Microstrips as Transmission Lines w Conductor Ground Plane h Effective Dielectric Constant Relative Dielectric Constant Winter 2005 ECE ECE 766 Computer Interfacing and Protocols

Microstrips as Transmission Lines Delay Define TD = 1/v as delay TD = 1.017ere Example: If ere = 5, TD = 0.06 ns/cm (vs. 0.033 ns/cm for free space) Characteristic Impedance Example: If er = 5, t/w<0.3, w/h=0.02, then z0=120Ω Winter 2005 ECE ECE 766 Computer Interfacing and Protocols

Computer Interfacing and Protocols Crosstalk Consider two microstrips Solve differential equations subject to termination conditions w S er = 5 CM: Mutual Capacitance LM: Mutual Inductance a: Rise time of the signal Winter 2005 ECE ECE 766 Computer Interfacing and Protocols

Computer Interfacing and Protocols Crosstalk z0 x=0 x=l V V(t) t a Input waveform z0 x=0 x=l - + V V2(t) t a at x=0 V2(t) at x=l t Winter 2005 ECE ECE 766 Computer Interfacing and Protocols

Computer Interfacing and Protocols Crosstalk Example: Suppose w = s = 0.3mm, h = 0.65mm, V = 5Volts, er = 5, a = 1ns rise time Winter 2005 ECE ECE 766 Computer Interfacing and Protocols

Grounding and Crosstalk in Cables Twisted Pair Grounded Shield Alternating Signal/Ground Good for balance Winter 2005 ECE ECE 766 Computer Interfacing and Protocols