Abstract:
A DLL circuit includes a fine delay circuit including a first inverter circuit, a second inverter circuit and delay units. The first inverter circuit has an output terminal connected to an output terminal of the second inverter and the first and second inverters are configured of inverters of different sizes. A phase comparator compares a delay clock&#39;s phase with a reference clock&#39;s phase and a result of the phase comparison is referred to to count addresses which are in turn used to selectively drive the inverters configuring the first and second inverter circuits, to allow the fine delay circuit to output a signal having a phase between signals having therebetween a phase difference of a fixed amount. Thus the clock&#39;s phase can be adjusted with high precision.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to delay locked loop (DLL) circuits useful for use in semiconductor integrated devices and particularly to DLL circuits capable of adjusting a clock&#39;s phase with high precision.  
           [0003]    2. Description of the Related Art  
           [0004]    A conventional DLL circuit employs a delay chain such as an inverter chain to provide phase matching. The phase matching is provided by automatically selecting from the delay chain&#39;s amount of delay varying by a fixed value an amount of delay as required, and holding the amount of delay selected. To provide phase matching with higher precision than the fixed value, as shown in FIG. 14, between inverters  60  and  70  capacitors  62 ,  64 ,  66  having different levels of capacitance are connected via N-channel MOS transistors  61 ,  63 ,  65  and addresses a 0 , a 1 , a 2  are applied to selectively turn on/off N-channel MOS transistors  61 ,  63 ,  65 . Thus, two inverters  60  and  70  provide an amount of delay in a fixed range for adjusting a clock&#39;s phase.  
           [0005]    In the conventional DLL circuit, however, the inverter chain provides a fixed amount of delay and the capacitors provide a delay smaller than the fixed amount of delay and the inverter chain and the capacitors employ different delay systems. As such, voltage, process and temperature affect the inverter chain and the capacitor differently and the clock&#39;s phase can hardly be adjusted.  
           [0006]    The FIG. 14 capacitors  62 ,  64 ,  66  capacitance variation disadvantageously results in capacitors  62 ,  64 ,  66  having an amount of delay exceeding an amount of delay provided by inverters  60  and  70 , so that the clock&#39;s phase cannot be adjusted in the range of the amount of delay of inverters  60  and  70  with high precision.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention contemplates a DLL circuit impervious to voltage, process, temperature and the like and thus capable of adjusting a phase of a clock with high precision.  
           [0008]    In accordance with the present invention the DLL circuit includes a phase comparator, a counter, a first delay circuit and a second delay circuit. The phase comparator compares a phase of a delay clock with a phase of a reference clock. The counter refers to a result received from the phase comparator, to provide a counting up/down operation and output first and second addresses. The first delay circuit in response to the reference clock generates first and second signals having therebetween a phase difference of a fixed amount and responds to the generated first and second signals and refers to the first signal to generate a fine adjustment clock existing between a phase of the first signal and a phase of the second signal. The second delay circuit refers to the second address to delay the fine adjustment clock by the fixed amount multiplied by an integer to output a delay clock.  
           [0009]    In the present DLL circuit, a result of comparing a phase of a delay clock with that of a reference clock can be referred to to provide a counting up/down operation to generate first and second addresses. The first address can be referred to to provide fine control to control the reference clock&#39;s phase in the range of a fixed amount T and the second address can be referred to provide coarse control to control the reference clock&#39;s phase with the precision of the fixed amount T. Thus the delay clock&#39;s phase can be matched to the reference clock&#39;s phase in the order smaller than the fixed amount T with high precision. 
       
    
    
       [0010]    The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    In the drawings:  
         [0012]    [0012]FIG. 1 is a block diagram showing a configuration of a DLL circuit in an embodiment of the present invention;  
         [0013]    [0013]FIG. 2 is a circuit diagram showing a configuration of the phase comparator of the FIG. 1 DLL circuit;  
         [0014]    [0014]FIG. 3 is a block diagram showing a configuration of the counter of the FIG. 1 DLL circuit;  
         [0015]    [0015]FIG. 4 is a circuit diagram showing a configuration of each counter unit of the FIG. 3 counter;  
         [0016]    [0016]FIG. 5 is timing plots representing the FIG. 4 counter unit operation;  
         [0017]    [0017]FIG. 6 is timing plots representing addresses output from the FIG. 3 counter at each low to high transition of a reference clock when a delay clock is logical high;  
         [0018]    [0018]FIG. 7 is timing plots representing an address output from the FIG. 3 counter at each low to high transition of a reference clock when a delay clock is logical low;  
         [0019]    [0019]FIG. 8 shows a configuration of a first delay circuit of the FIG. 1 DLL circuit;  
         [0020]    [0020]FIG. 9 is a circuit diagram showing a configuration of each fine delay unit of the FIG. 8 delay circuit;  
         [0021]    [0021]FIG. 10 is timing plots representing the FIG. 8 fine delay circuit operation;  
         [0022]    [0022]FIG. 11 illustrates that the FIG. 8 fine delay circuit can change a phase in the order smaller than a fixed amount;  
         [0023]    [0023]FIG. 12 is a circuit diagram showing a configuration of the coarse delay circuit of the FIG. 1 DLL circuit;  
         [0024]    [0024]FIG. 13 is a circuit diagram showing a configuration of each decoder of the FIG. 12 coarse delay circuit; and  
         [0025]    [0025]FIG. 14 is a circuit diagram showing a conventional inverter chain for fine adjustment of a phase of a clock. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    The embodiments of the present invention will now be described with reference to the drawings. In the figures, like portions are labeled like reference characters and a description thereof will not be repeated.  
         [0027]    With reference to FIG. 1, the present invention provides a DLL circuit  100  including a phase comparator  10 , a counter  20 , a fine delay circuit  30  and a coarse delay circuit  40 .  
         [0028]    Phase comparator  10  receives a reference clock CLK and a delay clock CLKD, compares a phase of delay clock CLKD with a phase of reference clock CLK, and outputs a result of comparing the phases of the clocks.  
         [0029]    Counter  20  refers to the result received from phase comparator  10 , to provide a counting up/down operation and output addresses a 0 -a 2  and addresses a 3 -a 5 .  
         [0030]    Fine delay circuit  30  delays a clock with precision. It receives reference clock CLK and addresses a 0 -a 2  from counter  20  and employs the method as described later to generate a fine adjustment clock CLKB from reference clock CLK and output the generated reference clock CLK. Coarse delay circuit  40  roughly delays a clock. It receives fine adjustment clock CLKB from fine delay circuit  30  and addresses a 3 -a 5  from counter  20  and employs a method described later to delay fine adjustment clock CLKB by a fixed amount multiplied by an integer to output a delay clock CLKD. The output delay clock CLKD is input to phase comparator  10  and also externally output via an output terminal OUT.  
         [0031]    With reference to FIG. 2, phase comparator  10  includes NANDs  101 - 107  and an inverter  108 . NANDs  101  and  102  function as a flip-flop and so do NANDs  103  and  104  and NANDs  106  and  107 . Thus, phase comparator  10  compares a phase of delay clock CLKD with that of reference clock CLK and outputs through a terminal UP a signal depending on the delay clock CLKD phase delay. It should be noted that the present embodiment does not use a terminal DN.  
         [0032]    With reference to FIG. 3, counter  20  includes counter units  201 - 206  and inverters  207 - 212 . Counter units  201 - 206  each includes, as shown in FIG. 4, inverters  213 ,  219 ,  220 ,  224 ,  225 ,  226 ,  231 , N-channel MOS transistors  214 ,  216 ,  221 ,  223 ,  227 ,  229 , P-channel MOS transistors  215 ,  217 ,  228 ,  230 , clocked inverters  218 ,  222 , and an NOR gate  232 .  
         [0033]    When the FIG. 4 counter unit receives a phase comparison result UP from phase comparator  10 , reference clock CLK,/CLK and a reset signal RST, the counter unit outputs a carrier signal C and a data signal D, as shown in FIG. 5. When phase comparator  10  compares the delay clock CLKD phase with the reference clock CLK phase and it has been found that whenever reference clock CLK transitions from low to high delay clock CLKD is logical high, the counter units  201 - 206  terminals UPs receive a high level signal and counter  20  generates the FIG. 6 addresses a 0 -a 5  in each cycle of reference clock CLK. If whenever reference clock CLK transitions from low to high delay clock CLKD is logical low, the counters  201 - 206  terminals UPs receive a low level signal and counter  20  generates the FIG. 7 addresses a 0 -a 5  in each cycle of reference clock CLK. Thus, counter  20  referring to the result obtained from phase comparator  10  generates addresses a 0 -a 5  and outputs addresses a0-a2 to fine delay circuit  30  and addresses a 3 -a 5  to coarse delay circuit  40 .  
         [0034]    With reference to FIG. 8, fine delay circuit  30  includes a delay unit  301 , clocked inverters  302 - 308 , delay units  309  and  310 , and an inverter  311 . Clocked inverter  302  has an output terminal connected to an output terminal of clocked inverter  303 . Clocked inverter  304  has an output terminal connected to an output terminal of clocked inverter  305 . Clocked inverter  306  has an output terminal connected to an output terminal of clocked inverter  307 . Clocked inverters  302 ,  304 ,  306 ,  308  are connected in parallel and so are clocked inverters  303 ,  305 ,  307 . Clocked inverters  302 ,  303  have a channel width (hereinafter simply referred to as a “size”) n allowing p and n channel MOS transistors configuring an inverter to be equal in channel width, clocked inverters  304  and  305  are of the same size 2 n, clocked inverters  306  and  307  are of the same size 4 n and clocked inverter  308  has size n. Clocked inverters  302 ,  303  are driven by addresses a 0 ,/a 0  output from counter  20 , and when clocked inverter  302  is driven clocked inverter  303  is not driven and when clocked inverter  302  is not driven clocked inverter  303  is driven. More specifically, when address a 0  is logical low clocked inverter  302  is driven and when address a 0  is logical high clocked inverter  303  is driven. Clocked inverters  304 ,  305  are driven by addresses a 1 ,/a 1  output from counter  20  and clocked inverters  306 ,  307  are driven by addresses a 2 ,/a 2  output from counter  20 . Clocked inverters  304  and  305  and clocked inverters  306  and  307  are driven in the same manner as clocked inverters  302  and  303 .  
         [0035]    With reference to FIG. 9, delay units  301 ,  309 ,  310  each include clocked inverters  312  and  313  and an inverter  314 . Clocked inverter  312  is driven in response to a signal R of logical low and for an input signal XA functions as an inverter, while clocked inverter  313  is not driven. Clocked inverter  313  is driven in response to signal R of logical high and for an input signal XB functions as an inverter, while clocked inverter  312  is not driven. Thus, depending on whether signal R is logical low or high, clocked inverter  312  or  313  is driven and input signal XA or XB is inverted and thus input to inverter  314 , which further inverts the received inverted signal and thus provides an output signal Y. Thus, delay units  301 ,  309 ,  310  delays the input signals XA and XB phases by a fixed amount T.  
         [0036]    Again with reference to FIG. 8, delay unit  301 , with signal R of logical high and signal /R of logical low, delays the received reference clock CLK phase by the predetermined amount T and thus outputs a signal INF. Similarly, delay unit  309  delays the received reference clock CLK phase by the fixed amount T and thus outputs a signal Y. Delay unit  310 , with signal R of logical low and signal /R of logical high, delays the received signal XA (Y) phase by the fixed amount T and thus outputs a signal IND. Thus, signal INF corresponds to the reference clock CLK phase delayed by the fixed amount T and signal IND corresponds to the reference clock CLK phase delayed by the fixed amount T multiplied by two. Thus signals INF and IND have therebetween a phase difference of the fixed amount T.  
         [0037]    Clocked inverters  302 - 307  are activated selectively by addresses a 0 -a 2  output from counter  20 . When counter  20  outputs addresses a 0 , a 1  and a 2  all equal to 0, clocked inverters  302 ,  304 ,  306 ,  308  are activated and clocked inverters  302 ,  304 ,  306 ,  308 , connected in parallel, have a composite size w f  of n+2 n+4 n+n  32  8 n, while clocked inverters  303 ,  305 ,  307  are not activated and clocked inverters  303 ,  305 ,  307 , connected in parallel, have a composite size w d  of 0.  
         [0038]    For addresses a 0 , a 1  and a 2  all equal to 1, clocked inverters  302 ,  304 ,  306  are not activated and clocked inverters  303 ,  305 ,  307 ,  308  are activated, resulting in composite size w f  of n and composite size w d  of 7 n. For all addresses a 0 -a 2 , composite sizes w f  and w d  are calculated, as provided in Table 1:  
                               TABLE 1                       a0   a1   a2   Wf   Wd                   0   0   0   8n   0       1   0   0   7n   n       0   1   0   6n   2n       1   1   0   5n   3n       0   0   1   4n   4n       1   0   1   3n   5n       0   1   1   2n   6n       1   1   1   n   7n                  
 
         [0039]    For addresses a 0 -a 2 , composite size w f  varies from 8 n to n and composite size w d  varies from 0 to 7 n. As such, clocked inverters  302 ,  304 ,  306 ,  308  connected in parallel are considered a single clocked inverter circuit  320  having a size varying from 8 n to n for addresses a 0 -a 2 , and clocked inverters  303 ,  305 ,  307  connected in parallel are considered another single clocked inverter circuit  330  having a size varying from 0 to 7 n for addresses a 0 -a 2 .  
         [0040]    With reference to FIG. 10, when addresses a 0 , a 1 , a 2  are all equal to 0 clocked inverter circuits  320  and  330  receive signals INF and IND, respectively, and a signal OUT 1  is output. For addresses a 0 =1, a 1 =0 and a 2 =0, a signal OUT 2  is output. For addresses a 0 , a 1 , a 2  all equal to one, a signal OUT 8  is output. Thus, signals OUT 1 , OUT 2 , . . . , OUT 8  are output with a phase determined by a ratio between the clocked inverter circuit  320  composite size w f  and the clocked inverter circuit  330  composite size w d . Thus, fine delay circuit  320  can output signals OUT 1 , OUT 2 , . . . , OUT 8  having a phase linearly varying with addresses a 0 -a 2 .  
         [0041]    When composite size w f  is 8 n and composite size w d  is zero, signal OUT 1  is output and thus corresponds to signal INF. As such, with reference to FIG. 11, fine delay circuit  30  outputs signals OUT 2 , OUT 3 , OUT 4 , OUT 5 , OUT 6 , OUT 7 , OUT 8  having a phase existing between signal INF and signal IND having a phase difference of the fixed amount T relative to signal INF.  
         [0042]    As described above, signals OUT 1 , OUT 2 , . . . , OUT  8  are output having a phase varying with the ratio between the clocked inverter circuit  320  composite size w f  and the clocked inverter circuit  330  composite size w d  that are determined by addresses a 0 -a 2 . This corresponds to receiving two signals INF and IND having therebetween a phase difference of the fixed amount T, and referring to addresses a 0 -a 2  to determine composite sizes w f  and w d  which are in turn referred to to variably weight signals INF and IND, respectively, to output signals OUT 1 -OUT 8  having a variable phase.  
         [0043]    While in the above description fine delay circuit  30  delays reference clock CLK and thus generates signals INF and IND with a phase difference of the fixed amount T, the present invention is not limited thereto and the reference clock CLK phase may be advanced or delayed to consequently generate two signals INF and IND with a phase difference of the fixed amount T.  
         [0044]    With reference to FIG. 12, coarse delay circuit  40  includes delay units  401 - 408  and decoders  409 - 416 . Delay units  401 - 408  have the same configuration as the FIG. 9 delay units  301 ,  309 ,  310  and delay the input signals XA and XB phases by the fixed amount T. Decoders  409 - 416  each include, as shown in FIG. 13, a 3-input NAND  417  and an inverter  418 . Decoders  409 - 416  respond to input signals A 1 , A 2 , A 3  by outputting signals R, /R.  
         [0045]    Again with reference to FIG. 12, decoders  409 - 416  receive addresses a 3 -a 5  from counter  20  and output signals R and /R to delay units  401 - 408 . When signal R is logical high delay units  401 - 408  delay input signal XA by the fixed amount T and when signal R is logical high they delay input signal XB by the fixed amount T. Thus, coarse delay circuit  40  determines the number of stages of delay units  401 - 408  delaying a phase of fine adjustment clock CLKB input by decoders  409 - 416 , and delays the fine adjustment clock CLKB phase by the determined number of stages. For example, when addresses a 3 =0, a 4 =1 and a 5 =0, decoders  409 ,  410 ,  411 ,  412 ,  413 ,  415 ,  416  output signal R of logical low and signal /R of logical high and decoder  414  outputs signal R of logical high and signal /R of logical low. As a result, delay units  401 - 405 ,  407 ,  408  delay the input signal XA phase by the fixed amount T and delay unit  406  delays the input signal XB phase by the fixed amount T. Since the initial-stage delay unit  401  input signal XA is constantly logical low, delay units  401 - 405  do not delay the received fine adjustment clock CLKB phase while delay units  406 - 408  each delay the fine adjustment clock CLKB phase by the fixed amount T. As such, for addresses a 3 =0, a 4 =1 and a 5 =0, fine adjustment clock CLKB has its phase delayed by three stages corresponding to delay units  406 ,  407 ,  408  by the fixed amount T multiplied by three and it is thus output as delay clock CLKD.  
         [0046]    As has been described above, in DLL circuit  100  the delay clock CLKD phase can be compared with the reference clock CLK phase and the result of the phase comparison can be referred to to generate address a 0 -a 2  and a 3 -a 5 . Addresses a 0 -a 2  can be used to allow fine delay circuit  30  to provide an amount of delay controlled in the order smaller than the fixed amount T with precision and addresses a 3 -a 5  can be used to allow coarse delay circuit  40  to provide an amount of delay with the precision of the fixed amount T. Thus the delay clock CLKD phase can be matched to the reference clock CLK phase. It should be noted that the above described DLL circuit  100  is useful when it is used in a fast-response semiconductor integrated circuit device such as a DRAM having memory cells arranged in array.  
         [0047]    Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.