Abstract:
Apparatuses and methods of for refresh control of a semiconductor device are described. An example apparatus includes a command control circuit that provides a plurality of pulses on a first control signal in series responsive to a plurality of refresh commands issued in series; a signal generation circuit that produces a plurality of pulses on a second control signal in sequence; and a refresh control circuit that receives two or more of the plurality of pulses on the first control signal during a period of time between one pulse and a succeeding pulse of the plurality of pulses on the second control signal, disables refresh operations responsive to at least one of the two or more of the plurality of first control signal and executes a refresh operation responsive to remaining one or more pulses of the two or more of the plurality of pulses on the first control signal.

Description:
BACKGROUND 
       [0001]    High data reliability, high speed of memory access, reduced chip size and low power consumption are features that are demanded from semiconductor memory. In recent years, there has been an effort to further reduce power consumption. 
         [0002]    In a semiconductor memory device, such as dynamic random access memory (DRAM), memory cells are refreshed in order to preserve the stored data. The semiconductor memory device typically has a normal operation mode and a self-refresh operation mode. The semiconductor memory device may conduct a refresh operation under the three conditions. First, the semiconductor memory device may conduct the refresh operation responsive to each auto-refresh (AREF) command. Second, the semiconductor memory device may conduct the refresh operation once at a self-refresh operation mode entry. Third, the semiconductor memory device may conduct the refresh operation responsive to refresh pulses provided by a signal generator, such as an oscillator. 
         [0003]    In the normal operation mode, the semiconductor memory device is active. A clock enable signal CKE controls whether the semiconductor memory device is active (e.g., CKE having a logic high level). In the self-refresh operation mode, typically the semiconductor memory device is in a stand-by state. The clock enable signal CKE controls whether the semiconductor memory device is inactive (e.g., CKE having a logic low level). In order to reduce power consumption, an interval of executing the refresh operation in the self-refresh operation mode is longer than in the normal operation mode activated by the auto-refresh (AREF) command. 
         [0004]      FIG. 1A  is a timing diagram of signals in a normal operation mode and in a self-refresh operation mode in a semiconductor memory device. For example, auto refresh commands (AREF) are issued from a controller. Refresh operations are performed in accordance with the auto refresh commands when in the normal operation mode (e.g., while the clock enable signal CKE is at the logic high level). Intervals of the auto refresh commands are controlled by the controller. On the other hand, in the self-refresh operation mode (e.g., while the clock enable signal CKE is at the logic low level) the refresh operations are performed in accordance with a signal OSC, which is from a signal generation circuit, such as an oscillator, in the semiconductor memory device. 
         [0005]    When the clock enable signal CKE becomes inactive (e.g., transition to the logic low level), the semiconductor memory device activates the oscillator to generate an internal refresh signal responsive to the signal OSC in the self-refresh operation mode, and refresh operations are performed in synchronism with the internal refresh signal. Intervals of the internal refresh signal are determined based on data retention ability of semiconductor memory device. Thus, the intervals of the internal refresh signal may be different, possibly longer than the intervals of the auto refresh commands (AREF). Refresh operation intervals of the auto-refresh command AREF in the normal operation mode tend to be shorter than necessary, resulting in more frequent refresh operation, and may cause higher power consumption. As described the above, the semiconductor memory device may be able to store data for a time longer than the interval of the auto-refresh command AREF, such as for the intervals of the signal OSC. 
         [0006]    A refresh operation may be executed each time the semiconductor memory device enters a self-refresh operation mode. When the semiconductor memory device frequently switches between the normal operation mode and the self-refresh operation mode, the refresh operations from entering the self-refresh operation mode may also occur frequently.  FIG. 1B  is a timing diagram of signals in a normal operation mode and in a self-refresh operation mode in a semiconductor memory device. In this example, the semiconductor memory device switches between the normal operation mode and the self-refresh operation mode frequently, and as shown a refresh operation is performed each time the self-refresh operation mode is entered. If the period of the self-refresh operation mode is much shorter (e.g., a quarter of the interval of the signal OSC) than the time to provide the active signal of OSC, and if the active period of the normal operation is much shorter (e.g., a quarter of the interval of the signal OSC) than the time to receive the auto-refresh command AREF, refresh operations may be performed at each entry of the self-refresh operation mode, which may be twice as frequent as the interval of the active OSC. 
         [0007]    Thus, the refresh operation intervals of each entry to the self-refresh operation mode tend to be more frequent than necessary and may cause unnecessary power consumption. For example, semiconductor memory devices used for mobile devices, such as Mobile DRAMs, are configured to quickly transit to the self-refresh operation mode when the semiconductor memory device does not receive read/write commands from the controller, and may experience the failure of the data retention or excess power consumption as described above due to frequent entries into the self-refresh operation mode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1A  is a timing diagram of signals in a normal operation mode and in a self-refresh operation mode in a semiconductor device. 
           [0009]      FIG. 1B  is a timing diagram of signals in a normal operation mode and in a self-refresh operation mode in a semiconductor device. 
           [0010]      FIG. 2  is a block diagram of a semiconductor device including a refresh control circuit, in accordance with an embodiment of the present disclosure. 
           [0011]      FIG. 3A  is a timing diagram of signals of a refresh control circuit in a semiconductor device, in accordance with an embodiment of the present disclosure. 
           [0012]      FIG. 3B  is a circuit diagram of a refresh control circuit according to an embodiment of the present disclosure. 
           [0013]      FIG. 4A  is a timing diagram of signals in a normal operation mode and in a self-refresh operation mode in a semiconductor device, in accordance with an embodiment of the present disclosure. 
           [0014]      FIG. 4B  is a timing diagram of signals in a normal operation mode and in a self-refresh operation mode in a semiconductor device, in accordance with an embodiment of the present disclosure. 
           [0015]      FIG. 5A  is a timing diagram of signals of a refresh control circuit in a semiconductor device, in accordance with an embodiment of the present disclosure. 
           [0016]      FIG. 5B  is a circuit diagram of a refresh control circuit according to an embodiment of the present disclosure. 
           [0017]      FIG. 6  is a circuit diagram of a refresh control circuit according to an embodiment of the present disclosure. 
           [0018]      FIG. 7A  is a timing diagram of signals of a refresh control circuit in a semiconductor device, in accordance with an embodiment of the present disclosure. 
           [0019]      FIG. 7B  is a timing diagram of signals of a refresh control circuit in a semiconductor device, in accordance with an embodiment of the present disclosure. 
           [0020]      FIG. 7C  is a timing diagram of signals of a refresh control circuit in a semiconductor device, in accordance with an embodiment of the present disclosure. 
           [0021]      FIG. 7D  is a timing diagram of signals of a refresh control circuit in a semiconductor device, in accordance with an embodiment of the present disclosure. 
           [0022]      FIG. 8A  is a timing diagram of signals in a normal operation mode and in a self-refresh operation mode in a semiconductor device, in accordance with an embodiment of the present disclosure. 
           [0023]      FIG. 8B  is a timing diagram of signals in a normal operation mode in a semiconductor device, in accordance with an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0024]    Various embodiments of the present invention will be explained below in detail with reference to the accompanying drawings. The following detailed description refers to the accompanying drawings that show, by way of illustration, specific aspects and embodiments in which the present invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present invention. Other embodiments may be utilized, and structure, logical and electrical changes may be made without departing from the scope of the present invention. The various embodiments disclosed herein are not necessary mutually exclusive, as some disclosed embodiments can be combined with one or more other disclosed embodiments to form new embodiments. 
         [0025]      FIG. 2  is a block diagram of a semiconductor device in accordance with an embodiment of the present disclosure. The semiconductor device  10  may be a LPDDR4 SDRAM integrated into a single semiconductor chip, for example. As shown in  FIG. 2 , the semiconductor device  10  includes a memory cell array  11 . The memory cell array  11  includes a plurality of banks, each bank including a plurality of word lines WL, a plurality of bit lines BL, and a plurality of memory cells MC arranged at intersections of the plurality of word lines WL and the plurality of bit lines BL. The selection of the word line WL is performed by a row decoder  12  and the selection of the bit line BL is performed by a column decoder  13 . Sense amplifiers SAMP  18  are coupled to corresponding bit lines BL and connected to local I/O line pairs LIOT/B. Local IO line pairs LIOT/B are connected to main IO line pairs MIOT/B via transfer gates TG  19  which are configured as switches. 
         [0026]    Turning to the explanation of a plurality of external terminals included in the semiconductor device  10 , the plurality of external terminals includes address terminals  21 , command terminals  22 , clock terminals  23 , data terminals  24  and power supply terminals  25  and  26 . The address terminals  21  are supplied with an address signal ADD and a bank address signal BADD. The address signal ADD and the bank address signal BADD supplied to the address terminals  21  are transferred via an address input circuit  31  to an address decoder  32 . The address decoder  32  receives the address signal ADD and supplies a decoded row address signal XADD to the row decoder  12 , and a decoded column address signal YADD to the column decoder  13 . The address decoder  32  also receives the bank address signal BADD and supplies the bank address signal BADD to the row decoder  12  and the column decoder  13 . 
         [0027]    The command terminals  22  are supplied with a command signal COM to a command control circuit  27 . The command control circuit  27  may include a command input circuit  33  and a command decoder  34 . The command signal COM may include one or more separate signals. The command signal COM input to the command terminals  22  is provided to the command decoder  34  via the command input circuit  33 . The command decoder  34  decodes the command signal COM to generate various control signals. For example, the control signals may include a row command signal to select a word line and a column command signal, such as a read command or a write command, to select a bit line, and a AREF-Ref signal, which is a first control signal, provided to a refresh control circuit  42 . 
         [0028]    Accordingly, when a read command is issued and a row address and a column address are timely supplied with the read command, read data is read from a memory cell MC in the memory cell array  11  designated by these row address and column address. The read data DQ is output externally from the data terminals  24  via a read/write amplifier  14  and an input/output circuit  15 . Similarly, when the write command is issued and a row address and a column address are timely supplied with the write command, and then write data DQ is supplied to the data terminals  24 , the write data DQ is supplied via the input/output circuit  15  and the read/write amplifier  14  to the memory cell array  11  and written in the memory cell MC designated by the row address and the column address. The input/output circuit  15  may include input buffers, according to one embodiment. 
         [0029]    The clock terminals  23  are supplied with external clock signals CK and /CK, respectively. These external clock signals CK and /CK are complementary to each other and are supplied to a clock input circuit  35 . The clock input circuit  35  receives the external clock signals CK and /CK and generates an internal clock signal ICLK. The internal clock signal ICLK is supplied to an internal clock generator  36  and thus a phase controlled internal clock signal LCLK is generated based on the received internal clock signal ICLK and a clock enable signal CKE from the command input circuit  33 . Although not limited thereto, a DL circuit can be used as the internal clock generator  36 . The phase controlled internal clock signal LCLK is supplied to the input/output circuit  15  and is used as a timing signal for determining an output timing of the read data DQ. The internal clock signal ICLK is also supplied to a command decoder  34  for decoding the command signal COM to generate various control signals. 
         [0030]    The power supply terminals  25  are supplied with power supply potentials VDDQ and VSSQ. These power supply potentials VDDQ and VSSQ are supplied to the input/output circuit  15 . The power supply potentials VDDQ and VSSQ may be the same potentials as the power supply potentials VDD and VSS that are supplied to the power supply terminals  25 , respectively. However, the dedicated power supply potentials VDDQ and VSSQ may be used for the input/output circuit  15  so that power supply noise generated by the input/output circuit  15  does not propagate to the other circuit blocks. The power supply terminals  26  are supplied with power supply potentials VDD and VSS. These power supply potentials VDD and VSS are supplied to an internal power supply circuit  37 . The internal power supply circuit  37  generates various internal potentials VPP, VOD, VARY, VPERI, and the like based on the power supply potentials VDD and VSS. The internal potential VPP is mainly used in the row decoder  12 , the internal potentials VOD and VARY are mainly used in the sense amplifiers  18  included in the memory cell array  11 , and the internal potential VPERI is used in many other circuit blocks. A power-on-reset circuit (PON)  39  provides a PON signal when the internal power supply circuit  37  becomes capable to supply a sufficient level of internal voltage in a power-on sequence. A temperature sensor  38  senses a temperature of the semiconductor device and provides a VTEMP signal, which is indicative of a temperature of the semiconductor device. For example, a voltage level of the VTEMP signal may become higher if the temperature of the semiconductor device becomes higher. 
         [0031]    A signal generation circuit  41  may be an oscillator that provides an OSC-Ref signal, which is a second control signal, responsive to the PON signal. The signal generation circuit  41  may control intervals of OSC-Ref responsive to the VTEMP signal. For example, the signal generation circuit  41  may decrease the intervals of activation of the OSC-Ref signal for more frequent refresh operations when the temperature is higher, responsive to the VTEMP signal indicating a higher temperature. The signal generation circuit  41  may also increase the intervals of activation of the OSC-Ref signal for less frequent refresh operations, responsive to the VTEMP signal indicating that the temperature is lower. A refresh control circuit  42  may receive the AREF-Ref signal from the command decoder  34 , the clock enable signal CKE from the command input circuit  33 , and the OSC-Ref signal from the signal generation circuit  41 . The refresh control circuit  42  provides an Internal-Ref signal for controlling refresh operations. The row decoder  12  receives the Internal-Ref signal and increments a row address for refresh operations responsive to the Internal-Ref signal. 
         [0032]      FIG. 3A  is a timing diagram of signals of a refresh control circuit in a semiconductor device, in accordance with an embodiment of the present disclosure.  FIG. 3B  is a circuit diagram of the refresh control circuit according to an embodiment of the present disclosure. Refresh control circuit  300  may include a set-reset (SR) latch circuit  301 . The SR-latch circuit  301  may receive the OSC-Ref signal at a set input (S) and sets a latch signal of a node N 1  to a logic high level. An AND circuit  302  receives the AREF-Ref signal and the latch signal on the node N 1 , and may further provide a signal on a node N 2 . The signal on node N 2  is set to a logic high level when both the latch signal on the node N 1  and the AREF-Ref signal are set to the logic high level. An AND circuit  303  receives the OSC-Ref signal and the latch signal on the node N 1 , and provides a signal on a node N 4  which is set to a logic high level when both the latch signal on the node N 1  and the OSC-Ref signal are set to the logic high level. A multiplexer MUX  304  provides either the signal on the node N 2  or the signal on the node N 4  as the Internal-Ref signal, responsive to a signal “Nom/Self” indicative of a normal operation mode or a self-refresh operation mode, respectively. For example, the signal “Nom/Self” may correspond to a clock enable signal CKE. A one shot pulse generator  305  provides a one shot pulse signal responsive to the Internal-Ref signal on a node N 3 . The one shot pulse signal on the node N 3  is received at a reset input (R) of the SR latch circuit  301  which resets the latch signal on the node N 1  to a logic low level. The latch signal on the node N 1  maintains the logic low level until the OSC-Ref signal is activated, regardless of activation of the AREF-Ref signal. 
         [0033]      FIG. 4A  is a timing diagram of signals in a normal operation mode and in a self-refresh operation mode in a semiconductor device, in accordance with an embodiment of the present disclosure. The OSC-Ref signal is provided through the normal operation mode and the self-refresh operation mode by the signal generation circuit  41  which may partly be responsive to the temperature of the semiconductor device. The intervals of pulses corresponding to activation timings of the OSC-Ref signal may be relatively constant as shown by the upward pointing arrow lines. The AREF-Ref signal resulting from an auto-refresh command may be ignored and the Internal-Ref signal remains inactive (e.g., the logic low level) regardless of the AREF-Ref signal, if the Internal-Ref signal has already been activated by the AREF-Ref signal after the last activation of the OSC-Ref signal, as represented by dark “Refresh” pulses. The refresh intervals in the normal operation mode become substantially the same as the refresh intervals in the self-refresh operation mode. Because the semiconductor device such as DRAM executes any operation based on commands with higher priority than the refresh operation in the normal operation mode, the semiconductor device is not able to execute refresh operation responsive to the OSC-Ref signal from the signal generation circuit  41 . The refresh control circuit  300  provides refresh timings responsive to the AREF-Ref signal originated from the auto refresh command, while keeping the refresh intervals substantially the same as the refresh intervals of the OSC-Ref signal, even in the normal operation mode. 
         [0034]      FIG. 4B  is a timing diagram of signals in a normal operation mode and in a self-refresh operation mode in a semiconductor device, in accordance with an embodiment of the present disclosure. When the semiconductor device frequently switches between the normal operation mode and the self-refresh operation mode, an auto-refresh command provided at an entry to the self-refresh operation mode may be ignored (represented by dark “Refresh” pulses), if a refresh operation has already been executed after the last activation of the OSC-Ref signal as represented by the upward pointing arrow lines. 
         [0035]      FIG. 5A  is a timing diagram of signals of a refresh control circuit in a semiconductor device, in accordance with an embodiment of the present disclosure.  FIG. 5B  is a circuit diagram of a refresh control circuit according to an embodiment of the present disclosure. The refresh control circuit  500  may include a set-reset (SR) latch circuit  501 , AND circuits  502  and  503 , a multiplexer MUX  504  and a one shot pulse generator  505  that function similarly as the SR latch circuit  301 , the AND circuits  302  and  303 , the multiplexer MUX  304  and the one shot pulse generator  305  in  FIG. 3B , consequently, description for the SR latch circuit  501 , the AND circuits  502  and  503 , the multiplexer MUX  504  and the one-shot pulse generator circuit  505  will not be repeated. When a clock enable signal CKE is inactive (e.g., a logic low level), the multiplexer  504  provides an output signal of the AND circuit  503  as the Internal-Ref signal. When the clock enable signal CKE is active (e.g., a logic high level), the multiplexer  504  provides an output signal of the AND circuit  502  as the Internal-Ref signal. 
         [0036]    The refresh control circuit  500  further comprises a data (D) flip-flop circuit  506  and a delay circuit  507 . The D flip-flop circuit  506  may receive an AREF-Ref signal including two or more of the plurality of pulses at a clock input (C). The D flip-flop circuit  506  may receive a latch signal on a node N 1  from the SR latch circuit  501  at a data input (D) and each of the plurality of pulses of the AREF Ref signal at a clock input. The D flip-flop circuit  506  may be set to a first state responsive to the latch signal in the first state upon receipt of one of the plurality of pulses of the AREF Ref signal. The D flip-flop circuit  506  may further provide an internal signal of one of the first state and the second state on a node Nx as one of input signals to the AND circuit  502 . The AREF-Ref signal may also be provided to the delay circuit  507  and the delayed AREF-Ref signal is provided on a node Ny. The delay provided by the delay circuit may correspond to a period while the internal signal of the node Nx from the D flip-flop circuit  506  may be in a metastable state. The AND circuit  502  receives the internal signal on the node Nx and the delayed AREF-Ref signal on the node Ny. 
         [0037]    As shown in  FIG. 5A , the signal on the node N 2  can be activated using a result of arbitration responsive to the internal signal from the D flip-flop circuit  506  on the node Nx and the delayed AREF-Ref signal on the node Ny which provides a detection timing of a stable activation of the internal signal on the node Nx instead of the AREF-Ref signal. Even if the internal signal Nx becomes metastable due to internal metastability of the D flip-flop circuit  506  responsive to the OSC-Ref signal and the latch signal on the node N 1 , a level of the internal signal Nx is provided based on active timings of the delayed AREF-Ref signal Ny instead of the AREF-Ref signal, and a stable level of the internal signal Nx is provided as the signal on the node N 2 . 
         [0038]    In some embodiments, an AREF-Ref signal may be activated repeatedly, due to frequently issued auto-refresh commands or a plurality of refresh commands consecutively (e.g., in series) with a frequency reflected by the OSC-Ref signal.  FIG. 6  is a circuit diagram of a refresh control circuit according to an embodiment of the present disclosure. For example, the refresh control circuit  600  may include an AND circuit  602 , a multiplexer MUX  604 , and a delay circuit  607  that function similarly as the AND circuits  502 , the multiplexer MUX  504 , and the delay circuit  507  in  FIG. 5B , consequently, description for the AND circuit  602 , the multiplexer MUX  604 , and the delay circuit  607  will not be repeated. When a clock enable signal CKE is inactive (e.g., a logic low level), the multiplexer  604  provides the OSC-Ref signal as the Internal-Ref signal. When the clock enable signal CKE is active (e.g., a logic high level), the multiplexer  604  provides an output signal of the AND circuit  602  as the Internal-Ref signal. 
         [0039]    The refresh control circuit  600  may further comprise an up-down counter  601 . For example, the up-down counter  601  receives the OSC-Ref signal, the AREF-Ref signal and the clock enable signal CKE as an enable signal. A count stored in the up-down counter  601  may be reset when the enable signal is activated, and the up-down counter  601  increments the count responsive to an active pulse of the OSC-Ref signal and decrements the count responsive to an active pulse of the AREF-Ref signal. The up-down counter  601  provides an output signal that is active (e.g., a logic high level) when the count is equal to or more than “1”, while the clock enable signal CKE is active (e.g., the logic high level). The up-down counter  601  provide the output signal that is inactive (e.g., the logic low level) when the count stored in the up-down counter is zero, while the clock enable signal CKE is active. Thus, the up-down counter  601  may inhibit propagating the active AREF-Ref signal on the output signal while the count is zero. The output signal of the up-down counter  601  is provided to one of two input nodes of the AND circuit  602 . Furthermore, the up-down counter  601  may include an arbiter portion in order to avoid a metastable state caused by simultaneous pulses of the OSC-Ref signal and the AREF-Ref signal. The delay circuit  607  may be provided for holding the AREF-Ref signal while waiting for a stable output from the up-down counter  601  even if a slight metastable may be caused in the up-down counter  601 . 
         [0040]      FIG. 7A  is a timing diagram of signals of a refresh control circuit in a semiconductor device, in accordance with an embodiment of the present disclosure. When the clock enable signal CKE is inactive, the Internal-Ref signal propagates active pulses on the OSC-Ref signal. 
         [0041]      FIG. 7B  is a timing diagram of signals of a refresh control circuit in a semiconductor device, in accordance with an embodiment of the present disclosure. After the PON signal provides a pulse for power-on, the OSC-Ref signal is provided. When the OSC-Ref signal provides one active pulse, the counter may increment the count to “1”. When the AREF-Ref signal provides one active pulse, the Internal-Ref signal provides one active pulse based on the count “1”, and the counter decrements the count responsive to the AREF-Ref signal. The count remains constant at “0” until a next pulse is provided by the OSC-Ref signal. For example, the AND circuit  602  of  FIG. 6  may disable the second and third pulses on the AREF-Ref signal to be provided on the node N 2  responsive to the internal signal on the node Nx. Thus, the first pulse AREF-Ref alone may be propagated on the Internal-Ref signal. Thus, the next two active pulses provided by the AREF-Ref signal may not be propagated to the Internal-Ref signal, responsive to the count that is “0”. 
         [0042]    The refresh control circuit described above may be used for “Burst refresh operation” when pulses on the AREF-Ref signal are issued in clusters.  FIG. 7C  is a timing diagram of signals of a refresh control circuit in a semiconductor device, in accordance with an embodiment of the present disclosure. In this example, an auto-refresh command instructing consecutive auto refresh operations may be provided and the AREF-Ref signal reflects the command. After the PON signal provides a pulse for power-on, the OSC-Ref signal is provided. A first pulse of the OSC-Ref signal increments the count to “1” and the Internal-Ref signal provides one pulse at a first time when the AREF-Ref signal provides consecutive four active pulses. The counter decrements the count to “0” responsive to the pulses of the AREF-Ref signal. Thereafter, pulses of the OSC-Ref signal increments the count to “1”, “2”, “3”, “4” after the consecutive four active pulses of the AREF-Ref signal. In this example, a next auto-refresh command is provided after the count becomes “4”. Thus, four pulses to instruct four refresh operations may be provided on the Internal-Ref signal, responsive to the AREF-Ref signal being active responsive to the next auto-refresh command. In this example, the number of the consecutive active pulses of the AREF-Ref signal is four, however, other numbers of active pulses may be used instead. 
         [0043]      FIG. 7D  is a timing diagram of signals of a refresh control circuit in a semiconductor device, in accordance with an embodiment of the present disclosure. Similar to  FIG. 7C , following the decrement of the counter to “0” responsive to the pulses of the AREF-Ref signal, pulses of the OSC-Ref signal increments the count to “1”, “2”, “3”, after the consecutive four active pulses of the AREF-Ref signal. In this example, a next auto-refresh command is provided after the count becomes “3”. Thus, three pulses to instruct three refresh operations may be provided on the Internal-Ref signal, when the AREF-Ref signal becomes active responsive to the next auto-refresh command, regardless of the number of consecutive pulses in the AREF-Ref signal that is four. A fourth pulse on AREF-Ref is disabled because the count was three. In this example, the number of the consecutive active pulses in the AREF-Ref signal is four, however, other numbers of active pulses may be used instead. 
         [0044]      FIG. 8A  is a timing diagram of signals in a normal operation mode in a semiconductor device, in accordance with an embodiment of the present disclosure. The OSC-Ref signal is provided through the normal operation mode when the clock enable signal CKE is active (e.g., CKE having a logic high level) and the self-refresh operation mode when the clock enable signal CKE is inactive (e.g., CKE having a logic low level). Any refresh timing based on the AREF-Ref signal originated from an auto-refresh command may be ignored and activation of the Internal-Ref signal may be disabled, if the Internal-Ref signal has already been activated by the AREF-Ref signal after the last activation of the OSC-Ref signal, as shown by dark “Refresh” pulses. For example, the Internal-Ref signal may not be activated if there is no OSC-Ref signal activation between the last AREF-Ref activation and the current AREF-Ref activation as shown in  FIG. 7A . The intervals of activation timings of the OSC-Ref signal may be fairly constant as represented by arrow lines in  FIG. 8A  for each of the normal operation and the self-refresh operation, and the intervals in the normal operation may be shorter than the intervals in the self-refresh operation. It is possible to design the shorter intervals for the normal operation so that refresh intervals may not become too long depending on patterns of pulses of the AREF-Ref signal. The refresh control circuit  600  may be used to provide refresh timings responsive to the AREF-Ref signal originated from the auto refresh command, while keeping the refresh intervals substantially the same as the refresh intervals of the OSC-Ref signal, even in the normal operation mode. 
         [0045]    In another example, the Internal-Ref signal may be activated for a number of times consecutively as shown in  FIGS. 7C and 71 ).  FIG. 8B  is a timing diagram of signals in a normal operation mode in a semiconductor device, in accordance with an embodiment of the present disclosure. The OSC-Ref signal may be constantly provided through the normal operation mode as represented by arrow lines in  FIG. 8B  for the normal operation. In this example, an auto-refresh command instructing consecutive auto refresh operations may be provided and the AREF-Ref signal reflects the command. Pulses of the OSC-Ref signal increments the count to “1”, “2”, “3” and “4” after consecutive four active pulses. In this example, next auto-refresh command is provided after the count becomes “4”. Thus, four pulses to instruct four refresh operations may be provided on the Internal-Ref signal, when the AREF-Ref signal becomes active responsive to the next auto-refresh command, regardless of the number of consecutive pulses in the AREF-Ref signal that is four. Next, pulses of the OSC-Ref signal increments the count to “1”, “2”, “3”, after consecutive four active pulses of the AREF-Ref signal. In this example, next auto-refresh command is provided after the count becomes “3”. A fourth pulse on the AREF-Ref signal is disabled because the count was three. Next, pulses of the OSC-Ref signal increments the count to “I”, “2”, after consecutive four active pulses of the AREF-Ref signal. In this example, next auto-refresh command is provided after the count becomes “2”. Third and fourth pulses on the AREF-Ref signal are disabled because the count was two. Next, pulses of the OSC-Ref signal increments the count to “I”, after consecutive four active pulses of the AREF-Ref signal. In this example, next auto-refresh command is provided after the count becomes “1”. Second, third and fourth pulses on the AREF-Ref signal are disabled because the count was one. The refresh control circuit  600  may be used to provide refresh timings responsive to pulses in series of the AREF-Ref signal provided by the command control circuit originated from the plurality of auto refresh commands in series. 
         [0046]    Although this invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the inventions extend beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the inventions and obvious modifications and equivalents thereof. In addition, other modifications which are within the scope of this invention will be readily apparent to those of skill in the art based on this disclosure. It is also contemplated that various combination or sub-combination of the specific features and aspects of the embodiments may be made and still fall within the scope of the inventions. It should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying mode of the disclosed invention. Thus, it is intended that the scope of at least some of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above.