Disk drive comprising current sense circuitry for a voice coil motor

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.