—On-chip decoupling capacitors (decaps) are generally used to reduce power supply noise. Passive decap designs are reaching their limits in 90nm CMOS technology due to higher operating frequency, lower supply voltage, increased concerns on electrostatic discharge (ESD) reliability and thin-oxide gate leakage. In this paper, a novel active decap design is proposed to provide better noise reduction than the passive decaps. The active decap is analyzed for ESD reliability and process/temperature variation adaptability. It is