Abstract:
A method for dividing a plurality of multiphase signals comprising performing resetable divider stages to the plurality of multiphase signals forming a plurality of divided multiphase signals having a monotonic increasing phase with equal spacing and an ideal duty cycle of 50% through a plurality of resetable dividers, wherein the plurality of divided multiphase signals have no phase ambiguity; and producing a plurality of periodic reset signals to the plurality of resetable dividers to enable the plurality of resetable dividers to divide the plurality of multiphase signals in a timely correct sequence to form the divided multiphase signal through a reset signal generator, the plurality of periodic reset signals being produced by a combinational network of the reset signal generator, the combination network is configured for generating a number of pulses based on the plurality of multiphase signals and performing a plurality of decimation stages and wherein the periodic reset signals are generated solely in response to the plurality of multiphase signals.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. patent application Ser. No. 11/871,578, filed Oct. 12, 2007, now U.S. Pat. No. 7,323,913, the contents of which are incorporated herein by reference thereto. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to frequency dividers that divide a set of multiphase signals such that the multiphase characteristic of having a monotonic and equally spaced phase increase with 50% duty cycle is still maintained in the divided multiphase output signals. 
   2. Description of Background 
   A multiphase signal is defined as a set of sinusoidal or rectangular signals with the individual signal components having equally spaced phase differences and a monotonic increase of phase when going from one signal to the next one. A typical example of a multiphase signal generator is a ring oscillator used for instance as voltage-controlled oscillator (VCO) in a phase-locked loop circuit (PLL). Such a ring oscillator consists of a ring of N identical delay cells each having a delay of τ D . The oscillation frequency is then given by f osc =1/T=1/2Nτ D . If each delay cell output is fed to the output of the VCO, the oscillator provides N output signals each oscillating with f osc  but also each having a phase difference of 2π/N with respect to its neighboring signal. The total of N signals is termed multiphase signal whereas the phase of the individual signals monotonically increases by the equal spacing of 2π/N when going from one signal to the next one. In terms of time units the phase differences between the individual components of the multiphase signal can also be expressed as T/N where T denotes the period of the multiphase signal. 
   A conventional multiphase divider is shown in  FIG. 1 . It consists of N toggle flip-flops according to the N components of the multiphase input signal. All of the toggle flip-flops are operated in parallel to each other. They are implemented as D-flip flops with a cross-connected feedback path from the inverting output Qb to the data input D. By cascading M of these toggle flip-flops a frequency division ratio of M can be obtained. The concatenation is carried out by connecting the non-inverting output Q of the previous divider stage to the clock input of the D-flip flop belonging to the succeeding divider stage. As will be explained in more detail below the straightforward implementation as shown in  FIG. 1  has the drawback of suffering from a so-called phase ambiguity problem. That phase ambiguity problem is associated to the cross-connected feedback path (connection from Qb to D) in the toggle flip-flops that can assume an arbitrary state (either logical one or zero) at start-up and is a consequence of the mutual independency of the individual dividers. Because of this non-well defined initial state the dividers may start dividing in such a way that the divided output signal is no longer a valuable multiphase signal as the characteristic of having a monotonic increase of equally spaced phases got lost. This characteristic is however of great importance for the application of a multiphase division as will be explained below. 
     FIG. 2  shows another multiphase divider configuration known in the art. This multiphase divider consists of a set of resetable dividers and a reset delay circuit, which is clocked by one of the multiphase input signals and delays a reset signal coming from an external source. The dividers only take one out of N multiphase signals for the division. To generate a plurality of divided multiphase signals at their output, each of the individual dividers receive a reset signal from the reset delay circuit, which is basically a shift register (sequential logic) for the reset signal and thereby defines the starting point for the division of each individual divider such that the divided outputs are appropriately time-shifted to represent the desired divided multiphase phase signal. The shortcoming of this prior art configuration is that a true multiphase division is not performed but rather a single phase division because only one out of N multiphase inputs is actually used for the division. Consequently, the phase ambiguity problem does not occur; however, the division scheme completely relies on a single phase of the multiphase input. If the phase signal is affected by timing jitter or duty cycle distortion, all of the divided multiphase outputs are affected in the same way, which may be detrimental to the application of such a multiphase divider in a serial link receiver. Moreover, the duty cycle distortion may become a problem because one of the multiphase signals at the input will be much more loaded (higher driving capacity) than all the others because that single phase signal has to drive all of the dividers and also provides the clock for the reset delay circuit. Furthermore, the timing of the multiphase output may also be affected to a certain degree by the timing accuracy of the shift register in the reset delay circuit. 
   The implementation of a multiphase divider is not as straightforward as it is compared to the case when just having to divide a single-ended or a differential signal. A phase ambiguity problem occurs because of the mutual independency of the dividers when only using a number of conventional dividers in parallel. 
   When a multiphase signal consisting of, for example, six phases is divided by means of three parallel differential conventional dividers, the divided outputs may have phase ambiguity. An exemplary graph of such phase ambiguity is shown in  FIG. 3 . It can be seen that the important requirement of having the phases of the six signals monotonically increasing is violated because two out of the six signals got swapped during the division. The incorrect phases are encircled with a dashed circle. The dashed straight line indicates how the individual phases should run if they were a correct multiphase signal with monotonic phase increase and equal spacing between the individual phases. The swapping can be regarded as a 180-degree phase shift applied to the corresponding signals. This is an example of the phase ambiguity problem that is caused by the fact that the feedback paths in a conventional divider (typically implemented as a cross-coupled feedback connected D-flip flop also known as toggle flip flop) either assumes a 0-degree (e.g. logical 0) or a 180-degree (e.g. logical 1) state with respect to the pertinent input signal. 
   One solution to the phase ambiguity problem is to have the parallel dividers be dependent on each other. However, this approach suffers from requiring the introduction of internal feedback loops that may affect the required 50% duty cycle requirement, which is of great importance to prevent bimodal jitter effects in a half-rate receiver architecture. Another solution is to have appropriate startup conditions that remedy these shortcomings. 
   Currently, no designs employ a multiphase divider in their feedback path from the VCO to the phase detector in order to make the phase-rotating PLL (P-PLL) a frequency multiplying PLL. Since no feedback divider is used (the feedback division ratio equals 1 in that case), most current designs have to use a reference signal for the P-PLL that equals in frequency the output signals of the P-PLL used to drive the sampling latches in the serial link receiver. 
   If for instance the serial data stream is transmitted at 10 Gb/s, the P-PLL needs to provide a 5 GHz multiphase signal with a perfect 50% duty cycle if the serial link receiver is of a half-rate architecture with 3-fold oversampling per bit and a multiphase signal consisting of 6 phases is assumed. As a consequence thereof, the reference signal of the P-PLL also needs to be at 5 GHz for this 10 Gb/s serial link. Typically there are tens or hundreds of serial links on a chip that all need to receive a reference signal for their P-PLL type of link receiver. Distributing for instance a 5 GHz clock signal to all of these many link receivers consumes a considerable amount of power because the power consumption P is in a first order proportional to the frequency (P=C·VDD 2 ·f where C denotes the load capacitance, VDD the supply voltage and f the frequency). Reducing the frequency of the reference clock signal would therefore help save a lot of power. 
   SUMMARY OF THE INVENTION 
   The shortcomings of the prior art are overcome and additional advantages are provided through the provision of a method for dividing a plurality of multiphase signals comprising: performing resetable divider stages to the plurality of multiphase signals forming a plurality of divided multiphase signals having a monotonic increasing phase with equal spacing and an ideal duty cycle of 50% through a plurality of resetable dividers, wherein the plurality of divided multiphase signals have no phase ambiguity; and producing a plurality of periodic reset signals to the plurality of resetable dividers to enable the plurality of resetable dividers to divide the plurality of multiphase signals in a timely correct sequence to form the divided multiphase signal through a reset signal generator, the plurality of periodic reset signals being produced by a combinational network of the reset signal generator, the combination network is configured for generating a number of pulses based on the plurality of multiphase signals and performing a plurality of decimation stages and wherein the periodic reset signals are generated solely in response to the plurality of multiphase signals 
   Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with advantages and features, refer to the description and to the drawings. 
   TECHNICAL EFFECTS 
   As a result of the summarized invention, technically we have achieved a solution for implementing a multiphase divider that solves the phase ambiguity problem and forms a plurality of divided multiphase signals having a monotonic increasing phase with equal spacing and an ideal duty cycle of 50%. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
       FIG. 1  illustrates a schematic diagram of a conventional multiphase divider scheme that suffers from phase ambiguity; 
       FIG. 2  illustrates a schematic diagram of another conventional multiphase divider scheme using a reset delay circuit and deriving a multiphase output from a single phase signal of a plurality of multiphase inputs; 
       FIG. 3  illustrates an exemplary timing diagram showing a divided multiphase signal having phase ambiguity; 
       FIG. 4  illustrates a schematic diagram of a multiphase divider in accordance with one exemplary embodiment being incorporated in a feedback path from an oscillator to a phase detector in accordance with one exemplary embodiment of the present invention; 
       FIG. 5  illustrates another exemplary timing diagram showing a divided multiphase signal using the multiphase divider in accordance with one exemplary embodiment of the present invention; 
       FIG. 6  illustrates a schematic diagram of the multiphase divider in accordance with one exemplary embodiment of the present invention; 
       FIG. 7  illustrates a schematic diagram of a resetable divider used in the multiphase divider in accordance with one exemplary embodiment of the present invention; and 
       FIG. 8  illustrates a timing diagram of signals of the multiphase divider in accordance with one exemplary embodiment of the present invention. 
   

   The detailed description explains the preferred embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
   DETAILED DESCRIPTION OF THE INVENTION 
   The inventor herein has recognized that appropriate startup conditions can be provided by means of a reset signal generation such that independent parallel dividers are forced to divide the multiphase signal in a correct order without phase ambiguity while maintaining a duty cycle that is ideally 50%. 
   Multiphase signals are typically used in serial link receivers to provide the required sampling phases for the latches that sample the received serial data stream. An example of a serial link receiver used in conjunction with the multiphase divider of the present invention is shown in  FIG. 4 . The serial link receiver communicates with a phase-rotating PLL (P-PLL) that provides, according to one example, six phases to the sampling latches of the receiver. The P-PPL may be any conventional P-PPL known in the art. The sampling latches take a number of edge and data samples (e.g. 4 edge samples and 2 data samples taken from 2 received bits) of the incoming serial data stream from the link transmitter, which could for instance be located in the input-output device (I/O) of a central-processing-unit (CPU) whereas the receiver might reside for instance in the I/O of a memory chip attached to the CPU. The edge and data samples are then further processed in a clock-data-recovery (CDR) unit of the serial link receiver that provides the received data bits to a succeeding higher-level logic. In addition, the CDR unit also outputs a control signal to a phase detector in the P-PLL that indicates whether the P-PLL has to increase or decrease the reference phase of its multiphase output signal. The reference phase could be any one of the multiphase signals that is correctly aligned to one of the edges of the received serial data stream. If for instance the edge of the sampling signal occurs prior to the edge of the data signal, the control signal generated by the CDR unit indicates that the phase should be increased (up control signal) because the sampling of the incoming data bit has occurred too early. Likewise, a signal for decreasing (down control signal) is indicated by the CDR unit if the sampling edge occurs after the data edge. In other words, if the phase needs to be adjusted, the P-PLL increments or decrements all of the phases of its multiphase signal by the same amount (e.g., α·2π/N, where α is a fractional number between 0 and 1). 
   The rotation of the phase is performed by means of a phase interpolation within the phase detector. A non-limiting example of how phase interpolation or phase blending works can be found in U.S. patent application Ser. No. 60/216,952, filed Aug. 31, 2005, the contents of which are incorporated herein by reference thereto. The phase detector in the P-PLL needs for a proper operation a multiphase signal with the characteristics of having a monotonic increase of equally spaced phases as described above. The P-PLL includes other components, such as the I/V-converter and the loop filter, which may be any conventional converter and loop filter used in a conventional PLL that does not rotate the phase of its output signal(s). 
   An example of a correctly performed multiphase division using the proposed multiphase divider as will later be described in greater detail below is shown in  FIG. 5 . It can be seen that the phase of the divided multiphase signal is monotonically increasing with equal spacing and a 50% duty cycle. The dashed straight line indicates how the phase gets increased when going from one component of the multiphase signal to the next one. The boxes shown around the first cycles of the divided multiphase signal indicate where the correcting measures imposed by the reset signals come into play. During these time intervals the individual divider output signals are forced to assume the correct states. 
   Now turning to a discussion of a multiphase divider in accordance with one exemplary embodiment of the present invention.  FIG. 6  illustrates a multiphase divider  100  in accordance with one exemplary embodiment of the present invention. The multiphase divider  100  may be incorporated in the feedback path from an oscillator (e.g., VCO) to a phase detector in order to make a P-PLL a frequency multiplying PLL as shown in  FIG. 4 . The multiphase divider  100  addresses the phase ambiguity problem occurring when dividing a multiphase signal with mutually independent divider stages. The multiphase divider  100  may be applied to a P-PLL type of serial link receiver. The multiphase divider  100  includes a first multiphase division section  102  (odd) and a second multiphase division section  104  (even) each dividing by a factor of two. The multiphase divider  100  further includes a reset signal generator  106  having combinational logic for producing periodic reset signals reset  1 , reset  2 , reset  3  to a resetable divider stage  108  of the multiphase divider  100 . 
   The multiphase divider  100  includes six input phases  109  (in_ph0, in_ph60, in_ph120, in_ph180, in_ph240 and in_ph300-degrees). In an actual P-PLL receiver the six phases  109  could be used to implement a half rate system with 2 data samples (obtained by the phases in_ph60 and in_ph240) and 4 edge samples (obtained by the phases in_ph0, in_ph120, in_ph180 and in_ph300). 
   In  FIG. 6 , the input phase signals  109  are first combined by XOR gates  110 ,  112 ,  114  in the following way:
 
 x 1=( i 0 ;i 180) XOR ( i 60; i 240)
 
 x 2=( i 60 ;i 240) XOR ( i 120; i 300)
 
 x 3=( i 120 ;i 300) XOR ( i 180 ;i 0)
 
where for instance (i 0 ;i 180 ) denotes the differential input phase pair consisting of phases 0 and 180-degrees. To simplify matters in_ph0 equals i 0 , and likewise this nomenclature also applies to the other phase signals. The input phase signals  109  are correspondingly combined by exclusive OR gates or XOR gates resulting in signals or pulse traces x 1 , x 2  and x 3  as shown in  FIG. 8 . Signals x 1 , x 2  and x 3  contain the desired reset pulses that need to be filtered out by means of the succeeding decimation stages applied to the signals x 1 , x 2  and x 3  in the next steps. The succeeding decimation stages are configured to reduce the number of pulses within the pulse traces as shown in  FIG. 8 .
 
   To perform the required filtering of the pulse traces x 1 , x 2 , x 3  obtained after the XOR-operation of the input phase signals  109 , two steps of decimation are performed. In the first decimation stage, the signals x 1 , x 2  and x 3  are fed to AND-gates  120 ,  122 ,  124  respectively whose second input signals correspond to those in-phase input signals  109  that have not been used at the XOR-gates  110 ,  112 ,  114  of that branch. For instance at the AND-gate  120  the signal i 120  is used because the second input signal x 1  was derived from a subset of the input signals—namely (i 0 ;i 180 ) and (i 60 ;i 240 )—that did not contain the signal i 120 . Likewise the phase signal i 0  is taken as the second input for the AND-gate  122 , while phase signal i 240  is used as the second input for the AND-gate  124 . This mapping of phase signals to the inputs of the AND-gates  120 ,  122 ,  124  of the first decimation stage takes into account that there are three independent in-phase components in this multiphase input signal  109 —namely i 0 , i 60  and i 120 , and three out-of-phase components—namely i 180 , i 240  and i 300  that are just the complement of the in-phase components. This first decimation stage yields the following signals:
 
y1=x1 AND i120
 
y2=x2 AND i0
 
y3=x3 AND i240
 
which are also shown in  FIG. 8 . This decimation stage reduces the number pulses in y 1  through y 3  by a factor of two with respect to the number of pulses in x 1  through x 3 .
 
   In the second decimation stage, the output (r 60 ;r 240 ) of a replica divider  126  located in the reset signal generator  106  performs a replica divide-by-2 stage. The replica divide-by-2 stage is performed in order to make sure that no feedback latency occurs that may deteriorate the duty cycle of the divided output signal. The replica divider  126  is considered a master divider performing a master divider stage. The differential outputs of the replica divider  126  labeled r 60  and r 240  are used to select the three final reset pulses reset 1 , reset 2 , reset 3  that are then applied to resetable dividers  160 ,  162 ,  164  in the resettable divider stage  108  in order to force them to divide in a timely correct synchronous way. 
   Because the replica divider  126  is operated in parallel to the combinational logic (XOR-gates  110 ,  112 ,  114  and AND-gates  120 ,  122 ,  124 ) used to generate and decimate the reset pulses, the rising or falling edges of the replica divider output signals r 60  and r 240  do not occur within the pulse width of one of the pulses in signals y 1  through y 3 . As such, outputs of the first decimation stage (XOR-gates  110 ,  112 ,  114  followed by the AND-gate  120 ,  122 ,  124 )—namely y 1 , y 2  and y 3 , are delayed by a delay τ  130 ,  132 ,  134  such that none of their pulses occur at the transitions of the replica divider signal. In other words, the delay τ is used to match the latency of the replica divider and the combinational logic so that the signals r 60  and r 240  can optimally be used in the final decimation stage to obtain the reset signals reset 1 , reset 2  and reset 3 . The value of τ  130 ,  132 ,  134  implemented for instance as a cascade of inverter stages can be determined at the time of the circuit design based on simulation results of the replica divider latency Δt 1  and the latency Δt 2  through the first part of the combinational network whereas all of the three branches (XOR gate  110  and AND gate  120 , XOR gate  112  and AND gate  122 , XOR gate  114  and AND gate  124 ) ideally have the same latency Δt 2  and hence the same amount of τ is needed for all of the three branches in the combinational network. 
   In  FIG. 8 , an example is shown of how the signals y 1 , y 2 , y 3  are shifted (delayed) by r. It can be seen that some of the pulses in y 3  are hit by the edges of r 60  and r 240  (see for instance the encircled pulse in y 3 ). The criterion for choosing τ is to avoid such a constellation between y 60 , r 240  and y 1 , y 2 , y 3 . In this example y 1 , y 2 , y 3  are therefore delayed by τ such that the edges of r 60 , r 240  do not hit any of the pulses of y 1 , y 2 , y 3 . 
   The delayed signals y 1 , y 2 , y 3  are indicated in  FIG. 6  and  FIG. 8  by a prime symbol:
 
 y 1 ′=y 1( t +τ)
 
 y 2 ′=y 2( t +τ)
 
 y 3 ′=y 3( t +τ)
 
Ideally the rising or falling edges of the replica divider output signals r 60 , r 240  have to occur in the middle of the spacing between two adjacent pulse pairs (e.g., in the middle of the spacing between the y 3 ′-pulses and y 1 ′-pulses). The spacing between two adjacent pulse pairs has a width of ⅙ of the period Tc 0  of the input signal  109 . Thus, the inserted delay τ  130 ,  132 ,  134  does not need to be very accurate as long as the condition is met that the edges of r 60  and r 240  occur within the period of time of ⅙ Tc 0 . This also greatly relaxes the requirements in terms of allowable process variations (PVT).
 
   The last decimation stage finally yields the required reset signals by another AND-operation  140 ,  142 ,  144  applied to the delayed pulse patterns y 1 ′, y 2 ′, y 3 ′ of the previous decimation stage and the replica divider output signals r 60 , r 240 . It can be expressed as
 
reset1=y1′ AND r240
 
reset2=y2′ AND r60
 
reset3=y3′ AND r240
 
Note that the signals reset 1  and reset 3  are obtained by the AND-operation  140 ,  144  with r 240  and signal reset 2  is obtained by the AND-operation  142  with r 60 . The same reset signals may be obtained even if the replica divider  126  starts dividing with an opposite polarity. Thus, the phase ambiguity of the resetable dividers  160 ,  162 ,  164  can be removed because the reset signals reset 1 , reset 2 , reset 3  still remain the same regardless of how the replica divider  126  starts dividing with respect to the multiphase input signal  109 .
 
     FIG. 7  illustrates a transistor-level schematic of each of the resetable dividers  160 ,  162 ,  166  as used in  FIG. 6 . It is implemented in complementary pass-gate transistor logic (CPL) comprising of a master  166  and a slave  168  part of a D-flip flop with differential reset, data and clock inputs and a differential output signal out and outb. The reset signals reset 1 , reset 2  and reset 3  of  FIG. 6  and  FIG. 8  force the internal feedback paths  170  to assume well-defined states such that the phase ambiguity problem does not occur. 
   The reset signal generation performed in the first multiphase division section  102  as described above and illustrated in  FIG. 6  results in a divided multiphase signal  172 , which is in reversed order of the phase order of the input phase signal  109 . This is indicated in  FIG. 6  by the order of how the individual components of the multiphase signals  109 ,  172  and  174  are labeled. For instance, the input phase signal  109  at the first multiphase division section  102 —the odd multiphase divider stage (left block), are labeled from top to bottom starting with in_ph0 down to in_ph300. At the output  104  of the first multiphase division section  102 , the signals are labeled from top to bottom starting with div2_ph300 and ending with div2_ph0. At the second multiphase division section  104 —the even multiphase divider stage (right block), outputs  174  are reversed so that the signal labeling starts with div4_ph0 at the top and ends with div4_ph300 at the bottom. This alternating order of multiphase signals is caused by the chosen definition of the XOR-operation and the successive decimation operations and makes it necessary to distinguish between odd and even divider stages. The distinction between the odd and even divider stages is associated to the last decimation stage where the reset 1 and reset 3 signals are generated with r 60  instead of r 240  (see  FIG. 6 ). In sum, the reset signals at the last decimation stage in the odd and even sections are as follows:
 
reset1_odd=y1′ AND r240
 
reset1_even=y1′ AND r60
 
reset2_odd=reset2_even=y2′ AND r60
 
reset3_odd=y3′ AND r240
 
reset3_even=y3′ AND r60
 
   However, if only a multiphase divide-by-two division is to be performed, it is sufficient to just use the above described odd divider stage. If the multiphase divider should perform a divide-by-four division, an odd followed by an even divider stage must be used. Analogously, at a divide-by-eight division, the succession of divider stages is: odd-even-odd and so forth for a higher division factor (e.g., 1/32: odd-even-odd-even-odd, where each odd and even stage is defined as shown in  FIG. 6 ). 
   If a different definition of the XOR-operation is applied, like for instance
 
 x 1 —   alt =( i 0 ;i 180) XOR ( i 300 ;i 120)
 
 x 2 —   alt =( i 300 ;i 120) XOR ( i 240 ;i 60)
 
 x 3 —   alt =( i 240 ;i 60) XOR ( i 180 ;i 0)
 
where _alt stands for ‘alternative’, the direction of phase increase indicated by the dashed diagonal lines in  FIG. 8  is reversed. Likewise the definition of the first and second decimation stages has to be changed as well:
 
y1_alt=x1 AND i60
 
y2_alt=x2 AND i180
 
y3_alt=x3 AND i300
 
 y 1′ —   alt=y 1 —   alt ( t +τ)
 
 y 2′ —   alt=y 2 —   alt ( t +τ)
 
 y 3′ —   alt=y 3 —   alt ( t +τ)
 
reset1_alt=y1′ AND r60
 
reset2_alt=y2′ AND r60
 
reset3_alt=y3′ AND r240
 
   This is an example of another implementation. It should be understood that there are many other versions of implementation depending on how the pulse generation, the pulse decimation and the replica divider input signals are defined with respect to each other. All of these potential implementations rely in principle on using a reset signal generator consisting of a replica divider and a combinational network to produce a set of reset signals that force the actual divider stages in the multiphase divider to divide in a timely correct manner such that the phase ambiguity problem is eliminated. 
   Advantageously, the present invention described above includes, without limitation: the application of a multiphase divider in a P-PLL type of serial link receiver to accomplish a frequency multiplication within the P-PLL, which in turn allows reducing the external reference signal by a factor equal to the division ratio of the multiphase divider and hence allows saving power in the clock distribution network because of the slower reference clock signal. 
   The flow diagrams depicted herein are just examples. There may be many variations to these diagrams or the steps (or operations) described therein without departing from the spirit of the invention. For instance, the steps may be performed in a differing order, or steps may be added, deleted or modified. All of these variations are considered a part of the claimed invention. 
   While the preferred embodiment to the invention has been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.