Abstract:
Methods and devices for increasing a sensor resolution are disclosed. In one example, a two measurement process is used. A first measurement is used to effectively measure across a full range (e.g. 0 to 5 VDC) of the sensor. This first measurement may identify the current operating point of the sensor (e.g. 3.5 VDC). A second measurement may then be made to effectively measure across a sub-range of the sensor that encompasses the current operating point of the sensor (e.g. across a sub-range of 3.0 to 4.0 VDC for a current operating point of 3.5 VDC). The gain of the amplifier may be raised during the second measurement to produce a higher resolution measurement. In some cases, the first measurement may be used to determine an appropriate offset that may be applied so as to scale the amplifier to the desired sub-range of sensor that includes the current operating point of the sensor. In some cases, the two measurements may be used together to compute an effectively higher resolution measurement signal. In some cases, this may allow for a smaller and/or cheaper sensor to be used, while still achieving good results.

Description:
FIELD 
     The present disclosure relates generally to sensors, and more particularly, to methods and devices for increasing the resolution of such sensors. 
     BACKGROUND 
     Sensors are commonly used to sense various parameters in a wide variety of applications including, for example, medical applications, flight control applications, industrial process applications, combustion control applications, weather monitoring applications, as well as many other applications. In some applications, users often desire increased sensor resolution in order to resolve smaller sensor signals and/or to control the dynamic range of such sensors. 
     SUMMARY 
     The present disclosure relates generally to sensors, and more particularly, to methods and devices for increasing the resolution of sensors during use. In one example, a two measurement process may be used. A first measurement may be used to effectively measure across a wide or full range (e.g. 0 to 5 VDC) of the sensor at hand, and may be used to identify the current operating point of the sensor (e.g. 3.5 VDC output). A second measurement may be used to measure across a sub-range of the sensor, where the sub-range encompasses the current operating point of the sensor determined during the first measurement (e.g. across a sub-range of 3.0 to 4.0 VDC for a current operating point of 3.5 VDC). The gain of the amplifier may be higher during the second measurement, which may produce a higher resolution measurement signal. To help prevent the amplifier from going out of range, the first measurement may be used to determine an appropriate offset that can be applied to the amplifier to offset the amplifier input to correspond to the desired sub-range that includes the current operating point of the sensor. In some cases, the result of the first measurement and the second measurement may be combined to provide an effectively higher resolution measurement signal from the sensor. In some cases, this may allow a smaller and/or cheaper sensor to be used, while still achieving good results. 
     In some cases, an analog sensor output signal may be received from a sensor. During a first measurement, the analog sensor output signal may be amplified by an amplifier using a first gain to produce a lower resolution amplified analog sensor output signal. To help prevent the amplifier from going out of range during a second measurement, a measure related to the lower resolution amplified analog sensor output signal may be used to determine an offset value, and the offset value may be applied to the analog sensor output signal during the second measurement, resulting in an offset analog sensor output signal. During the second measurement, the offset analog sensor output signal may be amplified using a second gain that is higher than the first gain to produce a higher resolution analog sensor output signal. 
     In some cases, the lower resolution amplified analog sensor output signal may be converted to a lower resolution digital sensor output signal, and stored in a memory. Likewise, the higher resolution analog sensor output signal may be converted to a higher resolution digital sensor output signal and stored in the memory. A composite digital sensor output signal may be computed using the lower resolution digital sensor output signal and the higher resolution digital sensor output signal. 
     An illustrative apparatus may include an variable gain amplifier block that has two or more gain settings. The amplifier block may receive an analog sensor output signal from a sensor. An offset block may selectively apply an offset to the analog sensor output signal when instructed to do so. A controller may be coupled to the amplifying block and the offset block. The controller may cause the amplifier block to amplify the analog sensor output signal using a first gain setting to produce a lower resolution analog sensor output signal. The controller may use a measure related to the lower resolution analog sensor output signal to determine an offset value, and may instruct the offset block to apply the determined offset value to the analog sensor output signal resulting in an offset analog sensor output signal. The controller may then cause the amplifier block to amplify the offset analog sensor output signal using a second gain setting that is higher than the first gain setting to produce a higher resolution analog sensor output signal. 
     The preceding summary is provided to facilitate an understanding of some of the features of the present disclosure and is not intended to be a full description. A full appreciation of the disclosure can be gained by taking the entire specification, claims, drawings, and abstract as a whole. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure may be more completely understood in consideration of the following description of various illustrative embodiments of the disclosure in connection with the accompanying drawings, in which: 
         FIG. 1  is a schematic block diagram of an illustrative apparatus for processing an analog sensor output signal from a sensor; 
         FIG. 2  is a schematic block diagram of an illustrative variable gain amplifier block; 
         FIG. 3  shows a first measurement and a second measurement in accordance with an illustrative method for processing an analog sensor output signal; 
         FIG. 4  is a flow diagram showing an illustrative method for processing an analog sensor output signal; 
         FIG. 5  is a flow diagram showing another illustrative method for processing an analog sensor output signal; 
         FIG. 6  is a flow diagram showing an illustrative method for processing an analog sensor output signal; and 
         FIG. 7  is a block diagram of an integrated circuit. 
     
    
    
     While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the disclosure to the particular illustrative embodiments described herein. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure. 
     DESCRIPTION 
     The following description should be read with reference to the drawings wherein like reference numerals indicate like elements throughout the several views. The description and drawings show several examples that are meant to be illustrative of the claimed disclosure. 
       FIG. 1  is a schematic block diagram of an illustrative apparatus  10  for processing an analog sensor output signal  12  of a sensor  14 . In the illustrative embodiment, the sensor  14  may be any suitable sensor, such as a pressure sensor, a flow sensor, a magnetic proximity sensor, an accelerometer, a gyro or any other suitable sensor. The illustrative sensor  14  shown in  FIG. 1  includes four sense resistors R 1 -R 4  connected in a full Wheatstone bridge configuration, which provides a differential analog sensor output signal  12 . This, however, is just one example sensor configuration, and it is contemplated that any suitable sensor type and/or sensor configuration may be used, as desired. Also, it is contemplated that the sensor  14  may produce a differential or single ended analog sensor output signal, as desired. 
     In the illustrative embodiment of  FIG. 1 , the analog sensor output signal  12  is provided to an “A” channel of a Multiplexer (MUX)  16 . A “B” channel of MUX  16  is shown to be connected to the output of a temperature sensor  18 . During operation, the MUX  16  can select between the “A” channel and the “B” channel, and can pass the selected signal to the input of a pre-amplifier  20 . That is, in the illustrative embodiment of  FIG. 1 , the MUX  16  may pass the analog sensor output signal  12  to the pre-amplifier  20  when the “B” channel is selected, and may pass the output of the temperature sensor  18  to the pre-amplifier  20  when channel “A” is selected. The MUX  16  may be controlled by a controller  24 . 
     In the illustrative embodiment of  FIG. 1 , the pre-amplifier  20  may amplify the analog sensor output signal  12 , often with a relatively low gain (e.g. gain of 1). This may help isolate the sensor  14  from the downstream circuitry. It should be understood that MUX  16 , pre-amplifier  20  and temperature sensor  18  are all optional and not required. Also, and in some instances, other circuitry may be included, such as conditioning circuitry (not shown) that can conditioning the analog sensor output signal  12 , at least to some degree, before providing the signal to a variable gain amplifier  30 . For example, conditioning circuitry may be included to help compensate for non-linearity or other non-desirable properties in the analog sensor output signal  12 . 
     The analog sensor output signal  12  (sometimes after being passed through MUX  16  and/or pre-amplifier  20 ) may be provided to an offset block  22 . In the illustrative embodiment, the offset block  22  may be controlled by an offset control block  40  of the controller  24 . The offset block  22  may be capable of adding a controlled voltage offset to the analog sensor output signal when instructed to by the offset control block  40 , resulting in an offset analog sensor output signal  28 . In one example, offset block  22  may shift the voltage of the analog sensor output signal that is provided to the offset block  22  by adding (or subtracting) a voltage via summing elements  26 , resulting in offset analog sensor output signal  28 . In some cases, the offset control block  40  may shift the analog sensor output signal by zero volts, or by some other voltage as desired. 
     In the illustrative embodiment of  FIG. 1 , the offset analog sensor output signal  28  is provided to the variable gain amplifier  30 . The gain of the variable gain amplifier  30  may be controlled by a gain control block  42  of the controller  24 . It is contemplated that the variable gain amplifier  30  may allow the controller  24  to vary the gain along a range of gain values, or may only allow discrete gain settings. An illustrative embodiment of a variable gain amplifier  30  that allows only discrete gain settings is shown in  FIG. 2 . In this illustrative embodiment, several amplifiers  50   a - 50 C each have their inputs connected to input terminals (Vin) of the variable gain amplifier  30 . Each of the amplifiers  50   a - 50 C has a different gain. For example, amplifier  50   a  has a gain of “X”, amplifier  50   b  has a gain of “2X”, and amplifier  50   c  has a gain of “nX”, where “n” is an integer greater than two. The outputs of the amplifiers  50   a - 50 C are each connected to a separate channel of a multiplexer  52 . A gain select terminal  54 , which may be connected to gain control block  42  of controller  24  (see  FIG. 1 ), may select which of the outputs of the amplifiers  50   a - 50 C are passed to the output terminals (Vout) of the variable gain amplifier  30 . This is just one example implementation of a variable gain amplifier, and it is contemplated that any suitable variable gain amplifier may be used, as desired. 
     Referring back to  FIG. 1 , in some instances, the output of the variable gain amplifier  30  may be passed to an Analog-to-Digital (A/D) Converter  60 . The A/D converter  60  may convert the analog sensor output signal produced by the variable gain amplifier  30  into a digital sensor output signal. In some cases, the A/D converter may have an offset control, which can be controlled by offset control block  40  of controller  24 , but this is not necessary. The digital sensor output signal produced by the A/D converter may be stored in a memory, such memory  62 . In some cases, a conditioning block  64  may be provided to condition the digital sensor output signal before storing the digital sensor output signal into memory. The conditioning block  64  may, for example, help compensate for non-linearity or other non-desirable properties in the digital sensor output signal. In some cases, the conditioning block  64  may receive one or more conditioning coefficients from a memory, such as memory  62  of controller  24 , but this is not required. In the embodiment shown, the controller may receive a compensated digital sensor output signal from the conditioning block  64  and store the result in memory  62 . The controller  24  may then produce an output signal on output terminal  70 . In some cases, a control block  38  of controller  24  may read program instructions from a memory, such as memory  62 , and may execute the program instructions to control the gain control block  42 , offset control block  40  and/or conditioning block  64 , as desired. 
     During operation, the controller  24  may use a two measurement process to achieve an increased resolution signal for the sensor  14 . During a first measurement, the offset control block  40  of the controller  24  may instruct the offset block  22  to add a zero (or low) offset to the analog sensor output signal. The gain control block  42  of the controller  24  may instruct the variable gain amplifier  30  to amplify the resulting signal using a first gain setting (e.g. gain 1-2) to produce a lower resolution analog sensor output signal. A graph  80  illustrating such a first measurement is shown in  FIG. 3 . As shown in  FIG. 3 , and because of the relatively low gain of the variable gain amplifier  30  (e.g. gain=1), the first measurement may be used to effectively measure across a wide or full range (e.g. 0 to 5 VDC) of the sensor  14 , and as such, may be effective at identifying the current operating point  82  of the sensor  14  (e.g. 3.5 VDC output). The controller  24  may then identify and store the current operating point  82  of the sensor  14 . In some cases, A/D converter  60  may convert the lower resolution analog sensor output signal to a lower resolution digital sensor output signal, and the controller  24  may store the lower resolution digital sensor output signal to the memory  62 . This lower resolution digital sensor output signal may itself represent the current operating point  82  of the sensor  14 . 
     A second measurement may then be used to measure across a sub-range of the sensor  14 , where the sub-range encompasses the current operating point  82  of the sensor  14  as determined by the first measurement (e.g. across a sub-range of 3.0 to 4.0 VDC for a current operating point of 3.5 VDC). The gain of the amplifier may be higher during the second measurement, which may thus produce a higher resolution measurement signal. To help prevent the variable gain amplifier  30  from going out of range, the first measurement may be used to determine an appropriate offset that can be applied to focus the variable gain amplifier input on the sub-range of sensor  14  that includes the current operating point  82  of the sensor  14 . 
     More specifically, during the second measurement, the controller  24  may use a measure related to the lower resolution analog sensor output signal to determine an offset value, and may instruct the offset block  22  of the controller  24  to add the determined offset value to the analog sensor output signal, resulting in an offset analog sensor output signal. The gain control block  42  of the controller  24  may then instruct the variable gain amplifier  30  to amplify the newly offset analog sensor output signal using a second gain setting that is higher than the first gain setting (e.g. gain 2-200) to produce a higher resolution analog sensor output signal. 
     A graph  86  illustrating an illustrative second measurement is shown in  FIG. 3 . As shown in  FIG. 3 , the controller  24  focuses the variable gain amplifier input on a sub-range 88 of sensor  14  that includes the current operating point  82  of the sensor  14 . The illustrative sub-range 88 spans across an input voltage range of 3.0 to 4.0 volts, which includes the current operating point  82  of 3.5 volts. In  FIG. 3 , the gain control block  42  of the controller  24  has instructed the variable gain amplifier  30  to amplify the newly offset analog sensor output signal using a gain of five (5) during the second measurement  86 , which is higher than the gain of one (1) used during the first measurement  80 . This increased gain may produce a higher resolution analog sensor output signal. As shown in the example of  FIG. 3 , this higher resolution may reveal that the current operating point  82  is about 3.55 Volts, rather than 3.5 Volts as might be indicated by the first measurement  80 . While a gain of five (5) is used as an example for the second measurement, it is contemplated that any suitable increased gain value may be used (e.g. 2-200). A high gain value will generally result in a narrow sub-range 88. 
     In some cases, A/D converter  60  may convert the higher resolution analog sensor output signal to a higher resolution digital sensor output signal, and the controller  24  may store the higher resolution digital sensor output signal to the memory  62 . A composite digital sensor output signal may be computed using the lower resolution digital sensor output signal and the higher resolution digital sensor output signal. The composite signal may be provided on output terminal  70 . 
       FIG. 4  is a flow diagram showing an illustrative method  100  for processing an analog sensor output signal. The illustrative method begins at  101 , and may include a two measurement process, including a first measurement  102  and a second measurement  104 . During the first measurement  102 , an analog sensor output signal may be received from a sensor, as shown at  106 . Next, the analog sensor output signal may be amplified using a first gain to produce a lower resolution amplified analog sensor output signal, as shown at  108 . 
     During the second measurement  104 , a measure related to the lower resolution amplified analog sensor output signal is used to determine an offset value, as shown at  110 . Next, the offset value may be applied to the analog sensor output signal, resulting in an offset analog sensor output signal, as shown at  112 . Then, the offset analog sensor output signal may be amplified using a second gain that is higher than the first gain to produce a higher resolution analog sensor output signal, as shown at  114 . The illustrative method  100  may then be exited as shown at  116 . 
       FIG. 5  is a flow diagram showing another illustrative method  200  for processing an analog sensor output signal. The illustrative method begins at  201 , and may include a two measurement process, including a first measurement  202  and a second measurement  204 . 
     During the first measurement  202 , an analog sensor output signal may be received from a sensor, as shown at  206 . Next, the analog sensor output signal may be amplified using a first gain to produce a lower resolution amplified analog sensor output signal, as shown at  208 . Next, the lower resolution amplified analog sensor output signal may be converted to a lower resolution digital sensor output signal, as shown at  210 , and store the lower resolution digital sensor output signal to a memory, as shown at  212 . 
     During the second measurement  204 , the lower resolution digital sensor output signal may be used to determine an offset value, as shown at  214 . The offset value may be applied to the analog sensor output signal, resulting in an offset analog sensor output signal as shown at  216 . The offset analog sensor output signal may then be amplified using a second gain that is higher than the first gain to produce a higher resolution amplified analog sensor output signal, as shown at  218 . The higher resolution amplified analog sensor output signal may be converted to a higher resolution digital sensor output signal, as shown at  220 . The higher resolution digital sensor output signal may then be stored to the memory, as shown at  222 . In some cases, a composite digital sensor output signal may be computed using the lower resolution digital sensor output signal of the first measurement  202  and the higher resolution digital sensor output signal of the second measurement  204 . The illustrative method  200  may then be exited as shown at  226 . 
       FIG. 6  is a flow diagram showing an illustrative method  300  for processing an analog sensor output signal. The illustrative method begins at  301 , and may include a two measurement process, including a first measurement  302  and a second measurement  304 . During the first measurement  302 , the gain of an amplifier may be set for a full scale sensor measurement, as shown at  306 . The offset may also be set for a full scale sensor measurement, as shown at  308 . Next, the sensor output may be measured using the above-mentioned gain and offset values, and the result may be converted to a digital value as shown at  310 . 
     During the second measurement  304 , the gain of the amplifier may be changed to a higher value to achieve a higher resolution, as shown at  312 . The full scale digital value measured during the first measurement  302  may be used to compute an offset needed for a higher resolution measurement, as shown at  314 . The offset may then be set accordingly, as shown at  316 . Then, the sensor output may be measured using the higher gain and computed offset value, as shown at  318 . The result may be converted to a digital value. The digital value of the first measurement  302  and the digital value of the second measurement  304  may be combined to achieve an increased resolution signal for the sensor, as shown at  320 . The illustrative method  200  may then be exited as shown at  322 . 
       FIG. 7  is a block diagram of an amplifier block  402 , an offset block  404  and a controller  406  situated on a common integrated circuit  400 . 
     Having thus described various illustrative embodiments of the present disclosure, those of skill in the art will readily appreciate that yet other embodiments may be made and used within the scope of the claims hereto attached. Changes may be made in details, particularly in matters of shape, size, and arrangement of parts without exceeding the scope of the disclosure. The disclosure&#39;s scope is, of course, defined in the language in which the appended claims are expressed.