A non-invasive characterization of a fast CMOS ring oscillator is reported. The optoelectronic technique exploits infrared emission from hot-carriers in high-field regions of switching transistors. By means of a fast solid-state single-photon detector (Single Photon Avalanche Detector SPAD), high time resolution and sensitivity are obtained. Experimental data with 50ps resolution enable to measure systematic variations of the period and jitter of switching transitions due to phase noise in a ring oscillator. The luminescence of pchannel MOSFET’s, previously reported to be barely detectable, is also measured.
