Signal Integrity Analysis And Research Of SAS Hard Disk Connectors

Whether it is a portable consumer electronic grade products,large-scale,enterprise-class servers,or extremely expensive space shuttle,in their circuitry,the electrical connectors are required to achieve the power and data transmission function of the components or systems.However,with the enhancement of network speed and the development of storage technology,people need to deal with the amount of data is growing in the unit time.At the same time in order to reduce the number of pins on the integrated circuit,the electrical connector transfers more data when using serial transmission.These factors have led to the signal transmission on the connector is getting higher and higher.While the steep rising edge of the high-speed signal contains a large number of high-frequency harmonic components that are sensitive to the parasitic parameters caused by the connector structure.The crosstalk,Impedance change,noise,time delay,loss,etc.of the connector transmission line may eventually cause the signal to be transmitted correctly through the connector to the receiver.In the high-speed connector design process,it can not only meet the realization of the circuit logic and mechanical connection function,but also study on the signal integrity of the electrical connector.It is necessary to understand the propagation process of the high-speed signal on the electrical connector from the perspective of the transmission line and the electromagnetic wave.By optimizing the connector structure,reducing the impedance of the transmission line mutation,reducing the impact of parasitic parameters,it making the signal can be done without distortion on the normal transmission process.In this paper,a SAS(Serial Attached SCSI)hard disk connector,which is commonly used in enterprise servers,is used to study the effect of electrical connector structure on its signal integrity through computer aided simulation.The redundant structure of the connector that is independent of the electromagnetic simulation is removed and the simulation model of the SAS hard disk connector is established in Pro/e.And then simulation model of the connector is imported into the electromagnetic simulation software HFSS(High Frequency Structure Simulator)for electromagnetic simulation.Through the simulation data curve,several structures that affect the signal integrity of the connector are found.The parasitic capacitance present in the contact portion of the connector plug and receptacle reduces the impedance of the SAS hard disk connector.The second signal port of the connector plug portion is bent at the tail so that the impedance of the port pin rises.The end of the pins structure of the contact portion of the plug and receptacle is optimized.By reducing the length of the signal pin and removing the excess part of the end of the signal pin of the socket,parasitic capacitive resistance is eliminated and the impedance of the point increase.At the end of the connector pin of the second signal port,the housing structure is optimized to reduce the point impedance value without affecting the normal welding of the connector.The two optimizations make the impedance of the differential pair in the connector more stable and the signal integrity performance is improved.In order to obtain the accurate measurement information of SAS hard disk connector,we use vector network analyzer(VNA)as test instrument.A SAS hard disk connector test fixture is designed according to the test requirements,and the SAS hard disk connector performance data is measured by using the calibrated instrument.Comparing the measured data with the simulation data,it is proved that the simulation results in this paper are correct and reasonable.