Bi-directional shift register

Abstract

A bi-directional shift register for scanning a liquid crystal display includes cascaded stages. A given stage includes an output transistor having a clock signal coupled thereto. A first input section is responsive to an output pulse of a second stage for generating a control signal that is coupled to the transistor to condition the output transistor periodically for operation in a conduction state when shifting in a first direction is selected. The input section is responsive to an output pulse of a third stage for periodically conditioning the output transistor to operate in the conduction state, when shifting in the opposite direction is selected. When the clock signal occurs and the transistor is conditioned for the operation in the conduction state, an output pulse is generated at an output of the given stage. A second input section is responsive to a corresponding output pulse of a corresponding stage for varying the control signal to condition periodically the output transistor for operation in a non-conductive state to disable the generation of the given stage output pulse, when the clock signal occurs.