Signal processing circuit, corresponding sensor device and apparatus

Abstract

The present application relates to signal processing circuitry, corresponding sensor devices and apparatuses. The circuitry comprises a first input terminal, a second input terminal, a third input terminal and an output terminal. A first summing node sums signals at the first input terminal and the third input terminal. A second summing node subtracts signals at the second input terminal and the third input terminal. A selector selects between the summed signals and the subtracted signals in response to a selection signal. An output of the selector is integrated to generate an integrated signal. The integrated signal is compared to a threshold by a comparator which generates an output signal having a first level and a second level at the output terminal. Feedback of the output signal generates the selection signal such that the selector selects the summed signals in response to the first level of the output signal and such that the selector selects the subtracted signals in response to the second level of the output signal.

Description

[0001] This divisional application is a divisional application of Chinese Patent Application No. 201810386440.3, filed April 26, 2018, entitled “Signal processing circuit, corresponding sensor device and apparatus,” the disclosure of which is hereby incorporated by reference in its entirety.

[0002] Cross Reference to Related Applications

[0003] This application claims priority to Italian Patent Application No. 102017000045616, filed April 27, 2017, the disclosure of which is hereby incorporated by reference in its entirety to the maximum extent legally permitted. TECHNICAL FIELD

[0004] This description relates to signal processing circuitry.

[0005] For example, one or more embodiments can be used in a non-contact temperature sensor device. BACKGROUND

[0006] Objects at temperatures above absolute zero emit energy in the form of electromagnetic radiation (“light”). In most cases, this radiation is at a lower frequency than visible light and is not visible to the human eye.

[0007] Such radiation can be detected by using electronic devices, such as non-contact temperature sensors. Non-contact temperature sensors can detect, for example, infrared (IR) radiation emitted by an object, and based on this detection can provide a measurement of the temperature of the object without coming into contact with the object. For example, infrared energy emitted by an object can be directed (e.g., using a lens) onto a certain surface at a receiving interface of a sensor, thereby providing an increase in temperature in the surface.

[0008] A thermopile is an electronic device that converts thermal energy into electrical energy.

[0009] Due to a physical effect known as the Seebeck effect, a voltage can be generated in a thermopile. As heating is concentrated on a surface corresponding to a “hot” junction of the thermopile and a “cold” junction designed to be insensitive to such temperature increases, the thermopile will generate, due to the Seebeck effect, a voltage difference that is a function of (e.g., proportional to) the effect of such heating, i.e., a voltage difference that is indicative of the temperature of the object. This voltage difference thus generated can be amplified at the receiving interface to provide a measurement of the temperature of the object as an output.

[0010] Non-contact temperature sensors can permit detection (measurement) of human body temperature, object temperature, ambient temperature, and the like.

[0011] The non-contact temperature sensor can comprise a filter designed to propagate only a certain wavelength range in the thermal radiation emitted by the object.

[0012] Despite the considerable activity in the field just discussed, there is still a need for improved solutions, in particular with regard to simplifying the overall structure of the sensor circuit, thus making production less expensive and / or less space-consuming, for example in terms of the silicon area occupied in a semiconductor device. SUMMARY

[0013] In one embodiment, the signal processing circuit according to one or more embodiments can be used to generate a signal having an average value given by a relationship such as <dout>a binary bitstream Dout:

[0014] <dout>= (V1+V3) / (V1+V2)

[0015] wherein V1, V2, V3 are three (analog) input signals (such as, for example, voltage signals).

[0016] The device can comprise a temperature sensor, which is implemented as a corresponding apparatus (such as a non-contact (e.g., body temperature) thermometer).

[0017] One or more embodiments permit reading out a temperature of an object using a compact architecture, wherein the temperature of the object is effectively tracked by taking a single conversion.

[0018] Hence, although developed in view of possible uses in non-contact temperature sensing, embodiments are not limited to such possible uses.

[0019] In one embodiment, the circuit comprises:

[0020] - a first input terminal, a second input terminal, a third input terminal and an output terminal,

[0021] - a first summing node, to which the first input terminal and the third input terminal are additively coupled,

[0022] - a second summing node, to which the third input terminal and the second input terminal are subtractively coupled,

[0023] - a selector having a first input coupled to the first summing node, a second input coupled to the second summing node, and an output selectably coupled to the first input or the second input,

[0024] - an integrator, activated on the selector output, which integrator has an integral signal at an integrator output,

[0025] - a comparator between the integrator and the output terminal, which comparator is sensitive to the integral signal at the integrator output, and which provides an output signal having a first level and a second level at said output terminal, and

[0026] - a feedback line from the output terminal to the selector, wherein the selector output is coupled to the first selector input or the second selector input with the output signal having the first level or the second level, respectively.

[0027] In one or more embodiments, the first level and the second level of the output signal can comprise binary levels "0" and "1".

[0028] In one or more embodiments, the device can comprise:

[0029] - a circuit according to one or more embodiments,

[0030] - a first sensor providing a signal that increases as ambient temperature increases, coupled to the first input terminal,

[0031] - a second sensor providing a signal that decreases as ambient temperature increases, coupled to the second input terminal,

[0032] - a thermopile providing a signal indicative of a temperature difference of an object relative to ambient temperature, the thermopile coupled to the third input terminal, wherein the average of the output signal is indicative of the temperature of the object.

[0033] In one or more embodiments, the first sensor can comprise a pair of bipolar transistors that are different from each other for at least one of a transistor area and a transistor bias current, wherein the signal that increases as ambient temperature increases comprises a difference in base to emitter voltage of a bipolar transistor in the pair of bipolar transistors.

[0034] In one or more embodiments, the second sensor can comprise a single bipolar transistor, wherein the signal that decreases as ambient temperature increases comprises a base to emitter voltage of the single bipolar transistor.

[0035] One or more embodiments can comprise an averaging circuit block to produce the average of the output signal.

[0036] In one or more embodiments, the averaging circuit block can comprise a decimation filter active on the output signal.

[0037] A method of operating a circuit or device according to one or more embodiments can comprise maintaining the third input terminal at a (voltage) level lower than the (voltage) level at the second input terminal, wherein the average of the output signal lies between 0 and 1.

[0038] In one embodiment, a device (e.g. a non-contact thermometer) can comprise:

[0039] - a device according to one or more embodiments,

[0040] - a temperature display unit coupled to the device, the temperature display unit configured to display the average of the output signal. BRIEF DESCRIPTION OF DRAWINGS

[0041] One or more embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:

[0042] Figure 1 is a block diagram of a non-contact temperature sensor,

[0043] is a block diagram of a non-contact temperature sensor, Figure 2 is a block diagram of a circuit according to one or more embodiments, and

[0044] Figure 3 is an example of possible use of a circuit according to one or more embodiments in a non-contact temperature sensor. DETAILED DESCRIPTION

[0045] In the following description, one or more specific details are described to provide an example embodiment. However, embodiments can be implemented using other methods, components, materials, etc. Other embodiments can omit, substitute, or add one or more of these specific details. Similarly, other embodiments can also employ additional methods, components, materials, etc. not expressly described to provide an example embodiment. Also, the description herein does not necessarily describe the only possible implementations, but rather also lends itself to the possession of the novelty claimed.

[0046] Reference throughout this specification to "an embodiment" or "one embodiment" means that a particular configuration, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase "in an embodiment" or "in one embodiment" in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular configurations, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0047] References used herein are provided merely for convenience and thus do not limit the scope of protection or embodiments.

[0048] Figure 1 is a block diagram of a non-contact temperature sensor.

[0049] As previously discussed, the thermopile TP can be used to generate a (voltage) signal proportional to the temperature Tobj of the object.

[0050] More specifically:

[0051] - if the "hot" junction of the thermopile receives radiated (electromagnetic) energy from the object at ambient temperature and the temperature of the "cold" junction of the thermopile is also at ambient temperature, the thermopile TP will generate a differential output voltage equal to zero,

[0052] - the cold junction of the thermopile can be designed (in a manner known per se) so as not to be exposed to radiation from the object: it can thus be assumed that the cold junction is at a temperature Tcold equal to the ambient temperature Tamb, where the radiation from the object reaches only the hot junction of the thermopile,

[0053] - when the hot junction of the thermopile receives radiated energy from the object at a temperature Tobj higher / lower than the ambient temperature, then the hot junction will be at a correspondingly higher / lower temperature Thot with respect to the ambient temperature, by a difference AT.

[0054] The voltage Vin from the thermopile will thus be indicative (proportional to) of the difference between the temperature of the hot junction and the temperature of the cold junction, i.e. the difference between the object temperature and the ambient temperature:

[0055] Vin = AT * S = (Thot - Tcold) * S = (a * Tobj - Tamb)

[0056] where:

[0057] - S is the Seebeck coefficient of the thermopile, and

[0058] - a is a proportionality factor between the temperature of the object and the temperature of the hot junction of the thermopile.

[0059] In the circuit arrangement as exemplified in Figure 1 the signal Vin from the thermopile TP is amplified in an amplifier (Amp) A and converted into a digital signal in a (first) analog-to-digital converter ADC1.

[0060] As previously discussed, the signal Vin is indicative of the amount by which the object temperature is higher / lower than the ambient temperature. Therefore, in the arrangement as exemplified in Figure 1 the ambient temperature Tamb is sensed (by any known type of temperature sensor TS) and then converted into a digital signal via a (second) analog-to-digital converter ADC2.

[0061] Based on the above published relationship, a processor DSP (e.g. a digital signal processor) configured to receive the signals from the two converters ADC1, ADC2 can compute the value of the object temperature Tobj starting from the ambient temperature Tamb and the signal Vin from the thermopile TP.

[0062] Figure 1 The arrangement as exemplified in uses a receiving chain comprising two converters ADC1, ADC2 to sense (simultaneously) the signal from the thermopile TP and the signal from the sensor TS of the ambient temperature. The use of two converters involves a certain current consumption; likewise, two converters occupy a corresponding area, e.g. in a semiconductor device such as an integrated circuit.

[0063] One possibility is to consider using a single converter operating according to a time-division multiplexing scheme, i.e., by alternately reading signals from the thermopile TP and from the sensor TS. While this approach may involve a reduction in area, the advantage in current consumption is likely negligible as long as the single converter needs to be on for a certain period, which is twice the activation time of a single converter in a device that includes two converters.

[0064] An additional drawback of multiplexing schemes may be that, compared to... Figure 1 Compared to the two illustrated converter devices, any change in ambient temperature between two subsequent measurements will cause an error in the temperature of the object being evaluated, and detecting signals from the thermopile TP and the temperature sensor TS at different times will also cause a corresponding error.

[0065] Figure 2 This is an example diagram of a circuit according to one or more embodiments.

[0066] As previously noted, although developed with the potential use in temperature sensors (including, for example, thermopile), Figure 2 The circuit 10 shown in the example can be applied in a variety of different situations, as long as such circuit can provide an analog-to-digital converter (ADC) to convert three (analog) input signals, generally designated as V1, V2, and V3, into an output digital signal Dout. Therefore, the references herein to temperature sensors that may be used are exemplary and not limiting to the embodiments.

[0067] In one or more embodiments, the output signal Dout may be a binary bit stream with a frequency of fs, which is generated using a first value (e.g., "0") and a second value (e.g., "1") at a (sampling) frequency of fs.

[0068] In such Figure 2 In one or more of the examples, circuit 10 may therefore include a first input terminal V1, a second input terminal V2 and a third input terminal V3, as well as an output terminal where the output signal Dout is located.

[0069] In such Figure 2 In one or more embodiments illustrated, circuit 10 includes a first summing node 121 and a second summing node 122.

[0070] The third input terminal V3 is coupled together with the first input terminal V1 to the first summing node 121. The first input terminal V1 and the third input terminal V3 are coupled "additively" (i.e., for example, both have the same positive sign, mathematically +V1+V3) at the first summing node 121, which actually acts as an adder node.

[0071] The third input terminal V3 is also coupled to the second summing node 122 together with the second input terminal V2. The second terminal V2 and the third terminal V3 are coupled "subtractively" (i.e. with opposite signs, e.g. negative and positive, mathematically -V2+V3) at the second summing node 122, which in effect acts as a subtractive node.

[0072] In Figure 2 the diagram, reference 14 denotes a selector (e.g. a multiplexer circuit) having a first input 141 coupled to the first summing node 121 and a second input 142 coupled to the second summing node 122.

[0073] The selector 14 further comprises an output terminal 143 which can be (alternatively) coupled to the first input 141 or the second input 142 depending on a control signal provided at a control input 144 of the selector 14, as discussed below.

[0074] Cascaded (downstream) to the selector 14, an integrator 16 is provided which receives the output 143 from the selector 14 on an input 161.

[0075] Depending on the signal output from the selector 14 at the output 143, the integrator 16 provides an integrated signal at an output 162 which is fed to a comparator 18 arranged between the integrator 16 and an output terminal providing a signal Dout. The comparator 18 thus provides an output signal Dout having a first level and a second level (e.g. "0" and "1") at the output terminal of the circuit 10.

[0076] The comparator 18 operates with a threshold value TV at a (sampling) frequency fs.

[0077] The (binary) output signal Dout is coupled to the control input 144 of the selector via a feedback line 182.

[0078] As Figure 2 illustrated, the operation of the circuit 10 can be arranged in such a way that the output signal from the integrator 16 (at the output 162) has an average value substantially equal to zero.

[0079] For example, as Figure 2 illustrated, the operation of the circuit 10 can be adjusted in such a way that when the output signal of the integrator 16 is above the threshold value TV, the input selector 144 will select a certain input signal (e.g. input 141 or input 142) in order to change the slope of the output signal of the integrator. Similarly, when the output signal is below the threshold value TV, the input selector will change the input signal (e.g. input 142 or input 141) and the slope of the output signal in order to make the average value of the output signal equal to zero.

[0080] For the purpose of such operation, the input signals V1, V2 and V3 can be reasonably assumed to be constant or to have a bandwidth relatively lower than the frequency clock fs of the whole system.

[0081] In one or more embodiments, the signals applied to the terminals V1, V2, V3 can be voltage signals (for simplicity, the same name is used herein for the terminals as well as for the respective signals at these terminals).

[0082] In one or more embodiments, the selector 14 can be controlled via the feedback line 182 so that, in the case of Dout = 0 (first level), the selector 14 is set so that the output signal at the output 143 corresponds to the input signal at the input 141 (i.e. V1 + V3), while for Dout = 1 (second level), the selector output 143 is coupled to the selector input 142 (-V2 + V3).

[0083] With such control logic, the average value of the integrated signal from the integrator 16 (output 162) can be substantially zero, and in this case the following relationship applies:

[0084] (1 - Dout)*(V1 + V3) + Dout*(-V2 + V3) = 0.

[0085] Therefore, the average value of the output signal Dout, i.e. <dout>may be expressed as:

[0086] <dout>= (V1+V3) / (V1+V2)

[0087] The signal Dout is a binary bit stream at the sampling frequency fs, whose average value is given by the above relation. The average value of the binary signal Dout can be obtained from the bit stream in a manner known per se, e.g. via a digital decimation filter, and presented on a display comprised in the unit D.

[0088] In one or more embodiments, the range of variation of the signals at the terminals V1, V2 and V3 can be chosen in such a way that the average value of Dout lies between 0 and 1, which can correspond to the signal at terminal V3 being (always) lower than the signal at terminal V2.

[0089] It is noted that, Figure 2 The signal processing circuit 10 of

[0090] With this condition, Figure 3 is Figure 2 An example of possible application of the circuit 10 of

[0091] In a device as Figure 3 illustred, the input terminal V1 can receive a signal Vptat, which can be a so-called PTAT (Proportional To Absolute Temperature) signal, i.e. a signal, e.g. a voltage, which increases with an increase of the temperature obtained in the sensor TS1.

[0092] In one or more embodiments, such a sensor can comprise two bipolar transistors (BJT) having different areas and / or biased at different currents, so that the difference between the respective base to emitter voltages Vbe of the two transistors can be an exemplary signal Vptat having the previously discussed characteristics.

[0093] Likewise, the signal applied to terminal V2 can be a signal Vbe in the form of a CTAT (Complementary To Absolute Temperature), i.e. a signal, e.g. a voltage, which decreases with an increase of the temperature obtained in the sensor TS2. Such a sensor can again comprise a bipolar transistor (BGT), the base to emitter voltage Vbe of which is an example of such a signal.

[0094] In one or more embodiments, the sensors such as TS1 and TS2 can rely on the fact that the base to emitter voltage of a bipolar transistor decreases as temperature increases, while the difference between the base to emitter voltages of two bipolar transistors having different regions and / or polarized with different bias currents can in fact increase as temperature increases.

[0095] By replacing the voltages applied to the input terminals V1, V2 and V3 with the corresponding values as previously defined:

[0096] V1 = M*Vptat (where M is a constant selected in such a way that a voltage Vref corresponding to the sum of Vbe+M*Vptat and Vref having a first order temperature coefficient equal to zero can be generated),

[0097] V2 = Vbe,

[0098] V3 = G*Vin

[0099] The previous expression of the average value of the output signal Dout can be expressed as

[0100] <dout>= (G * Vin + M * Vptat) / Vref

[0101] As noted, the signal Vref can reasonably be considered to be constant with temperature, and thus to be a simple constant.

[0102] The above-mentioned relationship indicates that, as Figure 3 The illustrated device will produce an output signal comprising a bitstream having an average value which is the sum of the signal Vin (which can be produced via a thermopile and thus be indicative of the difference between the temperature of the object and the ambient temperature) multiplied by a gain factor G plus the signal Vptat which is indicative of the ambient temperature, which can be represented as Sptat * Tamb, where Tamb is the ambient temperature and Sptat is a constant proportionality factor.

[0103] The previous relationship can thus result in an average value of Dout which can be represented as

[0104] <dout>= (G * (a * Tobj - Tamb) * S + M * Sptat * Tamb) / Vref

[0105] Thus, by choosing G = (M * Sptat) / S, the previous relationship translates into

[0106] <dout>= Tobj * (G * a * S / Vref).

[0107] The average value of the signal Dout is thus indicative (proportional) of the temperature of the object, which can be calculated, e.g. via decimation filtering, and displayed on the display unit D.

[0108] One or more embodiments can be advantageous over the devices exemplified in Figure 1 as far as they in fact rely on a single analog-to-digital conversion circuit providing the object temperature.

[0109] This is in contrast to the devices exemplified in Figure 1 which comprise two converters ADC1 and ADC2 when it is desired to sense the signals from the thermopile and the temperature sensor TS simultaneously.

[0110] The devices exemplified in Figure 2 and Figure 3 are also advantageous with respect to a single time-division multiplexing converter as far as in the devices exemplified in Figure 2 and 3 the signal from the thermopile and the signal from the temperature sensor are captured at the same time (instead of at two different times), thereby avoiding the risk of errors in case of a change in ambient temperature between two subsequent detection (sensing) times.

[0111] One or more embodiments exemplified in Figure 2 and Figure 3 may also provide advantages in terms of area and current consumption as far as the signals from the thermopile and the temperature sensor can be directly combined to provide the object temperature, thereby avoiding the drawbacks related to time-division multiplexing as previously discussed.

[0112] One or more embodiments can thus relate to a circuit (e.g. 10) comprising:

[0113] - a first input terminal (e.g. V1), a second input terminal (e.g. V2), a third input terminal (e.g. V3) and an output terminal (e.g. Dout),

[0114] - a first summing node (e.g. 121) having a first input terminal and a third input terminal coupled to the first summing node additively (with the same sign, e.g. plus),

[0115] - a second summing node (e.g. 122) having a third input terminal and a second input terminal coupled to the second summing node subtractively (with opposite signs, e.g. plus and minus),

[0116] - a selector (e.g. 14) having a first input (e.g. 141) coupled to the first summing node, a second input (e.g. 142) coupled to the second summing node, and an output (e.g. 143) selectively (e.g. 144) coupled to the first input or the second input,

[0117] - an integrator (e.g. 16) active on the selector output, the integrator having an integrated signal at an integrator output (e.g. 162),

[0118] - a comparator (e.g. 18) between the integrator and an output terminal, the comparator being sensitive to the integrated signal at the integrator output and providing an output signal having a first level and a second level at said output terminal, and

[0119] - a feedback line (e.g. 182) from the output terminal to the selector, wherein the selector output is coupled to the respective first selector input and second selector input, wherein said output signal is at the respective first level and second level.

[0120] In one or more embodiments, the first level and the second level of the output signal can comprise binary levels "0" and "1".

[0121] In one or more embodiments, the device can comprise:

[0122] - a circuit according to one or more embodiments,

[0123] - a first sensor (e.g. TS1) providing a signal that increases with an increase of an ambient temperature, coupled to said first input terminal,

[0124] - a second sensor (e.g. TS2) providing a signal that decreases with an increase of the ambient temperature, coupled to said second input terminal,

[0125] - a thermopile (e.g. TP) providing a signal indicative of a temperature difference of an object relative to the ambient temperature, coupled to said third input terminal, wherein an average of said output signal is indicative of a temperature of said object.

[0126] In one or more embodiments, the first sensor can comprise a pair of bipolar transistors that are different from each other for at least one of a transistor area and a transistor bias current, wherein the signal that increases with an increase of the ambient temperature comprises a difference of a base to emitter voltage of the bipolar transistors in said pair of bipolar transistors.

[0127] In one or more embodiments, the second sensor can comprise a single bipolar transistor, wherein the signal decreasing with increasing ambient temperature comprises a base to emitter voltage of the single bipolar transistor.

[0128] One or more embodiments can comprise an averaging circuit block (e.g. comprised in a display unit D of Figure 3 the output signal.

[0129] In one or more embodiments, the averaging circuit block can comprise a decimation filter activated on the output signal.

[0130] A method of operating a circuit or device according to one or more embodiments can comprise maintaining the third input terminal at a (voltage) level lower than a (voltage) level of the signal at the second input terminal, wherein the average of the output signal lies between 0 and 1.

[0131] A device (e.g. a non-contact thermometer) according to one or more embodiments can comprise:

[0132] - a device according to one or more embodiments,

[0133] - a temperature display unit (e.g. D) coupled to the device, the temperature display unit being configured to display the average of the output signal.

[0134] Details and embodiments can vary even significantly with respect to what is merely described by way of example, without departing from the scope of protection, without offending against the basic principles. The scope of protection is defined by the appended claims.< / dout> < / dout> < / dout> < / dout> < / dout> < / dout> < / dout>

Claims

1. A method for signal processing, comprising: additively combining a first signal and a third signal to generate an addition signal; subtractively combining a second signal and the third signal to generate a subtraction signal; generating a selection signal by selecting the addition signal in response to a first logic state of a bit in a selection bit stream, or selecting the subtraction signal in response to a second logic state of the bit in the selection bit stream; integrating the selection signal to generate an integrated signal; and comparing the integrated signal to a threshold and generating each bit of the selection bit stream.

2. The method of claim 1, further comprising: maintaining the third signal at a level that is lower than a level of the second signal.

3. The method of claim 1, wherein an average of the selection bit stream lies between 0 and 1.

4. The method of claim 1, further comprising: digitally decimating the selection bit stream.

5. The method of claim 3, further comprising: displaying the average generated by digitally decimating the selection bit stream.

6. The method of claim 5, wherein: the third signal is generated by a temperature sensor, and wherein the displaying comprises displaying a temperature value.

7. The method of claim 1, wherein the first signal is proportional to an absolute temperature signal, the second signal is complementary to the absolute temperature signal, and the third signal is generated by a temperature sensor.

8. The method of claim 7, wherein the temperature sensor is a thermopile.

9. The method of claim 7, further comprising: generating the signal proportional to an absolute temperature signal by determining a difference in base to emitter voltage of two bipolar transistors; and generating the signal complementary to an absolute temperature signal by determining a base to emitter voltage of another bipolar transistor.

10. The method of claim 1, wherein bits of the selection bit stream are generated at a rate corresponding to a sampling rate used to compare the integrated signal to the threshold.

11. The method of claim 1, wherein each of the first signal, the second signal, the third signal, the addition signal, the subtraction signal, the selection signal, and the integrated signal is an analog signal. generating the selection signal includes:

12. The method of claim 1, wherein: selecting the addition signal for output as the selection signal comprises controlling a multiplexer circuit having the addition signal as an input to pass the addition signal in response to the first logic state of the bit in the selection bit stream; and selecting the subtraction signal for output as the selection signal comprises controlling the multiplexer circuit having the subtraction signal as an input to pass the subtraction signal in response to the second logic state of the bit in the selection bit stream. ​ ​

Images