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GB2486164A - Using a single photon avalanche diode (SPAD) as a proximity detector - Google Patents

Using a single photon avalanche diode (SPAD) as a proximity detector Download PDF

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Publication number
GB2486164A
GB2486164A GB201020272A GB201020272A GB2486164A GB 2486164 A GB2486164 A GB 2486164A GB 201020272 A GB201020272 A GB 201020272A GB 201020272 A GB201020272 A GB 201020272A GB 2486164 A GB2486164 A GB 2486164A
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Prior art keywords
proximity
device
sensor
photon
single
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Withdrawn
Application number
GB201020272A
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GB201020272D0 (en )
Inventor
Barry Somerville
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STMicroelectronics (Research & Development) Ltd
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STMicroelectronics (Research & Development) Ltd
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Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06Systems determining position data of a target
    • G01S17/46Indirect determination of position data
    • G01S17/48Active triangulation systems, i.e. using the transmission and reflection of electromagnetic waves other than radio waves
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/026Systems using the reflection of electromagnetic waves other than radio waves for detecting the presence of an object
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04MTELEPHONIC COMMUNICATION
    • H04M1/00Substation equipment, e.g. for use by subscribers; Analogous equipment at exchanges
    • H04M1/60Substation equipment, e.g. for use by subscribers; Analogous equipment at exchanges including speech amplifiers
    • H04M1/6033Substation equipment, e.g. for use by subscribers; Analogous equipment at exchanges including speech amplifiers for providing handsfree use or a loudspeaker mode in telephone sets
    • H04M1/6041Portable telephones adapted for handsfree use
    • H04M1/605Portable telephones adapted for handsfree use involving control of the receiver volume to provide a dual operational mode at close or far distance from the user
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04MTELEPHONIC COMMUNICATION
    • H04M1/00Substation equipment, e.g. for use by subscribers; Analogous equipment at exchanges
    • H04M1/72Substation extension arrangements; Cordless telephones, i.e. devices for establishing wireless links to base stations without route selecting
    • H04M1/725Cordless telephones
    • H04M1/72519Portable communication terminals with improved user interface to control a main telephone operation mode or to indicate the communication status
    • H04M1/72563Portable communication terminals with improved user interface to control a main telephone operation mode or to indicate the communication status with means for adapting by the user the functionality or the communication capability of the terminal under specific circumstances
    • H04M1/72569Portable communication terminals with improved user interface to control a main telephone operation mode or to indicate the communication status with means for adapting by the user the functionality or the communication capability of the terminal under specific circumstances according to context or environment related information
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04MTELEPHONIC COMMUNICATION
    • H04M1/00Substation equipment, e.g. for use by subscribers; Analogous equipment at exchanges
    • H04M1/02Constructional features of telephone sets
    • H04M1/22Illuminating; Arrangements for improving visibility of characters on dials
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04MTELEPHONIC COMMUNICATION
    • H04M2250/00Details of telephonic subscriber devices
    • H04M2250/12Details of telephonic subscriber devices including a sensor for measuring a physical value, e.g. temperature or motion

Abstract

A communications device 400 comprises a proximity detector 412 for detecting the distance of a user from the device. Control circuitry may control audio and/or visual input/outputs of the device depending upon the distance of a user from the device. The proximity detector may comprise an array of single photon avalanche diodes (SPAD) and an illumination source for reflecting off the user.

Description

Application using a Single Photon Avalanche Diode (SPAD)

Description

Field of the invention

The present invention relates to an application using a single photon avalanche diode (SPAD).

1 0 Background of the invention

A SPAD is based on a p-n junction device biased beyond its breakdown region. The high reverse bias voltage generates a sufficient magnitude of electric field such that a single charge carrier introduced into the depletion layer of the device can cause a self-sustaining avalanche via impact ionisation. The avalanche is quenched, either actively or passively to allow the device to be "reset" to detect further photons. The initiating charge carrier can be photo-electrically generated by means of a single incident photon striking the high field region. It is this feature which gives rise to the name Single Photon Avalanche Diode'. This single photon detection mode of operation is often referred to as Geiger Mode'.

US 7,262,402 discloses an imaging device using an array of SPADs for capturing a depth and intensity map of a scene, when the scene is illuminated by an optical pulse.

US 2007/0182949 discloses an arrangement for measuring the distance to an object. The arrangement uses a modulated photonic wave to illuminate the object and an array of SPADs to detect the reflected wave. Various methods of analysis are disclosed to reduce the effects of interference in the reflected wave.

An objective of the present invention is to use a SPAD as a solid state photo-detector for ranging, proximity detection, accelerometry etc. This requires the use of new techniques and the development of new applications.

One such application is a SPAD proximity detector for use in a telephone or similar device to control the communication criteria such as volume, size of image etc. Mobile phones are often used in a so-called "hands-free" mode when the phone is located a distance away from the operator's head. Presently, in mobile phones, any change from "normal" mode to a "hands-free" mode is carried out by pressing buttons on the telephone. In addition, it is also necessary to adjust the speaker volume manually for either mode, if required.

Obiects of the invention It is an object of the present invention to overcome at least some of the

problems associated with the prior art.

It is a further object of the present invention to make use of SPADs in new applications and circumstances.

One object of the present invention is to provide a method and system for improving the operation of a mobile phone in a hands free mode.

Summary of the invention

The present invention provides a method and system as set out in the accompanying claims.

According to one aspect of the present invention there is provided a communications device comprising a proximity detector for detecting the distance of a user from the device.

Optionally, the proximity detector comprises an array of single photon avalanche diodes (SPAD); and an illumination source, wherein the illumination source is reflected by the user to the array of single photon avalanche diodes.

Optionally, the array of single photon avalanche diodes comprises a plurality of single photon avalanche diodes arranged in rows and columns.

Optionally, the array of single photon avalanche diodes is connected to a multiplex and a counter to enable measurement of the reflected illumination.

Optionally, the output from the proximity detector is passed to control circuitry for controlling the input and output of the communications device depending on the distance of the user from the device.

Optionally, the input and output are sound.

Optionally, the input and output are visual.

The present invention offers the following advantages: A telephone or other communications device can be automatically controlled such that, for example, volume can be changed to suit the distance of the user from the telephone.

Brief description of the drawings

Reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a diagram for illustrating the determination of phase shift in a SPAD, in accordance with an embodiment of the invention, Figure 2 is a diagram of a SPAD and associated timing diagram, in accordance with an embodiment of the invention, Figure 3 is a block diagram of a proximity detector, in accordance with an embodiment of the invention, Figure 4 is a diagram of a mobile phone including a proximity detector, in accordance with an embodiment of the present invention.

Detailed description of the preferred embodiments

The idea that a SPAD can be used as in a ranging application is borne out by the application of a Phase Shift Extraction Method for range determination, although alternative methods exist for range determination using S PADs based on direct time of flight measurement. The term ranging in this application is intended to cover all ranging devices and methods including by not limited to ranging devices, proximity devices accelerometers etc. Ranging can occur in a number of applications, including proximity detection which is relative easy to implement and inexpensive; Laser ranging which is more complex and costly than a proximity detector; and three-dimensional imaging which is a high-end application that could be used to recognize gestures and facial expressions.

A proximity sensor is the most basic of the ranging applications. At its simplest the sensor is capable of indicating the presence or absence of a user or object. Additional computation and illuminator complexity can provide enhanced data such as the range to an object. A typical range is of the order 0.01 m to 0.5m. In a simple proximity sensor the illumination source could be a modulated LED, at a wavelength of about 850nm.

The next application group is that of laser ranging, where the illumination source is a modulated diode laser. Performance can range from <1 cm to 20m range (and higher for top end systems) with millimetric accuracy.

Requirements on optics are enhanced, with hemispherical lenses and narrow bandpass filters being required. A near-field return may results in the introduction of parallax error, i.e. movement of the returned laser spot over the sensor pixel array dependent on distance to object. To overcome these problems the ranger includes calibration functions to enable the subtraction of the electronic and optical delay through the host system.

The illumination source wavelength should be visible so that the user can see what is being targeted and is typically around 635nm.

The third application group is that of 3D cameras. In this application a pixel array is used in order to avoid mechanical scanning of the array.

Systems can be based on a number of different architectures. Both time of flight (TOF) and modulated illuminator based architectures are used, however, the latter is more robust to ambient light and thus fits best with established photodiode construction. Additional features such as face and gesture recognition are applications of this type of ranging device.

Most optical ranging implementations use either stereoscopic, structured light, direct time of flight or phase extraction methods in order to ascertain the range to a target. Stereoscopic solutions use two conventional cameras, and can have a heavy computation overhead in order to extract range. The structured light scheme uses diffractive optics and the range is computed using a conventional camera based on how a known projected shape or matrix of spots is deformed as it strikes the target. The direct time of flight (TOF) method uses a narrow pulsed laser, with a time-digital converter (TDC) measuring the difference in time between transmission and first photon reception. Commonly, a reverse mode' is employed, where the TDC measures the back-portion of time, i.e. the time from first 1 0 photon reception to next pulse transmission. This scheme minimizes system activity to only the occasions where a photon is detected, and is therefore well matched to tightly controlled, low photon flux levels and medical applications such as fluorescent lifetime microscopy (FLIM).

The phase extraction method is probably the most commonly used method as it is well suited to systems which implement computation of the generalized range equation using existing photodiode technology. It is also robust to background ambient light conditions, and may be adapted to allow for varying illuminator modulation wave-shapes (i.e. sinusoidal or square). This scheme is favored for SPADs in proximity detection applications.

The present invention takes advantage of the fact that the phase extraction method system incorporates an inherent ambient light level detection function which can be used in conjunction with a SPAD for many applications, including detection of the location of a user to control telephone volume and the like.

It is important to understand the range equation derivation as it indicates the ease of applicability of SPADs to phase extraction proximity detection and ranging solutions. It also aids in the understanding of inherent features such as ambient light metering and measuring a depth of interest for a specific purpose.

Distance is determined from the speed of light and TOF, as follows: s=ct Where s is distance, c the speed of light and t is time. For a ranging system however, the distance is doubled due to the fact there are send and receive paths. As such the distance measured in a ranging system s is given by: s=1⁄2ct The time shift component (= t') due to the photon TOF, is dependent on the modulation frequency and phase shift magnitude of the waveform.

t = % shift of the returned waveform x tmoderjod and if tmocjperjod-l/fmod: 2,irf 0 2irof The units are in radians. Then by substituting the above equation back into the starting equation: the range equation' is expressed as.

s= co� 4.irof The critical component in this equation is 0, which is the unknown component of the % shift of the returned waveform. The following section discusses how this can be determined.

Since the values of c, f and ii are all constants; the range result simply scales with 0' (the % shift of the received light waveform in relation to that which was transmitted). Figure 2 demonstrates how 0 may be determined for a system employing a square wave modulated illuminator. The transmitted and received waveforms are shifted from one another by 0.

By measuring the photons that arrive in "a" and "b" in bins 1 and 2 respectively the value of �can be determined as follows: _i??_ = 2.ir (a + In this type of system there is a range limit set by the illuminator modulation frequency, which is known as the unambiguous range.

Photons received from targets that are further away than this range can introduce an aliasing error by erroneously appearing in a legitimate bin for a subsequent measurement. Since determination of range is enabled by the modulation process, it is desirable to maximize the number of edges of the modulation waveform in order to accumulate data for averaging purposes as fast as possible. However, a high modulation frequency may lower the unambiguous range and introduces more technical complexity in the illuminator driver circuitry. Therefore, two or more different modulation frequencies may be interleaved or used intermittently, so as to reduce or negate the impact of aliased photons via appropriate data processing.

Figure 2 illustrates a possible implementation of a SPAD based proximity sensor with an associated waveform diagram. Figure 2 shows a SPAD connected to a multiplexer 202. The output from the multiplexer passes through counters 1 and 2 (204). The SPAD device shown generally at 200 is of a standard type, including a photo diode 210, a p-type MOSFET 212 and a NOT gate 214.

The timing waveforms are shown in such a way so as to represent the relative photon arrival magnitudes. It can be seen that an extra phase has been added to enable computation of the background ambient light level offset c', although this can be significantly reduced by the use of a narrow optical band-pass filter matched to the illuminator wavelength if necessary.

The element c' is then accommodated in the computation of received light phase shift 0. The computed results for a, b, c are determined and written into either a temporary memory store or an 12C register. The computation of the phase shift 0, is calculated as follows: 0 -count (a + b)count -2c The predetermined selection of modulation frequency is performed by dedicated logic or host system which selects a suitable frequency or frequencies for the application of the range sensor. The range sensor of figure 2 is dependent on the amount of light that can be transmitted on to the scene, system power consumption and the target reflectivity.

Since the system shown in Figure 2 needs to compute the background light condition in order to ascertain the offset of the returned light pulse from the target, ambient light metering is included. A simplified timing scheme is employed if only the ambient light level data is required, since the target illumination cycle is not necessary. If a narrow band IR filter is employed in the optical path the value of c will represent only the content of the filter passband. This can then be extrapolated to an approximation of the general ambient light conditions.

Referring to figure 3 a block diagram of a proximity sensor is shown. The proximity sensor 300 includes SPAD function and the quenching thereof in block 302. The quenching can be passive as shown or of any other suitable type. The bias voltage for the SPAD may be provided by a charge pump or any other suitable device 304. The sensor module also includes an LED or other illumination source and an associated driver 306 to ensure that the required modulation is applied to the illumination source.

The sensor may include a distance computation logic module to determine range. Alternatively this can be located in a host device in which the range sensor is used. The sensor also includes multiplexers and counters 308 and a storage means 310, such as a 12C module. The sensor may also include a Phase Locked Loop (PLL) for clocking and subsequent timed signal generation purposes.

The power consumption of S PADs and their readout circuits is dependent on the incident photon arrival rate. The average power consumption of a ranging system could be reduced by using power saving modes such as pulsed on/off operation, at a rate of -l 0Hz for example, at the expense of target motion distortion.

The sensor may be implemented on a 1 mm die size and the 12C module could also be implemented on an appropriate die. The sensor may include an optical package, an integral IR band pass Filter (either coating or inherent in the optical elements) and an optimal field of view of about 3O.

As the sensor is not intended to "create an image" but is instead used to ensure that as many photons as possible are detected the optics could be made from injection molded hemispherical elements.

The illuminator source should ideally be of a non-visible wavelength, for example in the Near Infra Red (NIR) band, such as 850nm.

It should be noted that the terms "optical", "illumination" and "light" are intended to cover other wavelength ranges in the spectrum and are not limited to the visual spectrum.

The proximity sensor has been described with reference to simple low cost system, although it will be appreciated for certain applications the laser ranging and 3D camera technologies discussed above, could be used.

As previously indicated the proximity sensor of the present invention is very versatile and can be used in a vast array of different applications.

One such application based on a proximity detector is now described.

Referring to figure 4 a schematic view of a mobile phone 400 is shown.

The mobile phone includes a display 402; an alphanumeric keyboard 404; an earphone 406; and a speaker 408. In addition, the phone may include a mouse or equivalent navigation device 410 and a proximity semsor 412.

In one embodiment of the present invention the navigation device and the proximity sensor may be a single unit, since both can operate with an imaging element such as is used in an optical mouse. In an alternative embodiment the navigation device and proximity sensor are two separate elements.

The proximity sensor may comprise an array of single photon avalanche diodes (SPAD) and an appropriate illumination source as previously described. The proximity sensor is located on the phone in a position where it can face towards the user in use. The proximity sensor is connected to the mobile phone operating system in order to communicate the distance of the nearest object in the vicinity of the mobile phone. The nearest object is likely to be the user of the mobile phone.

Illumination from the illumination source is emitted and then reflected from the nearest object in the vicinity of the mobile phone back towards the array of single photon avalanche diodes. In this way the distance between the mobile phone and the nearest object is calculated as described above.

The mobile phone operating system can then use the distance measurement to set the mobile phone into either a normal mode or a hands-free mode depending on the distance between the mobile phone and the nearest object. In addition, the operating system can adjust the volume to a level that is appropriate to the distance detected. There may be a distance to volume profile stored within the operating system so that the volume is set to a level appropriate from the distance between the mobile phone and the nearest object (usually the user).

The proximity sensor could also be used in other types of communication device, where the medium is not sound, for example visual communications means, such as video. The proximity sensor may be used in any appropriate device which controls the volume and/or size of image depending on the distance of the user from the device.

The proximity sensor may be incorporated into a single unit with other applications or function such as a keyboard or scroll wheel. A single array of single photon avalanche diodes may be switched between a proximity sensor mode and another mode. For example a keyboard, as described in co-pending application P117047.GB.01 and herein included by reference, may include a space which provides the proximity function herein described. Similarly, a scroll wheel as described in co-pending application P11 7059.0 B.01 and herein included by reference may include a mode in which the proximity detector or function described herein can be implemented.

The illumination source may be located in any appropriate location that will enable reflection to be returned to the proximity detector. The illumination sources may include modulated light emitting diodes (LEDs), modulated lasers or any other appropriate illumination source. Similarly the proximity detector can be located on any suitable surface or location as long as it functions as described above.

The invention is described with reference to a mobile telephone. It will be appreciated that any type of telephone, PDA, or other type of device which is used by the user to communicate with the device may make use of the proximity sensor in accordance with the present invention. Accordingly the term phone in the present invention is intended to be non-limitative and include all types of communication devices where there is an input or output can be varied based on the distance of the user from the device.

The input and output could be oral, visual or any combination thereof.

The communications device can be used in any system where communication is required, such as entry systems, security systems, etc. It will be appreciated that many variations of the invention could apply and are intended to be encompassed within the scope of the claims.

Claims (8)

  1. Claims 1. A communications device comprising a proximity detector for detecting the distance of a user from the device.
  2. 2. The communications device of claim 1, wherein the proximity detector comprises an array of single photon avalanche diodes (SPAD); and an illumination source, wherein the illumination source is reflected by the user to the array of single photon avalanche diodes.
  3. 3. The communications device of claim 2, wherein the array of single photon avalanche diodes comprises a plurality of single photon avalanche diodes arranged in rows and columns.
  4. 4. The communications device of claim 2 or claim 3, wherein the array of single photon avalanche diodes is connected to a multiplex and a counter to enable measurement of the reflected illumination.
  5. 5. The communications device of any preceding claim, wherein the output from the proximity detector is passed to control circuitry for controlling the input and output of the communications device depending on the distance of the user from the device.
  6. 6. The communications device of claim 5, wherein the input and output are sound.
  7. 7. The communications device of claim 5 or claim 6, wherein the input and output are visual.
  8. 8. A system including a communication device of any preceding claim.
GB201020272A 2010-11-30 2010-11-30 Application using a single photon avalanche diode (SPAD) Withdrawn GB201020272D0 (en)

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GB2486164A true true GB2486164A (en) 2012-06-13

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8749765B2 (en) 2010-11-30 2014-06-10 Stmicroelectronics (Research & Development) Limited Application using a single photon avalanche diode (SPAD)
US9058081B2 (en) 2010-11-30 2015-06-16 Stmicroelectronics (Research & Development) Limited Application using a single photon avalanche diode (SPAD)
US9238393B2 (en) 2011-09-14 2016-01-19 Stmicroelectronics (Research & Development) Limited System and method for monitoring vibration isolators
GB2548157A (en) * 2016-03-11 2017-09-13 Sony Europe Ltd Apparartus, method and computer program

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US5396510A (en) * 1993-09-30 1995-03-07 Honeywell Inc. Laser sensor capable of measuring distance, velocity, and acceleration
WO2003026258A1 (en) * 2001-08-27 2003-03-27 Siemens Aktiengesellschaft Call signal volume- and/or hands-free function-controlled mobile radio device
US20070202858A1 (en) * 2006-02-15 2007-08-30 Asustek Computer Inc. Mobile device capable of dynamically adjusting volume and related method
US7301608B1 (en) * 2005-01-11 2007-11-27 Itt Manufacturing Enterprises, Inc. Photon-counting, non-imaging, direct-detect LADAR
US20090015425A1 (en) * 2007-07-13 2009-01-15 Sony Ericsson Mobile Communications Ab Camera of an electronic device used as a proximity detector
WO2009096643A1 (en) * 2008-02-01 2009-08-06 Lg Electronics Inc. A user interface for mobile devices

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5396510A (en) * 1993-09-30 1995-03-07 Honeywell Inc. Laser sensor capable of measuring distance, velocity, and acceleration
WO2003026258A1 (en) * 2001-08-27 2003-03-27 Siemens Aktiengesellschaft Call signal volume- and/or hands-free function-controlled mobile radio device
US7301608B1 (en) * 2005-01-11 2007-11-27 Itt Manufacturing Enterprises, Inc. Photon-counting, non-imaging, direct-detect LADAR
US20070202858A1 (en) * 2006-02-15 2007-08-30 Asustek Computer Inc. Mobile device capable of dynamically adjusting volume and related method
US20090015425A1 (en) * 2007-07-13 2009-01-15 Sony Ericsson Mobile Communications Ab Camera of an electronic device used as a proximity detector
WO2009096643A1 (en) * 2008-02-01 2009-08-06 Lg Electronics Inc. A user interface for mobile devices

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8749765B2 (en) 2010-11-30 2014-06-10 Stmicroelectronics (Research & Development) Limited Application using a single photon avalanche diode (SPAD)
US9058081B2 (en) 2010-11-30 2015-06-16 Stmicroelectronics (Research & Development) Limited Application using a single photon avalanche diode (SPAD)
US9238393B2 (en) 2011-09-14 2016-01-19 Stmicroelectronics (Research & Development) Limited System and method for monitoring vibration isolators
US9562807B2 (en) 2011-09-14 2017-02-07 Stmicroelectronics (Research & Development) Limited System and method for monitoring vibration isolators
GB2548157A (en) * 2016-03-11 2017-09-13 Sony Europe Ltd Apparartus, method and computer program

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