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I am in the process of routing a star-grounded amplifier pcb and wondered on how to connect the decoupling capacitors. As I see it I have two choices:

  1. Connect the ground of the capacitors directly to the star-ground point.
  2. Connect the ground of the capacitors "in series" between the star-ground point and the GND of the amplifier.

Basically:

schematic

simulate this circuit – Schematic created using CircuitLab

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The decoupling capacitor must be connected as close as possible to the supply pins of the device in order to minimize inductance in the high-frequency loop. This is true regardless of what grounding scheme is in use.

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  • \$\begingroup\$ Yep... It is as close as possible to the IC... But you didn't answer my question :-) \$\endgroup\$ – fho Dec 2 '15 at 11:03
  • \$\begingroup\$ The purpose of star grounding is to increase the inductance along the ground path. Anything that opposes this is incorrect practice. \$\endgroup\$ – Ignacio Vazquez-Abrams Dec 2 '15 at 11:07
  • \$\begingroup\$ So ... following your statements: star-ground increases inductance, decoupling capacitor should be placed with the goal of reducing inductance. So I should create a direct path between the IC GND and the capacitor GND and not run a trace back to the star ground point? \$\endgroup\$ – fho Dec 2 '15 at 15:42
  • \$\begingroup\$ Correct. The shortest possible direct path. \$\endgroup\$ – Ignacio Vazquez-Abrams Dec 2 '15 at 15:51

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