X-ray detectors

Abstract

Embodiments of the present disclosure relate to an X-ray detector comprising a first circuit having an NPN bipolar transistor and a second circuit configured to compare a voltage at a terminal of the NPN bipolar transistor with a reference value substantially equal to a value of a terminal voltage that would occur when the first circuit has been exposed to a threshold amount of X-rays.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to French Patent Application No. 2011963, filed on November 20, 2020, which is incorporated herein by reference to the fullest extent permitted by law. Technical Field

[0003] The present description relates generally to electronic devices and, more particularly, to devices including X-ray detection circuitry. Background Art

[0004] X-rays are a form of high-frequency electromagnetic radiation, formed by photons with energies ranging from a few hundred eV (electron volts) to several MeV.

[0005] X-rays can have a negative impact on the operation of electronic devices. For this reason, electronic device manufacturers typically recommend that devices such as cell phones not be subjected to large amounts of X-rays. The warranties for these electronic devices typically do not cover damage caused by X-rays. There is a need to detect the application of X-rays to devices. Summary of the invention

[0006] Embodiments overcome all or part of the disadvantages of known X-ray detectors.

[0007] An embodiment provides an X-ray detector comprising: a first electronic circuit including a first NPN bipolar transistor; and a second circuit configured to compare a voltage of the first electronic circuit with a reference value substantially equal to a value of a voltage that would occur when the first electronic circuit has received a threshold amount of X-rays.

[0008] Another embodiment provides an X-ray detection method including comparing a voltage of a first electronic circuit including a first NPN bipolar transistor to a reference value substantially equal to a value of the voltage that would occur when the first electronic circuit has received a threshold amount of X-rays.

[0009] According to an embodiment, the voltage is a voltage across one of the terminals of the first NPN-type bipolar transistor.

[0010] According to an embodiment, the voltage is a voltage on the emitter of the first NPN-type bipolar transistor.

[0011] According to an embodiment, the voltage is substantially constant during operation of the device in the absence of X-rays.

[0012] According to an embodiment, the threshold amount of X-rays is 10 Gray.

[0013] According to an embodiment, the first circuit is configured such that during operation of the detector, the voltage on the base of the first NPN bipolar transistor is within a range of values, for which the gain difference between the first NPN bipolar transistor that has not received X-rays and the first NPN bipolar transistor that has received a threshold amount of X-rays is greater than 10.

[0014] According to an embodiment, the first circuit is configured such that during operation of the detector, the base voltage of the first NPN bipolar transistor is within a range of values, for which the gain of the first NPN bipolar transistor that has not received X-rays is at least 1.5 times greater than the gain of the first NPN bipolar transistor that has received a threshold amount of X-rays.

[0015] According to an embodiment, the first circuit includes two branches, the first branch includes a first transistor and a first NPN bipolar transistor coupled in series, and the second branch includes a second transistor and a second NPN bipolar transistor coupled in series, the first transistor and the second transistor are coupled as a current mirror so that the current passing through the first NPN bipolar transistor and the second NPN bipolar transistor is substantially equal.

[0016] According to an embodiment, bases of the first NPN type bipolar transistor and the second NPN type bipolar transistor are coupled through a resistor.

[0017] According to an embodiment, a base of each of the first NPN type bipolar transistor and the second NPN type bipolar transistor is coupled to an application node of a reference voltage through a resistor.

[0018] According to an embodiment, the collector of the second NPN bipolar transistor is coupled to the base of the first NPN bipolar transistor.

[0019] According to an embodiment, the detector comprises a circuit for generating a reference value, the circuit comprising a third transistor connected in series with at least one resistor and at least one capacitor.

[0020] According to an embodiment, the third transistor is coupled as a current mirror to at least one of the first transistor and the second transistor. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above-mentioned features and advantages as well as other features and advantages will be described in detail in the following description of specific embodiments given by way of illustration and non-limiting manner with reference to the accompanying drawings, in which:

[0022] Figure 1 Illustrate the effect of X-rays on NPN bipolar transistors;

[0023] Figure 2 An embodiment of an X-ray detector is schematically shown in block form;

[0024] Figure 3 shows the effect of X-rays on an NPN bipolar transistor after several days; and

[0025] Figure 4 An embodiment of an X-ray detector is shown in more detail. DETAILED DESCRIPTION

[0026] In the various drawings, the same features are represented by the same reference numerals. In particular, common structural features and / or functional features in various embodiments may have the same reference numerals, and may be provided with the same structural characteristics, dimensional characteristics, and material characteristics.

[0027] For clarity, only the steps and elements that are useful for understanding the embodiments described herein are illustrated and described in detail.

[0028] Unless otherwise specified, when two elements are referred to as being connected together, this means a direct connection without any intermediate elements other than conductors, and when two elements are referred to as being coupled together, this means the two elements may be connected or they may be coupled via one or more other elements.

[0029] In the following disclosure, unless otherwise specified, when referring to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or when referring to relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or when referring to orientation qualifiers, such as "horizontal", "vertical", etc., reference is made to the orientation shown in the figure.

[0030] Unless otherwise indicated, the expressions "about," "approximately," "substantially," and "in the order of" mean within 10%, and preferably within 5%.

[0031] Figure 1 The effect of X-rays on an NPN bipolar transistor is illustrated. More specifically, Figure 1 is a graph showing how the gain G of an NPN type bipolar transistor varies according to the voltage Vbase on the base of the transistor.

[0032] The transistor under consideration is an NPN bipolar transistor, i.e., a transistor comprising two PN junctions. The transistor under consideration comprises: a junction between a first N-type semiconductor region forming an emitter and a P-channel semiconductor region forming a base, and a junction between the P-channel semiconductor region and a second N-type semiconductor region forming a collector.

[0033] The value in the abscissa, ie the value of the voltage Vbase, thus corresponds to the voltage across the P-channel semiconductor region. The value in the ordinate, ie the value of the gain G, corresponds to the ratio of the collector current divided by the base current according to the value of the base voltage Vbase.

[0034] The emitter and collector of the transistor are preferably coupled between two application nodes of a supply voltage during obtaining the gain value G. Preferably, the emitter is coupled to, preferably connected to, an application node of a reference voltage, such as ground, and the collector is coupled to, preferably connected to, an application node of the supply voltage.

[0035] Figure 1 A curve 12 is included corresponding to an NPN bipolar transistor that has not been subjected to X-rays (e.g., a transistor supplied directly by a manufacturer). The transistor has been subjected to less than a threshold dose or amount of X-rays, less than 1 gray, preferably less than 0.1 gray.

[0036] Figure 1 Also included is a curve 14 corresponding to an NPN bipolar transistor that has been subjected to X-rays. The transistors corresponding to curves 12 and 14 are substantially identical, preferably identical transistors. Curve 14 more precisely corresponds to an NPN bipolar transistor that has been subjected to an amount of X-rays greater than a threshold dose, for example greater than 1 Gy.

[0037] It can be observed that there is a range D of values ​​of Vbase, for example between 0.45 V and 0.7 V, where there is a significant difference between the gain values ​​of the two curves. More specifically, for values ​​of Vbase within the range D, the values ​​of curve 12 are significantly greater than the values ​​of curve 14. For values ​​of Vbase within the range D, the values ​​of curve 12 are greater than the values ​​of curve 14 by at least a value of 20.

[0038] Thus, for voltages Vbase in the range of 0.45 to 0.7, the gain of curve 12 is greater than the gain of curve 14 by a factor greater than 1.5.

[0039] More generally, the inventors have observed that an NPN transistor that has been subjected to an amount of X-rays greater than a threshold dose comprises a range of voltage values ​​Vbase in which the gain is at most one-half, preferably at most one-third, of the gain of the same transistor. The gain difference within the range of voltage values ​​is preferably at least equal to a value of 10.

[0040] The inventors have also observed that the higher the amount of X-rays, the greater the gain difference relative to the same transistor before being subjected to X-rays, i.e. Figure 1 The greater the difference in curve 12 for the transistor considered in . Therefore, the gain variation is monotonic.

[0041] Figure 2An embodiment of an X-ray detector 20 is schematically shown in block form.

[0042] The detector 20 is intended to determine whether a device having the detector (in which the detector is located) has been subjected to a significant amount of X-rays since the manufacture of the device, for example since the device has been sold, i.e. an amount greater than a threshold amount. For example, a significant amount of X-rays means greater than 1 Gray, preferably greater than 10 Gray, preferably in the range of 10 to 50 Gray. In other words, the threshold amount is, for example, equal to 1 Gray or 10 Gray.

[0043] The detector 20 includes a circuit 22 (NPN). The circuit 22 includes at least one NPN bipolar transistor 23, for example, a single NPN bipolar transistor. The transistor 23 is, for example, Figure 1 Description of an NPN bipolar transistor.

[0044] For example, circuit 22 is configured such that the base voltage of transistor 23 is within a range of values ​​during detector operation for which the difference in gain between a transistor that has not received X-rays and a transistor that has received a threshold amount of X-rays is preferably greater than 10, preferably greater than 20. Preferably, circuit 22 is configured such that the base voltage of transistor 23 is within a range of values ​​during detector operation for which the gain of a transistor that has not received X-rays is at least 1.5 times greater, preferably at least three times greater, than the gain of a transistor that has received a threshold amount of X-rays.

[0045] The circuit 22 comprises an output node 24 at which an output signal SG of the circuit 22 is delivered. The signal SG is, for example, a voltage. The signal SG represents the gain of the NPN bipolar transistor 23, or more specifically the effect of the X-rays on the transistor 23.

[0046] Node 24 is coupled to, preferably connected to, one of the terminals of transistor 23. In other words, node 24 is coupled to, preferably connected to, the collector or emitter, preferably the emitter, of transistor 23. Therefore, the value of output signal SG depends on the gain value of transistor 23.

[0047] Preferably, the circuit 22 is configured such that the value of the output signal SG is substantially constant, in particular during operation of the device. In other words, the circuit 22 is configured such that the value of the output signal SG is substantially constant when the gain of the transistor 23 does not vary.

[0048] Thus, when the device is subjected to a significant amount of X-rays, the gain of transistor 23 is as Figure 1 is changed, and the value of the output signal SG is also significantly changed. Therefore, the change in the output signal SG represents the amount of X-rays to which the device is subjected.

[0049] When the transistor is subjected to X-rays, the gain change of the transistor is monotonically changed. Similarly, the change of the signal SG is also monotonically changed. More precisely, the circuit 22 is configured so that the signal SG is substantially constant when the transistor does not receive X-rays, and changes monotonically when the transistor receives X-rays. Therefore, the greater the amount of X-rays, the more the signal SG changes monotonically. According to the circuit 22, when the transistor is subjected to X-rays, the value of the signal SG increases or decreases. For example, the greater the amount of X-rays, the more the signal SG increases. For example, the greater the amount of X-rays, the more the signal SG decreases.

[0050] The detector 20 comprises a comparison circuit 26 (COMP) configured to determine from the signal SG whether the device has received a significant amount of X-rays, in other words whether the gain of the transistor 23 has been modified in a way that indicates a significant amount of X-rays received by the device.

[0051] The comparison circuit 26 is configured to compare the signal SG with a threshold value Sref. The threshold value Sref is, for example, a voltage. The threshold value Sref is generated by a voltage generator circuit 28 (GEN). The circuit 28 is configured to generate a constant signal Sref in such a way that the threshold value Sref represents a threshold value of X-rays received by the transistor 23. More precisely, the threshold value Sref represents a threshold value of received X-rays (it is desired to detect a change from the received X-rays), for example, from which it is considered that the device is damaged, for example, from which it is considered that the device has received a larger amount of X-rays than the amount authorized or recommended by the manufacturer. When the transistor has received this amount of X-rays, the threshold value Sref is substantially equal to the value of the signal SG.

[0052] For example, if the signal SG increases when the device receives X-rays, the threshold value Sref is greater than the constant value of the signal SG, that is, the value of the signal SG when the device does not receive X-rays. Similarly, if the signal SG decreases when the device receives X-rays, the threshold value Sref is less than the constant value of the signal SG, that is, the value of the signal SG when the device does not receive X-rays.

[0053] The circuit 26 is configured to transmit an output signal SE representing a comparison between the signal SG and the threshold value Sref. Preferably, if the signal SG is less than the threshold value Sref, the signal SE takes a first value, and if the signal SG is greater than the threshold value Sref, the signal SE takes a second value. If the circuit 22 is configured so that the value of the signal SG increases when the device receives X-rays, the first value of the signal SE corresponds to the amount of X-rays less than the threshold value, and the second value of the signal SE indicates that the X-ray threshold value has been exceeded. Similarly, if the circuit 22 is configured so that the value of the signal SG decreases when the device receives X-rays, the second value of the signal SE corresponds to the amount of X-rays less than the threshold value, and the first value of the signal SE indicates that the X-ray threshold value has been exceeded.

[0054] Figure 3 shows the effect of X-rays on an NPN bipolar transistor after several days. More precisely, Figure 3 is a curve graph similar to Figure 1 The gain G of an NPN type bipolar transistor is shown as a function of the voltage Vbase on the base of the transistor.

[0055] Figure 3 Show about Figure 1 Curves 12 and 14 are described. Curve 12 shows the gain of a transistor that has not received X-rays, and curve 14 shows the gain of the same transistor after the transistor has received an amount of X-rays, for example equal to a threshold dose.

[0056] Figure 3 Also shown is curve 30. Curve 30 corresponds to the gain of the same transistor as curves 12 and 14 after a few days, for example five days, during which the transistor received no X-rays.

[0057] It can be observed that the values ​​of curves 14 and 30 are substantially equal. Therefore, when the transistor does not receive X-rays, the gain of the transistor does not change. In particular, the transistor gain does not return to its original value, that is, the value of curve 12. Therefore, the gain change of the transistor is permanent.

[0058] It is thus possible to determine whether the device has received a significant amount of X-rays a few days after the end of the X-ray reception. Therefore, the output signal SE representing the amount of X-rays received by the device in the past holds a value indicating that the X-ray threshold is exceeded, preferably explicitly exceeded. Thus, a device external to the device including the detector 20 may obtain information according to which whether the device has received an amount of X-rays greater than a threshold determined in the past.

[0059] Figure 4 An embodiment of the X-ray detector 20 is shown in more detail.

[0060] The detector 20 comprises a comparison circuit 26. The circuit 26 receives a threshold value Sref on an input 32 and a signal SG on an input 34. The circuit 26 delivers a signal SE on an output 35.

[0061] In this example, circuit 26 includes comparator 36. Comparator 36 is powered by supply voltage Vdd. Voltage Vdd is a supply voltage of detector 20, such as a supply voltage of a device. Comparator 36, for example, includes a non-inverting input that is coupled to, preferably connected to, an input of circuit 26, preferably input 32. Comparator 36, for example, includes an inverting input that is coupled to, preferably connected to, an input of circuit 26, preferably input 34.

[0062] Detector 20 includes circuit 22, generating signal SG. Circuit 22 includes two NPN bipolar transistors. Circuit 22 includes transistor 23. As mentioned above, transistor 23 is an NPN bipolar transistor. Transistor 23 is coupled between application node 38 of power supply voltage Vdd and application node 40 of reference voltage, such as ground, through its conductive terminal. Transistor 23 is coupled to node 40 through resistor R3 and is coupled to node 38 through transistor 42, such as a P-channel metal oxide semiconductor field effect transistor (MOSFET).

[0063] More specifically, the emitter of transistor 23 is coupled to node 40. A terminal of resistor R3 is thus coupled to, preferably connected to, node 40, and the other terminal of resistor R3 is coupled to, preferably connected to, the emitter of transistor 23. The emitter of transistor 23 is coupled to, preferably connected to, output node 24. The emitter of transistor 23 is thus coupled to, preferably connected to, input 34 of comparison circuit 26. Thus, signal SG corresponds to the voltage on the emitter of transistor 23.

[0064] The collector of transistor 23 is coupled to node 38. More specifically, a conduction terminal, such as a source, of transistor 42 is coupled to, preferably connected to, node 38, and another conduction terminal, such as a drain, of transistor 42 is coupled to, preferably connected to, the collector of transistor 23.

[0065] Transistor 42 is coupled as a current mirror to transistor 44, for example a P-channel MOSFET transistor, preferably the same transistor as transistor 42. In other words, transistor 44 is coupled between node 38 and node 46. More precisely, a conduction terminal, for example a source, of transistor 44 is coupled to, preferably connected to node 38, and a further conduction terminal, for example a drain, of transistor 44 is coupled to, preferably connected to node 46. Furthermore, a gate of transistor 44 is coupled to, preferably connected to a gate of transistor 42. Furthermore, a gate of transistor 42 is coupled to, preferably connected to a conduction terminal of transistor 42, which is coupled to, preferably connected to a drain of transistor 23, for example transistor 42.

[0066] Circuit 22 includes a second NPN bipolar transistor 48. Transistor 48 is preferably the same as transistor 23. Transistor 48 is coupled between node 38 and node 40. More specifically, the emitter of transistor 48 is coupled to, preferably connected to, node 40. The collector of transistor 48 is coupled to node 38 via transistor 44. In other words, the collector of transistor 48 is coupled to, preferably connected to, node 46. Therefore, the same current I flows through transistors 23 and 48.

[0067] Thus, the circuit 22 comprises two branches, each branch comprising a first transistor 42, 44, for example a P-channel MOSFET transistor, coupled in series with a second NPN-type bipolar transistor 23, 48. The first transistors are coupled as current mirrors. Thus, the same current I flows through the bipolar transistors.

[0068] Node 46 is coupled to the base of transistor 23, for example, via amplifier circuit 50. For example, circuit 50 has a gain substantially equal to 1. An input of circuit 50 is coupled to, preferably connected to, node 46, and an output of circuit 50 is coupled to, preferably connected to, the base of transistor 23.

[0069] The base of transistor 23 is further coupled to node 40. The base of transistor 23 is coupled to node 40, for example, via two resistors R1 and R2. More precisely, resistor R1 is connected between the base of transistor 23 and node 52. Resistor R2 is coupled between node 52 and node 40. In other words, a terminal of resistor R1 is coupled to, preferably connected to, the base of transistor 23, and a further terminal of resistor R1 is coupled to, preferably connected to, node 52. Furthermore, a terminal of resistor R2 is coupled to, preferably connected to, node 40, and a further terminal of resistor R2 is coupled to, preferably connected to, node 52. Furthermore, node 52 is coupled to, preferably connected to, the base of transistor 48. In other words, the bases of transistors 23 and 48 are coupled via resistor R2. The base of transistor 52 is coupled to node 40 via resistor R2. The base of transistor 23 is coupled to node 40 via resistor R1 and R2 connected in series.

[0070] The resistors R1 and R2 are preferably selected in such a way that the base voltage of the transistor 23 and, for example, the base voltage of the transistor 48 is within the aforementioned value range.

[0071] Figure 4 An advantage of the circuit 22 is that the voltage variation, in particular the variation of the voltage on the emitter of the transistor 23, i.e. the variation of the signal SG, is substantially independent of the temperature. Therefore, the variation of the signal SG representing the amount of X-rays received by the device is independent of the temperature of the device. Therefore, in the absence of X-rays, the signal SG is substantially constant.

[0072] The detector 20 also includes a circuit 28 configured to generate a threshold value Sref. The circuit 28 includes a transistor 54, such as a P-channel MOSFET transistor. The transistor 54 is coupled in series with a component including at least one resistor and at least one capacitor, for example. Figure 4 In the example of FIG. 5 , circuit 28 includes two resistors R4 and R5 . Transistor 54 and resistors R4 and R5 are coupled in series between node 38 and node 40 .

[0073] Transistor 54 is coupled between node 38 and node 56. More specifically, a conductive terminal, such as a source, of transistor 54 is coupled to, preferably connected to, node 38, and another conductive terminal, such as a drain, is coupled to, preferably connected to, node 56. Transistor 54 is coupled to transistor 42 as a current mirror. Thus, a gate of transistor 54 is coupled to, preferably connected to, a gate of transistor 42.

[0074] Resistor R4 is coupled between node 56 and node 58. In other words, a terminal of resistor R4 is coupled to, preferably connected to, node 56 and another terminal is coupled to, preferably connected to, node 58. Resistor R5 is coupled between node 58 and node 40. In other words, a terminal of resistor R5 is coupled to, preferably connected to, node 58 and another terminal is coupled to, preferably connected to, node 40.

[0075] Circuit 28 also includes a capacitor C. Capacitor C is coupled in parallel with resistor R5. In other words, a terminal of capacitor C is coupled to, preferably connected to, a terminal of resistor R5, and another terminal of capacitor C is coupled to, preferably connected to, another terminal of resistor R5. In other words, a terminal of capacitor C is coupled to, preferably connected to node 58, and another terminal of the capacitor is coupled to, preferably connected to node 40.

[0076] The threshold Sref corresponds to the voltage on the node 58. The value of the threshold Sref depends on the values ​​of the resistors R4 and R5 and the capacitance of the capacitor C. The values ​​of the resistors R4 and R5 and the capacitance of the capacitor C are selected to obtain a value of Sref corresponding to the value of the signal 24 when the device including the detector receives an amount of X-rays equal to a threshold value considered acceptable.

[0077] An advantage of the described embodiments is that they enable determination of whether the device has received an amount of X-rays greater than a threshold. In particular, the described embodiments enable determination of whether the device has received an amount of X-rays greater than a threshold after the reception of X-rays has ended. In fact, the effect of radiation on the transistor gain is permanent. Therefore, the device is able to detect the cumulative amount of radiation received by the device.

[0078] Various embodiments and variations have been described. Those skilled in the art will appreciate that certain features of these various embodiments and variations can be combined, and those skilled in the art will recognize other variations.

[0079] Finally, based on the functional indications given above, the practical implementation of the described embodiments and variants is within the capabilities of a person skilled in the art.

Claims

1. An X-ray detector, comprising: A first circuit includes a first NPN bipolar transistor; as well as a second circuit configured to compare the voltage of the first circuit to a reference value, the reference value being substantially equal to a value of the voltage that would occur when the first circuit has received a threshold amount of X-rays; Wherein, the first circuit is configured such that during operation of the detector, the base voltage of the first NPN bipolar transistor is within a range of values, for which the gain of the first NPN bipolar transistor that does not receive X-rays is at least 1.5 times greater than the gain of the first NPN bipolar transistor that receives the threshold amount of X-rays.

2. The detector according to claim 1, wherein The voltage is a voltage at one of the terminals of the first NPN-type bipolar transistor.

3. The detector according to claim 2, wherein: The one of the terminals is an emitter of the first NPN-type bipolar transistor.

4. The detector according to claim 1, wherein: The voltage is substantially constant during operation of a device comprising the X-ray detector in the absence of X-rays.

5. The detector according to claim 1, wherein: The threshold amount of X-rays is 10 Gray.

6. The detector according to claim 1, wherein: The first circuit includes two branches, the first branch includes a first transistor and a first NPN bipolar transistor coupled in series, and the second branch includes a second transistor and a second NPN bipolar transistor coupled in series, the first transistor and the second transistor are coupled as a current mirror so that the current flowing through the first NPN bipolar transistor and the second NPN bipolar transistor is substantially equal.

7. The detector according to claim 6, wherein: Bases of the first NPN bipolar transistor and the second NPN bipolar transistor are coupled via a resistor.

8. The detector according to claim 7, wherein: A base of each of the first NPN type bipolar transistor and the second NPN type bipolar transistor is coupled to an application node of a reference voltage through a resistor.

9. The detector according to claim 6, wherein: The collector of the second NPN bipolar transistor is coupled to the base of the first NPN bipolar transistor through a unity gain amplifier circuit.

10. The detector of claim 6, further comprising a voltage generator circuit configured to generate the reference value, the voltage generator circuit comprising a third transistor connected in series with at least one resistor and at least one capacitor.

11. The detector according to claim 10, wherein: The third transistor is coupled to at least one of the first transistor and the second transistor as a current mirror.

12. An X-ray detector, comprising: A first circuit includes a first NPN bipolar transistor; as well as a second circuit configured to compare the voltage of the first circuit to a reference value, the reference value being substantially equal to a value of the voltage that would occur when the first circuit has received a threshold amount of X-rays; Wherein, the first circuit is configured so that during operation of the detector, the voltage on the base of the first NPN bipolar transistor is within a range of values, for which the gain difference between the first NPN bipolar transistor that has not received X-rays and the first NPN bipolar transistor that has received the threshold amount of X-rays is greater than 10.

13. The detector according to claim 12, wherein: The voltage is a voltage at one of the terminals of the first NPN-type bipolar transistor.

14. The detector according to claim 13, wherein: The one of the terminals is an emitter of the first NPN-type bipolar transistor.

15. The detector according to claim 12, wherein: The voltage is substantially constant during operation of a device comprising the X-ray detector in the absence of X-rays.

16. The detector according to claim 12, wherein: The threshold amount of X-rays is 10 Gray.

17. The detector according to claim 12, wherein: The first circuit includes two branches, the first branch includes a first transistor and a first NPN bipolar transistor coupled in series, and the second branch includes a second transistor and a second NPN bipolar transistor coupled in series, the first transistor and the second transistor are coupled as a current mirror so that the current flowing through the first NPN bipolar transistor and the second NPN bipolar transistor is substantially equal.

18. The detector according to claim 17, wherein: Bases of the first NPN bipolar transistor and the second NPN bipolar transistor are coupled via a resistor.

19. The detector according to claim 18, wherein A base of each of the first NPN type bipolar transistor and the second NPN type bipolar transistor is coupled to an application node of a reference voltage through a resistor.

20. The detector according to claim 17, wherein: The collector of the second NPN bipolar transistor is coupled to the base of the first NPN bipolar transistor through a unity gain amplifier circuit.

21. The detector of claim 17, further comprising a voltage generator circuit configured to generate the reference value, the voltage generator circuit comprising a third transistor connected in series with at least one resistor and at least one capacitor.

22. The detector according to claim 21, wherein The third transistor is coupled to at least one of the first transistor and the second transistor as a current mirror.

23. An X-ray detector method, comprising: comparing a voltage of a first electronic circuit including a first NPN bipolar transistor with a reference value; wherein the reference value is substantially equal to a value of the voltage that would occur when the first electronic circuit has received a threshold amount of X-rays; and generating an output signal indicative of X-ray exposure if the comparison is satisfied; A base voltage is applied to the first NPN bipolar transistor, the base voltage being within a range of values, for which a gain of the first NPN bipolar transistor that does not receive X-rays is at least 1.5 times greater than a gain of the first NPN bipolar transistor that receives the threshold amount of X-rays.

24. The method according to claim 23, wherein: The voltage is a voltage across one of the terminals of the first NPN-type bipolar transistor.

25. The method according to claim 24, wherein: One of the terminals is an emitter of the first NPN-type bipolar transistor.

26. The method according to claim 24, wherein: The voltage is substantially constant during operation in the absence of X-rays.

27. The method according to claim 24, wherein: The threshold amount of X-rays is 10 Gray.

28. An X-ray detector method, comprising: comparing a voltage of a first electronic circuit including a first NPN bipolar transistor with a reference value; wherein the reference value is substantially equal to a value of the voltage that would occur when the first electronic circuit has received a threshold amount of X-rays; If the comparison is satisfied, generating an output signal indicative of X-ray exposure; and Applying a voltage at the base of the first NPN bipolar transistor is within a range of values ​​for which a gain difference between the first NPN bipolar transistor that does not receive X-rays and the first NPN bipolar transistor that receives the threshold amount of X-rays is greater than 10.

29. The method according to claim 28, wherein: The voltage is a voltage across one of the terminals of the first NPN-type bipolar transistor.

30. The method of claim 29, wherein: One of the terminals is an emitter of the first NPN-type bipolar transistor.

31. The method of claim 29, wherein: The voltage is substantially constant during operation in the absence of X-rays.

32. The method of claim 29, wherein: The threshold amount of X-rays is 10 Gray.

Images