A ring oscillator-based analog-to-digital converter (ADC). The ring oscillator-based ADC includes a ring oscillator and a transition detector. The ring oscillator may include a set of inverters coupled in a ring wherein an output of an inverter is coupled to an input of a successive inverter in the ring. The transition detector is configured to detect transitions of outputs of the inverters by comparing outputs of two separate inverters at two consecutive time instances. The transition detector may include two sets of registers configured to store outputs of the set of inverters at two consecutive time instances, respectively, and a set of comparators configured to compare the outputs stored in the two sets of registers. Each comparator may be configured to compare an output of one inverter at a first time instance and an output of another inverter at a second time instance.