Patent Description:
One type of radiation detectors is based on interaction between the radiation and a semiconductor. For example, a radiation detector of this type may have a semiconductor layer that absorbs the radiation and generate charge carriers (e.g., electrons and holes) and circuitry for detecting the charge carriers.

Radiation detectors may be negatively impacted by dark noise (e.g., dark current). Dark noise in a radiation detector includes physical effects present even if no radiation the radiation detector is configured to detect is incident on the radiation detector. Isolating or reducing the impact of the dark noise to the overall signals detected by the radiation detector is helpful to make the radiation detector more useful. An approach to reduce the impact of dark noise is to compensate for the dark noise by determining and removing dark noise contribution in a signal measurement circuitry of the radiation detector.

<CIT> discloses an anti-irradiation focal plane playback circuit comprising an adjustable compensation current source, an operational amplifier and an integrating capacitor. The adjustable compensation current source provides a compensating current and a dynamic adjusting current.

The compensating current offsets dark current increased after irradiation of the focal plane detector to enhance anti-irradiation performance of the focal plane detector.

<CIT> discloses a semiconductor X-ray detector having a sensor element, an amplifier and an integrating element comprising a capacitor and a resistor connected in parallel.

<CIT> discloses an input circuit for a charge detector having a sensor element and an amplifier. A controlled current source is coupled to the sensor element for feeding a major component of the leakage current therethrough, and a feedback resistor is coupled across the input terminal and the output terminal of the amplifier for feeding a residual component of the leakage current to the sensor element.

According to a first aspect of the present invention, there is provided an amplifier, comprising: an op-amp configured to receive at an input thereof a first electric current; a first MOS capacitor connected to the input and an output of the op-amp; an adjustable current source feeding a second electric current to the input, wherein the adjustable current source is adjustable by an electric signal; and wherein the adjustable current source comprises a second MOS capacitor and a third MOS capacitor in parallel to the second MOS capacitor; wherein a gate electrode of the second MOS capacitor is connected to the input and a bulk contact of the third MOS capacitor is connected to the input; and wherein a gate electrode of the third MOS capacitor is connected to the input of the op-amp and a bulk contact of the third MOS capacitor is connected to the electric signal.

According to an embodiment, the first MOS capacitor is a MOSFET with its source electrode shorted to its drain electrode.

According to an embodiment, the source electrode and the drain electrode are connected to the output of the op-amp, and a gate electrode of the MOSFET is connected to the input of the op-amp.

According to an embodiment, the source electrode and the drain electrode are connected to the input of the op-amp, and a gate electrode of the MOSFET is connected to the output of the op-amp.

According to an embodiment, the first electric current comprises a dark noise of a radiation detector; wherein the adjustable current source is configured to compensate for the dark noise.

According to an embodiment, the amplifier further comprises a processor configured to generate the electric signal based on a level at the output.

According to an embodiment, the processor is configured to generate the electric signal further based on an output of a comparator.

According to an embodiment, the processor comprises a charge pump.

According to an embodiment, the charge pump is configured to be switched on and off by a clock signal.

According to a second aspect of the present invention, there is provided a radiation detector, comprising: a radiation absorption layer comprising an electrode; the amplifier wherein the first electric current is from the electrode and the amplifier is configured to produce a voltage at the output based on the first electric current; a first voltage comparator configured to compare a voltage of the electrode to a first threshold; a second voltage comparator configured to compare the voltage to a second threshold; a counter configured to register a number of particles of radiation absorbed by the radiation absorption layer; a controller; wherein the controller is configured to start a time delay from a time at which the first voltage comparator determines that an absolute value of the voltage equals or exceeds an 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 cause the number registered by the counter to increase by one, if the second voltage comparator determines that an absolute value of the voltage equals or exceeds an absolute value of the second threshold.

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

According to an embodiment, the controller is configured to activate the second voltage comparator at a beginning or expiration of the time delay.

According to an embodiment, the radiation detector further comprises a voltmeter, wherein the controller is configured to cause the voltmeter to measure the voltage upon expiration of the time delay.

According to an embodiment, the controller is configured to determine radiation of a particle of radiation based on a value of the voltage measured upon expiration of the time delay.

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

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

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

According to an embodiment, the radiation absorption layer comprises silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof.

According to an embodiment, the radiation detector does not comprise a scintillator.

According to an embodiment, the radiation detector comprises an array of pixels.

<FIG> schematically shows a component diagram of an amplifier <NUM>, according to an embodiment. The amplifier <NUM> includes an op-amp <NUM>. The op-amp <NUM> has an input and an output. The op-amp <NUM> is configured to receive a first electric current at the input. The amplifier <NUM> may be configured to produce an amplified electric signal (e.g. electric voltage) at the output based on the first electric current.

As shown in <FIG>, the amplifier <NUM> has a first MOS capacitor <NUM>, which is a component in a feedback circuit <NUM> between the input and output of the op-amp <NUM>. The first MOS capacitor <NUM> is connected to the input and the output of the op-amp <NUM>. As shown in <FIG>, the first MOS capacitor <NUM> may be a MOSFET with its source electrode shorted to its drain electrode. In one embodiment, the source electrode and the drain electrode of the first MOS capacitor <NUM> are connected to the output of the op-amp <NUM>, and a gate electrode of the first MOS capacitor <NUM> is connected to the input of the op-amp <NUM>, as shown in <FIG>. In one embodiment, the source electrode and the drain electrode are connected to the input of the op-amp <NUM>, and the gate electrode of the first MOS capacitor <NUM> is connected to the output of the op-amp <NUM>, as shown in <FIG>.

The amplifier <NUM> includes an adjustable current source <NUM>, which is a component in the feedback circuit <NUM>. The adjustable current source <NUM> feeds a second electric current to the input of the op-amp <NUM>. The second electric current may flow from or into the input of the op-amp <NUM>. The adjustable current source <NUM> may be adjustable by an electric signal Vcomp. For example, the magnitude and direction of the second electric current depend on the electric signal Vcomp. The electric signal Vcomp may be an electric voltage but may be other types of electric signals. In one embodiment, when the first electric current at the input of the amplifier <NUM> includes a dark noise of a radiation detector, the adjustable current source <NUM> is configured to compensate for the dark noise, for example, by varying the magnitude and direction of the second electric current.

<FIG> each schematically show a configuration of the adjustable current source <NUM>, according to an embodiment. In the configuration shown in <FIG>, the adjustable current source <NUM> includes a diode-connected NMOSFET <NUM> with a gate electrode and a drain electrode short-connected. The diode-connected NMOSFET <NUM> functions as a biased diode, feeding the second electric current to the input of the op-amp <NUM> as a function of the electric signal Vcomp received at the drain electrode. In this configuration, the second electric current flows from the drain electrode to the source electrode.

In the configuration shown in <FIG>, the adjustable current source <NUM> includes a second MOS capacitor <NUM>. The second MOS capacitor <NUM> may be a NMOSFET with its source electrode shorted to its drain electrode. The adjustable current source <NUM> further includes a third MOS capacitor <NUM>, which may be a PMOSFET with its source electrode shorted to its drain electrode. The second MOS capacitor <NUM> and the third MOS capacitor <NUM> are connected in parallel. A gate electrode of the second MOS capacitor <NUM> is connected to the input of the op-amp <NUM>, and a bulk contact of the second MOS capacitor <NUM> is configured to receive the electric signal Vcomp. A gate electrode of the third MOS capacitor <NUM> is connected to the input of the op-amp <NUM>, and a bulk contact of the third MOS capacitor <NUM> is configured to receive the electric signal Vcomp. With this configuration, the adjustable current source <NUM> may source the second electric current bi-directionally, e.g., depending on Vcomp, directions of the second electric may change between flowing from the adjustable current source <NUM> to the input of the op-amp <NUM>, and flowing from the input of op-amp <NUM> to the adjustable current source <NUM>.

The electric signal Vcomp may be empirically chosen to allow sufficient compensation for the dark noise in the output of the op-amp <NUM>. The electric signal Vcomp may alternatively be determined based on the output of the op-amp <NUM>. <FIG> schematically shows that the amplifier <NUM> may further include a processor <NUM>, according to an embodiment. The processor <NUM> is configured to determine the electric signal Vcomp based on a level at the output of the op-amp <NUM> and optionally further based on an output of a comparator <NUM> that compares the output of the op-amp <NUM> with a threshold SH.

The processor <NUM> may further include a charge pump. The charge pump may be configured to be switched on and off by a clock signal CLK. The electric signal Vcomp may be determined for each individual pixel of a radiation detector and applied to the adjustable current source <NUM> for that pixel. The electric signal Vcomp may be determined based on one pixel's or several pixels' dark noise, and be applied to one or several pixels' adjustable current sources <NUM>. <FIG> shows an example of the processor <NUM> with the charge pump.

<FIG> schematically shows a radiation detector <NUM> comprising the amplifier <NUM> described herein, as an example. The radiation detector <NUM> may have an array of pixels <NUM>. The array may be a rectangular array, a honeycomb array, a hexagonal array or any other suitable array. Each pixel <NUM> is configured to detect radiation from a radiation source incident thereon and may be configured measure a characteristic (e.g., the energy of the particles, the wavelength, and the frequency) of the radiation. For example, each pixel <NUM> is configured to count numbers of particles of radiation incident thereon whose energy falls in a plurality of bins, within a period of time. All the pixels <NUM> may be configured to count the numbers of particles of radiation incident thereon within a plurality of bins of energy within the same period of time. Each pixel <NUM> may have its own analog-to-digital converter (ADC) configured to digitize an analog signal representing the energy of an incident particle of radiation into a digital signal. The pixels <NUM> may be configured to operate in parallel. For example, when one pixel <NUM> measures an incident particle of radiation, another pixel <NUM> may be waiting for a particle of radiation to arrive. The pixels <NUM> may not have to be individually addressable. Each pixel <NUM> may be configured to measure its dark current, such as before or concurrently with each particle of radiation incident thereon. Each pixel <NUM> may be configured to deduct the contribution of the dark current from the energy of the particle of radiation incident thereon.

<FIG> schematically shows a cross-sectional view of the radiation detector <NUM>, according to an embodiment. The radiation detector <NUM> may include a radiation absorption layer <NUM> and an electronics layer <NUM> (e.g., an ASIC) for processing or analyzing electrical signals incident radiation generates in the radiation absorption layer <NUM>. The radiation detector <NUM> may or may not include a scintillator. The radiation absorption layer <NUM> may include a semiconductor material such as, silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof. The semiconductor may have a high mass attenuation coefficient for the radiation of interest. The radiation may be X-ray.

As shown in a detailed cross-sectional view of the radiation detector <NUM> in <FIG>, according to an embodiment, the radiation absorption layer <NUM> may include one or more diodes (e.g., p-i-n or p-n) formed by a first doped region <NUM>, one or more discrete regions <NUM> of a second doped region <NUM>. The second doped region <NUM> may be separated from the first doped region <NUM> by an optional the intrinsic region <NUM>. The discrete regions <NUM> are separated from one another by the first doped region <NUM> or the intrinsic region <NUM>. The first doped region <NUM> and the second doped region <NUM> have opposite types of doping (e.g., region <NUM> is p-type and region <NUM> is n-type, or region <NUM> is n-type and region <NUM> is p-type). In the example in <FIG>, each of the discrete regions <NUM> of the second doped region <NUM> forms a diode with the first doped region <NUM> and the optional intrinsic region <NUM>. Namely, in the example in <FIG>, the radiation absorption layer <NUM> has a plurality of diodes having the first doped region <NUM> as a shared electrode. The first doped region <NUM> may also have discrete portions.

When radiation from the radiation source hits the radiation absorption layer <NUM> including diodes, the particle of radiation may be absorbed and generate one or more charge carriers by a number of mechanisms. The charge carriers may drift to the electrodes of one of the diodes under an electric field. The field may be an external electric field. The electric contact 119B may include discrete portions each of which is in electrical contact with the discrete regions <NUM>. In an embodiment, the charge carriers may drift in directions such that the charge carriers generated by a single particle of the radiation are not substantially shared by two different discrete regions <NUM> ("not substantially shared" here means less than <NUM>%, less than <NUM>%, less than <NUM>%, or less than <NUM>% of these charge carriers flow to a different one of the discrete regions <NUM> than the rest of the charge carriers). Charge carriers generated by a particle of the radiation incident around the footprint of one of these discrete regions <NUM> are not substantially shared with another of these discrete regions <NUM>. The pixel <NUM> associated with a discrete region <NUM> may be an area around the discrete region <NUM> in which substantially all (more than <NUM>%, more than <NUM>%, more than <NUM>%, or more than <NUM>% of) charge carriers generated by a particle of the radiation incident therein flow to the discrete region <NUM>. Namely, less than <NUM>%, less than <NUM>%, less than <NUM>%, or less than <NUM>% of these charge carriers flow beyond the pixel.

As shown in an alternative detailed cross-sectional view of the radiation detector <NUM> in <FIG>, according to an embodiment, the radiation absorption layer <NUM> may include a resistor of a semiconductor material such as, silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof, but does not include a diode. The semiconductor may have a high mass attenuation coefficient for the radiation of interest.

When the radiation hits the radiation absorption layer <NUM> including a resistor but not diodes, it may be absorbed and generate one or more charge carriers by a number of mechanisms. A particle of the radiation may generate <NUM> to <NUM> charge carriers. The charge carriers may drift to the electric contacts 119A and 119B under an electric field. The field may be an external electric field. The electric contact 119B includes discrete portions. In an embodiment, the charge carriers may drift in directions such that the charge carriers generated by a single particle of the radiation are not substantially shared by two different discrete portions of the electric contact 119B ("not substantially shared" here means less than <NUM>%, less than <NUM>%, less than <NUM>%, or less than <NUM>% of these charge carriers flow to a different one of the discrete portions than the rest of the charge carriers). Charge carriers generated by a particle of the radiation incident around the footprint of one of these discrete portions of the electric contact 119B are not substantially shared with another of these discrete portions of the electric contact 119B. A pixel <NUM> associated with a discrete portion of the electric contact 119B may be an area around the discrete portion in which substantially all (more than <NUM>%, more than <NUM>%, more than <NUM>% or more than <NUM>% of) charge carriers generated by a particle of the radiation incident therein flow to the discrete portion of the electric contact 119B. Namely, less than <NUM>%, less than <NUM>%, less than <NUM>%, or less than <NUM>% of these charge carriers flow beyond the pixel associated with the one discrete portion of the electric contact 119B.

The electronics layer <NUM> may include an electronic system <NUM> suitable for processing or interpreting signals generated by the radiation incident on the radiation absorption layer <NUM>. The electronic system <NUM> may include an analog circuitry such as a filter network, amplifiers, integrators, and comparators, or a digital circuitry such as a microprocessors, and memory. The electronic system <NUM> may include one or more ADCs. The electronic system <NUM> may include components shared by the pixels or components dedicated to a single pixel. For example, the electronic system <NUM> may include an amplifier dedicated to each pixel and a microprocessor shared among all the pixels. The electronic system <NUM> may be electrically connected to the pixels by vias <NUM>. Space among the vias may be filled with a filler material <NUM>, which may increase the mechanical stability of the connection of the electronics layer <NUM> to the radiation absorption layer <NUM>. Other bonding techniques are possible to connect the electronic system <NUM> to the pixels without using vias.

The signals generated by the radiation incident on the radiation absorption layer <NUM> may be in a form of an electrical current. Likewise, the dark noise may also be in a form of an electrical current (e.g., a DC current flowing from the electric contacts 119B). If the current may be ascertained, the electrical current may be compensated for (e.g., by the amplifier <NUM> described herein).

<FIG> show a component diagram of the electronic system <NUM>, according to an embodiment. The electronic system <NUM> includes the amplifier <NUM> electrically connected to a discrete portion of the electric contact 119B. Charge carriers from the discrete portion of the electric contact 119B may accumulate in the amplifier <NUM> over a period of time ("integration period"). After the integration period has expired, the output of the amplifier <NUM> is sampled and optionally reset by an optional switch <NUM>.

The dark noise in the form of an electric current charges the capacitor coupled with the amplifier <NUM> along with the signals generated by the radiation. The dark noise may be a very small current, such as in the range of picoamps (e.g., <NUM>-<NUM> pA). Compensating for the dark noise may be performed by the amplifier <NUM>. In one embodiment, the dark noise is measured when the radiation detector is not exposed to radiation. The electric signal Vcomp may be determined and applied to the adjustable current source <NUM> based on the measured dark noise. When the input of the amplifier <NUM> receive the first electric current comprising the dark noise (e.g., dark current), the adjustable current source <NUM> may feed the second electric current at an appropriate direction and magnitude to the op-amp <NUM> of the amplifier <NUM>. The second electric current may be similar in magnitude but opposite in direction of the dark noise.

The electronic system <NUM> may further include a first voltage comparator <NUM>, a second voltage comparator <NUM>, a plurality of counters <NUM> (including counters 320A, 320B, 320C, 320D. ), the optional switch <NUM>, a voltmeter <NUM> and a controller <NUM>.

The first voltage comparator <NUM> is configured to compare the voltage of the discrete portion of the electric contact 119B to a first threshold. The first voltage comparator <NUM> may be configured to monitor the voltage directly, or calculate the voltage by integrating an electric current flowing through the discrete portion of the electric contact 119B over a period of time. The first voltage comparator <NUM> may be controllably activated or deactivated by the controller <NUM>. The first voltage comparator <NUM> may be a continuous comparator. Namely, the first voltage comparator <NUM> may be configured to be activated continuously, and monitor the voltage continuously. The first voltage comparator <NUM> configured as a continuous comparator reduces the chance that the system <NUM> misses signals generated by an incident particle of radiation. The first voltage comparator <NUM> configured as a continuous comparator is especially suitable when the incident radiation intensity is relatively high. The first voltage comparator <NUM> may be a clocked comparator, which has the benefit of lower power consumption. The first voltage comparator <NUM> configured as a clocked comparator may cause the system <NUM> to miss signals generated by some incident particles of radiation. When the incident radiation intensity is low, the chance of missing an incident particle of radiation is low because the time interval between two successive particles is relatively long. Therefore, the first voltage comparator <NUM> configured as a clocked comparator is especially suitable when the incident radiation intensity is relatively low. The first threshold may be <NUM>-<NUM>%, <NUM>-<NUM>%, <NUM>%-<NUM>%, <NUM>-<NUM>%, <NUM>-<NUM>% or <NUM>-<NUM>% of the maximum voltage one incident particle of radiation may generate on the discrete portion of the electric contact 119B. The maximum voltage may depend on the energy of the incident particle of radiation (i.e., the wavelength of the incident radiation), the material of the radiation absorption layer <NUM>, and other factors. For example, the first threshold may be <NUM> mV, <NUM> mV, <NUM> mV, or <NUM> mV.

The second voltage comparator <NUM> is configured to compare the voltage to a second threshold. The second voltage comparator <NUM> may be configured to monitor the voltage directly, or calculate the voltage by integrating an electric current flowing through the discrete portion of the electric contact 119B over a period of time. The second voltage comparator <NUM> may be a continuous comparator. The second voltage comparator <NUM> may be controllably activate or deactivated by the controller <NUM>. When the second voltage comparator <NUM> is deactivated, the power consumption of the second voltage comparator <NUM> may be less than <NUM>%, less than <NUM>%, less than <NUM>% or less than <NUM>% of the power consumption when the second voltage comparator <NUM> is activated. The absolute value of the second threshold is greater than the absolute value of the first threshold. As used herein, the term "absolute value" or "modulus" |x| of a real number x is the non-negative value of x without regard to its sign.

Namely, <MAT>. The second threshold may be <NUM>%-<NUM>% of the first threshold. For example, the second threshold may be <NUM> mV, <NUM> mV, <NUM> mV, <NUM> mV or <NUM> mV. The second voltage comparator <NUM> and the first voltage comparator <NUM> may be the same component. Namely, the system <NUM> may have one voltage comparator that can compare a voltage with two different thresholds at different times.

The first voltage comparator <NUM> or the second voltage comparator <NUM> may include one or more op-amps or any other suitable circuitry. The first voltage comparator <NUM> or the second voltage comparator <NUM> may have a high speed to allow the system <NUM> to operate under a high flux of incident radiation. However, having a high speed is often at the cost of power consumption.

The counters <NUM> may be a software component (e.g., numbers stored in a computer memory) or a hardware component (e.g., <NUM> IC and <NUM> IC). Each counter <NUM> is associated with a bin for an energy range. For example, counter 320A may be associated with a bin for <NUM>-<NUM> KeV, counter 320B may be associated with a bin for <NUM>-<NUM> KeV, counter 320C may be associated with a bin for <NUM>-<NUM> KeV, counter 320D may be associated with a bin for <NUM>-<NUM> KeV. When the energy of an incident particle of radiation is determined by the voltmeter <NUM> to be in the bin a counter <NUM> is associated with, the number registered in the counter <NUM> is increased by one.

The controller <NUM> may be a hardware component such as a microcontroller and a microprocessor. The controller <NUM> is configured to start a time delay from a time at which the first voltage comparator <NUM> determines that the absolute value of the voltage equals or exceeds the absolute value of the first threshold (e.g., the absolute value of the voltage increases from below the absolute value of the first threshold to a value equal to or above the absolute value of the first threshold). The absolute value is used here because the voltage may be negative or positive. The controller <NUM> may be configured to keep deactivated the second voltage comparator <NUM>, the counter <NUM> and any other circuits the operation of the first voltage comparator <NUM> does not require, before the time at which the first voltage comparator <NUM> determines that the absolute value of the voltage equals or exceeds the absolute value of the first threshold. The time delay may expire after the voltage becomes stable, i.e., the rate of change of the voltage is substantially zero. The phase "the rate of change is substantially zero" means that temporal change is less than <NUM>%/ns. The phase "the rate of change is substantially non-zero" means that temporal change of the voltage is at least <NUM>%/ns.

The controller <NUM> may be configured to activate the second voltage comparator during (including the beginning and the expiration) the time delay. In an embodiment, the controller <NUM> is configured to activate the second voltage comparator at the beginning of the time delay. The term "activate" means causing the component to enter an operational state (e.g., by sending a signal such as a voltage pulse or a logic level, by providing power, etc.). The term "deactivate" means causing the component to enter a non-operational state (e.g., by sending a signal such as a voltage pulse or a logic level, by cut off power, etc.). The operational state may have higher power consumption (e.g., <NUM> times higher, <NUM> times higher, <NUM> times higher) than the non-operational state. The controller <NUM> itself may be deactivated until the output of the first voltage comparator <NUM> activates the controller <NUM> when the absolute value of the voltage equals or exceeds the absolute value of the first threshold.

The controller <NUM> may be configured to cause the number registered by one of the counters <NUM> to increase by one, if, during the time delay, the second voltage comparator <NUM> determines that the absolute value of the voltage equals or exceeds the absolute value of the second threshold, and the energy of the particle of radiation falls in the bin associated with the counter <NUM>.

The controller <NUM> may be configured to cause the voltmeter <NUM> to measure the voltage upon expiration of the time delay and to determine based on the voltage which bin the energy of the particle of radiation falls in.

The controller <NUM> may be configured to connect the discrete portion of the electric contact 119B to an electrical ground, so as to reset the voltage and discharge any charge carriers accumulated on the discrete portion of the electric contact 119B. In an embodiment, the discrete portion of the electric contact 119B is connected to an electrical ground after the expiration of the time delay. In an embodiment, the discrete portion of the electric contact 119B is connected to an electrical ground for a finite reset time period. The controller <NUM> may connect the discrete portion of the electric contact 119B to the electrical ground by controlling the optional switch <NUM>. The switch may be a transistor such as a field-effect transistor (FET).

In an embodiment, the system <NUM> has no analog filter network (e.g., a RC network). In an embodiment, the system <NUM> has no analog circuitry.

The voltmeter <NUM> may feed the voltage it measures to the controller <NUM> as an analog or digital signal.

<FIG> schematically shows a temporal change of the electric current flowing through the discrete portion of the electric contact 119B (upper curve) caused by charge carriers generated by a particle of radiation incident on the pixel <NUM> associated with the discrete portion of the electric contact 119B, and a corresponding temporal change of the voltage of the discrete portion of the electric contact 119B (lower curve). The voltage may be an integral of the electric current with respect to time. At time t<NUM>, the particle of radiation hits the diode or the resistor, charge carriers start being generated in the pixel <NUM>, electric current starts to flow through the discrete portion of the electric contact 119B, and the absolute value of the voltage of the discrete portion of the electric contact 119B starts to increase. At time t<NUM>, the first voltage comparator <NUM> determines that the absolute value of the voltage equals or exceeds the absolute value of the first threshold V1, and the controller <NUM> starts the time delay TD1 and the controller <NUM> may deactivate the first voltage comparator <NUM> at the beginning of TD1. If the controller <NUM> is deactivated before t<NUM>, the controller <NUM> is activated at t<NUM>. During TD1, the controller <NUM> activates the second voltage comparator <NUM>. The term "during" a time delay as used here means the beginning and the expiration (i.e., the end) and any time in between. For example, the controller <NUM> may activate the second voltage comparator <NUM> at the expiration of TD1. If during TD1, the second voltage comparator <NUM> determines that the absolute value of the voltage equals or exceeds the absolute value of the second threshold at time t<NUM>, the controller <NUM> waits for stabilization of the voltage to stabilize. The voltage stabilizes at time te, when all charge carriers generated by the particle of radiation drift out of the radiation absorption layer <NUM>. At time ts, the time delay TD1 expires. In the example of <FIG>, time ts is after time te; namely TD1 expires after all charge carriers generated by the particle of radiation drift out of the radiation absorption layer <NUM>. The rate of change of the voltage is thus substantially zero at ts. The controller <NUM> may be configured to deactivate the second voltage comparator <NUM> at expiration of TD1 or at t<NUM>, or any time in between.

The controller <NUM> may be configured to cause the voltmeter <NUM> to measure the voltage upon expiration of the time delay TD1. In an embodiment, the controller <NUM> causes the voltmeter <NUM> to measure the voltage after the rate of change of the voltage becomes substantially zero after the expiration of the time delay TD1. The voltage at this moment is proportional to the amount of charge carriers generated by a particle of radiation, which relates to the energy of the particle of radiation. The controller <NUM> may be configured to determine the energy of the particle of radiation based on voltage the voltmeter <NUM> measures. One way to determine the energy is by binning the voltage. The counter <NUM> may have a sub-counter for each bin. When the controller <NUM> determines that the energy of the particle of radiation falls in a bin, the controller <NUM> may cause the number registered in the sub-counter for that bin to increase by one. Therefore, the system <NUM> may be able to detect a radiation image and may be able to resolve particle of radiation energies of each particle of radiation.

After TD1 expires, the controller <NUM> connects the discrete portion of the electric contact 119B to an electric ground for a reset period RST to allow charge carriers accumulated on the discrete portion of the electric contact 119B to flow to the ground and reset the voltage. After RST, the system <NUM> is ready to detect another incident particle of radiation. If the first voltage comparator <NUM> has been deactivated, the controller <NUM> can activate it at any time before RST expires. If the controller <NUM> has been deactivated, it may be activated before RST expires.

Claim 1:
An amplifier (<NUM>), comprising:
an op-amp (<NUM>) configured to receive at an input thereof a first electric current;
a first MOS capacitor (<NUM>) connected to the input and an output of the op-amp; characterized in that the amplifier further comprises
an adjustable current source (<NUM>) feeding a second electric current to the input,
wherein the adjustable current source is adjustable by an electric signal; and
wherein the adjustable current source comprises a second MOS capacitor (<NUM>) and a third MOS capacitor (<NUM>) in parallel to the second MOS capacitor;
wherein a gate electrode of the second MOS capacitor is connected to the input and a bulk contact of the third MOS capacitor is connected to the input; and
wherein a gate electrode of the third MOS capacitor is connected to the input of the op-amp and a bulk contact of the third MOS capacitor is connected to the electric signal.