Abstract: A flip-flop circuit includes a first unit configured to receive a reference clock signal and a reset signal, and a second unit configured to change an output node to a first level in response to the reference clock signal and change the output node to a second level by precharging the output node in response to a signal output from the first unit according to the reset signal.

Abstract: A counter with overflow prevention capability includes a counting unit configured to count an output code in response to an input signal and an overflow preventing unit configured to control the counting unit to stop counting the output code when a current value of the output code is a maximum value but a previous value thereof is not the maximum value.

Abstract: Semiconductor memory device with duty correction circuit includes a clock edge detector configured to generate first and second detection pulses in response to a transition timing of a common clock signal in an initial measurement operation; a duty detector configured to compare the first and second detection pulses to output comparison result signals; and a code counter configured to control the duty detector based on the comparison signals outputted from the duty detector in the initial measurement operation.