Patent Publication Number: US-2017350770-A1

Title: Temperature Sensor Peripheral Having Independent Temperature Coefficient And Offset Adjustment Programmability

Description:
RELATED PATENT APPLICATION 
     This application claims priority to commonly owned U.S. Provisional Patent Application Ser. No. 61/735,243 filed Dec. 10, 2012; which is hereby incorporated by reference herein for all purposes. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to temperature sensing apparatus, and, in particular, a temperature sensor peripheral having independent temperature coefficient and offset adjustment programmability. 
     BACKGROUND 
     A prior technology temperature sensor apparatus is described in U.S. Pat. No. 7,439,601. The device disclosed therein sums two currents and then drives another resistor. By definition the voltage representing the temperature (Vtemp) is interrelated to the temperature coefficient of the voltage (TCVtemp) representing the temperature (Vtemp). Therefore Vtemp and d(Vtemp)/dTemp are not independent of each other. 
     SUMMARY 
     There exists a need for a temperature sensor peripheral used in integrated circuit (IC) micro-controllers that can generate a voltage that may be used for purposes external to the IC and that is: a) proportional to temperature, b) whose temperature coefficient can be adjusted at the temperature probe to any desired value, c) whose temperature coefficient can be either positive or negative, d) whose room temperature voltage can be adjusted at the temperature probe to any desired value, and e) whose temperature coefficient and room temperature voltage are completely independent of one another. 
     According to an embodiment, a circuit arrangement for measuring a temperature and producing a voltage representative thereof may comprise: first and second voltage-to-current converters each having a voltage input, a current adjust input and a current output; a first operational amplifier having first and second inputs and an output; a first resistor coupled to the current adjust input of the first voltage-to-current converter, wherein the first resistor may adjust a value of a first current from the current output thereof; a second resistor coupled to the current adjust input of the second voltage-to-current converter, wherein the second resistor may adjust a value of a second current from the current output thereof; a third resistor coupled between the output and the second input of the first operational amplifier; the outputs of the first and second voltage-to-current converters and the second input of the first operational amplifier may be coupled together; a first reference voltage may be coupled to the voltage input of the first voltage-to-current converter; a second reference voltage may be coupled to the voltage input of the second voltage-to-current converter; and a third reference voltage may be coupled to the first input of the operational amplifier; wherein a third current through the third resistor may be equal to the second current minus the first current. 
     According to a further embodiment, the first input of the first operational amplifier may be a positive input and the second input thereof may be a negative input. According to a further embodiment, the third reference voltage may be from a digital-to-analog converter (DAC). According to a further embodiment, an output voltage from the first operational amplifier may be equal to the second reference voltage value times the third resistor value divided by the second resistor value minus the first reference voltage value times the third resistor value divided by the first resistor value plus the third reference voltage value. According to a further embodiment, the first reference voltage may be from a temperature sensor having a voltage output proportional to a temperature thereof, and the second and third reference voltages may be from fixed voltage references having substantially zero temperature coefficients. According to a further embodiment, the first and second voltage-to-current converters may be provided by a second operational amplifier, and first and second transistors having sources coupled together, gates coupled to an output of the second operational amplifier, and drains coupled to the first and second resistors. 
     According to a further embodiment, the second and third reference voltages may be from the same voltage reference. According to a further embodiment, the first reference voltage may be from a temperature sensor, the third reference voltage and the second resistor value may determine a first output voltage representing a first calibration temperature, and the third resistor value may determine a second output voltage representing a second calibration temperature. According to a further embodiment, the first calibration temperature may be room temperature. According to a further embodiment, the temperature sensor may be a semiconductor diode providing a diode junction voltage as a function of temperature. According to a further embodiment, the temperature sensor may be a resistance temperature detector. According to a further embodiment, the temperature sensor may be a thermistor. According to a further embodiment, the second resistor may be adjusted so that a voltage from the output of the first operational amplifier may be equal to the third reference voltage, and the second current may be equal to the first current. 
     According to another embodiment, a mixed signal integrated circuit adapted for coupling to a temperature sensor and providing voltages proportional to temperatures measured by the temperature sensor may comprise: a digital processor and memory; a temperature sensor peripheral that may comprise a first operational amplifier having first and second inputs and an output, a third resistor coupled between the output and the second input of the first operational amplifier, a second operational amplifier having first and second inputs and an output, first and second transistors having sources coupled together, gates coupled to an output of the second operational amplifier, and drains coupled to first and second resistors; wherein a temperature sensor may be coupled to the first input of the second operational amplifier, and a reference voltage may be coupled to the first input of the first operational amplifier; wherein the output of the first operational amplifier may provide an output voltage proportional to a temperature measured by the temperature sensor. 
     According to a further embodiment, the first, second and third resistors may be programmable and controlled by the digital processor. According to a further embodiment, a digital-to-analog converter may be coupled to the digital processor and provide a programmable reference voltage. According to a further embodiment, an analog-to-digital converter may have an input coupled to the output of the first operational amplifier and an output coupled to the digital processor. According to a further embodiment, the mixed signal integrated circuit may comprise a microcontroller. 
     According to yet another embodiment, a circuit arrangement for measuring a temperature may comprise: two current generation circuits that may provide first and second currents in two different paths, wherein one of the first or second currents may be dependent upon temperature; the first and second currents may be combined and converted into a voltage Vtemp, wherein the voltage Vtemp may be dependent upon the temperature. 
     According to a further embodiment, the voltage Vtemp may be equal to a reference voltage when the first and second currents may be equal. According to a further embodiment, the combined first and second currents may be converted into the voltage Vtemp by an amplifier having a feedback resistor. According to a further embodiment, the feedback resistor may determine a variation of the voltage Vtemp over a variation of the temperature. According to a further embodiment, the two current generation currents may be voltage-to-current converters, and the temperature may be measured by a temperature sensor having a voltage output coupled to one of the two voltage-to-current converters. 
     According to still another embodiment, a method for measuring temperatures and producing voltages representative thereof may comprise the steps of: determining a first voltage representing a first calibration temperature; adjusting a first output voltage from a temperature sensor peripheral to equal the first voltage when a temperature sensor may be at the first calibration temperature; determining a range of voltages to represent a range of temperatures, wherein the first voltage may be within the range of voltages and the first calibration temperature may be within the range of temperatures; determining a second voltage representing a second calibration temperature within the range of temperatures; and adjusting a second output voltage from the temperature sensor peripheral to equal the second voltage when the temperature sensor may be at the second calibration temperature. 
     According to a further embodiment of the method, the first voltage may be equal to a reference voltage coupled to an input of an operational amplifier of the temperature sensor peripheral. According to a further embodiment of the method, the first calibration temperature may be room temperature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present disclosure may be acquired by referring to the following description taken in conjunction with the accompanying drawings wherein: 
         FIG. 1  illustrates a schematic diagram of a temperature sensor peripheral and circuit voltage relationships thereof, according to a specific example embodiment of this disclosure; 
         FIG. 2  illustrates a schematic diagram of the temperature sensor peripheral shown in  FIG. 1  and circuit voltage relationships thereof; 
         FIG. 3  illustrates a schematic diagram of a temperature sensor peripheral, temperature sensor probe connected thereto and circuit voltage relationships thereof, according to another specific example embodiment of this disclosure; 
         FIG. 4  illustrates a schematic diagram of the temperature sensor peripheral shown in  FIG. 3  and circuit voltage relationships thereof; 
         FIG. 5  illustrates a schematic diagram of the temperature sensor peripheral shown in  FIGS. 3 and 4  with exemplary component values and circuit voltage relationships thereof, according to the teachings of this disclosure; 
         FIG. 6  illustrates a schematic process flow diagram for calibration of a temperature sensor peripheral, according to specific example embodiments of this disclosure; 
         FIG. 7  illustrates a schematic temperature-voltage graph for temperature sensor peripheral calibration as more fully disclosed in the description of  FIG. 6 , according to specific example embodiments of this disclosure; and 
         FIG. 8  illustrates a schematic block diagram of a mixed signal integrated circuit having a temperature sensor peripheral, according to the teachings of this disclosure. 
     
    
    
     While the present disclosure is susceptible to various modifications and alternative forms, specific example embodiments thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific example embodiments is not intended to limit the disclosure to the particular forms disclosed herein, but on the contrary, this disclosure is to cover all modifications and equivalents as defined by the appended claims. 
     DETAILED DESCRIPTION 
     According to various embodiments, a circuit may be provided that generates a voltage proportional to temperature and whose temperature coefficient, polarity of temperature coefficient and room temperature voltage are independently user selectable. 
     Referring now to the drawings, the details of specific example embodiments are schematically illustrated. Like elements in the drawings will be represented by like numbers, and similar elements will be represented by like numbers with a different lower case letter suffix. 
     Referring to  FIG. 1 , depicted is a schematic diagram of a temperature sensor peripheral and circuit voltage relationships thereof, according to a specific example embodiment of this disclosure. A first voltage-to-current converter  102  has a voltage input coupled to a first reference voltage Vref 1  that is converted to a first current I 1  and is available at an output thereof. A second voltage-to-current converter  102  has a voltage input coupled to a second reference voltage Vref 2  that is converted to a second current I 2  and is available at an output thereof. An operational amplifier  106  has a negative input coupled to the outputs of the first and second voltage-to-current converters  102  and  104 , a positive input coupled to a third reference voltage Vref 3  and a resistor R 3  coupled between an output and the negative input of the operational amplifier  106 . The first and second reference voltages may or may not have the same temperature coefficient (TC). One of the reference voltages may be provided by a voltage reference having substantially no temperature coefficient (TC), e.g., substantially the same output voltage over all temperatures of operation, e.g., a bandgap voltage reference, etc. The other reference voltage may be provided by a temperature measurement sensor, e.g., diode junction, resistance temperature detector (RTD), thermistor, etc., having either a positive or negative temperature coefficient (TC). Any one or more of the reference voltages, e.g., Vref 3 , Vref 2 ; or Vref 3 , Vref 1 ; may be provided by a digital-to-analog converter (DAC)  108 . 
     The first current I 1  from the first voltage-to-current converter  102  may be adjusted with a first resistor R 1  coupled to a current adjustment input thereof. The second output current I 2  from the second voltage-to-current converter  104  may be adjusted with a second resistor R 2  coupled to a current adjustment input thereof. The operational amplifier  106  forces a third current I 3  to equal the difference between the first and second currents (I 3 =I 2 −I 1 ). 
     Shown in  FIG. 1  are the mathematical relationships between the output voltage Vout from the operational amplifier  106 ; the first, second and third voltage references Vref 1 , Vref 2  and Vref 3 ; and the first, second and third resistors R 1 , R 2  and R 3 . Also shown is the mathematical relationship of a change in output voltage dVout in relation to a change in temperature dT. When a dVref term(s) is (are) substantially zero, then only the non-zero dVref term determines dVout/dT, after Vout has been adjusted to substantially equal Vref 3 , as more fully described hereinafter. 
     According to the teachings of this disclosure, two currents I 1  and I 2  having different temperature coefficients, one negative and the other positive, may be generated then summed together and the resultant current I 3  converted back to a voltage Vout. The operational amplifier  106  regulates the summing node (I 3 =I 2 −I 1 ) to equal Vref 3 . The operational amplifier  106  feedback then forces the output voltage Vout to equal I 3  times R 3  plus Vref 3 . Therefore, when I 3  is substantially zero, i.e., I 2 =I 1 , I 2 −I 1 =0, then Vout=Vref 3 . So by selecting different reference voltages Vref 1 , Vref 2  and Vref 3 , a composite output voltage Vout may be generated having a desired voltage offset and slope. A real world design would most likely not vary all of these parameters. By varying only one of the reference voltages and keeping the other reference voltages constant a reliable output voltage with a well defined temperature coefficient may be provided. Either the first reference voltage Vref 1  or the second reference voltage Vref 2  may be controlled by a temperature sensor, e.g., diode junction, resistance temperature detector (RTD), thermistor, etc. Appropriate temperature-to-voltage conversion may be provided by controlling the second reference voltage Vref 2  with a temperature sensor having a positive temperature coefficient, or controlling the first reference voltage Vref 1  with a temperature sensor having a negative temperature coefficient. 
     Besides temperature measurement applications, it is contemplated and within the scope of this disclosure that the first and second reference voltages Vref 1  and/or Vref 2  may vary with temperature and the circuit described hereinabove adjusted in such a way that the output voltage Vout thereof may be used for voltage controlled temperature compensation of another circuit that may need either positive or negative temperature compensation, e.g., a voltage controlled oscillator having frequency determining components when coupled together have either a positive or negative temperature coefficient that must be compensated for over an operating temperature range. 
     Another feature of the present invention is completely independent output voltage adjustment (output voltage offset) and voltage/temperature coefficient adjustment (range of dVout/dT) when the output voltage Vout is adjusted to be substantially equal to the third reference voltage Vref at a first calibration temperature. For example, first determine what output voltage range is required over the temperature range of interest. Then determine what the output voltage Vout of that voltage range would be at room temperature, e.g., 27 degrees Centigrade (° C.). Then set the third reference voltage Vref 3  to that voltage, or use an existing third reference voltage Vref 3  to define the first calibration voltage, e.g., Vout at a first calibration temperature, e.g., room temperature. Next set the output voltage Vout to be substantially the same value as the third reference voltage Vref 3  by adjusting the second resistor R 2  at room temperature, whereby the third current I 3  will be substantially zero (0). What is being accomplished is to substantially match the first current I 1  (I 1 =Vref 1 /R 1 ) to the second current I 2  (I 2 =Vref 2 /R 2 ) that is being controlled by the temperature sensor voltage Vref 2  at room temperature (or any other first calibration temperature) and the second resistor R 2 . 
     Output voltage change dVout versus temperature change dT (temperature coefficient) may be determined next. Select a second temperature (second calibration temperature) different from the first calibration temperature (e.g., room temperature), e.g., higher or lower. Calculate what the output voltage Vout would be at the second temperature based upon the temperature coefficient desired (dVout/dT). At the second temperature adjust the third resistor R 3  so that the output voltage Vout is at substantially the calculated output voltage of the second calibration temperature. Thus accurate and independent adjustments of the output voltage and temperature coefficient (change in output voltage versus temperature) are easily accomplished for any output voltage offset and temperature coefficient desired with substantially no interaction therebetween. 
     Referring to  FIG. 2 , depicted is a schematic diagram of the temperature sensor peripheral shown in  FIG. 1  and circuit voltage relationships thereof. Below is an example showing how the room temperature voltage may be set independent of the temperature coefficient. For this example there are two assumptions: I 1 =I 2 , Vref 2  and Vref 3  do not change with temperature. If this is the case then the room temperature voltage may be set by adjusting the second resistor R 2  so that the first current I 1  equals the second current I 2  and the temperature coefficient may be changed by adjusting the third resistor R 3 . In this example the first resistor R 1  is held constant since it shows up in both the Vout and dVout/dT equations. 
     Referring to  FIGS. 3 and 4 , depicted is a schematic diagram of a temperature sensor peripheral, temperature sensor probe connected thereto and circuit voltage relationships thereof, according to another specific example embodiment of this disclosure. A second operational amplifier  308 , and transistors  316  and  318  may function as the first and second voltage-to-current converters  102  and  104  shown in  FIGS. 1 and 2 . The second reference voltage Vref 2  will automatically be substantially the same voltage as the third reference voltage Vref 3  due to operation of the operational amplifier  106  with the feedback resistor R 3 . Circuit function, adjustment and operation thereof may be substantially the same as described hereinabove for  FIGS. 1 and 2 . 
     A diode temperature sensor  314  may be coupled to a current source  312  and a resulting diode junction voltage Vbe dependent upon temperature may be coupled to a positive input of the operational amplifier  308 . Since the third reference voltage Vref 3  remains constant, e.g., from a band gap voltage reference (not shown) or a DAC  108 , etc., the change in output voltage dVout is dependent only upon the change in the diode junction voltage dVbe. Voltage output Vout, offset and range may be adjusted as described hereinabove for a desired room temperature output voltage (first calibration output voltage at a first calibration temperature) and a desired dVout/dT (based upon a second calibration voltage at a second calibration temperature). 
     It is contemplated and within the scope of this disclosure that any temperature sensor providing a voltage output corresponding to a temperature may be utilized, and one having ordinary skill in electronic circuit design and the benefit of this disclosure would readily understand how to implement such temperature sensors in combination with the teachings of this disclosure. 
     Referring to  FIG. 5 , depicted is a schematic diagram of the temperature sensor peripheral shown in  FIGS. 3 and 4  with exemplary component values and circuit voltage relationships thereof, according to the teachings of this disclosure. The calculated voltage and component values shown are derived at room temperature. 
     Referring to  FIG. 6 , depicted is a schematic process flow diagram for calibration of a temperature sensor peripheral, according to specific example embodiments of this disclosure. In step  620  a first voltage representing a first calibration temperature is selected. In step  622  a first output voltage is adjusted to the first voltage while the temperature sensor is at the first calibration temperature. By picking Vref 3  to be the first (trim) voltage, or visa versa, to represent the first calibration temperature, e.g., “room temperature” at the temperature sensor  314  (probe), the output voltage Vout is adjusted to Vref 3 , whereby I 3 =0, and I 2 =I 1 . In step  624  a range of voltages representing a range of temperatures is determined, e.g., slope dVout/dT (see  FIG. 7 ), wherein the first voltage is within the range of voltages. In step  626  a second voltage representing a second calibration temperature within the range of temperatures is determined. In step  628  the temperature sensor peripheral is adjusted so that a second output voltage therefrom is substantially the same as the second voltage while the temperature sensor  314  is at the second calibration temperature. This sequence of two calibration adjustments, first setting the output voltage Vout to the reference voltage Vref 3  while the temperature sensor  314  is at the first calibration temperature (e.g., room temperature) determines the output voltage offset, and next setting the output voltage Vout to the second voltage while the temperature sensor  314  is at the second calibration temperature, e.g., second calibration temperature different than the first calibration temperature, determines the slope of the change in output voltage dVout versus change in temperature dT with substantially no interaction between these two calibration adjustments. 
     Referring to  FIG. 7 , depicted is a schematic temperature-voltage graph for temperature sensor peripheral calibration as more fully disclosed in the description of  FIG. 6 , according to specific example embodiments of this disclosure. The first calibration adjustment determines the output voltage offset at the first calibration temperature, and the second calibration adjustment determines the slope of the change in output voltage versus the change in temperature, dVout/dT. By adjusting the third reference voltage Vref 3 , any output voltage offset may be selected, e.g., by using a digital-to-analog converter (DAC)  108  to generate Vref 3 . 
     Referring to  FIG. 8 , depicted is a schematic block diagram of a mixed signal integrated circuit having a temperature sensor peripheral, according to the teachings of this disclosure. A mixed signal integrated circuit  802 , e.g., a microcontroller, may comprise a temperature sensor peripheral  808 , an analog-to-digital converter (ADC)  806 , a digital processor and memory  804 , a digital-to-analog converter (DAC)  816 , and programmable resistors  810 ,  812  and  814 . A temperature sensor  314  may be coupled to an input of the temperature sensor peripheral  808 , and an output voltage Vout may be provided from the temperature sensor peripheral  808 . The output voltage Vout may be available for coupling to an external device and/or supplied to the ADC  806  for further processing by the digital processor  804 . The DAC  816  may provide a reference voltage Vref 3  to the temperature sensor peripheral  808 , and programmable resistors  810 ,  812  and/or  814  may be used to provide output voltage offset and dVout/dT slope calibration, as more fully described hereinabove. 
     While embodiments of this disclosure have been depicted, described, and are defined by reference to example embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those ordinarily skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and are not exhaustive of the scope of the disclosure.