High-speed digital circuit design means that if the rise time of the signal propagation delay times of less than 4, PCB.The signal on the board can present transmission line effect, such a design is called high speed digital circuit design.And the Series digital circuit design method is different, high speed digital design need SI simulation analysis.SI simulation analysis generally divided into before wiring two process simulation and post layout simulation, its main task is found in the system design process and improving the sI problems, ensure the quality of signal transmission functions and the right time, is to ensure that the key step in the design is successful. This post focus on SFP PCB design of Gigabit SFP transceiver high-speed circuit.
About SFP PCB design of Gigabit SFP optical transceiver
Gigabit SFP optical signal transceiver card is mainly composed of four modules: (SFP) fiber optic transceiver module, the large capacity data cache (SDRAM) (PCI9656), PCI bus interface module, control module (FPGA).Implementation of main function is to be able to send and receive gigabit Ethernet optical signals, on the physical layer and data link layer handling gigabit Ethernet protocol, IP packets and through PCI bus is extracted in the computer’s memory.Demand support vet2 PCI card. Agreement support DMA transfer mode, data transfer rate is not less than 125 MB/s.
Light module in the design of input and output electric signal frequency up to 1.25 Gbps, using the LVPECL difference signal, the gigabit difference signal simulation discussed in literature .First of all, establish simulation model as shown in figure 7.Single line impedance 50 1000 f2 differential impedance (X1), signal rate of 1.25 GHz.Outl LVPECL difference output IBIS model for sfp transceiver module, Inl for FPGA LVPECL differential input IBIS model.
Design by using based on SI simulation analysis and design of high-speed signal PCB wiring rules, solved the gigabit sfp ports signals in the process of sending and receiving card design, signal integrity problems of cloth plate a successful, completely meet the requirement of design index, and avoid the repeat design from the signal integrity issues.In the process of high speed digital circuit design, based on SI simulation analysis early in the design of the product as much as possible to solve the signal integrity problems, so as to minimize the product cost, shorten the development cycle.