Meaning
Frequency point in an electrical network where the impedance reaches a local maximum due to the cancellation of inductive and capacitive reactances. Anti-resonance occurs when the inductive reactance of a package lead or trace equals the capacitive reactance of a decoupling component. The resulting high impedance path blocks current flow at that specific frequency.
Impedance Peak
High impedance at this frequency creates a voltage drop that disrupts power delivery to high speed integrated circuits. Engineers monitor anti-resonance during power integrity simulations to ensure the impedance profile remains below the target impedance limit across the entire operating bandwidth. A mismatch between a ceramic capacitor and the board inductance often causes these peaks.
Network Interaction
The interaction between multiple decoupling capacitors with different self-resonant frequencies generates these problematic peaks. This frequency sits between the two self-resonant points of the individual components.
Mitigation Strategy
Damping the resonant loop through the selection of capacitors with specific equivalent series resistance values reduces the magnitude of the peak. The use of simulation tools allows for the verification of the impedance target across the full frequency range before the board design is finalized. Proper placement of components relative to the power pins minimizes the loop inductance that drives these effects.
