Patent ID: 8026740

Claim:
An apparatus comprising: a first switch coupled to a first voltage reference and to an output node, the first switch being configured to conduct the first voltage reference to the output node when activated and to be an open circuit when deactivated; a second switch coupled to a second voltage reference and to the output node, the second switch being configured to conduct the second voltage reference to the output node when activated and to be an open circuit when deactivated, wherein the second voltage reference has voltage lower than the first voltage reference; a first voltage drop circuit coupled to the first voltage reference, the first voltage drop circuit being configured to generate a third voltage reference having voltage lower than the first voltage reference, but higher than the second voltage reference; a third switch coupled to the third voltage reference and to the output node, the third switch being configured to conduct the third voltage reference to the output node when activated and to be an open circuit when deactivated; a second voltage drop circuit coupled to the second voltage reference, the second voltage drop circuit being configured to generate a fourth voltage reference having a voltage higher than the second voltage reference, but lower than the third voltage reference; a fourth switch coupled to the fourth voltage reference and to the output node, the fourth switch being configured to conduct the fourth voltage reference to the output node when activated and to be an open circuit when deactivated; and an encoder configured to activate at least one of the first switch, the second switch, the third switch, or the fourth switch at least partially in response to input data for the encoder for generation of a multi-level output signal at the output node, wherein the encoder is further configured to provide first, second, and third control signals to the first, second, and third switches, respectively.