Abstract:
An input current channel device is described. This device comprises a first terminal for receiving a reference signal; a second terminal for receiving a first target signal; a pass through device coupled to the first terminal, the pass through device operative for transmitting a delayed reference signal in response to receiving the reference signal; a first combination logic device coupled to the first terminal and the second terminal, the first combination logic device operative for transmitting a first combination logic signal in response to receiving the reference signal and the first target signal; a selection device coupled for receiving the delayed reference signal, the first combination logic signal, and a first synchronization signal, the selection device operative for selectively transmitting a second synchronization signal, and wherein selectively transmitting the second synchronization signal reduces skew between the reference channel and the first target channel.

Description:
This amendment claims priority under 35 USC §119(e)(1) of provisional application No. 61/186,184, filed Jun. 11, 2009. 
    
    
     DESCRIPTION OF RELATED ART 
     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 
       The input current channel device 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. 
         FIG. 1A , is a system drawing illustrating components within an optical disk drive. 
         FIG. 1B  is an environmental drawing including a laser diode driver current input signal processing system. 
         FIG. 2  is a block level diagram of one implementation of the CICD  167 . 
         FIG. 3  is a block diagram for one implementation of a receiver in the receiver stage described with reference to  FIG. 2 . 
         FIG. 4  is a block diagram for one implementation of a buffer in the buffer stage described with reference to  FIG. 2 . 
         FIG. 5  is a timing diagram illustrating how a driver output current varies for with the variation of individual output currents for each of the input channels of  FIG. 2 . 
         FIG. 6  is a circuit diagram of a CMOS implementation of a portion the ICCD of  FIG. 2  using two input current channels. 
         FIGS. 7A-7B  are circuit diagrams illustrating alternative implementations of the circuit diagram of  FIG. 6  using ECL logic circuits. 
     
    
    
     While the input current channel device 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 input current channel device 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 input current channel device as defined by this document. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     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. 
     Turning now to  FIG. 1A , is a system drawing illustrating components within an optical disk drive  100 . A controller  102  monitors the output light over level of a laser diode  115  using a Monitor PD  104 , or monitor photodiode, 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. 
     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. 
     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 . 
       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 (e.g., 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, 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. 
     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 diode 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 ). 
     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 . 
     As indicated in  FIG. 1B , the timing generator  160  includes an input current channel device (ICCD)  167 . This device may receive either a low voltage differential signal (LVDS) or a single-ended (SE) signal, which gives maximum flexibility. In addition, this device also works with single ended (SE) logic that is either approximately 2.5V or approximately 3.3V. At a high level, the ICCD  167  can maintain a very low skew among input channels using an equal delayed “AND”, and “OR” with a “Thru” function between the target channels and reference channel, which allows resynchronization. Normally, this skew results from different path lengths for either target signals, signals on the target channels, or reference signals, signals on the reference channel. With the ICCD  167 , the skew between channels may be approximately 10 ps with an overall propagation delay of only approximately 1 ns. Since the skew affects either the rising edges or falling edges of a write pulse, minimizing skew helps create a more well-defined write current pulse, which improves accuracy in writing data to an optical disk, such as optical media  117 . 
     To achieve an effective, or fast, rise time and fall time and generate a correct, or well-defined, write current pulse for good write marks in disk, the output current from the LDD  110  is usually a combination of several current channels. With the ICCD  167 , each target channel can be turned on and off via some switching control, or synchronization, signals from the controller chip as further described with reference to  FIGS. 2-3 . The target signals can be synchronized with the reference signal such that the corresponding channel&#39;s current edges line up with each other when they enter the output driver, or current driver  140 . 
       FIG. 2  is a block level diagram of one implementation of the CICD  167 . In this implementation, the CICD  167  has three different stages, though an alternative implementation may vary the number and types of stages. There is a receiver stage  210  that receives the input channel enable signals  165 , described with reference to  FIG. 1B . As mentioned above, the timing generator  160  determines the time at which a given input channel will be either turned on or turned off and supplies a signal to either enable or disable the associated input channel. In this implementation, the receiver stage  210  includes four input stages  211 - 214  or receivers for write channel  2 ,  3 ,  4 , and  5 , with each having three input terminals  215  (two for input signals and one for enable signal) and two output terminals  216 . Each of these receivers converts an input enable signal to a differential enable signal, which gets transmitted on the output terminals  216 ; hence, these receivers can receiver either an LVDS signal or an SE signal. 
     A buffer stage  220  receives the differential enable signals from the receiver stage  210 . This buffer stage includes at least one buffer associated with each of the receivers in the receiver stage  210 . More specifically, buffers  221 - 224  receive differential signals from the receivers  211 - 214 , respectively. These buffers may be a_ECL or some other suitable type buffer to convert receivers&#39; output signals to the correct voltage levels for the following stages. Each of these buffers has four input terminals of which two connect to the receiver output terminals  216 , one connects to the enable signal and the other connects to some biasing voltage. The buffers  221 - 224  transmits buffered enable signals on their associated output terminals  226  that have a voltage appropriate for re-synchronization, such that output voltage level of  222 ,  223 , and  224  is one VBE lower than those of the buffer  221 . Though shown here is one VBE, other shifting voltage levels are equally applicable. 
     Finally, the re-synchronization stage  230  receives the buffered enable signals from the buffer stage  220 . This re-synchronization stage has combinational logic devices associated with buffers. For example, the combinational logic device  231  is associated with the buffer  221  and the combinational logic device  234 , which is associated with the buffer  224 . In addition, the combinational logic devices  232 - 234  also include input terminals  235  for receiving a digital synchronization signal. For example, this digital synchronization signal may be a two-bit digital signal, such as signal  155  transmitted by the serial interface  150  described with reference to  FIG. 1B . In addition, the combinational logic devices  231 - 234  can provide any one of many type logic functions, such as a thru function, AND function, or an OR function. 
     As the re-synchronization stage  230  produces these synchronized enable signals, other devices within the LDD  110  may use these signals. The timing generator  150  transmits synchronized enable signals on output terminals  236  to the current switch  130 . This current switch uses these synchronized enable signals in either in enabling or disabling the input channels  123  (see  FIG. 1B ). As a result of this, the skew between these input may be substantially reduced, which means that the current driver can transmit a well-defined write pulse to associated laser diodes, which increases the accuracy in writing data to the optical media  117  (see  FIG. 1A ). 
       FIG. 3  is a circuit diagram  300  illustrating one implementation of a receiver in the receiver stage  210 . This circuit diagram is applicable to any of the receivers  211 - 214  in this receiver stage. When a channel enable signal (ENA) on the terminal  302  is a logic high, an associated switching device  305  (switch “SW”) will be “on” and the input is a LVDS signal. Otherwise, the switch will be open from terminal  307 , or on “inP” side, and the input will be a single-ended CMOS logic signal with the threshold voltage stored in a device  309  (C 0 ) through “VTH_dig_SE” associated with the terminal  310  on “inN” side. Thus, this receiver can accommodate either LVDS signals or SE signals. 
     In addition, the receiver illustrated with the circuit diagram  300  also includes emitter followers, resistors for level shifting and a feedback path. Active device  320  (Q 0 ) is an input of a first emitter follower biased via device  322  (Q 4 ) and device  324  (R 2 ); similarly, active device  330  (Q 1 ) is an input of a second emitter follower biased via device  332  (Q 4 ) and device  334  (R 2 ). Device  326  (C 1 ) serves as a bypass capacitor for both of these emitter followers. In selecting sizes or characteristics for these devices, one can select a threshold voltage of approximately 0.7V for the transistors, a resistance of approximately 1.2K, and capacitance of approximately 0.5 pF. Device  340  (R 0 ) and device  342  (R 1 ) can provide level shifting. Device  350  (C 2 ) and device  352  (C 3 ) provide a feed forward path that speeds up the signal transitions between different voltage levels. Device  360  (Q 2 ) and device  362  (Q 3 ) are clamp diodes that limit voltage difference between those two output terminals  370  and  372 . The terminals  307 ,  310 , and  302  may correspond to the input terminals  215  for any of the receivers of  FIG. 2 . Similarly, the terminals  370 ,  372  may correspond to the output terminals  216  for any of the receivers of  FIG. 2 . 
     Turning now to  FIG. 4 , this figure is a block diagram  400  for one implementation of a buffer in the buffer stage  220  described with reference to  FIG. 2 . Device  410  (Q 4 ) and device  420  (Q 5 ) are for level shifting. This level shifting may be particularly beneficial for certain input channels and less beneficial for others. For example, level shifting may be used for channel  3 ,  4 , and  5 , which may be connected to lower inputs of a combination logic device. In contrast, channel  2  which may serve as the reference channel may not include this level shifting and essentially bypass the buffer stage  220 . An alternative implementation may not include the buffer stage  220 . At a high level, this level shifting generally involves receiving signals from the terminals  370 ,  372  of the receiver stage  210  that connect to terminals  430 ,  432  of the buffer stage  220 . The voltage of these signals change by either including  410  and  420  or not including them. Therefore, the voltage level will differ by one VBE. Though shown here is one VBE, other shifting voltage levels are equally applicable. 
       FIG. 5  is a timing diagram  500  illustrating how the LDD output current varies with the variation of individual output current enable signals for each of the input channels described with reference to  FIG. 1B . Plot  505  illustrates the output current enables for a read pulse over time associated with a single read channel shown as one of the input channels  123 . Similarly, plots  506 - 509  correspond with output current enables for write pulses associated with four write channels within the input channels  123 . The plot  506  (EW 2 ) can be associated with the reference channel, while plots  507 - 509  can be associated with the target channels. When this is done, plot  507  (EW 3 ) transitions from a logic low state to a logic high state a little before, or leading, the plot  506 , as indicated by the region  511 . And, the plot  507  (EW 3 ) transitions from a logic high state to a logic low state a little after, or lagging, the plot  506 , as indicated by the region  512 . The region  511  has a great impact on how well data gets written, while the region  512  has a much smaller impact when the delay is small. In fact, the impact of the region  512  may be limited by a system controller. This system controller may reduce this region using predefined timing associated with feed forward path described with reference to the device  352  in  FIG. 3 . 
     Logic functions can be used in aligning pulse edges. As shown in this figure, if an “AND” function is used, one can line up the rising edges of the target channels with the reference channel if target channel&#39;s edge is leading. For example, the plot  527  is the outcome of “ANDing” the plot  506  with the plot  507 , which results in eliminating the region  511  and aligning the rising edges of the write pulse. If an “OR” function is used, one can line up the falling edges with the reference channel if target channel&#39;s edge is lagging. For example, the plot  529  is the outcome of “ORing” the plot  506  with the plot  509 , which results in adding a region  531  and aligning the falling edges. Instead of using the plot  507  as the enable signal associated with target channel EW 3 , the plot  527  is used as the new enable signal for target channel EW 3 . 
     Returning to  FIG. 1B , the ICCD  167  produces this enable signal and the timing generator  160  transmits to the current switch  130 . Since the enable signal for the reference channel EW 2  is a reference, it may remain the same, such that the timing generator merely re-transmits this enable signal. Though described with reference to one of the target channels, the logic functions can be used with any of the target channels. The logic functions synchronize the target channel and the reference channel, which correspondingly reduces skew. The timing generator transmits these synchronized channel enable signals  169  to the current switch  130 . The current driver  140  transmits output current signals  145  representative of the whether a channel current switch remains open or closed, which is controlled by the synchronized channel enable signals  169 . 
     Each of the output current signals  145  is a superposition of the output currents from the associated input current channels. In  FIG. 5 , the peak  540  represents a superposition of the output currents for each enabled channel. 
       FIG. 6  is a circuit diagram  600  for a CMOS implementation of a portion the ICCD  167  involving two input current channels. The input current channel connected to the terminal  605  may be a reference channel, such as the reference channel EW 2  associated with the plot  505 , described with reference to  FIG. 5 . In contrast, the input current channel connected to the terminal  607  may be any target channel, such as the target channel EW 5  associated with the plot  509 . In this implementation, a combination logic device implements each of the following logic functions: THRU, AND, and OR; this logic device may include a collection of logic gates, such as NOT gates, AND gates, and NOR gates. 
     Alternative implementations may exist by changing either the type of logic functions or the type of CMOS combination logic gates used in implementing the function. Though this implementation is essentially balanced, it can be slow in terms of propagation delay and rise/fall time. In addition, the circuit diagram  600  includes a multiplexer  610  for transmitting a synchronized current enable signal. In this implementation, the multiplexer&#39;s input terminals  611 - 612  connect to this digital synchronization signal may be a two-digital signal, such as signal  155  transmitted by the serial interface  150  described with reference to  FIG. 1B . The multiplexer  610  may be any type of multiplexer, such as a CMOS device. Since the circuit diagram only illustrates a portion of the ICCD  167  involving one reference channel and one target channel, the circuit diagram  600  may be replicated as many times as desired for a given number of target channels. In other words, this diagram may be duplicated two more time if there are a total of three target channels or four more times if there are 5 target channels. 
       FIGS. 7A-7B  are circuit diagrams illustrating alternative implementations of the circuit diagram  600  using ECL logic circuits. These logic circuits improve the propagation delay compared with circuit diagram  600  implementation.  FIG. 7A  is a circuit diagram  710  illustrating an ECL logic circuit for a reference input channel, such as the reference channel EW 2  described with reference to  FIG. 5 . This circuit includes a differential pair made of devices  712 - 714  with devices  716 - 718  that supply resistive loading. Devices  712 - 718  form one combination logic device and provide the “THRU” function for the reference channel. An output buffer  720  may include devices  721 - 724  that apply output signals to the output terminals  731 - 732 , which may one of the terminals  236  described with reference to  FIG. 2 . Devices  742 - 748  are “dummy” devices for capacitive loading compensation. The device  716  is a bypass capacitor, while devices  718 - 719  bias the current source. An alternative implementation may result from not including one or more of the following devices: device  721 , device  722 , device  742 , device  744 , device  746 , or device  748 . When selecting the types and sizes of devices within the circuit diagram  710 , circuit designers may use the following criteria: optimum speed at the given current density. 
     Turning now to  FIG. 7B , this is a circuit diagram  750  illustrating an ECL logic circuit for a target channel, such as the target channel EW 3  described with reference to  FIG. 5 . This circuit includes a differential pair made of devices  762 - 764  with devices  766 - 768  that supply resistive loading, which collectively serve as the “Thru” function for the target channel. This thru function can measure the delay between channels  2 ,  3 ,  4 , and  5  without the synchronization. Devices  772 - 778  and devices  782 - 788  form a combination logic device with the ECL AND logic function and the OR function; these same devices can form a combination logic device with the ECL NAND logic function and the NOR function. Devices  753 - 756  form an output buffer  752  that apply output signals to the output terminals  757 - 758 , which may one of the terminals  236  described with reference to  FIG. 2 . Devices  790 - 793  are the switching devices for a multiplex function, like multiplexer  610 . Device  793  is the bypass capacitor, while devices  794 - 795  are the biasing current source. 
     While various embodiments of the input channel current device 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 channel input current device 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 channel input current device and protected by the following claim(s).