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46 DESIGN007 MAGAZINE I JUNE 2021 Serial communication has been used long before computers ever existed. e telegraph system using Morse code is one of the first dig- ital modes of communication. All you need are two connections, which makes it simple and relatively robust. One wire is the signal and the other (dirt) ground. By interrupting the power with predefined patterns, information can be transferred over both short and long distances. e challenge is receiving the patterns cor- rectly and quickly enough to be useful. e simplest method of transferring data through the inputs or outputs (I/O) of ICs is to directly connect the data path from one IC to the next in parallel. But since most data consists High-Speed Serial Link PCB Design of more than one bit of information the paral- lel data path is multiple bits wide. is is fine for signal routing between ICs on a multilayer PCB over short distances. For instance, DDR memory devices take advantage of the fast data transfer rates of the parallel bus. However, it has two inherent problems for high-speed data transfer over long distances. e first problem is that one I/O pin is required for each data bit. e second involves meeting timing require- ments. Due to these two issues, parallel data is typically transformed to a serial data stream using serializer/deserializer (SERDES) mod- ules (Figure 1) for high-speed communication links. Beyond Design by Barry Olney, IN-CIRCUIT DESIGN PTY LTD / AUSTRALIA Figure 1: SERDES architecture.