Parallel Decoupling Strategy

Parallel Decoupling Strategy

A single capacitor only decouples effectively near its resonant frequency. For broad-spectrum decoupling, you parallelize capacitors of different values — each one handles a different frequency range.

Anti-resonance problem: Two parallel capacitors with different SRFs create an anti-resonance (impedance peak) between their resonant frequencies. This can cause worse noise than a single capacitor!

The impedance of N parallel capacitors (assuming they don't interact):

1/Z_total = 1/Z₁ + 1/Z₂ + ... + 1/Zₙ

The Strategy

A well-designed PDN uses a capacitance hierarchy:

• Bulk caps (10–470 μF): low-frequency (kHz range) bulk storage
• Ceramic MLCC (100 nF–10 μF): mid-frequency (1–100 MHz)
• Small ceramics (1–100 nF): high-frequency (100 MHz+)

Each capacitor's effective frequency range: from ~SRF/10 to ~SRF×10.

Your Task

Implement parallelImpedance(capacitors, f_MHz) where capacitors is an array of {C_nF, ESR_ohm, ESL_nH} objects.

Compute total impedance at frequency f_MHz using parallel combination.