Circuitry for linear control of head flying height using thermal means
View Patent ↗The spacing decrease between pole tips of a write element and a magnetic medium that is associated with the write element is linearly proportional to an input signal, such as an input voltage or current, to a slider flying height controller for a hard disk drive. The flying height controller includes a heater current controller and a multiplexer. The heater current controller receives the input signal and outputs a control current proportional to the input signal. The multiplexer couples the control current to a heating element associated with the write element on a selected slider body during a read operation. The heating element dissipates a power that is proportional to the control current and causes a decrease in the spacing between the pole tips of the write element and the magnetic medium that is linearly proportional to the control current and to the input signal.
1. A slider flying-height controller for a hard disk drive, the controller comprising:
a heater current controller including a square-root circuit that receives an input current and generates a first current that is proportional to the square root of the input current, the heater current controller outputting a control current that is proportional to the first current generated by the square root circuit in response to the input current; and
a multiplexer coupling the control current to a heating element associated with a write element on a selected slider body of the hard disk drive when the hard disk drive is in a read operation, the heating element dissipating a power that is proportional to the input current and causing a spacing decrease between pole tips of the write element and a magnetic medium that is associated with the write element that is proportional to the input current.
2. The controller according to claim 1 , wherein the first current is proportional to the square root of the product of the input current and a second current having a predetermined magnitude.
3. The controller according to claim 1 , wherein the heater current controller further includes a current-pass element coupled to the first current and outputting the control current.
4. The controller according to claim 3 , further comprising a low-pass filter coupled to the output of the heater current controller that reduces high frequency disturbances in the output of the heater current controller.
5. The controller according to claim 3 , wherein the heater current controller further includes a current-to-voltage converter that receives the first current and produces a voltage that is coupled to the current-pass element, and wherein the control current output from the current-pass element generates a voltage across the heater clement that is proportional to the first current.
6. The controller according to claim 5 , wherein current-to-voltage converter includes:
a resistor through which the first current passes and generates a first voltage; and
an operational transconductance amplifier that receives the first voltage and outputs a third current that drives the current-pass element.
7. The controller according to claim 6 , wherein the current-to-voltage converter includes a low-pass filter coupled to the output of the operational transconductance amplifier that reduces high frequency disturbances in the output of the operational transconductance amplifier.
8. The controller according to claim 1 , wherein the input current is generated by a digital-to-analog converter based on selected data input to the digital-to-analog converter.
9. The controller according to claim 1 , further comprising a common voltage level generator having an output that is connected to complete a current path for the control current through the heating element.
10. The controller according to claim 9 , wherein the common voltage level is a potential that is different from ground.
11. The controller according to claim 9 , wherein the common voltage level is selected to maximize a voltage headroom for the heating element.
12. The controller according to claim 1 , wherein the controller is part of a read/write electronics module for the hard disk drive.
13. A hard disk drive, comprising:
a plurality of slider bodies, each slider body including at least one read element and at least one write element; and
a read/write electronics module including:
a heater current controller including a square-root circuit that receives an input current and generates a first current that is proportional to the square root of the input current, the heater current controller outputting a control current that is proportional to the first current generated by the square root circuit in response to the input current; and
a multiplexer coupling the control current to a heating element associated with a write element on a selected slider body when the hard disk drive is in a read operation, the heating element dissipating a power that is proportional to the input current and causing a spacing decrease between pole tips of the write element and a magnetic medium that is associated with the write element that is proportional to the input current.
14. The hard disk drive according to claim 13 , wherein the first current is proportional to the square root of the product of the input current and a second current having a predetermined magnitude.
15. The hard disk drive according to claim 13 , wherein the heater current controller further includes a current-pass element coupled to the first current and outputting the control current.
16. The hard disk drive according to claim 15 , further comprising a low-pass filter coupled to the output of the heater current controller that reduces high frequency disturbances in the output of the heater current controller.
17. The hard disk drive according to claim 15 , wherein the heater current controller further includes a current-to-voltage converter that receives the first current and produces a voltage that is coupled to the current-pass element, and
wherein the control current output from the current-pass element generates a voltage across the heater element that is proportional to the first current.
18. The hard disk drive according to claim 17 , wherein current-to-voltage converter includes:
a resistor through which the first current passes and generates a first voltage; and
an operational transconductance amplifier that receives the first voltage and outputs a third current that drives the current-pass element.
19. The hard disk drive according to claim 18 , wherein the current-to-voltage converter includes a low-pass filter coupled to the output of the operational transconductance amplifier that reduces high frequency disturbances in the output of the operational transconductance amplifier.
20. The hard disk drive according to claim 13 , wherein the input current is generated by a digital-to-analog converter based on selected data input to the digital-to-analog converter.
21. The hard disk drive according claim 13 , wherein the read/write electronics module further includes a common voltage level generator having an output that is connected to complete a current path for the control current through the heating element.
22. The hard disk drive according to claim 21 , wherein the common voltage level is a potential that is different from ground.
23. The hard disk drive according to claim 21 , wherein the common voltage level is selected to maximize a voltage headroom for the heating element.