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This paper presents efficient noise isolation and suppression method in mixed-signal systems using alternating impedance electromagnetic bandgap (AI-EBG) structure-based power distribution network (PDN). Currently, split planes are used for isolation in mixed-signal systems for isolating sensitive RF/analog circuits from noisy digital circuits. However, split planes show good isolation only at low frequencies due to electromagnetic coupling through the gap. The AI-EBG structure-based PDN presented in this paper provides excellent isolation (-80 dB ~ -100 dB) in the frequency range of interest by suppressing almost all possible electromagnetic modes. The AI-EBG structure has been integrated into a mixed-signal test vehicle to demonstrate the isolation level achievable. The ability of the AI-EBG structure to suppress switching noise has been quantified in this paper. The AI-EBG structure provided greater than 100 dB of isolation in passive S-parameter measurement and suppressed in-band noise down to -88 dBm of isolation in a functional test.