1. Microstrips as Transmission Linesw
Conductor
Ground Plane h
Effective Dielectric Constant
Relative Dielectric Constant
Winter 2005
ECE
ECE 766
Computer Interfacing and Protocols

2. 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 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

3. 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

4. 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

5. 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

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