Abstract:
A current gain control system is described and comprises first and second gain blocks respectively associated with the first and second input channels, wherein first and second gain blocks transmit first and second gain signals in response to receiving first and second input signals; first and second converters adapted to be respectively coupled to the first and second gain blocks, the first and second converters operative for setting gains associated with the first and second input channel and for transmitting first and second converted signals in response to receiving the first and second gain signals; and first and second switches for selectively coupling the first and second converters to first and second channel drivers, respectively, wherein the first and second channel drivers transmit channel gain signals in response to receiving the first converted signal, and the channel gain signal allows control of the gain associated with the input channel.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
       [0001]    The present application claims priority to jointly owned U.S. Provisional Application corresponding to application No. 61/186,190 entitled, “Laser Diode Driver Current Input Signal Processing System.” This provisional application was filed on Jun. 11, 2009. The present application also claims priority to jointly owned U.S. Provisional Application corresponding to application No. 61/186,223 entitled, “Current Gain Control System.” This provisional application was filed on Jun. 11, 2009. 
     
    
     DESCRIPTION OF RELATED ART 
       [0002]    With the evolution of electronic devices, there is a continual demand for enhanced speed, capacity and efficiency in various areas including electronic data storage. Motivators for this evolution may be the increasing interest in video (e.g., movies, family videos), audio (e.g., songs, books), and images (e.g., pictures). Optical disk drives have emerged as one viable solution for supplying removable high capacity storage. When these drives include light sources, signals sent to these sources should be properly processed to reduce potential damage in appropriate light emission. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]    The current gain control system may be better understood with reference to the following figures. The components within the figures are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts or blocks throughout the different views. 
           [0004]      FIG. 1A , is a system drawing illustrating components within an optical disk drive. 
           [0005]      FIG. 1B  is an environmental drawing including a laser diode driver current input signal processing system. 
           [0006]      FIG. 2A-2B  are block diagrams illustrating one implementation of the current gain control system. 
           [0007]      FIG. 3A  is a graph illustrating output power variation with current. 
           [0008]      FIGS. 3B-3C  are graphs illustrating two different pulse types. 
       
    
    
       [0009]    While the current gain control system is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and subsequently are described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the current gain control system to the particular forms disclosed. In contrast, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the current gain control system as defined by this document. 
       DETAILED DESCRIPTION OF EMBODIMENTS 
       [0010]    As used in the specification and the appended claim(s), the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Similarly, “optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not. 
         [0011]    Turning now to  FIG. 1A , is a system drawing illustrating components within an optical disk drive  100 . A controller  102  monitors the output light power level of a laser diode  115  using a Monitor PD  104 , or monitor phorodiode, and an RF, or radio frequency, preamplifier  106 . This controller can keep an expected power level by changing an input control current of a laser driver  110  through an APC, or auto power controlling, feedback loop, even if a light source  115  such as a laser diode, has many changes of the output power due to various condition changes, such as temperature etc. 
         [0012]    Also, the controller  102  sets the enable signal for switching some current channels of the laser driver  110 , which arranges a data writing pulse. In the case of data reading, the controller  102  may only set the DC current by disabling the switching and applying the indicated input current. In the case of data writing, the controller  102  applies some adjustment signals, or enable-switching signals, to arrange the writing pulse waveform as a combination of switching timing, which also changes the power level by different indicated current of each channel. The controller  102  can arrange these indicated currents based on the Monitor PD  104  output with some detecting function in the RF preamplifier  106 . At the very least, this controller has two controlling levels for the reading power and the writing power. Sometimes the controller may get the top, bottom, or average level of a writing pulse and calculate to control some power levels independently. 
         [0013]    As illustrated in this figure, the laser driver  110  sends a signal that prompts an associated light source  115  (e.g., laser diode) to emit light. The light source  115  may emit light at any of a number of wavelengths (e.g., 400 nm, 650 nm, 780 nm). Light from this source contacts an associated optical media  117 , such as a compact disc (CD), blue ray device (Blu-ray), or digital versatile disk (DVD). Light contacting the optical media can either facilitate data storage or data retrieval from the optical media  117 . 
         [0014]      FIG. 1B  is an enlarged view of the innovative laser driver  110 , which may be a laser diode drive (LDD). The LDD  110  is an integrated, fully programmable, multi-function product that controls and drives laser diodes (e.g., light source  115 ) within optical drives as described with reference to  FIG. 1A . More specifically, the LDD  110  can apply the current for the read, write, and erase removable high capacity disks capacities greater than approximately 50 Gbytes/disk). The LDD  110  also has low noise (e.g., noise of approximately 0.5 nA/rt-Hz), high speed (e.g., 1 Gb/s, 0.850 Gb/s) and high current (e.g., approximately 1 amp). Any numbers included in this application are for illustrative purposes only and numerous alternative implementations may result from selecting different quantitative values. 
         [0015]    At a high level, the LDD  110  may include a current generator  120 . Generally, the current generator  120  receives some input signals  123  associated with several input channels, which have an associated input current. This current generator  120  works in tandem with a current driver  140  and produces a gain for the input current. As a result, the current generator  120  and current driver  140  control the amount of current for each output channel  145 . For the input signals that the current generator  120  receives, it transmits output signals that a current switch  130  receives. The current switch  130  decides which of the input channels should be turned on or turned off. For the channels that should be turned on, the current switch  130  makes those channels active. Similarly, the current switch  130  inactivates the channels that should be turned off and transmits output signals reflecting this change. The current driver  140  receives these output signals from the current switch  130  as input signals. The current driver  140  is the last current gain stage and drives the laser diodes directly. In other words, the output signals from the current driver  140  also serve as output signals for the LDD  110 , which are used in driving the lasers, or the light source  115  (see  FIG. 1A ). 
         [0016]    In addition to the above-mentioned devices, the LDD  110  includes additional components. A serial interface (I/F)  150  has several inputs  155  (e.g., serial data enable, serial data, serial clock) that may be used for an enable, feature selection, or setting the gain. Like the serial interface  150 , the timing generator  160  receives various channel enable inputs  165 . Though there are five channel enable inputs that are shown in  FIG. 1B , the LDD  110  may have any number of channel enable inputs, such as two, six, or the like. The timing generator  160  determines the time at which a given input channel will be either turned on or turned off. The LDD  110  also includes a high Frequency modulator (HFM)  170  and voltage/temperature monitor (V/Temp Monitor)  180 . The HFM  170  modulates the output current for reducing mode-hopping noise of the laser diodes. The voltage/temperature monitor  190  monitors the laser diode voltage drop and on-chip temperature. One skilled in the art will appreciate that numerous alternative implementations may result from removing any or several of the blocks within the LDD  110 . 
         [0017]    Typical drivers do not have an independent setting or adjusting function for gain of each current channel. In contrast, the innovative LDD  110  includes current gain control system (CGCS) that allows independent control of gain for each input current channel. The CGCS generates current for the LDD  110  based on the current input and the current gain of each channel. This current is essentially the summation of all channel currents. Each channel&#39;s current is defined by the relation, “channel gain ratio x input current of channel.” In the case of writing the information data on the optical media  117 , the LDD  110  normally turns on with writing current. 
         [0018]    In  FIG. 1B , this CGCS is shown as having three different sections housed in different parts of the LDD  110 , but an alternative implementation may include a different number of sections. More specifically, the current generator  120  includes a CGCS  129 , while the current switch  130  includes a CGCS  133 . The current driver  140  also includes a CGCS  147 . With these three sections, the innovative CGCS is applicable to various types of disc, like CD, DVD, and Blu-ray, as well as various types of optical pick up units. For example, this CGCS may be applicable to any one of the following types of or address variations for the optical pick-up units slim drive and half-height drive. To accomplish this, the current gain for each channel may be changed by using a serial interface setting associated with the serial interface (I/F)  150 . 
         [0019]    Turning now to  FIGS. 2A-2B , these figures show a block diagram  200  of one implementation of the CGCS. In this implementation, there are five input channels  201 - 205 , though other numbers of input channels are equally applicable. For example, there may be one implementation where a designer wants a reduction in the number of pin outs, which may result in including only input channels  201 - 202 . Of these five channels, channel  201  is used when reading data from the optical media  117 , while channels  202 - 205  are used when writing data to this optical media. For an alternative implementation, varying the number of input channels may necessarily vary the ratio of the read channel to the write channels. 
         [0020]    Filters  211 - 215  connect to the input channels  201 - 205  and receive input current signals, or input signals, on each of the input channels. There is a one to one relationship between the input channel and the low pass filter, which may mean an implementation with only two input channels, may also have only two filters. In addition, another implementation may result from changing the channel to filter ratio to something other than one to one. The on chip filters  211 - 215 &#39;s corner frequencies are adjustable by setting register  210 ; in one implementation, they are adjustable from approximately 3 KHz to approximately 675 KHz. While these filters receive input signals, they transmit filtered signals. Any numbers included in this application are for illustrative purposes only and numerous alternative implementations may result from selecting different quantitative values. 
         [0021]    After the filter  211 , the block diagram  200  includes an adder  217  that connects to a converter  219 . This adder may be any type of adder and effectively sums the filtered signal from the filter  211  and the converted signal received from the converter  219 . The converter may be one of several kinds of converters, such as a digital to analog converter (DAC). The converter  219  can compensate for any offset current that may result as the input signal associated with channel  201  traverses the current generator  120 , the current switch  130 , and finally the current driver  140 . Since the CGCS has a wide variation of gain settings, canceling a DC offset internally generated by the LDD  110  is helpful. The signal resulting from the adder is an offset filtered signal. While this implementation only shows an adder and an offset converter for the read channel, other implementations are possible. 
         [0022]    There is also a channel gain device for input channel; each channel gain device includes a gain block, alteration device, and a converter. The gain block  221  receives the offset filtered signal and applies a gain to this signal, which results in altering the gain associated with the input signal on channel  201 . An alteration device  220  connects to this gain block and controls the amount of gain applied to the offset filtered signal. For example, the alteration device  220  may be a two-bit attenuator. By varying the bits of the alteration device  220  correspondingly changes the dynamic range of the gain for channel  201 . Changing the dynamic range makes the LDD  110  with block diagram  200  particularly applicable to use with various types of media and optical pick up units. Moreover, the alteration devices  221 ,  226  enables dynamically adjusting the gains associated with both the channel  201  and the channel  202 . Similarly, channels  203 - 205  also have corresponding gain blocks  223 - 225  and alteration devices  227 - 229 . But these alteration devices have fixed gains associated with them; an alternative implementation may have a different number of fixed gain and dynamic gain alteration devices. 
         [0023]    While the gain blocks  221 - 225  produce an intermediate gain signal, converters  231 - 235  connect to each of these blocks, receive these intermediate, gain signals and produce converted signals. These DAC converters can be any number of bits depending on the requirements such as die area, resolution etc. 
         [0024]    Switches  263 - 265  selectively connect the converters  233 - 235  to the gain blocks  221 - 225 ; these switches receive enable signals from the blocks  273 - 275 . Each of these switches receives an intermediate gain signal from its associated gain block. For example, the switch  263  can receive an intermediate gain signal from the gain block  223  associated with the input channel  203 . In addition, these switches can also receive the following signals an intermediate gain signal from the gain block  222 , an intermediate gain signal from the gain block  221 , and a converted signal from the converter  232 . The enable signals from blocks  273 - 275  control the positions of the switches  263 - 265  and may come from digital core. Using these switches when there are only two control outputs (e.g., removing drivers  253 - 255 ), the CGCS can set a suitable combination of input signal for channels  203 - 205  and set the suitable dynamic range of input current that produces good resolution. 
         [0025]    After generating converted signals, the converters  231 - 235  transmit converted signals to the current switch  130 . This current switch includes switches  241 - 245  associated with each of the input channels  201 - 205 . As mentioned above, the current switch  130  decides which of the input channels should be turned on or turned off. For the channels that should be turned on, the current switch  130  makes those channels active. The timing generator  160  transmits enable signals for the switches  241 - 245  that either opens or closes the corresponding switch. These switches receive the converted signals and transmit switched signals. 
         [0026]    The channel drivers  251 - 255  connect to the switches  241 - 245 . As mentioned above, the current driver  140 , which includes the channel drivers  251 - 255 , is the last current gain stage and drives the laser diodes directly. In other words, these drivers transmit an output current signal that can be used in either turning on or turning off the light source  115 , which may be a laser diode. This output current signal may be approximately the sum of the products of the input current of each channel and the current gain of each channel. 
         [0027]    The drivers  251 - 255  receive signals from the selection device  266  and the registers  262 - 264 . The register  262  may be a one bit register and dynamically adjust the gain for signals on each of the channels  201 - 205 . Including this register means that the CGCS can now increase the channel gain as the light source  115 , which can compensate for some of the age effects (e.g., power reduction) associated with the light source  115 . While the register  262  may be a one bit register, other implementations may exist where this register has a different number of hits, such as a two-bit register. In addition to the register  262 , the register  264  also allows a further adjustment of the channel gain by varying the gain between channels. Actually, this register may also be a one-bit register, and there may be two relative gain ratios between each channel. The CGCS may have one gain range setting bit to change the range to take care of the data writing speed on the disc. Changing these ratios may be helpful depending on the material of recording optical media  117 . Since the block diagram  200  may be used with more than one light source  115 , the selection device  266  enables selection of the light source that should receive the output signal. For example, this selection device may send one output current signal to a blue laser diode, while sending another output signal to a red laser diode. 
         [0028]    Turning now to  FIGS. 3A-3C ,  FIG. 3A  demonstrates how the output light power characteristics from the LDD  110  vary with output signal from the current driver  140 . It is approximately linear for currents greater than the threshold current, which means that reductions in power can be compensated with increases in current. In other words, increasing the output current signal as the light source  115  ages can produce more power. 
         [0029]    In addition, the CGCS may be used with various types of pulses. In case of a mono pulse structure (see  FIG. 3B ), one can apply a main write current on channel CH 2 , a peak pulse on channel CH 3 , a bias for cooling pulse on channel CH 4 , a PWM pulse within space position on channel CH 5 , and a Bias DC current on channel CH 1 .  FIG. 3C  shows a PWM pulse of write current and power. As described with reference to the mono pulse, the channels may be assigned in a similar manner for the PWM pulse. Some types of writing pulse structure combine the switching control of each channel and also change for each current by changing input current and gain setting. To keep good resolution, it will be better to change the current gain in LDD  110  because of the limitation of the input current range and resolution. By accommodating both pulse types, the CGCS can be used with various disk types. Moreover, the innovative CGCS can set an input current without many of the conventional gain setting variations. 
         [0030]    While various embodiments of the current gain control system have been described, it may be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible that are within the scope of this system. Although certain aspects of the current gain control system may be described in relation to specific techniques or structures, the teachings and principles of the present system are not limited solely to such examples. All such modifications are intended to be included within the scope, of this disclosure and the present current gain control system and protected by the following claim(s).