = Vinv - Vnoninv. See Figure 1.