Abstract:
A control device and method are used for adjusting the refresh rate of a memory module in a computer system. The device includes a thermo sensor and a control circuit. In the control method, the thermo sensor actively outputs a temperature change signal in response to the temperature change in the memory module when a capacitor of the memory module incurs an aggravated current leakage due to the temperature rise. Next, the control circuit adjusts the refresh rate in response to the temperature change signal and refreshes the memory module at the refresh rate.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to a device and method for controlling the refresh rate of a memory module, and in particular relates to a control method and device for controlling the refresh rate of a memory module in a computer system. 
       BACKGROUND OF THE INVENTION 
       [0002]    Please refer to  FIG. 1 , which depicts a circuit diagram of a memory unit in a dynamic random access memory (DRAM) module. The memory unit includes a transistor  11  and a capacitor  12 . The capacitor  12  is fully charged if the data value stored in the memory unit is 1, and the capacitor  12  is discharged if the data value is 0. The electric charges accumulated in the capacitor  12  will be progressively lost while reading data. Moreover, charge loss of the capacitor  12  occurs after a period of time despite no access. Therefore, the charge should be refreshed several times in a second. Generally speaking, the entire DRAM module should be refreshed once about every 64 ms to keep the data accurate. 
         [0003]    Please refer now to  FIG. 2 , which depicts a functional block diagram of a conventional computer system. The conventional computer system includes a central processing unit (CPU)  20 , a Northbridge chip  21 , a Southbridge chip  22  and a DRAM module  23  connected to the Northbridge chip  21  via a bus  210 . Nowadays, most computer systems enter a suspend mode in which the CPU  20  stores some necessary data to the DRAM module  23  through the bus  210  after the computer system idles for a period of time. Then the CPU  20 , the Northbridge chip  21  and the Southbridge chip  22  are all powered down while only the DRAM module  23  remains powered on, which is called as “suspend to RAM.” Meanwhile, since all other chips are powered down, the DRAM module  23  has to refresh data by using a clock generator (not shown) of its own, i.e. self-refresh. 
         [0004]    The leakage current of the capacitor varies with temperature, for example, high temperature results in increased leakage current, which may cause data error since a great deal of charges in the capacitor are lost before the data are refreshed. Therefore, a thermo sensor (not shown) is integrated into the electrically erasable programmable read only memory (EEPROM)  230  of the DRAM module  23  to monitor the temperature in the DRAM module  23  any time. When the computer system has entered a power-saving mode to have all the other chips powered down, the DRAM module  23  can still react to the temperature change. For example, the self-refresh rate is increased in response to the rise in temperature to avoid data error, and the self-refresh rate is decreased in response to the drop in temperature to effectively reduce power consumption. In the prior art, no method has ever provided for effectively adjusting the refresh rate of the DRAM module  23  according to the temperature change when the computer system is in a normal mode. Hence, data error probably occurs in the DRAM module  23  when working in the normal mode. For this reason, the present invention is provided to overcome such disadvantage of the prior art. 
       SUMMARY OF THE INVENTION 
       [0005]    A control device for adjusting the refresh rate of a memory module in a computer system is provided. The control device includes a thermo sensor integrated into the memory module for actively outputting a temperature change signal in response to the temperature change in the memory module. The control device also includes a control circuit electrically connected to the memory module and the thermo sensor for refreshing the memory module at a preset refresh rate. The preset refresh rate can be adjusted in response to the temperature change signal outputted by the thermo sensor. 
         [0006]    Moreover, a control device for adjusting the refresh rate of a DRAM module in a computer system is also provided. The control device includes a thermo sensor integrated into the DRAM module for actively outputting a temperature change signal when a capacitor of the DRAM incurs aggravated leakage current due to the rise in temperature. The control device also includes a control circuit electrically connected to the DRAM module and the thermo sensor for refreshing the DRAM module at a preset refresh rate. The preset refresh rate can be adjusted in response to the temperature change signal outputted by the thermo sensor. 
         [0007]    Further, a control method applied to a computer system for controlling the refresh rate of a memory module is also provided. The computer system includes a DRAM module and a control circuit. A thermo sensor is integrated into the DRAM module and the control circuit is disposed in a chipset. The control method includes steps of: actively outputting a temperature change signal by the thermo sensor in response to the temperature rise of the DRAM module when a capacitor of the memory module incurs the leakage current due to the temperature rise; and refresh the DRAM module once every refresh period by the control circuit in response to the temperature change signal. The refresh period is shortened when the temperature change signal indicates the temperature rise. 
         [0008]    Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The accompanying drawings are incorporated into and form a part of the specification for the purpose of explaining the principles of the invention. The drawings are not to be constructed as limiting the invention to only the illustrated and described examples of how the invention can be made and used. Further features and advantages will become apparent from the following and more particular description of the invention, as illustrated in the accompanying drawings, wherein: 
           [0010]      FIG. 1  is a circuit diagram of a memory unit in a DRAM module; 
           [0011]      FIG. 2  is a functional block diagram of a traditional computer system; 
           [0012]      FIG. 3  is a functional block diagram showing an embodiment of a control device for adjusting the refresh rate of a memory in a computer system according to the present invention; 
           [0013]      FIG. 4  is a functional block diagram showing another embodiment of a control device for adjusting the refresh rate of a memory in a computer system according to the present invention; and 
           [0014]      FIG. 5  is a flowchart illustrating an embodiment of a method for controlling the refresh rate of a memory according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0015]    The illustrative embodiments of the present invention will be described with reference to the figure drawings wherein like elements and structures are indicated by like reference numbers. 
         [0016]    Please refer to  FIG. 3 , which depicts a functional block diagram showing an embodiment of a control device for adjusting the refresh rate of a memory module according to the present invention. The control device is provided for improving the prior art and applied to a computer system  3 , which includes a memory module  33  and a CPU  30 . The control device includes a thermo sensor  3300  and a control circuit  31 . In an embodiment, the memory module  33  can be a DRAM module in the form of a Dual Inline Memory Module (DIMM), and the thermo sensor  3300  is integrated into an EEPROM  330  of the memory module  33  for actively outputting a temperature change signal in response to the temperature change in the memory module  33 . 
         [0017]    In detail, when the computer system  3  is operated in the normal mode with rising temperature in the memory module  33  due to cooling inefficiency, for instance, the cooling fan has a breakdown, the thermo sensor  3300  actively outputs a temperature up signal to inform the control circuit  31 , separate from the memory module  33 , that the memory module  33  is overheating. On the other hand, the thermo sensor  3300  actively outputs a temperature down signal to the control circuit  31  if the temperature in the memory module  33  decreases. The thermo sensor  3300  is integrated into the EEPROM  330 , and the EEPROM  330  is connected to the Southbridge chip  312  in the control circuit  331  via a system management bus (SMBus)  32 . In this embodiment, the EEPROM  330  should serve as a master device on the SMBus  32  so that the thermo sensor  3300  is able to output signals actively. 
         [0018]    Accordingly, the Southbridge chip  312  in the control circuit  31  receives a temperature change signal from the EEPROM  330  via the SMBus  32  when the computer system  3  operates in the normal mode. In response to the temperature change signal, the Southbridge chip  312  in the control circuit  31  outputs a period change signal to the Northbridge chip  311  to make the Northbridge chip  311  change the refresh period in response to the period change signal outputted by the Southbridge chip  312 . Moreover, the Northbridge chip  311  in the normal mode refreshes the memory module  33  once every refresh period in accordance with the control signal transmitted via the DRAM bus  310 . 
         [0019]    In other words, the Northbridge chip  311  shortens the refresh period when the temperature in the memory module  33  increases and lengthens the refresh period when the temperature of the memory module  33  decreases. That is to say, the Northbridge chip  311  speeds/slows the refresh rate in response to the rise/drop of the temperature in the memory module  33 . As a result, even if the computer system  3  is not in the power-saving mode, the refresh rate of data can be adjusted according to the temperature change in the memory module  33  to effectively avoid data error. Furthermore, the present control device takes advantage of the thermo sensor  3300  that already exists in the conventional architecture rather than using an operating system or software as the control means. In this way, the disadvantage of the prior art can be improved and the object of the present invention can be achieved. 
         [0020]    Please refer to  FIG. 4  which depicts a functional block diagram of another embodiment of a control device for adjusting the refresh rate of a memory according to the present invention. The control device is provided for improving the prior art and applied to a computer system  3 , which includes a memory module  33  and a CPU  30 . The control device includes a thermo sensor  3300  and a control circuit  31 . In an embodiment, the memory module  33  can be a DIMM and the thermo sensor  3300  is integrated into the EEPROM  330  of the memory module  33  for actively outputting a temperature change signal in response to the temperature change in the memory module  33 . 
         [0021]    Similarly, the thermo sensor  3300  actively outputs a temperature up signal when the temperature in the memory module  33  increases and actively outputs a temperature down signal when the temperature in the memory module  33  decreases. The thermo sensor  3300  can be integrated into the EEPROM  330 . In this embodiment, the thermo sensor  3300  is connected to the Northbridge chip  311  and the Southbridge chip  312 , both of which are integrated into a chipset, via the SMBus  42 . The EEPROM  330  should serve as a master device on the SMBus  42  so as to actively output signals. Unlike the embodiment shown in  FIG. 3 , in which the EEPROM  330  is connected to the Southbridge chip  312  only, the EEPROM  330  in  FIG. 4  is connected to both the Northbridge chip  311  and the Southbridge chip  312 . 
         [0022]    As a result, in the normal mode, the Northbridge chip  311  in the control circuit  31  may directly receive a temperature change signal actively transmitted from the EEPROM  330  via the SMBus  42  rather than through other unit such as the Southbridge chip  312 . Therefore, the Northbridge chip  311  can directly change the refresh rate of the memory module  33  in response to the temperature change signal. Moreover, the Northbridge chip  311  operating in the normal mode outputs control signals at the refresh rate via the DRAM bus  310 , thereby refreshing the memory module  33 . Therefore, when the temperature in the memory module  33  rises, the Northbridge chip  311 , separate from the memory module  33 , can be informed of the rise in temperature and increase the refresh rate of the memory module  33 . On the contrary, the Northbridge chip  311  will control the memory module  33  to slow the refresh rate when the temperature in the memory module  33  decreases. The present control device can actively adjust the refresh rate of the memory module  33  in response to the temperature change in the normal mode, rather than controlling the refresh rate by an operating system or software. The refresh rate of data can be adjusted or controlled by the control circuit  31  to effectively avoid data error in the normal mode. 
         [0023]    Turning now to  FIG. 5 , a flowchart is shown to illustrate an embodiment of the present invention. First in step  501 , the computer system enters a normal mode. Followed by step  502 , the thermo sensor detects the temperature in the DRAM module. In step  503 , if the temperature rises over a first threshold value which has been preset before the running of the computer system, the thermo sensor actively outputs a temperature up signal to the control circuit in step  504 . And then in step  505 , the control circuit refreshes the DRAM module once every refresh period. In this condition, the refresh period is shortened, that is, the refresh rate increases in response to the temperature up signal. Otherwise, if the temperature doesn&#39;t rise over the first threshold value, another decision is made in step  506 . If the temperature drops over a second threshold value, the thermo sensor actively outputs a temperature down signal to the control circuit in step  507 . And then in step  508 , the control circuit lengthens the refreshes period to refresh the DRAM module. That is, the refresh rate decreases in response to the temperature down signal to save power consumption. 
         [0024]    As mentioned above, the disadvantage of the prior art can be improved and the object of the present invention can be achieved. While the invention has been described with respect to the physical embodiments constructed in accordance therewith, it will be apparent to those skilled in the art that various modifications, variations and improvements of the present invention may be made in light of the above teachings and within the purview of the appended claims without departing from the spirit and intended scope of the invention. In addition, those areas, in which it is believed that those of ordinary skill in the art are familiar, have not been described herein in order to not unnecessarily obscure the invention described herein. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrative embodiments, but only by the scope of the appended claims.