Abstract:
An apparatus and method for generating phase-related clocks are disclosed. A clock input is delayed by an alignment magnitude to generate a first phase signal. The first phase signal is delayed by the phase alignment magnitude to generate a first phase delay signal. The clock input is delayed by a phase delay magnitude to generate a second phase signal and the second phase signal is delayed by about the phase delay magnitude to generate a last phase delay signal. A phase difference is detected between the first phase delay signal and the last phase delay signal and adjustments are made to at least one of the phase delay magnitude and the alignment magnitude.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates generally to delay locked loops, and particularly to multiple phase generation using delay locked loops.  
         [0003]     Description of Related Art  
         [0004]     In modern high frequency integrated circuits, it is often necessary to generate internal clocks with predetermined phase relationships to a reference clock. Conventionally, a Phase Locked Loop (PLL) or Delay Locked Loop (DLL) has been used to generate these predetermined phase relationships. For example, many reference input clocks may not have a 50% duty cycle. However, with modern semiconductor devices, such as Double Data Rate (DDR) Dynamic Random Access Memory (DRAM) devices, two data cycles may occur within one clock cycle. An internal clock with a 50% duty cycle may be needed so the two data cycles may be accurately sampled at the rising edge and the falling edge of the clock. Alternatively, an additional clock with a phase delay of  180  degrees relative to the reference clock may be used to sample one data slice and the reference clock may be used to sample the other data slice. Furthermore, modern semiconductor devices, such as DRAM and processors, may require multiple clocks with defined phase relationships to trigger events at various times during a clock cycle. For example, it may be desirable to have clocks with phase relationships of 90°, 180°, 270°, and 360° relative to a reference clock.  
         [0005]     Various solutions exist for generating these desired duty cycles and clocks with defined phase relationships; these solutions are conventionally referred to as Duty Cycle Correctors (DCC) and phase generators. Conventionally, phase generators may be constructed as a DLL using either analog or digital delay lines. Analog delay lines may allow more precise control but may consume more silicon space or “real estate,” consume more power, and take longer to achieve lock. Digital delay lines, on the other hand, are easier to design, smaller, and may consume less power. Digital delay lines may achieve lock faster than analog delay lines; however, digital delay lines may not be able to achieve the continuous fine-tuning available in an analog delay line.  
         [0006]     A conventional phase generator constructed as a DLL is shown in  FIG. 1 . A clock input  5  (also referred to as a ph0 signal) connects to a first delay line  10 . A ph180 signal  15 , generated by the first delay line  10 , connects to a second delay line  20 . A ph360 signal  25 , from the output of the second delay line  20 , feeds back to a phase detector  30 . The phase detector  30  compares the phase of the clock input  5  to the second delay line  20  output. Because of the comparison, the phase detector  30  generates the delay control signal  35  controlling the delay lines ( 10  and  20 ) to either increase or decrease the delay. The first delay line  10  and second delay line  20  are of similar construction such that the delay control signal  35 , connected to both delay lines ( 10  and  20 ), causes both delay lines to generate the same amount of delay. With this closed loop, the DLL “locks” on to the clock input  5  so that the ph360 signal  25  is at substantially the same phase and frequency as the clock input  5 .  
         [0007]     Because the two delay lines generate equivalent delays, the ph180 signal  15  is at the same frequency as, and 180 degrees out of phase with, the clock input  5 . The phase detector  30  only compares rising edge to rising edge or falling edge to falling edge. As a result, the phase generator will lock and generate the ph180 signal  15  at 180 degrees out of phase regardless of the duty cycle of the clock input  5 .  
         [0008]     However, conventional digital DLL phase generators have their limits. Due to the structure of the delay lines, there is a minimum delay and a maximum delay possible through each delay line. The lowest frequency input clock that the DLL is able to lock to is defined by the maximum delay. For example, if the maximum delay through each delay line is 50 nSec, the total maximum delay is 100 nSec, and the DLL can lock to clock frequencies of 10 Mhz or higher. On the other hand, if the minimum delay through each delay line is 2.5 nSec, the total minimum delay is 5 nSec. Consequently, if the input clock is faster than 200 Mhz (i.e., a clock period of less than 5 nSec), the DLL cannot lock to the clock input because the ph360 signal  25  cannot be brought any closer to the ph0 signal  5  than the minimum delay. Conventionally, DLL design involves considerations such as locking range (i.e., maximum delay) versus die sized and power consumption.  
         [0009]     Other phase generator configurations have been proposed for increasing the clock frequencies beyond the minimum delay of the combined delay elements of a DLL. A phase generator  40  constructed as a DLL, which increases the operation frequency, is shown in  FIG. 2 . A phase generator  40  includes a phase detector  70 , a first delay line  50 , a second delay line  55 , a first phase aligner  75  and a second phase aligner  85 . A clock input  45  connects to the first delay line  50 . A dly180 signal  60  is generated by the first delay line  50  and connects to the second delay line  55 . A ph360 signal  95  is generated by the second delay line  55  and feeds back to the phase detector  70 .  
         [0010]     The clock input  45  also connects to the first phase aligner  75 . A ph0 signal  80  is generated by the first phase aligner  75  and feeds back to the phase detector  70 . A second phase aligner  85  connects to the dly180 signal  60  and generates a ph180 signal  90 . The first and second delay lines  50 ,  55 , respectively, are configured similarly with the same selectable delay increments. Consequently, both delay lines  50 ,  55  have substantially the same delay magnitude based on a phase adjustment signal  65 , which is generated by the phase detector  70  and selects the delay increments, and as a result, the delay magnitude for both delay lines.  
         [0011]     An alignment adjustment signal  70 , generated by the phase detector  70 , controls the alignment magnitudes (i.e., delay) of the first and second phase aligners  75 ,  85 . The second phase aligner  85  is generally configured with delay increments that are one-half the size of the delay increments for the first phase aligner  75 . Consequently, for any given value on the alignment adjustment signal  70 , the second phase aligner  85  generates a delay magnitude that is substantially one-half the delay magnitude generated by the first phase aligner  75 .  
         [0012]     While such a configuration may allow for a higher frequency input clock  45 , the forward path intrinsic delay is no longer substantially zero. As illustrated, the forward path intrinsic delay is the intrinsic delay for the ph0 signal through the first phase aligner  75  and has been purposely increased to be out of phase with the ph0 signal  80 .  
         [0013]     There is a need for a digital phase generator that can lock and operate at higher frequencies without affecting the overall locking range of the DLL within the digital phase generator and without unduly inserting excessive delay in the forward path.  
       BRIEF SUMMARY OF THE INVENTION  
       [0014]     The present invention enables digital phase generators and methods of generating multi-phase signals at higher clock speeds. An embodiment of the present invention comprises a method of generating multi-phase clocks. A clock input is delayed by an alignment magnitude to generate a first phase signal. The first phase signal is delayed by the phase alignment magnitude to generate a first phase delay signal. The clock input is delayed by a phase delay magnitude to generate a second phase signal and the second phase signal is delayed by about the phase delay magnitude to generate a last phase delay signal. A phase difference is detected between the first phase delay signal and the last phase delay signal and adjustments are made to at least one of the phase delay magnitude and the alignment magnitude.  
         [0015]     Another embodiment of the present invention comprises a phase generator for generating multi-phase clocks. The phase generator includes a first phase aligner configured to generate a first phase signal with an alignment magnitude relative to a clock input and a second phase aligner configured to generate a first phase delay signal with substantially the alignment magnitude relative to the first phase signal. The phase generator further includes a first delay line configured to generate a second phase signal with a phase delay magnitude relative to the clock input and a second delay line configured to generate a last phase delay signal with the phase delay magnitude relative to the second phase signal. The phase generator also includes a phase detector configured to compare the first phase delay signal and the last phase delay signal and generate at least one of a phase adjustment signal for modifying the phase delay magnitude and an alignment adjustment signal for modifying the alignment magnitude.  
         [0016]     Another embodiment of the present invention comprises a semiconductor device including at least one phase generator according to the invention described herein.  
         [0017]     Another embodiment of the present invention includes at least one semiconductor device including at least one phase generator according to the present invention fabricated on a semiconductor wafer.  
         [0018]     Yet another embodiment, in accordance with the present invention comprises an electronic system including at least one input device, at least one output device, at least one processor, and at least one memory device. The at least one memory device comprises at least one semiconductor memory incorporating at least one phase generator according to the present invention. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0019]     In the drawings, which illustrate what is currently considered to be the best mode for carrying out the invention:  
         [0020]      FIG. 1  is a block diagram of a conventional digital phase generator;  
         [0021]      FIG. 2  is a block diagram of a conventional digital phase generator with increased operating frequency, and including additional intrinsic delay;  
         [0022]      FIG. 3  is a block diagram of an exemplary digital phase generator, in accordance with an embodiment of the present invention;  
         [0023]      FIG. 4  is a block diagram of an exemplary delay line, in accordance with an embodiment of the present invention;  
         [0024]      FIG. 5A  is a timing waveform showing operation of various phases for the  FIG. 3  embodiment at a clock cycle of 14 units and substantially zero alignment delay, in accordance with an embodiment of the present invention;  
         [0025]      FIG. 5B  is a timing waveform showing operation of various phases for the  FIG. 3  embodiment at a clock cycle of 14 units and a predetermined alignment delay, in accordance with an embodiment of the present invention;  
         [0026]      FIG. 5C  is a timing waveform showing operation of various phases for the  FIG. 3  embodiment at a clock cycle of 12 units, in accordance with an embodiment of the present invention;  
         [0027]      FIG. 6A  is a timing waveform showing operation of various phases for the  FIG. 3  embodiment at a clock cycle of 10 units, in accordance with an embodiment of the present invention;  
         [0028]      FIG. 6B  is a timing waveform showing operation of various phases for the  FIG. 3  embodiment at a clock cycle of  8  units, in accordance with an embodiment of the present invention;  
         [0029]      FIG. 6C  is a timing waveform showing operation of various phases for the  FIG. 3  embodiment at a clock cycle of  6  units, in accordance with an embodiment of the present invention;  
         [0030]      FIG. 7  is a semiconductor wafer, including a plurality of semiconductor devices including a phase generator, in accordance with an embodiment of the present invention; and  
         [0031]      FIG. 8  is an electronic system diagram showing a plurality of semiconductor memories including a phase generator, in accordance with an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]     In the following description, circuits and functions may be shown in block diagram form in order not to obscure the present invention in unnecessary detail. Conversely, specific circuit implementations shown and described are exemplary only, and should not be construed as the only way to implement the present invention unless specified otherwise herein. Additionally, block definitions and partitioning of logic between various blocks is exemplary of a specific implementation. It will be readily apparent to one of ordinary skill in the art that the present invention may be practiced by numerous other partitioning solutions. For the most part, details concerning timing considerations and the like have been omitted inasmuch as such details are not necessary to obtain a complete understanding of the present invention and are within the abilities of persons of ordinary skill in the relevant art.  
         [0033]     The term “bus” is used to refer to a plurality of signals or conductors, which may be used to transfer one or more various types of information, such as data, addresses, control, or status. Additionally, a bus or collection of signals may be referred to in the singular as a signal.  
         [0034]     As shown in  FIG. 3 , a phase generator  100  according to the present invention includes a phase detector  150 , a first delay line  110 , a second delay line  120 , a first phase aligner  160  and a second phase aligner  170 . A clock input  105  connects to the first delay line  110 . A ph180 signal  125  (also referred to as a second phase signal) is generated by the first delay line  110  and connects to the second delay line  120 . A dly360 signal  199  (also referred to as a last phase delay signal) is generated by the second delay line  120  and feeds back to the phase detector  150 .  
         [0035]     The clock input  105  also connects to the first phase aligner  160 . A ph0 signal  165  (also referred to as a first phase signal) is generated by the first phase aligner  160  and feeds to a second phase aligner  170 . The second phase aligner  170  generates a dly0 signal  175  (also referred to as a first phase delay signal) and feeds back to the phase detector  150 .  
         [0036]     The first and second delay lines ( 110  and  120 ) may be configured similarly with the same selectable delay increments. Consequently, both delay lines ( 110  and  120 ) will have substantially the same delay magnitude based on a phase adjustment signal  152 , which is generated by the phase detector  150  and selects the delay increments, and as a result, the delay magnitude for both delay lines.  
         [0037]     An alignment adjustment signal  158 , generated by the phase detector  150 , controls the alignment magnitudes (i.e., delay) of the first and second phase aligners ( 160  and  170 ). The second phase aligner  170  may be configured with delay increments that are substantially equal to the size of the delay increments for the first phase aligner  160 . Consequently, for any given value on the alignment adjustment signal  158 , the second phase aligner  170  generates a delay magnitude that is substantially equal to the delay magnitude generated by the first phase aligner  160 .  
         [0038]     One of the improvements of the architecture of the various embodiments of the present invention is the reduction in the ph0 forward path delay (i.e., the delay between clock input  105  and ph0 signal  165 ) without surrendering the ability to minimize the frequency, tCKmin, of the clock input  105 . A set of equations may be defined to show the delay relationships from the clock input  105  to the ph0 signal  165 , the ph180 signal  125  and the dly360 signal  199 . In the equations, S indicates the magnitude of the alignment delay, t A , for the first phase aligner  160  and “D+I” indicates the phase delay magnitude, t D , in each delay line ( 110  and  120 ) including the selectable/adjustable “D” delay and the “I” intrinsic delay associated therewith. Accordingly, when the loop has locked (i.e., dly0 signal  175  and dly360 signal  199  are in phase with each other) at a particular frequency tCK: 
 
 tCK=t   D   +t   D   −t   A   −t   A =( D+I )+( D+I )− S−S= 2[( D+I )− S] 
 
t d1 =S 
 
 t   d2 =( D+I ) 
 
so,  t   d2   −t   d1 =( D+I )− S  
 
 proving that the delta between t d1  (Clkin to ph0) and t d2  (Clkin to ph180) remains ½ tCK. 
 
         [0039]     In the various embodiments of the present invention, the dly360 signal  199  is not in phase with the ph0 signal  165 , but instead is in phase with the dly0 signal  175 . The various embodiments of the present invention reduce the phase delay in the forward path, namely the path between clock input  105  and the ph0 signal  165  without compromising the tCKmin requirement.  
         [0040]     In  FIG. 3 , when the phase generator  100  is locked, the dly360 signal  199  is one integer clock cycle behind the dly0 signal  175 . In addition, the ph180 signal  125  should be substantially near the midpoint between a ph0 signal  165  and a subsequent ph0 signal  165 . It should be noted that the dly360 signal  199  is in phase with the dly0 signal  175  rather than the ph0 signal  165 . Therefore, in the present architecture and the respective embodiments of the present invention, there is no “true” phase  360  signal which in most applications is rarely used since the ph0 signal in the subsequent clock cycle contains a signal of the same phase.  
         [0041]     The phase generator  100  may be contemplated as having two operation modes. In a first operation mode, the phase aligners ( 160  and  170 ) may be set to a predetermined value and the pair of delay lines ( 110  and  120 ) may be adjusted to effectively lock to the phase and frequency of the clock input  105 . In other words, using the delay equations, hold t A  constant and vary t(D+I) to achieve lock.  
         [0042]     In a second operation mode, the pair of delay lines ( 110  and  120 ) may be set to a predetermined value and the alignment magnitude may be adjusted until the phase generator  100  locks the dly0 signal  175  to the dly360 signal  199 . In other words, using the delay equations, hold t D  or (D+I) constant and vary t A  or “S” to achieve lock. It should be noted that “S” cannot be set greater than or equal to “I”, as the loop would lock a signal to itself and be independent of tCK.  
         [0043]     A group of timing diagrams illustrates the locking process, adjustment of the phase delay magnitude, and adjustment of the alignment magnitude. In the timing diagrams, arbitrary units are used to illustrate the various timing edge movements. These arbitrary units are not intended to illustrate actual delay numbers. For example, the clock cycles in the timing diagrams vary between 14 units and 6 units, and illustrate a minimum delay for the delay lines of 6 units. As an example of current process parameters for a design that may implement the present invention, the minimum delay through the delay lines may be about one to two nanoseconds. In addition, the timing diagrams all show references to rising edges of the various signals. It will be readily apparent to a person of ordinary skill in the art that the phase detector  150  may, alternatively, operate with respect to falling edges and the timing diagrams would be referenced to falling edges.  
         [0044]     The first operation mode is illustrated by  FIGS. 5A, 5B , and  5 C. The first operation mode may typically be used when the clock cycle is larger than the minimum delay of the first delay line  110  and the second delay line  120  combined. In the first operation mode, with the phase aligners set to a predetermined amount, the phase delay magnitude is adjusted in each of the delay lines to achieve lock.  
         [0045]     For example, with reference to  FIGS. 3 and 5 A, the alignment magnitude (noted in the timing diagrams as t A  or “S”) is set to substantially near zero. This may be implemented as a bypass function within the first phase aligner  160  and second phase aligner  170 . With the alignment magnitude at substantially zero, the second phase aligner  170  has a delay of the alignment magnitude, which will also be substantially near zero (noted in the timing diagrams as t A ). With these settings for the alignment magnitudes, the ph0 signal  165  follows the clock input  105  and the ph180 signal  125  is generated from the delay through the delay line  110 . The phase detector  150  compares the dly0 signal  175  to the dly360 signal  199  to determine a phase error. As a result of the phase error, the phase detector  150  controls the phase adjustment signal  152  to either increase or decrease the phase delay magnitude (noted in the timing diagrams as t D  or (D+ 1 )).  
         [0046]     If the delay lines are implemented as a conventional set of delays controlled by a shift register, the phase adjustment signal  152  may be implemented as shift left/shift right set of signals. Shift left may indicate a larger phase delay magnitude (for an entry point delay architecture)while shift right may indicate a smaller phase delay magnitude (note: the reverse is true for exit point delay architectures). Because the first delay line  110  and second delay line  120  are in series, an indication to change the phase delay magnitude by one increment will actually increase the total delay between the clock input  105  and the dly360 signal  199  by two increments.  
         [0047]     The feedback loop, including phase comparison combined with increasing or decreasing adjustments of the phase delay magnitude, continues until the phase comparison shows the phase of the dly0 signal  175  and the dly360 signal  199  are substantially in phase. In  FIG. 5A , with a clock cycle of 14 units, when phase lock is achieved, the phase delay magnitude t D  or (D+I) is about 7 units if I=5 and D=2 resulting in tCKmin=10 without a phase aligner. The first alignment indicator  410  and the second alignment indicator  420  shows the rising edge of the ph180 signal  125  is substantially one-half the clock cycle after the ph0 signal  165 .  
         [0048]     In another example of the first operation mode, with reference to  FIGS. 3 and 5 B, the alignment magnitude is set to an initial value of four units since S must be less than I (set S=4 and I=5 for the present example). With the alignment magnitude at four units, the first and second phase aligners  160 ,  170  each have a delay of four units. In this example, the ph0 signal  165  starts out at a delay of four units relative to the clock input  105 . Similarly, the dly0 signal  175  starts out with a delay of eight units relative to the clock input  105 .  
         [0049]     The feedback loop, including the phase comparison combined with increasing or decreasing adjustments of the phase delay magnitude, continues until the phase comparison shows the phase of the dly0 signal  175  and the dly360 signal  199  are substantially in phase. In  FIG. 5B , assuming t Dmin =t I =5, and assuming t A  is fixed at 4, a clock cycle of 14 achieves lock when tCK=14=D+I+D+I−S−S or t D +t D −t A −t A . The first alignment indicator  410  and the second alignment indicator  420  show the rising edge of the ph180 signal  125  is substantially one-half the clock cycle after the ph0 signal  165 . This phase delay magnitude is consistent with the equations noted above.  
         [0050]     In a final example of the first operation mode, with reference to  FIGS. 3 and 5 C, the clock period of  12  is substantially near the minimum delay through the first delay line  110  and the second delay line  120 . In this example, the alignment magnitude is set to an initial value substantially near zero giving the first phase aligner  160  and the second phase aligner  170  delays substantially near zero.  
         [0051]     The feedback loop, including the phase comparison combined with increasing or decreasing adjustments of the phase delay magnitude, continues until the phase comparison shows the phase of the dly0 signal  175  and the dly360 signal  199  are substantially in phase. In  FIG. 5C , with a clock cycle of 12 units, when phase lock is achieved, the phase delay magnitude is about 6 units. The first alignment indicator  410  and the second alignment indicator  420  show the rising edge of the ph180 signal  125  is substantially one-half the clock cycle after the ph0 signal  165 . With the clock cycle at or near the minimum delay of the delay lines, the phase delay magnitude cannot be decreased any further and phase lock will not be possible at smaller clock periods unless the alignment magnitude is increased.  
         [0052]     This situation is when the second operation mode becomes advantageous. In the second operation mode, the phase delay magnitude is held constant, perhaps at the minimum delay, while the alignment magnitude is adjusted by starting at t A  or “S”=max and reducing until lock or t A ˜0. The second operation mode is illustrated in  FIGS. 6A, 6B , and  6 C. In the second mode of operation, the first phase aligner  160  may be contemplated as an element that effectively compresses the clock cycle (i.e., the delay between the ph0 signal  165  and the dly360 signal  199 ), which could not be completely compressed to match the clock input  105  by the phase delay lines because the phase delay magnitude is held constant. The second phase aligner  170  inserts additional alignment magnitude equal to phase aligner  160  into the feedback loop for comparison by the phase detector  150 .  
         [0053]     For example, with reference to  FIGS. 3 and 6 A, assume the phase delay magnitude t D  is set to a minimum delay of 6 units and the clock cycle is  10  units. With a phase delay magnitude at t D +t D =12, the rising edge of the dly360 signal  199  is greater than a clock cycle delay from the rising edge of the clock input  105 . However, the phase aligners  160  and  170  may be used to delay the dly0 signal  175  so that the delay from the dly0 signal  175  to the dly360 signal  199  is substantially near a clock cycle. Rather than changing the phase adjustment signal  152  to modify the phase delay magnitude, the phase detector  150  may change the alignment adjustment signal  158  to increasing or decreasing the alignment magnitude to achieve phase lock. If the alignment magnitude starts near its maximum but still less than or equal to t I ., the phase detector  150  will decrease the alignment magnitude until the dly0 signal  175  and the dly360 signal  199  are substantially in phase, or until t A  or “S” reaches φ (zero) delay. The delay t D  is then increased until lock is achieved.  
         [0054]     In  FIG. 6A , the alignment magnitude is adjusted to 1 unit. Since the dly360 signal  199  is essentially held at fixed point and the dly0 signal  175  is moved closer to the dly360 signal  199 , the ph180 signal  125  must also be moved closer to the dly360 signal  199 . The present example illustrates one of the advantages of the various embodiments of the present invention over the prior art of  FIG. 2 . With respect to the prior art of  FIG.2 , if clock input  105  were set to 10 units and the phase delay magnitude were set to the minimum delay of 6 units, then the alignment magnitude would need to be adjusted to 2 units which would cause ph0 signal  165  to be delay from the clock input  105  by twice the delay as is inserted by the various embodiments of the present invention.  
         [0055]     In another example of the second operation mode, with reference to  FIGS. 3 and 6 B, the phase delay magnitude is set near the minimum delay of 6 units and the clock cycle is 8 units. In similar operation to the  FIG. 6A  diagram explained above, the phase detector  150  adjusts the alignment magnitude until the dly0 signal  175  and the dly360 signal  199  are substantially in phase. In  FIG. 6B , this results in an alignment magnitude of 2 units for the delay through the first phase aligner  160 , and a delay through the second phase aligner  170  of 2 units. Similarly, the present example when implemented on one of the various embodiments of the present invention results in a 2 unit ph0 delay between clock input  105  and the ph0 signal  165  while in the prior art circuit of  FIG. 2 , the ph0 forward path intrinsic delay (ph0 FPID) is increased and the delay between ph0 signal and the input clock is 4 units.  
         [0056]     In another example of the second operation mode, with reference to  FIGS. 3 and 6 C, operation is shown illustrating an alignment magnitude that approaches the clock period. In the  FIG. 6C  example the phase delay magnitude is set near the minimum delay of 6 units and the clock cycle is 6 units. As a result, the dly360 signal  199  is about two clock cycles behind the clock input  105 . However, the alignment magnitude may still be adjusted to a value sufficient to adjust the dly0 signal  175  to be substantially in phase with the dly360 signal  199 . In this case, the phase lock occurs when the alignment magnitude is at 3 units. This operation may be extrapolated to multiple clock cycles difference between the clock input  105  and the dly360 signal  199 . Phase lock may still be achieved if the alignment magnitude is adjustable to at least a full clock period. Generally, S begins at the maximum level which is less than I and the phase aligner is shifted to the right (i.e., as minimum as possible) as much as possible in an attempt to find a locking point. If the phase aligner hits the far right (minimum delay) without locking, then the phase aligner is held at the far right and delay is added to the delay line until a lock is located.  
         [0057]     It will be readily apparent to a person of ordinary skill in the art that the first and second operation modes may be combined in various ways. As an example only, the phase detector  150  may set the alignment magnitude to substantially near zero and enter the first operation mode. The first operation mode may reduce the phase delay magnitude until it is substantially near the minimum delay, or some other desirable delay. The phase detector  150  may then enter the second operation mode and begin increasing the alignment magnitude until lock is achieved.  
         [0058]     The delay lines of the embodiments described above may be comprised of a coarse delay line  130  and a fine delay line  140  similar to the exemplary embodiment shown in  FIG. 4 . In the  FIG. 4  embodiment, the alignment adjustment signal  158  may include a group of coarse adjustment signals  158 A and fine adjustment signals  158 B. An input  132  to the delay line connects to the coarse delay line  130 . The coarse delay line output  134  connects to the fine delay line  140 . A fine delay output  136  may be used as the output of the delay line. It will be readily apparent to a person of ordinary skill in the art that many other configurations and connections of coarse delays and fine delays are possible and contemplated within the invention.  
         [0059]     As shown in  FIG. 7 , a semiconductor wafer  400 , in accordance with the present invention, includes a plurality of semiconductor devices  450  incorporating the phase generator  100  described herein. Of course, it should be understood that the semiconductor devices  450  may be fabricated on substrates other than a silicon wafer, such as, for example, a Silicon On Insulator (SOI) substrate, a Silicon On Glass (SOG) substrate, or a Silicon On Sapphire (SOS) substrate, a gallium arsenide wafer, an indium phosphide wafer, or other bulk semiconductor substrates. As used herein, the term “wafer” includes and encompasses all such substrates.  
         [0060]     As shown in  FIG. 8 , an electronic system  500 , in accordance with the present invention, comprises at least one input device  510 , at least one output device  520 , at least one processor  530 , and at least one memory device  540 . The memory device  540  comprises at least one semiconductor memory  450 ′ incorporating the phase generator  100  described herein in a DRAM device. It should be understood that the semiconductor memory  450 ′ may comprise a wide variety of devices other than, or in addition to, a DRAM, including, for example, Static RAM (SRAM) devices and Flash memory devices.  
         [0061]     Although this invention has been described with reference to particular embodiments, the invention is not limited to these described embodiments. Rather, the invention is limited only by the appended claims, which include within their scope all equivalent devices or methods that operate according to the principles of the invention as described.