Transmission Line Simulator
H. Johnson, 5/29/95
file: shortlin.mcd

Investigation of untermiated lines showing effects of rise time and line length.
Order of operations: Establish indices for FFT operations, generate frequency response of unterminated line, convert to time domain waveform and display.

Establish indices for FFT operations

Sampling resolution, in seconds

Desired trace length, in seconds

Pick next biggest power of two
trace length

Index to time points

Index to frequency points

List of frequency points

Dummy vector used to vectorize
some scaler functions

Vector operations

Source impedance

Load impedance

cl = load capacitance

Transmission line impedance

Delay function, argument t is delay in seconds

Generate frequency response of unterminated line

Transmission line response (delay only, assume no distortion)

Acceptance function

Near-end reflection

Transmission function at far end

Far-end reflection

System response

Driving waveform (a rectangular waveform, N/2 points in length)

Linear rise/fall slopes; 0-100% risetime = r

Gaussian rise/fall slopes, 10-90% risetime = r

Use linear or gaussian slope

Convert to time domain and display

Ideal driving waveform

Driving waveform with rise/fall slopes

Response of driven trace

Set nominal transmission line delay and risetime

Scale both delay and risetime to see
what happens

Sample some test functions

Unterminated line response
Risetime set to 0, 2 and 3 times transmission line delay

Unterminated line response
Risetime set to 4, 5 and 6 times transmission line delay

Unterminated line response
Risetime set to 4, 5 and 6 times transmission line delay
BLOWUP of vertical axis

Investigate effect of termination capacitance

Set nominal transmission line delay and risetime

Adjust load capacitance and produce step response for each c ase

Step response of 1/2 ns line with 0, 10 and 20 pF load
BLOWUP of vertical axis

Record frequency response for each value of load capacitance

Frequency response of 1/2 ns line with 0, 10 and 20 pF load

Hz ->

Knee frequency of driving waveform is 160 MHz (3-ns rise/fall time)