A circuit for detecting a phase error between a clock signal and a beam position includes a beam generator, a sensor, and a phase detector. The beam generator directs a beam toward a beam sweeper in response to the clock signal, and the sensor detects the beam as directed from the beam sweeper. The phase detector determines from the detected beam the error in the clock phase relative to the beam position. Such a circuit can automatically detect the phase error in the pixel clock and correct this error, thus eliminating the need for a manual phase-error corrector. The circuit may also be able to adjust the width and/or the height of a scan region, and thus may also be able to adjust the width and/or height of an image frame within the scan region.