05-12-2012, 06:03 PM
CENG4480_A4Transmission lines
Transmission lines.ppt (Size: 678.5 KB / Downloads: 142)
Transmission lines overview
(1) Characteristics of and applications of Transmission lines
(3) Reflections in transmission lines and methods to reduce them
Appendix1
Mathematics of transmission lines
Characteristics of and applications of Transmission lines
Advantages:
Less distortion, radiation (EMI), cross-talk
Disadvantage
More power required.
Applications, transmission lines can handle
Signals traveling in long distance in Printed-circuit-board PCB
Signals in a cables, connectors (USB, PCI).
Different transmission lines
(Case 1) Infinite transmission line; impedance looking from source is the characteristic impedance Z0.
(Case2) Matched line (finite line with load connected to Z0) has the same property as an infinite transmission line
(Case3) unmatched line : reflection will occur
Reflections on un-matched transmission lines
Reflection happens in un-terminated transmission line .
Ways to reduce reflections
End termination eliminates the first reflection at load.
Source reflection eliminates second reflection at source.
Very short wire -- 1/6 of the length traveled by the edge (lumped circuit) has little reflection.