Abstract: Disclosed is an output buffer circuit having low noise characteristics, comprising a control section for detecting whether a driving voltage of more than a normal voltage is applied or not, and generating a control signal on the basis of detection result thereof; and a pull-up section for enabling a voltage down to be selectively caused between a driving voltage supplying terminal and an output terminal of said buffer circuit in response to said control signal. By the output buffer, it is possible to considerably reduce a ground bounce noise occurring upon a driving voltage of more than a normal voltage being applied. Thus, the total ground level of a semiconductor device, in which the output buffer is embodied, can be stabilized, and therefore stability of the device can be enhanced.

Abstract: An ATD circuit of a semiconductor memory device includes a variable delay line for delaying an address signal, a logic comparator for comparing the logic of the address signal with that of the address signal delayed by the variable delay line to generate an ATD pulse signal having a constant width at the rising and falling edges of the address signal, and a power supply voltage detector for detecting a voltage level of the power supply voltage to adjust the length of the variable delay line according to the voltage level, so that the pulse width of the ATD pulse signal for controlling precharge and voltage equalization of a bit line and operation of a sense amplifier is constantly maintained independently of the variation of a power supply voltage to thus improve access speed of the semiconductor memory device.