Patent ID: 8102739

Claim:
An optical disk playback apparatus comprising: a signal playback device configured to read and decode information recorded to an optical disk through an optical pickup unit in order to reproduce said information; said signal playback device including a signal generation circuit configured to generate a carrier signal, a first signal processing device configured to sum up a plurality of signals output from a photodetector of said optical pickup unit in order to output a unipolar RFDC signal, a second signal processing device configured to sum up the plurality of signals output from said photodetector of said optical pickup unit and then remove a DC component from the summed-up signal in order to output a bipolar RFAC signal, a modulator configured to be fed with said unipolar RFDC signal and said carrier signal so as to modulate said carrier signal with said RFDC signal to output a modulated signal, a switch configured to be fed with either said bipolar RFAC signal or said modulated signal coming from said modulator, said switch being further configured to output either said bipolar RFAC signal if said bipolar RFAC signal is input or said modulated signal coming from said modulator following a switchover of signal paths if said RFDC signal is input, an analog to digital converter configured to digitize either said modulated signal or said RFAC signal output from said switch, and a third signal processing device configured to demodulate said modulated signal digitized by said analog to digital converter in order to derive at least either a modulation factor or an off-tracking signal from the demodulated signal.