Patent ID: 6923520

Claim:
A head driving unit for driving a liquid drop discharging head having a plurality of channels, the head driving unit comprising: a plurality of switching units corresponding to respective channels; a waveform generation unit that generates and provides a single sequence of driving pulses common to the plurality of switching units, a plurality of the common driving pulses being included in a driving cycle; a data holding unit that stores a data set corresponding to an image of a particular recording density; and a signal selection unit that selects one of a plurality of selection signals thereby to cause the switching unit to selectively pass a combination of the common driving pulses in the driving cycle based on the data set stored in said data holding unit, wherein each selectively passed common driving pulse causes the liquid drop discharging head to discharge a liquid drop; and the liquid drops discharged in the driving cycle form a single dot on a recording medium, the size of which is determined by the number of driving pulses in the driving cycle, the number being determined by the selected one of the plurality of selection signals.