5) SBAD Signal Circuit unit
In this unit, outputs from the photo detector, namely, E and F are processed through the addition amplifier. That is, E and F are added together and (E+F) signal is output from #15 pin of IC101 (TA2153FN), as SBAD signal. This SBAD signal, along with Focus Error signal, is used as one of the conditions that the system uses to internally judge Focus ON/OFF based on them. Also, SBAD signal is used to detect defects: defects that may be detected when the Pickup passes a scratch on the disk, for instance.
