# Patent

## Title
Data storage device comprising spindle motor current sensing with supply voltage noise attenuation

## Abstract

A data storage device is disclosed comprising a head actuated over a disk and a spindle motor configured to rotate the disk, wherein the spindle motor comprises a plurality of windings. The spindle motor is powered with a power voltage generated in response to a supply voltage. A clamping circuit is enabled when sensing a current flowing from the power voltage through at least one of the windings, wherein the clamping circuit is configured to clamp the power voltage to less than a peak voltage of the supply voltage in order to attenuate noise in the power voltage. The clamping circuit is disabled when not sensing the current.

## Background
BACKGROUND
Data storage devices such as disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and servo sectors. The servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo control system to control the actuator arm as it seeks from track to track.
FIG. 1 shows a prior art disk format 2 as comprising a number of servo tracks 4 defined by servo sectors 60-6N recorded around the circumference of each servo track. Each servo sector 6i comprises a preamble 8 for storing a periodic pattern, which allows proper gain adjustment and timing synchronization of the read signal, and a sync mark 10 for storing a special pattern used to symbol synchronize to a servo data field 12. The servo data field 12 stores coarse head positioning information, such as a servo track address, used to position the head over a target data track during a seek operation. Each servo sector 6i further comprises groups of servo bursts 14 (e.g., N and Q servo bursts), which are recorded with a predetermined phase relative to one another and relative to the servo track centerlines. The phase based servo bursts 14 provide fine head position information used for centerline tracking while accessing a data track during write/read operations. A position error signal (PES) is generated by reading the servo bursts 14, wherein the PES represents a measured position of the head relative to a centerline of a target servo track. A servo controller processes the PES to generate a control signal applied to a head actuator (e.g., a voice coil motor) in order to actuate the head radially over the disk in a direction that reduces the PES.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a prior art disk format comprising a plurality of servo tracks defined by servo sectors.
FIG. 2A shows a data storage device in the form of a disk drive according to an embodiment comprising a head actuated over a disk rotated by a spindle motor comprising a plurality of windings and powered by a power voltage generated in response to a supply voltage.
FIG. 2B is a flow diagram according to an embodiment wherein when sensing current flowing from the power voltage through at least one of the windings, the power voltage is clamped to less than a peak voltage of the supply voltage.
FIG. 2C illustrates the clamping of the power voltage when sensing the current in order to attenuate noise in the power voltage.
FIG. 3 shows an embodiment wherein a suitable clamp circuit is enabled/disabled based on whether the control circuitry is sensing the current flowing through at least one of the windings.
FIG. 4 shows an embodiment wherein the clamping circuit comprises a clamping field effect transistor (FET) configured as a source follower and controlled by a command voltage to clamp the power voltage.
FIG. 5 shows an embodiment wherein a feedback loop generates a gate voltage of the clamping FET based on a difference between the source voltage and the command voltage.
FIG. 6 shows an embodiment wherein a current sensor senses the current flowing through the clamping FET when sensing the current flowing through at least one of the windings.
FIGS. 7A and 7B illustrate an embodiment wherein when the supply voltage falls below a threshold the clamping FET is configured into an isolation mode by disconnecting the P-well body from the source and connecting the P-well body to the drain.



DETAILED DESCRIPTION
FIG. 2A shows a data storage device in the form of a disk drive according to an embodiment comprising a head 16 actuated over a disk 18 and a spindle motor 20 configured to rotate the disk 18, wherein the spindle motor 20 comprises a plurality of windings. The spindle motor 20 is powered with a power voltage generated in response to a supply voltage 22. The disk drive further comprises control circuitry 24 configured to execute the flow diagram of FIG. 2B, wherein when sensing a current flowing from the power voltage through at least one of the windings (block 26), the power voltage is clamped to less than a peak voltage of the supply voltage in order to attenuate noise in the power voltage (block 28). When not sensing the current (block 30), the clamping of the power voltage is disabled (block 32).
The control circuitry 24 may be configured to sense the current flowing from the power voltage through at least one of the windings of the spindle motor 20 for any suitable reason. In one embodiment, the current flowing through the windings may be sensed in order to detect the position of the rotor relative to the stator which may be useful to determine the initial state of a commutation sequence prior to spinning up the spindle motor 20. In the embodiment of FIG. 2A, the current 34 flowing through the windings is a function of the power voltage used to power the spindle motor 20. If the power voltage is generated as the supply voltage 22, the current sensing may be adversely affected by any noise in the supply voltage 22, such as the noise illustrated in the example of FIG. 2C. Accordingly, in one embodiment the power voltage for powering the spindle motor 20 may be clamped to a level below the peak voltage of the supply voltage, for example, to a level that is substantially equal to the peak voltage minus the amplitude of the noise in the supply voltage 22 as illustrated in FIG. 2C. In this manner, the noise in the power voltage is attenuated which increases the accuracy of the current sensing.
FIG. 3 shows control circuitry configured to control the operation of the spindle motor, including a clamp circuit 36 configured to clamp the power voltage 38 to less than the supply voltage 22 when sensing the current flowing through at least one winding of the spindle motor 20. During normal operation of the spindle motor 20, a back electromotive force (BEMF) voltage 40 generated by the windings of the spindle motor 20 may be processed in order to drive the commutation sequence of a commutation controller 42. A spindle control block 44 may process a BEMF signal 46 which may be a square wave representing the BEMF zero-crossings as detected by a BEMF detector 48. The commutation controller 42 may generate a control signal 50 which configures the BEMF detector 48 to detect the zero-crossing of the BEMF voltage generated by each winding as the disk rotates. The commutation controller 42 also generates a control signal 52 applied to commutation logic 54. In the embodiment of FIG. 3, the commutation logic 54 is configured by the control signal 52 to control the state of switches 56 in order to drive the windings with the power voltage 38. The commutation logic 54 may operate in any suitable manner, such as by driving the switches 56 as linear amplifiers that apply continuous-time sinusoidal voltages to the windings. In another embodiment, the commutation logic 54 may drive the switches 56 using pulse wide modulation (PWM), such as using square wave PWM, trapezoidal PWM, or sinusoidal PWM. Regardless as to how the windings are driven, the commutation controller 42 generates the control signal 52 so that the windings are commutated at the correct periods, thereby generating the desired rotating magnetic field that causes the spindle motor to rotate. In one embodiment, the spindle control block 44 may generate a control signal 58 that controls the effective amplitude of the driving voltages (continuous or PWM), thereby controlling the speed of the spindle motor 20.
When sensing the current flowing through at least one of the windings, for example, to detect the position of the rotor relative to the stator at the beginning of a spin-up operation, the clamp circuit 36 is enabled by control signal 60 to clamp the power voltage 38 less than the peak voltage of the supply voltage 22 as described above with reference to FIG. 2C, thereby attenuating noise in the power voltage 38. The current flowing from the power voltage 38 through at least one of the windings may be sensed in any suitable manner. In one embodiment, the switches 56 shown in FIG. 3 may comprise suitable circuitry for sensing the current flowing through the windings, and in other embodiment described below, the current flowing through the windings may be sensed by sensing the current flowing through the clamp circuit 36, or by sensing the current flowing through an isolation FET (ISOFET).
FIG. 4 shows an embodiment wherein the clamp circuit 36 comprises a clamping FET 62 configured as a source follower, wherein the control circuitry enables the clamping circuit 36 by adjusting a command voltage 64 configured to control a gate of the clamping FET 62. For example, in one embodiment the control circuitry configures the command voltage 64 to approximately:

Vd_peak−NoiseAmp+Vth

where Vd_peak represents the peak voltage of the supply voltage 22, NoiseAmp represents a noise amplitude in the supply voltage 22, and Vth represents a threshold voltage of the clamping FET 62. In this manner, the source voltage of the clamping FET 62 (and therefore the power voltage 38) is clamped to:

Vd_peak−NoiseAmp

as shown in the example of FIG. 2C, thereby attenuating the noise in the power voltage 38 during the current sense mode.

The embodiment of FIG. 4 also comprises an isolation FET (ISOFET) 66 which is configured to an ON state during normal operation. If the supply voltage 22 falls below a threshold (e.g., during a power failure), the ISOFET 66 is configured into an OFF state so that the body diode of the ISOFET 66 prevents current from flowing from the power voltage to the supply voltage 22. In one embodiment illustrated in FIG. 4, suitable current sensing circuitry 68 is coupled to the ISOFET 66 in order to sense the current flowing through the ISOFET 66 and therefore sense the current flowing through at least one of the windings of the spindle motor 20 during the current sense mode.
FIG. 5 shows an embodiment wherein the control circuitry 24 enables the clamping circuit 36 by setting a command voltage 70 to approximately:

Vd_peak−NoiseAmp

and using a feedback loop to generate a gate voltage 72 based on a difference (generated by comparator 74) between a source voltage of the clamping FET 62 and the command voltage 70. The gate voltage 72 is applied to the gate of the clamping FET 62 which drives the source voltage (and power voltage 38) to the desired clamp level.

In the embodiments described above with reference to FIGS. 4 and 5, when not sensing the current flowing through at least one of the windings the control circuitry 24 may disable the clamping circuit 36 by increasing the command voltage (64 or 70) to a suitable level. For example, in one embodiment the control circuitry 24 may increase the command voltage to a level higher than the supply voltage 22 (using a suitable boost circuit) so that there is no clamping of the power voltage 38 relative to the supply voltage 22 when the clamping circuit 36 is in the disabled state. In another embodiment, the control circuitry 24 may configure the command voltage to near the peak voltage of the supply voltage 22 or a suitable margin below the peak voltage so that the clamping circuit 36 may still provide some amount of clamping of the power voltage 38 even when the clamping circuit 36 is in the disabled state.
FIG. 6 shows an embodiment wherein the ISOFET 66 in FIG. 4 is removed and the clamping FET 62 is configured into an isolation mode when the supply voltage 22 falls below a threshold (e.g., during a power failure). In one embodiment illustrated in FIG. 6, suitable current sensing circuitry 76 is coupled to the clamping FET 62 in order to sense the current flowing through the clamping FET 62 and therefore sense the current flowing through at least one of the windings of the spindle motor 20 during the current sense mode.
FIGS. 7A and 7B illustrate an embodiment wherein the clamping FET 62 is configured by switch 78 to clamp the power voltage 38 when in the current sense mode. When the supply voltage 22 falls below a threshold (e.g., during a power failure), the clamping FET 62 is configured into an isolation mode by configuring switch 78 to disconnect a P-well body of the clamping FET 62 from a source of the clamping FET 62 and connecting the P-well body of the clamping FET 62 to a drain of the clamping FET 62. This effectively configures the clamping FET 62 into a diode that prevents current from flowing from the power voltage 38 to the supply voltage 22 similar to the body diode in the ISOFET 66 of FIG. 4. In another embodiment (not shown), the clamping FET 62 may be configured into an isolation mode by connecting the gate terminal and the P-well body to ground. This latter embodiment assumes the supply voltage 22 remains below a threshold level that would otherwise damage the clamping FET 62 when in the isolation mode.
The clamping circuit 36 of FIG. 3 may be configured to clamp the power voltage 38 to any suitable level relative to the supply voltage 22. In one embodiment, the clamping level may be selected to be lower than the amplitude of the noise as shown in the example of FIG. 2C, but in other embodiments the clamping level may be set somewhat higher so as to attenuate some but not all of the noise in the supply voltage 22. In one embodiment, the noise amplitude of the supply voltage 22 may be predetermined by evaluating a number of disk drives in different operating environments and evaluating the maximum noise amplitude affecting the supply voltage 22. In another embodiment, the control circuitry 24 may measure the noise amplitude in the supply voltage 22 prior to entering the current sense mode, and then configure the clamping circuit 36 in order to attenuate the noise level in the power voltage 38 relative to the measured noise amplitude in the supply voltage 22.
Any suitable control circuitry may be employed to implement the flow diagrams in the above embodiments, such as any suitable integrated circuit or circuits. For example, the control circuitry may be implemented within a read channel integrated circuit, or in a component separate from the read channel, such as a disk controller, or certain operations described above may be performed by a read channel and others by a disk controller. In one embodiment, the read channel and disk controller are implemented as separate integrated circuits, and in an alternative embodiment they are fabricated into a single integrated circuit or system on a chip (SOC). In addition, the control circuitry may include a suitable preamp circuit implemented as a separate integrated circuit, integrated into the read channel or disk controller circuit, or integrated into a SOC.
In one embodiment, the control circuitry comprises a microprocessor executing instructions, the instructions being operable to cause the microprocessor to perform the flow diagrams described herein. The instructions may be stored in any computer-readable medium. In one embodiment, they may be stored on a non-volatile semiconductor memory external to the microprocessor, or integrated with the microprocessor in a SOC. In another embodiment, the instructions are stored on the disk and read into a volatile semiconductor memory when the disk drive is powered on. In yet another embodiment, the control circuitry comprises suitable logic circuitry, such as state machine circuitry.
In various embodiments, a disk drive may include a magnetic disk drive, an optical disk drive, etc. In addition, while the above examples concern a disk drive, the various embodiments are not limited to a disk drive and can be applied to other data storage devices and systems, such as magnetic tape drives, solid state drives, hybrid drives, etc. In addition, some embodiments may include electronic devices such as computing devices, data server devices, media content storage devices, etc. that comprise the storage media and/or control circuitry as described above.
The various features and processes described above may be used independently of one another, or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of this disclosure. In addition, certain method, event or process blocks may be omitted in some implementations. The methods and processes described herein are also not limited to any particular sequence, and the blocks or states relating thereto can be performed in other sequences that are appropriate. For example, described tasks or events may be performed in an order other than that specifically disclosed, or multiple may be combined in a single block or state. The example tasks or events may be performed in serial, in parallel, or in some other manner. Tasks or events may be added to or removed from the disclosed example embodiments. The example systems and components described herein may be configured differently than described. For example, elements may be added to, removed from, or rearranged compared to the disclosed example embodiments.
While certain example embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions disclosed herein. Thus, nothing in the foregoing description is intended to imply that any particular feature, characteristic, step, module, or block is necessary or indispensable. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the embodiments disclosed herein.

## Claims

1. A data storage device comprising:
a disk;
a spindle motor configured to rotate the disk, wherein the spindle motor comprises a plurality of windings;
a head actuated over the disk; and
control circuitry configured to:
power the spindle motor with a power voltage generated in response to a supply voltage;
enable a clamping circuit when sensing a current flowing from the power voltage through at least one of the windings, wherein the clamping circuit is configured to clamp the power voltage to less than a peak voltage of the supply voltage in order to attenuate noise in the power voltage; and
disable the clamping circuit when not sensing the current.

2. The data storage device as recited in claim 1, wherein the clamping circuit is further configured to clamp the power voltage to approximately:


Vd_peak−NoiseAmp

where:
Vd_peak represents the peak voltage of the supply voltage; and
NoiseAmp represents a noise amplitude in the supply voltage.

3. The data storage device as recited in claim 1, wherein:
the clamping circuit comprises a field effect transistor (FET) configured as a source follower; and
the control circuitry is further configured to enable the clamping circuit by adjusting a command voltage configured to control a gate of the FET.

4. The data storage device as recited in claim 3, wherein the control circuitry is further configured to enable the clamping circuit by setting the command voltage to approximately:


Vd_peak−NoiseAmp+Vth

where:
Vd_peak represents the peak voltage of the supply voltage;
NoiseAmp represents a noise amplitude in the supply voltage; and
Vth represents a threshold voltage of the FET.

5. The data storage device as recited in claim 3, wherein the control circuitry is further configured to enable the clamping circuit by setting the command voltage to approximately:


Vd_peak−NoiseAmp

and using a feedback loop to generate a gate voltage based on a difference between a source voltage of the FET and the command voltage, where:
the gate voltage is applied to the gate of the FET;
Vd_peak represents the peak voltage of the supply voltage;
NoiseAmp represents a noise amplitude in the supply voltage; and
Vth represents a threshold voltage of the FET.

6. The data storage device as recited in claim 3, wherein when the supply voltage falls below a threshold, the control circuitry is further configured to configure the FET into an isolation mode to substantially prevent current flowing from the power voltage to the supply voltage.

7. The data storage device as recited in claim 6, wherein the control circuitry is further configured to configure the FET into the isolation mode by disconnecting a P-well body of the FET from a source of the FET and connecting the P-well body of the FET to a drain of the FET.

8. A method of operating a data storage device, the method comprising:
powering a spindle motor with a power voltage generated in response to a supply voltage, wherein the spindle motor comprises a plurality of windings and the spindle motor is configured to rotate a disk while actuating a head over the disk;
clamping the power voltage to less than a peak voltage of the supply voltage in order to attenuate noise in the power voltage when sensing a current flowing from the power voltage through at least one of the windings; and
disabling the clamping when not sensing the current.

9. The method as recited in claim 8, further comprising clamping the power voltage to approximately:


Vd_peak−NoiseAmp

where:
Vd_peak represents the peak voltage of the supply voltage; and
NoiseAmp represents a noise amplitude in the supply voltage.

10. The method as recited in claim 8, further comprising clamping the power voltage by adjusting a command voltage configured to control a gate of a field effect transistor (FET), wherein the FET is configured as a source follower.

11. The method as recited in claim 10, further comprising clamping the power voltage by setting the command voltage to approximately:


Vd_peak−NoiseAmp+Vth

where:
Vd_peak represents the peak voltage of the supply voltage;
NoiseAmp represents a noise amplitude in the supply voltage; and
Vth represents a threshold voltage of the FET.

12. The method as recited in claim 10, further comprising clamping the power voltage by setting the command voltage to approximately:


Vd_peak−NoiseAmp

and using a feedback loop to generate a gate voltage based on a difference between a source voltage of the FET and the command voltage, where:
the gate voltage is applied to the gate of the FET;
Vd_peak represents the peak voltage of the supply voltage;
NoiseAmp represents a noise amplitude in the supply voltage; and
Vth represents a threshold voltage of the FET.

13. The method as recited in claim 10, wherein when the supply voltage falls below a threshold, further comprising configuring the FET into an isolation mode to substantially prevent current flowing from the power voltage to the supply voltage.

14. The method as recited in claim 13, further comprising configuring the FET into the isolation mode by disconnecting a P-well body of the FET from a source of the FET and connecting the P-well body of the FET to a drain of the FET.

15. Control circuitry configured to:
power a spindle motor with a power voltage generated in response to a supply voltage, wherein the spindle motor comprises a plurality of windings and the spindle motor is configured to rotate a disk while actuating a head over the disk;
enable a clamping circuit when sensing a current flowing from the power voltage through at least one of the windings, wherein the clamping circuit is configured to clamp the power voltage to less than a peak voltage of the supply voltage in order to attenuate noise in the power voltage; and
disable the clamping circuit when not sensing the current.

16. The control circuitry as recited in claim 15, wherein the clamping circuit is further configured to clamp the power voltage to approximately:


Vd_peak−NoiseAmp

where:
Vd_peak represents the peak voltage of the supply voltage; and
NoiseAmp represents a noise amplitude in the supply voltage.

17. The control circuitry as recited in claim 15, wherein:
the clamping circuit comprises a field effect transistor (FET) configured as a source follower; and
the control circuitry is further configured to enable the clamping circuit by adjusting a command voltage configured to control a gate of the FET.

18. The control circuitry as recited in claim 17, wherein when the supply voltage falls below a threshold, the control circuitry is further configured to configure the FET into an isolation mode to substantially prevent current flowing from the power voltage to the supply voltage.

19. The control circuitry as recited in claim 18, further configured to configure the FET into the isolation mode by disconnecting a P-well body of the FET from a source of the FET and connecting the P-well body of the FET to a drain of the FET.