Abstract:
A system for controlling the fan speed is described. Specifically, one embodiment of the present invention set forth a computing system, which includes a first processing unit including a first sensor, wherein the first processing unit is configured to generate a first pulse-width modulation signal, and a first transmission line further including a first direct current voltage converter configured to convert the first pulse-width modulation signal to a first direct current voltage and a first diode coupled to the first direct current voltage converter, wherein the first diode determines whether the first direct current voltage passes through the first diode. The computing system further includes an amplifier coupled to the first diode, wherein the amplifier is configured to amplify a selected direct current voltage to drive a fan.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of People&#39;s Republic of China Application No. 200810146112.2, filed on Aug. 6, 2008 and having Atty. Docket No. NVDA/SZ-08-0093-CN. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Embodiments of the present invention relate generally to a fan speed control system and more specifically to a system for controlling fan speed in a computing system that includes multiple components capable of dissipating heat. 
         [0004]    2. Description of the Related Art 
         [0005]    Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. 
         [0006]    A computing system typically has a processing unit to process data. In order to improve the computing speed of a computing system, one approach is to integrate multiple processing units into a computing system. However, a processing unit consumes power and releases heat when it operates. This heat dissipation problem worsens if the computing system includes multiple processing units. Therefore, incorporating a cooling system in the computing system to take the released heat out of the computing system is essential to prevent the components in the computing system from malfunctioning or even burning down due to overheating. 
         [0007]    A cooling system may include a fan. A fan typically generates noises and consumes power. If the speed of the fan cannot be adjusted and simply operates at full speed all the time, then the fan tends to make undesirable levels of noises and consume unnecessary amount of power. In addition, the life of such fan may be shortened. 
         [0008]      FIG. 1  illustrates a conventional computing system  100  including three graphic processing units (GPUs), a first GPU  110 , a second GPU  120  and a third GPU  130 , that dissipate different levels of heat. The first GPU  110 , the second GPU  120 , and the third GPU  130  are associated with a first pulse-width modulation (PWM) signal  112 , a second PWM signal  122 , and a third PWM signal  132 , respectively. A multi-channel fan controller IC  140  controls the operating speed of a fan  150  according to the respective PWM signal associated with each GPU. 
         [0009]    The multi-channel fan controller IC  140  passes a specific PWM signal associated with a particular GPU dissipating the highest level of heat among the first GPU  110 , the second GPU  120  and the third GPU  130 . The fan  150  receives the specific PWM signal and adjusts its speed accordingly. In  FIG. 1 , the fan  150  is capable of interpreting a PWM signal passed through the multi-channel fan controller IC  140  directly. However, such fan capable of interpreting a PWM signal directly and the multi-channel fan controller IC are not a cost effective solution to a low cost computer system. 
         [0010]    To further reduce cost, another conventional system avoids using a multi-channel fan controller IC and a fan capable of interpreting a PWM signal and instead uses a DC voltage controlled fan.  FIG. 2  illustrates a computing system  200  including one GPU  210  and a DC voltage controlled fan  250 . The GPU  210  dissipates heat and associates with a PWM signal  212 . The PWM signal  212  is transferred to a DC voltage V 214  at a node  214  by a resistance  220  and a capacitor  230 , therefore, the DC voltage V 214  is associated with the PWM signal  212 . When the PWM signal  212  changes because of the operation of the GPU  210 , the DC voltage V 214  is changed accordingly. The DC voltage V 214  is then amplified by an amplifier  240  with a fixed amplified ratio to generate an amplified voltage V 216  at a node  216  which is strong enough to drive a fan  250 . 
         [0011]    In  FIG. 2 , the speed of the fan  250  is directly controlled by the amplified voltage  216 , rather than the PWM signal  212 . This type of fan is typically called as a DC voltage controlled fan and cheaper than the fan capable of interpreting a PWM signal directly. However, lacking of a component capable of selecting a highest voltage among different voltage sources, such as the multi-channel fan controller IC  140  illustrated in the  FIG. 1 , a DC voltage controlled fan and its control circuits cannot be used in a computing system including multiple processing units because the control circuits cannot control the speed of the fan  250  for a specific processing unit dissipating the highest level of heat among all processing units. 
         [0012]    As the foregoing illustrates, what is needed is a system for controlling fan speed in a computing system that includes multiple processing units and addressing at least the problems set forth above. 
       SUMMARY OF THE INVENTION 
       [0013]    A system for controlling the fan speed is described. Specifically, one embodiment of the present invention set forth a computing system, which includes a first processing unit including a first sensor, wherein the first processing unit is configured to generate a first pulse-width modulation signal, and a first transmission line further including a first direct current voltage converter configured to convert the first pulse-width modulation signal to a first direct current voltage and a first diode coupled to the first direct current voltage converter, wherein the first diode determines whether the first direct current voltage passes through the first diode. The computing system further includes an amplifier coupled to the first diode, wherein the amplifier is configured to amplify a selected direct current voltage to drive a fan. 
         [0014]    At least one advantage of the present invention disclosed herein is using a diode to determine whether a direct current voltage passes through the diode. By setting each diode on every transmission line between every respective processing unit in a computing system and the only fan in the computing system, only the diode on the transmission line coupled to the processing unit with the highest temperature is turned on and the speed of fan is associated with the processing unit with the highest temperature. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0016]      FIG. 1  is a block diagram of a conventional computing system including multiple processing units, a fan and a multi-channel fan controller IC configured to control the speed of fan; 
           [0017]      FIG. 2  is a circuit diagram of a conventional computing system including a processing unit, a fan configured to be controlled by a DC voltage converted from a PWM signal generated by a sensor of the processing unit; and 
           [0018]      FIG. 3  is a block diagram of a computing system including multiple processing units and a fan, according to one embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Throughout this disclosure, the term “electrical network” broadly refers to an interconnection of electrical elements, such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources, switches, diodes and amplifiers. The term “direct current voltage converter” broadly refers to an electrical circuit configured to convert a pulse-width modulation signal to a stable direct current voltage. The term “duty cycle” broadly refers to a function of time that a component is in an active state or a proportion of time during which a component is operated. The term “transmission line” broadly refers to a material medium or structure that forms all or part of a path from one place to another for directing the transmission of energy, such as electromagnetic waves or acoustic waves, as well as electric power transmission. 
         [0020]    In accordance with an embodiment of the invention, a computing system includes multiple processing units, a fan, and respective transmission lines coupled each processing unit to the fan. Each processing unit includes a sensor configured to detect the respective operating temperature of the processing units. Each processing units generates a pulse-width modulation signal associated with the operating temperature of each processing unit, respectively. Each pulse-width modulation signal has its own duty cycle. Each transmission line includes a direct current voltage converter configured to covert the pulse-width modulation signal to a stable direct current voltage. Each transmission line further includes a diode configured to determine whether the converted stable direct current voltage passes through the diode. 
         [0021]      FIG. 3  is a block diagram of a computing system  300  including multiple processing units and a fan, according to one embodiment of the invention. In one implementation, the computing system  300  includes three graphic processing units (GPUs), a GPU  310 , a GPU  320 , and a GPU  330 . The GPU  310  includes a sensor  312  and a general purpose I/O (GPIO)  313 . 
         [0022]    The GPU  310  generates a pulse-width modulation signal  314  in response to an operating temperature of the GPU  310  measured by the sensor  312 . The pulse-width modulation signal  314  is then delivered to a transmission line  315  through the GPIO  313 . 
         [0023]    Similarly, the GPU  320  includes a sensor  322  and a GPIO  323 . The GPU  320  generates a pulse-width modulation signal  324  in response to an operating temperature of the GPU  320  measured by the sensor  322 , and sends the pulse-width modulation signal  324  to a transmission line  325  through the GPIO  323 . The GPU  330  also includes a sensor  332  and a GPIO  333 . The GPU  330  generates a pulse-width modulation signal  334  in response to an operating temperature of the GPU  330  measured by the sensor  332 , and sends the pulse-width modulation signal  334  to a transmission line  335  through the GIPO  333 . 
         [0024]    If the GPU  310 , the GPU  320  and the GPU  330  are configured to process different data, then the corresponding work loads differ from each other. As a result, the GPU  310 , the GPU  320  and the GPU  330  dissipate different levels of heat and operate at different temperatures. As the pulse-width modulation signals  314 ,  324 , and  334  are associated with the operating temperatures of the GPUs  310 ,  320 , and  330  measured by the sensors  312 ,  322 , and  332 , respectively, the pulse-width modulation signals  314 ,  324 , and  334  differ from each other. 
         [0025]    The pulse-width modulation signal  314  then passes through a direct current voltage converter  316  and is converted to a stable direct current voltage V 317 at a node  317  on the transmission line  315 . The direct current voltage converter may be a capacitor-resistor circuit  316 . When a pulse-width modulated signal is in the high state, it charges the capacitor via the resistor. When the pulse-width modulated signal is in the low state, it discharges the capacitor. Therefore, the direct current voltage converter is charged and discharged periodically and thus outputs a substantially constant direct current voltage. Similarly, the pulse-width modulation signal  324  and the pulse-width modulation signal  334  are converted to stable direct current voltages V 327  at a node  327  and V 337 at a node  337  through direct current voltage converters  326  and  336 , respectively. 
         [0026]    A diode is a two-terminal device. Diodes have two active electrodes, one is cathode and the other is anode, between which the current may flow. Diodes exhibit a unidirectional current property and are usually used for the rectifying property as they only allow an electric current to pass in one direction and block it in the opposite direction. In a diode, when the voltage applied on the anode is greater than the voltage applied on the cathode, the diode is turned on and the electric current flows through the diode from the anode to the cathode. On the other hand, when the voltage applied on the anode is less than the voltage applied on the cathode, the diode is turned off and the electric current does not flow through the diode from the anode to the cathode. 
         [0027]    There are various types of diodes, such as Zener diode, Schottky diode, Tunnel diode, light-emitting diode, photodiode, and p-n diode. As an illustration, in a p-n diode, the p-type region is anode and the n-type region is cathode. When the voltage applied on the p-type region is greater than the voltage applied on the n-type region, the p-n diode is turned on and the electric current flows through the diode from the p-type region (anode) to the n-type region (cathode). On the other hand, when the voltage applied on the p-type region is less than the voltage applied on the n-type region, the p-n diode is turned off and the electric current does not flow through the diode from the p-type region (anode) to the n-type region (cathode). 
         [0028]    Referring back to  FIG. 3 , when the GPU  310 , the GPU  320 , and the GPU  330  operate at different temperatures, the direct current voltages V 317  at the node  317 , V 327  at the node  327  and V 337  at the node  337  are different. For illustration, in one implementation, the pulse-width modulation signal  314  has a 30% duty cycle, the pulse-width modulation signal  324  has a 50% duty cycle and the pulse-width modulation signal  334  has a 70% duty cycle. The GPU  310 , the GPU  320 , the GPU  330  are the same model and a pulse-width modulation signal with a 100% duty cycle generated by such model of the GPU is converted to a direct current voltage of 3.3 volts after passing through the direct current voltage converter. Therefore, the voltage V 317  at the node  317  is about 1 volt, the voltage V 327  at the node  327  is about 1.65 volts and the voltage V 337  at the node  337  is about 2.3 volts. 
         [0029]    In such implementation, when the diodes  318 ,  328  and  338  have the same voltage drop, such as 0.25 volt, then the voltage at node  339  is about 2.05 volts (V 339 ). The diode  338  is turned on because the voltage applied at the node  337  (V 337 ) is greater than the voltage applied at the node  339  (V 339 ). 
         [0030]    The voltages at the node  329  (V 329 ) and the node  319  (V 319 ) are the same with the voltage at the node  339  (V 339 ), therefore, V 329  is greater than V 327  and V 319  is greater than V 317 . In the implementation, the diodes  318  and  328  are not turned on because the voltages applied at the nodes  317  and  327  are less than voltages applied at nodes  319  and  329 , respectively. Therefore, only the direct current voltage V 337  is sent to an amplifier  340  to drive a fan  350 . As such, the speed of the fan  350  is controlled by the direct current voltage V 337  associated with the pulse-width modulation signal  334  having the highest duty cycle among the duty cycles of the pulse-width modulation signals generated by the GPUs in the computing system. Following the same principle, this system also works in a computing system with a minimum of two processing units or even more than three processing units. 
         [0031]    While the forgoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. Therefore, the above examples, embodiments, and drawings should not be deemed to be the only embodiments, and are presented to illustrate the flexibility and advantages of the present invention as defined by the following claims.