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December 2015 • The PCB Design Magazine 65 Figure 3: Automotive infotainment system. speed and higher pin-count microcontrollers, greater bandwidth for on-board and off-board data communications, reduced size and weight, and finally accommodate high levels of electro- magnetic noise unique to automotive environ- ments. Electrical simulations of system-level SI, PI and EMI effects are now unavoidable for au- tomotive ECU boards. Though PCB-centric, these system-level simulations involve both on-board and off- board interconnects, including the cable har- ness and its associated connectors (both inline and to PCB). Two-layer PCBs are inexpensive but not able to support the design complexity and electrical performance required for modern ECUs. Power delivery of multiple voltages with minimal loss and low noise, reduced emissions and lower immunity, as well as controlled im- pedance interconnect, require multiple plane layers for the power delivery network (PDN) of ECU boards. The on-board interconnect for these multi-layer boards is composed of inter- layer vias, microstrip with one PDN plane and stripline with two PDN planes, one above and one below. Off-board high-speed signals are typically serialized (converted from parallel to serial), which reduces cable harness complexity and weight because a single unshielded twisted pair of wires might be applied for cabling. The system-level simulations must con- sider the full hierarchy of chip/package/board to properly judge performance as well as repre- sent the actual operating condition of the sys- tem. "Bits-to-bits" simulations are performed whether for parallel interconnect between a microcontroller and external memory on the same PCB or for serial interconnect between a transmitter on one ECU board and a receiver on another ECU. Therefore, serial interconnect analyses involve multiple boards as well as the physical signal channel between them. Signal Integrity The challenges involved in designing an automotive infotainment subsystem that com- prises both in-dash components for the driver and remote components for the passengers, as shown in Figure 3, serve as an excellent exam- article ELECTRICAL DESIGN CHALLENGES FoR AUToMoTIVE PCBS