Improved ring oscillator design techniques to generate realistic AC waveforms for reliability testing

We have demonstrated the feasibility of having a single ring oscillator ringing at multiple frequencies ranging from its maximum allowable frequency to an arbitrarily low frequency by replacing one inverter stage in a ring oscillator with a different type of inverter. Furthermore, with the introduction of a few more circuit elements, the duty cycle of the waveform can also be controlled independently from the f_osc. This approach to designing ring oscillators eliminates the need of having many ring oscillators with different number of stages and fanout to simulate different type of AC waveforms a device may experience