Intro to pcb design

Resistance
- wires arent ideal
- 1 inch of 10mil trace (10/1000 inch) is 50 mOhms!
  - you can calculate using online calculator
  - with 1A current, that is 0.05V, significant
Capacitance
- there are naturally capacitors between the plates of metal, so try not to have traces running under/over one another too much
- differential signals, they have opposites on each one, so that they have high capacitance between them so theyre shielded from outside noise.
Inductance
- Any loop is created from signal/return
- the inductance can add up pretty fast

Current traveling along the signal trace,
current must travel in a loop, so it will take the ground plane back
- it will go directly under the trace for a high frequency, but will go in a straight line for a low frequency.
WHY??
- impedance is not just resistance, we must consider capacitance and inductance
- inductance caused by small loop area
- capacitance is maximized by smaller distance between planes
Return paths takeaway
- so for any AC signal, the return current will directly follow underneath the trace
- why does this matter? reference plane discontinuities
- Stackups

Why does this matter?

all PCBs you ever create need a solid, uninterrupted, ground plane for return currents to travel through

otherwise you will have crazy noise problems corrupting signals

If you have two close traces, you can get noise from one on the other, can mess with sensor readings
caused by coupling between the traces
- just add space between your traces -
prevention strategies
- maintain 3x trace width of spacing around sensitive traces
- keep your ground plane very close
The closer your ground plane is to a trace, the more coupled it is
this acts as a sort of shielding protecting the trace.
- most of the capactiance the traces see is to ground and couples to ground
another reason why ground planes are so important.