A random number generator includes a signal generator and a sampling unit. The signal generator is configured to generate an alternating sequence of metastable seed signals and oscillating signals during respective first and second half-periods of a clock signal. The oscillating signals having respective phases determined by corresponding ones of the metastable seed signals in the alternating sequence. The sampling unit is configured to detect a logic value of each consecutive oscillating signal during a portion of a respective half-period of the clock signal. The signal generator may be responsive to the clock signal and the sampling unit may be responsive to a delayed version of the clock signal.