Abstract:
Apparatuses and methods related to altering the timing of command signals for executing commands is disclosed. One such method includes calculating a forward path delay of a clock circuit in terms of a number of clock cycles of an output clock signal provided by the clock circuit and adding a number of additional clock cycles of delay to a forward path delay of a signal path. The forward path delay of the clock circuit is representative of the forward path delay of the signal path and the number of additional clock cycles is based at least in part on the number of clock cycles of forward path delay.

Description:
TECHNICAL FIELD 
       [0001]    Embodiments of the invention relate generally to semiconductor memory, and more specifically, in one or more described embodiments, to signal paths and altering the timing of command signals for executing commands in a memory. 
       BACKGROUND OF THE INVENTION 
       [0002]    In semiconductor memory, proper operation of the memory is based on the correct timing of various internal command and clock signals. For example, in reading data from the memory, internal clock signals that clock data block circuitry to provide (e.g. output) the read data may need to be provided substantially concurrently with internal read command signals to properly enable the data block circuitry to output the read data. If the timing of the internal read command signal is not such that the data block circuitry is enabled at the time the internal clock signal clocks the data block circuitry to output the read data at an expected time, the read command may be inadvertently ignored or the read data provided by the memory may not be correct (i.e., the data associated with another read command). Likewise, in writing data to memory internal clock signals that clock data path circuitry to latch write data may need to be provided with specific timing relationships with internal write command signals to properly enable the data path circuitry to provide the latched write data for writing to memory. Inaccurate timing of the internal command and clock signals could result in the write command being inadvertently ignored or incorrect write data being provided to the memory may (e.g., the write data is associated with another write command). Another example of a command that may require the correct timing of internal clock signals and the command for proper operation include, for example, on-die termination enable commands. 
         [0003]    Moreover, as known, a “latency” may be programmed to set a time, typically in numbers of clock periods tCK, between receipt of a read command by the memory and when the data is output by the memory. A “write latency” may also be programmed to set a time, also typically in numbers of tCK, between receipt of a write command by the memory and when the write data is provided to the memory. The latencies may be programmed by a user of the memory to accommodate clock signals of different frequencies (i.e., different clock periods). 
         [0004]    Complicating the generating of correctly timed internal clock and command signals is the relatively high frequency of memory clock signals. For example, memory clock signals can exceed 1 GHz. Further complicating the matter is that multi-data rate memories may provide and receive data at a rate higher than the memory clock signal, which may represent the rate at which commands may be executed. As a result, the timing domains of command and clock signals may need to be crossed in order to maintain proper timing. An example of a multi-data rate memory is one that outputs read data at a rate twice that of the clock frequency, such as outputting data synchronized with clock edges of the memory clock signal. 
         [0005]    An example conventional approach of timing internal command and clock signals is modeling both the clock path and the command path to have the same propagation delay. This may require, however, that delays and/or counter circuitry run continuously. As a result, power consumption may be higher than desirable. Additionally, the propagation delay of the various internal clock and command paths can often vary due to power, voltage, and temperature conditions. For clock and command paths having relatively long propagation delay or additional delay circuitry, the variations due to operating conditions may negatively affect the timing of the internal signals to such a degree that the memory does not operate properly. This invention relates generally to, and more specifically to methods and apparatus for. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a block diagram of an apparatus according to an embodiment of the invention. 
           [0007]      FIG. 2  is a block diagram of a signal path according to an embodiment of the invention. 
           [0008]      FIG. 3  is block diagram of a clock circuit and forward path measurement circuit according to an embodiment of an invention. 
           [0009]      FIG. 4  is a block diagram of a forward path measurement circuit according to an embodiment of the invention. 
           [0010]      FIG. 5  is a block diagram of a signal path according to an embodiment of the invention. 
           [0011]      FIG. 6  is a block diagram of a signal path according to an embodiment of the invention. 
           [0012]      FIG. 7  is a block diagram of a memory according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Certain details are set forth below to provide a sufficient understanding of embodiments of the invention. However, it will be clear to one skilled in the art that embodiments of the invention may be practiced without these particular details. Moreover, the particular embodiments of the present invention described herein are provided by way of example and should not be used to limit the scope of the invention to these particular embodiments. In other instances, well-known circuits, control signals, timing protocols, and software operations have not been shown in detail in order to avoid unnecessarily obscuring the invention. 
         [0014]      FIG. 1  illustrates an apparatus according to an embodiment of the invention. 
         [0015]    The apparatus includes a signal path  110 , clock circuit  120 , and forward path measurement circuit  130 . The signal path  110  is configured to receive a signal, for example, a command signal CMDIN as shown in  FIG. 1 , and propagate the CMDIN signal to an output signal, such as output command signal CMDOUT. The CMDIN signal may represent a memory command, for example, a read command, write command, or other memory command, and may include one or several signals. The signal path  110  should have a propagation delay to satisfy a CAS latency CL. In this manner, a CMDIN signal may be propagated to a circuit that may, for example, be enabled by the resulting CMDOUT signal at an appropriate time according to the CL. The signal path  110  may include an adjustable delay circuit to provide an adjustable delay (not shown) to the propagation delay of the signal path  110 . The signal path  110  may further include a shift circuit (not shown) to provide additional clock cycles of time in order to have a propagation delay to satisfy the CL. The clock circuit  120  is configured to provide a clock signal CLKOUT having a delayed phase relationship to an input clock signal CLKIN. The delay added to the CLKIN signal is adjustable and adjusted to be an amount suitable to substantially synchronize an operation to the CLKIN signal. The CLKOUT signal is provided to the signal path  110 , as well as a delay adjustment signal DELADJ. The DELADJ signal may result from determining a suitable amount of delay to add to the CLKIN signal and may be used to adjust a delay of an adjustable delay circuit in the signal path  110 . An example of a clock circuit that may be used for the clock circuit  120  is a delay-locked loop (DLL). Other clock circuits may be used as well. 
         [0016]    The forward path measurement circuit  130  is configured to measure a forward path delay for the signal path  110 . The forward path delay of the signal path  110  is the propagation delay of the signal path  110 . A minimum forward path delay results from the inherent propagation delays of circuits in the signal path  110 , and without any additional delay that may be added. As previously discussed, additional delay may be added to adjust the timing of a signal propagating through the signal path  110 , as well as to provide the signal path  110  with a propagation delay to satisfy CL. The forward path measurement circuit  130  provides a count CNT of clock cycles that is representative of the forward path delay of the signal path  110 . In some embodiments, for example, the embodiment of  FIG. 1 , the CNT count provided by the forward path measurement circuit  130  is based on signals from the clock circuit  120 . The CNT count may be stored after determination for later use. The CNT count may be stored by the forward path measurement circuit  130 , or by other circuitry. 
         [0017]    In operation, the forward path measurement circuit  130  provides a CNT count based at least in part on signals from the clock circuit  120 . For example, in the embodiment illustrated in  FIG. 1  the forward path measurement circuit  130  is provided REF and FB signals on which the CNT count is based at least in part. The CNT count is provided to the signal path  110 , which is further provided the DELADJ signal and the CLKOUT signal from the clock circuit  120 . The signal path  110  is further provided a CL signal representative of the CAS latency. A shift circuit included in the signal path  110  is set to provide additional delay (if needed) based on the CL and CNT count. As a result of the additional delay, a CMDIN signal will be provided by the signal path  110  as the CMDOUT signal after a propagation delay to satisfy the CL. 
         [0018]      FIG. 2  illustrates a signal path  200  according to an embodiment of the invention. The signal path  200  may be used for the signal path  110  of the embodiment of  FIG. 1 . The signal path  200  includes a buffer  210  configured to buffer an input signal, for example, a command signal CMDIN, and provide the buffered CMDIN signal to an adjustable delay circuit  220 . The adjustable delay circuit  220  provides a delayed CMDIN signal CMDINDEL having a delay relative to the buffered CMDIN signal that is based on a delay adjustment signal DELADJ. The CMDINDEL signal is provided to a buffer  230  configured to buffer the CMDINDEL signal and provide the buffered CMDINDEL signal to a shift circuit  240 . 
         [0019]    The shift circuit  240  is provided a CL signal representative of a CAS latency, a signal representative of a CNT count, and a CLKOUT signal, which may be an output clock signal CLKOUT that clocks the shift circuit  240 . The CNT count may be provided by the forward path measurement circuit  130  ( FIG. 1 ) and the CLKOUT signal may be provided by the clock circuit  120 . The shift circuit  240  is configured to shift commands represented by the buffered CMDINDEL signal N clock cycles of the CLKOUT signal before providing the shifted command as represented by a shifted command signal SH_CMD to a signal distribution network  250 . The signal distribution network  250  distributes the SH_CMD signal to various circuits that may rely on the SH_CMD to operate. 
         [0020]    The signal path  200  has a forward path delay that includes inherent propagation delays of the buffer  210 , buffer  230 , and the signal distribution network  250 . In determining a minimum forward path delay, the minimum delay of the adjustable delay circuit  220  is also considered, that is, the least amount of delay provided by the adjustable delay circuit  220 . As previously discussed, the signal path  200  should have a propagation delay to satisfy the CAS latency CL, and the CNT count represents the estimated forward path delay of the signal path  200  in terms of clock cycles. The value N is calculated as CL−CNT, which is the difference between a desired CAS latency (CL) and a forward path delay in number of clock cycles (CNT). By shifting commands by N clock cycles, the shift circuit  240  effectively adds N clock cycles to the minimum forward path delay of the signal path  200  so that the propagation delay of the signal path  200  satisfies the CL. 
         [0021]    As illustrated in  FIG. 2 , the delay through buffer  210 , adjustable delay circuit  220  (at minimum delay), and buffer  230  is D 1 +D 2 +D 3 . The delay through the shift circuit  240  is CL−CNT, and the delay through the signal distribution network is D 4 . The resulting minimum forward path delay of the signal path  200  is D 1 +D 2 +D 3 +D 4  (i.e., propagation delay of the signal path  200  without delay of the shift circuit  240 ). 
         [0022]    In operation, a command represented by the CMDIN signal is provided to the signal path  200  and propagated through the buffer  210 , adjustable delay circuit  220  and buffer  230  to the shift circuit  240 . The shift circuit  240  adds CL−CNT clock cycles (of the CLKOUT signal) to the propagating CMDIN signal before being provided to the signal distribution network  250  and output as the CMDOUT signal. With the additional clock cycles provided by the shift circuit  240  the resulting propagation delay of the signal path  200  will satisfy the CAS latency CL. 
         [0023]      FIG. 3  illustrates a clock circuit  300  and forward path measurement circuit  370  according to an embodiment of an invention. The clock circuit  300  may be used for the clock circuit  120  ( FIG. 1 ) and the forward path measurement circuit  370  may be used for the forward path measurement circuit  130 . The clock circuit  300  is illustrated in  FIG. 3  as a delay-locked loop and provides an output clock signal CLKOUT to a signal distribution network  10 . The clock circuit  300  includes a buffer  310  configured to buffer an input clock signal CLKIN and provide a buffered clock signal REF to an adjustable delay circuit  320 . The adjustable delay circuit  320  provides a delay to the buffered CLKIN signal based on a delay adjustment signal DELADJ. The delayed buffered CLKIN signal is provided to buffer  330 , which is configured to buffer the signal from the adjustable delay circuit  320  and provide an output clock signal CLKOUT. The CLKOUT signal is provided to the signal distribution network  10  to be distributed to circuits as a CLKSYNC signal that may need the CLKSYNC signal to operate. 
         [0024]    The CLKOUT signal is further provided to a model delay  340  that is configured to provide a delay that models an inherent propagation delay of the buffer  310  and the signal distribution network  10 . A feedback signal FB having a delay relative to the CLKOUT signal as provided by the delay of the model delay  340 , is provided to a phase detector  350 . The phase detector  350  is also provided the REF signal. The phase detector  350  is configured to provide the DELADJ signal based at least in part on a phase difference between the REF and FB signals. The adjustable delay circuit is adjusted by the DELADJ signal until the REF signal and FB signal are in phase. When the REF and FB signals are in phase, the resulting CLKSYNC signal is in phase with the CLKIN signal. 
         [0025]    The forward path measurement circuit  370  measures a propagation delay of a forward path of the clock circuit  300 . The forward path of the clock circuit  300  is generally represented by the minimum propagation delay of the CLKIN signal to the CLKSYNC signal. In the embodiment of  FIG. 3 , the forward path of the clock circuit  300  includes propagation delays of buffer  310 , buffer  330 , the signal distribution network  10 , and a minimum delay of the adjustable delay circuit  320 . 
         [0026]    In the embodiment of  FIG. 3 , the forward path measurement circuit  370  measures a propagation delay that represents a forward path delay of a signal path, for example, signal path  110  ( FIG. 1 ) or signal path  200  ( FIG. 2 ). As previously discussed with reference to  FIG. 2 , the minimum forward path delay of the signal path  200  is represented by the inherent propagation delays of the buffer  210 , buffer  230 , the signal distribution network  250 , and a minimum delay of the adjustable delay circuit  220 . In a specific example, where the buffer  310 , the adjustable delay  320 , and buffer  330  have a same propagation delay as the buffer  210 , adjustable delay circuit  220 , and buffer  230 , respectively, and the signal distribution network  10  has the same propagation delay as the signal distribution network  250 , the minimum forward path delay of the clock circuit  300  will be representative of the minimum forward path delay of the signal path  200 . Thus, measuring the minimum forward path delay of the clock circuit  300  will result in a measurement for the minimum forward path delay of the signal path  200 . 
         [0027]    In some embodiments, the forward path measurement circuit  370  measures the forward path delay by measuring a delay between the REF signal and the FB signal and calculating a resulting number of clock cycles of the CLKIN signal. The delay between the REF signal and the FB signal represents the delay of the forward path of the clock circuit  300 . As previously discussed, the FB signal is delayed relative to the REF signal by a delay provided by the adjustable delay circuit  320 , the buffer  330 , and the model delay  340 . As also previously discussed, the model delay models inherent propagation delay of the buffer  310  and the signal distribution network  10 . Thus, the sum delay between the REF signal and the FB signal may represent the propagation delay of the buffer  310 , the adjustable delay circuit  320 , buffer  330 , and the signal distribution network  10  (the buffer  310  and signal distribution network delays represented by the model delay  340 ), which represents the forward path delay of the clock circuit  300 . As a result, by measuring the delay between the REF and FB signals, and calculating a resulting number of clock cycles the forward path measurement circuit  370  measures the forward path delay of the clock circuit  300 . As previously described, the minimum forward path delay of the clock circuit  300  may represent the minimum forward path delay of a signal path  200  in  FIG. 2  that includes circuitry having the same propagation delays as the clock circuit  300 . 
         [0028]    In some embodiments, the adjustable delay circuit  320  and an adjustable delay of a signal path, for example, adjustable delay circuit  220  of the signal path  200  ( FIG. 2 ) are adjusted to provide a same adjustable delay based at least in part on the DELADJ signal. For example, an adjustable delay circuit in a signal path may exhibit the same adjustable delay characteristics as the adjustable delay circuit  320 , and consequently, may also be adjusted by the DELADJ signal. Such is the case when the adjustable delay circuit of the signal path is a “match” of the clock circuit. By providing the same adjustable delay for the clock circuit and the signal path, the change to the forward path delay of the clock circuit  300  due to the adjustable delay added by the adjustable delay circuit  320 , will change the forward path delay of the signal path  200  in a likewise manner. 
         [0029]      FIG. 4  illustrates a forward path measurement circuit  400  according to an embodiment of the invention. The forward path measurement circuit  400  is configured to measure a forward path delay of a clock circuit in terms of a number of clock cycles of a clock signal. The forward path measurement circuit  400  may be used for the forward path measurement circuit  370  ( FIG. 3 ). 
         [0030]    The forward path measurement circuit  400  includes a first series of data flip flops  410  configured to receive a first clock signal (e.g., a reference clock signal REF as illustrated in  FIG. 4 ) and provide a clock enable signal CLKEN. The CLKEN signal is provided to a counter  450  as a start input. The REF signal further clocks the counter  450 . The forward path measurement circuit  400  further includes a second series of data flip flops  420  configured to receive a second clock signal (e.g., a feedback clock signal FB as illustrated in  FIG. 4 ) and provide a measurement delay clock signal MDCLK. The MDCLK signal is provided to a delay element  430 . The delay element  430  provides a fixed minimum delay to allow a clock circuit to which the forward path measurement circuit  400  is coupled to operate over a wide range of conditions. The amount of delay provided by the delay element  430  may vary depending on the particular implementation. The delay element  430  is coupled to a data flip flop  440  that is clocked by the REF signal to generate a measurement pulse signal MSTROBE. The MSTROBE signal is provided to the counter  450  as a stop input. 
         [0031]    In operation, when an input clock signal to a clock circuit begins to transition, the REF signal clocks the first series of data flip flops  410 . At a later point in time, the REF signal propagates through a feedback path of the clock circuit and the rising edges are seen in the FB signal, which clocks the second series of data flip flops  420 . Following the third clock pulse (due to there being three flip flops in the first series of data flip flops  410 ), the CLKEN signal is asserted, and the counter  450  begins counting each pulse of the REF signal. The FB signal clocks second series of data flip flops  420 , and after the third pulse, the MDCLK signal is asserted. The MDCLK signal passes through the delay element  430  and is latched in the data flip flop  440  following the next rising edge of the REF signal, thus generating the MSTROBE signal. The MSTRBE signal stops the counter  450 . The start and stop signals provided to the counter  450  are synchronized with the rising edge of the REF signal. The value of the counter  450 , CNT, represents the number of clock signals required for the REF signal to propagate through the forward path of the clock circuit. In some embodiments, the CNT value is maintained in the counter  450  and stored and referenced when needed. 
         [0032]    In the embodiment illustrated in  FIG. 4 , three data flip flops are included in the first and second series of data flip flops  410 ,  420  to allow the forward path to be populated with clock signals and stabilize. In other embodiments, however, the number of flip flops in the series of data flip flops  410 ,  420  may vary depending on the particular implementation. 
         [0033]      FIG. 5  illustrates a signal path  500  according to an embodiment of the invention. The signal path  500  may be used for the signal path  110  of the embodiment of  FIG. 1 . The signal path is illustrated in  FIG. 5  as providing an on-die termination command ODTIN as an ODTOUT signal at a time that satisfy a CAS write latency CWL. The signal path  500  includes a buffer  510  configured to buffer the ODTIN signal and provide the buffered ODTIN signal to an adjustable delay circuit  520 . The adjustable delay circuit  520  provides a delayed ODTIN signal ODTINDEL having a delay relative to the buffered ODTIN signal that is based on a delay adjustment signal DELADJ. The ODTINDEL signal is provided to a buffer  530  configured to buffer the ODTINDEL signal and provide the buffered ODTINDEL signal to a shift circuit  540 . 
         [0034]    The shift circuit  540  is further provided a CWL signal representative of a CAS write latency, a signal representative of a CNT count, and a CLKOUT signal, which may be an output clock signal CLKOUT that clocks the shift circuit  540 . The CNT count may be provided by a forward path measurement circuit, for example, forward path measurement circuit  130  ( FIG. 1 ). As previously discussed, the CNT count may represent the estimated forward path delay of the signal path in terms of clock cycles. The CLKOUT signal may be provided by a clock circuit, for example, clock circuit  120 . The shift circuit  540  is configured to shift the ODT command represented by the buffered ODTINDEL signal N clock cycles of the CLKOUT signal before providing the shifted command signal SH_ODT to a signal distribution network  550 . The signal distribution network  550  distributes the SH_ODT signal to various circuits that may rely on the SH_ODT to operate, for example, on-die termination circuits used during write operations. 
         [0035]    The signal path  500  has a forward path delay that includes inherent propagation delays of the buffer  510 , buffer  530 , and the signal distribution network  550 . The signal path  500  should have a propagation delay to satisfy the CAS write latency CWL. By shifting the ODT command by N clock cycles, the shift circuit  540  effectively adds N clock cycles to the minimum forward path delay of the signal path  500  so that the propagation delay of the signal path  500  satisfies the CWL. In the embodiment of  FIG. 5 , the value N is calculated as CWL−CNT, which is the difference between a desired CAS write latency (CWL) and a forward path delay in number of clock cycles (CNT). 
         [0036]    In operation, an ODT command represented by the ODTIN signal is provided to the signal path  500  and propagated through the buffer  510 , adjustable delay circuit  520  and buffer  530  to the shift circuit  540 . The shift circuit  540  adds CWL−CNT clock cycles (of the CLKOUT signal) to the propagating ODTIN signal before being provided to the signal distribution network  550  and output as the ODTOUT signal. With the additional clock cycles provided by the shift circuit the resulting propagation delay of the signal path  500  will satisfy the CAS write latency CWL. In some embodiments, the shift circuit  540  shifts the ODT command by more or less than CWL−CNT, for example, where an ODT preamble is used with the ODTOUT signal. 
         [0037]      FIG. 6  illustrates a signal path  600  according to an embodiment of the invention. The signal path  600  may be used for the signal path  110  of the embodiment of  FIG. 1 . The signal path is illustrated in  FIG. 6  as providing read and write commands RDIN, WRIN as a CMDOUT signal at a time that satisfy a CAS latency CL and CAS write latency CWL. The signal path  600  includes a buffer  610  configured to buffer the RDIN, WRIN signal and provide the buffered RDIN, WRIN signal to an adjustable delay circuit  620 . The adjustable delay circuit  620  provides a delayed RDIN, WRIN signal RDINDEL, WRINDEL having a delay relative to the buffered RDIN, WRIN signal that is based on a delay adjustment signal DELADJ. The RDINDEL, WRINDEL signal is provided to a de-multiplexer  630  configured to provide RDINDEL signals to a shift circuit  640  and provide WRINDEL signals to a shift circuit  645 , as controlled by a read or write signal RDorWR. 
         [0038]    The shift circuit  640  is provided a CL signal representative of a CAS latency, a signal representative of a CNT count, and a CLKOUT signal that clocks the shift circuit  640 . The shift circuit  645  is provided a CWL signal representative of a CAS write latency, the CNT count, and the CLKOUT signal that clocks the shift circuit  645 . The CNT count may be provided by a forward path measurement circuit, for example, forward path measurement circuit  130  ( FIG. 1 ). As previously discussed, the CNT count may represent the estimated forward path delay of the signal path in terms of clock cycles. The CLKOUT signal may be provided by a clock circuit, for example, clock circuit  120 . 
         [0039]    The shift circuit  640  is configured to shift a read command represented by the RDINDEL signal N 1  clock cycles of the CLKOUT signal before providing the shifted read command signal SH_RD to a signal distribution network  650 . The signal distribution network  650  distributes the SH_RD signal as a read command signal RDCMDOUT. The shift circuit  645  is configured to shift a write command represented by the WRINDEL signal N 2  clock cycles of the CLKOUT signal before providing the shifted write command signal SH_WR to a signal distribution network  660 . The signal distribution network  660  distributes the SH_WR signal as a write command signal WRCMDOUT. The RDCMDOUT and WRCMDOUT signals are distributed to various circuits that may rely on the SH_RD, SH_WR signal to operate, for example, an read data driver or a write data driver. 
         [0040]    The signal path  600  has a forward path delay that includes inherent propagation delays of the buffer  610 , de-multiplexer  630 , and the signal distribution network  650 ,  660 . The signal path  600  should have a propagation delay to satisfy the CAS latency CL and CAS write latency CWL. By shifting the read command by N 1  clock cycles, the shift circuit  640  effectively adds N 1  clock cycles to the minimum forward path delay of the signal path  600  so that the propagation delay of the signal path  600  satisfies the CL. In the embodiment of  FIG. 6 , the value N 1  is calculated as CL−CNT, which is the difference between a desired CAS latency (CL) and a forward path delay in number of clock cycles (CNT). By shifting the read command by N 2  clock cycles, the shift circuit  645  effectively adds N 2  clock cycles to the minimum forward path delay of the signal path  600  so that the propagation delay of the signal path  600  satisfies the CWL. In the embodiment of  FIG. 6 , the value N 2  is calculated as CWL−CNT, which is the difference between a desired CAS write latency (CWL) and a forward path delay in number of clock cycles (CNT). 
         [0041]    In operation, a read command represented by the RDIN signal or a write command represented by the WRIN signal, is provided to the signal path  600  and propagated through the buffer  610  and adjustable delay circuit  620 . Based at least in part on the RDorWR signal, read commands are provided through the de-multiplexer  630  to the shift circuit  640  and write commands are provided through the de-multiplexer  630  to the shift circuit  645 . The shift circuit  640  adds CL−CNT clock cycles (of the CLKOUT signal) to a propagating read command signal before being provided to the signal distribution network  650  and output as the RDCMDOUT signal. With the additional clock cycles provided by the shift circuit  640  the resulting propagation delay of the signal path  600  will satisfy the CAS latency CL. The shift circuit  645  adds CWL−CNT clock cycles (of the CLKOUT signal) to a propagating write command signal before being provided to the signal distribution network  660  and output as the WRCMDOUT signal. With the additional clock cycles provided by the shift circuit  645  the resulting propagation delay of the signal path  600  will satisfy the CAS write latency CWL. The shift circuits  640  and  645  may shift the respective command by more or less than CL−CNT and CWL−CNT, for example, where read and write command preambles are used with the RDCMDOUT and WRCMDOUT signals. 
         [0042]    In some embodiments, the adjustable delay circuit  520  may be matched to an adjustable delay of a clock circuit providing the CLKOUT signal to the signal path  500 . In this manner, an DELADJ signal provided by the clock circuit may be used to adjust the adjustable delay of the adjustable delay circuit  520  to provide the same adjustable delay. As a result, the forward path delay of the signal path  300  may be changed in a likewise manner as a forward path delay of the clock circuit due to the adjustable delay added by its adjustable delay circuit. The adjustable delay circuit  620  may also be matched to an adjustable delay of a clock circuit as well. 
         [0043]    In some embodiments, a plurality of signal paths are included in an apparatus. For example, a first signal path, such as signal path  500 , and a second signal path, such as signal path  600  may be included together. The signal paths  500  and  600  may be configured to have respective adjustable delay lines that are matched to an adjustable delay line of a clock circuit providing both signal paths a CLKOUT signal. Other signal paths may be alternatively, or additionally included in other apparatuses. 
         [0044]      FIG. 7  illustrates a portion of a memory  700  according to an embodiment of the present invention. The memory  700  includes an array  702  of memory cells, which may be, for example, DRAM memory cells, SRAM memory cells, flash memory cells, or some other types of memory cells. The memory  700  includes a command decoder  706  that receives memory commands through a command bus  708  and provides (e.g. generates) corresponding control signals within the memory  700  to carry out various memory operations. Row and column address signals are provided (e.g., applied) to the memory  700  through an address bus  720  and provided to an address latch  710 . The address latch then outputs a separate column address and a separate row address. 
         [0045]    The row and column addresses are provided by the address latch  710  to a row address decoder  722  and a column address decoder  728 , respectively. The column address decoder  728  selects bit lines extending through the array  702  corresponding to respective column addresses. The row address decoder  722  is connected to word line driver  724  that activates respective rows of memory cells in the array  702  corresponding to received row addresses. The selected data line (e.g., a bit line or bit lines) corresponding to a received column address are coupled to a read/write circuitry  730  to provide read data to an input/output data block  734  via an input-output data bus  740 . Write data are provided to the memory array  702  through the I/O data block  734  and the memory array read/write circuitry  730 . The I/O data block  734  may include clocked circuitry that operate responsive to an internal clock signal CLKOUT and an internal command signal CMDOUT, for example. 
         [0046]    The memory  70 Q further includes clock circuit  712 , forward path measurement circuit  713 , and signal path  714 . The clock circuit  712  receives a input clock signal CLKIN and propagates the internal clock signal CLKOUT which is based at least in part on the CLKIN signal to the I/O data block  734 . The forward path measurement circuit  713  measures a forward path delay in number of clock cycles of the CLKOUT signal and provides a count CNT to the signal path  714 . The clock circuit  712 , forward path measurement circuit  713 , and signal path  714  may be implemented using embodiments of the invention. The signal path  714 , which is shown in  FIG. 7  as being included in the command decoder  706 , but is not limited to such a configuration, provides the internal command signal CMDOUT to the I/O data block  734 . The command decoder  706  responds to memory commands provided to the command bus  708  to perform various operations on the memory array  702 . In particular, the command decoder  706  is used to provide internal control signals to read data from and write data to the memory array  702 . 
         [0047]    From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.