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Transmission line

Transmission line. Transmission line. An apparatus to convey energy or signal from one place to another place. Transmitter to an antenna connections between computers in a network hydroelectric generating plant and a substation several miles away

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Transmission line

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  1. Transmission line

  2. Transmission line An apparatus to convey energy or signal from one place to another place. • Transmitter to an antenna • connections between computers in a network • hydroelectric generating plant and a substation several miles away • interconnect between components of a stereo system • CATV service provider and your TV set • Connections between devices on a circuit board

  3. Example – Cable TV

  4. Example – Computer network

  5. Example – Electric power transmission line

  6. Example – Printed circuit board

  7. Example – Printed circuit board

  8. Types of transmission lines Microstrip line Coaxial cable Two-wire transmission line

  9. Distribution of electric field strengths of typical TEM lines Microstrip Two-wire Parallel plate E/H distributions vary as the structures of transmission lines change. For electromagnetic compatibility, E/H should be confined to small area.

  10. Field representation in waveguides

  11. TEM mode (Transverse electromagnetic mode) Wave Solution

  12. Parallel plate waveguide With a wide enough line trace, variation along y-axis can be ignored.

  13. Transmission line 등가 회로 + + v (z, t) v (z, t) - - i (z, t) i (z+z, t) i (z, t) + L z v (z+ z,t) C z - z z

  14. Transmission line eq. solution

  15. Transmission line의 특징 H • For a magnetic field and an electric field propagating in the same direction, the ratio of E and H (E+/H+) is kept constant. • For a voltage and a currentcurrent propagating in the same direction, V+/I+ratio is equal to Z0 . • When the ratio is disturbed, reflected waves are generated. Direction of propagation H E

  16. Reflection coefficient + V -

  17. Influence of line length on load voltage + V - + V - + V - + V - + V - Vin Vout R R MLIN R2 VtPulse R1 R=1k Ohm SRC1 R=20 Ohm t Impedance mismatched Z0= 50  Zs = 20  Z0= 50  ZL= 1k  0.5m

  18. Ringing : Time domain

  19. Ringing ~ Signal source Load Mismatched load

  20. Impedance matching – Digital logic Source matching ~ Load matching ~

  21. Impedance matching topologies

  22. Frequency domain solution β : propagation constant, vp : speed of light

  23. Phasor representation + V -

  24. Transmission line terminated with short, open V inc o Out of phase (180 ) for short Vrefl Zs = Zo o In phase (0 ) for open Vrefl For reflection, a transmission line terminated in a short or open reflects all power back to source

  25. Transmission Line Terminated with 25 Ω V inc Zs = Zo ZL = 25 W Vrefl Standing wave pattern does not go to zero as with short or open

  26. Equivalent input impedance

  27. Input impedance of short

  28. Input impedance of open

  29. Some transmission line examples case 1) matched load

  30. case 2) unmatched load

  31. Ringing : Time/frequency domain

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