JPS6433704A - Magnetic disk device - Google Patents

Abstract

PURPOSE:To stabilize the operation of a device by providing a differentiator to differentiate a servo analog signal, a zero-cross pulse generator and an AND gate to obtain the logical production of these two signals, synchronizing and controlling a PLL circuit with a servo pulse signal which include no jitter. CONSTITUTION:A servo digital signal E which include the jitter is outputted from an OR circuit 10 and a differentiation signal F to differentiate a servo analog signal A is outputted from a differentiator 12. At such a time, since the characteristic of the circuit 12 does not have a gain in a low band frequency, a level change is not generated to the signal F and the time change of the peak point of the signal A is not generated. A zero-cross signal G not to have the jitter is generated from a cross pulse generator 13 and the logical production of the signals E and G is obtained in an AND circuit 14. Then, a servo pulse signal not to include the jitter and a false pulse is outputted. Thus, a PLL circuit 11 is synchronized controlled and the circuit 11 is stably operated.