Patent Abstract:
An improved method and apparatus for setting a trip-point temperature value for detection of an over-temperature condition in a chip when a reading from a main temperature sensor exceeds the trip-point temperature value. In one embodiment, the trip-point temperature value is set to a known temperature limit value offset by a temperature difference, ΔT. ΔT is calculated by taking the difference between a reading of the main temperature sensor and a reading of another temperature sensor, remote from the main temperature sensor, while a heat-generating circuit is enabled. The main temperature sensor is distal from heat-generating circuit on the chip and the remote temperature sensor is proximate the heat-generating circuit. For multiple heat-generating circuits on the chip, a ΔT is determined for each of the heat-generating circuits, and the largest ΔT is used to calculate the trip-point temperature value. Advantageously, the largest ΔT determination may be done only once.

Full Description:
TECHNICAL FIELD 
   The present invention relates to integrated circuits, and, in particular, to integrated circuit over-temperature detection techniques or the like. 
   BACKGROUND 
   The operational lifetime of an integrated circuit (a “chip”) is directly related to the operating temperature of the chip. Should any portion of the chip reach an over-temperature condition (where the portion of the chip exceeds a known temperature limit which may be as high as a temperature above which the chip will be irreversibly damaged), that portion the chip might fail for a variety of reasons, such as electromigration-induced failure of metal conductors on the chip. To protect the chip from overheating, a thermal protection circuit may be provided that disables or shuts down various circuits on the chip to reduce power consumption thereof. The thermal protection circuit is triggered when the temperature of the chip exceeds a trip-point temperature. Generally, the trip-point temperature is less than the known temperature limit which is less than the irreversible damage temperature. 
   A typical thermal protection circuit comprises an on-chip temperature sensor. But because the on-chip temperature sensor is typically much smaller than the chip as a whole, the temperature sensor might be located in an area of the chip that is colder than other areas of the chip. This could lead to premature chip failure notwithstanding the use of a thermal protection circuit. For example, even though a thermal protection circuit that has a trip-point temperature equal to the known temperature limit but does not detect an over-temperature condition, because the temperature sensor could be in a “cold” part of the chip, there might be portions of the chip significantly hotter than the known temperature limit and the life of the chip is thereby shortened. 
   Because of the uncertainty of where and what the highest temperature is on the chip at any given time, the trip-point temperature value is set significantly lower than the known temperature limit. To guarantee that no portion of the chip, regardless of where and how it is used, exceeds the known temperature limit, the trip-point temperature is typically set so low that the chip will shut down well before any part of the chip reaches the known temperature limit, effectively reducing the operating temperature range of the chip. 
   SUMMARY 
   In one embodiment, the present invention is a method of setting a trip-point temperature value for an over-temperature detector responsive to a main temperature sensor located in an integrated circuit, the method comprising the steps of: enabling at least one heat generating circuit on an integrated circuit; reading at least one remote temperature sensor in the integrated circuit that is proximate the at least one heat generating circuit; reading the main temperature sensor; calculating a temperature difference, ΔT, between the main temperature sensor reading and the remote temperature reading; and setting the trip-point temperature value to a known temperature limit value offset by the ΔT. The main temperature sensor is distal from the heat generating circuit. 
   In still another embodiment, the present invention is an integrated circuit comprising at least one heat generating circuit; at least one remote temperature sensor proximate the at least one heat generating circuit; a main temperature sensor distal from the heat generating circuit; a processor adapted to 1) read the remote temperature sensor and the main temperature sensor while the at least one heat generating circuit is enabled, 2) calculate a temperature difference, ΔT, between the main temperature sensor reading and the remote temperature sensor reading, and 3) calculate a trip-point temperature value, for use by an over-temperature detector responsive to the main temperature detector, substantially equal to a known temperature limit value offset by the ΔT. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The aspects, features, and advantages of the present invention will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings in which like reference numerals identify similar or identical elements. 
       FIG. 1  is a simplified block diagram of an exemplary preamplifier chip used in hard drive disk systems; and 
       FIG. 2  is a simplified, high-level flow chart illustrating a process for determining temperature differences across the chip of  FIG. 1  for different chip configurations, and for setting a trip-point temperature value while taking into account the temperature differences. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , an exemplary embodiment of the invention is shown, in which a simplified block diagram of an exemplary preamplifier chip  10  for use in a hard drive disk system. The chip  10  has N heat generating driver circuits  12   1 - 12   N  (also referred to collectively as heat generating circuits or drivers  12 ) used to drive write signals to write heads (not shown) in a disk system. Typical diver circuits dissipate a lot of power compared to other circuits on the chip  10 . Disposed between adjacent diver pairs, e.g., drivers  12   1  and  12   2 ,  12   3  and  12   4 , etc., are temperature sensors  14   1 - 14   K  (also referred to collectively as sensors  14 ). The temperature sensors  14  are proximate the divers  12   1 - 12   N  and provide relatively accurate reading of the temperature of the drivers  12 . Also included on the chip  10  is other circuitry  18 , such as bias circuits and control circuits, which dissipate relatively small amounts of power. Imbedded in the circuitry  18  is a main temperature sensor  20  distal from the drivers  12   1 - 12   N . Readings from the temperature sensors  14  (also referred to herein as “remote” temperature sensors  14  since they are “remote” from the main sensor  20 ), and the main sensor  20  are taken by appropriately configuring an analog multiplexer  22  (shown here as a multi-position switch), under control of a processor or the like (not shown) to couple the sensors  14  and  20  to a processor  24  (in this example, a processor with an analog-to-digital converter). The processor  24  “reads” the sensors  14 ,  20  by converting the analog signal at the output, ATEMP, of the multiplexer  22  into a temperature value (e.g., in degrees Celsius). Alternatively, the chip  10  may have therein an analog-to-digital converter and the output signal from the chip  10  is in digital form. 
   As will be discussed in more detail below, the processor  24  may also process readings from the main temperature sensor  20  to generate an over-temperature alarm (OVER-TEMP) and/or shut down circuits on the chip  10  should the temperature of the chip  10 , as measured by the main sensor  20 , exceed a trip-point temperature. 
   Briefly, because the main temperature sensor  20  is further away from the heat generating drivers  12  than the remote sensors  14 , the temperature readings from the main sensor  20  might be significantly different from the temperature readings from the remote sensors  14 . Ignoring any differences in electrical characteristics between the sensors  14 ,  20  due to design or manufacturing variations (as will be explained in more detail below), because of the finite thermal conductivity of the semiconductor material used to make the chip  10  (e.g., silicon) and the substrate to which chip  10  is attached (e.g., an epoxy bond of chip  10  to a metal heatsink), heat generated by an active one or more of the drivers  12  will remain localized to the active driver and the surrounding area and not completely reach sensor  20 . Thus, a temperature reading from the sensor  20  might be lower than the actual temperature of an active driver  12 . For example, a reading from the remote sensor  14   2  most proximate the driver  12   3  will be a better indication of the temperature of the driver  12   3  than a temperature reading from the main sensor  20 . However, for a variety of reasons, it may not be convenient to take readings from each of the remote sensors  14  during operation of the chip  10  but instead take chip temperature measurements from the main sensor  20  alone to determine the highest temperature within the chip  10 . It is therefore desirable that, when analyzing the readings from the main sensor  20 , the differences in temperature across the chip  10  are taken into consideration. To do so, a temperature-offset is calculated using measured temperature differences across the chip. Calculation of the temperature differences and the resulting temperature offset (done within processor  24  in this example) is illustrated in  FIG. 2 . 
   Exemplary process steps  200 - 234  illustrated in  FIG. 2  disclose a simplified process for determining temperature differences across the chip  10  of  FIG. 1  for different operating configurations of the drivers  12 , and for setting a trip-point temperature value (used to generate an alarm and/or shut down the chip  10 ) while taking into account the temperature differences. For purposes of this exemplary process and as explained above, there is one remote sensor  14   k  for every two drivers  12   n  (1≦k≦K, 1≦n≦N; K=N/2). However, the ratio between the sensors  14  to drivers  12  (or other heat-generating circuitry) may be different from the illustrative 1:2. 
   In step  202 , the chip  10  ( FIG. 1 ) is placed on a chuck or other controlled temperature environment and the main temperature sensor  20  ( FIG. 1 ) is calibrated with all of the drivers  12  off. Because the temperature sensors  14  and  20  have, in this example, substantially identical electrical characteristics, there is no need to calibrate the remote sensors  14 . However, if the main sensor  20  and the remote sensors  14  are of a different design, then at least one of the remote sensors  14  may need to be calibrated along with sensor  20 . It is understood that the calibration step  202  may be done just once, either during a test after manufacture thereof or when the chip is packaged/mounted. The steps  204 - 234  may be repeated as needed, depending on the final application of the chip  10 , e.g., during manufacture of the equipment in which the chip  10  is installed. 
   Step  204  initializes variables used in a loop comprising steps  206 - 228 . In steps  206 - 228 , all of the drivers  12  are individually and sequentially turned on (enabled) and the temperature as measured by the sensor  14   k , closest to the enabled driver  12   n , and the main sensor  20  are read. The difference in temperature, ΔT n , is calculated as the difference between the two temperature readings. For example, one heat generating circuit, e.g., driver  12   3  (n=3), is turned on and the temperatures from sensor  14   2  (k=2) and sensor  20  are read, the difference being ΔT 3 . Then driver  12   3  is turned off, driver  12   4  turned on, and the temperatures read from sensor  14   2  and sensor  20 , the temperature difference being ΔT 4 . 
   After all the ΔT n  values are calculated, the largest of the ΔT n  (1≦n≦N) values is selected as the temperature-offset value, ΔT MAX , in step  230 . Then in step  232  the trip-point temperature value is set to the known temperature limit value of the chip, T MAX , offset by the ΔT MAX . The trip-point temperature value may then used by the processor  24  and/or a thermal protection circuit (not shown), responsive to the ATEMP signal, to shutdown the heat generating circuits (drivers)  12  in the chip  10  and/or generate an alarm signal (OVER-TEMP) when the temperature read from the main temperature sensor  20  exceeds the trip-point temperature value. In this embodiment, the same result can be obtained by offsetting the readings from the sensor  20  with the temperature-offset value, ΔT MAX , and leaving the known temperature limit value unchanged. Because the trip-point temperature value is set in response to the measured temperature differences across the chip, the resulting trip-point temperature value will likely be higher (and more accurate) than a trip-point temperature value resulting from prior techniques. This allows a greater chip operating temperature range than with prior art techniques without shortening the operational lifetime of the chip. 
   The temperature sensors  14 ,  20  preferably have substantially identical electrical characteristics (made possible by all the sensors  14 ,  20  being of substantially identical design and the inherent uniformity of circuit components across the chip  10 ) such that, if the chip  10  has a uniform temperature, then the readings from the sensors  14 ,  20  will be substantially the same. The sensors  14 ,  20  may be of a conventional design, such as a forward-biased diode, a resistor with a known temperature characteristic (e.g., an implanted resistor), or a current source that produces a current proportional to absolute temperature (e.g., a PTAT current source) coupled to a precision resistor to produce an output voltage that is proportional to absolute temperature. Advantageously, the PTAT current source/precision resistor approach allows for accurate temperature readings as well as the ability to share the precision resistor (not shown) among the temperature sensors  14 ,  20  via multiplexer  22 . 
   It is understood that while the embodiment shown herein is a hard-disk head preamplifier chip, the invention may be used in other applications where the temperature of certain areas on a chip can be significantly different from other areas and an accurate estimation of the highest temperature on the chip is needed based on a small number of temperature measurements, e.g., in microprocessors, ASICs, etc. 
   Advantageously, all of the circuitry of the preamplifier chip  10  may be implemented in one mixed-signal integrated circuit. Further, the thermal protection circuit (not shown) and/or other various processors, including processor  24 , may be implemented on the chip  10 . 
   Although the present invention has been described in the context of a hard-disk head preamplifier chip, those skilled in the art will understand that the present invention can be implemented in the context of other types of storage systems and other kinds of chips. 
   For purposes of this description and unless explicitly stated otherwise, each numerical value and range should be interpreted as being approximate as if the word “about” or “approximately” preceded the value of the value or range. Further, signals and corresponding nodes, ports, inputs, or outputs may be referred to by the same name and are interchangeable. Additionally, reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the terms “implementation” and “example.” 
   Also for purposes of this description, the terms “couple,” “coupling,” “coupled,” “connect,” “connecting,” or “connected,” refer to any manner known in the art or later developed in which a signal is allowed to be transferred between two or more elements and the interposition of one or more additional elements is contemplated, although not required. Conversely, the terms “directly coupled,” “directly connected,” etc., imply the absence of such additional elements. 
   It is understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of this invention may be made by those skilled in the art without departing from the scope of the invention as expressed in the following claims. 
   The use of figure numbers and/or figure reference labels in the claims is intended to identify one or more possible embodiments of the claimed subject matter in order to facilitate the interpretation of the claims. Such use is not to be construed as necessarily limiting the scope of those claims to the embodiments shown in the corresponding figures. 
   Although the elements in the following method claims, if any, are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.

Technology Classification (CPC): 6