US Patent 7982549 Dual self-calibrating low-power oscillator system and operation

A system may include a first circuit configured to generate a first clock having a first period of oscillation, and a second circuit configured to generate a second clock having a second period of oscillation, where the difference (ΔT) between the first period of oscillation and the second period of oscillation remains within a specified limit even during variations in temperature and/or during variations in the supply voltage. The system may further include a control circuit, which may receive the first clock and the second clock, and adjust, according to ΔT, a first target parameter corresponding to a first number of cycles of the first clock, when a current cycle count of the second clock reaches a second target parameter corresponding to a second number of cycles of the second clock. The control circuit may also adjust, according to ΔT, the second target parameter when the current cycle count of the second clock reaches the second target parameter, and generate, based on counted cycles of the second clock, an output clock having an output period higher than the first period and the second period.