Ring oscillators are commonly utilized to generate clock signals in digital circuits. A ring oscillator typically includes an odd number of digital inverters connected in a loop fashion. The oscillation frequency, or oscillation period, of a ring oscillator is determined by the delay though the inverter stages within the ring oscillator.
With older complementary-metal oxide semiconductor (CMOS) technologies (such as 90 nm channel length and longer), inverter delays within ring oscillators tend to increase with temperature, which in turn decrease the oscillation frequency of ring oscillators. As a remedy, various circuit techniques had been developed to counteract this effect. However, with newer CMOS technologies (such as 45 nm channel length and shorter), the oscillation frequencies of ring oscillators tend to increase with temperature, so new circuit techniques for frequency compensation are needed for ring oscillators manufactured in newer CMOS technologies.
The present disclosure is related to an improved CMOS ring oscillator.