Energy measuring circuit with gain compensation

Abstract

The utility model provides an energy measuring circuit with gain compensation, which is used for performing gain compensation on a photoelectric conversion module, and comprises an energy acquisition module configured to acquire an energy signal of the photoelectric conversion module; the gain compensation module is configured to output compensation voltage; wherein the energy acquisition module comprises an integrator, and the integrator integrates a current signal into a voltage signal and outputs the voltage signal; the input end of the photoelectric conversion module is connected to a set bias voltage through an RC circuit, and the output end is connected to the input end of the integrator; the output end of the gain compensation module is connected with the other input end of the integrator and used for changing the equivalent bias voltage of the photoelectric conversion module so as to carry out gain compensation on the photoelectric conversion module, and the equivalent bias voltage is the sum of the set bias voltage and the compensation voltage.

Description

Technical Field

[0001] The utility model relates to an energy measurement circuit with gain compensation. Background Art

[0002] The front-end detector of a high-energy photon measurement system usually consists of a scintillation crystal, a photoelectric converter, and a photon measurement front-end circuit. When high-energy photons (such as gamma photons) interact with the scintillation crystal, visible photons with lower energy are generated. The photoelectric converter converts these visible photons into electrical signals, and the photon measurement front-end circuit obtains the energy of the high-energy photons by measuring these electrical signals. Photoelectric converters such as silicon photomultipliers (SiPMs), avalanche photodiodes (APDs), or photomultiplier tubes (PMTs) convert these visible photons into electrical signals, and the photon measurement front-end circuit is used to measure these electrical signals to obtain the energy information of gamma photons. However, these commonly used photoelectric converters are temperature-sensitive. Temperature changes will cause the gain of the photoelectric converter to change, and then the current signal converted and output by the same number of photons at different temperatures will change, and then the photon measurement front-end circuit cannot measure accurate energy signals. The positron emission tomography (PET) system based on SiPM has high sensitivity and excellent time resolution, but SiPMs are smaller in size and require more readout channels. A large PET system usually includes hundreds of SiPMs forming a large detector ring. Different temperature environments of each SiPM will lead to a decrease in channel consistency and inconsistent energy measurement accuracy. Therefore, it is also crucial to be able to perform independent temperature compensation for each SiPM without affecting other performance of the overall circuit. Currently, the commonly used solutions are to perform constant temperature control on electronic devices through a water chiller and a heat sink, but these methods can only control the temperature within a limited temperature range and cannot effectively and sensitively respond to temperature changes within a wide temperature range, thus unable to ensure accurate energy measurement. Summary of the Utility Model

[0003] To solve the above problems, the present application proposes an energy measurement circuit for independent gain compensation for a single photoelectric converter channel, which realizes the gain compensation for a single photoelectric conversion module while measuring the energy of a single channel, and the photoelectric conversion module converts a photon signal into a current signal for output. The energy measurement circuit with gain compensation according to the present application includes:

[0004] An energy acquisition module configured to acquire the energy signal of the photoelectric conversion module;

[0005] A gain compensation module, configured to output a compensation voltage;

[0006] Wherein, the energy harvesting module includes an integrator, and the integrator integrates the current signal into a voltage signal and outputs it;

[0007] The input end of the photoelectric conversion module is connected to a set bias voltage via an RC circuit, and the output end is connected to the input end of the integrator;

[0008] The output end of the gain compensation module is connected to the other input end of the integrator, and is used to output a compensation voltage to change the equivalent bias voltage of the photoelectric conversion module so as to perform the gain compensation on the photoelectric conversion module. The equivalent bias voltage is the sum of the set bias voltage and the compensation voltage.

[0009] Optionally, the integrator includes a first amplifier and a capacitor. The two ends of the capacitor are respectively connected to the inverting input end and the output end of the first amplifier, and the output end of the photoelectric conversion module is connected to the inverting input end of the first amplifier, and

[0010] The output end of the gain compensation module is connected to the non-inverting input end of the first amplifier.

[0011] Optionally, the energy harvesting module further includes:

[0012] A comparator, configured to compare the voltages output by the integrator and the gain compensation module. When the voltage output by the integrator is greater than the voltage output by the gain compensation module, the comparator outputs a high level; when the voltage output by the integrator is less than the voltage output by the gain compensation module, the comparator outputs a low level;

[0013] A register, configured to latch the output of the comparator and output a digital signal according to a clock signal;

[0014] A negative feedback loop, configured to convert the digital signal output by the register into a current signal and feedback it to the inverting input end of the first amplifier.

[0015] Optionally, the comparator includes a second amplifier, wherein the output end of the first amplifier is connected to the non-inverting input end of the second amplifier, and the output end of the gain compensation module is connected to the inverting input end of the second amplifier.

[0016] Optionally, the gain compensation module includes a digital-to-analog converter (DAC) that outputs a compensation voltage.

[0017] Optionally, both the photoelectric conversion module and the digital-to-analog converter are multi-channel.

[0018] Optionally, the circuit further includes a digital signal processing module configured to receive the digital signal output by the register to generate an energy spectrum diagram.

[0019] Optionally, the digital signal processing module includes an adder and a multiplier, and the adder and the multiplier perform operations on the high level of the digital signal to measure the energy of photons.

[0020] Optionally, the photoelectric conversion module is a silicon photomultiplier (SiPM), an avalanche photodiode (APD), or a photomultiplier tube (PMT).

[0021] Optionally, the gain compensation module further includes a temperature detection module configured to detect the temperature of the photoelectric conversion module and generate a control signal based on the temperature to adjust the compensation voltage output by the digital-to-analog converter.

[0022] Optionally, the buffer, comparator, and register are implemented by a field programmable gate array (FPGA).

[0023] Optionally, the input end of the digital-to-analog converter is connected to the field programmable gate array, and the field programmable gate array controls the signal input to the digital-to-analog converter through a protocol.

[0024] The circuit proposed by the present utility model adjusts the equivalent bias voltage of the photoelectric converter, thereby realizing the compensation of the gain of the photoelectric converter according to the temperature change within a wide temperature range. The feature of the present utility model is that by adjusting the programmable reference voltage (i.e., the compensation voltage) in the energy measurement circuit, the equivalent bias voltage of a single photoelectric converter can be independently adjusted, and the gain compensation of the photoelectric converter can be realized while performing energy measurement, aiming to accurately correct the gain offset caused by temperature, while maintaining high linearity and consistent energy resolution, and solving the technical problem of inaccurate energy measurement of the photoelectric converter caused by temperature change. This circuit can be widely applied to various high-energy photon systems affected by temperature for energy measurement. Description of the Drawings

[0025] Figure 1 is a structural diagram of an energy measurement circuit with gain compensation according to an embodiment of the present utility model;

[0026] Figure 2 is a circuit diagram of a single-channel energy measurement circuit with gain compensation for a single SiPM according to an embodiment of the present utility model;

[0027] Figure 3 is a structural schematic diagram of a single-channel digital-to-analog converter according to an embodiment of the present utility model;

[0028] Figure 4 is a circuit schematic diagram of an energy measurement circuit with gain compensation for multiple SiPM channels according to an embodiment of the present invention;

[0029] Figure 5 is a flowchart for constructing a look-up table for gain compensation using the proposed energy measurement circuit with gain compensation according to an embodiment of the present invention;

[0030] Figure 6 is a graph showing the variation of the normalized energy peak position with temperature and DAC output voltage for gain compensation using the proposed energy measurement circuit with gain compensation according to an embodiment of the present invention;

[0031] Figure 7 is a graph showing the relationship between the optimal DAC output voltage and temperature for gain compensation using the proposed energy measurement circuit with gain compensation according to an embodiment of the present invention;

[0032] Figure 8 is a graph showing the variation of energy resolution with DAC output voltage for gain compensation using the proposed energy measurement circuit with gain compensation according to an embodiment of the present invention;

[0033] Figure 9 is a graph showing the energy resolutions with and without gain compensation for gain compensation using the proposed energy measurement circuit with gain compensation according to an embodiment of the present invention;

[0034] Figure 10 is a graph showing the energy peak positions with and without gain compensation for gain compensation using the proposed energy measurement circuit with gain compensation according to an embodiment of the present invention;

[0035] Figure 11a -f is a gain compensation energy spectrum diagram for gain compensation using the proposed energy measurement circuit with gain compensation according to an embodiment of the present invention; Detailed implementation manners

[0036] To make the above objects, features, and advantages of the present application more obvious and understandable, the present application will be further described in detail below with reference to the accompanying drawings and specific implementation manners.

[0037] The energy measurement circuit with gain compensation is a circuit used for gain compensation of a photoelectric conversion module. Since the gain of a photoelectric conversion module, such as a silicon photomultiplier diode (SiPM), an avalanche photodiode (APD), a photomultiplier tube (PMT), etc., will change with temperature, which will in turn affect the energy measurement result. For the convenience of description, the present utility model uses an SiPM as an example of the photoelectric conversion module for illustration. However, those skilled in the art can understand that the energy measurement circuit with gain compensation can be used for any photoelectric conversion module whose gain changes with temperature. In a large PET system, there are often hundreds of SiPMs forming a large detector ring. Different temperature environments of each SiPM will lead to a decrease in channel consistency, resulting in inconsistent energy measurement accuracy. Therefore, it is also crucial to be able to perform separate temperature compensation for each SiPM without affecting other performances of the overall circuit. For this purpose, the single-channel energy measurement module with gain compensation is proposed, which can independently compensate for the gain change of the photoelectric converter caused by temperature change while performing single-channel energy measurement, so that the electrical signal obtained during the energy measurement process is already the electrical signal after gain compensation. The gain compensation and energy measurement are carried out simultaneously without hysteresis, and there is no mutual influence between the gain compensations of each channel.

[0038] Now refer to Figure 1 to illustrate the main structure of this circuit. As Figure 1 shown, the single-channel energy measurement circuit realizes the measurement and compensation control of the energy signal of a single SiPM, and mainly includes an energy acquisition module and a gain compensation module. Among them, the energy acquisition module includes an integrator for acquiring the energy signal of the photoelectric conversion module, thereby obtaining the energy of high-energy photons. The gain compensation module is used to compensate for the gain of the photoelectric conversion module that changes with temperature.

[0039] As Figure 1 shown, the photoelectric conversion module is connected to a set bias voltage via an RC circuit for providing a working voltage to the photoelectric conversion module. The RC circuit plays a role in overvoltage protection and filtering. Since the voltage at the capacitor terminal cannot change suddenly, it can effectively suppress the overvoltage surge spikes generated when the voltage changes. When high-energy photons hit the photoelectric conversion module, the photoelectric conversion module converts the photon signal into a current signal and inputs it to one input terminal of the integrator of the energy acquisition module. Then, the integrator integrates the current signal into a voltage signal and outputs it to subsequent components (not shown). This voltage signal can be used to calculate the photon energy through the subsequent components. Additionally, the compensation voltage output by the gain compensation module is connected to the other input terminal of the integrator to compensate for the gain of the photoelectric conversion module that changes with temperature, so as to change the equivalent bias voltage applied across the photoelectric conversion module under the action of the compensation voltage.

[0040] The above description Figure 1 only explains the connection structure of the main modules of the circuit. Next, the circuit structure will be described in detail with reference to the circuit diagram described in Figure 2 .

[0041] Figure 2 The circuit diagram of the single-channel energy measurement circuit with gain compensation for a single SiPM 201 in includes three parts: a photoelectric converter circuit, an energy measurement circuit, and a gain compensation circuit. The gain compensation circuit includes a multi-channel digital-to-analog converter (DAC) 202 and its input and output circuit parts. The remaining circuit part is the energy measurement circuit, including an integrator, a comparator 203 (composed of a second amplifier), a register 204, and a negative feedback loop. Among them, the integrator is composed of an amplifier 205 (the first amplifier) and a capacitor 206, and the negative feedback loop is composed of a buffer 207 and a resistor Rf 208. This Delta-Sigma energy measurement circuit uses a 1-bit Delta-Sigma modulator to convert the measurement of energy into the measurement of the time of a pulse signal. This time-based energy measurement method makes the measurement result have good linearity.

[0042] In this embodiment, the comparator 203, the register 204, and the buffer 207 are implemented by an FPGA, and the compensation voltage output by the DAC 202 is also controlled by the FPGA through the SPI protocol. However, those skilled in the art can understand that the FPGA is not an essential component of the present invention. The functional modules implemented by the FPGA in the present invention can also be implemented by a digital circuit composed of discrete components. Additionally or alternatively, the functional modules implemented by the FPGA in the present invention can also be implemented by an application-specific integrated circuit (ASIC).

[0043] Next, refer to Figure 2 to describe the single-channel connection method of the circuit.

[0044] In this embodiment, the cathode of the SiPM 201, which serves as a photoelectric converter, is connected to the inverting input terminal of the amplifier 205 via a unidirectional conduction diode 209, and the anode is connected to a set bias voltage via an RC circuit. Since the SiPM 201 operates in the reverse breakdown region, the polarity of this bias voltage is negative, i.e., -Vbias. Among them, the unidirectional conduction diode 209 is used to block the current flowing from the energy measurement circuit to the direction of the set bias voltage, and the RC circuit can be used to effectively suppress the overvoltage surge spikes generated when the voltage changes. However, those skilled in the art can understand that this circuit can perform gain compensation on any photoelectric converter whose gain changes with temperature. That is to say, the photoelectric converter can be any photoelectric sensor whose gain changes with temperature, including but not limited to SiPM, APD, and photomultiplier tube (PMT), etc. At the same time, in this embodiment, the connection directions of the cathode and anode of the SiPM 201 can be changed. For example, when the anode is connected to the inverting input terminal of the amplifier 203, the cathode is connected to a positive bias voltage +Vbias.

[0045] Another input of the energy measurement circuit is the compensation voltage output by the DAC 202. In this embodiment, the compensation voltage output by the multi-channel DAC 202 is connected to the non-inverting input terminal of the amplifier 205 as a reference level on the one hand, and to the inverting input terminal of the comparator 203 on the other hand. Since the compensation voltage output by the DAC 202 is usually on the order of millivolts (for example, a voltage range of 400 - 600 mV is adopted in this embodiment), when the voltage obtained by integrating the current excited by photons (i.e., the voltage to be measured) is input to the comparator 203, since this voltage is a relatively large value (greater than the millivolt level), the voltage at the non-inverting input terminal of the comparator 203 is greater than the voltage at the inverting input terminal, so the comparator 203 outputs a high level; in addition, when small signal interferences such as dark current (the current flowing in the photoelectric converter without light illumination) and noise existing in the circuit are input to the non-inverting input terminal of the comparator 203 after integrating the voltage, since its voltage is less than the compensation voltage, that is, the voltage at the non-inverting input terminal of the comparator 203 is less than the voltage at the inverting input terminal, the comparator 204 outputs a low level.

[0046] Further, the comparator 203 connects its output terminal to the input terminal of the register 204. In this embodiment, the register 204 can be a D flip-flop. That is, the high and low level signals output by the comparator 204 are input to the D input terminal of the register 204, and corresponding digital signals "1" and "0" corresponding to the high and low levels are output from the Q output terminal along with the clock signal (CLK). In subsequent circuits, an adder (not shown) can be used to perform a summation operation on the digital signal "1" to obtain the equivalent energy magnitude of the photon. For example, if the summation result is 300, the energy of the photon is regarded as 300. Additionally, a multiplier (not shown) can also be used to perform a weighting operation to obtain a more accurate equivalent energy. For example, at different time intervals, the magnitude of the current generated by the photon exciting the photoelectric converter may be different, and based on the magnitude of this current, a weighting operation is performed on the digital signal "1" corresponding to different time intervals. For example, when the current is 1 mA, the weight can be 1; when the current is 2 mA, the weight can be 2, and all the digital signals "1" are weighted and summed according to the weights to obtain the equivalent energy magnitude of the photon.

[0047] The digital signal output from the Q output terminal of the register 204 is fed back to the inverting input terminal of the amplifier 205 through the output buffer 207 and the resistor Rf208, providing a constant current with a polarity opposite to that of the input pulse.

[0048] In addition, the circuit can also include a temperature detection module for detecting the real-time temperature of the photoelectric converter to correspondingly adjust the compensation voltage based on the temperature. This temperature detection module can be integrated into the circuit or a separate module.

[0049] Next, in combination with Figure 2 and Figure 3 we will give a detailed description of the DAC 202. Referring to the circuit diagram in Figure 2 , the compensation voltage output by the DAC 202 is input to the non-inverting input terminal of the amplifier 205, and the cathode of the SiPM 201 is connected to the inverting input terminal of the amplifier 205. According to the "virtual open" concept of the amplifier 205, it can be known that the compensation voltage output by the DAC 202 is equal to the voltage at the cathode of the SiPM 201. Therefore, by only changing the magnitude of the compensation voltage, the magnitude of the voltage at the cathode of the SiPM 201 can be changed, and further the equivalent bias voltage applied to the SiPM 201 (i.e., V bias +V DAC ) can be changed to achieve the compensation of the gain of the SiPM 201. This circuit combines gain compensation with energy measurement. Therefore, the gain compensation process is fed into the energy measurement process in real time, and the two are synchronized, enabling real-time feedback, and thus the measurement result is more accurate.

[0050] Next, referring to Figure 3The single-channel DAC structure diagram shown in the figure is used to elaborate on the output of the DAC.

[0051] First, the transfer function of the DAC part is as follows:

[0052]

[0053] Among them, Gain is the gain of the output amplifier, and the default configuration here is 1. It can also be adjusted to 2 through the Gain pin of the DAC. The specific way for the Gain pin to change the gain is as follows: when the GAIN pin is connected to the GND pin of the FPGA, the gain of the DAC is 1, and the output voltage range is 0V to V REF ; when the GAIN pin is connected to the VLOGIC pin of the FPGA, the gain of the DAC is 2, and the output voltage range is 0V to 2×V REF , where V REF is the reference voltage. D is the decimal equivalent of the binary code loaded into the DAC register, and its range is 0 to 65,535 (16 bits). N is the DAC resolution, which is 16 bits. By controlling the FPGA to load the D value, the compensation voltage V OUT of the DAC output can be changed. Those skilled in the art can understand that Figure 3 the DAC shown is only for example, not restrictive. Any DAC that can implement the function of changing the compensation voltage in this application can be used in this solution.

[0054] In this embodiment, the optoelectronic converter circuit can also be used for multi-channel readout of the SiPM array, such as Figure 4 the multi-channel SiPM gain compensation circuit shown in the figure. In this circuit, each SiPM in the SiPM array is respectively connected to a previous energy measurement circuit with gain compensation for gain compensation. In other words, this circuit can be regarded as a combination of multiple non-interfering previous circuits. Each SiPM in the SiPM array can perform gain compensation through the connected circuit respectively. Therefore, this circuit can achieve separate fine adjustment of a single SiPM channel during the energy measurement process, improve channel consistency, rather than mechanically changing the bias voltage of the entire SiPM array, making the measurement result more accurate.

[0055] The proposed energy measurement circuit with gain compensation can be used to perform gain compensation on the optoelectronic converter. Next, the steps for performing gain compensation are described. It determines how much compensation voltage the DAC needs to output for gain compensation according to the real-time temperature of the optoelectronic converter and the look-up table. This look-up table includes the correspondence between the temperature of the optoelectronic converter and the compensation voltage.

[0056] Now refer to Figure 5Flowchart 500 is used to illustrate the construction of the lookup table. The construction of the lookup table includes the following steps:

[0057] In step 501, the bias voltage and temperature when the photoelectric conversion module is at optimal performance are used as the reference voltage and reference temperature, and the energy peak position in the energy spectrum of photons collected by the photoelectric converter operating at this reference voltage and reference temperature is used as the reference energy peak position.

[0058] Specifically, in this embodiment, 22 A Na point source is used as the gamma photon radiation source, the photoelectric converter is a single-channel SiPM, the bias voltage applied to its anode is 30V, the temperature is 20°C, and the energy peak position of 511 keV in the energy spectrum measured under these conditions is used as the reference energy peak position.

[0059] In step 502, the bias voltage of the photoelectric conversion module is set to a predetermined value, which is less than the reference voltage. In this embodiment, after obtaining the reference energy peak position, the bias voltage of the SiPM anode is set to 29.5V. It can be understood that other suitable bias voltages can also be applied.

[0060] In step 503, the operating temperature range of the photoelectric conversion module is set, and the temperature range is divided into multiple temperature points. In this embodiment, it is measured in the temperature range of 5 - 35°C, with a step of 5°C to divide into multiple temperature points. This temperature range is relatively wide and can meet most working conditions, so that gain compensation can be performed on the photoelectric converter in this relatively wide temperature range. In addition, this temperature range and the step size are only given as examples and do not constitute a limitation on the protection scope.

[0061] In step 504, at each temperature point, the compensation voltage is adjusted to change the equivalent bias voltage of the photoelectric conversion module, and the corresponding relationship between the energy peak position and the compensation voltage at each temperature point is obtained. In this embodiment, the range of the compensation voltage output by the DAC is 400 - 600 mV (i.e., the corresponding equivalent bias voltage is 29.9 - 30.1V). For each temperature point, starting from 400 mV, the compensation voltage is gradually adjusted in steps of 10 mV to obtain the energy peak positions corresponding to different compensation voltages at each temperature point. Multiple experiments are carried out in this embodiment, and 200,000 events are collected each time. Each time a photon excites the photoelectric converter, it is counted as one event. For easy viewing, these energy peak positions are normalized with reference to the reference energy peak position. As Figure 6 shown, the 7 curves from top to bottom in the figure are the corresponding relationship curves between the DAC output voltage and the normalized energy peak position at 7 temperature points from 5 - 35°C. Normalization means that the vertical axis represents the relative ratio of other energy peak positions to the reference energy peak position, where the reference energy peak position is 1.

[0062] At step 505, for each temperature point, the compensation voltage corresponding to the optimal energy peak position is selected to construct a lookup table of the correspondence between temperature and compensation voltage. The optimal energy peak position is the energy peak position with the smallest deviation from the reference energy peak position. In other words, this step is to, for Figure 6 each curve corresponding to each temperature in, respectively find the DAC output voltage corresponding when its energy peak position is closest to 1 (i.e., the value on the vertical axis is closest to 1), which is the optimal compensation voltage. It can be understood that the denser the selection of temperature points, the more accurate the obtained numerical value of the corresponding compensation voltage. Additionally, Figure 6 through further analysis and calculation, it can be obtained that the linearity of this curve is good. When the temperature changes by 5 °C, the energy peak position changes by 2.318%; when the bias voltage changes by 10 mV, the energy peak position changes by 0.932%. Therefore, it is also possible to fit the functional relationship corresponding to the curve based on multiple collected coordinate points, and obtain the compensation voltage when the energy peak position is 1 based on the functional relationship.

[0063] Furthermore, according to the optimal compensation voltage of each obtained curve and the corresponding temperature value, draw Figure 7 the correspondence curve between temperature and compensation voltage shown in. The coordinates of this curve form the lookup table. For example, points such as (5, 430), (10, 447), (15, 480) on the curve form the lookup table. When the measured temperature of the photoelectric sensor is 5, the corresponding compensation voltage can be output, and the same operation is performed when the photoelectric sensor is at other temperatures. In order to obtain more temperature-compensation voltage correspondence relationships in the lookup table, the temperature interval can be divided into more dense temperature points. For example, although in this application the temperature points are divided in steps of 5 °C, it is also possible to divide the temperature points in steps of 1 °C, 0.5 °C, or even 0.1 °C, etc., any step that meets the measurement accuracy. Additionally, due to the good linearity of this curve, it is also possible to obtain the functional relationship expression of the curve based on the coordinate points on the curve, and obtain the compensation voltage corresponding to the temperature according to the expression. Similar to the lookup table, the more points are selected, the more accurate the function value (compensation voltage) of the functional relationship expression will be.

[0064] Next, the measurement results of this gain compensation are analyzed to further illustrate the characteristics and advantages of this gain compensation.

[0065] Refer to Figure 8 the correspondence curve between energy resolution and DAC output voltage in. The energy resolution is the peak width at half of the full energy peak height. From Figure 8 it can be seen that under the action of this circuit, although the temperature and bias voltage change, their energy resolutions still maintain relative consistency, and the change range is 9.285% ± 0.556%. This indicates that the accuracy of this circuit in measuring photon energy is relatively high and the ability to eliminate scattered coincidence events is relatively strong.

[0066] Then refer to Figure 9 the comparison curves of the energy resolution with and without gain compensation. It can be seen from Figure 9 that the two curves are highly consistent and basically coincide. Thus, it can be seen that this gain compensation will not cause a negative impact on the energy resolution. Combining with Figure 8 it further illustrates the good consistency of this gain compensation in terms of energy resolution.

[0067] Next, refer to Figure 10 the comparison curves of the normalized 511 keV peak position with and without gain compensation. The uncompensated peak position refers to the peak position measured under the reference conditions, that is, when the bias voltage of the photoelectric converter is constantly 30 V (which can also be composed of a bias voltage of 29.5 V and a constant compensation voltage of 500 mV), and the temperature is constantly 20 °C. It can be seen that without compensation, the greater the deviation of the temperature from the reference temperature, the greater the deviation of the measured peak position from the reference peak position, and the relationship between the peak position and the temperature is linear. However, after introducing a compensation voltage to the circuit, within the temperature range of 5 - 35 °C, regardless of how large the deviation of the current temperature from the reference temperature is, the deviation of its peak position can always be stably maintained within a certain range. After calculation, the deviation value of this peak position is approximately 0.275% ± 0.137%, which means that the results measured for the same radiation source at different temperatures have a high degree of consistency. Thus, it can be seen that the compensation method proposed in this scheme has a very good effect.

[0068] Finally, refer to Figure 11a the energy spectra before and after gain compensation at different temperatures in

[0069] Figure 11a ~f to give a more intuitive illustration of the effect of this gain compensation.

[0070] The above describes the embodiments of the present application with specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in this specification. Although the description of the present application will be introduced in conjunction with preferred embodiments, this does not mean that the features of this utility model are limited to this embodiment. In addition, in order to avoid confusion or obscuring the key points of the present application, some specific details will be omitted in the description. It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0071] In addition, various operations will be described as multiple discrete operations in the most helpful way for understanding the illustrative embodiments; however, the order of description should not be construed as implying that these operations must be order-dependent. In particular, these operations do not need to be performed in the order presented.

[0072] Unless the context otherwise requires, the terms "comprising", "having" and "including" are synonyms. The phrase "A / B" means "A or B". The phrase "A and / or B" means "(A and B) or (A or B)".

[0073] As used herein, the term "module" or "unit" can refer to, be, or include: an application specific integrated circuit (ASIC), an electronic circuit, a (shared, dedicated, or group) processor and / or memory that executes one or more software or firmware programs, combinational logic circuitry, and / or other suitable components that provide the described functionality.

[0074] In the drawings, some structural or method features are shown in a particular arrangement and / or order. However, it should be understood that such a particular arrangement and / or ordering may not be required. In some embodiments, these features may be arranged in a manner and / or order different from that shown in the illustrative drawings. Additionally, the inclusion of a structural or method feature in a particular figure does not imply that such a feature is required in all embodiments, and in some embodiments, these features may not be included or may be combined with other features.

[0075] It should be understood that although terms such as "first", "second", etc. may be used herein to describe various units or data, these units or data should not be limited by these terms. These terms are only used to distinguish one feature from another. For example, without departing from the scope of the exemplary embodiments, a first feature may be referred to as a second feature, and similarly, a second feature may be referred to as a first feature.

[0076] It should be noted that in this specification, similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0077] Although the present utility model has been illustrated and described by reference to some preferred embodiments thereof, those of ordinary skill in the art should understand that various changes may be made in form and detail without departing from the spirit and scope of the present utility model.

Claims

1. An energy measurement circuit with gain compensation is used to perform the gain compensation on a photoelectric conversion module. The photoelectric conversion module converts a photon signal into a current signal for output, and is characterized in that Comprising: An energy harvesting module configured to harvest the energy signal of the photoelectric conversion module; A gain compensation module configured to output a compensation voltage; Wherein, the energy harvesting module includes an integrator that integrates the current signal into a voltage signal and outputs it; The input end of the photoelectric conversion module is connected to a set bias voltage via an RC circuit, and the output end is connected to the input end of the integrator; The output end of the gain compensation module is connected to the other input end of the integrator, and is used to change the equivalent bias voltage of the photoelectric conversion module to perform the gain compensation on the photoelectric conversion module, and the equivalent bias voltage is the sum of the set bias voltage and the compensation voltage.

2. The circuit according to claim 1, characterized in that The integrator includes a first amplifier and a capacitor, and both ends of the capacitor are respectively connected to the inverting input end and the output end of the first amplifier, and the output end of the photoelectric conversion module is connected to the inverting input end of the first amplifier, and The output end of the gain compensation module is connected to the non-inverting input end of the first amplifier.

3. The circuit according to claim 2, wherein, The energy harvesting module further includes: A comparator configured to compare the voltages output by the integrator and the gain compensation module. When the voltage output by the integrator is greater than the voltage output by the gain compensation module, the comparator outputs a high level; when the voltage output by the integrator is less than the voltage output by the gain compensation module, the comparator outputs a low level; A register configured to latch the output of the comparator and output a digital signal according to a clock signal; A negative feedback loop configured to convert the digital signal output by the register into a current signal and feedback it to the inverting input end of the first amplifier, and the negative feedback loop includes a buffer.

4. The circuit according to claim 3, wherein, The comparator includes a second amplifier, wherein the output end of the first amplifier is connected to the non-inverting input end of the second amplifier, and the output end of the gain compensation module is connected to the inverting input end of the second amplifier.

5. The circuit according to claim 4, characterized in that, The gain compensation module includes a digital-to-analog converter (DAC) that outputs a compensation voltage.

6. The circuit according to claim 5, wherein Both the photoelectric conversion module and the digital-to-analog converter are multi-channel.

7. The circuit according to claim 6, characterized in that, It further includes a digital signal processing module configured to receive the digital signal output by the register to generate an energy spectrum diagram.

8. The circuit according to claim 7, wherein The digital signal processing module includes an adder and a multiplier, and the adder and the multiplier perform operations on the high level of the digital signal to measure the energy of photons.

9. The circuit according to claim 8, wherein The photoelectric conversion module is a silicon photomultiplier (SiPM) or an avalanche photodiode (APD) or a photomultiplier tube (PMT).

10. The circuit according to claim 9, wherein The gain compensation module further includes a temperature detection module configured to detect the temperature of the photoelectric conversion module and generate a control signal based on the temperature to adjust the compensation voltage output by the digital-to-analog converter.

11. The circuit according to claim 10, characterized in that, The buffer, comparator and register are implemented by a field programmable gate array (FPGA).

12. The circuit according to claim 11, characterized in that, The input terminal of the digital-to-analog converter is connected to the field programmable gate array, and the field programmable gate array controls the signal input to the digital-to-analog converter through a protocol.

Images