Patent ID: 8035413

Claim:
An apparatus comprising: a first combined drive and termination circuit configured to operate with a first supply voltage, the first combined drive and termination circuit comprising: a variable impedance pull-up network; a variable impedance pull-down network; at least one control input for setting a configuration of the pull-up network; and at least one control input for setting a configuration of the pull-down network; a controller that controls calibration being performed in four steps: 1) pull-up network calibration for drive mode when a data output is logic high; 2) pull-down network calibration for drive mode when a data output is logic low; 3) pull-up network calibration for termination mode; and 4) pull-down network calibration for termination mode; and a replica of at least part of the combined drive and termination circuit for use in performing calibration; the apparatus having a termination mode of operation in which the variable impedance pull-up network is configured to have a pull-up network termination impedance and the variable impedance pull-down network is configured to have a pull-down network termination impedance, the pull-up network and the pull-down network in combination functioning as a split termination; the apparatus having a drive mode of operation in which: to drive a high output, the pull-up network is configured to generate a specific impedance when switched ON; to drive a low output, the pull-down network is configured to generate a specific impedance when switched ON; each of the pull-up network and the pull-down network having a plurality of transistors sized to provide identical impedances, and each of the pull-up network and the pull-down network being configured to have a desired impedance by progressively varying the number of switched ON transistors.