Patent ID: 6429858
Filing Date: 2002-08-06
Classification: G09G

Abstract:
In apparatus for applying various levels of voltage to individual pixels in a display device having a matrix of pixels arranged vertically in columns and horizontally in rows, said apparatus comprising:(a) a digital clock for producing a digital clock timing pulse signal at a first clock timing rate; (b) a digital counter, connected to the digital clock, for counting clock timing pulses and repetitively producing a ramp cycle signal upon receipt of a prescribed number of clock pulses; (c) a ramp generator, coupled to the digital counter for producing a substantially monotonic ramp voltage signal during each ramp cycle; (d) a number of column drivers, one for each column of the display device, which includes a sampling circuit, coupled to the pixels in the respective column of the display device, for storing the ramp voltage signal when it reaches a prescribed value corresponding approximately to a particular, desired brightness level of a pixel in the respective column and in a particular row during a given ramp cycle; (e) a column control circuit, coupled to all of the column drivers, for causing respective ones of the sampling circuits to sample and store the ramp voltage signal upon receipt of the next clock timing pulse after the ramp voltage signal reaches the prescribed value for each respective column; and (f) a row control circuit for repeatedly selecting one or more pixel rows which receive the voltage signals stored in the sampling circuits of the column drivers; the improvement wherein said column control circuit includes (1) a multiphase clock, coupled to the digital clock, for producing a plurality of phase-shifted waveforms, each waveform providing a trigger pulse, for switching the sampling circuit of the respective column drivers to store the instantaneous ramp voltage signal, and (2) a plurality of column selection circuits, one for each column, for selecting the one of the plurality of waveforms which causes the associated column driver to switch at the moment when the ramp voltage signal most closely corresponds to the desired brightness level of a particular pixel in the respective column.