Architecture for dc bias canceling and gain recovery for hard disk drive fly height detection

A circuit for monitoring spacing between a disk drive head and a disk surface using a resistive sensor that detects variations in thermal conductivity as the disk drive head approaches the disk surface, the circuit comprising:

• a first transistor configured to receive a cancelation current, wherein the cancelation current is equal to a bias current flowing through the resistive sensor;
• a second transistor and a third transistor coupled to a first output node and a second output node, respectively;
• and
• a fourth transistor receiving a composite current comprising the bias current and a sensor signal current from the resistive sensor,
• wherein the first transistor, the second transistor, the third transistor, and the fourth transistor are arranged in a translinear configuration to generate differential output currents proportional to a sensing voltage while eliminating dependence on resistance value of the resistive sensor.

A method for monitoring spacing between a disk drive head and a disk surface using a resistive sensor, the method comprising:

• establishing a bias voltage across the resistive sensor through a voltage feedback loop to generate a bias current;
• generating a cancelation current equal to the bias current;
• receiving, at a translinear cell, the cancelation current and a composite current comprising the bias current and a sensor signal current, wherein the sensor signal current corresponds to variations in thermal conductivity as the disk drive head approaches the disk surface;
• generating, by the translinear cell, differential output currents proportional to a sensing voltage across the resistive sensor while eliminating dependence on resistance value of the resistive sensor;
• and
• processing the differential output currents to determine the spacing between the disk drive head and the disk surface.