A ring oscillator (and test circuit incorporating the ring oscillator and test method therefor) includes an odd number of elements interconnected in a serially-connected infinite loop, each oscillator element having an associated programmable delay feature. The circuit can be used to measure effects...http://www.google.com/patents/US20030189465?utm_source=gb-gplus-sharePatent US20030189465 - System and method for measuring circuit performance degradation due to PFET negative bias temperature instability (NBTI)
