Magnetic disk drive and voice coil motor drive circuit

A magnetic disk drive that drives and positions an actuator using a voice coil motor, and comprising:

• a current sensing resistor connected in series to a terminal on current input side of a 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 the current output side of said voice coil motor via a second resistor, a third resistor and a first capacitor are connected in parallel to a reference voltage, and a reverse input terminal and output terminal are connected in parallel to a fourth resistor and 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, a seventh resistor is connected to a reference voltage, and a reverse 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, a 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 an eighth resistor.

A magnetic disk drive that drives and positions an actuator with a voice coil motor, and comprising:

• a current sensing resistor connected in series to a terminal on the current input side of a voice coil motor;
• a first operational amplifier in which a reverse input terminal is connected via a first resistor to a terminal on the current input side of said voice coil motor, a non-reverse input terminal is connected via a second resistor to the current output side of said voice coil motor, a third resistor and a first capacitor are connected in parallel to a reference voltage, and a reverse input terminal and output terminal are connected in parallel by a fourth resistor and second capacitor;
• a second operational amplifier in which a reverse input terminal is connected via a fifth resistor to a terminal on the input side of current of said current sensing resistor, a non-reverse input terminal is connected via a sixth resistor to a terminal on the current output side of said current sensing resistor, a seventh resistor is connected to a reference voltage, and a reverse input terminal and output terminal are connected by an eighth resistor;
• and
• a microcomputer having an AD converter that encrypts the output of said first operational amplifier and said second operational amplifier, a sampler that samples this encrypted output of said first operational amplifier and second operational amplifier, and a computation means that subtracts this sampled output of first and second operational amplifiers.