Amplifier for dark noise compensation

Abstract

The present disclosure discloses an amplifier (309), which includes: an operational amplifier (391) configured to receive a first current at its input terminal; and a first MOS (metal oxide semiconductor) capacitor (393) connected to the input terminal and the output terminal of the operational amplifier (391).

Description

Background Art

[0001] A radiation detector is a device that measures the characteristics of radiation. Examples of such characteristics may include the intensity, phase, and spatial distribution of polarization of the radiation. The radiation may be radiation that interacts with an object. For example, the radiation measured by the radiation detector may be radiation that has penetrated or been reflected from an object. The radiation may be electromagnetic radiation, such as infrared light, visible light, ultraviolet light, X-rays, or gamma rays. The radiation may be other types, such as alpha rays and beta rays.

[0002] One type of radiation detector is based on the interaction between radiation and a semiconductor. For example, this type of radiation detector may have a semiconductor layer that absorbs radiation and generates charge carriers (e.g., electrons and holes), and a circuit for detecting the charge carriers.

[0003] A radiation detector can be adversely affected by dark noise (e.g., dark current). Even when there is no radiation that the radiation detector is configured to detect incident on the radiation detector, the dark noise in the radiation detector includes physical effects. Isolating or reducing the effect of the dark noise on the overall signal detected by the radiation detector helps make the radiation detector more useful. One way to reduce the effect of the dark noise is to compensate for the dark noise by determining and eliminating the contribution of dark noise in the signal measurement circuit of the radiation detector.

Summary of the Invention

[0004] Disclosed herein is an amplifier, which includes: an operational amplifier configured to receive a first current at its input terminal; a first MOS capacitor connected to the input terminal and the output terminal of the operational amplifier.

[0005] According to an embodiment, the amplifier further includes an adjustable current source that feeds a second current to the input terminal.

[0006] According to an embodiment, the first MOS capacitor is a MOSFET, and the source of the MOSFET is shorted to its drain.

[0007] According to an embodiment, the source and the drain are connected to the output terminal of the operational amplifier, and the gate of the MOSFET is connected to the input terminal of the operational amplifier.

[0008] According to an embodiment, the source and the drain are connected to the input terminal of the operational amplifier, while the gate of the MOSFET is connected to the output terminal of the operational amplifier.

[0009] According to an embodiment, the adjustable current source can be adjusted by an electrical signal.

[0010] According to an embodiment, the adjustable current source includes a second MOS capacitor.

[0011] According to an embodiment, the adjustable current source includes a third MOS capacitor connected in parallel with the second MOS capacitor; wherein a gate of the second MOS capacitor is connected to the input terminal and a body contact of the third MOS capacitor is connected to the input terminal; wherein a gate of the third MOS capacitor is connected to the input terminal of the operational amplifier and a body contact of the third MOS capacitor is connected to the electrical signal.

[0012] According to an embodiment, the first current includes dark noise of the radiation detector; wherein the adjustable current source is configured to compensate for the dark noise.

[0013] According to an embodiment, the amplifier further includes a processor configured to generate the electrical signal based on a level of the output.

[0014] According to an embodiment, the processor is configured to further generate the electrical signal based on an output of a comparator.

[0015] According to an embodiment, the processor includes a charge pump.

[0016] According to an embodiment, the charge pump is configured to be turned on and off by a clock signal.

[0017] Disclosed herein is a radiation detector, comprising: a radiation absorption layer including an electrode; an amplifier as claimed in claim 1, wherein the first current is from the electrode, and the amplifier is configured to generate a voltage at the output terminal based on the first current; a first voltage comparator configured to compare a voltage of the electrode with a first threshold; a second voltage comparator configured to compare the voltage with a second threshold; a counter configured to record a number of radiation particles absorbed by the radiation absorption layer; a controller; wherein the controller is configured to start a time delay from a time when the absolute value of the voltage determined by the first voltage comparator is equal to or exceeds the absolute value of the first threshold; wherein the controller is configured to start the second voltage comparator during the time delay; wherein the controller is configured to, if the second voltage comparator determines that the absolute value of the voltage is equal to or exceeds the absolute value of the second threshold, increment the number recorded by the counter by one.

[0018] According to an embodiment, the radiation is X - ray.

[0019] According to an embodiment, the controller is configured to start the second voltage comparator at a start or expiration of the time delay.

[0020] According to an embodiment, the radiation detector further includes a voltmeter, wherein the controller is configured to cause the voltmeter to measure the voltage after the expiration of the time delay.

[0021] According to an embodiment, the controller is configured to determine the radiation of radiation particles based on the value of the voltage measured after the expiration of the time delay.

[0022] According to an embodiment, the controller is configured to connect the electrode of the radiation absorption layer to electrical ground.

[0023] According to an embodiment, the rate of change of the voltage is substantially zero at the expiration of the time delay.

[0024] According to an embodiment, the rate of change of the voltage is substantially non-zero at the expiration of the time delay.

[0025] According to an embodiment, the radiation absorption layer includes silicon, germanium, gallium arsenide, cadmium telluride, cadmium zinc telluride, or a combination thereof.

[0026] According to an embodiment, the radiation detector does not include a scintillator.

[0027] According to an embodiment, the radiation detector includes a pixel array.

Description of the Drawings

[0028] Figure 1A Schematically shows a component diagram of an amplifier according to an embodiment.

[0029] Figure 1B - Figure 1C Each schematically shows a detailed component diagram of the amplifier according to an embodiment.

[0030] Figure 1D and Figure 1E Each schematically shows the configuration of an adjustable current source of the amplifier according to an embodiment.

[0031] Figure 1F Schematically shows that the amplifier according to an embodiment may further include a processor.

[0032] Figure 1G Shows an example of the processor having a charge pump according to an embodiment.

[0033] Figure 2 Schematically shows a top view of a part of a radiation detector according to an embodiment.

[0034] Figure 3A Schematically shows a cross-sectional view of the radiation detector according to an embodiment.

[0035] Figure 3B Schematically shows a detailed cross-sectional view of the radiation detector according to an embodiment.

[0036] Figure 3C Schematically shows an alternative detailed cross-sectional view of the radiation detector according to an embodiment.

[0037] Figure 4 Schematically shows according to an embodiment Figure 3B or Figure 3C a component diagram of the electronic system of the radiation detector in

[0038] Figure 5 Schematically shows the time variation (upper curve) of the current caused by carriers generated by radiation particles incident on the pixels associated with the electrical contacts flowing through the electrical contacts, and the corresponding time variation (lower curve) of the voltage of the electrical contacts.

Detailed Description

[0039] Figure 1A Schematically shows a component diagram of amplifier 309 according to an embodiment. The amplifier 309 includes an operational amplifier 391. The operational amplifier 391 has an input terminal and an output terminal. The operational amplifier 391 is configured to receive a first current at the input terminal. The amplifier 309 may be configured to generate an amplified electrical signal (e.g., voltage) at the output terminal based on the first current.

[0040] As Figure 1B and Figure 1C shown, the amplifier 309 has a first MOS capacitor 393, which is a component in the feedback circuit 392 between the input terminal and the output terminal of the operational amplifier 391. The first MOS capacitor 393 may be connected to the input terminal and the output terminal of the operational amplifier 391. As Figure 1B and Figure 1C shown, the first MOS capacitor 393 may be a MOSFET, the source of which is shorted to its drain. As Figure 1B shown, in one embodiment, the source and the drain of the first MOS capacitor 393 are connected to the output terminal of the operational amplifier 391, and the gate of the first MOS capacitor 393 is connected to the input terminal of the operational amplifier 391. As Figure 1C shown, in one embodiment, the source and the drain are connected to the input terminal of the operational amplifier 391, and the gate of the first MOS capacitor 393 is connected to the output terminal of the operational amplifier 391.

[0041] In an embodiment, the amplifier 309 includes an adjustable current source 394, which is a component in the feedback circuit 392. The adjustable current source 394 feeds a second current to the input terminal of the operational amplifier 391. The second current can flow out of or into the input terminal of the operational amplifier 391. The adjustable current source 394 can be adjusted by an electrical signal Vcomp (field compensation). For example, the magnitude and direction of the second current depend on the electrical signal Vcomp. The electrical signal Vcomp can be a voltage or other types of electrical signals. In one embodiment, when the first current at the input terminal of the amplifier 309 includes the dark noise of the radiation detector, the adjustable current source 394 is configured to compensate for the dark noise, for example, by changing the magnitude and direction of the second current.

[0042] Figure 1D and Figure 1E each schematically shows the configuration of the adjustable current source 394 according to an embodiment. In Figure 1D the configuration shown, the adjustable current source 394 includes a diode-connected NMOSFET (N-type metal oxide semiconductor field effect transistor) 397, whose gate and drain are short-circuited. The diode-connected NMOSFET 397 serves as a bias diode, which feeds the second current to the input terminal of the operational amplifier 391 as a function of the electrical signal Vcomp received at the drain. In this configuration, the second current flows from the drain to the source.

[0043] In Figure 1EIn the configuration shown, the adjustable current source 394 includes a second MOS capacitor 395. The second MOS capacitor 395 can be an NMOSFET (N-type metal oxide semiconductor field effect transistor), and the source of this NMOSFET is shorted to its drain. In an embodiment, the adjustable current source 394 further includes a third MOS capacitor 396, which can be a PMOSFET (P-type metal oxide semiconductor field effect transistor), and the source of this PMOSFET is shorted to its drain. The second MOS capacitor 395 and the third MOS capacitor 396 can be connected in parallel. The gate of the second MOS capacitor 395 is connected to the input terminal of the operational amplifier 391, and the body contact of the second MOS capacitor 395 is configured to receive the electrical signal Vcomp. The gate electrode of the third MOS capacitor 396 is connected to the input terminal of the operational amplifier 391, and the body contact of the third MOS capacitor 396 is configured to receive the electrical signal Vcomp. With this configuration, the adjustable current source 394 can provide the second current bidirectionally. For example, according to Vcomp, the direction of the second current can flow from the adjustable current source 394 to the input terminal of the operational amplifier 391, or can flow from the input terminal of the operational amplifier 391 to the adjustable current source 394.

[0044] The electrical signal Vcomp can be selected empirically to provide sufficient compensation for the dark noise in the output of the operational amplifier 391. The electrical signal Vcomp can also be determined based on the output of the operational amplifier 391. Figure 1F Schematically shown, according to an embodiment, the amplifier 309 can further include a processor 350. The processor 350 is configured to determine the electrical signal Vcomp based on the level at the output terminal of the operational amplifier 391 and optionally also based on the output of a comparator 380 that compares the output of the operational amplifier 391 with a threshold SH.

[0045] The processor 350 can further include a charge pump. The charge pump can be configured to be turned on and off by a clock signal CLK. The electrical signal Vcomp can be determined for each individual pixel of the radiation detector and applied to the adjustable current source 394 of that pixel. The electrical signal Vcomp can be determined based on the dark noise of one pixel or several pixels and applied to the adjustable current source 394 of one or several pixels. Figure 1G An example of the processor 350 having the charge pump is shown.

[0046] As an example, Figure 2Schematically shows a radiation detector 100 including the amplifier 309 described herein. The radiation detector 100 may have an array of pixels 150. The array may be a rectangular array, a honeycomb array, a hexagonal array, or any other suitable array. Each pixel 150 is configured to detect radiation incident thereon from a radiation source and may be configured to measure characteristics of the radiation (e.g., the energy, wavelength, and frequency of the radiation particles). For example, each pixel 150 is configured to count the number of radiation particles whose incident energy falls into multiple bins over a period of time. All the pixels 150 may be configured to count the number of radiation particles incident thereon within multiple energy bins over the same period of time. Each pixel 150 may have its own analog-to-digital converter (ADC) that is configured to digitize an analog signal representing the incident radiation particle energy into a digital signal. The pixels 150 may be configured to operate in parallel. For example, while one pixel 150 is measuring incident radiation particles, another pixel 150 may be waiting for radiation particles to arrive. The pixels 150 may not have to be individually addressable. Each pixel 150 may be configured to measure its dark current before or simultaneously with each radiation particle incident thereon. Each pixel 150 may be configured to subtract the contribution of the dark current from the energy of the radiation particles incident thereon.

[0047] Figure 3A Schematically shows a cross-sectional view of the radiation detector 100 according to an embodiment. The radiation detector 100 may include a radiation absorption layer 110 and an electronics layer 120 (e.g., an ASIC) for processing or analyzing electrical signals generated by incident radiation in the radiation absorption layer 110. The radiation detector 100 may or may not include a scintillator. The radiation absorption layer 110 may include a semiconductor material such as silicon, germanium, gallium arsenide, cadmium telluride, cadmium zinc telluride, or a combination thereof. The semiconductor may have a high mass attenuation coefficient for the radiation of interest. The radiation may be X-rays.

[0048] As Figure 3B shown in the detailed cross-sectional view of the radiation detector 100 in, according to an embodiment, the radiation absorption layer 110 may include one or more diodes (e.g., p-i-n or p-n) consisting of one or more discrete regions 114 of a first doped region 111 and a second doped region 113. The second doped region 113 may be separated from the first doped region 111 by an optional intrinsic region 112. The discrete regions 114 are separated from each other by the first doped region 111 or the intrinsic region 112. The first doped region 111 and the second doped region 113 have opposite types of doping (e.g., the first doped region 111 is p-type and the second doped region 113 is n-type, or the first doped region 111 is n-type and the second doped region 113 is p-type). InFigure 3B In the example of Figure 3B , the radiation absorption layer 110 includes a plurality of diodes that have the first doped region 111 as a common electrode. The first doped region 111 may also have discrete portions.

[0049] When a radiation particle strikes the radiation absorption layer 110 that includes diodes, the radiation particle may be absorbed and generate one or more charge carriers through several mechanisms. The charge carriers may drift towards an electrode of one of the diodes under an electric field. The electric field may be an external electric field. The electrical contact 119B may include discrete portions, each of which is in electrical contact with the discrete region 114. In an embodiment, the charge carriers may drift in different directions such that the charge carriers generated by a single radiation particle are generally not shared by two different discrete regions 114 (“generally not shared” herein means that less than 2%, less than 0.5%, less than 0.1%, or less than 0.01% of these charge carriers flow to one of the discrete regions 114 different from the remaining charge carriers). The charge carriers generated by a radiation particle incident around the footprint of one of the discrete regions 114 are generally not shared by the other discrete region 114. The pixel 150 associated with a discrete region 114 may be the surrounding region of the discrete region 114, and the charge carriers generated by a radiation particle incident therein generally all (more than 98%, more than 99.5%, more than 99.9%, or more than 99.99%) flow to the discrete region 114. That is, less than 2%, less than 1%, less than 0.1%, or less than 0.01% of the charge carriers flow outside the pixel

[0050] As Figure 3C shown in an alternative detailed cross-sectional view of the radiation detector 100 of

[0051] When the radiation particles strike the radiation absorption layer 110 that includes a resistor but not a diode, the radiation particles can be absorbed and generate one or more carriers through several mechanisms. A single radiation particle can generate from 10 to 100,000 carriers. The carriers can drift under an electric field towards the electrical contact 119A and the electrical contact 119B. The electric field can be an external electric field. The electrical contact 119B includes discrete portions. In an embodiment, the carriers can drift in different directions such that the carriers generated by a single radiation particle are generally not shared by two different discrete portions of the electrical contact 119B ("generally not shared" here means that less than 2%, less than 0.5%, less than 0.1%, or less than 0.01% of these carriers flow to discrete portions that are in a different group from the remaining carriers). The carriers generated by radiation particles incident around the footprint of one of the discrete portions of the electrical contact 119B are generally not shared by the other discrete portion of the electrical contact 119B. A pixel 150 associated with one of the discrete portions of the electrical contact 119B can be the surrounding area of the discrete portion, and the carriers generated by the radiation particles incident therein generally all (more than 98%, more than 99.5%, more than 99.9%, or more than 99.99%) flow to the discrete portion of the electrical contact 119B. That is, less than 2%, less than 0.5%, less than 0.1%, or less than 0.01% of the carriers flow outside the pixel associated with that one discrete portion of the electrical contact 119B.

[0052] The electronic device layer 120 can include an electronic system 121 that is suitable for processing or interpreting signals generated by radiation particles incident on the radiation absorption layer 110. The electronic system 121 can include analog circuits such as filter networks, amplifiers, integrators, comparators, or digital circuits such as microprocessors and memories. The electronic system 121 can include components shared by the pixels or components dedicated to a single pixel. For example, the electronic system 121 can include an amplifier dedicated to each pixel and a microprocessor shared among all pixels. The electronic system 121 can be electrically connected to the pixels through vias 131. The space between the vias can be filled with a filling material 130, which can increase the mechanical stability of the connection of the electronic device layer 120 to the radiation absorption layer 110. Other bonding techniques are possible to connect the electronic system 121 to the pixels without using vias.

[0053] The signal generated by the radiation incident on the radiation absorption layer 110 can be in the form of a current. Similarly, the dark noise can also be in the form of a current (e.g., a direct current flowing out of the electrical contact 119B). If the current can be determined, the current can be compensated (e.g., by the amplifier 309 described herein).

[0054] Figure 4 A component diagram of the electronic system 121 according to an embodiment is schematically shown. The electronic system 121 includes the amplifier 309 electrically connected to the discrete part of the electrical contact 119B. Carriers from the discrete part of the electrical contact 119B can accumulate in the amplifier 309 over a period of time (“integration period”). After the expiration of the integration period, the output terminal of the amplifier 309 is sampled and optionally reset by the optional switch 305.

[0055] The dark noise in the form of current charges the capacitor coupled to the amplifier 309 together with the signal generated by the radiation. The dark noise may be a very small current, for example, in the range of picoamperes (e.g., 1 - 1000 pA). Compensation of the dark noise can be performed by the amplifier 309. In one embodiment, the dark noise is measured when the radiation detector is not exposed to radiation. The electrical signal Vcomp can be determined based on the measured dark noise and applied to the adjustable current source 394. When the input terminal of the amplifier 309 receives the first current including the dark noise (e.g., dark current), the adjustable current source 394 can feed the second current to the operational amplifier 391 of the amplifier 309 in an appropriate direction and amplitude. The magnitude of the second current may be similar, but the direction of the dark noise is opposite.

[0056] The electronic system 121 may further include a first voltage comparator 301, a second voltage comparator 302, a plurality of counters 320 (which includes counters 320A, 320B, 320C, 320D...), an optional switch 305, a voltmeter 306, and a controller 310.

[0057] The first voltage comparator 301 is configured to compare the voltage of the discrete portion of the electrical contact 119B with a first threshold. The first voltage comparator 301 may be configured to directly monitor the voltage, or calculate the voltage by integrating the current flowing through the discrete portion of the electrical contact over a period of time. The first voltage comparator 301 may be controllably activated or deactivated by the controller 310. The first voltage comparator 301 may be a continuous comparator. That is, the first voltage comparator 301 may be configured to be continuously activated and continuously monitor the voltage. The first voltage comparator 301 configured as a continuous comparator reduces the chance for the electronic system 121 to miss signals generated by incident radiation particles. The first voltage comparator 301 configured as a continuous comparator is particularly suitable when the incident radiation intensity is relatively high. The first voltage comparator 301 may be a clocked comparator, which has the benefit of lower power consumption. The first voltage comparator 301 configured as a clocked comparator may cause the electronic system 121 to miss signals generated by some incident radiation particles. When the incident radiation intensity is low, since the time interval between two consecutive radiation particles is relatively long, the chance of missing the incident radiation particles is very low. Therefore, the first voltage comparator 301 configured as a clocked comparator is particularly suitable when the incident radiation intensity is relatively low. The first threshold may be 1-5%, 5-10%, 10%-20%, 20-30%, 30-40% or 40-50% of the maximum voltage that an incident radiation particle can generate on the discrete portion of the electrical contact 119B. The maximum voltage may depend on the energy of the incident radiation particle (e.g., the wavelength of the incident radiation), the material of the radiation absorption layer 110, and other factors. For example, the first threshold may be 50 mV, 100 mV, 150 mV or 200 mV.

[0058] The second voltage comparator 302 is configured to compare the voltage with a second threshold V2. The second voltage comparator 302 may be configured to directly monitor the voltage, or calculate the voltage by integrating the current flowing through the discrete portion of the electrical contact 119B over a period of time. The second voltage comparator 302 may be a continuous comparator. The second voltage comparator 302 may be controllably activated or deactivated by the controller 310. When the second voltage comparator 302 is deactivated, the power consumption of the second voltage comparator 302 may be less than 1%, less than 5%, less than 10% or less than 20% of the power consumption when the second voltage comparator 302 is activated. The absolute value of the second threshold is greater than the absolute value of the first threshold. As used herein, the "absolute value" or "modulus" |x| of a real number x is the non-negative value of x regardless of its sign. That is, The second threshold may be 200%-300% of the first threshold. For example, the second threshold may be 100 mV, 150 mV, 200 mV, 250 mV, or 300 mV. The second voltage comparator 302 and the first voltage comparator 301 may be the same component. That is, the electronic system 121 may have the same voltage comparator, which can compare voltages with two different thresholds at different times.

[0059] The first voltage comparator 301 or the second voltage comparator 302 may include one or more operational amplifiers or any other suitable circuits. The first voltage comparator 301 or the second voltage comparator 302 may have a high speed to allow the electronic system 121 to operate under high-throughput incident radiation. However, having a high speed usually comes at the cost of power consumption.

[0060] The counter 320 may be a software component (e.g., a number stored in a computer memory) or a hardware component (e.g., 4017 IC and 7490 IC). Each counter 320 is associated with a bin of an energy range. For example, counter 320A may be associated with the bin of 70-71 keV, counter 320B may be associated with the bin of 71-72 keV, counter 320C may be associated with the bin of 72-73 keV, and counter 320D may be associated with the bin of 73-74 keV. When the energy of the incident radiation particle is determined by the voltmeter 306 to be within the bin associated with the counter 320, the number recorded in the counter 320 is incremented by one.

[0061] The controller 310 may be a hardware component, such as a microcontroller and a microprocessor. The controller 310 is configured to start a time delay when the absolute value of the voltage determined by the first voltage comparator 301 is equal to or exceeds the absolute value of the first threshold (e.g., the absolute value of the voltage increases from being lower than the absolute value of the first threshold to being equal to or exceeding the absolute value of the first threshold). The absolute value is used here because the voltage can be negative or positive. The controller 310 may be configured to keep the second voltage comparator 302, the counter 320, and any other circuits not required for the operation of the first voltage comparator 301 deactivated before the first voltage comparator 301 determines that the absolute value of the voltage is equal to or exceeds the absolute value of the first threshold. After the voltage becomes stable (i.e., the rate of change of the voltage is substantially zero), the time delay may expire. The phrase "the rate of change is substantially zero" means that the change over time is less than 0.1% / ns. The phrase "the rate of change is substantially non-zero" means that the change over time of the voltage is at least 0.1% / ns.

[0062] The control 310 may be configured to activate the second voltage comparator during the time delay, which includes the start and expiration. In an embodiment, the controller 310 is configured to activate the second voltage comparator at the start of the time delay. The term "activate" means to bring a component into an operating state (e.g., by sending a signal such as a voltage pulse or a logic level, by providing power, etc.). The term "deactivate" means to bring a component into a non-operating state (e.g., by sending a signal such as a voltage pulse or a logic level, by cutting off power, etc.). The operating state may have a higher power consumption than the non-operating state (e.g., 10 times higher, 100 times higher, 1000 times higher). The controller 310 itself may be deactivated until the absolute value of the output voltage of the first voltage comparator 301 equals or exceeds the absolute value of the first threshold, at which point the controller 310 is activated.

[0063] If, during the time delay, the second voltage comparator 302 determines that the absolute value of the voltage equals or exceeds the absolute value of the second threshold, and the energy of the radiation particle falls into a bin associated with the counter 320, the controller 310 may be configured to increment by one the number recorded by one of the counters of the counter 320.

[0064] The controller 310 may be configured to cause the voltmeter 306 to digitize the voltage at the expiration of the time delay and determine into which bin the energy of the radiation particle falls based on the voltage.

[0065] The controller 310 may be configured to connect the discrete portion of the electrical contact 119B to electrical ground to reset the voltage and discharge any carriers accumulated on the discrete portion of the electrical contact 119B. In an embodiment, the discrete portion of the electrical contact 119B is connected to electrical ground after the expiration of the time delay. In an embodiment, the discrete portion of the electrical contact 119B is connected to electrical ground for a finite reset period. The controller 310 may connect the discrete portion of the electrical contact 119B to electrical ground by controlling the optional switch 305. The switch may be a transistor, e.g., a field effect transistor (FET).

[0066] In an embodiment, the electronic system 121 does not have an analog filter network (e.g., an RC network). In an embodiment, the electronic system 121 does not have an analog circuit.

[0067] The voltmeter 306 may feed the voltage it measures to the controller 310 as an analog or digital signal.

[0068] Figure 5Schematically shows the time variation (upper curve) of the current caused by carriers generated by radiation particles incident on the pixel 150 associated with the discrete portion of the electrical contact 119B flowing through the discrete portion of the electrical contact 119B, and the corresponding time variation (lower curve) of the voltage of the discrete portion of the electrical contact 119B. The voltage may be the integral of the current with respect to time. At time t0, the radiation particle strikes the diode or the resistor, carriers start to be generated in the pixel 150, current starts to flow through the discrete portion of the electrical contact 119B, and the absolute value of the voltage of the discrete portion of the electrical contact 119B starts to increase. At time t1, the first voltage comparator 301 determines that the absolute value of the voltage is equal to or exceeds the absolute value of the first threshold V1, and the controller 310 starts a time delay TD1 and the controller 310 may deactivate the first voltage comparator 301 at the start of the TD1. If the controller 310 is deactivated before t1, the controller 310 is activated at t1. During the TD1, the controller 310 activates the second voltage comparator 302. The term "during" the time delay as used herein means the start and expiration (i.e., end) of the time delay and any time in between. For example, the controller 310 may activate the second voltage comparator 302 at the expiration of the TD1. If during the TD1, the second voltage comparator 302 determines that at time t2 the absolute value of the voltage is equal to or exceeds the absolute value of the second threshold, the controller 310 waits for the voltage to stabilize. The voltage stabilizes at time t e when all carriers generated by the radiation particle drift out of the radiation absorption layer 110. At time t s , the time delay TD1 expires. In Figure 5 the example, time t s is after time t e ; i.e., TD1 expires after all carriers generated by the radiation particle drift out of the radiation absorption layer 110. The rate of change of the voltage is thus substantially zero at time t e . The controller 310 may be configured to deactivate the second voltage comparator 302 at the expiration of TD1 or at time t2, or at any time in between.

[0069] The controller 310 may be configured to cause the voltmeter 306 to measure the voltage when the time delay TD1 expires. In an embodiment, after the time delay TD1 expires, the controller 310 causes the voltmeter 306 to measure the voltage after the rate of change of the voltage is substantially zero. The voltage at this time is proportional to the number of carriers generated by the radiation particles, which is related to the energy of the radiation particles. The controller 310 may be configured to determine the energy of the radiation particles based on the voltage measured by the voltmeter 306. One method of determining the energy is to bin the voltage. The counter 320 may have sub-counters for each bin. When the controller 310 determines that the energy of the radiation particle falls into a bin, the controller 310 may increment the number recorded in the sub-counter for that bin by one. Thus, the electronic system 121 may be able to detect a radiation image and may be able to resolve the particles of the radiation energy of each radiation particle.

[0070] After TD1 expires, the controller 310 connects the discrete portion of the electrical contact 119B to electrical ground for a reset period RST to allow the carriers accumulated on the discrete portion of the electrical contact 119B to flow to the ground and reset the voltage. After RST, the electronic system 121 is ready to detect another incident radiation particle. If the first voltage comparator 301 has been deactivated, the controller 310 may activate it at any time before RST expires. If the controller 310 has been deactivated, it may be activated before RST expires.

[0071] The radiation detector 100 described herein may have other applications, such as in X-ray telescopes, mammography, industrial X-ray defect detection, X-ray microscopy or microphotography, X-ray casting inspection, X-ray non-destructive testing, X-ray welding inspection, X-ray digital subtraction angiography, etc. The radiation detector 100 is used in place of photographic negatives, photographic films, photostimulable phosphor plates, X-ray image intensifiers, scintillators, or X-ray detectors.

[0072] Although various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for illustrative purposes and not restrictive, and the true scope and spirit should be determined by the claims herein.

Claims

1. An amplifier, comprising: An operational amplifier configured to receive a first current at its input terminal; A first MOS (metal oxide semiconductor) capacitor connected to the input terminal and the output terminal of the operational amplifier; And An adjustable current source that feeds a second current to the input terminal, Wherein the adjustable current source is adjustable by an electrical signal, Wherein the adjustable current source includes a second MOS capacitor, Wherein the adjustable current source includes a third MOS capacitor connected in parallel with the second MOS capacitor, Wherein the gate of the second MOS capacitor is connected to the input terminal and the body contact of the third MOS capacitor is connected to the input terminal, Wherein the gate of the third MOS capacitor is connected to the input terminal of the operational amplifier and the body contact of the third MOS capacitor is connected to the electrical signal.

2. The amplifier according to claim 1, wherein the first MOS capacitor is a MOSFET (metal oxide semiconductor field effect transistor) whose source is shorted to its drain.

3. The amplifier according to claim 2, wherein the source and the drain are connected to the output terminal of the operational amplifier, and the gate of the MOSFET is connected to the input terminal of the operational amplifier.

4. The amplifier according to claim 2, wherein the source and the drain are connected to the input terminal of the operational amplifier, while the gate of the MOSFET is connected to the output terminal of the operational amplifier.

5. The amplifier according to claim 1, wherein the first current includes the dark noise of a radiation detector; wherein the adjustable current source is configured to compensate for the dark noise.

6. The amplifier according to claim 1, further comprising a processor configured to generate the electrical signal based on the level at the output terminal.

7. The amplifier according to claim 6, wherein the processor is configured to further generate the electrical signal based on the output of a comparator.

8. The amplifier according to claim 6, wherein the processor includes a charge pump.

9. The amplifier according to claim 8, wherein the charge pump is configured to be turned on and off by a clock signal.

10. A radiation detector, comprising: A radiation absorption layer including an electrode; The amplifier according to claim 1, wherein the first current is from the electrode, and the amplifier is configured to generate a voltage at the output terminal based on the first current; A first voltage comparator configured to compare the voltage with a first threshold; A second voltage comparator configured to compare the voltage with a second threshold; A counter configured to record the number of radiation particles absorbed by the radiation absorption layer; And A controller, Wherein the controller is configured to start a time delay starting from the time when the absolute value of the voltage is determined by the first voltage comparator to be equal to or exceed the absolute value of the first threshold; Wherein the controller is configured to activate the second voltage comparator during the time delay; Wherein, the controller is configured to increment the number recorded by the counter if the second voltage comparator determines that the absolute value of the voltage is equal to or exceeds the absolute value of the second threshold.

11. The radiation detector according to claim 10, wherein the radiation is X-ray.

12. The radiation detector according to claim 10, wherein the controller is configured to activate the second voltage comparator at the start or expiration of the time delay.

13. The radiation detector according to claim 10, further comprising a voltmeter, wherein the controller is configured to cause the voltmeter to measure the voltage after the expiration of the time delay.

14. The radiation detector according to claim 10, wherein the controller is configured to determine the radiation of radiation particles based on the value of the voltage measured after the expiration of the time delay.

15. The radiation detector according to claim 10, wherein the controller is configured to connect the electrode of the radiation absorption layer to electrical ground.

16. The radiation detector according to claim 10, wherein the rate of change of the voltage is substantially zero at the expiration of the time delay.

17. The radiation detector according to claim 10, wherein the rate of change of the voltage is substantially non-zero at the expiration of the time delay.

18. The radiation detector according to claim 10, wherein the radiation absorption layer comprises silicon, germanium, gallium arsenide, cadmium telluride, cadmium zinc telluride, or a combination thereof.

19. The radiation detector according to claim 10, wherein the radiation detector does not include a scintillator.

20. The radiation detector according to claim 10, wherein the radiation detector includes a pixel array.

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