Abstract:
A method and system of temperature compensated integrated circuits. Operating characteristics of integrated circuitry are enhanced by application of temperature compensation.

Description:
FIELD OF THE INVENTION 
     Embodiments in accordance with the present invention relate to the design and operation of integrated circuits. 
     BACKGROUND 
     The characteristics of integrated circuits, e.g., operating frequency, gate delay and the like, vary widely with changes in operating temperature. 
     SUMMARY OF THE INVENTION 
     A method and system of temperature compensated integrated circuits are disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates a temperature compensated transfer resistor circuit, in accordance with embodiments of the present invention. 
         FIG. 1B  illustrates a temperature compensated transfer resistor circuit, in accordance with embodiments of the present invention. 
         FIG. 2  illustrates a temperature compensated inverter circuit, in accordance with embodiments of the present invention. 
         FIG. 3  illustrates a temperature compensated NAND circuit, in accordance with embodiments of the present invention. 
         FIG. 4  illustrates a temperature compensated NOR circuit, in accordance with embodiments of the present invention. 
         FIG. 5  illustrates a temperature compensated ring oscillator circuit, in accordance with embodiments of the present invention. 
         FIG. 6  illustrates a flow diagram of a method of operating an integrated circuit, in accordance with embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description of the present invention, temperature compensated integrated circuits, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by one skilled in the art that the present invention may be practiced without these specific details or with equivalents thereof. In other instances, well-known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention. 
     TEMPERATURE COMPENSATED INTEGRATED CIRCUITS 
     Embodiments of the present invention are described in the context of design and operation of integrated semiconductors. More particularly, embodiments of the present invention relate to temperature compensated integrated circuits. It is appreciated, however, that elements of the present invention may be utilized in other areas of semiconductor operation. 
     Although the following description of embodiments in accordance with the present invention describes semiconductors formed in p-type materials, it is to be appreciated that symmetries with n-type materials are well known. For example, in general, exchanging p-type materials and processes with n-type materials and processes, can create symmetric structures and behaviors. Consequently, embodiments in accordance with the present invention are well suited to semiconductors formed in n-type materials, and such embodiments are within the scope of the present invention. 
     Variations in the operation of integrated circuits corresponding to changes in temperature are well known. For example, the same integrated circuit generally operates faster, e.g., has a higher maximum operating frequency, at a lower temperature than it does at a higher temperature. 
     It is often desirable to minimize such variations in operation of integrated circuits with respect to variations in temperature. For example, a design may desire for gate delay characteristics to remain relatively constant over a range of temperatures. As another example, it may be advantageous to operate an integrated circuit at extreme temperatures, e.g., temperatures beyond a typical commercial temperature range, for example, as required by the automotive market. 
       FIG. 1A  illustrates a temperature compensated transfer resistor circuit  100 , in accordance with embodiments of the present invention. Temperature compensated transfer resistor circuit  100  comprises p-type transistor device  102  and p-type transistor device  110 . It is to be appreciated that transistor device  110  is configured as a diode. The sources of transistor devices  102  and  110  are coupled to a higher voltage. Such higher voltage is frequently a power rail. However, it is to be appreciated that transfer resistor circuit  100  may be used in conjunction with other circuit elements and that sometimes a higher voltage comprises a terminal of another circuit. Similarly, the drains of transistor devices  102  and  110  are coupled to a lower voltage. Such lower voltage is typically an output terminal. However, it is to be appreciated that transfer resistor circuit  100  may be used in conjunction with other circuit elements and that sometimes a lower voltage comprises a terminal of another circuit. 
     As operating temperature of temperature compensated transfer resistor circuit  100  decreases, thermal lattice scattering decreases, and carrier mobility increases. Consequently, transistor device  102  becomes “stronger,” for example, demonstrating an increase in maximum frequency of operation and a decrease in switching time. In addition, the threshold voltages of devices  102  and  110  increase with decreasing temperature. An increase in threshold voltage generally decreases current drive capabilities of such devices. A decrease in current drive tends to “weaken” a transistor, for example, decreasing frequency of operation. In general, the “strengthening” due to increased carrier mobility dominates any “weakening” due to threshold voltage increases for a transistor configured in the manner of device  102 . For a transistor configured in the manner of transistor device (diode)  110 , the “weakening” due to an increasing threshold voltage dominates the “strengthening” due to increased carrier mobility. 
     In temperature compensated transfer resistor circuit  100 , diode  110  is coupled to transistor device  102  so as to oppose the increase in operating frequency of transistor device  102  with decreasing temperature. As diode  110  becomes weaker with decreasing temperature, it counteracts the effects of transistor device  102  becoming stronger. As temperature increases, diode  110  becomes stronger, having less of a counteraction to transistor device  102 . As a beneficial consequence, temperature compensated transfer resistor circuit  100  exhibits less dependence of operating characteristics on temperature than does transistor device  102  alone. 
     It is to be appreciated that transistor device  102  and diode  110  create a parallel current path. The amount of total current through the combination of devices  102  and  110  is stable over temperature because device  102  has a frequency versus temperature characteristic of opposite sign to that of device  110 . More specifically, device  102  becomes faster with decreasing temperature and device  110  becomes slower with decreasing temperature. 
     The size and shape of transistor devices  102  and  110  to achieve a desired frequency response to temperature characteristic can be determined through a process of simulation. Size and shape of transistor devices in integrated circuits are generally given as a ratio, e.g., “10/8.” The first number specifies the width of the cell, e.g., “10,” and the second number specifies the length of the cell, e.g., “8.” It is appreciated that the terms “length” and “width” have specific meanings within the semiconductor arts, and that in general the dimensions are not interchangeable. The numbers typically indicate the dimension in microns. For an exemplary temperature compensated transfer resistor circuit  100  constructed in a 0.13 micron process, transistor device  102  can comprise a 10/8 p-type transistor device. Diode device  110  can be a 20/1.4 p-type transistor device. 
     Still referring to  FIG. 1A , devices  102  and  110  form a basis for a temperature compensated circuit element. The addition of pull up (p-type) transistor device  112  forms a generally more functional circuit, and completes transfer resistor circuit  100 . Exemplary dimensions for pull up transistor device  112  are 10/1.6. 
       FIG. 1B  illustrates a temperature compensated transfer resistor circuit  120 , in accordance with embodiments of the present invention. Temperature compensated transfer resistor circuit  100  comprises n-type transistor device  103  and n-type transistor device  111 . It is to be appreciated that transistor device  111  is configured as a diode. The sources of transistor devices  103  and  111  are coupled to a higher voltage. Such higher voltage is frequently an output terminal. However, it is to be appreciated that transfer resistor circuit  100  may be used in conjunction with other circuit elements and that sometimes a higher voltage comprises a terminal of another circuit. Similarly, the drains of transistor devices  102  and  110  are coupled to a lower voltage. Such lower voltage is typically a ground rail. However, as above, it is to be appreciated that transfer resistor circuit  100  may be used in conjunction with other circuit elements and that sometimes a lower voltage comprises a terminal of another circuit. 
     As operating temperature of temperature compensated transfer resistor circuit  120  decreases, thermal lattice scattering decreases, and carrier mobility increases. Consequently, transistor device  103  becomes “stronger,” for example, demonstrating an increase in maximum frequency of operation and a decrease in switching time. In addition, the threshold voltages of devices  103  and  111  increase with decreasing temperature. An increase in threshold voltage generally decreases current drive capabilities of such devices. A decrease in current drive tends to “weaken” a transistor, for example, decreasing frequency of operation. In general, the “strengthening” due to increased carrier mobility dominates any “weakening” due to threshold voltage increases for a transistor configured in the manner of device  103 . For a transistor configured in the manner of transistor device (diode)  111 , the “weakening” due to an increasing threshold voltage dominates the “strengthening” due to increased carrier mobility. 
     In temperature compensated transfer resistor circuit  120 , diode  111  is coupled to transistor device  103  so as to oppose the increase in operating frequency of transistor device  103  with decreasing temperature. As diode  111  becomes weaker with decreasing temperature, it counteracts the effects of transistor device  103  becoming stronger. As temperature increases, diode  111  becomes stronger, having less of a counteraction to transistor device  103 . As a beneficial consequence, temperature compensated transfer resistor circuit  100  exhibits less dependence of operating characteristics on temperature than does transistor device  103  alone. 
     It is to be appreciated that transistor device  103  and diode  111  create a parallel current path. The amount of total current through the combination of devices  103  and  111  is stable over temperature because device  103  has a frequency versus temperature characteristic of opposite sign to that of device  111 . More specifically, device  103  becomes faster with decreasing temperature and device  111  becomes slower with decreasing temperature. 
     The size and shape of transistor devices  103  and  111  to achieve a desired frequency response to temperature characteristic can be determined through a process of simulation. For an exemplary temperature compensated transfer resistor circuit  120  constructed in a 0.13 micron process, transistor device  103  can comprise a 5/10 p-type transistor device. Diode device  111  can be a 10/1.4 p-type transistor device. 
     Still referring to  FIG. 1B , devices  103  and  111  form a basis for a temperature compensated circuit element. The addition of pull down (n-type) transistor device  115  forms a generally more functional circuit, and completes transfer resistor circuit  100 . Exemplary dimensions for pull down transistor device  115  are 5/1.6. 
     In accordance with embodiments of the present invention, temperature compensated transfer resistor circuit  100  can generally be substituted for conventional p-type transistor devices in a circuit design, and temperature compensated transfer resistor circuit  120  can generally be substituted for conventional n-type transistor devices in a circuit design. Such substitutions will generally cause operating characteristics, e.g., maximum operating frequency or switching time, to exhibit less variation with changes in temperature in comparison with the original circuit design. It is appreciated that adjustments to size and/or shape of components of transfer resistor circuits  100  and  120  can be made so as to better match characteristics, e.g., drive capability, of transistors in a design when substituted for such transistors. 
       FIG. 2  illustrates a temperature compensated inverter circuit  200 , in accordance with embodiments of the present invention. It is to be appreciated that temperature compensated inverter circuit  200  comprises temperature compensated transfer resistor circuit  100  coupled to temperature compensated transfer resistor circuit  120 . 
     In accordance with embodiments of the present invention, temperature compensated inverter circuit  200  exhibits less frequency dependence upon temperature than conventional inverter designs. As a beneficial consequence, temperature compensated inverter circuit  200  can be utilized in circuits intended for operation across a wide range of temperatures and/or at extreme temperatures. 
       FIG. 3  illustrates a temperature compensated NAND circuit  300 , in accordance with embodiments of the present invention. It is to be appreciated that temperature compensated NAND circuit  300  comprises two instances of temperature compensated transfer resistor circuit  100  coupled to two instances of temperature compensated transfer resistor circuit  120 . 
     In accordance with embodiments of the present invention, temperature compensated NAND circuit  300  exhibits less frequency dependence upon temperature than conventional NAND gate designs. As a beneficial consequence, temperature compensated NAND circuit  300  can be utilized in circuits intended for operation across a wide range of operating temperatures and/or at extreme operating temperatures. 
       FIG. 4  illustrates a temperature compensated NOR circuit  400 , in accordance with embodiments of the present invention. It is to be appreciated that temperature compensated NOR circuit  400  comprises two instances of temperature compensated transfer resistor circuit  100  coupled to two instances of temperature compensated transfer resistor circuit  120 . 
     In accordance with embodiments of the present invention, temperature compensated NOR circuit  400  exhibits less frequency dependence upon temperature than conventional NOR gate designs. As a beneficial consequence, temperature compensated NOR circuit  400  can be utilized in circuits intended for operation across a wide range of operating temperatures and/or at extreme operating temperatures. 
     A ring oscillator circuit generally comprises an odd number of inverter stages coupled in a ring configuration. It is to be appreciated that rings comprising other inverting circuits, e.g., a NAND gate, are well suited to embodiments in accordance with the present invention. A ring oscillator will oscillate, or “ring,” at a frequency determined, in part, by switching delay times of the inverter stages and the number of inverter stages. Ring oscillators are a straightforward source of oscillating clock signals in integrated circuits, and are an ideal frequency source for many applications. Since a ring oscillator does not require external components, e.g., a crystal, ceramic resonator or external resistors and/or external capacitors, ring oscillators can be implemented at lower cost and in a smaller size than many other clock sources. 
     However, ring oscillators are sometimes not used in integrated circuit designs because their frequency of operation is determined (in part) by the switching delay time of each inverter stage. As has been discussed previously, switching delay time of a conventional inverter stage varies with operating temperature. Consequently, the frequency of a conventional ring oscillator varies with operating temperature. Because a conventional ring oscillator frequently has many stages, the variation of switching delay time due to operating temperature variations for a single stage is magnified by the number of stages, producing great frequency variations in response to operating temperature changes for the entire oscillator. 
       FIG. 5  illustrates a temperature compensated ring oscillator circuit  500 , in accordance with embodiments of the present invention. Temperature compensated ring oscillator circuit  500  comprises three stages. Each stage is comprised of a temperature compensated inverter circuit  200  as described above. Ring oscillators comprising other voltage compensated circuits, e.g., temperature compensated NAND circuit  300  or temperature compensated NOR circuit  400 , comprising homogeneous or heterogeneous stages, and/or circuits comprising more stages of feedback, are well suited to embodiments in accordance with the present invention. The frequency of operation of a ring oscillator, e.g., temperature compensated ring oscillator circuit  500 , depends, in part, on the delay inherent to each inverter stage and the number of stages provided in the ring. 
     Because the stages comprising temperature compensated ring oscillator circuit  500  have a stable frequency response over a range of operating temperatures, temperature compensated ring oscillator circuit  500  exhibits a similar desirable stable frequency response over a range of operating temperatures. Temperature compensated ring oscillator circuit  500  can be advantageously utilized to provide a stable frequency, e.g., for use as a microprocessor clock or to control a charge pump circuit, while operating an integrated circuit across a wide range of temperatures, e.g., for the automotive market. Further, temperature compensated ring oscillator circuit  500  can beneficially provide a stable frequency while operating at extreme temperatures, e.g., in a small computer system with limited cooling capacity. 
       FIG. 6  illustrates a flow diagram of a method  600  of operating an integrated circuit, in accordance with embodiments of the present invention. In block  610 , an output signal from a first circuitry is generated. 
     The first circuitry comprises a first transistor device having a first frequency-operating temperature characteristic. 
     In block  620 , an output signal from a second circuitry is generated. The second circuitry comprises a second transistor device configured as a diode having a second frequency-operating temperature characteristic. The second circuitry is coupled in parallel to the first circuitry. More specifically, the outputs of the first and second circuitry are coupled. 
     In block  630 , the second frequency-operating temperature characteristic dampens the first frequency-operating temperature characteristic. In this novel manner, the second circuit enhances the stability of characteristics, e.g., maximum frequency, switching and delay times, with respect to supply voltage of the combination of the two circuits in comparison to the characteristics of the first circuitry alone. 
     Embodiments in accordance with the present invention, temperature compensated integrated circuits, are thus described. While the present invention has been described in particular embodiments, it should be appreciated that the present invention should not be construed as limited by such embodiments, but rather construed according to the below claims.