Patent ID: 6850383

Claim:
A disk drive comprising: (a) a disk; (b) an actuator arm; (c) a head connected to a distal end of the actuator arm; (d) a voice coil motor (VCM) comprising a voice coil, the VCM for rotating the actuator arm about a pivot to actuate the head radially over the disk; and (e) a VCM driver comprising: an H-bridge driver comprising a plurality of driver switches for driving current from a supply voltage through the voice coil to ground; a first sense resistor-connected in series between the supply voltage and at least one of the driver switches; a second sense resistor connected in series between at least one of the driver switches and ground; a first transistor having a first transistor terminal, a second transistor terminal, and a gate terminal; a second transistor having a first transistor terminal, a second transistor terminal, and a gate terminal; a third sense resistor having a first end connected to a node between the first sense resistor and the at least one of the driver switches and a second end connected to the first transistor terminal of the first transistor; a fourth sense resistor having a first end connected to a node between the second sense resistor and the at least one of the driver switches and a second end connected to the first transistor terminal of the second transistor; a first gain resistor having a first end and a second end, wherein: the first end is connected to at least the second transistor terminal of the first transistor; the second end connected to a reference voltage; and when the gate terminals of the first and second transistors are forward biased, a voltage across the gain resistor represents the current flowing through the voice coil.