Disturbance-detecting matrix detector

Abstract

The invention relates to a matrix detector organized into rows and columns of pixels, the detector being sensitive to a variable physical phenomenon, the detector comprising row conductors (Phi_line), column conductors (Col) connected to each pixel (P), and a readout circuit connected to each column conductor (Col). The pixels comprise a component sensitive (D) to the physical phenomenon, a first switch (T1) connected between the sensitive component (D) and one of the column conductors (Col). The first switch (T1) is controlled by one of the row conductors (Phi_line) in at least one of the pixel columns. The pixels of this column comprise a second switch (T2) controlled by one of the row conductors (Phi_line), connected at one of its terminals (T2a) to one of the column conductors (Col41) not connected to the first switch (T1) and coupled without connection to the sensitive component (D). Figure for the abstract: Fig. 1

Description

Title of the invention: Matrix disturbance detection detector

[0001] The invention relates to a matrix detector. The invention is particularly useful for creating a photosensitive detector used to produce visible images. The invention is not limited to the production of this type of detector. The invention can be implemented to create a detector capable of producing pressure or temperature maps, or two-dimensional representations of chemical or electrical potentials. These maps or representations form images of physical quantities.

[0002] The invention applies in particular to the implementation of passive or active matrix detectors used, for example, for detection purposes in devices that produce visible images. The physical phenomenon is then electromagnetic radiation, for example, in the visible wavelength band. The device can be adapted to detect ionizing radiation, for example, X-rays or gamma rays, either directly or through a scintillator.

[0003] In a matrix detector, a pixel represents the elementary sensitive element of the detector. Each pixel converts a physical phenomenon to which it is subjected into an electrical signal. The electrical signals from the different pixels are collected during a readout phase of the matrix and then digitized so that they can be processed and stored to form an image. The pixels comprise a component sensitive to the physical phenomenon and deliver, for example, a current of electrical charge. The physical phenomenon can be electromagnetic radiation carrying a flux of photons, and hereafter, the invention will be explained using this type of radiation, and the charge current is a function of the photon flux received by the sensitive component. Generalization to any type of matrix detector will be straightforward.

[0004] A matrix image detector comprises row conductors, each connecting the pixels of the same row, and column conductors, each connecting the pixels of the same column. The row conductors are connected to driver modules, generally located on an edge of the matrix, which control the individual pixels. The column conductors are connected to conversion circuits, also generally located on an edge of the matrix, which can be called the "column foot." The conversion circuits read the pixel matrix. It is understood that the terms "rows" and "columns" are purely conventional and can be reversed.

[0005] Each pixel generally comprises a sensitive component, in particular a photodetector, which may, for example, be a photodiode, a photoresistor, or a phototransistor. Large photosensitive arrays exist that can have several million pixels arranged in rows and columns. Each pixel further comprises an electronic circuit including at least one switch. The electronic circuit may also include other switches, capacitors, and resistors, downstream of which the switch is located. The assembly consisting of the sensitive component and the electronic circuit makes it possible to generate and collect electrical signals. The electronic circuit may allow the collected signal in each pixel to be reset after a transfer for reading the pixel.The role of the switch is to transfer or copy, into a column conductor, the signals collected by the electronic circuit according to the information received from the sensing component. This transfer occurs when the switch receives the instruction from a line conductor. The switch is connected, at one of its terminals, to the sensing component, directly or indirectly, and at its other terminal to the conversion circuit via one of the column conductors. This other terminal of the switch corresponds to the pixel output.

[0006] Matrix photosensitive detectors are by nature devices that are very sensitive to disturbances that may originate from the environment in which they are used. These disturbances may be mechanical (shocks, vibrations), electromagnetic (electric and / or magnetic fields originating, for example, from electric motors or radio frequencies emitted by radiating devices) or thermal (temperature variation inducing a change in the leakage currents of the photosensitive components).

[0007] These disturbances can alter the signal collected by the pixels and thus create defects in the images. These defects are generally correlated structures along lines due to the principle of reading the pixel matrix when, for example, it is performed line by line. The defects can also have various appearances depending on the type of disturbance and the principle of signal detection and reading.

[0008] These disturbances are particularly difficult to eliminate, especially in cases of use of the detector autonomously or when correction must be done in real time, for example in fluoroscopy mode in the case of medical imagers.

[0009] It is possible to evaluate a disturbance during the reading of a line or a portion of a line and to subtract the signal corresponding to an estimate of this disturbance. This evaluation can use information acquired at a time other than that of a complete image capture cycle. The evaluation can result from a calculation or a measurement. All methods consisting of temporally separating the reading of the useful signal and the reading of a signal used to estimate the disturbance lead to this same difficulty is linked to the impossibility of predicting exactly the exact value of the disturbance from a previous or subsequent measurement.

[0010] It is also possible to use a double readout, with and without a useful signal, which has the major drawback of lengthening the image acquisition time. This double readout is performed during the image cycle and is known as Correlated Double Sampling, or by its acronym CDS. It involves reading the information contained in the pixel matrix twice. The first readout is used to read the useful signal, and the second is used to read the disturbances without a useful signal. Subtracting the two readouts corrects the offset of the useful signal. This correction eliminates the offset drift generated by various external disturbances. However, this process reduces the overall readout speed of the detector by requiring two readouts of the matrix. This process also tends to increase the detector's power consumption.Furthermore, correlated double sampling cannot account for offset variations that may occur between the two readings.

[0011] Other predictive evaluation methods based on prior knowledge of the disturbance allow for estimating a disturbance by a frequency-based approach but do not allow for knowing exactly the actual level of disturbance.

[0012] Another method for correcting disturbances consists of spatially separating the reading of the useful signal from the reading of the signal used to estimate the disturbance. This approach is possible when it is assumed that the local variation of the disturbance is small or negligible. It is then possible to simultaneously read, in two areas as close as possible, the disturbed signal and a signal used to estimate the disturbance. This method requires pixels dedicated to the estimation of the disturbance, often called masked pixels, which do not receive a useful signal, and is not very precise in the local estimation of disturbances.

[0013] The common characteristic of all the methods mentioned above is to use information that is temporally or spatially offset from the desired information: either this information corresponds to the value of the disturbance at a different time, assuming that the variation is sufficiently small or well modeled, or it corresponds to the value of the disturbance at a different location but requires a double reading and therefore a lengthening of the time required to obtain the image.

[0014] The invention aims to overcome all or part of the problems mentioned above by providing a matrix detector that allows for synchronous estimation of the disturbance without delaying image readout. More specifically, the invention relates to a matrix detector comprising at least one pixel configured to simultaneously acquire a useful signal and a disturbance signal. Thus, the disturbance can be measured without spatial offset from the acquisition location of a useful signal. Furthermore, the disturbance is read synchronously with the reading of the useful signal.

[0015] To this end, the invention relates to a matrix detector organized into rows and columns of pixels, the detector being sensitive to a variable physical phenomenon, the detector comprising row conductors, column conductors connected to each pixel and a readout circuit connected to each column conductor, the pixels comprising: - a component sensitive to the physical phenomenon, configured to acquire information whose value varies according to the variation of the physical phenomenon, - a first switch connected between the sensitive component and one of the column conductors, and configured to transfer the information acquired by the sensitive component to the column conductor, the first switch being controlled by one of the line conductors, - in at least one of the pixel columns, the pixels of that column include a second switch controlled by one of the line conductors, connected at one of its terminals to one of the column conductors not connected to the first switches and coupled without connection to the sensitive component.

[0016] Several columns of pixels whose pixels include the second switch connected to one of the column conductors can be distributed at regular intervals in the pixel matrix.

[0017] The pixel column(s) whose pixels include the second switch connected to one of the column conductors can be arranged at the edge of the matrix.

[0018] The matrix detector may include columns of pixels not having any second switch.

[0019] Alternatively, all pixels of the detector can include the second switch.

[0020] The first and second electronic switches are advantageously of the same nature.

[0021] The first and second electronic switches are advantageously identical.

[0022] The coupling of the second switch to the sensitive component is, for example, mainly a capacitive coupling.

[0023] The invention will be better understood and other advantages will become apparent upon reading the detailed description of an embodiment given by way of example, a description illustrated by the accompanying drawing in which:

[0024] [Fig.1] schematically represents an example of a matrix detector according to the invention;

[0025] [Fig.2] represents a variant of the detector in [Fig.1].

[0026] For the sake of clarity, the same elements will bear the same references in the different figures.

[0027] Figure 1 schematically represents a matrix detector having a matrix of two rows 11 and 12 and four columns c1, c2, c3, and c4 for simplicity of understanding. Eight pixels are formed, each at the intersection of a row and a column. It is understood that real matrices are generally much larger and have a large number of rows and columns.

[0028] Each pixel comprises a sensitive component, represented here by a photodiode D, and an electronic processing circuit including an electronic switch formed, in the example shown, by a transistor T1. Alternatively to the transistor, other components may form the electronic switch. A diode, in particular, may be used. Furthermore, this type of pixel may include other components, notably other electronic switches.

[0029] A matrix detector according to the invention, based on photodiodes or phototransistors sensitive to light in the visible band, is generally combined, for X-ray or gamma radiography, with a scintillator, for example made of cesium iodide (Csl), enabling the conversion of X-ray or gamma photons into visible photons to which the photodiodes or phototransistors are sensitive. The combination of photodetectors and a scintillator ensures so-called indirect conversion of X-ray or gamma photons.

[0030] Alternatively, the invention can be implemented in a so-called direct conversion detector in which X-ray or gamma photons are directly converted into electrical charges in a conversion layer associated with a matrix, each pixel of which may include an associated storage capacitor, and, as in indirect conversion detectors, with an electronic switch. The storage capacitor is itself associated with an electrode in contact with the conversion layer to locally receive the electrical charges resulting from the conversion of the received X-ray photons.

[0031] To date, several materials have been successfully tested for use in creating a conversion layer. These include cadmium telluride (CdTe), amorphous selenium (a:Se), thallium bromide (TIBr), perovskites, lead oxides (PbO)...

[0032] In a direct conversion detector, the storage capacity is considered as the component sensitive to the variable physical phenomenon that a matrix detector according to the invention can image.

[0033] Any other type of sensitive component can be implemented within the framework of the invention, such as for example a photoconductor.

[0034] In general, it is known to produce pixel matrices comprising transistors implementing complementary semiconductors in crystalline silicon known in the Anglo-Saxon literature by their abbreviation CMOS for: “ Complementary Metal Oxide Semiconductor. The invention is not limited to this type of transistor; it can, for example, be implemented for matrices comprising thin-film field-effect transistors known in the English-language literature as TFTs, short for "Thin-film transistor." TFT-type transistors can be based on metal oxides, such as amorphous or crystalline indium, gallium, and zinc oxide transistors, known by their English abbreviation: IGZO. Other families of TFT-type transistors can be implemented, such as organic TFTs, amorphous silicon TFTs, polycrystalline silicon TFTs, etc.

[0035] The pixels of the same line are connected to a line conductor, respectively Phi_line1 and Phi_line2, carrying a signal to control each of the pixel lines. In the case of pixels having other transistors, these can be controlled by other line conductors. For example, each pixel can include another electronic switch allowing the photodiode D to be reset.

[0036] The pixels in the same column are connected by a column conductor, respectively Col1, Col2, Col3, and Col4, allowing the charges accumulated by the photodiode D to be read, line by line. Each column conductor Col1 is connected to a readout circuit L configured to read the signal level accumulated by the sensitive components connected to it when the transistor T1, connected to the sensitive component in question, is conducting. Each readout circuit can be configured to read an electrical signal present in the column to which it is connected. This signal is representative of the level of the physical phenomenon detected by the sensitive component. The signal can be an electrical charge, a voltage, a current, etc.

[0037] In the example shown, where the sensitive component is a photodiode and the electronic circuit comprises only transistor T1, the signal representing the illumination received by the photodiode is formed from the electrical charges read by the corresponding readout circuit. The electronic circuit may further include a follower transistor configured to convert the electrical charges accumulated by the photodiode into a voltage. This additional transistor is placed between the photodiode and transistor TL. The follower transistor is often associated with a photodiode reset transistor. This type of pixel is often called a 3T pixel, as opposed to the 1T pixel shown in [Fig. 1].

[0038] During an image acquisition phase, the illumination received by the photodiode D causes the potential of its cathode to decrease. This image acquisition phase is followed by a readout phase during which the potential of the photodiode D is read. To do this, the transistor T1, which therefore acts as a switch, is turned on by the control signal carried on the Phi_line conductor and applied to its gate. The reading of The photodiode D drains the charges accumulated on its cathode, which ensures the pixel is reset before the next image capture phase.

[0039] According to the invention, in at least one of the pixel columns, for example column c4, the pixels of this column comprise a switch T2 coupled without connection to the sensitive component. The switch T2 is connected at one of its terminals T2a to a column conductor Col41 not connected to the first switches T1.

[0040] We saw previously that the column conductors Coll, Col2, Col3, and Col4 connect the corresponding electronic switches T1 to readout circuits for reading the useful signals from the corresponding pixels. Similarly, the column conductor Col41 connects the electronic switches T2 of pixel column c4 to a readout circuit L for reading the disturbance collected by each of the electronic switches T2. The disturbances are read line by line, as with the reading of the useful signals accumulated by the photodiodes D.

[0041] The read circuits L are advantageously all identical. The read circuits can be arranged on the same substrate as that carrying the pixels or on a separate substrate arranged on an edge of the matrix.

[0042] In the example shown in [Fig. 1], the electronic switches T2 of a single column of pixels, column c4, are connected to the column conductor Col41 to enable reading. Column c4 can be located on an edge of the matrix. Thus, the spacing between the column conductors can remain constant, which facilitates connection to the reading circuits L. It is of course possible to arrange, within the matrix, columns of pixels where the electronic switches T2 are connected to reading circuits L by means of column conductors. These columns of pixels where the disturbances are read can be arranged at regular intervals, for example, one column in ten. The column conductors are connected either to electronic switches T1 or to electronic switches T2. It is preferable not to change the spacing between pixels, which results in a non-constant spacing of the column conductors.The connection to the L reading circuits is adapted according to this step.

[0043] The electronic switches, and in particular the transistors T1 and T2, are advantageously of the same type, diode or transistor, and even more advantageously identical except for their connection. Thus, the two electronic switches T1 and T2 have the same sensitivity to disturbances. Moreover, their identical nature simplifies the design and implementation of the detector.

[0044] The proximity of the photodiode D and the transistor T2 allows for a predominantly capacitive coupling between the photodiode D and the transistor T2. It is also possible to extend the terminal of the transistor T2, the terminal not connected to the conductor of column Col41 by means of a track extending along the photodiode D allowing to add an inductive coupling to the capacitive coupling.

[0045] Switch T2 is controlled by the signal carried by one of the line conductors. In the same pixel of column c4, it is entirely possible to control switches T1 and T2 by the same line conductor Phi_line. Alternatively, as illustrated in the example shown in [Fig. 1], switch T1 is connected to the line conductor of the same position and switch T2 is connected to the line conductor of the next position. For example, for the pixel labeled P(1,4) located in row 1 and column 4, the gate of transistor T1 is connected to the line conductor Phi_line1 and the gate of transistor T2 is connected to the line conductor Phi_line2. This simplifies the layout and connection of the various components of each pixel.

[0046] During the read phase, for column c4, a transistor T1 and a transistor T2 are read simultaneously. As mentioned above, for the connection of the gates of transistors T1 and T2 to their respective line conductors, the transistors T1 and T2 read simultaneously can belong to the same pixel or to two adjacent pixels. In both cases, the simultaneous readout makes it possible to obtain so-called useful information transferred by transistor T1 and information representing disturbances in the immediate vicinity of the photodiode. At the level of the readout circuits, or downstream thereof, it is possible to subtract the information representing disturbances from the useful information, in order to obtain useful information free of these disturbances. The invention makes it possible to obtain information representing disturbances of one pixel at a time at the same instant as the useful information and in a spatially close location.

[0047] To achieve perfect simultaneity between useful information and information representing disturbances, it is possible to subtract the information from two adjacent pixels on two neighboring lines. In the example of [Fig. 1], the information from transistor T2 on line 11 is subtracted from the information from transistor T1 on line 12. Indeed, the same line conductor Phi_line2 controls both transistor T1 on line 12 and transistor T2 on line 11, which ensures perfect simultaneity between the readings of these two transistors.

[0048] The subtraction operation is of course given only as an example. It is possible to provide a more complex operation for correcting the useful signal from a transistor T1 using the signal from an adjacent transistor T2.

[0049] In the example shown in [Fig. 1], all pixels include transistor T2. This allows all pixels of the detector to have the same components, namely the photodiode D and the two transistors T1 and T2. As mentioned above, the pixels They can also include other components that are then found in all pixels, whether or not the T2 transistors are connected to a column conductor. This improves the homogeneity of the different detector pixels, particularly in terms of interference.

[0050] For pixel columns containing T2 transistors not connected to a column conductor, these T2 transistors can be left unconnected. Alternatively, to prevent their potential from floating, it is advantageous to connect them, for example, to a reference voltage as shown in [Fig. 1]. Furthermore, in each pixel, the anode of the photodiode D is connected to the reference voltage Vref. It is advantageous to connect the T2 transistors to this same voltage, which is already available.

[0051] Figure 2 represents an alternative variant in which only the pixels in column c4 include T2 transistors. The other pixel columns do not include T2 transistors. This simplifies the detector design. As mentioned above, this simplification may introduce differences in behavior between pixels equipped with T2 transistors and pixels in which the T2 transistor is absent.

Claims

Demands

1. A matrix detector organized in rows and columns of pixels, the detector being sensitive to a variable physical phenomenon, the detector comprising row conductors (Phi_row), column conductors (Col) connected to each of the pixels (P) and a readout circuit connected to each column conductor (Col), the pixels comprising: - a component sensitive (D) to the physical phenomenon configured to acquire information whose value varies according to the variation of the physical phenomenon, - a first switch (Tl) connected between the sensitive component (D) and one of the column conductors (Col), and configured to transfer the information acquired by the sensitive component (D) to the column conductor (Col), the first switch (Tl) being controlled by one of the row conductors (Phi_row), - in at least one of the pixel columns,The pixels in this column include a second switch (T2) controlled by one of the line conductors (Phi_ligne), connected at one of its terminals (T2a) to one of the column conductors (Col41) not connected to the first switches (Tl) and coupled without connection to the sensitive component (D).

2. Matrix detector according to claim 1, wherein several columns of pixels whose pixels comprise the second switch (T2) connected to one of the column conductors (Col41) are distributed at regular intervals in the pixel matrix.

3. Matrix detector according to claim 2, wherein the pixel column(s) whose pixels comprise the second switch (T2) connected to one of the column conductors (Col41) are arranged at the edge of the matrix.

4. Matrix detector according to any one of the preceding claims, wherein the matrix detector comprises columns of pixels (cl, c2, c3) not having any second switch (T2).

5. Matrix detector according to any one of claims 1 to 3, wherein all pixels of the detector include the second switch (T2).

6. Matrix detector according to any one of the preceding claims, wherein the first (T1) and the second (T2) electronic switches are of the same nature.

7. 11 Matrix detector according to any one of the preceding claims, wherein the first (T1) and second (T2) electronic switches are identical.

8. Matrix detector according to any one of the preceding claims, wherein the coupling of the second switch (T2) to the sensitive component (D) is mainly a capacitive coupling.

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