Abstract:
A system and method for measuring die temperature of chips within an ATU-C modem and reporting the results to a central management entity such that, in the event of a thermal overload condition, an adaptive algorithm can change modem operation so a data connection can be maintained. The system and method may include integrating temperature detection sensors on each semiconductor device in an ATU-C modem chipset and the power supply module. The temperature sensors then report the die temperatures of each component in the chipset to the central management entity that can interact with the individual modem datapumps to manage power dissipation within the modem system.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates generally to DSL modems and more particularly to a method for adaptive thermal management of DSL modems.  
           [0003]    2. Description of the Prior Art  
           [0004]    There is currently no way to know the die operating temperature of chips within an ATU-C DSL modem chipset. In the event of a thermal overload condition, ATU-C modems fail in an unpredictable manner causing end users to lose their data connection.  
           [0005]    In the competitive central office ADSL environment, equipment providers desire to support the largest possible number of ATU-C ADSL modems in each linecard in order to enable service providers to support the largest number of end users with the minimum dedicated equipment space in the central office. It follows that semiconductor vendors are constantly increasing the number of modems supported by ATU-C modem chipsets and searching for more aggressive chipset packaging techniques to reduce the PCB space required for each ATU-C modem. A consequence of this aggressive integration is that, although the power consumed by each ADSL ATU-C modem is decreasing from generation to generation, the reduction in footprint per modem is tending to increase the power density at the PCB level. The increased power density poses many thermal challenges for the modem design engineer. In general, ATU-C modems have to be designed to meet various NEBS specifications for system level thermal performance. NEBS specifications define ambient air temperature conditions for various classes of equipment.  
           [0006]    There are two problems associated with the thermal design process. First, a given PCB design can be stressed in a test laboratory to the limits of the appropriate NEBS specification; but it is difficult to determine the exact chipset die temperatures at the NEBS specification limit; and so it is difficult to know what “safety margin” has been built into a given design or which component is thermally critical. Second, when a modem is deployed in the field, if the operating conditions stray outside the chosen NEBS limit (i.e. an equipment fan fails, causing excessive localized temperature elevation), then modems will fail unpredictably, causing loss of service for attached customers. A consequence of the trend toward increasing ATU-C modem density is than when such a thermal violation exists, a large number of customers can be adversely impacted.  
           [0007]    PCBs are conventionally designed to meet the NEBS specifications using thermal simulation tools. After the PCB is fabricated, temperature sensors are connected to the case of each semiconductor in a test lab to measure the operating case temperature of each device. The disadvantage of this approach is that the semiconductor die temperature has to be approximated from knowledge of the case temperature, a process prone to error. Further, the application of a large external temperature sensor to a small semiconductor package can distort the measured temperature because the thermal probe tends to conduct heat from the semiconductor package. In order to measure safety margin, the thermal stress is increased until “something goes wrong” and the margin is measured by comparing the failing temperature with the desired maximum operating temperature. This process does not provide good visibility into the thermal performance of the PCB, nor does it easily identify the thermally critical components in the design.  
           [0008]    Conventional ATU-C modems make no provision for adaptive thermal management. The general assumption is made that the modems meet Bellcore® NEBS specifications. For systems with forced air cooling, a mechanism is usually provided for varying air flow rate via fan control as a function of gross air temperature, but no attempt is made to monitor individual die temperature. If a cooling system failure (such as a mechanical problem with a fan or HVAC system) exists, then eventually, if the problem is not addressed, the modems will overheat and fail in an unpredictable way, causing data loss for the end user. If a large number of users experience data loss, the penalties for a service provider can be serious, both from a financial and regulatory perspective (the FCC has to be informed).  
           [0009]    U.S. Pat. No. 5,978,864, entitled Thermal Overload Detection and Prevention in an Integrated Circuit Processor, discloses a method to control die temperature. The method disclosed and claimed in the &#39;864 patent, however, is specifically directed to a simple reduction in processor clock frequency with excessive die temperature, and does not disclose or suggest use of a more general adaptive thermal management approach to realize an analog DSL modem application.  
           [0010]    In view of the foregoing, a need exists for a method for measuring die temperature of chips within an ATU-C modem and reporting the results to a management entity such that, in the event of a thermal overload condition, an adaptive algorithm can change modem operation so that a data connection can be maintained.  
         SUMMARY OF THE INVENTION  
         [0011]    The present invention is directed to a system and method for measuring die temperature of chips within an ATU-C modem and reporting the results to a central management entity such that, in the event of a thermal overload condition, an adaptive algorithm can change modem operation so a data connection can be maintained. The method includes integrating temperature detection sensors on each semiconductor device in an ATU-C modem chipset and the power supply module. The temperature sensors then report the die temperatures of each component in the chipset to the central management entity that can interact with the individual modem datapumps to manage power dissipation within the modem system.  
           [0012]    According to one aspect, die temperature sensors are provided to allow precise measurement of semiconductor die temperature, eliminating the approximations associated with a measurement of case temperature.  
           [0013]    According to another aspect, die temperature sensors are provided to allow precise measurement of semiconductor die temperature, eliminating the thermal distortion associated with an external sensor with large thermal mass.  
           [0014]    According to yet another aspect, die temperature sensors are provided to allow precise measurement of semiconductor die temperature, allowing precise measurement of the safety margin between the actual and maximum die operating temperatures. This in turn allows the thermally critical components on a given PCB to be identified.  
           [0015]    According to still another aspect, chip level sensing of the die temperature for each modem component is provided, allowing the modem to adaptively change service levels to manage die temperature. This means that in the event of a system thermal problem, e.g. HVAC system failure, the management system can be informed and take one on many desired actions so that data communication can be maintained without a failure.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    Other aspects and features of the present invention and many of the attendant advantages of the present invention will be readily appreciated as the same become better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:  
         [0017]    [0017]FIG. 1 illustrates implementation of an adaptive thermal management scheme in association with an AC5 modem chipset available from Texas Instruments Incorporated of Dallas, Tex. according to one embodiment of the present invention.  
         [0018]    While the above-identified drawing figures set forth alternative embodiments, other embodiments of the present invention are also contemplated, as noted in the discussion. In all cases, this disclosure presents illustrated embodiments of the present invention by way of representation and not limitation. Numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    The exact die temperature of each chip within a modem chipset is now available in a test laboratory environment so that the thermal “safety margin” of a given PCB implementation can easily be determined by operating the PCB in a thermal test chamber set to the appropriate stress conditions and recording the temperature of each die. The difference between the die temperature and the maximum operating temperature of the die (defined by the semiconductor manufacturer) provides the safety margin for each component in the PCB design; so it is easy to identify the thermally critical components. Once thermally critical components have been identified, necessary changes to PCB design, airflow, heatsinking, and the like, can be made to ensure reliable operation of the system in the field.  
         [0020]    When a modem is deployed in the field, in the event of a failure in a fan system, CO HVAC, or some other environmental problem, die temperature detectors can flag an impending chip level thermal overload problem to an attached management entity. Instead of having the modems fail en masse or be undesirably turned off, the management entity can adaptively manage the modem configuration (e.g. by reducing modem data throughput) to control local power dissipation; so that the die temperatures remain within acceptable limits. The value of adaptive thermal management to a telecom service provider is that a data connection can be maintained (at reduced throughput) without having to shut equipment down immediately and cut end users off. A further advantage of this approach is that the temperature data can be exposed to customer management equipment allowing continuous monitoring of thermal status.  
         [0021]    [0021]FIG. 1 is a block diagram illustrating a system architecture  10  that implements an adaptive thermal management scheme in association with an AC5™ modem chipset available from Texas Instruments Incorporated (TI) of Dallas, Tex. according to one embodiment of the present invention. The system architecture  10  can implement an adaptive thermal management scheme simply by adding an on-chip diode/thermal detector (TD) within each device in the chipset, with PCB traces to a slow, inexpensive, external multi-input analog-to-digital converter (ADC), read via GPIO from the modem datapump  12  or equivalent. Alternatively, the on-chip thermal detector (TD) could be mated with an on-chip ADC to provide a digital output that is fed to the modem datapump  12 .  
         [0022]    With continued reference to FIG. 1, the AC5 chipset can be seen to include a TNETD5800™ datapump  12  that acts as an ADSL datapump for eight independent ATU-C modems, converting a Utopia ATM cell stream into samples that are fed to a TNETD5080™ octal (eight channel) codec  14 . The codec  14  supports eight analog interfaces to eight TNETD7102™ line driver receiver chips  16 . In conjunction with a hybrid circuit  18 , each TNETD7102™ line driver receiver chip  16  forms the copper loop interface for a single ATU-C modem. Two “Line Ranger” components  20  allow individual control of the supply voltage applied to the line driver receiver chips  16 . This control allows for optimization of the ATU-C modem power consumption to match the needs of the attached copper loop.  
         [0023]    Looking again at FIG. 1, an adaptive thermal management system according to one embodiment can include a temperature sensitive structure (TD)  24 , for example a diode, on each die in the chipset as stated herein before. In the case of the TNETD7102™ line driver receiver chips  16 , the TD would be connected via an additional signal pin to an ADC. System architecture  10  shows the ADC as being located in the Line Ranger  20 . This arrangement leverages the natural proximity of the Line Ranger  20  the line driver receiver chips  16 , as well as the existing serial connection  22  between the Line Ranger  20  and the TNETD5800™ datapump  12 . This configuration allows the datapump  12  to control the supply voltage for each line driver receiver chip  16  and also read the die temperature of each line driver receiver chip  16 . The TNETD5080™ octal (eight channel) codec  14  also can seen to contain a temperature sensing element (TD)  24  as well as an ADC  26  that allows the TNETD5800™ datapump  12  to read the codec  14  die temperature along with other codec  14  control parameters via the existing serial control interface  22 . The TNETD5800™ datapump  12  also contains a temperature sensing element  24  as well as a small ADC  28  that allows the die temperature to be measured. An additional temperature sensing element  24  in the main power supply  30  brick heatsink is also interfaced to one of the ADC channels in the Line Ranger  20 . This allows the temperature of the power supply  30  brick heatsink to be monitored. The present invention is not so limited however, and it shall be understood that a wide variety of other implementations are possible. One example includes deployment of a custom ADC that monitors all the die temperature sensors directly.  
         [0024]    During operation, at power-up in a cold environment, the thermal detectors  24  can be used to hold each device in a non-operational “warm-up” mode until each die has reached a desired operating temperature, as stated herein before. The system  10  then boots normally and the ARM core in the TNETD5800™ datapump  12  periodically (e.g. once every second) reads the die temperatures. Temperature measurements are made available to an external management entity  40  via the TNETD5800™ datapump  12  OAM register interface  32 . The measured die temperatures are compared to a table of alarm threshold die temperatures. The default alarm thresholds reflect the characteristics of the semiconductor process used to manufacture each chip. The default alarm thresholds are chosen such that operating each device below the alarm threshold will allow for normal modem operation. When a given die temperature exceeds the alarm threshold, an alarm condition is recorded. This can optionally notify the external management entity, which then has responsibility to take action, or alternatively, the modem datapump  12  can take action. The action taken will reflect the source of the alarm. Example actions are shown in Table I below.  
                   TABLE I                       Alarm Source   Action(s)                   TNETD7102 Line driver/receiver   Reduce modem throughput via re-           negotiation.           Gradually reduce ATU-C modem           transmit power.           Increase system airflow by changing           fan speed.           Disable modem channel.           Reduce line driver supply voltage via           Line Ranger.       TNETD5080 Codec   Increase system airflow by changing           fan speed.       TNETD5800 ™ datapump 12   Disable non core user applications           running on the ARM or DSP           subsystems.           Increase system airflow by changing           fan speed.           Disable 1-8 modem channels.           Alter core clock speed.       Power Supply heatsink   Any action listed above.           Shut down/reduce power to user           specific circuitry on the           line card, e.g data interface           of management processor.                  
 
         [0025]    In view of the above, it can be seen the present invention presents a significant advancement in the art of thermal management associated with DSL modems. A system architecture has been described to include placement of thermal structures on each die in a CO modem chipset to allow temperature measurement of each die and reporting to a modem OAM system. Programmable thermal thresholds are supported to allow the modem OAM system to use ADSL features such as power swap, dynamic rate adaptation, forced retrain to lower speed, Line Ranger re-biasing of drivers, balancing of user applications on CPU, and the like, to adaptively manage die temperatures, and thus avoid hard thermal failures. Independent thresholds allow thermal alarms to be issued to the host before or after a modem take adaptive action.  
         [0026]    This invention has been described in considerable detail in order to provide those skilled in the DSL modem art with the information needed to apply the novel principles and to construct and use such specialized components as are required. In view of the foregoing descriptions, it should be apparent that the present invention represents a significant departure from the prior art in construction and operation. However, while particular embodiments of the present invention have been described herein in detail, it is to be understood that various alterations, modifications and substitutions can be made therein without departing in any way from the spirit and scope of the present invention, as defined in the claims which follow.