Ink injection type writing system using amplitude-modulated electrical signals

An ink ejection system comprising a writing unit including a chamber, means defining an inlet channel connected in use to a source of liquid for introducing the liquid into the chamber, means defining an outlet channel connected to the chamber, and an electromechanical transducer for generating pressure rises in the liquid in the chamber to discharge the liquid in a series of droplets through the outlet channel onto a surface, means for generating an alternating sinusoidal signal of constant amplitude and frequency higher than the highest instantaneous frequency of a video signal, means for detecting a zero crossover point of said alternating signal, and generating a sampling signal in step with each zero crossover point, sample-and-hold circuit means effective to sample the instantaneous value of the video signal in response to said sampling signal and to hold the sampled video signal until the next sampling signal occurs, and means for modulating the amplitude of the sinusoidal alternating signal in accordance with the output from the sample-and-hold circuit means.