pcb traces: impedance and reflexion

tahtouh · Mar 23, 2013

hello

i have to connect two traces with different width(https://obrazki.elektroda.pl/3377586100_1364035260.png),

the second trace is a trace of a connector pad

it think that it will cause reflexion (i'm not sure)

in the case of the reflexion, what can be the solution?

is it enougth to ensure the continuity of the trace impedance?

can this be a solution: https://obrazki.elektroda.pl/7848937200_1364035993.png (ensure the continuity of the trace width)

FvM · Mar 23, 2013

There are several prerequisites for impedance controlled design, no idea if they are met in your circuit:
- You have a matched impedance signal connection, partcularly a defined source and/or load impedance
- Dimensions of transmission line segments are larger than 1/10 of signal wavelength

A short (< 0.1 λ) segment of different impedance can be considered as a lumped capacitance or inductance.

Making a width step smooth or steep doesn't make a big difference.

crutschow · Mar 24, 2013

What is the frequency of the signals on that trace (rise/fall time or frequency of sinewave)?

tahtouh · Mar 25, 2013

crutschow said:
What is the frequency of the signals on that trace (rise/fall time or frequency of sinewave)?

rise time = 0.7ns

freq = 125 MHz

length of the segment = about 15 cm

pcb traces: impedance and reflexion

tahtouh

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crutschow

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tahtouh

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pcb traces: impedance and reflexion

tahtouh

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