Patent ID: 7710678

Claim:
A VCM driver comprising a forward path and a feedback path, thereby producing a drive current of a voice coil motor for position control of a magnetic head using as an input signal a digital current control signal being formed corresponding to positional information read from the magnetic head and position command information from a controller, wherein the forward path includes: a digital operation type phase compensator receiving the input signal; a ΔΣ modulator receiving an output signal of the phase compensator to convert the output signal into a control code of predetermined bits; a PWM modulator receiving the control code converted by the ΔΣ modulator to produce a PWM signal; and an output circuit receiving the PWM signal produced by the PWM modulator to drive a voice coil; wherein the feedback path includes: a sense amplifier sensing a current flowing in the voice coil; an ADC receiving an output signal of the sense amplifier; a first low-pass filter receiving an output signal of the ADC; and a first decimation filter receiving an output signal of the first low-pass filter; and wherein an output signal of the decimation filter is fed back to the input side of the phase compensator to form a major feedback loop having a first-order characteristic loop gain; and an output signal of the decimation filter is fed back to the output side of the phase compensator to form a minor feedback loop having a loop gain being flat until a target band frequency when viewed from the output side of the phase compensator.