Patent ID: 7656422

Claim:
A device for generating a pulse-width modulated signal according to image data and based on a pixel clock signal, comprising: a pixel clock generating unit that is configured to generate the pixel clock signal and includes a multi-phase clock signal generating unit configured to generate multi-phase clock signals each having a cycle T, wherein a number of the multi-phase clock signals is P and a phase difference between each adjacent pair of the multi-phase clock signals is T/P, a comparing unit configured to measure a period of time between a time when a first synchronizing signal is detected and a time when a second synchronizing signal is detected, to compare the measured period of time with a target value, and to output a difference between the measured period of time and the target value, a frequency calculation unit configured to calculate a pixel clock frequency setting value based on the difference between the measured period of time and the target value and to generate a frequency specifying signal based on the calculated pixel clock frequency setting value which frequency specifying signal specifies a frequency of the pixel clock signal, a counting unit configured to calculate a rise timing and a fall timing of the pixel clock signal by counting a number of time units each corresponding to the phase difference T/P according to the frequency specifying signal, and a pixel clock signal output unit configured to generate the pixel clock signal according to the rise timing and the fall timing of the pixel clock signal and based on the multi-phase clock signals; and a modulated data generating unit that is configured to generate the pulse-width modulated signal and includes a data converting unit configured to convert density data specifying density of a dot in the image data into pulse width data expressed in units of the phase difference T/P according to one of conversion rules predetermined based on the frequency of the pixel clock signal, an edge time calculation unit configured to calculate a rise timing and a fall timing of the pulse-width modulated signal according to the pulse width data and the rise timing of the pixel clock signal, a set/reset signal generating unit configured to generate a set signal and a set phase signal according to the rise timing of the pulse-width modulated signal and to generate a reset signal and a reset phase signal according to the fall timing of the pulse-width modulated signal, and a modulated data output unit configured to delay the set signal according to the set phase signal, to delay the reset signal according to the reset phase signal, and to generate the pulse-width modulated signal according to the delayed set signal and the delayed reset signal and based on the multi-phase clock signals.