WO2019037719A1

WO2019037719A1 - Apparatus for measuring photon information

Info

Publication number: WO2019037719A1
Application number: PCT/CN2018/101550
Authority: WO
Inventors: 龚政; 杨静梧; 谢思维; 昝云龙; 翁凤花; 杨明明; 苏志宏; 闫泽武
Original assignee: 中派科技（深圳）有限责任公司
Priority date: 2017-08-23
Filing date: 2018-08-21
Publication date: 2019-02-28
Also published as: CN107450092B; CN107450092A

Abstract

An apparatus (200) for measuring photon information, comprising a main measurement circuit (220) and a time measurement circuit (210). The time measurement circuit (210) comprises: a conversion module (211), which is used for converting an initial signal output by a photoelectric sensor into a converted signal in a voltage form; a differential module (212), which has an input end connected to an output end of the conversion module (211) and is used for performing differentiation on the converted signal and outputting a differential signal; a first comparator (213), which has one input end connected to an output end of the differential module (212) and the other input end connected to a first reference level and is used for comparing the differential signal with the first reference level and generating a first comparison signal; and a time measurement module (214), which has an input end connected to an output end of the first comparator (213) and is used for measuring, according to the first comparison signal, an arrival time of high-energy photons detected by the photoelectric sensor. The main measurement circuit (220) is used for receiving the initial signal and determining relevant information about the high-energy photons by using the signal. The apparatus (200) can realize high-precision measurement of an arrival time of high-energy photons and other information.

Description

Device for measuring photon information

Technical field

The present invention relates to the field of circuits and, in particular, to an apparatus for measuring photon information.

Background technique

The front-end detection device of the high-energy photon (X-ray, gamma photon, etc.) measurement system generally includes a scintillation crystal, a photodetector (or photosensor), and a photon measurement front-end circuit. High-energy photons interact with scintillation crystals to produce a lower energy subset of visible light. The photoelectric sensor converts the optical signal carried by the visible light subgroup into an electrical signal. The main purpose of the photon measurement front-end circuit is to obtain the energy and arrival time of high-energy photons by measuring the electrical signals generated by the photosensors. For example, in positron emission tomography (PET) and single photon emission imaging (SPECT) systems, gamma photons interact with scintillation crystals, such as yttrium silicate (LYSO) crystals, to produce a lower energy subset of visible light. A photoelectric sensor, such as a photomultiplier tube (PMT) or a silicon photomultiplier tube (SiPM), converts an optical signal carried by the visible light subgroup into an electrical signal. The photon measurement front-end circuit measures the electrical signal generated by the photosensor to obtain the energy and arrival time of the gamma photon.

In order to avoid the problem that the energy calculated by the analog-to-digital converter (ADC) sampling in the conventional technology is affected by the start time of the electrical signal output by the photosensor, an improved photon measurement front-end circuit is proposed, which utilizes an integration module. The electrical signal output by the photoelectric sensor is integrated, and when the accumulated charge in the integrating module reaches a certain amount, the pulse signal can be triggered. Information such as energy and arrival time of high energy photons can then be obtained based on the pulse signal.

When using an improved photon measurement front-end circuit to measure the arrival time of high-energy photons, the following problems exist. Studies have shown that the best time resolution can be achieved by measuring the time of the first few photons generated when high-energy photons act on the scintillation crystal. Therefore, in the improved photon measurement front-end circuit, it is desirable to generate a pulse signal usable for time measurement by setting system parameters such that after the integration module accumulates charges generated by n (for example, five) photons. However, this method does not necessarily achieve the best time resolution for the following reasons: (1) Most photosensors such as SiPM have a longer response time to a single photon, and the generated charge takes a long time to fully Collected by the integration module. Thus, the waveforms of the electrical signals generated by the plurality of visible light sources may overlap in time. That is, it is possible that the integral signal has not yet fully completed the integration of the electrical signal generated by the first photon, the electrical signal generated by the second photon has been received and the electrical signal is initially integrated. Therefore, the integration module accumulates the charge generated by the n photons and triggers the pulse signal for a longer time than the actual occurrence of the nth photon. For example, when n=5, the trigger time may be the time when the tenth or even the tens of visible photons occur. (2) Under the current technical conditions, the dark event rate in the photoelectric sensor such as SiPM is high. The charge generated by the dark event accumulates in the integration module. When high-energy photons act on the scintillation crystal, if the integration module has accumulated the charge generated by m dark events, the trigger theoretically occurs after the integration module accumulates the charge generated by the n-mth photon, instead of the nth. Since dark events and high-energy photons are randomly present, the value of m may be evenly distributed in the range of 0 to n-1. Therefore, when generating a pulse signal usable for time measurement, the charge accumulated in the integration module caused by high-energy photons is not necessarily the charge generated by n photons, but may be any number in the range of 1 to n. The charge produced by the visible light. That is to say, the baseline of the charge used to determine the arrival time of the high-energy photon may drift, so the measured arrival time may also drift as compared to the actual arrival time. For the above reasons, measurement accuracy may be affected when using an improved photon measurement front-end circuit to measure the arrival time of high-energy photons.

Accordingly, it is desirable to provide an apparatus for measuring photon information to at least partially address the above-discussed problems that exist in the prior art.

Summary of the invention

In order to at least partially solve the problems in the prior art, according to an aspect of the invention, an apparatus for measuring photon information is provided. The device includes a main measurement circuit and a time measurement circuit. The time measuring circuit includes: a conversion module, configured to convert an initial signal output by the photosensor into a conversion signal in a voltage form; a differentiation module, an input end of the differentiating module is connected to an output end of the conversion module, and the differential module is used for Differentiating the converted signal and outputting a differential signal; a first comparator, an input of the first comparator is connected to an output of the differential module and another input of the first comparator is connected to a first a reference level, the first comparator is configured to compare the differential signal with the first reference level and generate a first comparison signal; and a time measurement module, the input of the time measurement module is coupled to the An output of the first comparator, the time measuring module is configured to measure an arrival time of the high-energy photon detected by the photosensor according to the first comparison signal. A primary measurement circuit is operative to receive the initial signal and utilize the initial signal to make a desired measurement associated with the high energy photon.

Illustratively, the main measurement circuit comprises an integration module, a second comparator, a transmission controller, a negative feedback module and a main measurement module, wherein the integration module is connected to the output of the negative feedback module, and the integration module is configured to receive the initial signal and from the negative Feedback signal of the feedback module, and integrating the difference between the initial signal and the feedback signal and outputting the integrated signal; one input of the second comparator is connected to the output of the integration module and the other input of the second comparator is connected to the second a reference level, the second comparator is for comparing the integrated signal with the second reference level and generating a second comparison signal; the input of the transmission controller is coupled to the output of the second comparator, and the transmission controller is configured to utilize the clock signal control Transmitting a second comparison signal to output a digital signal, wherein a high level of the digital signal having a duration equal to a period of the clock signal represents a first logic level, and a duration of the digital signal equal to a period of the clock signal Flat represents the second logic level; the input of the negative feedback module is connected to the output of the transmission controller, negative feedback Block for converting the digital signal to the feedback signal and the feedback signal to the integrator module; primary measurement module connected to the input of the transmit controller output for a desired primary measurement means for measuring the digital signal.

Exemplarily, the first reference level is greater than a voltage value of the differential signal obtained after the initial signal corresponding to the specific number of dark events is processed via the conversion module and the differential module.

Illustratively, the specific number is equal to one.

Illustratively, the primary measurement circuit is a primary measurement circuit that includes one or more time measurement circuits that are in one-to-one correspondence with one or more photosensors.

Illustratively, the time measurement circuit is a time measurement circuit that includes one or more primary measurement circuits that are in one-to-one correspondence with one or more photosensors.

Illustratively, the time measuring circuit includes one or more time measuring circuits that are in one-to-one correspondence with one or more rows in an array of a plurality of photosensors, the main measuring circuit including one-to-one correspondence with one or more columns in the array One or more primary measurement circuits, the device further comprising an integrated measurement module, the input of the integrated measurement module being coupled to the output of one or more primary measurement circuits and the output of one or more time measurement circuits,

The integrated measurement module is configured to determine a specific photosensor that detects high-energy photons based on a desired measurement signal output by one or more main measurement circuits and a time measurement signal output by one or more time measurement circuits and to combine the desired measurement signal and the time measurement signal with Specific photosensors are associated.

Illustratively, one or both of the first comparator and the time measurement module are implemented by a field programmable logic array.

Illustratively, the primary measurement circuit includes an energy measurement module for measuring the energy of the high energy photons using the initial signal.

Illustratively, the primary measurement circuit includes a dark current measurement module for measuring the dark current detected by the photosensor using the initial signal.

Illustratively, the main measurement circuit includes a waveform measurement module for performing waveform reconstruction and waveform measurement on the initial signal.

The apparatus for measuring photon information according to an embodiment of the present invention has a simple circuit structure, and can realize high-accuracy measurement of arrival time of high-energy photons and other information.

A series of simplified concepts are introduced in the Summary of the Invention, which are further described in detail in the Detailed Description section. The summary is not intended to limit the key features and essential technical features of the claimed embodiments, and is not intended to limit the scope of protection of the claimed embodiments.

Advantages and features of the present invention are described in detail below with reference to the accompanying drawings.

DRAWINGS

The following drawings of the invention are hereby incorporated by reference in their entirety in their entirety. The embodiments of the invention and the description thereof are shown in the drawings In the drawing,

1 shows a schematic block diagram of an improved photon measurement front end circuit in accordance with one example;

2 shows a schematic block diagram of an apparatus for measuring photon information, in accordance with one embodiment of the present invention;

3 is a graph showing a relationship between an energy measurement obtained using a device for measuring photon information and a peak value of an initial signal output by a photosensor according to an embodiment of the present invention;

4 is a schematic diagram showing waveforms of an initial signal output by the photosensor and a differential signal output by the differential module;

Figure 5 shows a schematic diagram of an apparatus for measuring photon information in accordance with one embodiment of the present invention;

6 shows a schematic diagram of an apparatus for measuring photon information and a photosensor according to an embodiment of the present invention;

7 shows a schematic diagram of an apparatus for measuring photon information and a photosensor according to another embodiment of the present invention;

Figure 8 is a diagram showing the correspondence between a device for measuring photon information and a photosensor, in accordance with one embodiment of the present invention.

Detailed ways

In the following description, numerous details are provided in order to provide a thorough understanding of the invention. However, those skilled in the art will appreciate that the following description is directed to the preferred embodiments of the invention, and that the invention may be practiced without one or more such details. Moreover, in order to avoid confusion with the present invention, some of the technical features well known in the art are not described.

As described above, in order to avoid the problem that the energy calculated by the ADC sampling in the conventional art is affected by the start time of the electrical signal output from the photosensor, an improved photon measurement front end circuit is currently proposed. FIG. 1 shows a schematic block diagram of an improved photon measurement front end circuit 100 in accordance with one example. It should be noted that the direction of the arrow shown in the figures herein is the direction of transmission of the signal, not necessarily the direction of flow of the signal.

As shown in FIG. 1, the improved photon measurement front end circuit 100 includes an integration module 110, a comparator 120, a transmission controller 130, a negative feedback module 140, and a measurement module 150.

The integration module 110 is for connecting an output of a photosensor (not shown) and an output of the negative feedback module 140. The integration module 110 can receive an initial signal from the photosensor and a feedback signal from the negative feedback module 140, integrate the difference between the initial signal and the feedback signal, and output an integrated signal.

One input of comparator 120 is coupled to the output of integration module 110 and the other input of comparator 120 is coupled to a reference level. Comparator 120 can compare the integrated signal to a reference level and generate a comparison signal. For example, when the voltage value of the integrated signal is higher than the reference level, the comparator 120 may output a high level, and when the voltage value of the integrated signal is equal to or smaller than the reference level, the comparator 120 may output a low level. Therefore, only the high level and low level states can exist in the comparison signal output by the comparator 120.

The input of the transmission controller 130 is coupled to the output of the comparator 120. The transmission controller 130 can control the transmission of the comparison signal to output a digital signal using a clock signal. Wherein, a high level in the digital signal having a duration equal to a period of the clock signal represents a first logic level, and a low level in the digital signal having a duration equal to a period of the clock signal represents a second logic level. In one example, the first logic level may be a logic level "1", the second logic level may be a logic level "0", and the digital signal is composed of logic levels "1" and "0" sequence.

An input of the negative feedback module 140 is coupled to an output of the transmission controller 130, and the negative feedback module 140 can convert the digital signal to a feedback signal and feed the feedback signal back to the integration module 110. The feedback signal is opposite to the flow direction of the initial signal.

It can be understood that when an effective event or a dark event occurs, the integrated signal obtained at the beginning is relatively small, and the comparison signal and the digital signal can always be in a low state. When the voltage value of the integrated signal is greater than the reference level, a high level appears in the comparison signal. Subsequently, a high level also appears in the digital signal. The time at which the first high level in the comparison signal or digital signal occurs when the valid event occurs can be taken as the arrival time of the high energy photon. The effective event described herein refers to an event in which a high-energy photon (such as a gamma photon, etc.) acts in a scintillation crystal connected to a photosensor to generate a current signal in a photosensor, and a dark event refers to noise (usually a hot electron) An event that causes a current signal to be generated in the photosensor. The photosensor can output a pulsed current signal (ie, the initial signal) when a valid event or a dark event occurs. The energy of the current signal generated by the effective event is much larger than the energy of the current signal generated by the dark event, and the former is usually tens to thousands of times of the latter. Therefore, by analyzing the energy of the current signal output by the photosensor, it can be determined whether the event that occurred is a valid event or a dark event.

The measurement module 150 can measure various information such as energy, arrival time, and the like of high-energy photons using digital signals.

As described above, the best temporal resolution can be achieved by measuring the time at which the first few photons generated by the energetic photons acting on the scintillation crystal (i.e., when an effective event occurs). According to the operation of the improved photon measurement front end circuit 100, the charge that needs to be accumulated in the integration module 110 when the first high level of the comparison signal or digital signal occurs can be controlled by setting the reference level of the comparator 120. Therefore, it is desirable that the optimum time resolution can be obtained by setting the reference level to a voltage value of the integrated signal obtained by integrating the electrical signals generated by the n visible light sub-integrators in the integration module 110. However, due to the two factors described above, it may be difficult to obtain the desired time measurement accuracy in this manner.

It should be understood that FIG. 1 and the related description are merely illustrative of the structure of the improved photon measurement front end circuit, which does not indicate that the apparatus provided by the embodiment of the present invention is only applicable to the photon measurement front end circuit shown in FIG. The device provided by the embodiment of the invention can be applied to other photon measurement front-end circuits adopting similar structures and principles.

In order to solve the above problems, according to an aspect of the present invention, an apparatus for measuring photon information is provided. 2 shows a schematic block diagram of an apparatus 200 for measuring photon information, in accordance with one embodiment of the present invention.

As shown in FIG. 2, the apparatus 200 includes a time measuring circuit 210 and a main measuring circuit 220. The time measurement circuit 210 includes a conversion module 211, a differentiation module 212, a first comparator 213, and a time measurement module 214. The conversion module 211 is configured to convert an initial signal output by the photosensor into a conversion signal in the form of a voltage. The input of the differentiation module 212 is connected to the output of the conversion module 211, and the differentiation module 212 is configured to differentiate the converted signal and output a differential signal. One input end of the first comparator 213 is connected to the output end of the differential module 212 and the other input end of the first comparator 213 is connected to the first reference level, and the first comparator 213 is used to convert the differential signal with the first reference power. The comparison is performed and a first comparison signal is generated. The input of the time measuring module 214 is connected to the output of the first comparator 213, and the time measuring module 214 is configured to measure the arrival time of the high-energy photons detected by the photosensor according to the first comparison signal. The primary measurement circuit 220 is configured to receive an initial signal and utilize the initial signal to make a desired measurement associated with the high energy photon.

Illustratively, the desired measurement may include one or more of energy measurement, dark current measurement, waveform measurement, and gain measurement of the photosensor of the high energy photon. Alternatively, the desired measurement may include a time measurement of high energy photons. That is, the main measurement circuit 220 and the time measurement circuit 210 can be used to simultaneously measure the arrival time of high energy photons.

Alternatively, the photosensors described herein can be any suitable photosensor, such as SiPM, PMT, avalanche photodiode (APD), and the like. In addition, the photosensors described herein may be photodetection devices of various scales such as sensor micro-elements, sensor units, and sensor arrays, and are not limited to a complete independent sensor. Those skilled in the art will appreciate that in a PET system, when positron annihilation occurs, a pair of gamma photons are generated. When the scintillation crystal is struck by gamma photons, the photosensor outputs an initial signal, which is usually a pulse current signal. The photosensor can output the initial signal to the device 200, so that the device 200 obtains energy information, time information, and the like of the gamma photon by measuring the initial signal, thereby obtaining information about the positron annihilation event.

The conversion module 211 can convert the initial signal output by the photosensor from a current form to a voltage form to obtain a converted signal. The conversion signal can be input to a subsequent differentiation module 212 for differentiation. In one example, the conversion module 211 can be implemented by a resistor. The resistor can be connected in series to the cathode or anode of a photosensor (eg, SiPM). Alternatively, a current limiting resistor normally configured in the SiPM bias circuit may be used as the conversion module 211.

The differentiation module 212 may differentiate the conversion signal output by the conversion module 211 and input the differential result to the first comparator 213. In one example, the differentiation module 212 can include a differentiator. Illustratively, the differentiator can be implemented by a high pass filter that includes a capacitor and a resistor. In one example, the differentiation module 212 can include only the differentiator. The differentiator is for differentiating the converted signal and outputting the differential signal. The implementation circuit of the differential module is relatively simple, and the implementation manner can be adopted when the size of the signal output by the differentiator satisfies the requirement. In another example, the differentiating module 212 can further include an amplifying circuit, the input end of the amplifying circuit is connected to the output of the differentiator, wherein the differentiator is used to differentiate the converted signal and output the primary differential signal; the amplifying circuit is used for the primary differential The signal is amplified to obtain a differential signal. In the case that the signal output from the differentiator is too small to meet the demand, the amplifier output signal can be amplified by the amplifying circuit so that the amplified signal is large enough to be used for correctly measuring high-energy photons. Time of arrival.

The first comparator 213 can compare the received differential signal with a first reference level and generate a first comparison signal. For example, when the voltage value of the differential signal is greater than the first reference level, the first comparator 213 may output a high level, and when the voltage value of the differential signal is equal to or smaller than the first reference level, the first comparator 213 may output a low power. level. Therefore, only the high level and low level states can exist in the first comparison signal output by the first comparator 213. Typically, the initial signal output by the photosensor is a pulsed current signal that varies over time, in which case the differential signal is also a time varying signal. Therefore, the first comparison signal output by the first comparator 213 is a signal that switches between the high level and the low state over time. Illustratively, when the differential signal is greater than the first reference level, the first comparator 213 can output a pulse to the time measurement module 214, which is the first comparison signal.

Illustratively, the first reference level may be greater than a voltage value of the differential signal obtained after the initial signal corresponding to the specific number of dark events is processed via the conversion module 211 and the differentiation module 212. For example, a particular number can be equal to one. That is, the first reference level may be set to be slightly larger than the voltage value of the differential signal obtained after the initial signal corresponding to one dark event is processed by the conversion module 211 and the differential module 212 to obtain an optimal time resolution. In this way, the effective event can be distinguished from the signal generated by the dark event, and the arrival time can be measured only according to the initial signal generated when the effective event occurs, thereby avoiding false positives caused by noise. The first comparator 213 can be implemented by a field programmable gate array (FPGA), and its input can be a pair of low voltage differential signaling (LVDS) input pins of the FPGA.

The time measurement module 214 can measure the first comparison signal output by the first comparator 213, for example, the time of occurrence of the rising edge (or falling edge) of the first comparison signal. The rise time of this rising edge (or falling edge) can be used to characterize the arrival time of high energy photons. The time measurement module 214 can be any suitable hardware, software, and/or firmware capable of measuring the time of arrival based on the first comparison signal, such as a time to digital converter (TDC) or the like. For example, the clock of an FPGA digital system can be used to directly record the rise time of a rising edge (or falling edge), or a high-precision analog TDC or digital TDC (such as an FPGA-based delay line-based digital TDC) for time measurement.

The means for measuring photon information has the following advantages:

(1), hardware costs are low. Based on the improved photon measurement front-end circuit, it can be obtained by adding a conversion module (which can be realized by a resistor), a differential module (which can be realized by a high-pass filter composed of a resistor and a capacitor), a first comparator and a time measuring module. The device of the embodiment of the invention has a relatively simple circuit structure and is easy to implement. In addition, the time measurement module can be implemented in the FPGA along with the main measurement module to further save hardware costs.

(2) It does not affect the measurement of energy, gain and other aspects. The time measuring circuit processes the voltage signal, and the main measuring circuit processes the current signal, and the two do not interfere with each other. Therefore, the time measurement does not affect the other measurement operations such as the energy measurement of the main measurement circuit, and does not affect the accuracy of other measurement operations. 3 is a graph showing a relationship between an energy measurement obtained using a device for measuring photon information and a peak value of an initial signal output by a photosensor, in accordance with one embodiment of the present invention. In Figure 3, the unit "au" of the energy measurement in the ordinate represents an arbitrary unit, and the unit "au" is typically used for measurements that are not calibrated. As can be seen from Figure 3, the energy measurements obtained with the means for measuring photon information can maintain very good linearity.

(3) High-precision time measurement. 4 is a waveform diagram showing an initial signal output from the photosensor and a differential signal output from the differential module. In FIG. 4, waveform 410 represents the waveform of the initial signal, and waveform 420 represents the waveform of the differential signal. As can be seen from Figure 4, the differentiation module extracts the high frequency components of the initial signal such that the slope of the pulse front of the differential signal, which is the falling edge, is much larger than the slope of the pulse front of the initial signal, which is the falling edge. The time of arrival of the falling edge of the differential signal can be utilized to characterize the arrival time of the high energy photon. The differential signal can be used to capture the pulse in the initial signal in a timely and sensitive manner, and the occurrence of an effective event or a dark event can be detected in time. In addition, the differential module has a strong ability to suppress baseline drift. Therefore, a higher measurement accuracy can be obtained in a manner of measuring the arrival time based on the differential signal instead of the pulse edge of the initial signal.

According to the apparatus provided by the embodiment of the present invention, since the arrival time of the high-energy photon is measured based on the differential signal obtained from the initial signal output from the photosensor, waveform overlap due to the initial signal and the baseline existing in the improved photon measurement front-end circuit can be avoided. The time measurement caused by drift may be inaccurate. The device according to the embodiment of the present invention has a simple circuit structure, and can realize high-precision measurement of the arrival time of high-energy photons and other information.

According to an embodiment of the invention, the main measurement circuit may include an integration module, a second comparator, a transmission controller, a negative feedback module, and a main measurement module. Referring back to FIG. 2, the main measurement circuit 220 is shown to include an integration module 221, a second comparator 222, a transmission controller 223, a negative feedback module 224, and a main measurement module 225.

The integration module 221 is coupled to the output of the negative feedback module 224 for receiving the initial signal and the feedback signal from the negative feedback module 224, and integrating the difference between the initial signal and the feedback signal and outputting the integrated signal.

The main measurement circuit 220 is a circuit including a negative feedback link, and a feedback signal is input to the integration module 221. At the same time, the integration module 221 also receives an initial signal output by the photosensor. Both the initial signal and the feedback signal are current signals, and their flow directions are opposite. For example, if the initial signal is flowing from the integration module 221, the feedback signal can be set to flow from the negative feedback module 224 to the integration module 221. Therefore, for the integration module 221, the final input is actually the difference between the initial signal and the feedback signal, and the integration module 221 can integrate the difference. The integration module 221 can be implemented by an analog integration circuit, for example, by a circuit composed of components such as a resistor, a capacitor, and an operational amplifier.

One input of the second comparator 222 is connected to the output of the integration module 221 and the other input of the second comparator 222 is connected to the second reference level, and the second comparator 222 is used to integrate the integrated signal with the second reference The comparison is performed and a second comparison signal is generated.

For example, when the voltage value of the integrated signal is higher than the second reference level, the second comparator 222 may output a high level, and when the voltage value of the integrated signal is equal to or smaller than the second reference level, the second comparator 222 may output a low level. Level. Therefore, only the high level and low level states can exist in the comparison signal output by the second comparator 222. That is, the comparison signal output by the second comparator 222 may be a signal that switches between the high level and the low state over time. Alternatively, the second reference level may be a ground level. The second reference level can have any suitable voltage value. The second reference level is a simple implementation of the ground level, and the final obtained measurement result is more accurate.

The input end of the transmission controller 223 is connected to the output end of the second comparator 222, and the transmission controller 223 is configured to control the transmission of the second comparison signal by using a clock signal to output a digital signal, wherein the duration of the digital signal is equal to the clock signal. The high level of the period represents the first logic level, and the low level in the digital signal having a duration equal to the period of the clock signal represents the second logic level.

The second comparison signal may be a signal that switches between a high level and a low state over time. In the comparison signal, the duration of the high and low levels may be changed in real time and cannot be determined. Therefore, the second comparison signal can be temporally quantized by the transmission controller 223 such that the duration of each successive high level or low level is an integer multiple of the period of the clock signal. This temporal quantization corresponds to the time discretization in the analog-to-digital conversion process, and therefore, from the functional point of view, both the second comparator 222 and the transmission controller 223 can be regarded as a 1-bit ADC. In the digital signal output from the transmission controller 223, a high level having a duration equal to a period of the clock signal represents a first logic level, and a low level having a duration equal to a period of the clock signal represents a second logic level. In one example, the first logic level may be a logic level "1", the second logic level may be a logic level "0", and the digital signal is composed of logic levels "1" and "0" sequence. Assuming that the frequency of the clock signal is 100 Hz, that is, the period is 0.01 s, the duration of a single "1" or "0" in the digital signal is 0.01 s. In addition, it can be understood that when a plurality of "1"s or a plurality of "0"s appear consecutively, the duration of the plurality of "1"s or a plurality of "0"s is an integer multiple of 0.01 s. The transmission controller 223 may be a register or a switching circuit controlled by a clock signal or the like.

The input of the negative feedback module 224 is coupled to the output of the transmission controller 223, which is used to convert the digital signal to a feedback signal and to feed back the feedback signal to the integration module 221. The negative feedback module 224 can include a digital to analog converter (DAC) for digital to analog conversion of the digital signal to convert it to an analog signal. Specifically, the DAC may be a 1-bit DAC to convert a sequence consisting of "1" and "0" output from the transmission controller 223 into an analog signal, for example, a voltage signal whose amplitude changes with time. The negative feedback module 224 can further include a current output circuit (which can be considered a "controlled current source"), such as a current output circuit composed of a resistor. The DAC is connected to the input of the integration module 221 via a current output circuit. The current output circuit generates a current signal, that is, a feedback signal, based on the voltage signal described above. The DAC and current output circuit can also be implemented simply by a resistor. The digital signal output by the transmission controller 223 is a voltage signal that can be converted into a current signal, that is, a feedback signal, through the resistor. The feedback signal is opposite to the initial signal direction, and the cumulative effect of the initial signal on the integration module 221 cancels each other, and the integral signal output by the integration module 221 can be prevented from being excessively large to keep the circuit stable. Optionally, the negative feedback module 224 is coupled to the primary measurement module 225. The main measurement module 225 can be further configured to adjust the amplitude of the feedback signal output by the negative feedback module 224.

Since the feedback signal is positively and negatively depleted from the cumulative effect of the initial signal on the integration module 221, when the pulse duration of the initial signal has ended and the amplitude of the feedback signal stabilizes at zero (ie, the negative feedback action for the initial signal has ceased) The accumulated value of the feedback signal caused by the initial signal can be regarded as the accumulated value of the initial signal. Also, the accumulated value of the feedback signal is proportional to the number of "1"s in the digital signal. Therefore, digital signals can be utilized to calculate the energy of high energy photons. Of course, the second comparison signal output by the second comparator 222 can also be used to calculate the energy of the high energy photon, and only the same circuit as the transmission controller 223 is added to the subsequent main measurement module 225. It should be noted that the feedback signal should not be too large or too small. If the feedback signal is too large, the initial signal cancellation speed is too fast, which causes the error contained in the digital signal to increase, which affects the measurement accuracy. Conversely, if the feedback signal is too small, the initial signal cancellation speed will be too slow, which will make it impossible to reduce the value of the integrated signal in time, resulting in saturation distortion and affecting measurement accuracy. The magnitude of the feedback signal can be determined according to actual needs, and the present invention does not limit this.

The input of the main measurement module 225 is coupled to the output of the transmission controller 224, which is used to make the desired measurements based on the digital signals.

In addition to the energy measurement, the main measurement module 225 can also perform other desired measurements according to the digital signal, such as the dark current measurement, the waveform measurement, the gain measurement, etc. described above, and can even measure the arrival time of the high energy photon for the time measurement module. The measurement results are compared or calibrated.

The main measurement circuit provided according to the embodiment of the invention has a simple circuit structure, and an active device such as an amplifier or an ADC can be used or less. Therefore, such a main measurement circuit is low in cost and low in power consumption.

According to an embodiment of the invention, one or more of the first comparator, the time measuring module, the second comparator, the transmission controller and the main measurement module may be implemented by an FPGA. In addition, modules or devices implemented by FPGAs can be implemented in different FPGAs or in the same FPGA.

Figure 5 shows a schematic diagram of an apparatus for measuring photon information in accordance with one embodiment of the present invention. The initial signals described herein may be from one or more photosensors. Fig. 5 shows the case where a plurality of photosensors share a device including a time measuring circuit and a main measuring circuit.

Illustratively, the time measuring circuit can be a time measuring circuit, and the main measuring circuit can include one or more main measuring circuits in one-to-one correspondence with one or more photosensors. Figure 6 shows a schematic diagram of an apparatus for measuring photon information and a photosensor in accordance with one embodiment of the present invention. As shown in FIG. 6, a plurality of SiPMs may have respective main measurement circuits, and a time measurement circuit may be shared. The apparatus for measuring photon information may further comprise an integrated measurement module, the input of the integrated measurement module being connected to the output of one or more main measurement circuits and the output of the time measurement circuit, and the integrated measurement module may be used according to one or more The desired measurement signal output by the primary measurement circuit determines which photosensor the time measurement signal output by the time measurement circuit is from, ie, determines a particular photosensor that detects high energy photons, and associates the time measurement signal with a particular photosensor. This method can reduce the number of channels and reduce system cost. For example, in the case where the photon measurement results detected by the array of 64 SiPMs are independently read out, 64 main measurement circuits and 64 time measurement circuits are required. According to the present embodiment, 64 main measurement circuits and one time measurement circuit are required.

The time measurement signal and the desired measurement signal are explained below. As described above, the time measuring circuit is used to measure the arrival time of the high-energy photon, and the time measuring circuit can output the time information obtained by the measurement as an electrical signal. The time measuring signal is used to represent the signal output by the time measuring circuit. Similarly, the main measurement circuit can output the information obtained by the measurement as an electrical signal, and the desired measurement signal is used herein to represent the signal output by the main measurement circuit. For example, where the primary measurement circuit includes an energy measurement module, the desired measurement signal can include an energy measurement signal, and where the primary measurement circuit includes a dark current measurement module, the desired measurement signal can include a dark current measurement signal, in the primary measurement circuit In the case of a waveform measurement module, the desired measurement signal can include a waveform measurement signal.

Illustratively, the primary measurement circuit can be a primary measurement circuit, and the time measurement circuit can include one or more time measurement circuits that are in one-to-one correspondence with one or more photosensors. FIG. 7 shows a schematic diagram of an apparatus for measuring photon information and a photosensor according to another embodiment of the present invention. As shown in FIG. 7, a plurality of SiPMs may have respective time measurement circuits, and at the same time, one main measurement circuit may be shared. The apparatus for measuring photon information may further comprise an integrated measurement module, the input of the integrated measurement module being coupled to the output of the primary measurement circuit and the output of one or more time measurement circuits, the integrated measurement module being operable for one or more The time measurement signal output by the time measurement circuit determines which photosensor the desired measurement signal output by the main measurement circuit is from, ie, determines a particular photosensor that detects high energy photons, and associates the desired measurement signal with a particular photosensor. This approach also reduces the number of channels and reduces system cost. For example, in the case where the photon measurement results detected by the array of 64 SiPMs are independently read out, 64 main measurement circuits and 64 time measurement circuits are required. According to the present embodiment, one main measurement circuit and 64 time measurement circuits are required.

The number of main measurement circuits and time measurement circuits can be further reduced. Illustratively, the time measuring circuit can include one or more time measuring circuits that correspond one-to-one with one or more rows in an array of a plurality of photosensors, the main measuring circuit can include one or more columns in the array The one-to-one corresponding one or more main measurement circuits, the means for measuring photon information may further comprise an integrated measurement module, the input of the integrated measurement module being connected to the output of one or more main measurement circuits and one or more time measurements An output of the circuit, the integrated measurement module is configured to determine a specific photosensor that detects high energy photons based on a desired measurement signal output by the one or more main measurement circuits and a time measurement signal output by the one or more time measurement circuits and to determine a desired measurement signal And the time measurement signal is associated with a particular photosensor.

Figure 8 is a diagram showing the correspondence between a device for measuring photon information and a photosensor, in accordance with one embodiment of the present invention. As shown in FIG. 8, in an array of 64 SiPMs, there are 8 rows and 8 columns, wherein 8 SiPMs in each column share one main measurement circuit, and 8 SiPMs in each row share a time measurement circuit. If the structure shown in Fig. 8 is adopted, only 8 main measurement circuits and 8 time measurement circuits are required to measure the information of the high-energy photons detected by 64 SiPMs.

In the example shown in FIG. 8, the integrated measurement module can determine which SiPM detects high-energy photons based on the signals measured by the eight main measurement circuits and the eight time measurement circuits. For example, when the SiPM of the first row of the first row (marked by a circle in FIG. 8) detects high-energy photons, the main measurement circuit 1 outputs an energy measurement signal, and the time measurement circuit 1 outputs a time measurement signal, and the main measurement circuit 2 to 8 and the time measuring circuits 2 to 8 do not output signals. According to this feature, the integrated measurement module can determine that the SiPM in the first column of the first row detects high-energy photons. For another example, when the SiPM of the second row and the second column (marked by a triangle in FIG. 8) detects high-energy photons, the main measurement circuit 2 outputs an energy measurement signal, and the time measurement circuit 2 outputs a time measurement signal, and the main measurement circuit 1 And 3 to 8 and time measuring circuits 1 and 3 to 8 do not output signals. According to this feature, the integrated measurement module can determine that the SiPM in the second row and the second column detects high-energy photons.

It should be understood that the schematic or corresponding diagram of the apparatus shown in FIGS. 5-8 is merely an example and not a limitation, and the apparatus for measuring photon information may have other suitable circuit configurations. For example, a plurality of photosensors may share not only a separate time measurement circuit or a separate main measurement circuit, but also some of the time measurement circuits and/or some of the main measurement circuits. Further, in the case where a plurality of photosensors share part of the circuits in the time measuring circuit and/or part of the circuits in the main measuring circuit, the plurality of photosensors may each have a remaining portion of the means for measuring photon information.

Optionally, the primary measurement circuit can include one or more of an energy measurement module, a dark current measurement module, and a waveform measurement module. In one example, the primary measurement circuit includes an energy measurement module for measuring the energy of the high energy photons using the initial signal. In another example, the primary measurement circuit includes a dark current measurement module for measuring the dark current detected by the photosensor using the initial signal. In yet another example, the primary measurement circuit includes a waveform measurement module for performing waveform reconstruction and waveform measurement on the initial signal.

Further, one or more of the energy measurement measurement module, the dark current measurement module, and the waveform measurement module may be included in the main measurement module described above.

For example, the primary measurement module can include an energy measurement module. The energy measurement module can be connected to the output of the transmission controller in the main measurement circuit and measure the energy of the high energy photons using digital signals. The digital signal contains energy information that reflects the amount of energy of the high energy photons detected by the photosensor. The energy measurement module can calculate or estimate the energy level of high-energy photons by performing certain operations on the digital signal (such as summation). It can be understood that the energy measurement module can obtain the relative value of the energy of the high energy photon through the digital signal, and the relative value can represent the exact value of the energy of the high energy photon. Additionally, the energy measurement module can include the same circuitry as the transmission controller and connect the circuit to the output of the second comparator, which, after processing the second comparison signal, outputs the same signal as the digital signal, energy The measurement module then uses the signal to measure the energy of the high-energy photon, and the calculation process is the same as the process of directly calculating the digital signal, and will not be described again.

Alternatively, the energy measurement module can include a counter (not shown) for energy measurement of high energy photons by counting the first logic level. That is to say, the energy measurement can be performed by accumulating the number of "1"s in the digital signal. Alternatively, the energy measurement module can include an adder (not shown) for performing energy measurements on the high energy photons by summing the first logic levels. That is to say, the "1" in the digital signal can be directly added, and the sum obtained last is the energy of the high-energy photon. The method of performing energy measurement by counting or summing the first logic levels is simple, fast, and efficient.

The main measurement module can include a dark current measurement module. Similar to the energy measurement module, the dark current measurement module can be coupled to the output of the second comparator or transmission controller for dark current measurement using the second comparison signal or digital signal. For example, the dark current measurement module can perform dark current measurements by computing a digital signal from a transmission controller. For example, the magnitude of the dark current can be measured by calculating the number of "1"s in the digital signal per unit time when no valid event occurs. The magnitude of the dark current is proportional to the number of "1"s in the digital signal per unit time.

The main measurement module can include a waveform measurement module. Similar to the energy measurement module and the dark current measurement module, the waveform measurement module can be coupled to the output of the second comparator or the transmission controller to perform waveform reconstruction and waveform measurement on the initial signal using the second comparison signal or digital signal. For example, the waveform measurement module can perform waveform reconstruction on the initial signal by digital low-pass filtering. In some applications, reconstructed waveforms can be used to implement advanced measurements.

Furthermore, the main measurement circuit may comprise circuit modules for performing gain measurements and/or time measurements.

The FPGA is used to exemplify the implementation method of the present invention. It should be noted that the FPGA is not a necessary implementation of the present invention. The functional module implemented by the FPGA according to the present invention can also be realized by a digital circuit composed of discrete components, such as a digital signal processor (DSP), a complex programmable logic device (CPLD), a micro control unit (MCU) or a central unit. Implementation of a processing unit (CPU), etc.

Although the principles and applications of the present invention have been described herein using SiPM as an example, it should be understood that the present invention is not limited thereto. The apparatus for measuring photon information provided by the present invention can also be applied to PMT or any other suitable photosensor.

The present invention has been described by the above-described embodiments, but it should be understood that the above-described embodiments are only for the purpose of illustration and description. Further, those skilled in the art can understand that the present invention is not limited to the above embodiments, and various modifications and changes can be made according to the teachings of the present invention. These modifications and modifications are all claimed in the present invention. Within the scope. The scope of the invention is defined by the appended claims and their equivalents.

Claims

An apparatus for measuring photon information, comprising a main measurement circuit and a time measurement circuit, the time measurement circuit comprising:

a conversion module, configured to convert an initial signal output by the photosensor into a conversion signal in a voltage form;

a differential module, an input end of the differentiating module is connected to an output end of the conversion module, and the differentiating module is configured to differentiate the converted signal and output a differential signal;

a first comparator, an input of the first comparator is connected to an output of the differential module and another input of the first comparator is connected to a first reference level, the first comparator is for Comparing the differential signal with the first reference level and generating a first comparison signal;

a time measuring module, an input end of the time measuring module is connected to an output end of the first comparator, and the time measuring module is configured to measure an arrival time of the high energy photon detected by the photoelectric sensor according to the first comparison signal ;

The primary measurement circuit is operative to receive the initial signal and utilize the initial signal to make a desired measurement associated with the high energy photon.
The apparatus according to claim 1, wherein the main measurement circuit comprises an integration module, a second comparator, a transmission controller, a negative feedback module, and a main measurement module, wherein

The integration module is connected to an output end of the negative feedback module, and the integration module is configured to receive the initial signal and a feedback signal from the negative feedback module, and perform a difference between the initial signal and the feedback signal Integrate and output an integrated signal;

One input of the second comparator is coupled to an output of the integration module and another input of the second comparator is coupled to a second reference level, the second comparator for integrating the integrated signal Comparing with the second reference level and generating a second comparison signal;

An input end of the transmission controller is coupled to an output of the second comparator, and the transmission controller is configured to control transmission of the second comparison signal to output a digital signal by using a clock signal, wherein a high level having a duration equal to a period of the clock signal represents a first logic level, and a low level of the digital signal having a duration equal to a period of the clock signal represents a second logic level;

An input end of the negative feedback module is connected to an output end of the transmission controller, and the negative feedback module is configured to convert the digital signal into the feedback signal and feed the feedback signal to the integration module;

An input of the main measurement module is coupled to an output of the transmission controller, and the main measurement module is configured to perform the desired measurement according to the digital signal.
The apparatus according to claim 1 or 2, wherein the first reference level is greater than a differential signal obtained by processing the initial signal corresponding to the specific number of dark events via the conversion module and the differential module Voltage value.
The apparatus of claim 3 wherein said specified number is equal to one.
The apparatus of claim 1 wherein said primary measurement circuit is a primary measurement circuit, said time measurement circuit comprising one or more time measurement circuits in one-to-one correspondence with one or more photosensors.
The apparatus of claim 1 wherein said time measuring circuit is a time measuring circuit comprising one or more primary measuring circuits in one-to-one correspondence with one or more photosensors.
The apparatus of claim 1 wherein said time measuring circuit comprises one or more time measuring circuits in one-to-one correspondence with one or more of said plurality of photosensors, said main measuring circuit Included in the one or more primary measurement circuits corresponding to one or more columns in the array, the device further comprising an integrated measurement module, the input of the integrated measurement module being coupled to the one or more primary measurement circuits Output and an output of the one or more time measuring circuits,

The integrated measurement module is configured to determine, according to a desired measurement signal output by the one or more main measurement circuits and a time measurement signal output by the one or more time measurement circuits, a specific photosensor that detects high energy photons and A desired measurement signal and the time measurement signal are associated with the particular photosensor.
The apparatus of claim 1 wherein one or both of the first comparator and the time measurement module are implemented by a field programmable logic array.
The apparatus of claim 1 wherein said primary measurement circuit includes an energy measurement module for measuring energy of said high energy photons using said initial signal.
The apparatus of claim 1 wherein said primary measurement circuit comprises a dark current measurement module for measuring a dark current detected by said photosensor using said initial signal.
The apparatus of claim 1 wherein said primary measurement circuit comprises a waveform measurement module for performing waveform reconstruction and waveform measurement on said initial signal.