Abstract:
Temperature stabilization of an integrated circuit to reduce effects of data and activity variation. Heat dissipating load structures are integrated onto the die and controlled in response to sensed device characteristics. In a first embodiment, heat dissipating load structures on the device are used to maintain constant device power dissipation. In a second embodiment, the heat dissipating load structures are used in conjunction with on-device temperature sensors to maintain constant device temperature.

Description:
TECHNICAL FIELD 
       [0001]    Embodiments in accordance with the invention are related to temperature stabilization of integrated circuit devices. 
       BACKGROUND 
       [0002]    Complex integrated circuits, particularly mixed signal and high frequency integrated circuits such as analog to digital converters, digital to analog converters, and radio frequency circuits consume electrical power, which results in device heating. This heating in some circuit topologies is dependent on activity and/or data. As an example, data patterns in a high speed converter may affect device operating temperatures. While the integrated circuit substrate and packaging act to even out and dissipate these data and activity dependent effects, temperature variations so caused can affect device calibration premised on operation at a constant or specified temperature. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]      FIG. 1  shows a block diagram of an integrated circuit, 
           [0004]      FIG. 2  shows a second diagram of an integrated circuit, 
           [0005]      FIG. 3  shows a third diagram of an integrated circuit, and 
           [0006]      FIG. 4  shows a fourth diagram of an integrated circuit. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0007]      FIG. 1  is a simplified diagram of an integrated circuit showing power connections. Die  100  has multiple bonding pads  110 ,  112 ,  114  for supplying power from source  120  through lead wires. Multiple ground bonding pads  130 ,  132 ,  134  connect via lead wires to ground  140  completing the electrical circuit. Die  100  is commonly mounted to a substrate or other packaging, not shown, which helps dissipate heat generated by the operation of the circuitry contained in die  100 . Target circuitry, such as analog to digital or digital to analog conversion and associated bonding pads, are not shown. 
         [0008]    While the present invention is shown with one power supply, it is equally applicable to integrated circuits using multiple power supplies. 
         [0009]    In operation of an integrated circuit, particularly in high-speed integrated circuits, electrical power is turned into heat. In many cases, this heating may be signal or data dependent. Such temperature variations affect calibration premised on device operation at a constant or specific temperature. 
         [0010]    In a first embodiment of the invention as shown in  FIG. 2 , die  100  is operated in a mode where the power supply current to the die is held constant. Die  100  contains heat generating load element  160  which connects through bonding pad  110  to power supply  220 . Power regulator  220  provides a fixed and regulated voltage to die  100  through bonding pads  110 ,  112 ,  114 , with supply return through pads  130 ,  132 ,  134 . 
         [0011]    Die  100  is operated in a constant-current mode using controller  200  and sense resistor  210 . Applying Ohm&#39;s law, current flowing through resistor  210  results in a voltage drop across resistor  210 . This voltage is sensed by controller  200 , which controls  170  the current flowing through load element  160  in such a manner that the voltage drop across sense resistor  210  is held constant. Since regulator  220  provides a fixed voltage to die  100 , the product of this fixed voltage and a constant current as maintained by controller  200  holds die  100  at a constant power dissipation level, stabilizing die temperature. 
         [0012]    Other methods may also be used to sense the operating current of die  100 . A Hall effect sensor may be used to sense current flowing through a supply line or trace. It may be possible to sense current through the operation of regulator  220 ; as an example, some switching regulator topologies will vary switching frequency as a function of load current. While  FIG. 2  shows a single load element  160  on die  100 , multiple heat generating load elements  160  may be used to provide a more uniform thermal environment. 
         [0013]    Additionally, while transistor  230  controlling  170  current through load  160  is shown as part of controller  200 , it may be located on die  100 . It may be advantageous to use transistors as heat generating load elements on die  100 , or transistor-resistor combinations. 
         [0014]    Controller  200  may be an analog control loop, or a digital or mixed analog and digital loop. This functionality may also be substantially embedded on die  100 ; while active elements such as op amps, logic gates, and such may be easily integrated onto die  100 , the circuit topology chosen may require timing components such as resistors and/or capacitors which may be desirable to place off-die and connect through bonding pads. The bandwidth of the control loop must consider thermal time constants of the die and its packaging. 
         [0015]    A second embodiment of the present invention is shown in  FIG. 3 . Load element  160  and transistor  165  are part of die  100  and generate heat when conducting current from supply pad  110  to ground pad  130  under control  170  of controller  200 . Sense resistor  210  senses the current flowing through die  100 , developing a voltage drop proportional to the current. In operating die  100  in a constant-current mode, controller  200  operates to keep the voltage drop across sense resistor  210  at a constant value. 
         [0016]    In the embodiment of  FIG. 2 , the voltage drop introduced by sense resistor  210  is compensated for by placing sense resistor  210  before voltage regulator  220 . In the embodiment of  FIG. 3 , the voltage drop introduced by sense resistor  210  must be compensated for by recharacterizing the operation of the devices on die  100  at a slightly reduced operating voltage, or by raising the operating voltage supplied to die  100  through sense resistor  110  to compensate for the voltage drop. 
         [0017]    The embodiment of  FIG. 3  also allows sense resistor  210  to be integrated into die  100 . In such an embodiment, sense resistor  210  may also be used as a source of heat. 
         [0018]    Where the embodiments shown in  FIGS. 2 and 3  use heat generating load elements in a constant-current operating regime, the embodiment of  FIG. 4  senses die temperature and provides that information to controller  200 . The embodiment shown in  FIG. 4  uses on-die PN junctions  310   312   314  to provide  320   322  an indication of die temperature to controller  200 . The forward voltage drop of a PN junction varies with the junction temperature. While three PN junctions  310   312   314  are shown, a single junction may be used. Sense junctions  310   312   314  may be placed in different areas of die  100  and may be brought out to separate bonding pads, or wired in series as shown. By monitoring the temperature dependent characteristics of PN junctions  310   312   314 , controller  200  can adjust  170  the current flowing through load  160  and  165  to maintain die  100  at a predetermined temperature. Other temperature sensing may also be used, such as applying a constant voltage across one or more PN junctions and measuring the current, which will be an exponential function of temperature. Temperature-dependent resistors may also be used. Multiple heat generating load resistors  160  may be used to heat the die, or semiconductor devices such as transistor  165  may be used to generate heat. Single or multiple heat generating loads may be placed on die  100 . 
         [0019]    While the embodiments of the present invention have been illustrated in detail, it should be apparent that modifications and adaptations to these embodiments may occur to one skilled in the art without departing from the scope of the present invention as set forth in the following claims.