# Patent

## Title
Disk drive slider with sense amplifier for coupling to a preamp through a supply/bias line and a read signal line

## Abstract

A disk drive slider is disclosed comprising a first read element for generating a first read signal, and a first sense amplifier comprising a first input terminal coupled to the first read element, a first output terminal coupled to a first output line, and a first supply terminal coupled to a supply line. The first sense amplifier is for amplifying the first read signal to generate a first amplified read signal, the first output line is for transmitting the first amplified read signal to a preamp, and the supply line is for coupling to the preamp in order to supply power to the first sense amplifier and supply a first bias to the first read element.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a divisional of U.S. patent application Ser. No. 14/090,873, filed on Nov. 26, 2013, which is hereby incorporated by reference in its entirety.


BACKGROUND
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 embedded servo sectors. The embedded servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo controller to control the actuator arm as it seeks from track to track.
A number of heads are typically fabricated on a substrate of a wafer (e.g., an aluminum titanium carbide (ALTiC) wafer) which is then sliced to form sliders. Each slider is coupled to one of the actuator arms through a suspension that biases the slider toward the disk surface. The slider comprises an air-bearing surface (ABS) wherein as the disk rotates, an air-bearing is formed between the slider and the disk that counteracts the bias force of the suspension. Accordingly, the head essentially flies just above the disk surface during write/read operations. Data is typically written to the disk by modulating a write current in an inductive coil of the head to record magnetic transitions onto the disk surface in a process referred to as saturation recording. During readback, the magnetic transitions are sensed by a read element (e.g., a magnetoresistive element) of the head and the resulting read signal demodulated by a suitable read channel.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A shows a disk drive according to an embodiment comprising a head fabricated on a slider that is actuated over a disk.
FIG. 1B shows an interconnect for connecting the first read element to a preamp through a first sense amplifier of the slider according to an embodiment.
FIG. 1C shows an embodiment wherein the first sense amplifier comprises a first input terminal coupled to the first read element, a first output terminal coupled to a first output line, and a first supply terminal coupled to a first input line.
FIG. 2 shows an embodiment of the first sense amplifier for amplifying a first read signal generated by the first read element.
FIG. 3 shows an embodiment wherein the slider comprises multiple read elements and a separate sense amplifier for amplifying each read signal generated by each read element.



DETAILED DESCRIPTION
FIG. 1A shows a disk drive comprising a head 2 actuated over a disk 4 according to an embodiment, wherein the head 2 is fabricated on a disk drive slider 6 (FIG. 1C) comprising a first read element 81 for generating a first read signal 101, and a first sense amplifier 121. The first sense amplifier 121 comprises a first input terminal coupled to the first read element 81, a first output terminal coupled to a first output line 141, and a first supply terminal coupled to a supply line 16. The first sense amplifier 121 is for amplifying the first read signal 101 to generate a first amplified read signal, the first output line 141 is for transmitting the first amplified read signal to a preamp 18, and the supply line 16 is for coupling to the preamp 18 in order to supply power to the first sense amplifier 121 and supply a first bias to the first read element 81.
In the embodiment of FIG. 1A, the preamp 18 is mounted on the side of an actuator arm 20 that is rotated about a pivot by a voice coil motor (VCM) 22. In one embodiment, the preamp 18 is coupled to the slider 6 through a suitable interconnect 24 an example of which is shown in FIG. 1B. In one embodiment, the interconnect 24 comprises a suitable flex circuit comprising any suitable number of transmission lines, including the first output line 141 and the supply line 16. In one embodiment, the first sense amplifier 121 of FIG. 1C provides an initial amplification of the first read signal 101 so as to reduce the effective distortions of the interconnect 24. That is, the first sense amplifier 121 may allow a gain of the preamp 18 to be reduced so as to reduce the noise amplification of the preamp 18. In addition, the first sense amplifier 121 may be fabricated so that it's output impedance better matches the impedance of the interconnect 24 transmission line and the preamp 18 as compared to the impedance of the first read element 81.
FIG. 1C illustrates another embodiment as comprising a disk drive preamp 18 comprising a supply line 16 for coupling to a first supply terminal of a first sense amplifier 121 of a slider 6, and a first input line 141 for coupling to a first output terminal of the first sense amplifier 121. The first sense amplifier 121 is for amplifying a first read signal generated by a first read element 81 of the slider 6 to generate a first amplified read signal. The first input line 141 is for receiving the first amplified read signal, and the supply line 16 is for supplying power to the first sense amplifier 121 and for supplying a first bias to the first read element 81.
The preamp 18 receives the amplified read signal from the first sense amplifier 121 over line 141 and further amplifies the read signal to generate an amplified read signal transmitted to control circuitry 26 over line 28 (FIG. 1A). The control circuitry 26 may process the amplified read signal in order to demodulate user data recorded on the disk 4 as well as servo data, such as servo data recorded in concentric servo sectors. The control circuitry 26 processes the servo data in order to generate an actuator control signal, such as a VCM control signal 30 applied to the VCM 22, in order to actuate the head 2 over the disk 4.
FIG. 2 shows an embodiment of the first sense amplifier 121 as an integrated circuit that may be fabricated with the slider 6 or fabricated separate from the slider 6 and then adhered to the slider 6. FIG. 2 shows a particular circuit configuration for implementing an amplifier; however, other embodiments may employ any suitable amplifier circuit configuration. In addition, the circuit components shown in FIG. 2 (resistors, transistors, capacitors, etc.) may take on any suitable values, and in one embodiment, the values may depend on the amplitude of the supply voltage applied to the first sense amplifier 121 over the supply line 16 as well as the desired amplitude range of the amplified read signal applied to the first output line 141.
In the embodiment of FIG. 2, the first sense amplifier 121 generates the first amplified read signal as a single ended signal as compared to a differential signal. That is, the first amplified read signal is generated relative to ground using a single polarity supply voltage. In an embodiment described below, generating the amplified read signal as a single ended signal enables a multiple read element head wherein the read signal generated by each read element is transmitted over a single transmission line to the preamp 18.
In the embodiment of FIG. 2, the preamp 18 comprises a suitable voltage source 32 for generating a supply voltage applied to the supply line 16. The supply voltage provides power to the first sense amplifier 121 as well biases the first read element 81. The preamp 18 in the embodiment of FIG. 2 also comprises a first current source 34 coupled to the first output line 141 of the first sense amplifier 121. In one embodiment, the first current source 34 is configured in order to control an output impedance of the first sense amplifier 121. For example, the first current source 34 may be configured to better match the output impedance of the first sense amplifier 121 to the transmission line as well as to the input impedance of the preamp 18.
FIG. 3 shows an embodiment wherein the slider 6 comprises multiple read elements 81-8N, including a second read element 82 for generating a second read signal, and a second sense amplifier 122 comprising a second input terminal coupled to the second read element 82, a second output terminal coupled to a second output line 142, and a second supply terminal coupled to the supply line 16. The second sense amplifier 122 is for amplifying the second read signal to generate a second amplified read signal. The second output line 142 is for transmitting the second amplified read signal to the preamp 18. The supply line 16 is for coupling to the preamp 18 in order to supply power to the second sense amplifier 122 and supply a second bias to the second read element 82.
The embodiment of FIG. 3 reduces the number of transmission lines in the flex circuit of the interconnect 24 (FIG. 1B) by using the supply line 16 to supply power and bias all of the read elements 81-8N of the slider 6. When the amplified read signals are generated as single ended signals such as shown in the embodiment of FIG. 2, the flex circuit of the interconnect 24 may comprise as few as N+1 transmission lines as compared to 4N transmission lines if each read element 81-8N were powered and biased using separate lines, and if each amplified read signal were generated as a differential signal.
Any suitable read element may be employed in the embodiments, such as a magnetoresistive (MR) read element having a resistance that varies relative to the magnetic field emanating from the surface of the disk. In one embodiment, the read element is biased (e.g., using a voltage or current applied over the supply line 16) so as to optimize the sensitivity of the read element. In an embodiment where the head 2 comprises multiple read elements 81-8N such as shown in the embodiment of FIG. 3, the control circuitry 26 (FIG. 1A) may execute a calibration procedure to determine an optimal bias setting for each read element. The control circuitry 26 may then configure the preamp 18 to bias the read elements 81-8N based on the optimal bias setting calibrated for each read element 81-8N. For example, the control circuitry 26 may configure the preamp 18 to apply an operating bias to at least two of the read elements 81-8N over the supply line 16, wherein the operating bias may be generated as the average (or other suitable statistic) of the optimal bias settings calibrated for each read element. In this manner, at least two of the read elements may operate in parallel, for example, to simultaneously read multiple data tracks, or to read a single data track using multiple read elements to improve the signal-to-noise ratio (SNR) by combining the resulting read signals.
In one embodiment the control circuitry 26 of FIG. 1A may comprise a suitable microprocessor executing instructions, the instructions being operable to cause the microprocessor to perform the embodiments described herein, such as executing the calibration procedure to configure the bias setting for the read elements as well as configure the preamp 18 during normal access operations. 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 26 comprises suitable logic circuitry, such as state machine circuitry.

## Claims

1. A disk drive comprising:
a disk;
a slider actuated over the disk, the slider comprising a first read element and a second read element; and
control circuitry configured to:
calibrate a first bias supplied to the first read element;
calibrate a second bias supplied to the second read element;
generate an operating bias based on the first bias and the second bias; and
apply the operating bias to the first read element and the second read element when reading data from the disk.

2. The disk drive as recited in claim 1, wherein the control circuitry is configured to generate the operating bias by averaging the first bias and the second bias.

3. A method of operating a disk drive comprising:
calibrating a first bias supplied to a first read element;
calibrating a second bias supplied to a second read element;
generating an operating bias based on the first bias and the second bias; and
applying the operating bias to the first read element and the second read element when reading data from a disk.

4. The method as recited in claim 3, further comprising generating the operating bias by averaging the first bias and the second bias.