Time fast signal grouping reading circuit and reading method of SiPM array

Abstract

The invention relates to a time fast signal grouping readout circuit and readout method of an SiPM array, and the circuit comprises a resistor network which is connected with a slow signal, and discretizes the SiPM position of an output signal; the signal conditioning circuit performs pole-zero compensation and Gaussian shaping on the amplified pulse signal; the analog-to-digital converter obtains a digital signal based on the pulse signal; the time packet network is connected with the fast signals, non-adjacent SiPMs are divided into one group, and the fast signals in each group are summed to output time pulse signals; the constant proportion discriminator performs timing triggering on a constant proportion point at the front edge of the amplified time pulse signal to form a digital signal; the time-to-digital converter obtains time information based on the digital signal; and the FPGA chip obtains the signal size based on the digital signal, further obtains the occurrence position of the event, searches the time group corresponding to the position, and takes the time information at the position of the group as the occurrence time of the event. The signal reading circuit has the beneficial effects that signal noise and parasitic capacitance can be reduced, so that the timing precision of signal reading is improved.

Description

Technical Field

[0001] The present invention relates to the field of photoelectric detection technology, and in particular to a time-fast signal grouping readout circuit and a readout method for a SiPM array. Background Art

[0002] Positron Emission Tomography (PET) is a nuclear medicine imaging device. Its basic principle is to inject a tracer containing positron-emitting radionuclides into a living body. When the radionuclides decay, they release a pair of gamma rays with an energy of 511 keV in opposite directions. The gamma rays are captured by the scintillation crystals of the detector and converted into weak visible light. The visible light is then converted into an electrical pulse signal through a photomultiplier tube. After amplification, shaping and identification, the energy, time and position information of the pulse signal are obtained, and then an image is generated after conformity and reconstruction.

[0003] The new generation of PET systems currently widely use silicon photomultiplier tubes (SiPM) instead of traditional photomultiplier tubes (PMT) as photoelectric conversion devices. Silicon photomultiplier tubes (SiPM) are a surface array composed of avalanche diodes SPDA with quenching resistors in parallel working in Geiger mode. Compared with traditional photomultiplier tubes, they can work at low voltages, are insensitive to magnetic fields, have good consistency, and have fast response times.

[0004] The area of ​​silicon photomultiplier (SiPM) is small, and PET detectors require multiple SiPMs to form a large-area SiPM array. The main readout methods of SiPM arrays are to read out each channel signal separately through a dedicated ASIC readout chip, or to compress multi-channel signals into 4 channels for readout through a resistor network; ASIC readout chips are expensive, have many channels, and complex back-end processing; using the resistor network readout of the center of gravity method, data processing is simple, but the accuracy of the readout position and time information is low.

[0005] The resistor network constructed by traditional discrete components can compress the output signal of the M×N SiPM array into 4 signals, and then use the centroid method to find the position of the scintillation crystal where the event occurred. At the same time, the 4 signals output a time signal after the summing amplifier, and then obtain the time information of the event through identification and timing measurement. When the resistor network is added, the noise accompanying the signal is also added. Therefore, the larger the SiPM array, the greater the noise after addition, resulting in a poor signal-to-noise ratio; at the same time, the parasitic capacitance of the resistor network will cause the signal front edge to slow down, resulting in inaccurate timing. Summary of the invention

[0006] Technical issues to be solved

[0007] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a time-fast signal grouping readout circuit and readout method for a SiPM array, which solves the technical problems of inaccurate timing caused by large signal noise and slow signal front edge of the existing resistor network.

[0008] Technical Solution

[0009] In order to achieve the above object, the main technical solutions adopted by the present invention include:

[0010] In a first aspect, the present invention provides a time-fast signal grouping readout circuit of a SiPM array, comprising:

[0011] Resistor network, slow signal connection to SiPM array, SiPM position for discrete output signal;

[0012] A signal conditioning circuit performs pole-zero compensation and Gaussian shaping on the amplified pulse signal;

[0013] Analog-to-digital converter, digitizes the pulse signal to obtain a digital signal;

[0014] The time grouping network is connected to the fast signal of the SiPM array to group the non-adjacent SiPMs into a group. The fast signals of each group are summed up to output a time pulse signal.

[0015] The constant ratio discriminator triggers the constant ratio point on the leading edge of the amplified time pulse signal to form a digital signal;

[0016] A time-to-digital converter converts digital signals into time to obtain time information;

[0017] The FPGA chip obtains the digital signal, obtains the signal size, and then obtains the location of the event; according to the location of the event, the time grouping of the SiPM corresponding to the location is found, and the time information at the grouping location is selected as the occurrence time of the event.

[0018] Optionally, the resistor chain of the resistor network can make the charge of the SiPM output signal at any position in the four directions of the network proportional to the resistance from the position to the four directions of the network, so as to discretize the SiPM position of the output signal.

[0019] Optionally, the DC signal output by the SiPM anode is a slow signal, and the AC signal output by the SiPM anode terminal through capacitor coupling is a fast signal.

[0020] Optionally, the digital signal size is calculated based on energy integration.

[0021] Optionally, the occurrence location of the event is obtained based on the centroid method.

[0022] Optionally, the circuit further comprises a voltage amplifier for amplifying the pulse signal output by the resistor network.

[0023] Optionally, the circuit further comprises a high-speed amplifier for amplifying the time pulse signal.

[0024] In a second aspect, the present invention provides a time-fast signal grouping readout method of a SiPM array, which is used in a time-fast signal grouping readout circuit of a SiPM array described in any of the above technical solutions, and the method comprises:

[0025] S1, compress the SiPM array output signal into 4 signals through the resistor network, and then calculate the location of the event through the centroid method;

[0026] S2, each SiPM output signal is coupled into a fast time signal by capacitor, the fast signals of the SiPM array are grouped according to non-adjacent ones, and each group outputs a time signal;

[0027] S3, TDC simultaneously measures the arrival time of multiple time grouping signals;

[0028] S4, according to the occurrence location of the event, selecting the arrival time of the time packet signal connected to the SiPM at the location as the occurrence time of the event;

[0029] S5, obtaining location and time information of a single event according to the location and time of occurrence of the event.

[0030] In a third aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed, implements a time-fast signal grouping readout method for a SiPM array as described in any one of the first aspects above.

[0031] In a fourth aspect, the present invention provides a storage device comprising a storage medium and a processor, wherein the storage medium stores a computer program, and when the program is executed by the processor, the method for time-fast signal grouping readout of a SiPM array as described in any one of the first aspects above is implemented.

[0032] Beneficial Effects

[0033] The beneficial effects of the present invention are as follows: a time fast signal grouping readout circuit of a SiPM array of the present invention, a slow signal of the SiPM array is connected to a resistor network, the resistor network outputs 4 signals which are amplified and digitized, and then the energy signal of the event is obtained by energy integration, and the position information of the event is calculated at the same time; the output signal of the SiPM array is coupled into a time fast signal by capacitor, and then the non-adjacent time fast signals are divided into multiple groups, each group is added into a time fast signal, and then multiple digital signals are obtained after amplification and screening, and finally TDC measures multiple time information at the same time, and the time information corresponding to the time fast signal group where the event occurs is selected as the time information of the event. Compared with the traditional method of adding all SiPM output signals of the SiPM array into one signal for timing, the circuit provided by the present invention, after the time fast signal is grouped, the SiPM array is added into multiple signals for simultaneous timing, and the number of SiPM additions is reduced, which is conducive to improving the signal-to-noise ratio of the fast time pulse signal; the use of capacitor coupling instead of the resistor network to output the time fast signal can reduce the slowing of the signal front. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic diagram of a fast signal packet network provided by an embodiment of the present invention;

[0035] Figure 2 A schematic diagram of the structure of a detector signal readout circuit provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0036] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below in conjunction with the accompanying drawings through specific embodiments. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a clearer and more thorough understanding of the present invention and to be able to fully convey the scope of the present invention to those skilled in the art.

[0037] First, refer to Figure 1 and Figure 2 This embodiment provides a time-fast signal grouping readout circuit of a SiPM array, including:

[0038] In the SiPM array, the DC signal output by the SiPM anode is a slow signal, and the AC signal output by the SiPM anode end through capacitor coupling is a fast signal.

[0039] The resistor network is connected to the slow signal of the SiPM array. The resistor chain of the resistor network can make the charge of the SiPM output signal at any position in the four directions of the network proportional to the resistance from the position to the four directions of the network, so that the SiPM position of the output signal can be discrete.

[0040] The voltage amplifier amplifies the four voltage pulse signals output by the resistor network.

[0041] The signal conditioning circuit performs pole-zero compensation and Gaussian shaping on the pulse signal to facilitate subsequent energy integration.

[0042] 4-channel analog-to-digital converter, digitizes 4 pulse signals.

[0043] FPGA obtains 4 digital signals, obtains the size of the 4 signals through energy integration, and then obtains the location of the event through the center of gravity method.

[0044] The time grouping network divides non-adjacent SiPMs into a group, so that the probability of simultaneous events in each group is small, while preventing interference from noise signals at adjacent positions. Each group of fast signals is summed up and output as a time signal.

[0045] For example, the fast signals of the M×N SiPM array are divided into N groups, and the number of SiPMs in each group is M. In this way, the time signal output by the SiPM array increases from 1 to N, and the number of SiPMs added is reduced, which is beneficial to improving the signal-to-noise ratio of the fast time pulse signal and reducing the slowing of the signal front.

[0046] High-speed amplifier further amplifies weak fast-time pulse signals.

[0047] The constant ratio discriminator triggers the constant ratio point of the leading edge of the input fast time pulse signal at a fixed time to form a standard digital signal.

[0048] The time-to-digital converter can realize N-channel time measurement at the same time and can be realized by FPGA or dedicated ASIC TDC chip.

[0049] Since the TDC measures N time information, according to the occurrence position of the event, the time group of the SIPM corresponding to the position is found, and the time information measured by the TDC at the group position is selected as the occurrence time of the event.

[0050] Compared with the traditional resistor network, which outputs 4 signals and uses the centroid method to calculate the location of the event, and then adds the 4 signals into 1 time signal, TDC measures the time signal to obtain the occurrence time of the event.

[0051] The advantages of the present invention are as follows: each SiPM output signal is coupled into a fast-time signal by capacitor, instead of using the signal output by the resistor network as the time signal, which reduces the problem of slowing down the signal front edge caused by the parasitic capacitance of the resistor network, and the timing is more accurate. The fast-time signals of adjacent SiPMs are divided into a group, and several groups of grouped signals are simultaneously measured with a multi-channel TDC to obtain multiple time information, and the time information corresponding to the fast-time signal group where the event occurs is selected as the time information of the event. Although the number of TDC measurement channels has increased, the number of SiPMs added to the output signals of each group of SiPMs has decreased, and the superimposed noise after the addition has been reduced, thereby improving the signal-to-noise ratio. The detection area of ​​each group of SiPMs has been reduced, which reduces the probability of capturing two γ photons at the same time, reduces the probability of pileups in the same group, and reduces the interference of adjacent groups of SiPM signals, so that the front edge can be better identified and the time resolution is more accurate.

[0052] like Figure 1 As shown, Figure 1 The fast time signal grouping network of the 4×4 SiPM array of an embodiment of the present invention is shown in the figure. In practical applications, the size of the SiPM array can be expanded as needed. The 4×4 slow signals output by the 4×4 SiPM array are connected to a resistor network, and the resistor network outputs 4 pulse signals, namely E1, E2, E3 and E4. The anode output terminal of each SiPM is connected to a capacitor of about 10nF, and 4×4 fast signals are coupled by the capacitor. Then, the non-adjacent SiPM fast time signals are connected together through hard wires to achieve the summation of the fast signals in the group; the non-adjacent SiPM fast time signals are divided into a group, and the number of fast signals added after grouping is reduced from 16 to 8. This has two advantages. First, the number of channels for the added signal is reduced, which can reduce the added noise. Second, the detection area of ​​each group of SiPM is reduced, which can reduce the probability of capturing two γ photons at the same time, that is, reducing the probability of pileups in the same group. At the same time, it reduces the interference of SiPM signals in adjacent groups, which can better identify the leading edge and make timing more accurate. In this implementation scheme, a reference design is given, such as Figure 1 As shown, put C 11 , C 12 , C 13 , C 14 , C 31 , C 32 , C 33 , C 34 The coupled fast signals are divided into a group and the output time signal T1 is output; 21 , C 22 , C 23 , C 24 , C 41 , C 42 , C 43 , C 44The coupled fast signals are grouped together to output the time signal T2. The T1 and T2 time grouping signals are identified and measured simultaneously.

[0053] like Figure 2 As shown, the embodiment of the present invention provides a structure of a time-based grouping readout circuit. For ease of description, only the parts related to the embodiment of the present invention are shown, including:

[0054] The 4×4 SiPM array outputs 4×4 slow signals and 4×4 fast signals. The DC signal output by the SiPM anode is a slow signal, and the AC signal coupled by the SiPM anode end through the capacitor is a fast signal. The capacitor size is about 10nF. The M×N slow signals output by the SiPM array are connected to a resistor network; the four voltage pulse signals discretely output by the resistor network are amplified by four voltage amplifiers; then the four pulse signals are subjected to pole zero compensation and Gaussian shaping through the signal conditioning circuit. The pole zero compensation mainly suppresses dark pulses and shortens the recovery time of the pulse signal baseline. The Gaussian shaping conditioning conditions the signal into a near-Gaussian signal, which is more suitable for subsequent electronic processing; then the four pulse signals are digitized through a 4-channel ADC (Analog to Digital Converter); the FPGA obtains the four digital signals and obtains the size of the four signals through energy integration, and then the location of the event is obtained through the centroid method.

[0055] The time grouping network divides the fast time signals output by non-adjacent SiPMs into one group. The number of SiPMs in each group can be obtained through Monte Carlo simulation to ensure that the probability of each group capturing two or more events at the same time is small under a certain activity; at the same time, the interference of noise at adjacent positions is prevented, and each group of fast signals is summed and output as a time signal; this embodiment divides the fast time signals output by the 4×4 SiPM array into 2 groups. Through a high-speed amplifier, the weak fast time pulse signal is further amplified for subsequent processing; this embodiment uses a 2-way RF amplifier because the RF amplifier has a high signal-to-noise ratio and linearity. The constant ratio discriminator is used to time-trigger the constant ratio point of the leading edge of the input fast time pulse signal. The constant ratio discriminator generally adopts zero-crossing timing, that is, the input signal is divided into two paths, one for delay and the other for attenuation, and then the two signals are passed through a high-speed comparator to obtain a standard digital signal. This embodiment adopts a 2-path constant ratio discriminator; based on TDC (Time Digital Converter, time digital converter), time measurement of multiple standard digital signals can be realized, which can be realized by FPGA or dedicated ASIC TDC chip. This embodiment adopts TDC realized by 2-path FPGA; since TDC measures 2 time information, according to the location of the event, the time grouping of the SIPM fast signal output at the location is found, and the time information measured by TDC at the grouping position is selected as the occurrence time of the event.

[0056] In a second aspect, this embodiment provides a time-fast signal grouping readout method of a SiPM array, which is used in a time-fast signal grouping readout circuit of a SiPM array described in any of the above embodiments, and the method includes:

[0057] S1, compress the SiPM array output signal into 4 signals through the resistor network, and then calculate the location of the event through the center of gravity method.

[0058] S2, each SiPM output signal is coupled into a fast time signal through capacitance, the fast signals of the SiPM array are grouped according to non-adjacent ones, and each group outputs a time signal.

[0059] S3, TDC simultaneously measures the arrival time of multiple time grouping signals.

[0060] S4, according to the occurrence location of the event, select the arrival time of the time packet signal connected to the SiPM at that location as the occurrence time of the event.

[0061] S5, according to the occurrence position of the event and the occurrence time of the event, obtain the position and time information of the single event. According to the time fast signal grouping readout method of the SiPM array provided in this embodiment, since it is used in a time fast signal grouping readout circuit of a SiPM array provided in the first aspect of the present invention, the time fast signal grouping readout method of the SiPM array has all the technical effects of the time fast signal grouping readout circuit of the SiPM array, which will not be repeated here.

[0062] In a third aspect, an embodiment of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed, implements a time-fast signal grouping readout method for a SiPM array as described in any one of the first aspects above.

[0063] In a fourth aspect, an embodiment of the present invention provides a storage device, including a storage medium and a processor, wherein the storage medium stores a computer program, and when the program is executed by the processor, a time-fast signal grouping readout method of a SiPM array as described in any one of the first aspects above is implemented.

[0064] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0065] Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention should also include these modifications and variations.

[0066] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may alter, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A time-fast signal grouping readout circuit for a SiPM array, characterized in that: include: Resistor network, slow signal connection to SiPM array, SiPM position for discrete output signal; A signal conditioning circuit performs pole-zero compensation and Gaussian shaping on the amplified pulse signal; Analog-to-digital converter, digitizes the pulse signal to obtain a digital signal; The time grouping network is connected to the fast signal of the SiPM array to group the non-adjacent SiPMs into a group. The fast signals of each group are summed up to output a time pulse signal. The constant ratio discriminator triggers the constant ratio point on the leading edge of the amplified time pulse signal to form a digital signal; A time-to-digital converter converts digital signals into time information; The FPGA chip obtains the digital signal, obtains the signal size, and then obtains the location of the event; according to the location of the event, the time grouping of the SiPM corresponding to the location is found, and the time information at the grouping location is selected as the occurrence time of the event.

2. The time-fast signal grouping readout circuit of a SiPM array according to claim 1, characterized in that: The resistor chain of the resistor network can make the charge of the SiPM output signal at any position in the four directions of the network proportional to the resistance from the position to the four directions of the network, so as to discretely determine the SiPM position of the output signal.

3. The time-fast signal grouping readout circuit of the SiPM array according to claim 2, characterized in that: The DC signal output by the SiPM anode is a slow signal, and the AC signal output by the SiPM anode end through capacitor coupling is a fast signal.

4. The time-fast signal grouping readout circuit of the SiPM array according to claim 3, characterized in that: The digital signal size is calculated based on the energy integration.

5. The time-fast signal grouping readout circuit of the SiPM array according to claim 4, characterized in that: The location of the event is obtained based on the centroid method.

6. The time-fast signal grouping readout circuit of the SiPM array according to claim 5, characterized in that: The circuit also includes a voltage amplifier for amplifying the pulse signal output by the resistor network.

7. The time-fast signal grouping readout circuit of the SiPM array according to claim 6, characterized in that: The circuit also includes a high-speed amplifier for amplifying the time pulse signal.

8. A method for reading out fast time signal groups of a SiPM array, characterized in that: A time-fast signal grouping readout circuit for a SiPM array according to any one of claims 1 to 7, the method comprising: S1, compress the SiPM array output signal into 4 signals through the resistor network, and then calculate the location of the event through the centroid method; S2, each SiPM output signal is coupled into a fast time signal by capacitor, the fast signals of the SiPM array are grouped according to non-adjacent ones, and each group outputs a time signal; S3, TDC simultaneously measures the arrival time of multiple time grouping signals; S4, according to the occurrence location of the event, selecting the arrival time of the time packet signal connected to the SiPM at the location as the occurrence time of the event; S5, obtaining location and time information of a single event according to the location and time of occurrence of the event.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method for reading out fast-time signal groups of a SiPM array as claimed in claim 8 is implemented.

10. A storage device comprising a storage medium and a processor, wherein the storage medium stores a computer program, wherein: When the processor executes the computer program, the method for reading out fast-time signal groups of a SiPM array as claimed in claim 8 is implemented.

Images