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Understanding the supply fluctuations of various frequency harmonics is essential to maximizing microprocessor performance. Conventional methods used for analog validation of the power delivery system fall short in one or more of: a) Measurement accuracy in both frequency and time domains, especially for very high frequency noise caused by large di/dt events. The multi-GHz power supply noise attenuates very quickly away from the die. Conventional approaches of measuring the noise at the pins of the package or at the die using capacitive probes are not accurate for multi-GHz clocks. For this reason, the observability of high frequency on die noise has been very tricky. b) Implementation, e.g. delivery of analog references to multiple areas across a "noisy" die, and compactness/modularity of the measurement units. c) Automation to enable a timely volume of measurements. The efficiency of the measurements is key to correlating a particular speed path to poser supply noise. To address the above issues this paper presents an On-Die Droop Detector (ODDD), a scaleable IC solution implemented and validated on a 90 nm process, for analog sensing of differential high bandwidth supply noise.