Liquid crystal display driver with threshold voltage drift compensation

Claim 1

A shift register, comprising: a source of a plurality of phase shifted clock signals; a sensor for generating a threshold voltage indicative signal; a plurality of cascaded stages, a given one of said cascaded stages, including: a first transistor of a push-pull amplifier responsive to a first clock signal of said clock signals for generating an output pulse at an output of said given stage; an input section responsive to an output pulse developed at an output of a second of said cascaded stages when a clock signal that is phase shifted with respect to said first clock signal occurs for generating a control signal at a control electrode of said first transistor, said control signal conditioning said first transistor to generate said output pulse of said given stage when an active level of said first clock signal occurs; and a second transistor of said push-pull amplifier coupled to said output of said given stage for clamping said output to an inactive level of said output pulse, said second transistor being responsive to said threshold voltage indicative signal in a manner to compensate for a change in a threshold voltage of said second transistor.