I'm designing an (single sided) extension board that will hold a 3-pin temperature sensor (TSIC 506). As the order of the pins go from 1 Vcc, 2 Signal, 3 GND I wonder if I should follow the same order in the cable connecting the board to an MCU? Or would it be better to have 1 Vcc, 2 GND, 3 Signal on the cable?
As a more general question, should ground and power lines in a cable also carrying signals be next to each other, or as far as possible from each other?
I attach two layouts of the board I did.
First, power lines apart:
Second one, with power and ground next to each other:
Best Answer
Its not a question of „who should be next to who“.
If you want a design that is robust concerning EMI (I assume that‘s what you‘re after), then you have to defeat 3 enemies:
1) inductive coupling (loop to loop). Current only flow in loops and loops carrying current affect each other. So you must figure out all loops and find a way not to interfere. Usually this is done by minimizing loop area.
2) capacitive coupling. A plate of a plate capacitor influences the other plate through cap. coupling. Making use of this is called “shielding”. You can shield signals with e.g. a GND plane so they won’t be affected by cap. coupling.
3) galvanic coupling. The simplest form of interference happens when multiple currents (signals) share a line. The receiver of one signal will also see the other signals. This can be addressed with seperate lines for each signal or a star grounding concept.
In your design, you could make GND as a plane (2 sided board) and you could use a shielded cable where you connect GND. You could also make the area (loop) between +5V and SIGNAL as small as possible.