Description
Overview: This check finds the number of vias that exist between a bypass capacitor and its associated pin.
Passing Criteria: This check passes if the number of vias on the path between a bypass capacitor and its associated pin is below a specified threshold.
Reporting Units: COUNT
Examples
Passing Message:
Via count of 0 within acceptable range (0 to 1)
Failing Message:
Via count of 2 outside acceptable range (0 to 1)
Physics Justification
Vias between a pin and a bypass capacitor introduce parasitic inductance, which:
Reduces Filtering Effectiveness
Parasitic inductance slows the capacitor’s ability to respond to high-frequency noise.
Increases Impedance
Vias add impedance to the path, disrupting the low-impedance connection needed for proper decoupling.
Affects Power Stability
Higher impedance and slower response times can cause voltage fluctuations at the pin, impacting the power integrity of the connected component.
Helpful Definitions
Parasitic Inductance
The unintended inductance present which arises from the magnetic field created by current flow and opposes changes in current, especially at high frequencies. It can degrade circuit performance by slowing responses and causing noise.
Decoupling
The use of capacitors placed near pins to stabilize voltage and filter out noise on the power supply