100 GBE DDR4
16 layer PCB with 90 & 100 OHM diff pairs. Xilinx Ultrascale FBGA & DDR4 memory DDR4 tracking DDR4 signals to Dimm Socket 100 Ohm 25 Ghz
Month: April 2021
Case Study – Cloud based telecoms system
Case Study - Cloud based telecoms system Background We were approached by a company specialising in cloud-based telecoms to develop a revolutionary comms device for virtual call centres. The PCB would need to interface with other bespoke and off-the-shelf devices. All with their own functions and requirements. Our PCB would have to be the “brain” to control all of these devices. Requirements All of these peripherals have their own high speed signal requirements: PCI-E connector, Ethernet connector, USB connector, QSFP+ connector, DDR4 SODIMM connectors, DDR4 RAM 8Gbit. If any one of the interactions between PCBs does not perform correctly, costly reworks would be required. Time would also be lost to identify the problem, this could also lead to our customer losing ground to competition. The PCB would also be the power supply for most of these interfacing PCBs. 60 A is required, flowing through various SMPS (switch mode power supply) to provide power to each connector. The high speed requirements for this PCB are extremely complicated, adding SMPS as well can cause problems with the high frequency electrical noise. For the high speed signals, we would need to route the signals at 50 ohms (DDR), 90 ohms (USB), 100 ohms (PCI-E, DDR diff pairs, Ethernet connector). The QSFP connector would need to use 100 ohm tracks at 25 Ghz. Most complex microprocessors have rules to follow. Chip manufacturers supply these rules as well as guidelines and reference designs to follow Using the numerous tools at our disposal, we were able to adjust the PCB stack up, the gap and track thickness to obtain the required impedance for each peripheral to operate correctly. Rules Nets are assigned to differential pairs, buses and classes to for complex rules to be assigned. These rules control the track thickness, track length and clearances to other nets and classes. Assigning the rules accurately allows the PCB to be routed without reworking and unnecessary mistakes. As the majority of these signals need to run at 50 ohms, we decided to organise the PCB stack for all of the signals to run at 50 ohms. PCB Layout QSFP connector - TE Connectivity 2299940-5 16 diff pairs 100 ohm 25 GHZ, tracks with no 45 corners. The diff pairs are connected using 100 ohm diff pair coplaner signals. As the tracks are running at 25 GHz, there can be no 45 degree bends in the tracks. Track lengths…