Abstract:
A pressure monitoring device comprises an analog-to-digital converter (ADC) to receive an analog signal and to convert the analog signal to a digital signal. The pressure monitoring device is configured to apply in a first state a first set of calibration coefficients to the digital signal, the first set of calibration coefficients being associated with a first pressure range. The pressure monitoring device is further configured to apply in a second state a second set of calibration values to the digital signal, the second set of calibration coefficients being associated with a second pressure range different than the first pressure range.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/955,105 which was filed on Nov. 29, 2010 and claims the benefit of the priority date of the above US application, the contents of which are herein incorporated in its full entirety by reference. 
    
    
     BACKGROUND 
     Pressure monitoring systems are used in many applications. For example, a tire pressure monitoring system (TPMS) often measures tire pressure for a vehicle and notifies a vehicle&#39;s operator if the measured tire pressure falls outside of an ideal tire pressure range. Thus, a TPMS improves safety for the vehicle operator and for surrounding vehicle operators. 
     A TPMS for a vehicle often includes one tire pressure monitoring sensor per wheel, plus an electronic control unit (ECU).  FIG. 1  shows an example of a conventional tire pressure monitoring sensor  100 , The sensor  100  includes a pressure sensor  102 , an analog-to-digital-converter (ADC)  104 , and a microcontroller  106 . During operation, the pressure sensor  102  provides an analog signal  108 , and the ADC  104  converts the analog signal  108  to a digital signal  110 . The microcontroller  106  puts the digital signal into a formal suitable for transmission to the ECU. The ECU then evaluates the formatted digital signal to determine whether the measured pressure falls within an acceptable tire pressure range, and can alert the driver if the pressure falls outside this acceptable range. 
     Although conventional pressure monitoring systems are adequate in many respects, they suffer from a shortcoming in that they are unable to flexibly monitor different pressure ranges. For example, although one sensor is useful in measuring pressures for tires of passenger vehicles, which can have normal tire pressures in the range of about 100 kPa-450 kPa; the same sensor is unable to effectively measure pressures for tires of commercial vehicles, which can have normal tire pressures in the range of bout 100 kPa-850 kPa. Consequently, the present disclosure provided improved methods and systems for monitoring pressure. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a conventional pressure sensor system; 
         FIG. 2  is a block diagram illustrating a pressure sensor system in accordance with some embodiments of the present disclosure; 
         FIG. 3  is a plot illustrating functionality consistent with one example of FIG.  2 &#39;s block diagram; 
         FIG. 4  is a flowchart illustrating a methodology consistent with one example of FIG.  2 &#39;s block diagram; 
         FIG. 5  is a block diagram illustrating a pressure sensor system in accordance with some embodiments of the present disclosure; 
         FIG. 6  is a plot illustrating functionality consistent with one example of FIG.  5 &#39;s block diagram. 
         FIG. 7  is a block diagram of a dual-sensor module consistent with one embodiment; 
         FIG. 8  is a flow chart illustrating a methodology consistent with one example of FIG.  7 &#39;s block diagram. 
     
    
    
     DETAILED DESCRIPTION 
     The claimed subject matter is now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the claimed subject matter. It may be evident, however, that the claimed subject matter may be practiced without these specific details. 
     In order to provide better resolution over a potentially wider pressure range than previously available, the techniques disclosed herein set an output precision of an ADC based on a control signal provided by a control element. The control signal sets the output precision of the ADC to a first level to measure an ambient pressure within a first pressure range; and signal sets the output precision of the ADC to a second level to measure an ambient pressure within a second pressure range. 
       FIG. 2  shows a pressure monitoring system  300  in accordance with some embodiments of this disclosure. The pressure monitoring system  300  includes a pressure sensor  302 , a variable gain stage  304 , an ADC  306 , a microcontroller  308 , and a memory  310 ; which are operably coupled as shown. A timer  314 , such as a watch-dog timer, can also be included in some implementations. In one embodiment, the microcontroller  308  utilizes a calibration routine  312  (e.g., in the form of firmware stored in read-only memory or flash memory), wherein the calibration routine  312  selects one of a number of sets of calibration coefficients  313  that is specific to the pressure sensor  302  and devices included for a particular pressure monitoring system (a number of sets of calibration coefficients  313  can be included to accommodate part-to-part variation). In some embodiments, the calibration coefficients  313  are stored in some sort of programmable, but not necessarily re-programmable, memory (e.g., read-only memory, flash). 
     During operation, the pressure sensor  302  outputs an analog signal  316 , wherein a signal level of the analog signal  316  is indicative of an ambient pressure sensed by the pressure sensor  302 . The variable gain stage  304  selectively adjusts the signal level of the analog signal  316  based on a control signal  318  provided by the microcontroller  308 . The ADC  306  then converts the analog signal having a selectively adjusted signal level  320  into an N-bit digital value  322 . Typical values for N are 8, 9, 10, 11, or 12 bits, although N can be any integer number ranging in theory from 1 to infinity. 
     More particularly, if the control signal  318  is in a first state, the gain stage  304  adjusts the signal level of the analog signal  316  according to a first gain, thereby tuning the N-bit output of the ADC  306  to correspond to a first pressure range (e.g., 100 kPa-850 kPa used for commercial vehicles.) If the control signal  318  is in a second state, the gain stage  304  adjusts the signal level of the analog signal  316  according to a second gain, thereby tuning the N-bit output of the ADC  306  to correspond to a second pressure range (e.g., 100 kPa-450 kPa used for passenger vehicles.) In this way, the control signal  318  provides a single pressure monitoring system with sufficient flexibility to be used in a number of different applications. 
       FIG. 3  shows a more detailed example of a 3-bit ADC (e.g., ADC  306  in  FIG. 2 ) consistent with FIG.  2 &#39;s implementation. In this example, a control signal (e.g., control signal  318  in  FIG. 2 ) changes the gain of the ADC between a first state and a second state to measure a first pressure range  402  and a second pressure range  404 , respectively. 
     When the control signal is in the first state during  402 , the gain of the variable gain stage is set to a first level, causing the analog input value of the ADC to range from 0V to 7V 1 /8. Consequently, the eight unique digital output values of the ADC are approximately equally spread over the entire first pressure range  402  (e.g., a first pressure range for commercial vehicles having an ideal tire pressure ranging from 100 kPa-850 kPa). Thus, the first output code can correspond to a pressure measurement of 100 KPa, the second output code can correspond to a pressure measurement of 193.75 kPa, and so on such that the eighth pressure measurement is near the top of the first pressure range (e.g., 850 kPa). 
     When the control signal is in the second state during  404 , the gain of the variable gain stage is set to a second level, causing the analog input value to be “compressed”. In the illustrated example, the ADC now ranges from 0V to 2V 1 /8 V. Consequently, the eight unique digital output values of the ADC are approximately equally spread over the entire second pressure range (e.g., a second pressure range for passenger vehicles having an ideal tire pressure ranging from 100 kPa-450 kPa). Thus, the first output code can correspond to a pressure measurement of 100 KPa, the second output code can correspond to a pressure measurement of 143.75 kPa, the third output code can correspond to a pressure measurement of 187.5 kPa, and so on such that the eighth pressure measurement is near the top of the second pressure range (e.g., 450 kPa). 
     Although  FIG. 3  shows the lower boundary of the ADC at 0V, it will be appreciated that often a monitored pressure range will have a lower boundary of other than 0V. The lower boundary of 0V has been chosen simply for ease of illustration and is in no way limiting. 
       FIG. 4  shows a method  500  consistent with one example carried out by the pressure monitoring system  300  of  FIG. 2 , although this methodology could also be carried out using other pressure monitoring systems. 
     At  502 , a microcontroller (e.g., microcontroller  308  in  FIG. 2 ) can program a timer (e.g., timer  314  in  FIG. 2 ) to assert an interrupt or wakeup signal at a predetermined time. The predetermined time can follow a regularly spaced periodic pattern, or can occur at non-regularly spaced intervals. 
     At  504 , the timer “fires” at the predetermined time and the gain of a variable gain stage (e.g., variable gain stage  304  in  FIG. 2 ) is set to a first level. The first level often corresponds to a first pressure range. 
     At  506  while the gain is set to the first level, a pressure sensor (e.g., pressure sensor  302  in  FIG. 2 ) takes a “raw” analog ambient pressure measurement. 
     At  508 , the ADC transforms the analog signal to a first N-bit digital value while the gain is set to the first level. 
     At  510 , when this first N-bit digital value is read, a first set of calibration coefficients is applied to the first N-bit digital value to account for non-linearities and offset errors in the pressure sensor and/or ADC over the first pressure range (e.g., 100 kPa-450 kPa). In this way, a first calibrated N-bit digital value is provided. Note that there&#39;s no requirement that the number of bits in the calibrated digital value area the same as the number of bits of ADC. For example, in one implementation, the ADC is 10 bits, yet the calibrated value is a 16-bit number. 
     At  512 , the method  500  determines whether the first calibrated N-bit digital value is within the first pressure range. If so (‘YES’ at  512 ), then no further processing is performed, and the method returns to  502  or  504  to wait for the next predetermined time. 
     If the first calibrated measurement falls outside of the first pressure range (‘NO’ at  512 ), then a second pressure measurement is performed in blocks  514 - 520 —this time with a different gain setting for the variable gain stage. Often, the gain setting used during block  514 - 520  is greater than the gain setting used during  504 - 510  (i.e. first pressure range is a subset of the second pressure range). 
     More particularly, at  514 , the gain of the variable gain stage is set to a second level. At  516 , a second “raw” analog ambient pressure measurement is taken with the gain set to the second level. At  518 , the second “raw” analog ambient pressure measurement is transformed into a second N-bit digital value via the ADC. When this second N-bit digital value is read, a second set of calibration coefficients is applied to the second N-bit digital value to account for non-linearities and offset errors in the pressure sensor and/or ADC over a second pressure range (e.g., 100 kPa-850 kPa), as shown in  520 . 
     After  520 , the method analyzes the first and second N-bit digital values, and makes a determination which measured pressure is accurate. The microprocessor then determines whether the measured pressure falls outside of a specified pressure range. If the measured pressure is outside of this specified range, the microcontroller can notify the vehicle operator or take other suitable remedial action to help ensure that the unexpected pressure is suitably dealt with. 
     In some embodiments, rather than always performing two pressure measurements in a fixed sequence, the microcontroller can attempt to use the same pressure range as was determined for the previous ambient pressure measurement. For example, if the microcontroller determines the ambient pressure for one measurement falls within a 100 kPa-450 kPa pressure range, the microcontroller can then take the next ambient pressure measurement under conditions for the same pressure range. With the assumption that the pressure inside the tire is changing slowly over time, the previous range is more often than not the appropriate range for subsequent measurements, also. By taking only a single pressure measurement instead of two pressure measurements, such an implementation reduces power. A second measurement is taken only when the microcontroller determines that the single pressure measurement may be erroneous. 
     Although pressure measurements as described above with regards to  FIG. 4  are taken only at predetermined times, in other embodiments the pressure sensor can monitor continuously without being triggered based on an interrupt or periodic wakeup. However, because pressure often changes relatively slowly and because such continuous monitoring tends to consume more power, an interrupt based or periodic wakeup approach is often more desirable. 
       FIGS. 5-6  show another embodiment wherein a pressure monitoring system includes a comparator  602  in addition to the previously discussed components. Rather than carrying out two separate ambient pressure measurements (e.g., one pressure measurement assuming a first pressure range and a second pressure measurement assuming a second pressure range as in FIG.  3 &#39;s example), the comparator  602  acts as a control element to provide a control signal  604  that notifies the microcontroller whether the ambient pressure is in the first or second pressure range. 
       FIG. 6  shows an example of how a comparator could be used in the context of a 3-bit ADC. The comparator compares the level of the analog signal with a threshold signal. If the control signal is in a first state (e.g., indicating the comparator detected the pressure was less than the threshold), the microcontroller sets the variable gain stage to a first gain level, such that the ADC output codes are spread approximately equally over the first pressure range. If the control signal is in a second state (e.g., indicating the comparator detected the pressure was greater than the threshold), the microcontroller sets the variable gain stage to a second gain level, such that the ADC output codes are spread approximately equally over the second pressure range. Thus, in embodiments consistent with  FIGS. 6-7 , the control signal  604  acts as a flexible control bit. 
       FIG. 8  shows an embodiment of a dual sensor module  700  consistent with some embodiments. The dual sensor module includes a first sensor  702  (e.g., an accelerometer) and a second sensor  704  (e.g., a pressure sensor), although other embodiments can include more than two sensors. To take sensor measurements, the dual sensor module  700  also includes a multiplexer  706 , a variable gain stage  708 , an ADC  710 , a microcontroller  712 , a memory unit  714  and a decoder/state machine  716 . Although the first and second sensors  702 ,  704  are described with respect to an accelerometer and a pressure sensor, respectively, it will be appreciated that any type of sensor can be utilized in accordance with this present disclosure. 
     During operation, the microcontroller  712  provides an N-bit sensor control word on control bus  718  to the decoder/state machine  716 . For example, in one embodiment the N-bit sensor control word can include 5-bits and take the format shown in Table 1: 
     
       
         
               
             
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Sample Sensor control word format 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Bit 5 (sensor type) 
                 0 = acceleration 
               
               
                   
                 1 = pressure 
               
               
                 Bit 4 (pressure range) 
                 0 = low pressure 
               
               
                   
                 1 = high pressure 
               
               
                 Bit 3 (automatic range selection) 
                 0 = manual range selection 
               
               
                   
                 1 = automatic range selection 
               
               
                 Bits 2:1 (ADC gain) 
                 00 = gain 76 
               
               
                   
                 01 = gain 60 
               
               
                   
                 10 = gain 50 
               
               
                   
                 11 = gain 38 
               
               
                   
               
             
          
         
       
     
     Thus, upon the decoder/state machine receiving the control word from the microcontroller, the decoder/state machine can enable the proper blocks to carry out the functionality indicated by the control word. 
       FIG. 8  shows a method illustrating one example of how an N-bit control word can induce functionality in the dual-sensor module consistent with  FIG. 7 . 
     At  802 , the method analyzes the control word to determine the type of sensor to be read. If the method determines an acceleration measurement is to be taken (‘YES’ at  802 ), then the method proceeds to  804  where it sets the gain of the ADC to a first level. Subsequently at  806 , an acceleration measurement is taken by converting the analog voltage from the accelerometer to a digital value while the first gain level is used for the ADC. 
     In contrast if a pressure measurement is to be taken (‘NO’ at  802 ), the method continues to  808  wherein it determines if manual or automatic pressure sensing is to be performed. If manual pressure sensing is selected (‘YES’ at  808 ), the method continues to  810  where the method evaluates whether a low pressure range or a high pressure range is to be read. If the low pressure range is to be read (‘YES’ at  810 ), the ADC gain is set to a second level in  812  after which an analog voltage from the pressure sensor is converted to a digital value using the second ADC gain level at  814 . If the high pressure range is to be read (‘NO’ at  810 ), the ADC gain is set to a third level in  816  after which an analog voltage from the pressure sensor is converted to a digital value using the third ADC gain level at  814 . 
     If automatic pressure sensing is selected (‘NO’ at  808 ), the method progresses to  818  to determine whether a high pressure range or low pressure range is to be read first. If the low range is to be read first (‘YES’) at  818 , the gain level of the ADC is set to a second level at  820 , where the second ADC gain level can be different from the first ADC gain level (at  804 ). In  822 , an analog voltage of the pressure sensor is converted to a digital value. At  824 , the method determines whether the ambient pressure is greater than a high pressure threshold (PTh_High). If not (‘NO’ at  824 ), then the digital value from  822  is believed to be correct and no further measurements are taken, thereby tending to limit power. If so, however (‘YES’ at  824 ), then the method sets the ADC gain to a third level to carry out a high pressure measurement in  826 . In  828 , an analog value is then read and converted into a digital value using the third ADC gain level. 
     If the high pressure range is to be read first (‘NO’ at  818 ), then blocks  830 - 838  are followed. Notably, blocks  838  can utilize a different pressure threshold PTh_Low (wherein PTh_Low is not necessarily the same as PTh_High) to determine whether the high pressure measurement is reliable. 
     Although the disclosure has been shown and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art based upon a reading and understanding of this specification and the annexed drawings. For example, although examples illustrated herein show only two pressure ranges, in other embodiments more than two pressure ranges can be included. Whatever the precise number of pressure ranges included, the pressure ranges can be entirely non-overlapping, partially overlapping, and/or may be spaced apart from one another. The pressure ranges be the same size (e.g., have respective endpoints that share a common difference therebetween) or can be different sizes (e.g., have respectively endpoints that have different differences therebetween). In addition, the range of the ADC range can not only changed by a gain stage, it could also be changed by changing the number of bits N is the digital output value. 
     The disclosure includes all such modifications and alterations and is limited only by the scope of the following claims. In particular regard to the various functions performed by the above described components (e.g., elements and/or resources), the terms used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the disclosure. In addition, while a particular feature of the disclosure may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. In addition, the articles “a” and “an” as used in this application and the appended claims are to be construed to mean “one or more”. 
     Furthermore, to the extent that the terms “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.”