SERVO DEVICE AND OPTICAL DISC INFORMATION RECORDING/PLAYING DEVICE

摘要

PURPOSE: A servo device and an optical disc information recording/playing device are provided to perform focus control by detecting a focus error signal for an optical disc as detecting/comparing a spot size of two spots that is an irradiating range of a sub beam on the optical disc. CONSTITUTION: Two sub photo detectors respectively detect/output an intensity distribution of a reflecting light of each sub beam as a sub beam intensity signal. A focus error signal generating circuit(5) generates/outputs a focus error signal by comparing the sub beam intensity signal of both sides. A focus controlling circuit(6) controls a focus of a main beam for the optical disc based on the focus error signal.