Abstract:
An oscillator circuit includes a capacitor device, a current source for supplying a current to the capacitor device, a reference voltage, and a control circuit. The reference voltage is a first input to a comparator. An output of the capacitor device and an output of the current source are a second input to the comparator. The control circuit resets the oscillator circuit when the first and second inputs to the comparator are equal.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to power conservation in electronics, and more particularly, conserving power by controlling the refresh rate of an oscillator using temperature variation.  
       BACKGROUND  
       [0002]     In recent years, the demand for low-power and low-voltage memory has increased as portable and handheld devices such as PDAs, cellular phones, and notebook computers have become more popular. With such features, i.e., low power and low voltage memory, longer battery life in these popular portable devices is possible.  
         [0003]     An issue when designing low-power and low-voltage memory is accounting for the self-refresh current. The self-refresh current (IDD 6 ) is a current used by devices in standby modes. As such, the self-refresh current is an important parameter in the low-power and low-voltage memory design.  
         [0004]     The self-refresh current can be expressed as follows:  
             IDD6   =         Iarray   +   Iperi     Tref     +     I   DC               (   1   )             
 
 where Iarray, Iperi, IDC, and Tref denote an array current, a peripheral current, a DC current, and a refresh period, respectively. The DC current IDC is generally small, and the array current Iarray is the largest factor in the self-refresh current IDD 6 . Tref is a fixed refresh period and is determined by the refresh characteristics of the cells. Since cells generally refresh most frequently at a higher temperature, the refresh period Tref is determined using high temperature conditions. 
 
         [0005]     Referring to  FIGS. 1A, 1B ,  2 A, and  2 B, conventional analog and/or digital designs have attempted to minimize/address power consumption by the self-refresh current IDD 6 . The oscillator  100  generates a base frequency, for example, 0.5X and the frequency divider generates additional refresh periods, i.e., 1X, 2X and 4X refresh periods, using the base frequency. A conventional oscillator circuit and the timing diagram of the oscillator is a current analog solution, as shown in  FIGS. 1A and 1B . Such a prior art oscillator has a current source  110 , a capacitor  120 , a comparator  130 , and a reset circuit  140 . The reset circuit  140  initializes node l  150  to ground. The current source  110  provides a constant current i to node l  150 , and the value at node l  150  increases linearly according to the capacitance C  120  and current i provided by the current source  110 . When the voltage at the node l  150  reaches the level of the reference voltage Vref  170 , the output  180  of the comparator  130  is switched to ‘H’, and node l  150  is reset to ground for the next operation. The oscillator period Tosc (see  FIG. 1B ) is determined by the capacitor C  120 , the current i from the current source  110 , and the reference voltage Vref  170 .  
         [0006]     Referring to  FIG. 2A , a solution using digital logic to generate various refresh periods is also known. The oscillator  200  generates a base frequency, for example, 0.5X and the frequency divider  290  generates additional refresh periods, i.e., 1X, 2X and 4X refresh periods  292 ,  294 ,  296 , using the base frequency. As shown in the table (see  FIG. 2B ), intermediate refresh periods, i.e., 1.5X, 2.5X, and 3.5X, are generated by combinational logic  220 . Using the refresh periods generated by the oscillator  200 , the frequency divider  290 , and the combinational logic  220 , one refresh period can be selected, i.e., TD&lt;0:7&gt;. The refresh period can be selected by the temperature information device (not shown), which provides the temperature information from a Temperature Compensated Self Refresh (TCSR) mode or an on-chip thermometer.  
         [0007]     However, using only digital logic requires a large amount of space and is very complex. A frequency divider and combinational logic further increase the complexity in order to determine the additional refresh periods.  
         [0008]     A simple method to vary refresh periods of an oscillator using minimal space as compared to a purely digital solution is desirable.  
       SUMMARY  
       [0009]     A method to provide various refresh periods using the temperature information provided by an on-chip temperature sensor or a TCSR mode can assist in power conservation and can reduce power consumption by a self-refresh current. An oscillator can be modified to provide various refresh periods using temperature information from an on-chip thermometer or a TCSR mode. A power-conserving oscillator can include digital logic to effectively determine various refresh periods.  
         [0010]     In a general aspect, an oscillator circuit includes a capacitor device, a current source for supplying a current to the capacitor device, a reference voltage, and a control circuit. The reference voltage can be a first input to a comparator. An output of the capacitor device and an output of the current source can be a second input to the comparator. The control circuit can reset the oscillator circuit when the first and second inputs to the comparator are equal.  
         [0011]     Some or all of the following features may be included in the above implementation. The current source can include a plurality of transistors. Based upon temperature information, a value of the current from the current source can vary as each transistor being on or off and the current provided by the current source to the capacitor device can be modified such that a refresh period of the oscillator circuit can be generated.  
         [0012]     The temperature information can be provided by an external source. Alternately, the temperature information can be provided by an on-chip thermometer.  
         [0013]     The capacitor device can include a plurality of capacitors. Based upon temperature information, a capacitor ratio can be modified and a value of the capacitor device can vary such that a refresh period of the oscillator circuit can be generated.  
         [0014]     The temperature information can be provided by an external source. Alternately, the temperature information can be provided by an on-chip thermometer.  
         [0015]     The reference voltage can vary, and based upon temperature information, a refresh period of the oscillator circuit of the oscillator can be generated.  
         [0016]     The temperature information can be provided by an external source. Alternately, the temperature information can be provided by an on-chip thermometer.  
         [0017]     In another general aspect, an oscillator circuit includes a capacitor device, a current source for supplying a charging current for the capacitor device, a reference voltage, and a control circuit. The capacitor device can include a plurality of capacitors. The current source can include a plurality of transistors. The reference voltage can be a first input to a comparator. An output of the capacitor device and an output of the current source can be a second input to the comparator. Based upon temperature information, a capacitor ratio can be modified and a value of the capacitor device can vary, each transistor can be on or off and a value of the current from the current source to the capacitor device can vary, and the reference voltage can vary such that a refresh period of the oscillator circuit of the oscillator can be generated. The control circuit can reset the oscillator circuit when the first and second inputs to the comparator are equal.  
         [0018]     Some or all of the following features may be included in the above implementation. The temperature information can be provided by an external source. Alternately, the temperature information can be provided by an on-chip thermometer.  
         [0019]     In another general aspect, a circuit configuration includes an oscillator circuit that has a capacitor device, a current source for supplying a current to the capacitor device, a reference voltage, a control circuit, and a frequency divider.  
         [0020]     The reference voltage can be a first input to a comparator. An output of the capacitor device and an output of the current source can be a second input to the comparator. The control circuit can reset the oscillator circuit when the first and second inputs to the comparator are equal.  
         [0021]     Some or all of the following features may be included in the above implementation. The frequency divider can include at least one latch and a multiplier. Based upon temperature information, the frequency divider can select and output a multiplier for a refresh period of the oscillator circuit.  
         [0022]     The temperature information can be provided by an external source. Alternately, the temperature information can be provided by an on-chip thermometer.  
         [0023]     The current source can include a plurality of transistors. Based upon temperature information, a value of the current from the current source can vary as each transistor being on or off and the current provided by the current source to the capacitor device can be modified such that a refresh period of the oscillator circuit can be generated.  
         [0024]     The temperature information can be provided by an external source. Alternately, the temperature information can be provided by an on-chip thermometer.  
         [0025]     In another general aspect, a method of providing temperature control to an oscillator circuit includes providing an oscillator circuit that has a capacitor device, a current source for supplying a current to the capacitor device, a reference voltage, and a control circuit. The reference voltage can be a first input to a comparator. An output of the capacitor device and an output of the current source can be a second input to the comparator. The control circuit can reset the oscillator circuit when the first and second inputs to the comparator are equal.  
         [0026]     Some or all of the following features may be included in the above method. The current source can include a plurality of transistors. Based upon temperature information, a value of the current from the current source can vary as each transistor being on or off and the current provided by the current source to the capacitor device can be modified such that a refresh period of the oscillator circuit can be generated.  
         [0027]     The temperature information can be provided by an external source. Alternately, the temperature information can be provided by an on-chip thermometer.  
         [0028]     The capacitor device can include a plurality of capacitors. Based upon temperature information, a capacitor ratio can be modified and a value of the capacitor device can vary such that a refresh period of the oscillator circuit can be generated.  
         [0029]     The temperature information can be provided by an external source. Alternately, the temperature information can be provided by an on-chip thermometer.  
         [0030]     The reference voltage can vary, and based upon temperature information, a refresh period of the oscillator circuit of the oscillator can be generated.  
         [0031]     The temperature information can be provided by an external source. Alternately, the temperature information can be provided by an on-chip thermometer.  
         [0032]     In another general aspect, a method of providing temperature control to an oscillator circuit that includes providing an oscillator circuit that has a capacitor device, a current source for supplying a charging current for the capacitor device, a reference voltage, and a control circuit. The capacitor device can include a plurality of capacitors. The current source can include a plurality of transistors. The reference voltage can be a first input to a comparator. An output of the capacitor device and an output of the current source can be a second input to the comparator. Based upon temperature information, a capacitor ratio can be generated and a value of the capacitor device can vary, each transistor can be on or off and a value of the current from the current source to the capacitor device can vary, and the reference voltage can vary such that a refresh period of the oscillator circuit of the oscillator can be generated. The control circuit can reset the oscillator circuit when the first and second inputs to the comparator are equal.  
         [0033]     Some or all of the following features may be included in the above method. The temperature information is provided by an external source. Alternatively, the temperature information is provided by an on-chip thermometer.  
         [0034]     In another general aspect, a method of providing temperature control to an oscillator circuit includes providing an oscillator circuit that has a capacitor device, a current source for supplying a current to the capacitor device, a reference voltage, a control circuit, and providing a frequency divider.  
         [0035]     The reference voltage can be a first input to a comparator. An output of the capacitor device and an output of the current source can be a second input to the comparator. The control circuit can reset the oscillator circuit when the first and second inputs to the comparator are equal.  
         [0036]     Some or all of the following features may be included in the above method. The frequency divider can include at least one latch and a multiplier. Based upon temperature information, the frequency divider can select and output a multiplier for a refresh period of the oscillator circuit.  
         [0037]     The temperature information can be provided by an external source. Alternately, the temperature information can be provided by an on-chip thermometer.  
         [0038]     The current source can include a plurality of transistors. Based upon temperature information, a value of the current from the current source can vary as each transistor being on or off and the current provided by the current source to the capacitor device can be modified such that a refresh period of the oscillator circuit can be generated.  
         [0039]     The temperature information can be provided by an external source. Alternately, the temperature information can be provided by an on-chip thermometer.  
         [0040]     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings and from the claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0041]      FIG. 1A  illustrates a known analog oscillator circuit;  
         [0042]      FIG. 1B  is a timing diagram for the oscillator of  FIG. 1A ;  
         [0043]      FIG. 2A  is a block diagram of a known oscillator with a frequency divider with digital logic;  
         [0044]      FIG. 2B  is a table reflecting refresh periods for the oscillator of  FIG. 2A ;  
         [0045]      FIG. 3A  is a block diagram of an embodiment of an oscillator according to the present invention;  
         [0046]      FIG. 3B  is a block diagram of another embodiment of an oscillator according to the present invention;  
         [0047]      FIG. 4A  illustrates an oscillator with modification to the current according to the present invention;  
         [0048]      FIG. 4B  is a table reflecting refresh periods for the oscillator of  FIG. 4A ;  
         [0049]      FIG. 5A  illustrates an oscillator with a modification to the capacitance according to the present invention;  
         [0050]      FIG. 5B  is a table reflecting refresh periods for the oscillator of  FIG. 5A ;  
         [0051]      FIG. 6A  illustrates an oscillator with a modification to the reference voltage according to the present invention;  
         [0052]      FIG. 6B  is a table reflecting refresh periods for the oscillator of  FIG. 6A ;  
         [0053]      FIG. 7A  illustrates an oscillator with a modification to the current, capacitance, and reference voltage according to the present invention;  
         [0054]      FIG. 7B  is a table reflecting refresh periods for the oscillator of  FIG. 7A ;  
         [0055]      FIG. 8A  illustrates an oscillator with a modification to the current;  
         [0056]      FIG. 8B  is a block diagram of the oscillator of  FIG. 8A  in combination with a frequency divider and a series of latches; and  
         [0057]      FIG. 8C  is a table reflecting refresh periods for the device of  FIG. 8B . 
     
    
       [0058]     Like reference symbols in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0059]     Various refresh periods using temperature information provided by an on-chip temperature sensor or a Temperature Compensated Self Refresh (TCSR) mode can assist in conserving power used as a result of the self-refresh current IDD 6 . An oscillator with an on-chip thermometer or a TCSR mode can determine various refresh periods using the temperature information.  
         [0060]     Referring to  FIGS. 3A and 3B , an oscillator can receive temperature information from an on-chip thermometer  310  or through a Temperature Compensated Self Refresh (TCSR) mode. An on-chip thermometer  310  would provide temperature information TD to the oscillator  300 . The temperature information provided by an on-chip thermometer can be more accurate than the temperature information from registers. Using this temperature information and calculated or known refresh characteristics over temperature, different refresh periods at different temperatures can be used to reduce the self-refresh current IDD 6 .  
         [0061]     In order to reduce the frequency of refresh of the self-refresh current IDD 6 , a TCSR mode can be used in low-power SDRAM design. In the TCSR mode, the temperature information T from an outside chip or an external temperature sensor (not shown) can be stored in registers  410  and provided to the oscillator  400 , and the refresh period Tref (DRAM refresh period) can be adjusted according to the temperature information. Since the refresh characteristics at cooler temperatures are generally better than at higher temperatures, the refresh period Tref at cooler temperatures can be increased to reduce the self-refresh current IDD 6 .  
         [0062]     The base frequency of an oscillator can be changed based on received temperature information. The temperature information is received from an external thermometer that has generally been stored in mode registers of memory chips or from an on-chip thermometer, for instance, as described above.  
         [0063]     Generally, there are three parameters that can change the base frequency of an oscillator: (1) current values, (2) capacitor values, and/or (3) change the value of the reference voltage level Vref.  
         [0064]     Referring to  FIG. 4A , an oscillator with a modification to the current is one way to change the base frequency. By changing the base frequency of the oscillator, the refresh period Tref can be changed.  
         [0065]     The oscillator  500  includes a current source  510  with temperature controls, a capacitor C  520 , a comparator  530 , and a reset circuit  540 . Temperature information TD 1 , TD 2 , TD 3 , TD 4  can control the current flow to node l  550  so that the base frequency of the oscillator  500  can be changed. The temperature information can be provided from a TCSR mode or an on-chip thermometer, as described above. In this example, the size of transistors P 3 , P 4 , P 5 , and P 6  are the same. So, for example, when the four transistors are turned on, the refresh period is the shortest, i.e., 1X. When P 10  is turned off, the current can be reduced 25%, and the oscillator period can be increased 33%. When P 10  and P 9  are turned off, the current can be reduced 50%, and the oscillator period can be increased 100%. Likewise, other transistors can be turned on and off to adjust the oscillator period. With additional PMOS transistors, more refresh periods can be generated in the oscillator.  
         [0066]     Structurally, the current source  510  includes a plurality of transistors, in this example, both PMOS and NMOS. Specifically, there are two NMOS transistors N 1  and N 2 , and ten PMOS transistors P 1 , P 2 , P 3 , P 4 , P 5 , P 6 , P 7 , P 8 , P 9 , and P 10 . Temperature information is provided, for example, along four paths TD 1 , TD 2 , TD 3 , and TD 4 . There are four parallel paths. The current i is controlled by switching various transistors on and off. The gates of the PMOS transistors P 1 , P 2 , P 3 , P 4 , P 5 , and P 6  are tied together and the gates of the NMOS transistors N 1 , N 2  are tied together. The sources of the PMOS transistors P 1 , P 2 , P 3 , P 4 , P 5 , and P 6  are tied together. The drain of one NMOS transistor N 1  is tied to the gates of the NMOS transistors N 1  and N 2 . The drain of one NMOS transistor N 2  is tied to the gates of the PMOS transistors P 1 , P 2 , P 3 , P 4 , P 5 , and P 6 . The drain of PMOS transistors P 3 , P 4 , P 5 , and P 6  are tied to the sources of PMOS transistors P 7 , P 8 , P 9 , and P 10 , respectively. Temperature information TD 1 , TD 2 , TD 3 , and TD 4  is provided at the drain of PMOS transistors P 7 , P 8 , P 9 , and P 10 , respectively. This analog oscillator solution is relatively simple to control and uses a relatively small area.  
         [0067]      FIG. 4B  is a table that shows exemplary periods that can be generated. For example, at a temperature less than 10° C., PMOS transistors P 7 , P 8 , and P 9  would be off, i.e., H, and. PMOS transistor P 10  would be on, i.e., L, and therefore the oscillator refresh period Tosc that is generated would be 4X the base frequency. Whereas, at a temperature greater than 70° C., PMOS transistors P 7 , P 8 , P 9 , and P 10  would be on, i.e., L, and therefore the oscillator refresh period Tosc that is generated would be 1X the base frequency.  
         [0068]     Referring to  FIG. 5A , an oscillator with a modification to the capacitance at the node l can also change the base frequency of the oscillator. The oscillator  600  includes a current source  610 , a capacitor C  620 , a comparator  630 , and a reset circuit  640 . The capacitor C  620  includes temperature controls. Structurally, the capacitor C  620  includes, for example, four capacitors  622 ,  624 ,  626 ,  628  tied to the source of four NMOS transistors N 2 , N 3 , N 4 , N 5 , respectively. The drains of the capacitors  622 ,  624 ,  626 ,  628  are tied together. Temperature information TD 1 , TD 2 , TD 3 , and TD 4  are provided at the gates of each capacitor  622 ,  624 ,  626 ,  628 , respectively. As a result, the capacitors  622 ,  624 ,  626 ,  628  can be used to generate periods, such as 1X, 2X, 3X, and 4X.  
         [0069]     The temperature information TD 1 , TD 2 , TD 3 , TD 4  affects capacitance ratios, and thus, the capacitance C at node l so that the base frequency of the oscillator can be changed. The temperature information can be provided from a TCSR mode or an on-chip thermometer as described above.  
         [0070]     Referring to  FIG. 5B , the table shows the periods that can be generated by the oscillator. For example, as capacitance ratios are changed, i.e., like 0.5C, 0.25C, 1C, and 2C, based upon TD 1 , TD 2 , TD 3 , and TD 4 , many oscillator periods can be created. Specifically, for example, at a temperature less than 10° C., the capacitors  622 ,  624 ,  626 ,  628  would be on, i.e., H, and therefore the oscillator refresh period Tosc that is generated would be 4X the base frequency. Whereas, at a temperature greater than 70° C., only capacitor  628  would be on, i.e., H, the other capacitors  622 ,  624 ,  626  would be off, i.e., L, and therefore the oscillator refresh period Tosc that is generated would be 1X the base frequency.  
         [0071]     Referring to  FIG. 6A , the base frequency of an oscillator can be changed by changing the reference voltage level Vref. The oscillator  700  includes a current source  710 , a capacitor C  720 , a comparator  730 , and a reset circuit  740 . In this example, the reference voltage Vref  770  varies.  
         [0072]      FIG. 6B  is a table illustrating the various refresh periods created. For example, for a reference voltage level Vref of 1.2V at a temperature less than 10° C., the oscillator refresh period Tosc is 2X.  
         [0073]     Alternatively, referring to  FIG. 7A , various periods can be generated by varying current, capacitance, and the reference voltage level, i.e., a mixed scheme. The oscillator  800  includes a current source  810  with temperature controls, a capacitor C  820  with temperature controls, a comparator  830 , and a reset circuit  840 . The reference voltage Vref  870  also varies.  
         [0074]     Structurally, the current source  810  includes a plurality of transistors, in this example, both PMOS and NMOS. Specifically, there are two NMOS transistors N 1  and N 2 , and nine PMOS transistors P 1 , P 2 , P 3 , P 4 , P 5 , P 6 , P 7 , P 8 , and P 9 . Temperature information is provided, for example, along one path TD 5 . There are three parallel paths, however. The current i is controlled by switching various transistors on and off. The gates of the PMOS transistors P 1 , P 2 , P 3 , P 4 , and P 5  are tied together and the gates of the NMOS transistors N 1 , N 2  are tied together. The sources of the PMOS transistors P 1 , P 2 , P 3 , P 4 , and P 5  are tied together. The drain of one NMOS transistor N 1  is tied to the gates of the NMOS transistors N 1  and N 2 . The drain of one NMOS transistor N 2  is tied to the gates of the PMOS transistors P 1 , P 2 , P 3 , P 4 , and P 5 . The drains of PMOS transistors P 3 , P 4 , and P 5  are tied to the sources of PMOS transistors P 7 , P 8 , and P 9 , respectively. Temperature information TD 5  is provided at the drain of PMOS transistors P 9 . The drains of PMOS transistors P 7  and P 8  are connected to V SS , a ground supply voltage.  
         [0075]     The capacitor C  820  includes temperature controls. Structurally, the capacitor C  820  includes, for example, four capacitors  822 ,  824 ,  826 ,  828  tied to the source of four NMOS transistors N 1 , respectively. The drains of the capacitors  822 ,  824 ,  826 ,  828  are tied together. Temperature information TD 1 , TD 2 , TD 3 , and TD 4  are provided at the gates of each capacitor  822 ,  824 ,  826 ,  828 , respectively. As a result, the capacitors  822 ,  824 ,  826 ,  828  can be used to generate periods, such as 1X, 2X, 3X, and 4X.  
         [0076]     Temperature information can be provided, as described above. In this example, the capacitors  822 ,  824 ,  826 ,  828  can be used to generate integer periods like 1X, 2X, 3X, and 4X, and current source (with P 1 , P 2 , P 3 , P 4 , P 5 , P 6 , P 7 , P 8 , and P 9 ) can be used to generate intermediate periods like 1.5X, 2.5X, 3.5X, and 4.5X.  
         [0077]      FIG. 7B  is a table showing exemplary generated periods. For example, as capacitance ratios are changed, i.e., like 0.5C, 0.25C, 1C, and 2C, based upon TD 1 , TD 2 , TD 3 , and TD 4 , many oscillator periods can be created. Specifically, for example, at a temperature of 10° C., the capacitors  822 ,  824 ,  826 ,  828  would be on, i.e., H, PMOS transistor P 9  would on, i.e., L, and therefore the oscillator refresh period Tosc that is generated would be 4X the base frequency. Whereas, at a temperature of 70° C., only capacitor  828  would be on, i.e., H, the other capacitors  822 ,  824 ,  826  and PMOS transistor P 9  would on, i.e., L, and therefore the oscillator refresh period Tosc that is generated would be 1X the base frequency.  
         [0078]     Alternatively, referring to  FIGS. 8A-8C , an oscillator can be combined with digital technology to also provide various refresh periods. The oscillator  900  includes a current source  910  with temperature controls, a capacitor C  920 , a comparator  930 , and a reset circuit  940 . The structure of the current source  910  is like the current source  810  described above in relation to  FIG. 7A . Specifically, there are two NMOS transistors N 1  and N 2 , and nine PMOS transistors P 1 , P 2 , P 3 , P 4 , P 5 , P 6 , P 7 , P 8 , and P 9 . Temperature information is provided, for example, along one path TD 5 . There are three parallel paths, however. The current i is controlled by switching various transistors on and off. The gates of the PMOS transistors P 1 , P 2 , P 3 , P 4 , and P 5  are tied together and the gates of the NMOS transistors N 1 , N 2  are tied together. The sources of the PMOS transistors P 1 , P 2 , P 3 , P 4 , and P 5  are tied together. The drain of one NMOS transistor N 1  is tied to the gates of the NMOS transistors N 1  and N 2 . The drain of one NMOS transistor N 2  is tied to the gates of the PMOS transistors P 1 , P 2 , P 3 , P 4 , and P 5 . The drains of PMOS transistors P 3 , P 4 , and P 5  are tied to the sources of PMOS transistors P 7 , P 8 , and P 9 , respectively. Temperature information TD 5  is provided at the drain of PMOS transistors P 9 . The drains of PMOS transistors P 7  and P 8  are connected to V SS , a negative supply voltage. The base frequency of such an oscillator  900 , for example, is 0.5X.  
         [0079]     Temperature information TD 5  can control the current flow to node l  950  so that the base frequency of the oscillator  900  can be changed. The temperature information can be provided from a TCSR mode or an on-chip thermometer, as described above.  
         [0080]     As shown in  FIG. 8B , the mixed scheme can be combined with a digital scheme. In this example, an oscillator  900  with current modification ( FIG. 8A ) in combination with a digital circuit, e.g., a frequency divider,  990  can generate integer periods, like 1X, 2X, and 4X  992 ,  994 ,  996 , and a current source  910  can generate intermediate periods, like 1.5X, 3X, and 6X (see  FIG. 8C ). The current source  910  can be a current mirror. The frequency divider  990  in conjunction with temperature information TD 2 , TD 3 , TD 4   993 ,  995 ,  997  can provide additional refresh periods. This mixed scheme also needs less area compared to pure digital scheme.  
         [0081]      FIG. 8C  is a table showing exemplary refresh periods that can be generated. Specifically, for example, at a temperature of 20° C., PMOS transistor P 9  would on, i.e., L, latches  993  and  995  would be open, i.e., off, latch  997  would be closed, i.e., on, and therefore the oscillator refresh period Tosc that is generated would be 6X [4X times 0.5X (the base frequency)]. Whereas, at a temperature of 70° C., PMOS transistor P 9  would off, i.e., H, latches  995  and  997  would be open, i.e., off, latch  993  would be closed, i.e., on, and therefore the oscillator refresh period Tosc that is generated would be 1X.  
         [0082]     An oscillator with temperature control can provide many refresh periods in a small area. If the new oscillator with temperature control is combined with a digital frequency divider, additional refresh periods can be provided in a simpler and smaller way are possible.  
         [0083]     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope. Accordingly, other embodiments are within the scope of the following claims.