Disclosed is a focus servo circuit for an optical pickup actuator capable of performing a normal focusing operation accurately and fast with detecting predetermined regions of a focus error signal and focus servo drive signal. The circuit has a focus zero detection unit for generating a focus zero detection...http://www.google.com.tw/patents/US5572501?utm_source=gb-gplus-share專利 US5572501 - Optical pickup actuator focus control with reference to a focus zero detection signal and a focus servo drive zero detection signal
