Active pixel intraoral radiographic image sensor and related image capture method

Abstract

The present invention relates to an active-pixel intraoral radiographic image sensor and an associated image capture method. In the first stage of detecting the onset of an X-ray flash, a switching circuit MUX1 allows connection of a common connection node NC, corresponding to the drain of a photodiode initialization transistor M1 at the input of a current-to-voltage conversion detection circuit DTX1. This drain provides an output signal to detect the onset of an X-ray flash when the current generated by all photodiodes in the matrix exceeds a predetermined threshold. The same principle can be used to detect the end of an X-ray flash using certain pixels of the matrix by injecting current generated by the photodiodes of these pixels and collected at a different common connection node electrically isolated from the first. The end of the flash signal corresponds to a change in this current below a predetermined threshold.

Description

Technical Field

[0001] The present invention relates to the field of medical imaging, and more particularly to an active pixel intraoral dental radiographic image sensor using CMOS technology. Background Art

[0002] The structure of these active pixels is based on a photosensitive element (photodiode, photogate) associated with a transistor that controls the various stages of image capture: the initialization phase of the photosensitive element, preceded by the charge integration phase, and then the pixel reading phase. For this reading phase, for each pixel in a row of the matrix, a voltage level corresponding to the amount of charge accumulated in the pixel during the integration phase is transferred to the column conductor via a transistor installed as a voltage follower associated with the node used to read the pixel. The reading is then performed by a readout circuit located at the bottom of the column, which actually samples two voltage levels: that corresponding to the amount of charge accumulated in the node used to read the pixel, and that corresponding to the reinitialization level of the readout node, so that they are subtracted from each other. This therefore improves the signal-to-noise ratio (double sampling and subtraction of correlated noise).

[0003] Dental radiographic images are typically captured in the following manner: a sensor is placed in the patient's mouth behind the anatomical region to be observed. An X-ray source is positioned and activated to emit a flash of X-rays through the biological tissue and material of the anatomical region to be radiographed toward the active face of the sensor. Upon detecting the onset of the X-ray flash on the active face of the sensor, the sensor's sequencing circuitry triggers image capture. Depending on the type of photodiode, X-rays reaching the active face of the sensor are converted directly into electrical signals or, after conversion to visible radiation from a scintillator, are converted by pixels into electrical signals. After the pixels are read out, an image of the radiographed anatomical region can be displayed, for example, on a computer screen.

[0004] Detecting the onset of an X-ray flash is part of the approach required to reduce the radiation dose applied to patients. In medical imaging, the radiation dose recommendations of standardization bodies regarding patients and physicians are quite stringent. For each image capture, the intensity and duration of the X-ray flash must be adjusted according to the morphology, patient age, and the anatomical region being radiographed. This ensures that the exposure dose is as low as possible without any unnecessary loss, allowing for a high-quality image to be acquired in a single pass. For image sensors, this involves synchronizing the charge integration phase with the effective exposure of the active surface to the useful radiation in the best possible manner, thereby optimizing the signal-to-noise ratio with respect to radiation intensity and duration. If the integration phase begins too early, charge corresponding to dark current accumulates. If it begins too late, the useful signal is lost. The end of the X-ray flash is often also detected. This improves the signal-to-noise ratio (no dark current integration) compared to solutions where the integration duration is preset to be greater than the X-ray flash duration (source adjustment data). Furthermore, the readout phase is triggered more quickly, thereby increasing the speed and efficiency of image acquisition.

[0005] Therefore, the sensor must integrate a detection circuit whose purpose is to optimally set the start of the integration phase at the onset of the X-ray flare on the sensor's active surface. This detection circuit typically uses photodetector strips arranged horizontally and / or vertically around the pixel matrix. These photodetector strips are therefore positioned directly behind absorptive anatomical areas (teeth, gums), which impairs or delays the sensor's detection of the X-ray flare. From this perspective, the optimal detection area on the sensor's active surface can be the free area between the patient's upper and lower jaws (i.e., without absorptive obstacles), corresponding to a detection strip located in the middle of the sensor's pixel matrix. This is detrimental to the image capture pixels, necessitating interpolation calculations and filtering to reconstruct the corresponding image data, as practitioners prefer to see a complete image of the radiographic area. This also implies a loss of image quality due to inaccuracies introduced by interpolation.

[0006] It is also known to perform detection using pixels dispersed in a matrix as reference pixels, as described, for example, in patent US 6404854. During detection, these reference pixels are read individually in a non-destructive manner (without reinitialization between readings) for comparison with a threshold value, and this continues until an image capture decision is made when enough reference pixels provide a signal above a certain threshold value. A disadvantage of this solution is that a specific ordering of these pixels is required. However, above all, this solution is imperfect in terms of detecting the occurrence of X-rays independently of the position of the sensor: depending on the position of the sensor, it is impossible to avoid that most of the reference pixels are placed behind a highly absorbing area, which would delay the detection process.

[0007] Furthermore, to help reduce the X-ray dose required for radiological image capture, it is necessary to be able to detect very low signal levels to signal the onset of radiation exposure in the photosensitive area, thereby triggering the integration phase with no (or minimal) loss of useful information. In other words, the goal is to have the emission of the detection signal very close to the time when the X-rays actually arrive at the active surface of the sensor. For these reasons, it is more advantageous to directly detect the current supplied by all photodetectors using a capacitive transimpedance amplifier, as the amplifier's significant gain lowers the detection threshold, meaning that the arrival of the X-ray flash can be determined earlier, and therefore integration can begin earlier. Such amplifiers are well known and are commonly used to read out pixels in infrared image sensors. Furthermore, in the field of medical radiology, patent application WO 2017 / 121728 describes a circuit for detecting the onset of an X-ray flash based on such an amplifier, which reads the current supplied by a set of detection photodiodes placed on either side of the pixel matrix.

[0008] Therefore, there is an urgent need to find a technical solution that allows the occurrence of X-rays to be detected effectively independently of the position of the sensor, without sacrificing or losing the accuracy of the image data, and that is easy to implement in existing topologies, i.e. without having to completely rethink the design and without affecting the active image capture surface. Summary of the Invention

[0009] The subject of the invention is an active pixel dental radiographic image sensor with integrated X-ray occurrence detection, which allows efficient detection of X-ray occurrences independently of the sensor's position in the patient's mouth and maximizes the active surface (matrix) applicable to the size of the sensor.

[0010] More specifically, the present invention relates to an intraoral radiographic image sensor using MOS technology, comprising:

[0011] a matrix of photosensitive pixels arranged in rows and columns, each pixel comprising a photodiode and a transistor, including a photodiode initialization transistor connected between a photodiode node of said pixel and a first connection node common to said pixels;

[0012] - a sequencing circuit that provides signals to control the transistors of the pixels to control an image capture sequence during exposure to an X-ray flash, including a phase of overall initialization of the photodiodes of the pixels, a phase of charge integration during an integration period, and a phase of reading the pixels.

[0013] According to the invention, the sensor comprises a first coupling switch controlled by a first logic signal for connecting the first connection node to a signal input of a first current detection circuit or to a photodiode initialization voltage source, so that the first logic signal is in a first logic state or a second logic state, respectively; and

[0014] The sequencing circuit of the sensor, configured to control the phase of detecting the start of exposure to the X-ray flash by the first detection circuit to trigger the image capture sequence, comprises the following operations:

[0015] -a) commanding the photodiode initialization transistor to switch to a conducting state simultaneously in all pixels; and

[0016] -b) confirming that the first logic signal is in the first logic state, the effect of which is to inject at the signal input of the first detection circuit the current collected at the first connection node originating from the photodiode of the pixel; and then

[0017] -c) when the output logic signal of the first detection circuit switches from a first logic state to a second logic state, corresponding to detecting that the input current level is higher than a predetermined threshold, confirming that the first logic signal is in the second logic state, its function is to couple the initialization transistor that is always in the on state to the initialization voltage source, thereby activating the overall initialization phase of the image capture sequence to initialize the photodiode before the integration phase.

[0018] In a refinement, the initialization transistors of the groups of pixels of the matrix are connected not to the first connection node but to a second connection node, the second connection node being electrically isolated from the first connection node, and the sensor comprises a second current detection circuit of the same type as the first detection circuit and controlled by the same clock signal, the input signal of which is connected to the second connection node, and the initialization transistors of the pixels of the group are in the on state at least until the second detection circuit detects the end of exposure to X-rays, the end corresponding to a current injected at the input and collected at the second connection node being below a predetermined threshold; and

[0019] - upon detecting the end of exposure to the X-ray flash, stopping the integration phase of the image capture sequence to start the reading phase.

[0020] Advantageously, a second coupling circuit is provided to connect the second connection node to the signal input of the second detection circuit or to an initialization voltage source depending on a second control logic signal, which is configured in the sensor to configure the pixels in the group as end-of-exposure detection pixels or image capture pixels.

[0021] According to one aspect of the present invention, the gain of the capacitive transimpedance amplifier and / or the voltage threshold of the comparator are adjustment parameters of the sensors adjusted in the first detection circuit and the second detection circuit for detecting the start and end of the X-ray flash respectively.

[0022] According to another aspect of the invention, the sequencing circuit is configured to trigger another image capture sequence that applies the same integration duration and uses the same pixels for image capture as a previous image capture sequence that was performed during exposure to the X-ray flash and that provided first image data, thereby allowing dark noise on the first image data to be measured and subtracted.

[0023] The sensor according to the invention is particularly applicable to active pixels having three or more transistors, in particular five and more transistors.

[0024] According to one embodiment of the present invention, the current detection circuit of the sensor includes a capacitive transimpedance amplifier, which includes a non-inverting input connected to a common mode voltage and an inverting input forming the signal input, wherein the signal input is coupled to the common connection node of the pixels, and the amplifier is controlled by a clock signal to periodically generate a voltage ramp at the signal output, wherein the voltage ramp depends on the level of the current injected at the signal input, and the ramp is applied to a comparator for comparison with a voltage threshold.

[0025] The present invention also relates to a corresponding radiological image capturing method. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The invention will be better understood and further advantages will become apparent on reading the detailed description of embodiments, which are provided by way of example and illustrated using the accompanying drawings, in which:

[0027] Figure 1 is a functional block diagram of detecting the onset of an X-ray flash according to the present invention, applicable to an image sensor based on a three-transistor (3T) type active pixel structure;

[0028] Figure 2 is a block diagram of such a 3T pixel matrix image sensor according to the present invention, the 3T pixel matrix image sensor comprising means for detecting the onset of exposure to an X-ray flash;

[0029] Figure 3 is a block diagram of a capacitive transimpedance amplifier detection device;

[0030] Figure 4is a timing diagram of control signals for a phase of detecting an X-ray flash occurrence and an image capturing sequence in an image sensor having an X-ray flash onset detection circuit according to the present invention;

[0031] Figure 5 is a timing diagram of signals of a circuit for detecting the start of an X-ray flash and signals of a detection circuit of the same type for detecting the end of an X-ray flash according to the present invention;

[0032] Figure 6 is a functional block diagram of the present invention as applied to at least a five-transistor (5T) type active pixel;

[0033] Figure 7 is a block diagram of a 3T pixel sensor that allows detection of the start and end of an X-ray flash according to one embodiment of the present invention;

[0034] Figure 8 is with Figure 7 A block diagram of a 5T pixel sensor corresponding to this embodiment; and

[0035] Figure 9 is a timing diagram of control signals for radiographic image capture according to the present invention, including detection of the start and end of an X-ray flash for triggering and stopping, respectively, the integration phase of a radiographic image capture sequence. DETAILED DESCRIPTION

[0036] It should be noted that the accompanying drawings are simple diagrams illustrating the present invention and are not drawn to scale. Only functional elements or signals necessary for understanding the present invention are shown. For the sake of clarity and simplicity, the same symbols or reference numerals are used throughout the specification and drawings to represent the same or similar elements.

[0037] Furthermore, in the following description, the terms "coupled" or "connected" when used indicate direct or indirect electrical connections. The term "connected" indicates a direct electrical connection.

[0038] The present invention relates to radiographic image sensors, and more particularly to intraoral dental image sensors utilizing CMOS technology using active pixels.

[0039] Active pixels are Figure 1 The pixel shown by way of example in FIG. 1 comprises a light-sensitive element, typically a photodiode (PH), and a number of transistors (MOS), all of the same type, used as switches (in the ON or OFF state) or voltage followers to control the various stages of the image capture sequence. Strictly speaking, CMOS technology (a combination of N and P transistors) refers more specifically to the electronics surrounding the pixel (control, readout, interface electronics, etc.).

[0040] The invention is more particularly illustrated in the context of an image sensor fabricated with a P-type doped semiconductor substrate, which is placed at a ground reference potential, typically zero potential.

[0041] The photodiode PH is preferably of the "pinned" type, i.e. the junction PN is formed by an N-type doped region in a lightly doped substrate (P-), and this region N (cathode) is covered by a highly doped P-type surface layer (P++), the photodiode being placed at the ground reference potential of the substrate: this sets the potential of the well N (region N) of the photodiode to the potential V pin (the quiescent voltage of the photodiode), which depends only on the concentrations of the N and P dopants.

[0042] The transistors of the active pixels are N-type. By applying a positive potential V to the gates of these transistors, ON To command them to switch to the conducting state (off or on), this potential usually corresponds to the positive supply voltage V of the sensor electronics. DD The voltage V DD The level (for example Figure 4 These transistors are commanded to switch to the OFF state (open or blocking) by applying a potential to their gates g, which typically corresponds to the ground reference potential of the substrate (zero potential), or even to a more negative potential.

[0043] The sensor's logic control signal can take two logical values, "0" or "1", which correspond to the ground reference potential of the substrate and V DD .

[0044] The figures and description reflect these conventions. One skilled in the art will know how to easily convert all of these into active pixels with P-type MOS transistors.

[0045] For dental radiology, active pixels are often used with three control transistors (3T), which increases the pixel's storage capacity. These pixels only allow the generation of so-called "sliding shutter" images, as the end of the integration period is offset row by row, coinciding with the sequential reading of the pixels by scanning the rows. The start of the integration period, in the context of dental radiology, is identical for all pixels, as it is synchronized upon the detection of an X-ray flash (or more simply, an "X-flash") on the active face of the sensor. The effective integration duration of a row therefore increases with the scanning direction of the row. The difference in total integration duration is small, but this leads to line effects in the image that can be attenuated by image processing. This is well known.

[0046] The invention will be explained in more detail for a sensor using such a 3T pixel matrix. However, it will be seen later that the invention can be easily applied to structures with more transistors, which in particular have the advantage of allowing instantaneous image capture ("snapshots") with the start and end of the integration being the same for all pixels, and in particular to 5T structures, i.e. comprising (at least) 5 transistors. It should be noted that in the context of the present invention, the sensor is only sensitive to X-rays (by construction): therefore, it cannot see visible rays. During the integration period, it only integrates the charge corresponding to the received X-rays.

[0047] Figure 1 and Figure 2 The principle of detecting the onset of an X-ray flash according to the invention in an image sensor based on a 3T active pixel matrix M-PIX, which in the example comprises N rows and P columns of pixels, is shown. Figure 1 This is shown by focusing on a pixel of the matrix, Figure 2 The implementation of the invention in a sensor is shown which allows using all pixels of the matrix, firstly detecting the start of exposure to a flash and then performing an image capture sequence upon detection of the start of this flash.

[0048] The pixel row R of rank i in the matrix i and pixel column Col with rank j j Pixel P ij ( Figure 1 )include:

[0049] - a photodiode PH (preferably of the "pinned" type) connected to the photodiode node KN i (cathode) and the reference ground voltage;

[0050] - Photodiode initialization transistor M1, which is connected to the photodiode node KN i , and receives the signal RSKN on its gate g i , the signal RSKN i Used to initialize the pixel row of rank i to command the charge (electrons) accumulated in the photodiode to move toward the reference voltage source V RS (hereinafter also referred to as photodiode initialization voltage) release;

[0051] - Transistor M2, which is installed as a voltage follower and has its gate connected to the photodiode node KN i (capacitive), when the pixel is selected for reading, the photodiode node converts the charge accumulated in the photodiode PH into a charge that is transferred to the column conductor Col j the voltage level of

[0052] - Transistor M3, which is used to select the pixel to be read and is connected in series between transistor M2 and column conductor Col j The column conductor is connected to the read circuit RD, and the transistor M3 receives the signal on the gate g for selecting the pixel row R to be read. i Signal Sel i .

[0053] About the mark: KN i represents the photodiode node of the pixel in row rank i. This allows this node to be easily connected to the photodiode reinitialization signal of each row (denoted as RS KNi ) is associated with.

[0054] For each pixel of the relevant column, the reading circuit RD makes it possible to obtain a digital value representative of the amount of charge integrated by the pixel.

[0055] like Figure 2 As shown, for each row of pixels R i There are two control signals: RS for initializing the photodiode KNi and a signal Sel for selecting read i , which are applied to the gates of transistors M1 and M3 of all pixels in row rank i, respectively. These signals are commanded by the sequencing circuit DM of the sensor to control the dental radiographic image capture sequence, which generally consists of the following series of stages (see Figure 4 ):

[0056] - Phase 301 of global initialization RSG of the photodiodes (ie applied simultaneously to all pixels of the matrix), activated by commanding all transistors M1 to switch to the ON state simultaneously: all signals RS KNi (i=1 to N) is activated (set to V ON );

[0057] - an integration phase 302 which starts simultaneously for all pixels by deactivating all signals RSKN i (Return V OFF ) to command;

[0058] - a sequential readout phase 303 by scanning the pixel rows, which is performed during the integration duration d INT (duration elapsed since the start of the integration phase). In this phase, after reading the duration d r During this period, the signal Sel i One by one (one at a time) are activated (set to V ONThe read circuit RD is typically configured to acquire two samples: a signal level (SHS) sample corresponding to the amount of charge integrated by the photodiode since the start of the integration phase, and an initialization signal RS for the current row selected for reading by activating KNi to reinitialize the RSi photodiode after a sample of the reference level.

[0059] In fact, electrically speaking, the drain d of the initialization transistor M1 of each pixel is connected to a connection node NC common to all pixels, usually connected to a reference voltage source VRS for reinitializing the photodiode (releasing any charge accumulated in the potential well of each photodiode).

[0060] From a topological perspective, Figure 2 As shown, for each pixel, this common connection node NC corresponds to a connection point represented by a black dot, connected to a conductive gate GRS (shown as a thick line) generated at the level of the conductive topology of the sensor chip. The term "gate" should be understood as a periodic 2D grid synchronized with the matrix. The gate GRS, appropriately electrically connected to the reference voltage source VRS, allows the global initialization phase RSG and the selective initialization phase (RSG) during the sequential reading of the pixels. i 、RS i+1 ,......) to initialize the photodiode.

[0061] According to the present invention, and as Figure 1 and Figure 2 As shown, a circuit is provided which is not directly connected to the initialization voltage source VRS, but is connected to the source V through a switch circuit according to the logic state "0" or "1" of the control logic signal PROB1. RS The switching circuit MUX1 comprises two channels for connecting the node NC: a first channel X1 is connected to the source VRS; a second channel X2 is connected, via a current-to-voltage converter, to the signal input IN-DTX1 of the current detection circuit DTX1 of the sensor. The purpose of this circuit DTX1 is to provide as an output a signal OUT-DTX1, which indicates the detection of the beginning of exposure of the sensor to an X-ray flash, when the current I generated by all the photodiodes (of the pixels) of the matrix and collected on the common connection node NC via the initialization transistors M1, all of which are active and in the on state, and the circuit MUX1, exceeds a predetermined threshold.

[0062] More specifically, and as Figure 4 As shown in the timing diagram of FIG, the sequencing circuit DM commands the phase 200 of detecting the start of the X-ray flash (when the standby phase STANDBY 100 is completed) through the following series of steps:

[0063] - placing the signal PROB1 in a first logic state, in this example a high state (“1”) for selecting channel X2 of the switch MUX1 : the common connection node NC of all pixels is then connected to the current input IN-DTX1 ; and

[0064] - Activate all photodiode initialization signals RSKN simultaneously i , allowing each pixel's transistor M1 to function as a photodiode at the pixel's photodiode node KN i The gates of the sensor transfer charge between the photodiodes (cathodes) and a common connection node NC. In this way, all the charge from all the photodiodes of the matrix is ​​collected at node NC, resulting in a photocurrent I injected at the input IN-DTX1 of the circuit DTX1. This makes the detection of the occurrence of an X-ray flash according to the present invention efficient and precise, because the current contribution of all the pixels of the sensor's photosensitive matrix is ​​taken into account: the pixel matrix then acts as a giant charge sink for detecting the onset of exposure to an X-ray flash. Therefore, no matter where the sensor is located in the patient's mouth, there will always be some pixels in the matrix that will be reached by X-rays with little or no attenuation.

[0065] When the current detection circuit DTX1 detects that the current exceeds a predetermined threshold, the output logic signal OUT-DTX1 changes state: in this example, it transitions from a high logic state “1” to a low logic state “0”, which is detected by the sequencing circuit DM, which then triggers the image capture sequence 300 in the following way:

[0066] - The signal PROB1 is placed in another logic state, in this example a low state ("0") for channel X1 of the selection switch MUX1: the common connection node NC of all pixels is then connected to the initialization voltage V RS ;

[0067] - Keeping the initialization transistor M1 active for the duration of the phase 301 of initialization of the entire RSG.

[0068] The other stages of the image capture sequence controlled by the sequencing circuit DM are then performed in the usual manner (integration 302, sequential reading 303). This means that in the present invention, the pixels of the matrix are first used as pixels for detecting the start of exposure to an X-ray flash and then as image capture pixels.

[0069] Figure 3An embodiment of a current detection circuit DTX1, comprising a capacitive transimpedance amplifier CTIA1 and a voltage comparator COMP1, is shown, allowing for the implementation of the detection phase 200. It should be noted that the use of capacitive transimpedance amplifiers is known for integrating the current provided by detection photodiodes arranged at the edge of a pixel matrix and then detecting the arrival of an X-ray flash, as described, for example, in the aforementioned application WO 2017 / 121728. These capacitive transimpedance amplifiers are also used for reading infrared sensor pixels, as described, for example, in application number EP 1 399 746.

[0070] The capacitor transimpedance amplifier CTIA1 ensures that the ctia The input current I is periodically integrated and then the voltage comparator COMP1 compares the signal V provided as output. out-ctia1 With programmable voltage threshold V th1 The voltage comparator is configured to provide a logic signal OUT-DTX1 as an output when the signal level V out-ctia1 Exceeds the threshold V th1 When the logic signal switches from an initial logic state (usually "0") to another state ("1").

[0071] Figure 3 The amplifier CTIA1 corresponds to a possible embodiment of the basic configuration of a capacitive transimpedance amplifier, the feedback loop of which comprises an initialization switch T1 placed in parallel with the integrating capacitor Cf. However, the invention is not limited to this embodiment and also covers other implementations of the prior art.

[0072] The non-inverting input (+) of amplifier CTIA1 is connected to the common-mode voltage V cm1 , the inverting input (-) is the signal input IN-DTX1, through which the current I to be measured is injected. The switch T1 controls the signal Φ in the initialization phase. ctia It is closed (ON) periodically to discharge the integral capacitor Cf and make the output voltage V out-ctia1 and the input IN-DTX1 reaches the common mode voltage V cm1 The level of the input current I is used as a reference point for the periodic integration of the input current I. This integration begins when switch T1 returns to the open state (OFF), and all the current I injected at the input is integrated in the terminals of capacitor Cf with a gain that depends on the ratio of the feedback loop capacitor (Cf in this example) to the capacitor Cp on the signal input, which represents the parasitic capacitance of the photodiode (equivalent value).

[0073] like Figure 5 As shown, at the output V out-ctia1 The signal obtained at is a voltage ramp.

[0074] The comparator includes, for example, a voltage Vout-ctia1 With a configurable threshold V th1 An analog stage that performs comparison and a stage that shapes the signal to provide the logic signal OUT-DTX1 as output. When the voltage V out-ctia1 Exceeds the threshold V th1 This signal typically switches from a low state to a high state when Figure 5 ). The sequencing circuit DM detects this switching in order to synchronize (trigger) the image capture sequence when the X-ray flash arrives.

[0075] The sequencing circuit DM then switches the signal PROB1 to another logic state (“0” in this example) to select the first input channel X1 of the circuit MUX1: the common connection node NC of each pixel is then connected to the initialization voltage source V of the photodiode. RS When transistor M1 is in conduction mode (RSKN i In V ON ), they maintain this mode ( Figure 4 ), which serves to trigger a phase 301 of global reinitialization RSG of the pixels, which is the first phase of an image capture sequence 300 (I-FX) during exposure to an X-ray flash. The sequencing circuit DM then controls the integration phase in a conventional manner, which starts simultaneously for all pixels, followed by a sequential readout phase.

[0076] Figure 4 The complete sequence of detecting an X-ray flash and capturing an image is shown after the practitioner places the sensor behind a selected anatomical region with the active surface facing the X-ray source, and then triggers the source, for example, by a control computer or by directly activating the source. This activation causes the sensor to exit standby mode 100 (STANDBY) via an activation signal transmitted by the computer and / or source via a wireless or wired (USB) interface.

[0077] The sensor exits the standby mode (STANDBY) and enters the initialization phase 101, allowing the power supply V DD and reference V RS Voltage. Amplifier CTIA1 initialization (Φ ctia , Figure 5 ): Output V out-ctia1 and the voltage at the input IN-DTX1 to achieve the common-mode V cm1 voltage level that is higher than the photodiode's quiescent voltage V pin In this example, V pin is 0.8 volts, V cm1 is 1 volt. Figure 4 As shown, this also makes the common connection node NC (gate GRS) and the node KN of the photodiode (cathode)i The potential rises to the same common-mode level V cm1 .

[0078] The sequencing circuit DM then controls the phase 200 of detecting the X-ray flash in the following way:

[0079] -Set all lines RSKN i To control the gate of the initialization transistor M1 to V ON ;as well as

[0080] - Activation of the signal PROB1 in logic state (“1”) which selects the second channel X2 of the circuit MUX1 , which results in all the common connection nodes NC (and the conduction gates GRS) of the transistors M1 of the pixels being connected to the input IN-DTX1 of the current detection circuit DTX1 .

[0081] During the entire period of the detection phase 200, the signal Sel for selecting the pixel row to be read is i All remain in an inactive state (low state).

[0082] When the light of the flash X-ray reaches the active surface of the sensor, the photodiodes generate a charge, which generates a current I at the input IN-DTX1 that represents the contribution of all the photodiodes in the matrix. This current is integrated by the amplifier CTIA1, generating a voltage ramp at the output. When the ramp voltage V out-ctia1 Exceeds the threshold V th1 (set to 1.5 volts in the example), the output OUT-DTX1 switches to a high (logic) state ( Figure 4 ), and this switching of the signal OUT-DTX1 (detection of a rising edge and / or a high logic state) indicates that the start of the X-ray flash is detected on the sequencing circuit DM. In a non-limiting practical embodiment, the comparator COMP1 comprises a sampling clock Φ S / H With the clock Φ ctia The same frequency, but with a phase-shifted activation latch output stage ( Figure 5 ).

[0083] As described above, when circuit DM detects a toggle of signal OUT-DTX1 indicating that the start of exposure has been detected, it can then control successive phases of the image capture sequence 300 (I-FX):

[0084] - Signal PROB1 changes logic state (arrow 2). In the example, it switches to "0", selecting the other channel X1 of circuit MUX1: node NC ( Figure 2 The gates GRS in the circuit are then all electrically connected to a reference voltage source V RSThe input IN-DTX1 is separated from the node NC and no longer receives any current. The output voltage V out-ctia1 Returns to (and remains at) the common-mode voltage level V cm1 , and then the output OUT-DTX1 of the comparator COMP1 switches back to the low state ( Figure 4 and 5 );

[0085] - Used to command the photodiode to initialize and switch to the active state (V DD ) signal RSKN i remains in the active state (transistor M1 is conducting), thus allowing the execution of phase 301 of the overall initialization RSG of the image capture sequence: the charge of the photodiode is depleted and the capacitor node KN is i is brought (arrow 3) to voltage level 2 (2 volts in the example), which corresponds to a reference voltage V that is less than the threshold voltage of transistor M1. RS (3 volts).

[0086] The sequencing circuit DM then converts all signals RSKN i Transition to inactive state ( Figure 4 ), thereby blocking all transistors M1, which marks the beginning of the pixel integration phase 302: the photodiode begins to integrate the charge through the photoelectric conversion effect and accumulates this charge (parasitic photodiode capacitance). Node KN i The potential of the battery drops to a minimum value V according to the accumulated charge (depending on the lighting) sat , which corresponds to the saturation of the pixel or the readout chain.

[0087] exist Figure 4 In the example shown, the sequential reading phase 303 is performed during the integration duration d INT After that, the integration duration d INT is preset to a value higher than the emission duration dX of the X-ray source used. INT At the end of the reading (for example by a counter of the sequencing circuit DM), the sequencing circuit DM activates the sequential reading phase 303 , allowing the pixels of each of the N rows of the matrix to be read row by row.

[0088] Consider the pixel row R i : Signal Sel used to select the row i is activated to read for a duration of d r The select transistor M3 of each pixel in the row is switched to the conducting state (ON): For each pixel in the row, the voltage level provided by the transistor M2 (which is the same as the voltage level at the photodiode (capacitor) reading node KN) is iThe amount of charge accumulated in the pixel is transferred to the column conductor Col j (via M3) in order to be sampled (SHS) by the corresponding read circuit RD; then only the row is reinitialized by activating the signal RSKN i To reinitialize the photodiode of each pixel in the row (it can be seen that the next row R i+1 The signal RSKNi+1 is still inactive at this time) and then the new voltage level is transmitted to the column conductor Col as the reinitialization level j , and is sampled by the readout circuit (SHR). The difference between the signal level and the reinitialization level represents the image data provided by the pixel. The same readout sequence is repeated for each row of the matrix in turn.

[0089] The sequencing circuit DM is typically configured to sequentially capture the first radiological image I-FX sequence 300 by applying the same integration duration d INT The second dark noise I-obs image capture sequence 300 is controlled to measure the dark current level when the sensor is no longer exposed to X-rays. The image data of the dark noise I-obs is then subtracted point by point from the data of the first image to obtain a better quality radiological image.

[0090] Since the integration duration d is set INT (This means that there is no end of X-ray flash detection in the sensor.) Therefore, the second sequence 300 (I-obs) is only performed sporadically, in order to take into account any changes, in particular temperature changes, each time a radiographic image is taken, but not systematically. Between two updates, the image data of the dark noise is stored, for example, in a memory circuit associated with the control circuit DM and subtracted from the acquired radiographic image data.

[0091] The present invention has been explained for a 3T pixel sensor, but it can be extended to active pixels using more than three transistors, thereby allowing the same integration duration to be applied to all pixels by having a readout node separated from the photodiode node by at least one transfer transistor. In this way, the effects of dark noise in the image are reduced.

[0092] The present invention is particularly applicable to 5T pixels (understood as comprising at least 5 transistors), which, like 3T pixels, include a photodiode-specific initialization transistor M1, such as Figure 6 Thus, the present invention is implemented in the same way, wherein, at the stage of detecting the start of exposure to an X-ray flash, the current detection circuit DTX1 and the circuit MUX1 allow the common connection node NC to be connected first to the signal input IN-DTX1 of the circuit DTX1 and then to the reference voltage source V RS, thereby allowing the photodiode to be initialized before the integration phase of the image capture sequence triggered by this detection.

[0093] and Figure 1 and 2 Compared with the 3T pixel, it should be noted that the 5T pixel ( Figure 6 ) also includes a capacitance reading node SN i (usually a floating diffusion), this node is connected to the photodiode node KN i The gate of the transfer transistor (represented by M4) is separated from the gate of the transfer transistor by the transfer control signal TF i Control. This signal is activated to transfer the charge integrated by the photodiode to the read node. Thus, a whole transfer phase commanded simultaneously by transistors M4 in all pixels can be controlled before the sequential read phase, which marks the end of the current integration phase in all pixels. The 5T pixel also includes a read node SN i Initialization transistor M5: This transistor is represented as RSSN during the pixel reading stage. i The control signal of is activated, and then the corresponding initialization level SHR is sampled which will be subtracted from the signal level (SHS).

[0094] In an alternative embodiment of the present invention applicable to pixels having three or more transistors, the same principle used to detect the start of exposure to an X-ray flash is also used to detect the end of exposure to the X-ray flash and then determine the end of the integration period. This allows the pixel's integration duration to be adjusted as close as possible to the actual duration dX of the flash, thereby allowing the integrated dark current level to be reduced.

[0095] More specifically, according to the invention, this end-of-exposure detection according to the invention is performed by a detection circuit DTX2 similar to the circuit DTX1 , but based on the current I′ generated by a group of pixels in the matrix configured as detection pixels. Figure 7 As shown in Figures 8 (3T pixel) and 8 (5T pixel), these pixels are coupled to a different common connection node NCE electrically isolated from the node NC, and the sensor includes a second detection circuit DTX2 for receiving the current I' generated by the pixel coupled to the node NCE. The circuit DTX2 includes a capacitive transimpedance amplifier CTIA2 and a comparator COMP2, which is used to compare with a configurable voltage threshold V th2 The two detectors can be compared with the same operating frequency (Φ ctia ) operation. In principle, the two amplifiers CTIA1 and CTIA2 have the same common-mode voltage (V cm1 =V cm2 ).

[0096] From a topological perspective, in this alternative embodiment, there may be two conductive gates isolated from each other, one interconnected to the node NC and the other interconnected to the node NCE.

[0097] like Figure 5 As shown in the timing diagram, in the stage of detecting the start of exposure, the two detection circuits DTX1 and DTX2 operate in a similar manner, one integrating the current I originating from the pixels of the image capture matrix, and the other integrating the current I' originating from the matrix pixels configured as detection pixels (this will be explained later). In these two circuits, the amplifier generates an output voltage ramp, and once the ramp voltage exceeds the comparison threshold (V th1 、V th2 ), the comparator outputs OUT-DTX1 and OUT-DTX2 switch, in this example switching to "1".

[0098] Then, the circuit DTX1 for detecting the onset of an X-ray flash is disconnected from the node NC (by the action of the signal PROB1 ): the amplifier CTIA1 of the detection circuit DTX1 no longer receives current as input: the output voltage V out-ctia1 Maintaining the common mode voltage V cm1 The level of , and at the output of the comparator COMP1, the signal OUT-DTX1 switches back, in this example back to the "0" state. The image capture sequence is then performed using the matrix pixels coupled to the node NC; as already seen, the sequencing circuit first controls the phase of global reinitialization RSG of the photodiodes and then activates the integration phase ( Figure 9 ).

[0099] As long as the sensor is exposed to the X-ray flash, the detection circuit DTX2 continues to receive the current I' generated by the matrix pixels coupled to the node NCE: the amplifier CTIA2 continues to produce as output a periodic voltage ramp that exceeds the threshold V th2 Therefore, the output OUT-DTX2 of the comparator COMP2 remains unchanged, and remains at "1" in this example.

[0100] The end of exposure to the X-ray flash is indicated by the current I' which practically no longer increases: the slight increase is related to the dark current in the photodiode. The ramp voltage then drops to the threshold V th2 Following: The signal OUT-DTX2 switches back, in this example back to the “0” state. This switch is detected by the sequencing circuit DM and is used to stop the integration phase of the current image capture sequence.

[0101] The number of pixels in the matrix used to detect the end of exposure is low compared to the total number of pixels, in the ratio of 1 to 2000. In practice, this is achieved by adjusting the gain of the amplifiers CTIA1 and CTIA2 and / or by using different comparison thresholds (V th1 、V th2 ) to take this into account. It is also possible to reduce the operating frequency (Φ ctia , Φ S / H ): Since the patient is no longer being irradiated, the speed at which the end of exposure is detected may not be ideal.

[0102] The number of pixels in the matrix used to detect the end of exposure is smaller than the total number of pixels, for example, the ratio is 1 to 2000. It is also possible to adjust the gain of the amplifiers CTIA1 and CTIA2 and / or use different comparison thresholds (V th1 、V th2 The operating frequency of the second detector (CTIA2, COMP2) can also be reduced. Since the patient is no longer being irradiated, the speed of detecting the end of exposure may not be ideal.

[0103] In practice, the detection pixels coupled to the node NCE may be pixels in certain pixel columns and / or pixel rows of the matrix and / or pixels dispersed in the matrix. Figure 7 and 8 In the example shown, the pixels used to detect the end of an X-ray flash are those in the first column (group E1) and the last column (group E2) of the matrix. To simplify the graphical representation, groups E1 and E2 are consecutive columns at each matrix edge (consecutive rows could be used). In practice, however, it is preferable to select rows and / or columns that are interleaved with "normal" pixel columns for image capture: for example, one could select two or four of the first 20 and last 20 columns of a matrix consisting of hundreds of columns, or even pixels scattered throughout the matrix. In practice, for the pixels used to detect the end of an X-ray flash, signal loss prevents reading. Image information needs to be reconstructed for each end-of-flash detection pixel by interpolating from neighboring pixels. Therefore, it is best to space these detection pixels apart to limit any interpolation errors.

[0104] The common connection node NCE of the pixels used for flash end detection is connected to the input IN-DTX2 of the circuit DTX2, while the matrix pixels coupled to the node NC are used for the current image capture sequence, and this common connection node NC is connected to the reference voltage source (V RS ).

[0105] During the current image capture sequence, the transistors M1 of the pixels coupled to the node NCE must remain in the conducting state to allow the collection and injection of the current I' originating from the photodiodes of these pixels in the circuit DTX2, while at the end of the phase of global initialization RSG, the transistors M1 of the pixels coupled to the node NC and performing the current image capture are deactivated to allow the integration of the charges.

[0106] Therefore, for the pixels coupled to the node NCE, a signal denoted RSKN_D is provided to control the separate transistor M1, which signal is the same for all these pixels. Once the sensor exits the standby state, the signal RSKN D becomes active and remains active at least until the end of exposure is detected.

[0107] The sequencing circuit DM uses the end-of-exposure signal OUT-DTX2 to terminate the integration phase in the current image capture sequence: the signal OUT-DTX2 thus sets the effective integration duration d in the current radiographic image capture sequence I-FX. INTV .

[0108] like Figure 7 and 8 As shown, by providing a multiplexer MUX2 controlled by a logic control signal PROB2, for coupling the node NCE to the input IN-DTX2 of the circuit DTX2 (channel X'2), then the associated pixel is used as an X-ray flash end detection pixel, and even the node NCE is coupled to the voltage reference source V RS (Channel X'1), then using the associated pixels solely as image capture pixels, can advantageously make end-of-exposure detection an optional feature in the sensor. The operator then typically configures the logic state of signal PROB2 in the sensor's parameter register to activate or deactivate the X-ray flash end-of-exposure detection feature. For example, as shown, the parameter register contains a DTX stop bit, which can be configured to, for example, be 0 to deactivate the end-of-exposure detection option and 1 to activate it, which positions logic signal PROB2.

[0109] In this case, the transistor M1 of the pixel coupled to the node NCE needs to be appropriately controlled depending on whether it is used for end-of-exposure detection or as an image capture pixel. For example, as shown in the figure, a logic circuit, such as a multiplexer MUX3 controlled by the same signal PROB2, can be provided so as to:

[0110] - When the detection option is disabled, PROB2 is 0 and the transistor M1 of each pixel coupled to the node NCE is controlled by the control signal RSKN corresponding to the row of pixels in the matrix i control;

[0111] - When the detection option is activated, PROB2 is 1 and the transistors M1 of the pixels coupled to the node NCE are all controlled by the control signal RSKN_D.

[0112] Figure 7 and 8 The principle of detecting the end of exposure according to the invention that has just been described is shown to be analogously applicable to 3T or 5T pixel sensors.

[0113] Figure 9 More specifically, a timing diagram of the signals used to detect the start and end of exposure to an X-ray flash and the associated control signals for implementing end-of-exposure detection (in this example, PROB2 is "1") is shown. In this example, the I-FX and I-obs image capture sequence 400 includes an overall transfer phase 403 for transferring charge to the read node SN of the pixel before a sequential read phase 404. i , which corresponds to Figure 8 The 5T pixel image sensor shown. Figure 7 For the 3T pixel sensor shown, the overall transfer phase 403 is not present, and end-of-exposure detection triggers the sequential readout phase 404 .

[0114] For an image capture sequence 400 (I-FX or I-obs) controlled by the sequencing circuit DM, after detecting the start of exposure (arrow 5), a phase 401 of global initialization RSG activates simultaneously all signals RSKN i (i=1 to N) to initialize the photodiode node KN of the pixel coupled to the node NC i Activate signal RSKN_D to initialize the photodiode node KN of the pixel coupled to node NCE i ; Activate all signal RSSN at the same time i Read node SN for initializing all pixels of the matrix i (regardless of whether these pixels are coupled to nodes NC or NCE).

[0115] The end-of-exposure detection (arrow 6) triggers the overall transfer phase 403TFG for transferring the charge from the photodiode node KN i Transfer to read node SN i , which is simultaneously applied to all image capture pixels by transistor M4 of the 5T pixel (signal TF i ). It sets the integration duration, which is the same for all pixels: when the signal RSKN is deactivated at the same time i , which corresponds to the end of phase RSG; and when simultaneously deactivating signal TF iThe same ends when TFG ends. The phase 404 of reading the pixels begins. For the row of rank i selected for reading, this phase consists in sampling the signal levels of the pixels of this row (SHS); by activating the signal RSSN of this row before sampling the corresponding reference level (SHR). i , reinitialize the reading node SN i It should be noted that the acquired data stream includes the data of the pixels coupled to the node NCE that have been used to detect the end of exposure: the data acquired (read) for these pixels are not actually used but are replaced by data calculated by interpolation. This does not change anything in the sequence; this must be taken into account in the image processing.

[0116] It should be noted that the effective integration duration no longer has a predetermined (adjusted) set value: it is a value d defined by the two detection signals OUT-DTX1 and OUT-DTX2. INTV Therefore, it is necessary to consider whether to apply the same integration duration in the image capture sequence I-obs of the dark noise. The sequencing circuit then includes a counter that measures the photodiode node KN i The effective exposure duration d between the end of the phase 301 of the global reinitialization RSG and the detection of the end of the flash (OUT-DTX2) of the trigger read phase (3T pixels) or the global transfer phase TFG (5T pixels) INTV .

[0117] Since the duration d INTV It may change with each new exposure to the X-ray flash, so the dark current image capture is systematic.

[0118] In practice, the sequencing circuit DM applies filters to the detection signals OUT-DTX1 and OUT-DTX2, thereby eliminating (i.e. not taking into account) spurious pulses which are generated, in particular, by the connection nodes NC or NCE and the photodiode node KN when switching channels in the switching circuits MUX1 and MUX2. i Furthermore, circuit DM can therefore filter to ignore signal OUT-DTX1 during image capture sequence 300, and to ignore signal OUT-DTX2 during phase 200 of detecting the start of flash exposure. These various filtering measures ("anti-glitch" filters) are common measures implemented to avoid false detections.

[0119] The inventions just described allow improving the quality of radiographic images, in particular dental images, at less expense, since they use matrix pixels and current detection circuits well known to those skilled in the art.

Claims

1. An intraoral radiographic image sensor using MOS technology, comprising: - a matrix of light-sensitive pixels arranged in rows and columns (M-PIX), each pixel (P ij ) includes a photodiode (PH) and a transistor, including a photodiode node (KN) connected to the pixel i ) a photodiode initialization transistor (M1) between the first connection node (NC) shared by the pixel; - a sequencing circuit (DM) providing signals to command the transistors of the pixels to control an image capture sequence (300) during exposure to an X-ray flash (FX), comprising a phase of global initialization (301) of the photodiodes of the pixels, a phase of charge integration during an integration period (302), and a phase of reading the pixels (303); The sensor is characterized in that it comprises a first coupling switch (MUX1) controlled by a first logic signal (PROB1) for connecting the first connection node (NC) to a signal input (IN-DTX1) of a first current detection circuit (DTX1) or to a photodiode initialization voltage source (VRS), so that the first logic signal is in a first logic state or a second logic state, respectively; as well as - a sequencing circuit (DM) of the sensor configured to control the phase (200) of detecting the start of exposure to an X-ray flash by the first current detection circuit (DTX1) to trigger the image capture sequence (300), comprising the following operations: -a) commanding the photodiode initialization transistor (M1) to switch to a conducting state simultaneously in all pixels; as well as -b) confirming that the first logic signal (PROB1) is in the first logic state, which has the effect of injecting the current (I) originating from the photodiode of the pixel collected at the first connection node (NC) at the signal input (IN-DTX1) of the first current detection circuit; and then -c) when the output logic signal (OUT-DTX1) of the first current detection circuit switches from a first logic state to a second logic state, corresponding to detecting an input current level above a predetermined threshold, confirming that the first logic signal (PROB1) is in the second logic state, which has the effect of coupling the initialization transistor (M1) that is always in the on state to the initialization voltage source (VRS), thereby activating the overall initialization phase (301) of the image capture sequence to initialize the photodiode prior to the integration phase; wherein the initialization transistors of the pixel groups (E) of the matrix are not connected to the first connection node (NC) but to a second connection node (NCE), the second connection node being electrically isolated from the first connection node, and the sensor further comprising a second current detection circuit (DTX2) of the same type as the first current detection circuit and driven by the same clock signal (Φ ctia ) is controlled, its input signal (IN-DTX2) is connected to the second connection node (NCE), and the sequencing circuit (DM) of the sensor is configured to: - commanding the switching to a conducting state of the initialization transistors (M1) of all pixels of the matrix, including the pixels of the group coupled to the second connection node; and - upon detecting a switching of the output signal (OUT-DTX1) of the first current detection circuit (DTX1): - keeping the initialization transistors (M1) of the pixels in the group in a conducting state at least until a switching of the output signal (OUT-DTX2) of the second current detection circuit is detected, the switching corresponding to a current injected at the input and collected on the second connection node (NCE) being below a predetermined threshold; as well as - upon detecting that a switching of the output signal (OUT-DTX2) of the second current detection circuit indicates detection of the end of exposure to an X-ray flash, stopping the integration phase of the image capture sequence (300) to initiate the read phase.

2. The image sensor according to claim 1 , wherein the first current detection circuit ( DTX1 ) comprises a capacitive transimpedance amplifier ( CTIA1 ) comprising a non-inverting input connected to a common-mode voltage ( Vcm1 ) and an inverting input forming the signal input ( IN-DTX1 ), the signal input ( IN-DTX1 ) being coupled to the first connection node ( NC ), the amplifier being driven by a clock signal ( Φ ctia ) control to output the signal (V out-ctia1 ) periodically generates a voltage ramp at the input, the voltage ramp depending on the level of the current injected at the signal input, the ramp being applied to a comparator (COMP1) for comparison with a voltage threshold (V th1 ) for comparison.

3. The image sensor according to claim 1 or 2, wherein each of the pixels comprises the photodiode initialization transistor (M1); a voltage follower transistor (M2) having a gate connected to the photodiode connection node (KN); i ); and a read select transistor (M3) connected in series between the voltage follower transistor (M2) and each column conductor (Col) connected to the pixel read circuit (RD) j )between.

4. The image sensor according to claim 1 or 2, wherein each of the pixels comprises the initialization transistor (M1); a charge transfer transistor (M4) connected in series to the photodiode connection node (KN); i ) and pixel read node (SN i ) between; the read node initialization transistor (M5); a voltage follower transistor (M2), which is installed as a voltage follower and has its gate connected to the read node (SN i ), and a read select transistor (M3) connected in series between the voltage follower transistor (M2) and each column conductor (Col) connected to a pixel read circuit (RD) j )between.

5. The image sensor according to claim 1 , comprising a second coupling circuit (MUX2) allowing the second connection node (NCE) to be connected to the signal input (IN-DTX2) of the second current detection circuit or an initialization voltage source (VRS) controlled by a second control logic signal (PROB2), the second control logic signal being configured in the sensor to configurably configure the pixels in the group as end-of-exposure detection pixels or image capture pixels.

6. The image sensor according to claim 2 , wherein the gain of the capacitive transimpedance amplifier and / or the voltage threshold of the comparator are adjustment parameters of the sensor adjusted in the first current detection circuit and the second current detection circuit for respectively detecting the start and end of the X-ray flash.

7. The image sensor according to claim 1 , wherein the sequencing circuit (DM) is configured to trigger a further image capture sequence (300(I-obs)) applying the same integration duration (d ) as a previous image capture sequence (300(I-obs)) performed during exposure to the X-ray flash and providing first image data. INT d INT V) and using the same pixels for image capture, thereby allowing dark noise on the first image data to be measured and subtracted.

8. A radiological image capturing method using an intraoral radiological image sensor utilizing MOS technology, said sensor comprising a matrix (M-PIX) of light-sensitive pixels arranged in rows and columns, each pixel (P ij ) includes a photodiode (PH) and a transistor, including a photodiode node (KN) connected to the pixel i ) and a first connection node (NC) shared by the pixel, wherein: The method comprises: in a first phase (200) coupling said first connection node (NC) to a signal input (IN-DTX1) of a current detection circuit (DTX1) provided in said sensor for detecting when a current injected at said signal input (IN-DTX1) exceeds a predetermined threshold, which corresponds to detecting the start of exposure to an X-ray flash, said detection triggering an image capture sequence (300) having the effect of coupling said first connection node (NC) to an initialization voltage source (VRS) thereby allowing a phase of initialization (301) of the entirety of said photodiode prior to an integration phase (302) during an integration duration, followed by a phase (303) of reading pixels; The method allows controlling the integration duration in a current image capture sequence by means of an end-of-exposure detection signal provided by another current detection circuit (DTX2) of the sensor, the sensor having a signal input (IN-DTX2) coupled to a second connection node (NCE), the second connection node being electrically isolated from the first connection node and connected to the initialization transistor (M1) of a pixel group (E) of the matrix, the another current detection circuit (DTX2) having a signal output configured to activate an end-of-exposure detection signal (OUT-DTX2) when the current (I') originating from the photodiode of the pixel in the group is lower than a predetermined threshold.

9. A radiological image capture method according to claim 8, wherein the control of the integration duration by the exposure end detection signal is activated or stopped by a second configurable control logic signal (PROB2) applied to the second coupling circuit (MUX2), thereby allowing the second connection node (NCE) to be connected to the signal input (IN-DTX2) of the other current detection circuit or the initialization voltage source (VRS). 10 . The radiological image capturing method according to claim 8 , wherein the one or more current detection circuits provided in the sensor are of a capacitive transimpedance amplifier and comparator type.

Images