## Monday, September 17, 2012

### PowerPoint Presentation On Transmission Line Basics

PPT On Transmission Line Basics
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Transmission Line Basics Presentation Transcript:
1. Real Computer Issues
An engineer tells you the measured clock is non-monotonic and because of this the flip flop internally may double clock the data. The goal for this class is to by inspection determine the cause and suggest whether this is a problem or not.

2. Agenda
The Transmission Line Concept
Transmission line equivalent circuits and relevant equations
Reflection diagram & equation
Loading
Termination methods and comparison
Propagation delay
Simple return path ( circuit theory, network theory come later)

3. Two Transmission Line Viewpoints
Steady state ( most historical view)
Frequency domain
Transient
Time domain Not circuit element Why?
We mix metaphors all the time
Why convenience and history

4. Key point about transmission line operation
The major deviation from circuit theory with transmission line, distributed networks is this positional dependence of voltage and current!
Must think in terms of position and time to understand transmission line behavior
This positional dependence is added when the assumption of the size of the circuit being small compared to the signaling wavelength

5. Segment 2: Transmission line equivalent circuits and relevant equations
Physics of transmission line structures
Basic transmission line equivalent circuit
?Equations for transmission line propagation

6. Transmission Line “Definition”
General transmission line: a closed system in which power is transmitted from a source to a destination
Our class: only TEM mode transmission lines
A two conductor wire system with the wires in close proximity, providing relative impedance, velocity and closed current return path to the source.
Characteristic impedance is the ratio of the voltage and current waves at any one position on the transmission line
Propagation velocity is the speed with which signals are transmitted through the transmission line in its surrounding medium.

7. Presence of Electric and Magnetic Fields
Both Electric and Magnetic fields are present in the transmission lines
These fields are perpendicular to each other and to the direction of wave propagation for TEM mode waves, which is the simplest mode, and assumed for most simulators(except for microstrip lines which assume “quasi-TEM”, which is an approximated equivalent for transient response calculations).
Electric field is established by a potential difference between two conductors.
Implies equivalent circuit model must contain capacitor.
Magnetic field induced by current flowing on the line
Implies equivalent circuit model must contain inductor.

8. T-Line Equivalent Circuit
General Characteristics of Transmission Line
Propagation delay per unit length (T0) { time/distance} [ps/in]
Or Velocity (v0) {distance/ time} [in/ps]
Characteristic Impedance (Z0)
Per-unit-length Capacitance (C0) [pf/in]
Per-unit-length Inductance (L0) [nf/in]
Per-unit-length (Series) Resistance (R0) [W/in]
Per-unit-length (Parallel) Conductance (G0) [S/in]

9. Ideal T Line
Ideal (lossless) Characteristics of Transmission Line
Ideal TL assumes:
Uniform line
Perfect (lossless) conductor (R00)
Perfect (lossless) dielectric (G00)
We only consider T0, Z0 , C0, and L0.
A transmission line can be represented by a cascaded network (subsections) of these equivalent models.
The smaller the subsection the more accurate the model
The delay for each subsection should be no larger than 1/10th the signal rise time.

10. For more please refer our PPT. Thank You.