CN111665200B

CN111665200B - Stable measurement of sensor methods and systems

Info

Publication number: CN111665200B
Application number: CN202010151441.7A
Authority: CN
Inventors: S·德立瓦拉
Original assignee: Analog Devices Inc
Current assignee: Analog Devices Inc
Priority date: 2019-03-06
Filing date: 2020-03-06
Publication date: 2024-04-12
Anticipated expiration: 2040-03-06
Also published as: CN111665200A

Abstract

The present disclosure relates to stable measurements of sensor methods and systems. The present disclosure provides gain independent reference channel measurement systems and methods. Methods of making robust, stable measurements in a variety of different applications are disclosed. More specifically, the present disclosure describes systems and methods related to performing gain independent reference channel measurements by making two phase measurements of a device under test. Mathematically, the measurements are merged together and many common mode parameters are lost. The result is an analysis of the device under test analysis that reduces errors due primarily to changes in circuit behavior due to environmental changes and signal input fluctuations.

Description

Stable measurement of sensor methods and systems

Cross Reference to Related Applications

This application is in accordance with 35U.S. c. ≡119 (e) for the benefit of priority of U.S. provisional patent application No.62/814,291 entitled "stable measurement of sensor method and system" filed on 3 month 6 of 2019, and for U.S. utility patent application No.16/181,878 entitled "compact optical smoke detector system and apparatus" filed on 11 month 6 of 2018, U.S. utility patent application No.16/699,677 entitled "flame detection system" filed on 12 month 1 of 2019, U.S. utility patent application No.14/500,129 entitled "low frequency noise improvement in plethysmography measurement system" filed on 9 month 29 of 2014, U.S. utility patent application No.15/993,188 entitled "compact optical gas detection system and apparatus" filed on 5 month 30 of 2018, U.S. utility patent application No.16/699,677 entitled "temporary gas detection using differential path length measurement filed on 10 month 10 of 2019, and is incorporated herein by reference in its entirety.

Technical Field

The present disclosure relates to methods of making stable measurements in a variety of different applications. More particularly, the present disclosure describes systems and methods related to performing gain independent reference channel measurements and applications thereof.

Background

The reference channel measurements are system measurements performed in parallel with measurements of the Device Under Test (DUT). The reference channel measurement is used as a control measurement to be used in comparison to a Device Under Test (DUT) measurement. Theoretically, environmental changes and signal changes should affect both measurement paths equally. For this reason, the difference between the Device Under Test (DUT) path and the reference channel measurement path should reflect only the change in stimulus. Thus, the circuit can be calibrated after assembly to compensate for differences in measurement paths.

However, the inventors of the present invention have found that this is not complete, especially when attempting sensitive measurements. In particular, environmental changes and signal changes (e.g., nonlinearities caused by high currents, etc.) can affect the individual gain amplifiers differently. Thus, the measurement accuracy of a Device Under Test (DUT) may sometimes be compromised in order of magnitude. Thus, there is a long felt need for a reference channel measurement that can be implemented with only nominal architectural modifications.

The inventors of the present disclosure have discovered these drawbacks and recognized a need for new reference channel measurement techniques that are more stable and superior to conventional reference channel measurements. That is, reliable reference channel measurements take into account not only common mode variations but also gain differences between amplifiers.

This disclosure is intended to provide an overview of the subject matter of the present patent application. It is not intended to provide an exclusive or exhaustive explanation of the invention. Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.

Disclosure of Invention

Gain independent reference channel measurement systems and methods. Methods of making robust, stable measurements in a variety of different applications are disclosed. More specifically, the present disclosure describes systems and methods related to performing gain independent reference channel measurements by making two phase measurements of a device under test. Mathematically, the measurements are merged together and many common mode parameters are lost. The result is an analysis of the device under test analysis that reduces errors due primarily to changes in circuit behavior due to environmental changes and signal input fluctuations.

According to one aspect of the present disclosure is an apparatus for an analog signal processing circuit having at least two amplifiers connected by a switch that allows the amplifiers to be connected to either input in series.

According to another aspect, these measurements of the two sensors are performed consecutively, such that in a first instance the first amplifier is connected to the first sensor and the second amplifier is connected to the second sensor. And according to a second example, the first amplifier is connected to the second sensor and the second amplifier is connected to the first sensor. These measurements are then combined to provide a measurement that depends only on the relative sensor response and not on the amplifier gain.

According to one aspect of the present disclosure, an Analog Front End (AFE) is used as an analog signal processing circuit.

According to one or more aspects of the present disclosure, AFE is used to measure a plethysmographic (PPG) signal, where two photodiodes are placed at two different distances, both photodiodes measuring light passing through tissue.

According to one or more aspects of the present disclosure, the AFE is used to measure the PPG signal placing two photodiodes such that one photodiode directly monitors the LED and the other photodiode measures the light passing through the tissue.

According to one or more aspects of the present disclosure, AFE is used to measure optical signals, wherein the LEDs or excitation light sources are monitored by electrical measurement using their current through electrical measurement, while optical signals are measured by photodiodes.

According to one or more aspects of the present disclosure, AFE is used to measure impedance, where the test impedance is measured directly relative to a standard impedance or a reference impedance.

According to one or more aspects of the present disclosure, AFE is used to measure light attenuation from smoke and other scattering particles placed between the light source and the detector.

According to one or more aspects of the present disclosure, the AFE is used to measure light changes due to distance changes from the light source to the detector.

According to one or more aspects of the present disclosure, the AFE is used to measure absorption changes due to changes in absorber concentration in which the sensing channel and the reference channel are at two different distances from the light source.

The figures illustrate exemplary stable, robust methods for measuring sensors in a variety of applications and configurations thereof. Variations of such circuits, such as changing the position of certain elements in the circuit, adding or removing certain elements, do not depart from the scope of the invention. The stability measurement circuit arrangement and configuration shown is intended to be complementary to the support found in the detailed description.

Drawings

The disclosure will be best understood from the following detailed description when read in connection with the accompanying drawings. It is emphasized that, in accordance with the standard practice in the industry, various features are not necessarily drawn to scale and are used for illustration purposes only. Where the scale is explicitly or implicitly displayed, it provides only one illustrative example. In other embodiments, the dimensions of the various features may be arbitrarily increased or decreased for clarity of discussion.

For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description of the preferred embodiment taken in conjunction with the accompanying drawings in which:

fig. 1 illustrates an exemplary optical reference channel monitoring circuit in a first mode according to some embodiments of the disclosure provided herein.

Fig. 2 illustrates an exemplary optical reference channel monitoring circuit in another mode according to some embodiments of the disclosure provided herein.

FIG. 3 illustrates an exemplary reference channel monitoring circuit in impedance variation (complex or otherwise) in accordance with some embodiments of the disclosure provided herein;

fig. 4 illustrates an exemplary reference channel monitoring circuit within a hybrid reference channel, in which the sensing measurement signal is optical and the reference signal is electrical, according to some embodiments of the disclosure provided herein.

Fig. 5 illustrates an exemplary optical reference channel monitoring circuit within the context of another application in accordance with some embodiments of the disclosure provided herein.

Fig. 6 illustrates an exemplary optical reference channel monitoring circuit within an application of yet another application in accordance with some embodiments of the disclosure provided herein;

fig. 7 illustrates a side view of an exemplary optical gas detection measurement system according to some embodiments of the disclosure provided herein.

Fig. 8 depicts a side view of an exemplary differential gas detection system according to some embodiments of the present disclosure provided herein.

Detailed Description

The following description and the annexed drawings set forth in detail certain illustrative embodiments of the disclosure, indicating several exemplary ways in which the various principles of the disclosure may be implemented. However, the illustrative examples are not exhaustive of the many possible embodiments of the disclosure. Other objects, advantages and novel features of the disclosure are set forth in the drawings which follow, where applicable.

A new reference channel measurement technique is disclosed that is more stable and superior to conventional reference channel measurements. Many sensing modes require stimulation of a Device Under Test (DUT) with light or electromagnetic radiation or voltage or current and measurement of the response. The change in response is representative of a change in the sensor environment. Examples include optical measurements due to potential material property changes, transmittance or reflectance changes, material impedance changes as a function of temperature and/or some other environmental parameter.

This list of applications is numerous. In many of these cases, it is important to ensure that the measurement value does not depend on gain changes in the electronic signal processing or stimulus intensity changes due to temperature or voltage changes.

The traditional way to make these measurements in a more stable manner is to use a reference channel. This will now be discussed in the context of the present disclosure. Fig. 1 illustrates an exemplary optical reference channel monitoring circuit 100 in a first mode according to some embodiments of the disclosure provided herein.

Optical reference channel monitor circuit 100 includes a Light Emitting Diode (LED) 105, a function generator 110, a Device Under Test (DUT) 125, a detector 135, a reference detector 140, a sense amplifier 150, and a reference amplifier 145.

Function generator 110 is an electronic test device or software for generating different types of electrical waveforms over a wide range of frequencies. Some of the most common waveforms generated by function generators are sine waves, square waves, triangular waves, and saw-tooth shapes. These waveforms may be repeated or single-shot (requiring an internal or external trigger source). In one or more embodiments, function generator 110 is a current source configured to generate square wave pulses 155. However, any type of current and/or voltage source is not beyond the scope of the present disclosure. Furthermore, it is not necessary to generate a specific signal. Reproducibility is the goal to achieve the desired result.

The current from the function generator 110 flows through a Light Emitting Diode (LED) 105. In turn, light Emitting Diodes (LEDs) 105 produce light, some of which (light 105) impinges on a Device Under Test (DUT) 125, while other light 120 is received directly at a reference detector 140. The specificity of the Device Under Test (DUT) 125 depends on the application. Some applications will be discussed in more detail later in this disclosure. For the present exemplary embodiment, the Device Under Test (DUT) 125 is an abstraction whose light output 130 depends on the received light 105.

The sensing detector 135 receives the light output 130. In one or more embodiments, the sensing detector 135 and the reference detector 140 are photodetectors. The photodetectors are sensors of light or other electromagnetic energy. The photodetector has a p-n junction that converts photons into a current. The absorbed photons form electron-hole pairs in the depletion region for detecting the received light intensity. In some embodiments, the photodetector is a photodiode or phototransistor. However, any light detection device, such as an avalanche, photomultiplier tube, etc., is not beyond the scope of the present disclosure.

In one or more embodiments, the LED 105 is a ready-made green (495 nm-570 nm) light emitting diode. However, any suitable compact lighting device, whether coherent, incandescent, or thermal blackbody radiation, etc., is not beyond the scope of this disclosure.

In an embodiment of the present invention, the stimulus or light 115, 120 emitted from a light source, such as an LED 105, is measured in two ways. After interacting with the DUT 125 that forms a sense channel at the sense detector 135, a portion of the stimulus (light) is measured. At the same time, the same stimulus (light 120) forming the reference channel is measured directly at the reference detector 140.

These two metrics can be written as:

here, I _l Is a current excitation with an efficiency eta _l Converts into light and then interacts with the DUT through H _dut Switching excitation, then using sensitivity R ₃ Is converted back to the electrical domain and then processed by an electronic circuit with a gain G. Similar measurements were made using the reference channel. Obviously, the ratio is taken such that it is not affected by variations in the stimulus itself. The following is shown:

since the measure of interest is the first term in bracketsChanges, i.e. G _dut And thus the variation of the other two bracket terms must be minimized or eliminated. The present disclosure proposes a method of eliminating the last bracket and allowing the measurement and ratio Unrelated methods will now be discussed in more detail.

Fig. 2 illustrates an exemplary optical reference channel monitoring circuit in another mode according to some embodiments of the disclosure provided herein. The optical reference channel monitor circuit 200 includes a Light Emitting Diode (LED) 205, a function generator 210, a Device Under Test (DUT) 225, a sense detector 235, a reference detector 240, a switch structure 260, a sense amplifier 250, and a reference amplifier 245.

Similarly, as previously described, function generator 210 is a piece of electronic testing equipment or software that generates different types of electrical waveforms over a wide range of frequencies. Some of the most common waveforms generated by function generators are sine waves, square waves, triangular waves, and saw-tooth shapes. These waveforms may be repeated or single-shot (requiring an internal or external trigger source). In one or more embodiments, function generator 210 is a current source configured to generate square wave pulses 155. However, any type of current and/or voltage source is not beyond the scope of the present disclosure. Furthermore, it is not necessary to generate a specific signal. Reproducibility is the goal to achieve the desired result.

The current from function generator 210 flows through Light Emitting Diode (LED) 205. In turn, light Emitting Diodes (LEDs) 205 generate light, some of which (light 205) impinges on a Device Under Test (DUT) 225, while other light 220 is received directly at a reference detector 240. The specificity of the Device Under Test (DUT) 225 depends on the application. Some applications will be discussed in more detail later in this disclosure. For the present exemplary embodiment, the Device Under Test (DUT) 225 is an abstraction whose light output 230 depends on the received light 205.

In one or more embodiments, the switching structure 260 includes one or more transistors configured to cross-switch at predetermined times, which may or may not be coordinated with the input signal 255. A transistor is a semiconductor device for amplifying or switching an electronic signal and power. It is composed of a semiconductor material and typically has at least three terminals for connection to external circuitry. The voltage or current applied to the terminals of one pair of transistors controls the current through the other pair of terminals.

Transistors that can be used include Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) and bipolar junction transistors (bipolar transistors or BJTs), which are transistors that use both electrons and holes as charge carriers. A MOSFET is an Insulated Gate Field Effect Transistor (IGFET) that can be manufactured by controlled oxidation of a semiconductor, typically silicon. However, any transistor or digital circuit would not be beyond the scope of the present disclosure.

In some embodiments, the switching structure 260 is a switching circuit known in the art. In other embodiments, the switch structure 260 is an analog multipole relay. In practice, the switching structure 260 directs the signal received from the sense detector 235 to either the sense amplifier 250 or the reference amplifier 245. Similarly, the switch structure 260 directs the signal received from the reference detector 240 to either the sense amplifier 250 or the reference amplifier 245. Cross-coupling will be discussed later in this disclosure.

The sensing detector 235 receives the light output 230. In one or more embodiments, the sensing detector 235 and the reference detector 240 are photodetectors. The photodetectors are sensors of light or other electromagnetic energy. The photodetector has a p-n junction that converts photons into a current. The absorbed photons form electron-hole pairs in the depletion region for detecting the received light intensity. In some embodiments, the photodetector is a photodiode or phototransistor. However, any light detection device, such as an avalanche, photomultiplier tube, etc., is not beyond the scope of the present disclosure.

In embodiments of the present invention, the stimulus or light 215, 220 emitted from the light source (e.g., LED 205) is measured in two ways. After interacting with the DUT 225 that forms a sense channel at the sense detector 235, a portion of the stimulus (light) is measured. At the same time, the same stimulus (light 220) forming the reference channel is measured directly at the reference detector 240.

For the sake of illustration in practice, an optical measurement embodiment is taken as an example, but the idea is more generally applicable. From the broadest perspective, this is done by at least two-phase measurement to divide out all common mode variations in the measurement system path, including variations in the Signal Conditioning Circuit (SCC). Fig. 2 extends on the basis of fig. 1 and illustrates how this can be achieved.

This is done in two steps. In the first phase of the measurement sequence, the switch connects the sense channel to gain G _A And the reference channel is connected to an amplifier having a gain G _B Is provided. From equation (1) above, the following can be rewritten:

in the second phase of the measurement, the excitation occurs again, but the switch is moved to the crossover position so that the sense channel is now connected to gain G _B Is connected to G _A . This results in:

from these two measurements, a combination can be formed to eliminate excitation variations as in conventional reference channel based measurements, as well as to eliminate the gain of the amplifier. This is accomplished by:

this simple operation gives great advantages in signal measurement, since it relieves the signal processing AFE from the very high gain stability burden. Typically, the two phases of measurement are performed in rapid succession. This method can be highly suppressed even if the gain varies between the two measurements. Let δG be the small change in amplifier gain between two consecutive measurements. The simple algebra will then show that the error in ρ is:

the error term may be less than 10 ^-5 Because the gain δG change may be less than 10 in a short time between phases ^-3 And for nominally matched gains,items may also be less than 1%. This shows that the measurement method is very reliable.

Even though reference channel measurements are very popular and are typically performed at the system level or at the circuit board level, even at the instrument level, as a new built-in technology, the circuit architecture provides a novel approach that can provide better, more efficient reference channel measurements. It eliminates concerns over long-term drift of the amplifier and circuit that can be used in systems requiring long-term stability, such as smoke detectors, gas absorption sensors, optical tissue measurements, sensors that can change impedance according to the environment (e.g., temperature, humidity, etc.).

In practice, the standard may be provided by providing at the time of calibrationTo calibrate some of the terms in equation (5). Then the new ratio:

thus, the method facilitates direct comparison of the measured value with the standard.

This method can be applied more widely than the previous embodiments above. Fig. 3 illustrates the application of this method in very high precision and stability resistance (or impedance) measurements.

Fig. 3 illustrates an exemplary reference channel monitoring circuit 300 in an impedance variation (complex or otherwise) in accordance with some embodiments of the disclosure provided herein. Reference channel monitor circuit 300 includes an input node 365, a sense impedance 370, a reference impedance 375, a switching structure 360, a sense amplifier 350, and a reference amplifier 345.

In one or more embodiments, the switching structure 360 includes one or more transistors configured to cross-point the switch at a predetermined time, which may or may not be coordinated with the input signal 355. Transistors that can be used include Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) and bipolar junction transistors (bipolar transistors or BJTs), which are transistors that use both electrons and holes as charge carriers.

In some embodiments, the switching structure 360 is a switching circuit known in the art. In other embodiments, the switch structure 360 is an analog multipole relay. In practice, the switching structure 360 directs the signal received from the sense detector 335 to either the sense amplifier 350 or the reference amplifier 345. Similarly, the switch structure 360 directs the signal received from the reference detector 340 to either the sense amplifier 350 or the reference amplifier 345.

In this case, the light source is replaced with a voltage stimulus on node 365 and the current is measured directly. In this case, the ratio is directly:

in fig. 4, a "hybrid" reference channel measurement is demonstrated in implantation and practice. The sensing is optical, while the reference channel is electrical. Fig. 4 illustrates an exemplary reference channel monitoring circuit 400 within a hybrid reference channel, in which the sensing measurement signal is optical and the reference signal is electrical, according to some embodiments of the disclosure provided herein.

The electrical reference channel monitor circuit 400 includes a Light Emitting Diode (LED) 405, a function generator 410, a Device Under Test (DUT) 425, a series resistance 480, a sense detector 435, a reference circuit (capacitor 485 and reference resistance 490) switching structure 460, a sense amplifier 450, and a reference amplifier 445.

A small series resistor 480 is added in series with the LED (or laser) 405 and the voltage (V) is measured on it _ref ) Thereby measuring the current. Fig. 4 shows resistor 480 near the power supply (not shown) of LED 405, and then "converts" this small voltage back to current input through dc blocking capacitor 485 and series reference resistor 490.

It can thus be connected via the switching structure 460 to the same amplifier as the photodiode input amplifier. Sense resistor r _led 480 may also be placed near ground. In the case of fig. 4, the reference channel will "cancel" the variation in the driver current, but will not "cancel" the variation due to the LED 405 itself. This ratio is approximately given by the following formula (more accurate expressions including capacitance etc. can be written more easily, while omitting the capacitor c _s The basic idea can be easily explained):

some practical, non-exhaustive applications of this idea will now be discussed.

Application 1: ultra-stable intensity measurement of reflection, transmission, absorption and scattering

This is shown in fig. 5 with flue gas measurements. Fig. 5 illustrates an exemplary optical reference channel monitoring circuit within the context of another application according to some embodiments of the disclosure provided herein.

The reference channel monitor circuit 500 includes a Light Emitting Diode (LED) 505, a function generator 510, a sensing detector 535, a reference detector 540, and a blocking element 585. Those skilled in the art will appreciate that some circuit elements are omitted, but the principles are the same as in one or more of the foregoing embodiments.

In fact, some of the light 575 generated by the Light Emitting Diode (LED) 505 passes through the aperture defined by the blocking element 585. Some light 575 is scattered 590 from smoke particles 595. And, some light 575 proceeds unimpeded and is received at inductive detector 535. One or ordinary skill recognizes this embodiment as an occlusion sensor. Other light 520 generated by a Light Emitting Diode (LED) 505 is incident on a reference detector 540.

Smoke particles 595 between detector 535 and LED 505 cause a decrease in light intensity by scattering light 590. Typical smoke alarm thresholds may be as low as 1%/ft-or smoke may result in a 1% attenuation of light for a one foot path length. A path length of 1 cm (which makes the device very compact) means that we need to be at 10 ^-4 Is measured at the level of (a). This is not very difficult-maintaining SNR 80dB. It is difficult to maintain the stability of the amplifier, LED, etc. at this level so that heat and other environmental parameters do not cause the measured value to drift. Also, the presented technology enables such measurements in compact sensors.

This stability can be used to measure small changes in distance by using the fact that the intensity and strength decrease with distance. Again, this requires that all other environmental parameter variations be suppressed.

Application 2: PPG measurement

Photoplethysmograph (PPG) is an optically acquired plethysmograph that can be used to detect blood volume changes in tissue micropipettors. PPG is typically obtained by using a pulse oximeter that illuminates the skin and measures the change in light absorption. Traditional pulse oximeters monitor blood perfusion to the dermis and subcutaneous skin tissue.

Fig. 6 illustrates an exemplary optical reference channel monitoring circuit within an application of yet another application in accordance with some embodiments of the disclosure provided herein. The reference channel monitor circuit 600 includes a Light Emitting Diode (LED) 605, a sensing detector 635, and a reference detector 640. Those skilled in the art will appreciate that some circuit elements have been omitted, but the principles remain the same as in one or more of the previous embodiments.

In effect, light Emitting Diode (LED) 605 produces light 620, which in turn is emitted from a predetermined chemical (e.g., spO) within the subject's (patient) tissue ₂ ) Zhongsan (Chinese character) powderAnd (5) emitting. Subsequently, depending on the scatter trajectory and the mean free path, scattered light 690 is detected by reference detector 640 or sensing detector 635. This is a function of the wavelength of light and chemical interactions known in the art.

In one or more embodiments, a separate photodiode may be deployed as a reference channel to eliminate low frequency variations in the LED output due to temperature and power supply variations. Since the beating frequency of the heart is about 1Hz, this low frequency method of eliminating LED variations and gain variations can achieve a higher SNR even though the use of a noisy power supply typically adds much noise and system variations at low frequencies.

In another embodiment associated with fig. 6, two photodiodes may be used, one of which is closer to the LED designated as the reference PD, and the other photodiode is used as the signal PD.

In this case, even the variation of the light of the LEDs coupled to the tissue will become common mode and be eliminated. This will allow more accurate measurement of the scattering and absorption of the tissue.

Application 3: gas absorption rate measurement

Fig. 7 illustrates a side view of an exemplary optical gas detection measurement system 700 according to some embodiments of the disclosure provided herein. The optical gas detection measurement system 700 includes a substrate 720, LEDs 710, a reflective surface 780, a cap 760, a cover 970, a photodetector 740, a photodetector 750, and a spacer 730.

In practice, the gas detection proceeds as follows. LED 750 produces light, some of which enters a gas chamber defined by reflective surface 780. Another portion of the light is at least partially directly incident on the photodetector 740 that serves as the aforementioned reference channel. Cap 760 is a packaging option. In one or more embodiments, the cap 760 includes a plenum defined by the boundary of the reflective surface 780. Typically, the plenum includes inlet and outlet apertures (not shown) to allow gas to pass through the plenum.

In some embodiments, cap 760 is a surface of three-dimensional conical cross-sectional shape, such as an oval or parabolic shape. However, other shapes are not beyond the scope of the present invention. For example, a two-dimensional conical cross-section (from the side shown) is nearly as effective in detection. Still further, one side may be a simple plane oriented at a 45 degree angle relative to photodetector 750. In practice, light will be reflected twice on average before passing through the gas cell before being detected by the photodetector 750.

Spacer 730 is disposed between LED 710 and photodetector 750 such that light does not pass directly through photodetector 750. In this embodiment, photodetector 750 is at least partially a sensing detector as described above. In one or more embodiments, the cover 770 may be used to simplify packaging. In other cases, the cover 770 may be an optical filter as known in the art.

Fig. 8 depicts a side view of an exemplary differential gas detection system 800 according to some embodiments of the present disclosure provided herein. Differential gas detection system 800 includes a substrate, LEDs 810, reflective surfaces 880, 890, photodetectors 840, photodetectors 850, and spacers 830.

In practice, differential gas detection proceeds as follows. The LED 810 generates light, a primary path 860 and a reference path 870, which enter the plenum. Similar to that previously described, the air cells are defined by the boundaries of the reflective surfaces 880, 890. Typically, the plenum includes inlet and outlet apertures (not shown) to allow gas to pass through the plenum.

In some embodiments, the reflective surfaces 880, 890 may be surfaces of three-dimensional conical cross-sectional shape, such as ellipsoids or paraboloids. However, other shapes are not beyond the scope of the present invention. For example, a two-dimensional conical cross-section (from the side shown) is nearly as effective in detection. Still further, one side may be a simple plane oriented at a 45 degree angle relative to photodetector 850. In practice, the light (primary path 860) will be reflected twice on average before passing through the plenum and then detected by the photodetector 850. The reference path 870 will reflect only once before the photodetector 840 detects the reference path 870.

The spacers 830 are provided to prevent direct illumination of the photodetectors 840, 850. In this embodiment, photodetector 850 is the aforementioned sensor, and photodetector 840 is at least in part a reference detector for the signal and amplifier. In some embodiments, filters known in the art may be disposed near the LEDs 810.

Our differential absorption measurement application illustrates this. Those of ordinary skill in the art will appreciate that the reference path 870 will inherently have a shorter path length than the main path 860. This is a known (or determined) path length difference that is used to calculate the light absorption of a predetermined gas having a corresponding wavelength spectrum.

Selection example

Example 1 provides an apparatus for performing gain independent reference channel measurements, the apparatus comprising: a first circuit configured to measure stimulus passing through the test subject; a first amplifier; a second circuit configured to measure stimulus that fails the test volume; a second amplifier; and a switching circuit in electrical communication with the first circuit, the second circuit, the first amplifier, and the second amplifier.

In a first example, the switching circuit is configured to change between: a first mode, wherein the first circuit is in electrical communication with the first amplifier and the second circuit is in electrical communication with the second amplifier; and a second mode, wherein the first circuit is in electrical communication with the second amplifier and the second circuit is in electrical communication with the first amplifier.

Example 2 provides the apparatus of example 1, wherein the first circuit comprises a sensor.

Example 3 provides the device of examples 1-2, wherein the sensor is a photodetector.

Example 4 provides an apparatus according to any one or more of the preceding examples, wherein the second circuit comprises a photodetector.

Example 5 provides the apparatus according to any one or more of the preceding examples, further comprising a light source to generate the stimulus.

Example 6 provides the apparatus of example 5, wherein the light source is an LED.

Example 7 provides an apparatus according to any one or more of the preceding examples, further comprising a current source.

Example 8 provides the apparatus of example 7, wherein the current source is configured to generate the predetermined waveform in both the first mode and the second mode.

Example 9 provides the apparatus according to any one or more of the preceding examples, further comprising an Analog Front End (AFE) configured to compare outputs from the first gain amplifier and the second gain amplifier in the first and second modes.

Example 10 provides an apparatus according to any one or more of the preceding examples, wherein the first circuit comprises a transducer.

Example 11 provides the apparatus according to any one or more of the preceding examples, wherein the test object is a device under test whose impedance is measured by the stimulus.

Example 12 provides the apparatus of any one or more of the preceding examples, wherein the test object is a test volume.

Example 13 provides the device according to any one or more of the preceding examples, wherein the test object is a subject.

Example 14 provides a method for making gain independent reference channel measurements, comprising: measuring a stimulus passing through a test object at a first circuit, measuring a stimulus failing the test volume at a second circuit, receiving measurements from the first and second circuits at a switching circuit, in a first mode, outputting first and second measurements from the switching circuit to first and second amplifiers, respectively, switching the switching circuit, and in a second mode, outputting first and second measurements from the switching circuit to the second and first amplifiers, respectively.

Example 15 provides the method of example 14, further comprising amplifying the first and second measurements in the first and second amplifiers, respectively, during the first mode.

Example 16 provides the method according to any one or more of the preceding examples, further comprising amplifying the first and second measurements in the second and first amplifiers, respectively, during the second mode.

Example 17 provides the method according to any one or more of the preceding examples, further comprising calculating the ratio based at least on measurements amplified during the first and second modes.

Example 18 provides the method according to any one or more of the preceding examples, further comprising determining the presence of a predetermined substance based on the calculated ratio.

Example 19 provides the method of example 18, wherein the substance is smoke particles.

Example 20 provides the method of example 18, wherein the substance is a biochemical.

Example 21 provides the method of example 18, wherein the substance is an inorganic chemical.

Example 22 provides the method of example 18, wherein the substance is an organic chemical agent.

Example 23 provides a method according to any one or more of the preceding examples, wherein the first circuit comprises a sensor.

Example 24 provides the method of example 23, wherein the sensor is a photodetector.

Example 25 provides the method according to any one or more of the preceding examples, wherein the second circuit comprises a photodetector.

Example 26 provides the method according to any one or more of the preceding examples, further comprising illuminating the light source.

Example 27 provides the method of example 26, wherein the light source is an LED.

Example 28 provides the method of example 27, further comprising providing a current through the LED.

Example 29 provides the method according to any one or more of the preceding examples, further comprising generating a predetermined waveform during both the first and second modes.

Example 30 provides the method of example 17, wherein the ratio is calculated using an Analog Front End (AFE) configured to compare outputs from the first gain amplifier and the second gain amplifier in the first and second modes.

Example 31 provides the method according to any one or more of the preceding examples, wherein the test object is a test volume.

Example 32 provides the method according to any one or more of the preceding examples, wherein the test subject is a subject.

Example 33 provides an apparatus for performing gain independent reference channel measurements, comprising: means for measuring, at the first circuit, stimulation through the test subject; means for measuring at the second circuit a stimulus that fails the test volume; means for receiving measurements from the first and second circuits at a switching circuit; in a first mode, means for outputting first and second measurements from the switching circuit to first and second amplifiers, respectively; means for switching the switching circuit; and in a second mode, means for outputting the first and second measurements from the switching circuit to the second and first amplifiers, respectively.

Having thus described several aspects and embodiments of the technology of this application, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the technology described herein. For example, various other means and/or structures for performing a function and/or obtaining a result and/or one or more of the advantages described herein will be apparent to one of ordinary skill in the art, and each of such variations and/or modifications is deemed to be within the scope of the embodiments described herein.

Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, embodiments of the invention may be practiced otherwise than as specifically described. In addition, if two or more features, systems, articles, materials, kits, and/or methods described herein are not mutually inconsistent, any combination of these, systems, articles, materials, kits, and/or methods may be included within the scope of the present disclosure.

The foregoing outlines features of one or more embodiments of the subject disclosed herein. These embodiments are provided so that those of ordinary skill in the art (PHOSITA) will be better able to understand the various aspects of the present disclosure. Without detailed description, certain well-understood terms, as well as basic techniques and/or standards, may be referenced. It is contemplated that PHOSITA will possess or have access to background knowledge or information in those techniques and standards sufficient to practice the teachings of the present disclosure.

PHOSITA will appreciate that they can readily use the present disclosure as a basis for designing or modifying other processes, structures or variants to achieve the same purposes and/or achieve the same advantages of the embodiments described herein. PHOSITA will also recognize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.

The above embodiments may be implemented in any of a variety of ways. One or more aspects and embodiments of the present application relating to the execution of a process or method may utilize program instructions executable by a device (e.g., a computer, processor, or other device) to perform or control the execution of the process or method.

In this regard, the various inventive concepts may be embodied as a computer readable storage medium (or multiple computer readable storage media) (e.g., a circuit configuration or other tangible computer storage medium in a computer memory, one or more floppy disks, optical tapes, flash memories, field programmable Gate arrays or other semiconductor devices) encoded with one or more programs that, when executed on one or more computers or other processors, perform methods that implement one or more of the various embodiments described above.

One or more computer-readable media may be removable, such that one or more programs stored thereon may be loaded onto one or more different computers or other processors to implement various aspects as discussed above. In some embodiments, the computer readable medium may be a non-transitory medium.

Note that the activities discussed above with reference to the figures apply to any integrated circuit that involves signal processing (e.g., gesture signal processing, video signal processing, audio signal processing, analog-to-digital conversion, digital-to-analog conversion), particularly those that may execute dedicated software programs or algorithms, some of which may be associated with processing digitized real-time data.

In some cases, the teachings of the present disclosure may be encoded in one or more tangible, non-transitory computer-readable media having stored thereon executable instructions that, when executed, instruct a programmable device (e.g., a processor or DSP) to perform the methods or functions disclosed herein. Where the teachings herein are at least partially embodied in a hardware device (e.g., an ASIC, IP block, or SoC), a non-transitory medium may include a hardware device programmed with logic to perform the methods or functions disclosed herein. The teachings may also be practiced in the form of Register Transfer Level (RTL) or other hardware description languages such as VHDL or Verilog, which may be used to program a manufacturing process to produce the disclosed hardware elements.

In example embodiments, at least some portions of the processing activities outlined herein may also be implemented in software. In some embodiments, one or more of these features may be implemented in hardware provided external to the elements of the disclosed figures, or combined in any suitable manner to achieve the intended functionality. The various components may include software (or shuttle software) that may coordinate to achieve the operations outlined herein. In other embodiments, these elements may include any suitable algorithms, hardware, software, components, modules, interfaces, or objects that facilitate the operation thereof.

Any suitably configured processor component may execute any type of instructions associated with the data to implement the operations detailed herein. Any of the processors disclosed herein may convert an element or article (e.g., data) from one state or thing to another state or thing. In another example, some of the activities outlined herein may be implemented with fixed logic or programmable logic (e.g., software and/or computer instructions that are executed by a processor), and the elements identified herein could be some type of programmable processor, programmable digital logic (e.g., an FPGA, an Erasable Programmable Read Only Memory (EPROM), an Electrically Erasable Programmable Read Only Memory (EEPROM)), an ASIC that includes digital logic, software, code, electronic instructions, flash memory, optical disks, CD-ROMs, DVD ROMs, magnetic or optical cards, other types of machine-readable media suitable for storing electronic instructions, or any suitable combination thereof.

In operation, the processor may store information in any suitable type of non-transitory storage medium (e.g., random Access Memory (RAM), read Only Memory (ROM), FPGA, EPROM, electrically Erasable Programmable ROM (EEPROM), etc.), software, hardware, or any other suitable component, device, element, or object where appropriate and according to particular needs. Furthermore, the information being tracked, transmitted, received, or stored in the processor may be provided in any database, register, table, cache, queue, control list, or storage structure, all of which may be referenced in any suitable time frame, depending upon the particular needs and implementation.

Any storage terms discussed herein should be construed as being encompassed within the broad term "memory". Similarly, any potential processing elements, modules, and machines described herein should be construed as being encompassed within the broad term "microprocessor". Further, in various embodiments, the processors, memories, network cards, buses, storage devices, related peripherals and other hardware elements described herein may be implemented through processors, memories and other related devices configured by software or firmware to simulate or virtualize the functions of those hardware elements.

Further, it should be appreciated that a computer may be embodied in any of a variety of forms, such as a rack-mounted computer, a desktop computer, a laptop computer, or a tablet computer, as non-limiting examples. Furthermore, a computer may be embedded in a device that is not typically considered a computer, but that has suitable processing capabilities, including a Personal Digital Assistant (PDA), a smart phone, a mobile phone, an iPad, or any other suitable portable or fixed electronic device.

Further, a computer may have one or more input and output devices. These devices may be used, inter alia, to present a user interface. Examples of output devices that may be used to provide a user interface include printers or display screens for visual presentation of output, speakers or other sound generating devices for auditory presentation of output. Examples of input devices that may be used for the user interface include keyboards and pointing devices, such as mice, touch pads, and digitizing tablets. As another example, a computer may receive input information through speech recognition or other audible format.

Such computers may be interconnected by one or more networks IN any suitable form, including as a local area network or a wide area network, such as an enterprise network, as well as an Intelligent Network (IN) or the Internet. Such a network may be based on any suitable technology and may operate according to any suitable protocol and may include a wireless network or a wired network.

Computer-executable instructions may take many forms, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Generally, the functionality of the program modules may be combined or distributed as desired in various embodiments.

The term "program" or "software" is used herein in a generic sense to refer to any type of computer code or set of computer-executable instructions that can be employed to program a computer or other processor to implement the various aspects described above. In addition, it should be appreciated that according to one aspect, one or more computer programs, when executed, need not reside on a single computer or processor, but may be distributed in a modular fashion amongst a number of different computers or processors to implement various aspects of the present application.

Furthermore, the data structures may be stored in any suitable form in a computer readable medium. For simplicity of illustration, the data structure may be shown with fields related by location in the data structure. Likewise, the relationships between fields may be achieved by allocating storage for the fields at locations that convey the relationships in a computer-readable medium. However, any suitable mechanism may be used to establish relationships between information in fields of a data structure, including through the use of pointers, tags or other mechanisms that establish relationships between data elements.

When implemented in software, the software code can be executed on any suitable processor or collection of processors, whether provided in a single computer or distributed among multiple computers.

Computer program logic embodying all or part of the functionality described herein is embodied in various forms including, but in no way limited to, source code forms, computer-executable forms, hardware description forms, and various intermediate forms (e.g., a mask work, or forms generated by an assembler, compiler, linker, or locator). In an example, the source code includes a series of computer program instructions implemented in various programming languages (e.g., object code, assembly language, or high level language, such as OpenCL, RTL, verilog, VHDL, fortran, C, C ++, JAVA, or HTML, which may be used in various operating systems or operating environments). The source code may define and use various data structures and communication messages. The source code may be in a computer-executable form (e.g., via an interpreter), or the source code may be converted (e.g., via a translator, assembler, or compiler) into a computer-executable form.

In some embodiments, any number of the circuitry of the figures may be implemented on a board of an associated electronic device. The board may be a universal circuit board that may house various components of the internal electronic system of the electronic device and further provide connectors for other peripheral devices. More specifically, the board may provide an electrical connection through which other components of the system may communicate electrically. Any suitable processor (including digital signal processors, microprocessors, supporting chipsets, etc.), memory elements, etc. may be suitably coupled to the board in accordance with particular configuration requirements, processing requirements, computer designs, etc.

Other components (e.g., external memory, additional sensors, controllers for audio/video displays, and peripherals) may be connected to the board by cables as plug-in cards, or may be integrated into the board. In another embodiment, the circuitry of the figures may be implemented as stand-alone modules (e.g., devices with associated components and circuitry configured to perform specific applications or functions) or as plug-in modules in dedicated hardware of an electronic device.

Note that with many of the examples provided herein, interactions may be described in terms of two, three, four, or more electronic components. However, this is done for clarity and illustration only. It should be appreciated that the systems may be combined in any suitable manner. Any of the illustrated components, modules, and elements in the figures may be combined in a variety of possible configurations along similar design alternatives, all of which are clearly within the broad scope of the present disclosure.

In some cases, it may be easier to describe one or more functions of a given set of processes with reference to only a limited number of electrical components. It should be understood that the circuitry of the figures and their teachings are readily scalable and can accommodate a large number of components, as well as more complex/complex arrangements and configurations. Accordingly, the examples provided should not limit the scope or inhibit the broad teachings of electronic circuits that may potentially be applied to a myriad of other architectures.

Moreover, as described, some aspects may be embodied as one or more methods. Acts performed as part of the method may be ordered in any suitable manner. Thus, embodiments may be constructed in which acts are performed in a different order than shown, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.

Clause interpretation

All definitions as defined and used herein should be understood to control dictionary definitions, definitions in documents incorporated by reference and/or ordinary meanings of the defined terms. Throughout the specification and claims unless the context clearly requires otherwise:

"including," "comprising," and the like are to be construed as inclusive, and not exclusive or exhaustive; that is, in the sense of "including but not limited to".

"connected," "coupled," or any variant thereof, refers to any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements may be physical, logical, or a combination thereof.

When used in describing the present specification, the terms "herein," "above," "below," and the like should be taken to refer to the specification in general, and not to any particular portion of the specification.

When referring to a list of two or more items, "or" encompasses all of the following interpretations of the word: any item in the list, all items in the list, and any combination of items in the list.

The singular forms "a", "an" and "the" also include any suitable plural referents.

Directional words such as "vertical," "lateral," "horizontal," "upward," "downward," "forward," "rearward," "inward," "outward," "vertical," "lateral," "left," "right," "front," "rear," "top," "bottom," "below," "above," "below," and the like as used in this specification and any appended claims, if any, depend on the particular direction of the device being described and illustrated. The subject described herein may take on a variety of alternative orientations. Accordingly, these directional terms are not strictly defined and should not be interpreted narrowly.

The indefinite articles "a" and "an" as used herein in the specification and claims should be understood to mean "at least one" unless explicitly stated to the contrary.

The phrase "and/or" as used in the specification and claims should be understood to refer to "one or both" of such incorporated elements, i.e., elements that are in some cases co-existence and in other cases co-existence. The various elements listed with "and/or" should be interpreted in the same manner, i.e., "one or more" of the elements so connected.

In addition to elements specifically identified by the "and/or" clause, other elements may optionally be present, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, reference to "a and/or B" when used in conjunction with an open language such as "comprising" may refer in one embodiment to a alone (optionally including elements other than B); in another embodiment, refer to B only (optionally including elements other than a); in yet another embodiment, refer to a and B (optionally including other elements); etc.

As used herein in the specification and claims, the phrase "at least one" when referring to a list of one or more elements is understood to mean at least one element selected from any one or more elements in the list of elements, but does not necessarily include at least one of each element specifically listed in the list of elements, and does not exclude any combination of elements in the list of elements. The definition also allows that other elements, whether related or unrelated to those specifically identified, may optionally be present in addition to those elements explicitly identified in the list of elements to which the phrase "at least one" refers.

Thus, as a non-limiting example, "at least one of a and B" (or equivalently, "at least one of a or B," or equivalently "at least one of a and/or B") may refer, in one embodiment, to at least one, optionally including more than one, a, absent B (and optionally including elements other than B); in another embodiment, at least one, optionally including more than one, B, absent a (and optionally including elements other than a); in yet another embodiment, at least one, optionally including more than one, a, and at least one, optionally including more than one, B (and optionally including other elements); etc.

As used herein, the term "between" shall be included unless otherwise indicated. For example, unless otherwise indicated, "between a and B" includes a and B.

Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having," "containing," "involving," and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

In the claims and in the above description, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding," "composing," and the like are to be construed as open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of … …" and "consisting essentially of … …" should be closed or semi-closed transitional phrases, respectively.

Numerous other changes, substitutions, variations, alterations, and modifications may be ascertained by those skilled in the art and it is intended that the present disclosure encompass all such changes, substitutions, variations, alterations, and modifications as falling within the scope of the appended claims.

To assist the reader of the United States Patent and Trademark Office (USPTO), and any patent related to this application, in understanding the appended claims, applicants wish to note that applicant: (a) Unless the phrase "means for … …" or "step for … …" is used specifically in a particular claim, it is not intended that any appended claim recite 35u.s.c. ≡112 (f) that it exists on the date of filing the present application; (b) It is not intended that the disclosure be limited by any statement in this disclosure in any manner that is not otherwise reflected in the appended claims.

Therefore, the present invention should not be considered limited to the particular examples described above. Various modifications, equivalent processes, as well as numerous structures to which the present invention may be applicable will be readily apparent to those of skill in the art to which the present invention is directed upon review of the present disclosure.

Claims

1. An apparatus for making gain independent reference channel measurements, the apparatus comprising:

a first circuit configured to measure stimulus passing through the test subject;

a first amplifier;

a second circuit configured to measure stimulus that fails the test volume;

a second amplifier; and

a switching circuit in electrical communication with the first circuit, the second circuit, the first amplifier, and the second amplifier, the switching circuit configured to change between:

a first mode, wherein the first circuit is in electrical communication with the first amplifier and the second circuit is in electrical communication with the second amplifier; and

a second mode, wherein the first circuit is in electrical communication with the second amplifier and the second circuit is in electrical communication with the first amplifier.

2. The apparatus of claim 1, wherein the first circuit comprises a sensor.

3. The apparatus of claim 2, wherein the sensor is a photodetector.

4. The apparatus of claim 3, wherein the second circuit comprises a photodetector.

5. The apparatus of claim 4, further comprising a light source that generates the stimulus.

6. The apparatus of claim 5, wherein the light source is an LED.

7. The apparatus of claim 6, further comprising a current source.

8. The apparatus of claim 7, wherein the current source is configured to generate a predetermined waveform in both the first mode and the second mode.

9. The apparatus of claim 8, further comprising an Analog Front End (AFE) configured to compare outputs from the first and second gain amplifiers in the first and second modes.

10. The apparatus of claim 1, wherein the first circuit comprises a transducer.

11. The apparatus of claim 1, wherein the test object is a device under test whose impedance is measured by the stimulus.

12. The apparatus of claim 1, wherein the test object is a test volume.

13. The apparatus of claim 1, wherein the test object is a subject.

14. A method for performing gain independent reference channel measurements, the method comprising

Measuring, at a first circuit, a stimulus passing through a test subject;

measuring at the second circuit the stimulus that fails the test volume;

receiving measurements from the first and second circuits at a switching circuit;

in a first mode, outputting a first measurement value and a second measurement value from the switching circuit to a first amplifier and a second amplifier, respectively;

switching the switching circuit; and

in the second mode, the first and second measurement values are output from the switching circuit to the second and first amplifiers, respectively.

15. The method of claim 14, further comprising amplifying the first and second measurements in the first and second amplifiers, respectively, during the first mode.

16. The method of claim 15, further comprising amplifying the first and second measurements in the second and first amplifiers, respectively, during the second mode.

17. The method of claim 16, further comprising calculating a ratio based at least on measurements amplified during the first and second modes.

18. The method of claim 17, further comprising determining the presence of a predetermined substance based on the calculated ratio.

19. The method of claim 18, wherein the substance is smoke particles.

20. The method of claim 18, wherein the substance is a biochemical agent.

21. The method of claim 18, wherein the substance is an inorganic chemical agent.

22. The method of claim 18, wherein the substance is an organic chemical agent.

23. The method of claim 14, wherein the first circuit comprises a sensor.

24. The method of claim 23, wherein the sensor is a photodetector.

25. The method of claim 24, wherein the second circuit comprises a photodetector.

26. The method of claim 25, further comprising illuminating a light source.

27. The method of claim 26, wherein the light source is an LED.

28. The method of claim 27, further comprising providing a current through the LED.

29. The method of claim 28, further comprising generating a predetermined waveform during both the first and second modes.

30. The method of claim 17, wherein the ratio is calculated using an Analog Front End (AFE) configured to compare outputs from the first and second gain amplifiers in the first and second modes.

31. The method of claim 14, wherein the test object is a test volume.

32. The method of claim 14, wherein the test subject is a subject.

33. An apparatus for making gain independent reference channel measurements, the apparatus comprising:

means for measuring stimulation by the test subject at the first circuit;

means for measuring at the second circuit the stimulus that did not pass the test volume;

means for receiving measurements from the first and second circuits at a switching circuit;

in a first mode, means for outputting a first measurement value and a second measurement value from the switching circuit to the first amplifier and the second amplifier, respectively;

means for switching the switching circuit; and

in a second mode, means for outputting a first measurement value and a second measurement value from the switching circuit to the second amplifier and the first amplifier, respectively.