Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
  • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
  • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light

Definitions

• the present invention relates to the general field of devices capable of quantifying and locating a light signal.
• the invention is concerned with the observation of a light signal picked up by a plurality of photodiodes, this light being modulated at a predetermined frequency. Having multiple receivers can actually locate the signal.
• a photodiode is an opto-electronic component that behaves like a current generator. The generated current is proportional to the light power that illuminates the sensitive part of the photodiode.
• the invention is particularly interested in the measurement of the light power emitted by an emitter then reflected by an actuator.
• the light emitter will typically be a light emitting diode emitting in the infrared or visible light field, such that the emitted light intensity is modulated at a given predetermined frequency.
• the actuator will advantageously be the finger of a user in the applications specifically targeted by the invention.
• the light power reflected by the actuator is then received by at least one photodiode and the measurement of the current from this photodiode allows to know the light power received by the latter after processing by a logic system microcontroller type.
• the simplest device consists of a resistor placed in parallel with the photodiode and behaving as a voltage current converter accompanied by an analog / digital converter allowing the acquisition of the voltage measured at terminals of the resistance and, subsequently, the processing of the latter by a microcontroller.
• transimpedance amplification circuit using, for example, an operational amplifier whose output is connected to the analog / digital converter.
• This arrangement has the advantage of setting a virtually zero voltage across the photoreceptor and thus eliminates voltage problems at the terminals of the photodiode. Having a much lower input impedance, such an assembly has no problem of reaction speed.
• the operational amplifier has a gain-band product of 10 7 Hz, at a frequency of 10 kHz, the assembly has an input impedance of 100 ohms, for a load resistance of 100 kOhm.
• Such an assembly is therefore commonly used to amplify very weak currents. Nevertheless, it suffers from the disadvantage of amplifying all the currents whatever their frequency. Also, in optical applications, the effect of ambient light is manifested by the appearance of a DC component or a very low frequency having an amplitude exceeding several orders of magnitude, that of the signal to be amplified.
• HSDL 5420 photodiode which provides an average photocurrent of 6 microamperes for an irradiance of 1 milliwatt per square centimeter
• at the wavelength of 875 nanometers can provide a photocurrent of the order 0.1 milliampere size for an irradiance of 140 milliwatt per square centimeter with a solar spectrum.
• the current from the light signal reflected by the finger of a user can go down to a value of the order of 10 nanoamperes with a desired accuracy of 1 nanoampere. Therefore there is a factor of 10 5 comes the DC component or low frequency and the signal to be measured.
• filament lamps generate a light flux fluctuating at a frequency of 100 or 120 Hertz depending on the frequency at 50 or 60 Hertz sector.
• Conventional fluorescent tubes also generate a luminous flux that fluctuates at a frequency of
• Fluorescent tubes with an electronic power supply such as fluorescent tubes or energy saving light bulbs, generate a higher frequency light flux, typically around 20 kHertz.
• One of the possibilities to overcome these disturbances is to modulate the signal emitted with a frequency chosen to be as little as possible subject to external disturbances.
• the low frequencies are then converted into current by a transconductance amplifier before this current is subtracted from the input signal of the transimpedance amplifier.
• the patent application EP 1 881 599 describes, in turn, an assembly for producing a trans-impedance amplifier amplifying only one frequency band. Such an arrangement has the advantage of being simple and requiring only an operational amplifier and no external active component. Nevertheless, the immunity to electromagnetic interference is no better than in the case of continuous component suppression systems.
• the main purpose of the present invention is therefore to overcome the disadvantages of the devices of the prior art by proposing a device for quantifying and locating a light signal modulated at a predetermined frequency, characterized in that it comprises a digital control unit, a plurality of photodiodes arranged along two adjacent, parallel receiving lines of similar electrical and dimensional characteristics extending from an amplifier device connected to a demodulator and constituting a differential pair at the input of the amplifier device, the two terminals of each photodiode being respectively connected to one of the reception lines, one of these terminals being connected to the reception line through a switch of the two-output type and an input controlled by the digital control unit, this switch being suitable to bypass the photodiode on itself, the controls switches being such that the photodiodes are connected successively to the two reception lines, the control of the sequence of successive connections by the numerical control unit allowing the knowledge, at each instant, of the photodiode from which the differential signal received as input comes from of the amplifier device, the output of which at each instant has
• the combination of the two parallel reception lines and similar characteristics carrying the plurality of photodiodes and the use of a trans-impedance amplification stage whose inputs are each connected to one of the receiving lines and supporting a filtering stage ensures insensitivity to external electric and magnetic fields whatever the frequency of these.
• reception lines by using similar reception lines, it is ensured that the electrical and magnetic disturbances received by these reception lines will be identical and that the use of the differential pair at the input of the amplification stage will allow the suppression of electrical disturbances and magnetic data on all the frequencies in which they can take place. Indeed, the two lines receiving the same external electrical disturbances and both leading to the input of the amplification stage, these disturbances are mainly suppressed by the differential nature of the amplification.
• the invention also combines the use of such lines connected to a differential amplifier with a direct connection of the photodiodes, each via their own switch. Indeed, the use of an individual switch for each photodiode ensures an implantation where the lines of the differential pair are as close as possible parallel and close.
• the direct connection instead of a star connection or other, also avoids a variation in the length of the lines between the different receivers and transmitters in which would take place different electrical and magnetic disturbances depending on the length or characteristics of these lines.
• the photodiode implantation characteristics with respect to the receive lines is combined with the use of the receive lines as a differential pair at the input of the amplifier stage.
• the short-circuiting of the diodes by the switches allows the current produced by the diode to be isolated from the rest of the circuit.
• the photodiode will not have stored charge through its internal capacitance. If the photodiode were only disconnected from the receive line by being turned on open, its internal capacitance would charge for the entire time the photodiode was disconnected, and would discharge directly into the amplifier, causing problematic transient disturbances.
• a minimum low-pass filter in combination with the other features of the invention makes it possible to eliminate the low-frequency transient light which can not be suppressed by the differential character of the pair of reception lines.
• the successive connections of the photodiodes on the reception lines allow the digital control unit to know at each instant which diode is connected to the lines.
• the control unit knows how to locate the diode that receives light when the emitter emits light.
• the commands of the switches may be such that it will be several diodes, for example two diodes placed symmetrically on each side of a transmitter, which will be connected at the same time on the receiving lines.
• each input of the transimpedance amplification stage is connected to ground through a resistor, the ratio between the values of these resistors being regulated and / or adjustable so as to ensure identity of the potential differences due to the currents caused by the external electric fields and the frequency near the filter passing frequency on the two reception lines at the input of the transimpedance amplification stage.
• This feature makes it possible to ensure that the electrical disturbances are very similar on the two reception lines at the input of the transimpedance amplification stage in the case, for example, where they receive different interfering signals despite their parallelism.
• Such a setting allows the effect of the disturbances to be canceled by the differential effect provided by the amplifier. This setting does not change over time, it is usually set once and for all when tuning the circuit.
• the transimpedance amplification stage comprising an operational amplifier
• the filtering stage comprises a gyrator circuit mounted in charge of the operational amplifier and simulating an inductance in the operating domain of the device.
• the gyrator arrangement comprises a direct negative feedback operational amplifier by direct connection of the negative input of this operational amplifier to its output connected to the two terminals of the load impedance of the operational amplifier of the amplifier.
• transimpedance amplification stage the negative input being further connected to the negative input of the operational amplifier of the transimpedance amplification stage through a resistor
• the positive input being connected to the input negative of the operational amplifier of the transimpedance amplification stage through a capacitance and at the output of the operational amplifier of the transimpedance amplification stage through a resistor.
• the digital control unit controls the demodulator at the predetermined frequency and so synchronous with the control signal of the transmitter so that it accumulates the charges during the illumination periods.
• the demodulator may be a switched capacitor integrator.
• the lines are twisted in order to limit the magnetic disturbances.
• the invention also relates to a device for detecting the presence or position of an object comprising a device for quantifying and locating a light signal modulated at a predetermined frequency according to the invention and transmitters emitting light at a predetermined predetermined frequency. by the control unit of the device for quantifying and locating a light signal, these emitters being arranged alternately with the photodiodes of the device for quantifying and locating a light signal.
• FIG. 1 is a schematic representation of a device according to the invention
• FIGS. 2A and 2B show an example of implementation of the reception lines used in a device according to the invention, respectively according to an electrical diagram and according to an implementation of tracks on an integrated circuit;
• FIG. 3 represents a conventional amplifier amplifier with an operational amplifier
• FIG. 4 represents an advantageous embodiment of a differential amplifier device as used in the invention
• FIG. 5 shows the diagram of a gyrator assembly as advantageously used according to the invention
• FIG. 6 is an equivalent assembly of the gyrator assembly shown in FIG. 4;
• FIGS. 7A and 7B show the results obtained for a particular implementation of the invention;
• FIG. 8 is a schematic representation of a switched capacity integrator as used in a device according to the invention.
• FIG. 9 represents a device for detecting the position of an object according to the invention
• FIG. 10 shows signals as present at different points of the detection device of FIG. 9;
• FIG. 11 shows an exemplary flow chart of operation of a detection device according to the invention.
• FIG. 1 schematically represents a device for quantifying and locating a light signal according to the invention.
• This device comprises a digital control unit 100, a plurality of photodiodes, here four photodiodes D1 to D4, arranged along a pair 200 of parallel L- and L + reception lines and similar electrical and dimensional characteristics.
• reception lines L-, L + extend from an amplifier device 300 connected to an integrating demodulator 400 whose output signal is processed by an analog digital converter 500 which sends the data obtained to the control unit 100
• the L- and L + receive lines constitute a differential pair at the amplifier device input 300.
• each photodiode Di is each connected to one of the lines L-, L +.
• One of these terminals is connected through a switch SW1 SW4 type two outputs and an input.
• Each switch is controlled by the digital control unit 100 using signals denoted C D i to C 04 synchronized to a clock t.
• the two outputs of the switches SWi correspond to a connection from the terminal of the diode Di to the reception line, here L-, and to a short-circuiting of the diode Di.
• Controlling the sequence of the successive connections of the photodiodes to the reception line L- by the digital control unit 100 makes it possible to know at each instant the photodiode Di from which the differential signal received at the input of the amplifier device 300 comes from. to locate the light received by identifying the photodiode on which the largest light power is received during the same illumination.
• diodes may be connected to the two reception lines at the same time.
• two diodes symmetrical with respect to the same transmitter can be connected simultaneously to the two reception lines.
• the amplifier device 300 has, at its output, at each instant, a signal noted V A quantifying the light received by the photodiode (s) connected (s) to the two reception lines L- and L + at this time.
• each reception line L- and L + is connected to ground by a resistor RI1 and R12 respectively, placed at the input of the amplification device 300.
• resistors RI1 and R12 are advantageously adjusted during the creation of the assembly according to the invention or offered in adjustment to the user in order to adapt the device to various configurations.
• the line connected to the inverting input of the transimpedance operational amplifier carries the components and the multiplexers a two output input ("SPDT" for Single PoIe, Double Throw). It is therefore slightly more sensitive to electric fields.
• the value of resistor R12 is then adjusted iteratively, by subjecting the circuit to an electric field of fixed frequency and attempting to minimize the resulting signal at the output of the amplifier. For example, we obtain 1 k ⁇ for the resistor RI1 connected to the non-inverting input, and 920 ⁇ on the other R12.
• the device can be adapted to environments where the two reception lines L- and L + receive different electrical and / or magnetic interference signals.
• the amplifier device 300 comprises a transimpedance amplification stage whose inputs are each connected to one of the reception lines L- and L + of the differential pair 200 and a frequency filtering stage capable of allowing the signals to pass at the predetermined frequency and filtering at least the continuous or low frequency signals.
• FIG. 3 An example of such an amplifier device 300 is shown in FIG. 3. It consists of two parts 310 and 320, the part 310 incorporates the characteristics of a simple transverter-impedance assembly with an operational amplifier AO310 while the part 320 allows to filter the differential signal at a predetermined frequency.
• FIG. 4 shows a stage 301 with operational amplifier AO301 as conventionally used in known electronic assemblies.
• the amplifier arrangement as shown in FIG. 4 has no particularly interesting performance with respect to sensitivity to ambient electric and magnetic fields. This sensitivity is particularly problematic when the gains of the amplifier are high. The latter then parasitize the received signal and deforms it.
• FIG. 5 shows a gyrator assembly as implemented as a filter stage 320 in the amplifier device 300 of FIG. 3.
• a gyrator arrangement simulates the presence of an inductance and leads to the desired frequency filtering.
• this gyrator arrangement is placed in charge of the operational amplifier AO310 and receives an input current.
• this current is shown schematically by the presence of a photodiode D321 which injects a given current into the gyrator circuit 321.
• This current is denoted I in the following.
• the voltage across the photodiode D321 is equal to:
• V A R l2 i + + (i + -L) Z _ Note that this is not a real differential amplifier since the factor Ri 2 I + disturbs the measurement.
• the impedance Z is much greater than the resistor R12 and it can then be considered that the amplifier thus obtained is a good differential amplifier approximation.
• the gain of the amplifier which depends on the frequency, makes it possible precisely to isolate certain amplified frequency bands from the others. We are in the presence of a filter.
• the representation of the gain as a function of the frequency makes it possible to visualize the filtered frequencies.
• An amplifier having a narrow frequency filtering is thus obtained and which can be implemented with an operational amplifier with a more limited performance than those necessary for carrying out the arrangements made in the prior art.
• the AO310 operational amplifier used is a Texas Instruments TLC2272 dual operational amplifier.
• the AO320 operational amplifier is a STMicroelectronics TS461 operational amplifier.
• the frequency filter then has a bandwidth centered on 10 5 Hertz as shown in Figure 7A.
• filtering 320 realized here thanks to the gyrator assembly are common mode interference, that is to say that they have the same effect on the two lines of the pair 200.
• the differential amplifier therefore eliminates them.
• the current coming from the photodiode Di connected to the two reception lines is differential and the polarity of this current on one of the lines is opposite to the polarity of this current on the second line.
• the independent and successive activation of the photodiodes makes it possible to avoid the impedance changes on each photodiode since each short-circuited photodiode is charged with almost zero impedance and since the amplifier also has an input impedance very weak.
• FIG. 8 shows a mounting of an integrating capacitor demodulator switched 400. This assembly 400 receives as input the amplified voltage V A at the output of the amplifier device 300.
• This integrator assembly 400 comprises a first part for further eliminating a possible residue of low frequency spurious signals. These are the elements CB and RB performing an RC filter.
• the signal V A is sent to the part of the assembly able to integrate it only when one of the emitters Ei is on.
• a switch two outputs an input SW400 goes from a position where the voltage V A is transmitted for integration and a position where the voltage V A is sent in a load resistor R401.
• the switch SW400 is advantageously controlled with the control signal of the emitters C El .
• the voltage V A is transmitted to a capacitor C400, placed in feedback on the negative input of the operational amplifier AO400. This capacitor C400 then accumulates the current sent to the input of the integrator 400.
• the cumulative signal Vc 40 O is then able to be recovered by the digital analog converter 500 at times synchronous with the control signals C Dl .
• the signal Vc 40 O is then able to be recovered by the digital analog converter 500 at times synchronous with the control signals C Dl .
• V C4 oo is recovered by the digital analog converter and then the capacitance C400 is discharged via a switch SW401 which switches to a position where the capacitor C400 is looped with the resistor R404 where the accumulated current discharges.
• the switch SW401 is advantageously controlled by signals synchronous with the signals C D1 , controlling the successive connections of the diodes Di to the reception lines but slightly shifted in order to avoid the transients.
• FIG. 9 schematically represents a device for detecting an object according to the invention.
• this detection device comprises transmitters E1 to E4 also controlled by the digital control unit 100 with signals C E1 synchronized on a clock t.
• the control signals C Ei to C E4 make it possible to activate the emitters E1 to E4 successively one after the other for periods of time sufficient to allow each diode Di to be connected to the reception lines for a time sufficient to allow an integration of the signal received by each of these diodes under the same illumination.
• only certain diodes will be able to receive light when illuminated by a given transmitter. In this case, only these diodes will be connected one after the other to the two reception lines during illumination by the given transmitter. This makes it possible to shorten the reaction time of the detection device since only the relevant diodes are questioned.
• control signals C Ei to C E4 are such that the emitters E1 to E4 are turned off at the same time as the connection of one of the photodiodes to the differential pair is stopped.
• CeIa is illustrated in FIG. 10, which shows the control signal of one of the emitters C El during the successive connection of two of the diodes C D i and C D2 during a duration T.
• the transmission of the transmitter Ei is also stopped after the duration T during which the diode D1 is connected to the two lines. It can also be seen that the output signal V A of the amplifier device 300 vanishes when the emitter E1 is stopped or when the diode D1 is short-circuited.
• the transmitter El starts transmitting again and a non-zero signal V A but of smaller amplitude appears at the output of the device 300.
• This signal V A corresponds to the intensity received on the diode connected successively to the diode D1, here the diode D2.
• the signal V C4 oo at the output of the integrator will be larger with the first diode D1 than with the second D2.
• the intensity received is associated with a transmitter Ei and a particular diode Dj and the signal thus obtained is denoted Sij. It is these signals associated with transmitters and receivers / photodiodes that will determine the position of the object.
• the reflection of the light emitted by the emitter El is greater on the diode D1, it will be possible to deduce that the object is placed closer to the diode D1 than to the diode D2 .
• FIG. 9 gives a schematic representation of a device for detecting the position of an object OB on a plane P extending facing the emitters Ei and the photodiodes Di.
• the emitters Ei and the photodiodes Di are here aligned and arranged alternately emitter / photodiode.
• the emitters Ei are controlled by the control signals C El synchronized on a clock t.
• the photodiodes Di are controlled by the control signals C D1 also synchronized on the clock t.
• FIG. 11 An example of the overall operation of the detection device according to FIG. 9 is described in the flowchart of FIG. 11. It is an application method for which a detection device according to the invention will advantageously be used.
• the method is initialized in an ETO step.
• a transmitter Ei is turned on in a step ET1. Note that, in this example, unlike what has been described in Figure 10, the transmitter Ei is not turned off at the end of each measurement on a photodiode. Disturbances can then be summed when the transmitter goes off. These disturbances are then found in the final signal.
• a step ET3 the emitter Ei is off.
• the sum of the received signals Sii + Sii + 1 by the two neighboring diodes Di, Di + 1 of the emitter Ei is carried out in a step ET4.
• a step ET5 verifies that all the N transmitters have been turned on successively. If not, a step ET6 increments i and the next emitter Ei + 1 is turned on in a new step ET1.
• the sum Sii + Sii + 1 maximum is determined in a step ET7 before the calculation of the ratio of the signals of the neighboring diodes is calculated in a step ET8.
• the use of the maximum sum and the SiMiM / SiMiM + 1 ratio between the signals received by the neighboring diodes makes it possible to determine the position (X, Y) of the object in a step ET9.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Amplifiers (AREA)
• Optical Communication System (AREA)
• Optical Transform (AREA)
• Measurement Of The Respiration, Hearing Ability, Form, And Blood Characteristics Of Living Organisms (AREA)

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• 2008
  • 2008-12-23 FR FR0859048A patent/FR2940432B1/fr not_active Expired - Fee Related
• 2009
  • 2009-12-11 CA CA2756626A patent/CA2756626A1/fr not_active Abandoned
  • 2009-12-11 JP JP2011542867A patent/JP2012513274A/ja not_active Withdrawn
  • 2009-12-11 WO PCT/FR2009/052498 patent/WO2010072941A2/fr not_active Ceased
  • 2009-12-11 US US13/139,820 patent/US20110248150A1/en not_active Abandoned
  • 2009-12-11 EP EP09802166A patent/EP2368095A2/de not_active Withdrawn
  • 2009-12-11 AU AU2009332843A patent/AU2009332843A1/en not_active Abandoned

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