As the question says, I want to know why do longer traces/longer lengths of non-terminated signals of the PCB cause reflections and not the short length ones? I am ignoring the negligible amount of reflection a short trace may cause. I am not new to transmissions lines and impedance matching, but somehow I am not able to recall why exactly is reflection is more prominent on long non-terminated transmission lengths?
Is it because for longer trace there is higher chances of encountering discontinuities on the signal path, thereby causing reflection from that particular discontinuity, and even with the termination in place at the source, the signal gets reflected before it reaches back to the termination where it should ideally die off?
I would really appreciate your answer. Even if you link me to some document that answers this question well, it would be great.
Best Answer
All traces cause reflections. As the trace length approaches significant fractions of a given signals electrical length, the reflection can start to interfere with the signal (constructive or destructive interference).
You could also keep the trace length the same and increase the frequency of the signal, the effect will be the same. As mentioned in the comments, when considering the frequency of the signal it is important to note the frequency components. That is, the frequency of the fourier series components of the signal.