A timing adjustment circuit includes a detection unit to generate a detection signal in response to a first clock having a duty cycle of 50% and a first frequency, a second clock having a duty cycle of 50% and a second frequency that is half the first frequency, and a third clock having a duty cycle of 50%, the second frequency, and a phase displacement of 90 degrees relative to the second clock, the detection signal indicating timing relationship between the first clock and the second and third clocks, a low-pass filter to receive the detection signal, and a variable-delay circuit to adjust relative timing relationship between the first clock and the second clock in response to an output of the low-pass filter such that a center point of a pulse of the first clock is aligned with a center point of a pulse of the second clock.