Abstract:
In the conventional temperature compensation circuit, the thermal resistor is used to perform the temperature compensation, but the provided compensation range is limited due to the temperature coefficient of the thermal resistor. The embodiment of the invention provides a temperature coefficient modulating circuit capable of amplifying the temperature coefficient of the thermal resistor, so as to provide a wider compensation range in different applications.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority benefit of China application serial no. 200910222705.7, filed on Nov. 12, 2009. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a temperature coefficient modulating circuit and a temperature compensation circuit, and more particularly to a temperature coefficient modulating circuit and a temperature compensation circuit capable of enhancing the temperature coefficient. 
         [0004]    2. Description of Related Art 
         [0005]    The characteristic of electric device will vary with the operation temperature. In order to avoid the change of the temperature affecting the characteristic of electric device, the temperature compensation is generally used to modify the effect due to the temperature. For the temperature compensation, the popular reference device is the thermal resistor. The characteristic of thermal resistor of which the resistance changes along with the temperature is used to compensate the characteristic of electric device changing along with the temperature, so that the compensated characteristic of electric device does not change along with the temperature. 
         [0006]    The temperature coefficient range provided by the thermal resistor is limited. Therefore, the thermal resistor can not be used to sufficiently compensate the temperature effect under the application in which a larger temperature coefficient is needed. For the situation in which the larger temperature coefficient is needed to perform the temperature compensation, the temperature compensation circuit as shown in  FIG. 1  is used to enhance the temperature coefficient in the prior art.  FIG. 1  is a schematic circuit diagram of a conventional temperature compensation circuit. Referring to  FIG. 1 , the conventional temperature compensation circuit includes a current source IDC, a thermal resistor RNTC, an analog-to-digital converter A/D, and a programmable current source IC. The current source IDC provides a stable, temperature-independent current flowing through the thermal resistor RNTC, and the thermal resistor RNTC is a resister having the negative temperature coefficient. Accordingly, when the temperature is raised, the voltage drop across the thermal resistor RNTC will fall down. The analog-to-digital converter A/D detects the change of the voltage drop across the thermal resistor RNTC, and converts it to a digital control signal to control the output current IOUT_TC of the programmable current source IC, so that the output current IOUT_TC changes along with the temperature. Through the analog-to-digital converter A/D, the change of the voltage drop across the thermal resistor RNTC is proportionally amplified as the change of the output current IOUT_TC of the programmable current source IC. Accordingly, the temperature compensation circuit has a temperature coefficient larger than the temperature coefficient of the thermal resistor. 
         [0007]    However, by using the analog-to-digital converter A/D, the chip area of the circuit is increased, so that the cost thereof is increased, and the complexity thereof is also increased. Furthermore, the precision of the temperature coefficient is affected by that of the analog-to-digital converter A/D, too. 
       SUMMARY OF THE INVENTION 
       [0008]    Accordingly, in the prior art, the cost of the temperature compensation circuit is high, and the configuration thereof is complex. In the embodiment of the invention, one or more than one temperature coefficient modulating circuits are used to enhance the temperature coefficient, so that the temperature coefficient can be correspondingly amplified in different applications. Furthermore, the temperature coefficient modulating circuit can be achieved by a simple analog amplifier. Accordingly, the configuration of the circuit of the invention is simple, the temperature coefficient is precise, and the cost of the circuit is low. 
         [0009]    An embodiment of the invention provides a temperature coefficient modulating circuit including a first coefficient modulating circuit, a first resistor, and a second coefficient modulating circuit. The first coefficient modulating circuit has a first temperature coefficient. The first coefficient modulating circuit receives an input signal and outputs a first current according to the input signal and the first temperature coefficient. The first resistor has a first opposite temperature coefficient, and the first resistor is coupled to the first coefficient modulating circuit to generate a first voltage according to the first current. Herein, the first opposite temperature coefficient and the first temperature coefficient have opposite signs. The second coefficient modulating circuit has a second temperature coefficient device, and the second temperature coefficient device has a second temperature coefficient. The second coefficient modulating circuit receives the first voltage and outputs a second current according to the first voltage and the second temperature coefficient. Herein, the second temperature coefficient and the first temperature coefficient have equal sign. 
         [0010]    Another embodiment of the invention provides a temperature compensation circuit including a detecting circuit, a first resistor, and a coefficient modulating circuit. The detecting circuit has a first temperature coefficient and is coupled to a detected unit to output a first current. Herein, a temperature coefficient of the detected unit and the first temperature coefficient have equal sign. The first resistor has a first opposite temperature coefficient, and the first resistor is coupled to the detecting circuit to generate a first voltage according to the first current. Herein, the first opposite temperature coefficient and the first temperature coefficient have opposite signs. The coefficient modulating circuit has a second temperature coefficient. The coefficient modulating circuit receives the first voltage and outputs a second current according to the first voltage and the second temperature coefficient. Herein, the second temperature coefficient and the first temperature coefficient have equal sign. 
         [0011]    It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. In order to make the features and the advantages of the present invention comprehensible, exemplary embodiments accompanied with figures are described in detail below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
           [0013]      FIG. 1  is a schematic circuit diagram of a conventional temperature compensation circuit. 
           [0014]      FIG. 2  is a schematic circuit diagram of a temperature coefficient modulating circuit according to a first embodiment of the invention. 
           [0015]      FIG. 3  is a schematic circuit diagram of a temperature coefficient modulating circuit according to a second embodiment of the invention. 
           [0016]      FIG. 4  is a schematic circuit diagram of a temperature coefficient modulating circuit according to a third embodiment of the invention. 
           [0017]      FIG. 5  is a schematic circuit diagram of a temperature coefficient modulating circuit according to a fourth embodiment of the invention. 
           [0018]      FIG. 6  is a schematic circuit diagram of a temperature compensation circuit according to an embodiment of the invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0019]      FIG. 2  is a schematic circuit diagram of a temperature coefficient modulating circuit according to a first embodiment of the invention. Referring to  FIG. 2 , the temperature coefficient modulating circuit includes a coefficient modulating circuit TCB and a current minor circuit CM. The coefficient modulating circuit TCB includes a first thermal resistor RP, an amplifier EA, a transistor M, and a second thermal resistor RN, wherein the first thermal resistor RP has a positive temperature coefficient, and the second thermal resistor RN has a negative temperature coefficient. The coefficient modulating circuit TCB receives an input signal ITC, and in the present embodiment, the input signal ITC is a current signal. The current signal passes through the first thermal resistor RP to generate a voltage drop, and is inputted to the non-inverting input end of the amplifier EA. The transistor M has a first end, a second end, and a control end. The first end of the first transistor provides an amplified current ITC′, and the second end thereof is connected to the second thermal resistor RN to generate a signal to the inverting input end of the amplifier EA. The output end of the amplifier EA is connected to the control end of the transistor M. Because the amplifier EA and the transistor M form a voltage follower, the voltages of the inverting input end and the non-inverting input end of the amplifier EA are equal, thereby obtaining: 
         [0000]    
       
      
       Itc*Rp=Itc′*Rn;  
      
     
         [0020]    Herein, Itc is the amount of the input signal ITC, Itc′ is the amount of the amplified current ITC′, Rp is the resistance of the first thermal resistor RP, and Rn is the resistance of the second thermal resistor RN. 
         [0021]    The above equation can be rewritten as I tc′=I tc*(Rp/Rn). 
         [0022]    Accordingly, the current of the input signal ITC is proportionally amplified as the amplified current ITC′ by the ratio RP/RN. In the present embodiment, the resistance Rn of the second thermal resistor RN has a negative temperature coefficient (&lt;1), and thus, the resistance Rn falls down along with the raise of temperature. On the contrary, the resistance Rp of the first thermal resistor RP has a positive temperature coefficient (&gt;1), and thus, the ratio RP/RN is greater than the temperature coefficient of the resistance Rp, thereby achieving the effect of amplifying the temperature coefficient. 
         [0023]    Because the current direction of the amplified current ITC′ is that of flowing into the coefficient modulating circuit TCB, for some applications, such as the requirement of the current direction of flowing out of the coefficient modulating circuit TCB, the current mirror circuit CM can be connected and used to provide an output current IBPTC having the current direction of flowing out of the coefficient modulating circuit TCB as the present embodiment. The width/length ratio of the channel of the two PMOSFET forming the current mirror circuit CM is 1:N, so that the amount of the provided current can be further modulated to satisfy the requirements of different currents. 
         [0024]    The input signal ITC may be a detecting signal or a temperature-independent signal. If the input signal ITC is the detecting signal, through the temperature coefficient modulating circuit in the embodiment of the invention, the detecting signal affected by the temperature can be compensated, so that the output signal IBPTC can represent a temperature-independent detecting result. If the input signal ITC is the temperature-independent signal, the output signal IBPTC can be a signal changing along with the temperature to provide the reference of the change corresponding to the temperature for other circuits. These applications can refer to other embodiments in following. 
         [0025]      FIG. 3  is a schematic circuit diagram of a temperature coefficient modulating circuit according to a second embodiment of the invention. Referring to  FIG. 3 , the temperature coefficient modulating circuit includes a bandgap reference circuit VBG, a coefficient modulating circuit TCB and a current mirror circuit CM. The difference between the temperature coefficient modulating circuit of the present embodiment and that of the first embodiment lies in the coefficient modulating circuit TCB. The coefficient modulating circuit TCB includes a bipolar junction transistor BJT and a temperature coefficient device Rtc. The bandgap reference circuit VBG provides a temperature-independent voltage signal to the base of the BJT. The emitter of the BJT is coupled to the temperature coefficient device Rtc. The temperature coefficient device Rtc may be a thermal resistor having a negative temperature coefficient. The threshold voltage Vbe of the BJT has a negative temperature coefficient. Accordingly, when the temperature is raised, the voltage drop across the temperature coefficient device Rtc is also raised, so that the slope of the current raised along with the temperature (i.e. the temperature coefficient) is greater than that of the current raised along with the temperature by only the temperature coefficient device Rtc. After the current passes through the current mirror circuit CM, an output current IBPTC is generated. 
         [0026]      FIG. 4  is a schematic circuit diagram of a temperature coefficient modulating circuit according to a third embodiment of the invention. Referring to  FIG. 4 , the temperature coefficient modulating circuit includes a first coefficient modulating circuit TCB 1 , a resistor RP 1 , a second coefficient modulating circuit TCB 2 , a first current mirror circuit CM 1 , and a second current mirror circuit CM 2 . The first coefficient modulating circuit TCB 1  has a first temperature coefficient device, and in the present embodiment, the first temperature coefficient device is formed by coupling a first negative temperature coefficient thermal resistor RN 0  and a second negative temperature coefficient thermal resistor RN 1  in series. The first coefficient modulating circuit TCB 1  includes a voltage follower formed by an amplifier and a transistor to receive an input signal Vbg generated by a bandgap reference circuit VBG, so that the voltage drop across the first temperature coefficient device is equal to the voltage of the input signal Vbg, wherein the voltage of the input signal Vbg is a temperature-independent voltage. Regarding the voltage follower, the description thereof can refer to that of  FIG. 2 . Accordingly, a first current ITC 1  flows through the first temperature coefficient device and the transistor, and the amount of the first current ITC 1  is equal to the value by dividing the voltage drop of the first temperature coefficient device with the resistance of the first temperature coefficient device, so that the first current ITC 1  has a positive temperature coefficient. 
         [0027]    The first current minor circuit CM 1  is coupled between the first coefficient modulating circuit TCB 1  and the resistor RP 1  to amplify the first current ITC 1  as an amplified current ITC 2  to be provided to the resistor RP 1 . In the present embodiment, the temperature coefficient of the resistor RP 1  and the temperature coefficient of the first temperature coefficient device in the first coefficient modulating circuit TCB 1  have opposite signs. That is, if the temperature coefficient of the resistor RP 1  is positive, the temperature coefficient of the first temperature coefficient device is negative. On the contrary, if the temperature coefficient of the resistor RP 1  is negative, the temperature coefficient of the first temperature coefficient device is positive. In the present embodiment, the resistor RP 1  has a positive temperature coefficient. Accordingly, the temperature coefficient of the voltage signal generated by the amplified current ITC 2  flowing through the resistor RP 1  is further enhanced. The configuration of the second coefficient modulating circuit TCB 2  is similar to that of the first coefficient modulating circuit TCB 1 . The second coefficient modulating circuit TCB 2  includes a voltage follower formed by an amplifier and a transistor and a second temperature coefficient device RN 2 . In the present embodiment, the second temperature coefficient device RN 2  is a thermal resister RN 2  having a negative temperature coefficient, and the temperature coefficient of the second temperature coefficient device RN 2  and that of the first temperature coefficient device have equal sign. Accordingly, the temperature coefficient of the voltage signal generated by the resister RP 1  is enhanced again, and after amplified by the second current mirror circuit CM 2 , an output current IBPTC is generated. 
         [0028]    Compared with that of the foregoing two embodiments, the temperature coefficient modulating circuit of the third embodiment shown in  FIG. 4  further includes the resistor RP 1  and the second coefficient modulating circuit TCB 2  for performing the enhancement of the temperature coefficient. Accordingly, the enhancement of the temperature coefficient is more obvious in the present embodiment. 
         [0029]      FIG. 5  is a schematic circuit diagram of a temperature coefficient modulating circuit according to a fourth embodiment of the invention. Referring to  FIG. 5 , the input signal ITC 0  becomes the output signal ITCn after being amplified stage by stage through the first coefficient modulating circuit ITCB 1 , the first resistor Rt 1 , the second coefficient modulating circuit ITCB 2 , the second resistor Rt 2 , . . . , the n th  coefficient modulating circuit ITCBn, and the n th  resistor Rtn. The coefficient modulating circuits ITCB 1 , ITCB 2 , . . . , and ITCBn can be implemented by the coefficient modulating circuit in the foregoing embodiments, and the temperature coefficient modulating amount of each coefficient modulating circuit (i.e. the output signal/the received signal) has equal sign. Furthermore, whether the first resistor Rt 1 , the second resistor Rt 2 , and the n th  resistor Rtn are used can be determined according to the signal to be outputted being a voltage or a current, or the type of the signal which can be processed by next stage circuit. As shown in  FIGS. 2-4 , the input of the coefficient modulating circuit is a voltage signal, and the output of the coefficient modulating circuit is a current signal. Accordingly, through the resistors Rt 1 -Rtn, the outputted current signal is converted to a voltage signal. 
         [0030]      FIG. 6  is a schematic circuit diagram of a temperature compensation circuit according to an embodiment of the invention. Referring to  FIG. 6 , the temperature compensation circuit includes a detecting circuit DET, a resistor Rtc 2 , and a coefficient modulating circuit TCB 3 . The detecting circuit DET has a first temperature coefficient device Rtc 1 , and through a first detecting end D 1  and a second detecting end D 2 , the detecting circuit DET is coupled to a detected unit DUT to output a first current IDE. In the present embodiment, the first detecting end D 1  and the second detecting end D 2  are two input ends of the amplifier in the detecting circuit DET. In order to compensate the change of the voltage drop Vde of the detected unit DUT along with the temperature, the temperature coefficient of the first temperature coefficient device Rtc 1  and that of the detected unit DUT have equal sign, but the temperature coefficient of the first temperature coefficient device Rtc 1  and that of the resistor Rtc 2  have opposite signs. The first current IDE is amplified as the current ITCC 1  through the first current mirror circuit CM 1 , and the current ITCC 1  is inputted to the resistor Rtc 2  to generate a voltage signal to be inputted to the coefficient modulating circuit TCB 3 . The coefficient modulating circuit TCB 3  has a temperature coefficient which has an equal sign with the first temperature coefficient device Rtc 1 . The coefficient modulating circuit TCB 3  outputs the current according to the voltage signal and the temperature coefficient thereof, and the current is amplified as the current ITCC 2  to be outputted through a second current mirror circuit CM 2 . 
         [0031]    The detected unit DUT may be a detecting resistor (e.g. the feedback detecting resistor used in the feedback control circuit), an on-resistance of a MOSFET, an LED, or other electric devices, even circuits of which the characteristics change along with the temperature. The equivalent temperature coefficient of the temperature compensation circuit in the present embodiment can be changed by modulating the temperature coefficients of the coefficient modulating circuit and the thermal resistor, so as to be just the reciprocal of the temperature coefficient of the detected unit DUT. Accordingly, an output signal of the temperature compensation circuit is temperature-independent. 
         [0032]    To sum up, the temperature coefficient modulation in the embodiment of the invention is achieved through simple analog circuits and devices, such as the amplifier, the thermal resister, and the transistor. Accordingly, the configuration of the circuit is quite simple, and the cost thereof is quite low. Furthermore, the number or the temperature coefficient of the coefficient modulating circuit can be correspondingly modulated to obtain the temperature compensation satisfying the requirement in different applications. 
         [0033]    As the above description, the invention completely complies with the patentability requirements: novelty, non-obviousness, and utility. It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing descriptions, it is intended that the present invention covers modifications, and variations of this invention if they fall within the scope of the following claims and their equivalents.