电子元器件应用-接地概要(英文).pdfVIP

Grounding Outline • Ground definitions • Ground plane effects: – Magnetic field reduction – Partial inductance reduction • Grounding of cable shields • Grounding loops 1 Grounding Noisy ground Signal (relays, motors, Hardware high-power ground (low circuits) ground level circuits) (chassis, racks, cabinets) 0V Keep separated to avoid noise coupling 2 Chassis (Hardware) Ground • Also often a “safety ground” • Includes metallic chassis, framework, etc. • Often tied to a true “earth” • As a rule, not used as a power return conductor (except in some low-voltage DC applications, like autos) • Not good as ground plane due to seams, joints and openings • Also common mode conducted noise return 3 Circuit Ground • Usually refers to “circuit common” or “signal ground” • May be connected to chassis ground, but it is best considered as separate and isolated during design • Often the negative rail in DC systems, but the positive voltage rail may also be used AC Quiet Rail • Also known as AC LOW or RF LOW • Used for local HF bypassing in EMI control • Typically one of the DC or LF AC supply rails • Not necessarely the same as circuit common 4 Safety Grounds