Abstract:
In an embodiment, a method includes monitoring a temperature of a semiconductor chip and adjusting a supply voltage to the semiconductor chip based on the monitored temperature. The temperature may be monitored by a temperature sensor located on-chip or off-chip. Adjusting the supply voltage includes increasing the supply voltage as a function of the monitored temperature decreasing. The increase to the supply voltage occurs only if the monitored temperature is below a threshold temperature. The supply voltage adjustment is determined by a linear relationship having a negative slope with temperature.

Description:
BACKGROUND 
     In semiconductor chip-design processing, it has generally been the case that the worst-case delay for a device is at the high-temperature corner. With recent advanced process technologies (40 nm and below) a temperature-inversion phenomenon has been observed. This phenomenon is where device performance worsens at cold temperature. 
     Transistor performance is highly correlated to supply voltage, i.e., higher voltage means higher performance. Chip power dissipation is composed of two components, dynamic and leakage. Dynamic power increases with the square of the supply voltage and is temperature insensitive. Leakage power also increases with supply voltage and is exponential with temperature. 
     SUMMARY 
     With the approach of the present disclosure, the problem with temperature inversion is addressed based on increasing a supply voltage to the chip in a region of low temperature. Accordingly, the example embodiments can increase transistor performance at low temperatures. 
     In an embodiment, a method includes monitoring a temperature of a semiconductor chip and adjusting a supply voltage to the semiconductor chip based on the monitored temperature. The temperature may be monitored by a temperature sensor located on-chip or off-chip. Adjusting the supply voltage includes increasing the supply voltage as a function of the monitored temperature decreasing. The increase to the supply voltage may occur only if the monitored temperature is below a threshold temperature. The supply voltage adjustment is determined by a linear relationship having a negative slope with temperature. 
     In another embodiment, an apparatus includes a temperature sensor for monitoring a temperature of a semiconductor chip and a controller configured to adjust a supply voltage to the semiconductor chip based on the monitored temperature. In some embodiments, the temperature sensor and the controller are located on the semiconductor chip. In other embodiments, the temperature sensor and the controller are located off the semiconductor chip. 
     The controller may be configured to send a control signal to a voltage regulator module (VRM) to cause the VRM to adjust the supply voltage. The controller may adjust the supply voltage by increasing the supply voltage as a function of the monitored temperature decreasing. The controller may increase the supply voltage only if the monitored temperature is below a threshold temperature. 
     In some embodiments the apparatus may include an on-chip thermal diode coupled to the temperature sensor that monitors a junction temperature on the chip. 
     The controller may be configured to adjust the supply voltage as determined by a linear relationship having a negative slope. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention. 
         FIG. 1  is a block diagram of a first example embodiment of supply voltage adjustment circuitry. 
         FIG. 2  is a line chart illustrating a relationship between supply voltage and temperature for an example supply voltage adjustment circuitry. 
         FIG. 3  is a block diagram of a second example embodiment of supply voltage adjustment circuitry. 
         FIG. 4  is a block diagram of a third example embodiment of supply voltage adjustment circuitry. 
     
    
    
     DETAILED DESCRIPTION 
     A description of example embodiments of the invention follows. 
     Embodiments of the present invention relate to an on chip temperature sensor which feeds a control block. The control block, based on an algebraic equation, can instruct an external voltage regulator module (VRM) to increase or decrease the chip supply voltage. Higher supply voltage is provided by the VRM when the chip is at relatively low temperatures so as to compensate for the effect of lower temperature on transistor performance, with the result that the chip performance can be maintained more constant across temperatures. The fact that this is dynamic is important. The chip voltage cannot be increased all the time because when the chip is hot it will be drawing the most power and increasing supply voltage will result in exceeding the chip&#39;s power specification. Increasing the supply voltage when the chip is cold is possible because the reduced power from leakage can be traded off for the increased power from the higher supply voltage. Thus, the total power envelope of the chip will not be increased because of the vastly reduced leakage at low temperatures. It may also be permissible to exceed the stated power envelope when cold because the primary concern for power dissipation is keeping the chip cool. This is not a problem when the chip is cold. 
     It should be noted that increasing the supply voltage does not necessarily increase the system clock frequency. Without the present approach, the chips need to be tested at the lowest temperature in order to characterize the clock. With the present approach, it is likely that the worst case temperature is at the threshold temperature. 
       FIG. 1  is a block diagram of a first example embodiment of supply voltage adjustment circuitry. The adjustment circuitry includes a thermal diode  104 , a temperature sensor  106 , a controller  108 , and a voltage regulator module (VRM)  110 . The thermal diode  104 , temperature sensor  106 , and controller  108  are embedded on a semiconductor chip  102 . The VRM  110  is external to the chip  102 . 
     The thermal diode  104  provides an indication of the junction temperature on the chip and is coupled at inputs  112 A,  112 B of the temperature sensor  106 . The temperature sensor  106  is configured to monitor the junction temperature provided by the thermal diode  104 . An output of the temperature sensor  106  is a signed 8 bit signal  114 . This 8 bit signal  114  allows for reading temperatures between −128 degrees C. to +127 degrees C. with a 1 degree increment. The temperature sensor output  114  changes every time a temperature acquisition occurs, e.g., on the order of every millisecond. 
     The temperature sensor output  114  is provided as input to controller  108 . The controller  108  is configured to control a supply voltage (Vdd)  118  output from the VRM  110 . In particular, the controller  108  instructs the VRM  110  to dynamically increase or decrease the supply voltage Vdd based on the monitored temperature signal  114  provided to the controller  108 . The controller  108  instructs the VRM  110  over connection  116  to increase the supply voltage Vdd with decreasing temperature when the monitored temperature is below a threshold temperature. An example relationship is as follows:
 
Vdd=Nominal_Vdd+MINIMUM(0,Temperature−Threshold)*Slope  (Eq. 1)
 
Nominal_Vdd, Threshold and Slope may be programmable values, controlled by writing a control/status register (CSR) or by blowing one or more one-time programmable (OTP) fuses. Values for a 28 nm process may be, for example:
 
     Nominal_Vdd=900 m V 
     Threshold=50 C 
     Slope=−1 m V/C 
     It should be understood to one skilled in the art that, while (Eq. 1) includes a linear function, non-linear functions can be used to effect an increase in supply voltage with decreasing temperature. 
     In an embodiment, the connection  116  between the controller  108  and the VRM  110  uses Power Management Bus (PMBus), an open standard power-management protocol. In other embodiments, the connection can be provided using the Serial VID interface (SVID) specification or other suitable protocol. The VRM  110  can be, for example, an Intersil part number ISL6367 or other similar device. 
       FIG. 2  is a line chart illustrating a relationship between supply voltage and temperature for an example supply voltage adjustment circuitry that is controlled based on (Eq. 1) and given the example values noted above. As shown, the supply voltage Vdd increases 50 mV when at 0 C and 90 mV when at −40 C. A flat or constant region for keeping the supply voltage at the nominal value 900 mV occurs for temperatures above the threshold value of 50 C. Below the threshold, the curve is linear with a negative slope. 
       FIG. 3  is a block diagram of a second example embodiment of supply voltage adjustment circuitry. The adjustment circuitry includes a thermal diode  304 , a temperature sensor  306 , a controller  308 , and a voltage regulator module (VRM)  310 . The thermal diode  104  is embedded on a semiconductor chip  302 . The temperature sensor  306 , controller  308 , and VRM  310  are external to chip  302 . The thermal diode  304  provides an indication of the junction temperature on the chip and is coupled at inputs  312 A,  312 B of the temperature sensor  306 . The temperature sensor  306  is configured to monitor the junction temperature provided by the thermal diode  304 . External temperature sensors are available from a number of sources, including Texas Instruments, Maxim, Analog Devices, and National Semiconductor. For example, a Texas Instruments TMP421 temperature sensor is suitable. The VRM  310  can be an Intersil part number ISL6367 or other similar device. 
     An output of the temperature sensor  306  is a signed 8 bit signal  314 . This 8 bit signal  314  allows for reading temperatures between −128 degrees C. to +127 degrees C. with a 1 degree increment. The temperature sensor output  314  changes every time a temperature acquisition occurs, e.g., on the order of every millisecond. 
     The temperature sensor output  314  is provided as input to controller  308 . The controller  308  is configured to control a supply voltage (Vdd)  318  output from the VRM  310 . In particular, the controller  308  instructs the VRM  310  on connection  316  to dynamically increase or decrease the supply voltage Vdd based on the monitored temperature signal  314  provided to the controller  308 . The controller  308  instructs the VRM  310  to increase the supply voltage Vdd with decreasing temperature when the monitored temperature is below a threshold temperature based on the relationship (Eq. 1). 
       FIG. 4  is a block diagram of a third example embodiment of supply voltage adjustment circuitry. The adjustment circuitry includes a thermal diode  404 , a temperature sensor  406 , a controller  408 , and a voltage regulator module (VRM)  410 . The thermal diode  404  and controller  408  are embedded on a semiconductor chip  402 . The temperature sensor  406  and VRM  410  are external to chip  402 . The thermal diode  404  provides an indication of the junction temperature on the chip and is coupled at inputs  412 A,  412 B of the temperature sensor  406 . The temperature sensor  406  is configured to monitor the junction temperature provided by the thermal diode  404 . Similar to the embodiment described above for  FIG. 3 , the Texas Instruments TMP421 temperature sensor and Intersil part number ISL6367 are suitable devices for the temperature sensor  406  and VRM  410 , respectively. 
     An output of the temperature sensor  406  is a signed 8 bit signal  414  which allows for reading temperatures between −128 degrees C. to +127 degrees C. with a 1 degree increment. The temperature sensor output  414  changes every time a temperature acquisition occurs, e.g., on the order of every millisecond. 
     The temperature sensor output  414  is provided as input to controller  408  over a two-wire serial interface (TWSI) on the chip  402 . The controller  408  is configured to control a supply voltage (Vdd)  418  output from the VRM  340  by instructing the VRM  410  on connection  416  (e.g., PMBus or SVID) to dynamically increase or decrease the supply voltage Vdd based on the monitored temperature signal  414  provided to the controller  408 . The controller  408  instructs the VRM  410  to increase the supply voltage Vdd with decreasing temperature when the monitored temperature is below a threshold temperature based on the relationship (Eq. 1). 
     While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.