Abstract:
A master-slave delay locked loop system comprises a master delay locked loop (“MDLL”) and at least one slave delay locked loop (“SDLL”). The MDLL generates one or more biases. Each of the at least one SDLL has a slave calibration unit and slave delay elements. The slave calibration unit calibrates the slave delay elements using a slave calibration loop and the generated one or more bias. Thus, each of the SDLL is calibrated to account for any electrical noise, pressure, voltage, and temperature variations that the respective SDLL experiences.

Description:
FIELD OF INVENTION 
       [0001]    This invention generally relates to a clock alignment scheme for an integrated circuit, and, in particular, to circuits, methods, and systems for clock alignment by a master-slave delay locked loop network. 
       BACKGROUND 
       [0002]    In a high speed source-synchronous semiconductor memory system, such as a double data rate synchronous dynamic random access memory (“DDR SDRAM”), data is transferred to or from other devices, where the data is synchronized with a clock signal (e.g., a reference clock or an external clock signal). The high speed source-synchronous semiconductor memory device performs an input or output operation in synchronization with not only a rising edge, but also a falling edge of the clock signal. Typically, in a system or a circuit including a semiconductor memory, the clock signal is used as a reference clock signal for adjusting operation timing to guarantee stable data access and data transfer without error. For stable data access and data transfer, the data transfer should occur with respect to the clock edges in such a way that the memory or physical layer (“PHY”) can recover the data send synchronized to each clock edge. A delay locked loop (“DLL”) can generate internal clock signals for the system based upon the reference clock signal by compensating for clock skew occurring in the data path and adding phase delays to the reference clock signal. The data path has a predetermined delay amount estimated from the clock skew, where the data or the clock signal passes through the semiconductor memory device. The generated internal clock signals can then be used for synchronizing data input/output. 
         [0003]    DLLs can be used to supply these internal clock signals based on the reference clock signal. Typically, DLLs are based on a variable multi-stage delay line, in which the delay is controlled by a phase/frequency detector which compares the signal at the end of the delay line with the reference clock signal. It is appreciated that DLLs may also comprise of other components, including a charge pump and filter to name a couple. Taps between stages in the delay line provide multiple copies of the reference signal with various phase shifts so as to subdivide the clock period into different phase delay levels. 
         [0004]    A DLL usually provides delays in steps up to a full clock cycle delay for the input signal. Typically, the DLL can have eight delay segments (also referred to as octants) or any other number of segments, e.g., 4 or 16 stages, that are connected in series to provide total delay up to one clock period. Each delay element of the DLLs can provide a delay of around ⅛ th  of a full clock cycle (assuming it has 8-stages; if N-stages delay, then each can provide 1/N of a period). In particular, a DDR system&#39;s data strobe and data bits require alignment across the system. In order to do so, the DDR system typically implements a master-slave DLL network, where a master DLL sets the required delay times and can drive one or more slave delay lines for delaying signals, including a DQS strobe. Thus, the master DLL can force a specific delay onto the slave DLLs. 
         [0005]      FIG. 1  illustrates a prior art master-slave delayed locked loop system. A master-slave delayed locked loop system of the prior art comprises a master delay locked loop (“MDLL”) regulator  10 , an MDLL  9 , a slave delay locked loop (“SDLL”)  32 , a phase interpolator (“PI”) array  34 , and a SDLL regulator  36 . The MDLL regulator  10  provides a stable and lower noise supply to the components used in the MDLL  9 . The MDLL  9  comprises flip-flop (“FF”)  12 , FF  14 , a delay logic  16 , an AND gate  18 , current sources  20  and  26 , switch transistors  22  and  24 , a filter capacitor  28 , and master delay elements  30 . The MDLL  9  uses a voltage control to adjust the delay elements of the master delay elements  30  for aligning signal CK 0  with CK 360 . CK 0  is usually a delayed version of the clock in signal CKIN_MDLL. The master delay elements  30  include delay elements as well as any logic or circuitry for the delay elements to function. 
         [0006]    The MDLL  9  can generate slave bias currents for controlling one or more slave DLLs (e.g., the SDLL  32 ) based on the adjustments made to the master delay elements  30 . The controlled SDLL  32  replicates the desired calibrations of the master delay elements  30  and applies it to a clock in signal CKIN_SDLL to generate its output clocks that have phase shifts from 0 degrees to 360 degrees. The phase shifted clock signals are inputted to the PI array  34  for generating clocks with much finer shifts in phase than can be provided by the delay lines themselves to use in clocking read and write commands and data. The SDLL regulator  36  can be used to provide information from the PI array  34  to the SDLL  32 . The SDLL regulator  36  provides a stable supply to the components of the SDLL  32 . 
         [0007]    Due to the design and/or process, voltage and temperature (“PVT”) fluctuations between the MDLL  9  and SDLL  32 , the SDLL  32  may not operate identically as the MDLL  9 . Thus the delay provided by the MDLL  9  is not exactly replicated in the SDLL  32 , there will be differences in the set delays. For instance in DDR systems, data strobe and data bits need to be aligned across the system spanning several 100&#39;s μms such that the eye is maximized. There is usually one MDLL (or master phase locked loop) that generates the bias voltages or currents that determine the delay. This control bias is then distributed to various data macros where the local slave delay lines are used to align the strobe to the data byte. 
         [0008]    DDR physical layer (“PHY”) systems can easily span several 100&#39;s μm. Hence, the delay generated in the MDLL is substantially different from delay in slave DLLs due to PVT variations across these distances. These differences in delays will reduce the available valid timing eye for aligning data and strobes. Usually data strobe is aligned to data by delaying it by 90°-180° based on settings from the MDLL. At certain speeds, this delay difference can reduce the eye and be a significant issue, which can lead to read failures, write failures, and other failures. 
         [0009]    Therefore, it is desirable to provide new circuits, methods, and systems for a clock alignment scheme to account for PVT variations in a slave DLL. 
       SUMMARY OF INVENTION 
       [0010]    Briefly, the present invention discloses a master-slave delay locked loop system, comprising: a master delay locked loop (“MDLL”), wherein the MDLL generates one or more biases; and at least one slave delay locked loop (“SDLL”), wherein each of the at least one SDLL has a slave calibration unit and slave delay elements, and wherein the slave calibration unit calibrates the slave delay elements using a slave calibration loop and the generated bias. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0011]    The foregoing and other objects, aspects, and advantages of the invention can be better understood from the following detailed description of the preferred embodiment of the invention when taken in conjunction with the accompanying drawings in which: 
           [0012]      FIG. 1  illustrates a prior art master-slave delayed locked loop system. 
           [0013]      FIG. 2 a    illustrates a master-slave delay locked loop system of the present disclosure. 
           [0014]      FIG. 2 b    illustrates another embodiment of a master-slave delay locked loop system of the present disclosure. 
           [0015]      FIG. 3  illustrates master delay elements of a master-slave delay locked loop system of the present disclosure. 
           [0016]      FIG. 4  illustrates slave delay elements of a master-slave delay locked loop system of the present disclosure. 
           [0017]      FIG. 5  illustrates an embodiment of a phase detector and control logic of the present disclosure for calibrating a slave delay locked loop. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    In the following detailed description of the embodiments, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration of specific embodiments in which the present invention may be practiced. 
         [0019]      FIG. 2 a    illustrates a master-slave delay locked loop system of the present disclosure. A master-slave delay locked loop comprises a MDLL  54  and a SDLL  56 . The MDLL  54  comprises a master bias generator  40  and master delay elements  42 . The master bias generator  40  generates one or more bias signals to calibrate the master delay elements  42  and a slave bias signal to calibrate any delay elements of the SDLLs with similar calibrations. It is appreciated that the bias signal and the slave bias signal can each be a single bias or each be a plurality of biases depending on the implementation of the respective system. 
         [0020]    The SDLL  56  comprises a coarse bias generator  44 , a current digital-to-analog converter (“IDAC”)  46  for fine adjust logic, slave delay elements  48 , and a phase detector and control logic  50 . The coarse bias generator  44 , IDAC  46 , and the phase detector and control logic  50  can be referred to as a slave calibration unit for providing a slave calibration loop. The coarse bias generator  44  receives the slave bias from the master bias generator  40 , and can generate biases PBIAS and NBIAS to the slave delay elements  48 . The coarse bias generator  44  can be implemented by a voltage to current converter or other mechanism for communicating the master biasing information to the SDLL  56  so that the SDLL  56  can apply similar biasing to the slave delay elements  48 . In particular, the biases PBIAS and NBIAS control the delay between CLK 0  and CLK 360 , or in other words the delay of the cell and can be implemented by currents and/or voltages. For the sake of understanding the present disclosure, a current-based bias implementation is disclosed. However, a person having ordinary skill in the art can implement a voltage-based bias signal in accordance with the present disclosure. Additionally, the biases PBIAS and NBIAS can be implemented using a single bias or additional biases depending on the implementation of the respective system. 
         [0021]    The coarse bias generator  44  receives the slave bias, and translates that slave bias to generate the biases PBIAS and the NBIAS. The biases PBIAS and NBIAS are inputted to the slave delay elements  48 . The slave delay elements  48  generate phase shifted signals from an inputted clock signal, including 0-degree-phase-shifted signal CK 0  and the 360-degree-phase-shifted signal CK 360 . The 0-degree-phase-shifted signal CK 0  and the 360-degree-phase-shifted signal CK 360  are inputted to the phase detector (“PD”) and control logic  50  for comparison. Ideally the CK 0  and CK 360  need to be phase aligned when the SDLL is locked. Any delay difference between the two signals are measured by the PD and control logic  50  and used to calibrate the slave delay elements  48  by outputting a fine adjust signal to the IDAC logic  46 . The IDAC logic  46  can alter the biases PBIAS and NBIAS inputted to the slave delay elements  48  to improve phase alignment of the CK 0  and CK 360  signals. 
         [0022]    For instance, the PD of the phase detector and control logic  50  measures whether CLKO is leading (i.e., delay is more than a single period) or lagging CLK 360  (i.e., delay is less than a single period). The output of the PD is sent to a respective control logic of the phase detector and control logic  50 , which decodes the data and averages the PD outputs. The control logic also decides whether to increment or decrement the IDAC signal. This IDAC signal can then be used to add or subtract the coarse bias current of the coarse bias generator  44 . Thereby, adjusting the biases PBIAS and NBIAS generated by the coarse bias generator  44 , which further causes the delay to change in the delay elements  48 . The slave calibration loop can be repeated until the clocks are very close in phase alignment. 
         [0023]    The MDLL  54  can drive a plurality of SDLLs of the present disclosure. To aid in the understanding of the invention, a single SDLL is illustrated and described in conjunction with the MDLL. However, a plurality of SDLLs having a slave calibration loop can be coupled with the MDLL. Furthermore, it is possible to share components of the slave loop like the control logic between two or more SDLLs, but this may require some additional logic. 
         [0024]    A person having ordinary skill in the art can apply the present disclosure to various clock alignment issues, including aligning internal clocks for DDR clocks, aligning pleisosynchronous systems through a clock and data recovery (“CDR”) loop, etc. Even more so, it can be understood that the following disclosure can be used for aligning several clocks if needed by cascading such master-slave networks. 
         [0025]      FIG. 2 b    illustrates another embodiment of a master-slave delay locked loop system of the present disclosure. In another embodiment, a single voltage-based bias signal can be outputted by a master DLL to a slave DLL of the present disclosure. The master-slave delay locked loop system of the present disclosure comprises a master DLL (“MDLL”)  80  and a slave DLL (“SDLL”)  82  where the SDLL  82  further comprises an analog-to-digital converter (“ADC”)  84 , an adder/subtractor (“adder/sub”)  86 , a digital-to-analog converter (“DAC”)  88 , a voltage-to-current converter (“V2I”)  90 , slave delay elements  94 , and a phase detector and control logic  92 . The coarse bias generator  44  and IDAC  46  of the previous example in  FIG. 2 a    can be implemented in the instant  FIG. 2 b    by the ADC  84 , adder/sub  86 , DAC  88 , and V2I 90 . Furthermore, the ADC  84 , adder/sub  86 , DAC  88 , V2I  90 , and phase detector and control logic  92  can be referred to as a slave calibration unit for providing a slave calibration loop. 
         [0026]    Referring to  FIG. 2 b   , the MDLL  80  generates a bias voltage for calibrating the slave delay elements  94 . The ADC  84  converts the bias voltage to a digital bias signal. The digital bias signal is outputted to the adder/subtractor  86  for performing adding or subtracting functions on the inputted digital bias signal based on an inputted sign and code. The adder/sub  86  outputs an adjusted digital bias signal to the DAC  88 . The DAC  88  converts the signal for output as an adjusted bias voltage to the V2I  90 . The ADC  84  and the DAC  88  are powered by the same power level so that the codes for conversion are the same. 
         [0027]    The V2I  90  converts the adjusted bias voltage to a current bias and outputs the current bias to the slave delay elements  94  for calibration of the slave delay elements  94 . The slave delay elements  94  output phase delayed signals to the phase detector and control logic  92  to update the adjusted bias signals. The phase detector and control logic  92  can determine if the slave delay elements  94  require adjustment by comparing two more or more of its outputted phase delayed signals. Based on that comparison, the phase detector and control logic  92  output a sign and a code to the adder/sub  86  for applying that adjustment to generate the adjusted bias voltage. Thus, a feedback loop can be employed to make adjustments to the calibration of the slave delay elements  94 . 
         [0028]      FIG. 3  illustrates master delay elements of a master-slave delay locked loop system of the present disclosure. The master delay elements  42  comprise delay buffers  60   a - 60   h  serially connected, where each of the buffers  60   a - 60   h  apply a predefined amount of delay to the inputted signal. For instance, each of the buffers  60   a - 60   h  can provide a 45 degree phase shift to its inputted signal such that the output of the first buffer  60   a  provides a 45-degree-phase-shifted signal of the inputted differential signal CK 0  and CK 0 _B. The second buffer  60   b  applies another 45 degree phase shift such that it outputs a 90-degree-phase-shifted differential signal CK 90  and CK 90 _B. The other buffers after the second buffer can also apply additional delays to further delay the inputted differential signal CK 0  and CK 0 _B. The last buffer  60   h  can provide an additional 45 degree delay to provide for a 360-degree-phase-shifted differential signal CK 360  and CK 360 _B relative to the input of the first buffer  60   a . The biases PBIAS and NBIAS can adjust the calibration of the buffers  60   a - 60   h  to adjust for any variation in operation from its intended amount of phase shift. In particular, the biases PBIAS and NBIAS can adjust the delay of each delay element and hence the delay of the entire stage. 
         [0029]      FIG. 4  illustrates slave delay elements of a master-slave delay locked loop system of the present disclosure. The slave delay elements  48  comprise delay buffers  70   a - 70   h  serially connected, where each of the buffers  70   a - 70   h  apply a predefined amount of delay to the inputted signal. The delay buffers  70   a - 70   h  operate in a similar manner to the delay buffers  60   a - 60   h . For instance, each of the buffers  70   a - 70   h  can provide a 45 degree phase shift to its inputted signal. The first buffer  70   a  can provide a 45 degree phase shifted signal of the inputted differential signal CK 0  and CK 0 _B. The second buffer  70   b  applies another 45 degree phase shift such that it outputs a 90 degree-phase-shifted differential signal CK 90  and CK 90 _B. The other buffers after the second buffer can also apply additional delays to further delay the inputted differential signal CK 0  and CK 0 _B. The last buffer  70   h  can provide an additional 45 degrees delay to provide for a 360-degree-phase-shifted differential signal CK 360  and CK 360  _B relative to the input of the first buffer  70   a . The biases PBIAS and NBIAS can be adjusted to calibrate the amount of actual delay applied by the buffers  70   a - 70   h . As stated above, PVT variations may cause the operation of the buffers  70   a - 70   h  to vary from its intended amount of phase shift. 
         [0030]    In certain embodiments, the master delay elements and slave delay elements can be designed and implemented in the same manner, which can save time and effort. However, in other embodiments, the master delay elements and the slave delay elements can also be implemented differently depending on the design requirements of the respective system or device. 
         [0031]      FIG. 5  illustrates an embodiment of a phase detector and control logic of the present disclosure for calibrating a slave delay locked loop. The phase detector and control logic  200  comprises a bang-bang phase detector  102 , a sampler  104 , a majority logic  106 , an accumulator  108 , a first divider logic  110 , a second divider logic  112 , a sign detector  114 , and a code generator  116 . The phase detector and control logic  200  provide for a slave calibration loop to calibrate the delay elements of the SDLL  100 . 
         [0032]    The 0-degree-phase-shifted signal CK 0  and the 360-degree-phase-shifted signal CK 360  are outputted by the delay elements of the respective SDLL for input to the bang-bang phase detector  102 . Depending on whether one of the signals are ahead or behind of the second one of the signals, an up or a down output signal can be provided by the bang-bang phase detector  102  to indicate such leading or lagging. For instance, if the CK 360  signal comes before the CK 0  signal (i.e., the delay cells are faster than 45° or the required phase for 1-period delay), a slow down (“Dn”) signal is generated by the bang-bang phase detector  102 . If the CK 360  signal comes after the CK 0  signal (i.e., delay cells are slower than 45° or the required phase for 1-period delay), a speed up (“Up”) signal is generated by the bang-bang phase detector  102 . 
         [0033]    The sampler  104  samples the up or down signals from the bang-bang phase detector and is clocked by the CK 360  signal. The sampler can be reset every predefined number of cycles (e.g., eight cycles). A majority logic  106  is used to determine whether a majority of the samples are up signals or are down signals for a period of time (e.g., for eight cycles of the output of the divider logic  110 ). If the majority logic samples an Up signal, a sampler value is incremented by outputting an increment signal to the accumulator  108 . If the majority logic samples a Dn signal, the sampler value is decremented by outputting a decrement signal to the accumulator  108 . The accumulator  108  increments or decrements the value based on the sampler output until time the accumulator  108  is reset, which can occur at a predefined amount of time (e.g., every m cycles) or at a programmable time. The CK 360  signal can be divided by the divider  110  to generate a longer signal period to clock the majority logic  106 , the accumulator  108 , and the divider logic  112 . The divider logic  112  further divides that inputted signal to clock the sign detector  114  and the code generator  116 . 
         [0034]    The accumulator outputs an accumulated decision made over N clock cycles (or another predefined number clock cycles) to the sign detector  114 . The sign detector  114  outputs whether the calibration should be ahead or behind to the code generator  116 . The code generator  116  converts that decision to a sign and a code for the adjusting the slave biasing of the respective SDLL to calibrate its delay elements such that the phase difference between the outputted CK 0  and CK 360 . The sign and code values can be outputted to IDAC and/or the coarse bias generator for adjusting the slave bias signal(s). 
         [0035]    For instance, the code can indicate to the SDLL to increment, decrement, lock detection, unlock detection, relock, and other commands for controlling the SDLL. In particular, for lock detection, the accumulator can provide a dither value for a programmable amount of time. The code can then be frozen, and a lock detection generated. For unlock detection, if the accumulator signals an increment up or down in another predefined number of consecutive cycles, then a de-assert lock detection code is generated and relocking can be performed. For a relock code indication, the relock indication can be user-based, counter-based, unlock-detection-based, or otherwise programmable. 
         [0036]    The slave calibration loop can correct for both increasing delay and decreasing delay. The timing of the calibration can be programmable from a single time, to scheduled times, or even continuously. The SDLL calibration can thus reduce any PVT and Montecarlo mismatch. 
         [0037]    While the present invention has been described with reference to certain preferred embodiments or methods, it is to be understood that the present invention is not limited to such specific embodiments or methods. Rather, it is the inventor&#39;s contention that the invention be understood and construed in its broadest meaning as reflected by the following claims. Thus, these claims are to be understood as incorporating not only the preferred apparatuses, methods, and systems described herein, but all those other and further alterations and modifications as would be apparent to those of ordinary skilled in the art.