Pixel clock generator and image forming apparatus

An image forming apparatus that forms an image by driving a light source by a pulse modulation signal obtained by pulse-modulating image data based on a pixel clock scanning a target medium with a light beam output from the light source, the image forming apparatus comprising:

• a high frequency clock generating unit that generates a high frequency clock;
• a pixel clock generating unit that generates the pixel clock based on the high frequency clock;
• an error calculating unit that detects a first synchronization signal corresponding to a scanning start point and a second synchronization signal corresponding to a scanning end point, and calculates an error between a first time period starting from a time when the first synchronization signal is detected until a time when the second synchronization signal is detected and a second time period obtained by integrating a cycle of the pixel clock for a target number of times;
• and
• a frequency setting unit that sets a frequency of the pixel clock to be generated by the pixel clock generating unit based on the error calculated by the error calculating unit, wherein
• the frequency setting unit includes
• a pixel clock frequency average calculating unit that calculates an average of the frequency of the pixel clock based on the error calculated by the error calculating unit, and
• a pixel clock frequency offset value calculating unit that determines a reference error value from an error in N-cycles that is a predetermined operation cycle from the error calculated by the error calculating unit, and calculates offset values of frequencies of N pieces of pixel clocks based on a difference between the reference error value and the error, and
• the frequency setting unit circularly selects the N pieces of offset values calculated by the pixel clock frequency offset value calculating unit, and calculates the frequency of the pixel clock generated by the pixel clock generating unit based on a result obtained by adding selected offset values and the average of the frequency of the pixel clock calculated by the pixel clock frequency average calculating unit.