From TI Reducing EMI: http://www.ti.com/lit/an/szza009/szza009.pdf
===Sources of noise:
- IC's I/O pins
- Noise from clock switching within IC appears as glitches on a static output. Caused by common impedance of the shared pins that supply each power and ground.
- Power-supply system
- Includes voltage regulation and bypass capacitors at both regulator and microcomputer. Source of all RF energy in system (feed clocked circuits inside IC with current required for switching)
- Oscillator circuit
- Oscillator swings rail to rail. In addition to fundamental freq, harmonics included due to the output buffer being digital, which squares the sine wave.
- Solution: proper separation between crystal and tank circuits from other componenets and traces on PCB, AND loop areas are kept small.
===SMD vs. TH Components
- SMDs are better than leaded devices because of the reduced inductances and closer component placements available.
- Generally leaded capacitors all go self-resonant (more inductive than capacitive) at ~80MHz.
- Thus designs with only TH parts should not be considered as highly.
===
From Reducing Noise https://ece480group6.files.wordpress.com/2012/11/low-noise-printed-circuit-board-design.pdf
Reducing Impedance
- Avoid Long Traces
- Avoid Cutting the ground plane
- If neccecary run a long trace along the outside of the board to avoid cutting the ground plane in half
Avoiding stray capacitance
Last modified 9 years ago
Last modified on May 29, 2015, 4:17:41 PM