Issue link: https://iconnect007.uberflip.com/i/615135
68 The PCB Design Magazine • December 2015 compliance-driven SI simulations are per- formed with protocol-specific system schemat- ics. Broadband power-aware S-parameter mod- els are extracted for the memory bus or byte lanes of interest. Vendor-provided power-aware IBIS models are applied along with 3D extract- ed package models and used in simulations required for protocol-compliance verification. Simulation results are captured into interactive reports where violations are flagged and wave- forms are accessible for each net simulated, enabling issues to be investigated. This signoff- accurate simulation might easily be setup to de- termine simultaneous switching noise (SSN) ef- fects. For DDR4, this detailed parallel bus analy- sis might also consider serial channel analysis to determine the requisite bit error rate (BER) compliance checks. With the mention of serial channel analysis, let's next consider the timely topic of automo- tive Ethernet in the framework of serial com- munication between the in-dash ECU and the remote terminals of the infotainment system. Just as memory subsystem design is not unique to automotive applications, serial link design is also common among many high-speed elec- tronics designs. However, unlike memory, au- tomotive serial communications apply unique protocols and physical channel hardware. Each of the system's PCB and physical chan- nel components is designed independently. Vendors provide cables and connectors to form the physical channel and commercially avail- able chipsets are applied, which are likely to use third-party IP blocks. These chipsets and IP blocks might seem to simplify the PCB design process for serial links, but in reality, it is more complex. Design performance must be verified through characterization of the full system, from serialized digital output from the trans- mitter (TX) to serialized digital input to the re- ceiver (RX). As for memory subsystems, a few nets might be characterized with layout-centric simulation, but these results are not the desired performance and system-level block schematic simulations are a requirement. Presently available capabilities supported by automotive Ethernet include infotainment sys- tems, sensors and backup cameras. A new IEEE standard, 100BASE-T1, defines 100Mbps auto- motive communication. Closely related to the 100Mbps prioprietary protocol BroadR-Reach from Broadcom, 100BASE-T1 applies a single unshielded twisted-pair cable as the physical channel. This channel solution is significantly lighter and dramatically cheaper than other alternatives but is susceptible to the unique automotive environment's cable-routing un- certainties and crosstalk, radiated electromag- netic noise and thermal effects. Another IEEE standard, 1000BASE-T1, is under development for 1Gbps (1000Mbps) automotive Ethernet. Future infotainment needs, as well as many en- visioned ADAS capabilities, require very high bandwidth communication internal to the ve- hicle. Though the 1000BASE-T1 standard is only at a draft stage, there have already been product announcements concerning its sup- port. It is therfore important for system SI solu- tions for automotive applications to have sup- port for 100BASE-T1 and 1000BASE-T1 protocol compliance. The factor of 10 increase in data rate has implications for PCB design and SI simulations required to ensure reliable operation. As pre- viously observed for computing, telecom and mobile designs, as signals approach the gigabit- per-second range, effects that were safely over- looked in the past start to matter. Things like reflections, crosstalk, interconnect losses, and equalization all become critically important. For serial links, vias are often the largest impedance discontinuity on the PCB, causing potential reflections along the channel and crosstalk between channels. Methodologies to maintain high signal quality for routing within ELECTRICAL DESIGN CHALLENGES FoR AUToMoTIVE PCBS " Future infotainment needs, as well as many envisioned aDas capabilities, require very high bandwidth communication internal to the vehicle. " article