Circuit approach for common mode control in high-frequency clocks

Abstract

An example embodiment is directed to shifting the common mode voltage of an analog oscillation stage toward a center line between the upper and lower power-supply rails of a first digital circuit. The first digital circuit has a digital input port adapted to respond to signal transitions defined between the supply rails, and the analog oscillation stage generates an oscillating analog signal that has a common-mode voltage that is not centered between the upper and lower power-supply rails. The oscillating analog signal, which drives the digital input port, changes alternately with the phases of the oscillating analog signal. To shift the common mode voltage of an analog oscillation stage toward the center line between the rails, a feedback circuit generates a contending digital signal that drives the digital input port with alternating states as defined by opposite phases.