APPARATUS AND METHOD OF FORMING EVALUATION SIGNAL USED IN ADJUSTING FOCUS BIAS AND ADJUSTING SKEW OF DISK DRIVE

An apparatus of forming an evaluation signal used in adjusting focus bias and adjusting skew of a disk drive in which phase error information between a phase of a read data signal and a phase of a clock signal formed in synchronism with the read data signal, is detected, the phase error signal is converted into an analog signal and is outputted as an evaluation signal having a signal level in accordance with the phase error amount and the evaluation signal is inputted after A/D conversion to a portion for carrying out signal quality evaluation by using the evaluation signal whereby pertinent signal evaluation can be carried out by a simple constitution.