Signal Routing -- Star Routing vs. Multi-Point Routing

[tpayne03]

Hi all,

I built a 2 layer RF transmitter (433mhz) board, and then realized the impedance would not correct. So then I built a 4 layer board that works with the impedance.

I have one question, I am looking through TI SZZA009 APP Note, and they mention star routing vs multi-point. In my layout I used more multipoint. I could have used more of a star routing through.

This system is not HIGH SPEED (2mhz clock, with 433mhz RF signal) or complicated. But I am trying to learn best practices.

Does the star routing vs. multipoint matter with GND and VDD lines as well signal lines?

I understand with clock signals why star matters, so the signals get routed at the same time.

Thanks,
-Tim

[robertferanec]

I use star routing also in cases when I prefer take the signal / power directly from the source and I do not want the signal / power to be influenced by pins and components on the way between source and my pin. Even in clock signals it doesn't have to be about timing and length matching, but influencing.

For example, very simple explanation for easy imagination: Let's say you have: A power jack -> First 10A regulator -> Second 10A regulator -> Third 10A regulator connected in series. Now, the input power of the Third regulator will be influenced by peak currents and voltage drops on the First and Second regulator (and the third regulator will influence also the first and second regulator). If you place them into star, they all are taking power and driving currents directly from the power jack. I am sure you understand.

[tpayne03]

Yep, I totally get what you are saying. It is hard to imagine the currents peaking and dropping in a DC system, but they do. Hence using the star routing! Thanks.