1、How to Interpret the Electrical Signal Integrity Report,Signal Integrity Analysis of Straddle Type PCI Express Connector,Introduction,This report is for analyzing the signal integrity of the straddle type PCI express connector for Wistrons request. The connector model was provide by #. I used Ansoft
2、/Q3D to analyze a 20-pin simplified connector model and get the SPICE model of it. Then, a SPICE simulation was used to get both time domains ( 75ps, 150ps, 300 ps risetime ) and frequency domains ( 500MHz 3GHz) signal integrity performance ( differential impedance, propagation delay, insertion loss
3、, return loss, and crosstalk ) of the connector.In this report, only the connector, without the motherboard and the module PCB, was analyzed.,Software we used,The SI spec. we analyzed,The risetime of signal is critical to the time domain performance.,time,voltage,UI: Unit interval,VH,VL,Tr: rise tim
4、e,Tf: fall time,UI, also called bit time, = “1/ data rate (bps)”,Risetime and falltime are usually measured between 10% and 90% of the pulse magnitude. Sometimes 20% and 80% are used.,Slower Rise time,Faster Rise time,The faster the rise time is, the more impedance mismatch will be seen.,Ansoft Anal
5、ysis Model,Housing :PA6T (Er = 4.0),The dielectric constant will affect the capacitance of contacts.,Choose the interested area according to the pin assignment.Modify the contact model to be in the deflected state.Simplify the 3D model to exclude all arc sections (chamfers, fillets,). Modify the arc
6、 into polylines. The contact and housing models must have no interference.,3D model pre-processing is needed to for meshing.,SPICE Simulation,According to the pinout of the PCI express, the following pin assignment was used to do the SPICE simulation.,S5 S6 G G S7 S8 G G S9 S10 G G S1 S2 G G S3 S4 G
7、 G,Pinout -,SPICE model of the connector,* The terminator resistors are all 50 ohms.,* The crosstalk between (S1,S2) and (S3,S4) was analyzed.,Pin assignment is very important for the SI analysis.,G,G,G,G,G,G,G,G,G,G,G,G,G,G,G,G,G,G,G,G,G,G,G,S:G = 5:1,S:G = 3:1,S:G = 1:1 (In-line),S:G = 1:1 (Stagge
8、red),Better Xtalk minimization preformance,Time Domain Simulation Result- 75 ps risetime (20%-80%),Z = 115.0 81.8 ohm,Tpd = 61.2 ps,NEXT=-0.1%,FEXT=-0.02%,Cable,Connector,Fixture,Vr = Vi (ZL - Zo ) / (ZL + Zo ),0 : reflection coefficient,ZL = Zo ( 1+0) / ( 1-0) Thats how TDR measures the impedance !
9、,Characteristic impedance,Time Domain Simulation Result- 150 ps risetime (20%-80%),Z = 107.5 92.3 ohm,Tpd = 59.2 ps,NEXT=-0.06%,FEXT-0.01%,Near End Crosstalk (Backward Crosstalk) - NEXT Far End Crosstalk (Forward Crosstalk) - FEXT,Time Domain Simulation Result- 300 ps risetime (20%-80%),Z = 103.7 96
10、.1 ohm,Tpd = 58.2 ps,NEXT=-0.03%,FEXT -0.01%,Frequency Domain Simulation Result - Insertion Loss,Frequency Domain Simulation Result - Return Loss,A1 & A2 : incident signal,B1 & B2 : reflected signal,S21 = B2 / A1 when A2 = 0,S12 = B1 / A2 when A1 = 0,Insertion Loss,S-parameter of two-port system,S11 = B1 / A1 when A2 = 0,S22 = B2 / A2 when A1 = 0,Return Loss,Frequency Domain Simulation Result - Crosstalk,NEXT,FEXT,
