Abstract:
A circuit may be configured to reduce the power consumption and extend the life of a near field transducer of a heat-assisted magnetic recording (HAMR) device by pulsing a laser. The current that drives the laser may be of a frequency and magnitude so as to approximate the value of a continuous current in a continuous, non-pulsed laser. A system on chip (SOC), which may include a HAMR channel, can generate a laser data signal that may be synchronous with, and offset from, a write signal by a certain period of time, and may calculate certain parameters such as peak current and pulse width that may be applied to the signals in a preamp. The preamp signals can be used to program data to a disc medium.

Description:
BACKGROUND 
     The present disclosure generally relates to data storage systems, such as disc memory. Specifically, the present disclosure relates to HAMR channel to preamp interface. 
     SUMMARY 
     In certain embodiments, an apparatus may comprise an output configured to provide a laser data signal to a preamp and a sub-circuit configured to manipulate the laser data signal prior to providing the laser data signal to the output. 
     In certain embodiments, an apparatus may comprise a data storage including a laser configured to heat a data storage medium and a preamp configured to provide laser current to the laser. The apparatus may further comprise a circuit having an output configured to provide a laser data signal to the preamp to generate the laser current. 
     In certain embodiments, a method may include determining a laser current required to heat a disc so that write data can be stored to a disc in a heat-assisted magnetic recording (HAMR) process and manipulating a laser data signal in a circuit prior to providing the laser data signal to a preamp. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of HAMR channel to preamp interface, in accordance with certain embodiments of the present disclosure; 
         FIG. 2  is a diagram of HAMR channel to preamp interface, in accordance with certain embodiments of the present disclosure; 
         FIG. 3  is a diagram of HAMR channel to preamp interface, in accordance with certain embodiments of the present disclosure; 
         FIG. 4  is a diagram of HAMR channel to preamp interface, in accordance with certain embodiments of the present disclosure; 
         FIG. 5  is a diagram of HAMR channel to preamp interface, in accordance with certain embodiments of the present disclosure; 
         FIG. 6  is a diagram of HAMR channel to preamp interface, in accordance with certain embodiments of the present disclosure; 
         FIG. 7  is a flowchart of a method of HAMR channel to preamp interface, in accordance with certain embodiments of the present disclosure; and 
         FIG. 8  is a flowchart of a method of HAMR channel to preamp interface, in accordance with certain embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description of the embodiments, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustrations. It is to be understood that features of the various described embodiments may be combined, other embodiments may be utilized, and structural changes may be made without departing from the scope of the present disclosure. It is also to be understood that features of the various embodiments and examples herein can be combined, exchanged, or removed without departing from the scope of the present disclosure. 
     Heat-assisted magnetic recording (HAMR) can use a laser to heat a disc medium and then magnetically record data to the disc. In some embodiments, a laser diode may generate laser light which may be sent to a near field transducer (NFT) where the signal can be conditioned and directed to the disc. In certain embodiments, the laser light may be continuous which can lead to high power consumption and premature failure of the data storage device (DSD) due to high wear on the NFT. 
     A laser light waveform, and a preceding laser current waveform, can be determined by firmware, hardware (e.g. as a controller), or another device such as a system on chip (SOC). In some embodiments, the waveform may be continuous, while in other embodiments, it may be modulated or pulsed. It may be possible to generate a modulated laser current (and by extension, a laser light) waveform whose average value is substantially equal to a comparable continuous laser current. The average value of the laser current can be a function of several parameters, including pulse width, and minimum and maximum current settings. 
       FIG. 1  depicts a system with a HAMR channel to preamp interface, generally designated  100 . Specifically, the system  100  provides a functional block diagram of a data storage device (DSD) and in particular, a hard disc drive with HAMR. The DSD  101  can optionally connect to be removable from a host device  102 , which can be a desktop computer, a laptop computer, a server, a telephone, a music player, another electronic device, or any combination thereof. The data storage device  101  can communicate with the host device  102  via the hardware/firmware based host interface circuit  104  that may include a connector (not shown) that allows the DSD  101  to be physically removed from the host  102 . 
     The DSD  101  can include a programmable controller  106  with associated memory  108  and processor  110 . The programmable controller  106  may be part of a system on chip (SOC). A buffer  112  can temporarily store user data during read and write operations and can include a command queue (CQ)  113  where multiple access operations can be temporarily stored pending execution. Further, the DSD  101  can include a read/write (R/W) channel  117 , which can also include a HAMR channel. The channel  117  can encode data during write operations and reconstruct user data during read operations. A preamplifier/driver circuit (preamp)  118  can apply write currents to the head(s)  119  and can provide pre-amplification of readback signals. The preamp  118  can also generate a laser data current that can drive a laser diode  126 , which can in turn heat the disc  109  for recording via the recording head  119 . A servo control circuit  120  may use servo data to provide the appropriate current to the coil  124  to position the head(s)  119  over disc(s)  109 . The controller  106  can communicate with a processor  122  to move the head(s)  119  to the desired locations on the disc(s)  109  during execution of various pending commands in the command queue  113  or during other operations. The channel configurations and systems described herein may be implemented in the R/W channel  117  as hardware circuits, software, memory, or any combination thereof. Further, the circuits described and shown in the DSD  101  may be incorporated into the SOC (not shown). 
     During operation of a HAMR channel, write data from the host  102  or other source may be sent to the preamp  118  via a channel-to-preamp interface (not shown); in certain embodiments, the channel-to-preamp interface may be positive emitter-coupled logic (PECL), emitter-coupled logic (ECL), or other type of logic interfaces. The write data may be conditioned in the preamp  118  and sent to a writer element (not shown) in the recording head  119 , which can then store the write data to the disc  109  in a heat-assisted magnetic recording (HAMR) process. 
     A system on chip (SOC) can interface with a preamp to generate a modulating laser signal. The SOC, which can include a HAMR channel, can determine constants and can program them to registers in the preamp, and may also generate a laser data signal that can be sent to a circuit within the preamp that can generate a laser current of a predetermined shape. The laser current can be directed to a laser diode which can generate a laser light (whose waveform may be substantially equal to that of the laser current) that may be used to heat the disc in a HAMR process. The write data signal from the host may be routed through the SOC to the preamp and may be directed to a recording head so that it may be stored to the disc. 
     Referring to  FIG. 2 , a diagram of a HAMR channel-to-preamp interface is shown and generally designated  200 . The SOC  202  can transmit the write data to the preamp  204 , where it can be conditioned (e.g. amplified, buffered, filtered, etc.) by a circuit  206 . The write signal may then be sent to a recording head  210  where it may drive a writer coil  212  to program the disc  218 . 
     The SOC  202 , which can include a HAMR channel, may generate a laser data signal and send it to the preamp  204 . A circuit  208  can generate a laser data current that can drive a laser diode  214  which may transmit the laser light to an NFT  216  which, in turn, can heat the disc  218  for HAMR recording. 
     Data can be read from the disc  218  by a reader element  220  and can be conditioned by a circuit  222  prior to reaching the SOC  202 . 
     The SOC  202  can program constants (for example, amplification, minimum and maximum laser current values, etc.) to the registers in the preamp  224  via an interface; in some embodiments, the interface may be a serial port. The constants in the registers may be changed anytime by the SOC  202 . 
     A write data signal from the host or other source may be routed to the disc via the system on chip (SOC) and the preamp, can have a minimum pulse width (the minimum required transition time necessary to write to a disc), 1T, and may have larger pulse widths (e.g. 3T). The SOC can generate a laser data signal that can instruct a preamp output to transition from a minimum laser current to a maximum laser current. Both the rising and falling edges of the laser data signal can trigger a low to high transition of the laser current signal. Furthermore, the laser data signal can be synchronous with the write signal and have a pulse width equal to 1T, but may lag the write signal by a time delay, Td, which can be determined by, and implemented in the HAMR channel. 
     The SOC can determine a laser current waveform required for heat-assisted magnetic recording in a particular environment (including temperature, writer coil, and so forth). The preamp can generate the laser current based on the laser data signal and the constants stored in its registers, such as pulse width and current values. The laser data current can drive a laser diode, which can produce a laser light with a substantially equal waveform to that of the laser current. The pulse width of the laser current signal, Tw, can be a constant value programmed to the preamp by the SOC (Tw may be recalculated and reprogrammed on the fly). As the pulse width increases, which may be up to a maximum of 1T, the duty cycle can increase until it reaches 100%. Conversely, the as the pulse width decreases, the duty cycle can reach 0 percent. A brief explanation regarding how Tw can affect the average current can be found later in this document. 
     Referring to  FIG. 3 , a diagram of a HAMR channel to preamp interface is shown and is generally designated  300 . A write data signal  302  may contain a data stream having a plurality of pulses, where each pulse may be one or more minimum pulse widths in duration. In an embodiment, there can be a minimum pulse width 1T, at  304 , and another pulse of duration 3T, at  306 . A laser data signal  308  may be synchronous with the write signal  302  and may be of a pulse duration 1T  304 , but may lag by a time Td  310  (Td can be determined by the SOC). 
     The laser current signal  312  can be generated by the preamp based on the laser data signal and the constants in the preamp registers. Similar to the laser signal  308 , the laser current  312  can lag the write signal  302  by a time Td, at  310 . The pulse duration of the laser current, Tw,  314  can be calculated by the SOC and programmed to the preamp. 
     The waveform of the laser light signal  318 , can be substantially equal to, and may be in synchrony with the laser current signal  312 . The time delay Td, at  316 , and pulse width  320  can be similar to the time delay Td,  310 , and pulse width  314  of the laser current signal. 
     An artifact of magnetic recording can be non-linearities at the low-to-high and high-to-low transitions of the write data signal. The write signal or the laser data signal may be transition shifted, or precompensated, by a time Tcomp to mitigate the effects of the non-linearities. 
     During precompensation, the pulse widths can be widened or shortened to avoid non-linearities at the transition points of the laser or write data signal. For example, referring to  FIG. 4 , a diagram of a HAMR channel to preamp interface is shown and is generally designated  400 . In the embodiment of  400 , the write signal  402  is precompensated  404 , and the widths of negative pulses may be narrowed by 2Tcomp  406 , which can result in the positive pulses being widened by 2Tcomp  408 . In another embodiment, the widths of the positive pulses may be narrowed while the widths of the negative pulses may be widened. 
     Referring to  FIG. 5 , a diagram of a HAMR channel to preamp interface is shown and is generally designated  500 . In this particular embodiment, the laser signal  502  can be precompensated  504 . The positive pulse width can be narrowed by 2Tcomp  506 , which can cause the negative pulse widths to be widened by 2Tcomp  508 . In another embodiment, precompensation of the laser signal can result in the positive pulse widths being widened and the negative pulse widths being narrowed. 
     In some embodiments, the SOC can set the operating points (values of the peak, continuous, and minimum currents, and so forth) and program them as constants to the preamp. In other embodiments, firmware or other circuits may set the operating points. The current constants, in conjunction with other parameters such as pulse width (discussed earlier) can be used by the preamp to generate a predetermined laser current waveform. 
     The average value of the pulsed laser current waveform can be determined by a minimum current, Imin, a peak current, Ipeak, and a pulse width, Tw. When Tw is equal to the laser data pulse width (1T) the laser current duty cycle can be at 100 percent and can be considered continuous with an average value equal to Ipeak. When Tw is 0, that is, when the duty cycle is 0 percent, the laser data can also be considered continuous with an average value equal to Imin. When the laser data current is not continuous, the average current can be a function of Imin, Ipeak, and Tw. For example, when Tw=T/2, the average laser data current can be (Ipeak−Imin)/2. 
     The values for Imin and Ipeak may be chosen for reasons other than to generate a laser data current with a specific average value. Other considerations, such as power supply capabilities and laser diode characteristics, may dictate what Imin and Ipeak can be. For example, the laser diode may have Ipeak restrictions because current that is too high can damage it. 
     The SOC and preamp may have different operating modes: continuous current and pulsed current. During continuous current mode operation, the SOC can stop generating a laser data signal, and the preamp can generate a dc laser current. In pulsed current mode operation, the preamp can generate a pulsed laser data current based on input from the laser data signal from SOC and the set operating points. 
     Referring to  FIG. 6 , a diagram of a HAMR channel to preamp interface is shown and is generally designated  600 . A pulsed laser current  602  and a continuous laser current  604  are plotted verse time. The pulsed current  602  has a peak current, Ipeak, and a minimum current, Imin, and a pulse width Tw  606 , and can be substantially equal to the continuous laser current  604 . 
     Precompensation, time delay and preamp constants may be set at startup. There may be circumstances, such as changes in the ambient temperature of the data storage device, where it may be beneficial to change the settings in the system on chip (SOC) as well as constants in the preamp. In some embodiments, SOC settings and preamp constants can be changed on the fly, and can take effect after the write data has been recorded to the disc. 
     Precompensation of a laser data signal or a write data signal can widen or shorten the signal&#39;s pulse width to avoid non-linearities at the transition points of the signal. The SOC can set the precompensation levels that were determined during an optimization process, such as during manufacturing. In some embodiments, the laser data signal may be precompensated, while in other embodiments, the write data signal can be precompensated. 
     When the selected signal is precompensated, both the laser data signal and the write data signal can be sent from the SOC to a preamp over an interface; in some embodiments, the interface can be positive emitter-coupled logic (PECL). The preamp can condition the write data signal and generate a laser current such that the write data can be stored. 
     Referring to  FIG. 7 , a flowchart of a method for a HAMR channel to preamp interface is shown and generally designated  700 . Firmware, which may use values from a read adapter parameter (RAP) file, can set SOC settings and preamp constants, at  702 , and a signal can be precompensated at  704 . The laser data signal and write data signal can be sent to the preamp from the SOC at  706 , and the write data signal can be recorded to the SOC at  708 . 
     Referring to  FIG. 8 , a flowchart of a method for a HAMR channel to preamp interface is shown and generally designated  800 . Initially, the SOC, which can use values from a RAP file, may program constants, such as peak and minimum current values, to registers in the preamp, at  802 . The SOC may determine whether to precompensate the write data signal or the laser data signal, at  804 , and then precompensate the write data signal or laser data signal, at  806  and  808 , respectively. 
     Once the constants have been programmed and the precompensation calculations have been made, the data storage device (DSD) may process write data from the host (or other source), and the SOC can generate a laser data signal, at  810 . The write signal and laser data signal may be transmitted from the HAMR channel to the preamp via an interface, such as an emitter-coupled logic (ECL) or a positive emitter-coupled logic (PECL), at  812 . The preamp can generate a laser current and route it to a laser diode at  814 , and the laser diode can generate a laser light with a waveform substantially equal to the laser current waveform. 
     Light from the laser diode can drive a near field transducer (NFT), at  816 . The NFT can condition the light signal and direct it to the disc so that the disc can be heated and the write data signal recorded in a HAMR process, at  818 . 
     After the data has been recorded, the DSD can determine if any changes to the SOC settings (e.g. Td, Tcomp, precompensation channel, laser data waveform, etc.) or preamp constants (e.g. Tw, Ipeak, Imin, etc.) need to be made at  820 . When changes are necessary, new constants can be programmed at  802 , otherwise the DSD may continue to process data at  810 . 
     In accordance with various embodiments, the methods described herein may be implemented as one or more software programs running on a computer processor or controller. In accordance with another embodiment, the methods described herein may be implemented as one or more software programs running on a computing device, such as a personal computer that is using a disc drive. Dedicated hardware implementations including, but not limited to, application specific integrated circuits, programmable logic arrays, and other hardware devices can likewise be constructed to implement the methods described herein. Further, the methods described herein may be implemented as a computer readable storage medium or device including instructions that when executed cause a processor to perform the methods. 
     The illustrations, examples, and embodiments described herein are intended to provide a general understanding of the structure of various embodiments. The illustrations are not intended to serve as a complete description of all of the elements and features of apparatus and systems that utilize the structures or methods described herein. Many other embodiments may be apparent to those of skill in the art upon reviewing the disclosure. Other embodiments may be utilized and derived from the disclosure, such that structural and logical substitutions and changes may be made without departing from the scope of the disclosure. Moreover, although specific embodiments have been illustrated and described herein, it should be appreciated that any subsequent arrangement designed to achieve the same or similar purpose may be substituted for the specific embodiments shown. 
     This disclosure is intended to cover any and all subsequent adaptations or variations of various embodiments. Combinations of the above examples, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the description. Additionally, the illustrations are merely representational and may not be drawn to scale. Certain proportions within the illustrations may be exaggerated, while other proportions may be reduced. Accordingly, the disclosure and the figures are to be regarded as illustrative and not restrictive.