Clock signal generation device and memory device including the same

A clock signal generation device includes a variable voltage providing circuit, a fixed voltage providing circuit and a clock signal generating circuit. The variable voltage providing circuit provides a variable reference voltage based on a selection signal, a reference voltage and a temperature coefficient. The variable reference voltage is varied according to temperature. The fixed voltage providing circuit provides a fixed reference voltage that is determined according to the selection signal. The fixed reference voltage is a constant voltage. The clock signal generating circuit provides a clock signal based on the fixed reference voltage and the variable reference voltage. The performance of the clock signal generation device may be increased by providing the clock signal based on the variable reference voltage that is varied according to the temperature and based on the fixed reference voltage.