Patent ID: 6864656

Claim:
A magnetic disk drive that drives and positions an actuator using a voice coil motor, comprises: a current sensing resistor connected in series to a terminal on a current input side of said voice coil motor; a first operational amplifier in which a reverse input terminal is connected to a terminal on the current input side of said voice coil motor via a first resistor, a non-reverse input terminal is connected to a terminal on a current output side of said voice coil motor via a second resistor, said non-reverse input terminal is connected via a third resistor and a first capacitor which are arranged in parallel to a reference voltage, and a reverse input terminal and output terminal are connected in parallel to a fourth resistor and a second capacitor; a second operation amplifier in which a reverse input terminal is connected via a fifth resistor to a terminal on the current input side of said current sensing resistor, a non-reverse input terminal is connected via a sixth resistor to the current output side of said current sensing resistor, said non-reverse input terminal is connected via a seventh resistor to a reference voltage, and a reverse in input terminal and output terminal are connected by an eighth resistor; and a third operational amplifier in which a reverse input terminal is connected via a ninth resistor to an output terminal of said second operational amplifier, non-reverse input terminal is connected via a tenth resistor to output terminal of said first operational amplifier and via an eleventh resistor to a reference voltage, and a reverse input terminal and output terminal are connected via a twelfth resistor.