Patent ID: 7663399

Claim:
An output driver for use in a semiconductor memory device, comprising: a pull-up metal oxide semiconductor (MOS) transistor having a first type for pulling-up a voltage loaded on an output node in response to a pull-up control signal; a pull-up linear element having a second type transistor connected between the pull-up MOS transistor and the output node for increasing a linearity of an output current in response to a first bias signal; a pull-down transistor having the second type for pulling-down the voltage loaded on the output node in response to a pull-down control signal; and a pull-down linear element having the first type transistor connected between the pull-down transistor and the output node for increasing the linearity of the output current in response to a second bias signal, wherein a pull-up valid resistance is determined by the pull-up MOS transistor and the pull-up linear element having different typed transistors and a pull-down valid resistance is determined by the pull-down transistor and the pull-down linear element having different typed transistors to allow a pull-up current to pull-down current ratio to have a constant value by using contrary characteristics of the different typed transistors according to process, voltage and temperature (PVT) variation, and wherein the pull-up linear element and the pull-down linear element are respectively controlled.