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WO2017097147A1 - 用于测量传感器增益的装置、设备及方法 - Google Patents

用于测量传感器增益的装置、设备及方法 Download PDF

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Publication number
WO2017097147A1
WO2017097147A1 PCT/CN2016/107715 CN2016107715W WO2017097147A1 WO 2017097147 A1 WO2017097147 A1 WO 2017097147A1 CN 2016107715 W CN2016107715 W CN 2016107715W WO 2017097147 A1 WO2017097147 A1 WO 2017097147A1
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WO
WIPO (PCT)
Prior art keywords
energy
event
dark
gain
sensor unit
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Application number
PCT/CN2016/107715
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English (en)
French (fr)
Inventor
许剑锋
赵指向
黄秋
龚政
彭旗宇
Original Assignee
武汉中派科技有限责任公司
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Publication of WO2017097147A1 publication Critical patent/WO2017097147A1/zh
Priority to US16/004,290 priority Critical patent/US10838088B2/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T7/00—Details of radiation-measuring instruments
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T7/00—Details of radiation-measuring instruments
    • G01T7/005—Details of radiation-measuring instruments calibration techniques
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16—Measuring radiation intensity
    • G01T1/20—Measuring radiation intensity with scintillation detectors
    • G01T1/208—Circuits specially adapted for scintillation detectors, e.g. for the photo-multiplier section
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16—Measuring radiation intensity
    • G01T1/20—Measuring radiation intensity with scintillation detectors
    • G01T1/2018—Scintillation-photodiode combinations
    • G01T1/20184—Detector read-out circuitry, e.g. for clearing of traps, compensating for traps or compensating for direct hits
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16—Measuring radiation intensity
    • G01T1/24—Measuring radiation intensity with semiconductor detectors
    • G01T1/248—Silicon photomultipliers [SiPM], e.g. an avalanche photodiode [APD] array on a common Si substrate

Definitions

  • the present invention relates to the field of circuits, and in particular to an apparatus, device and method for measuring sensor gain.
  • SiPM silicon photomultipliers
  • SiPM is a silicon-based photoelectric sensor.
  • the SiPM is composed of small sensor cells having a side length of about 10 to 100 ⁇ m.
  • Each sensor micro-element is an avalanche photodiode operating in Geiger mode.
  • Each sensor micro-element can only detect one photon at a time.
  • Hundreds of sensor micro-components form a sensor unit (pixel).
  • the size of the sensor unit is usually from 1 square millimeter to several tens of square millimeters.
  • SiPM-based front-end detectors are widely used for high-energy photon detection.
  • SiPM has the advantages of small size, low bias voltage, high time resolution, and compatibility with nuclear magnetic resonance (MRI) magnetic fields.
  • MRI nuclear magnetic resonance
  • One disadvantage of SiPM is that its gain is greatly affected by temperature. Variations in SiPM gain have a large impact on many of the performance of SiPM-based front-end detectors and can affect high-energy photon measurements. To compensate for the effects of the gain variation of the SiPM, the gain of the SiPM can be measured first to know the gain variation of the current SiPM.
  • an apparatus for measuring sensor gain includes a current detecting circuit and a processing power road.
  • the input of the current detection circuit is connected to the output of the sensor unit.
  • the current detecting circuit is configured to detect a current signal output by the sensor unit and generate a corresponding detection signal.
  • the input of the processing circuit is connected to the output of the current detecting circuit.
  • the processing circuit is configured to calculate an energy of a dark event occurring in the sensor unit based on the detection signal, generate an energy spectrum of the dark event, and calculate a gain of the sensor unit based on the energy spectrum.
  • an apparatus for measuring sensor gain includes a plurality of means for measuring sensor gain as described above in one-to-one correspondence with a plurality of sensor units in the sensor array.
  • a method for measuring sensor gain includes: detecting a current signal output by the sensor unit and generating a corresponding detection signal; calculating energy of a dark event occurring in the sensor unit according to the detection signal; generating an energy spectrum of the dark event; and calculating the sensor unit based on the energy spectrum Gain.
  • the gain of the sensor unit is determined by the energy of the dark event in the sensor unit, and since the dark event rate in the sensor unit is high, it can be shorter A large amount of reference data is obtained in time, so that the gain of the sensor unit can be determined quickly, accurately, and efficiently, which is beneficial for subsequent compensation of the gain variation of the sensor unit.
  • FIG. 1 shows a schematic block diagram of a sensor unit and means for measuring sensor gain, in accordance with one embodiment of the present invention
  • FIG. 2 shows a schematic block diagram of a current detecting circuit in accordance with one embodiment of the present invention
  • FIG. 3 is a circuit diagram showing a current detecting circuit according to an embodiment of the present invention.
  • Figure 5 illustrates an energy spectrum of a dark event in accordance with another embodiment of the present invention
  • FIG. 6 shows an energy spectrum of a dark event in accordance with yet another embodiment of the present invention.
  • Figure 7a is a graph showing the gain versus overvoltage of a particular model of SiPM measured according to the embodiment of Figure 6;
  • Figure 7b shows a plot of dark event rate versus overvoltage for the particular model of SiPM measured according to the embodiment of Figure 6;
  • Figure 8 shows a schematic block diagram of a sensor array and apparatus for measuring sensor gains, in accordance with one embodiment of the present invention
  • Figure 9 shows a flow chart of a method for measuring sensor gain, in accordance with one embodiment of the present invention.
  • an apparatus for measuring sensor gain is provided.
  • 1 shows a schematic block diagram of a sensor unit 110 and means 120 for measuring sensor gain, in accordance with one embodiment of the present invention.
  • device 120 includes current detection circuit 122 and processing circuit 124.
  • An input of the current detecting circuit 122 is connected to an output of the sensor unit 110.
  • the current detecting circuit 122 is configured to detect a current signal output by the sensor unit 110 and generate a corresponding detection signal.
  • Current detection circuit 122 can be any suitable circuit capable of detecting a current signal output by sensor unit 110.
  • current sense circuit 122 can include an oscilloscope for detecting current signals and performing some desired processing on the current signals. It can be understood that the current detecting circuit 122 detects the current signal that the sensor unit 110 outputs during the gain measurement period. During this gain measurement period, a valid event or a dark event may occur, or no event may occur. In the period in which no event occurs, the current signal output by the sensor unit is 0, and the detection signal generated by the current detecting circuit 122 is also 0.
  • an effective event refers to an event in which a high-energy photon (eg, a gamma photon, etc.) acts in a scintillation crystal connected to a sensor unit to generate a current signal in the sensor unit.
  • a dark event is an event caused by noise (usually hot electrons) that produces a current signal in the sensor unit.
  • the sensor unit 110 may output a pulse current signal when an active event or a dark event occurs.
  • the pulse current signal output by the sensor unit 110 when an effective event occurs is referred to as an effective current signal
  • the pulse current signal output by the sensor unit 110 when a dark event occurs is referred to as a dark current signal.
  • the energy of the effective current signal is much larger than the energy of the dark current signal, and the former is usually tens to thousands of times the latter. Therefore, by analyzing the energy of the current signal output from the sensor unit 110, it can be determined whether a valid event or a dark event occurs in the sensor unit 110.
  • An input of the processing circuit 124 is coupled to the output of the current detecting circuit 122.
  • the processing circuit 124 is configured to calculate the energy of the dark event occurring in the sensor unit according to the detection signal, generate an energy spectrum of the dark event, and calculate the gain of the sensor unit based on the energy spectrum.
  • the gain (or gain and crosstalk rate) of the photosensor is related to the temperature and the bias voltage applied to the photosensor.
  • the bias voltage is usually constant, so its gain (or gain and crosstalk) is primarily affected by temperature.
  • SiPM when the temperature rises, the gain (or gain and crosstalk rate) of the SiPM decreases, and the number of dark events (the magnitude of the dark current) per unit time increases.
  • the gain variation of the SiPM can be directly determined by detecting the energy of a single dark event. In one example, a standard dark event energy can be pre-set based on experience or theory.
  • the average energy of a dark event occurring in the SiPM at a temperature of 25 degrees and a bias voltage of 30V can be set as the standard dark event energy, and the gain in this case is set to the standard gain.
  • the processing circuit 124 can know the change of the energy of a dark event occurring in the gain measurement period relative to the standard dark event energy by analyzing the energy spectrum of the dark event, thereby obtaining the change of the gain of the SiPM relative to the standard gain during the gain measurement period. . Later, an appropriate compensation strategy can be developed based on the change in gain to compensate for the effects of gain changes.
  • the gain of the sensor unit is determined by the energy of the dark event in the sensor unit, and since the dark event rate in the sensor unit is high, the comparison can be obtained in a shorter time.
  • the large amount of reference data can quickly, accurately and efficiently determine the gain of the sensor unit, which is beneficial for subsequent compensation of the gain variation of the sensor unit.
  • the detection signal is a digital signal.
  • the digital signal consists of a high level and a low level of equal duration. The sum of all high levels in the digital signal is positive with the integration of the current signal with time. ratio.
  • the current sensing circuit can be implemented in the form shown in Figure 2 to generate the digital signal described above.
  • FIG. 2 shows a schematic block diagram of a current detecting circuit 200 in accordance with one embodiment of the present invention.
  • the current detecting circuit 200 may include an integrating circuit 210, a comparing circuit 220, a transmission control circuit 230, and a negative feedback circuit 240.
  • the integrating circuit 210 is connected to the output of the sensor unit (such as the sensor unit 110 shown in FIG. 1) and the output of the negative feedback circuit 240.
  • the integration circuit 210 is configured to receive a current signal from the sensor unit and a feedback signal from the negative feedback circuit 240, integrate the difference between the current signal and the feedback signal, and output an integrated signal.
  • the current detecting circuit 200 is a circuit including a negative feedback link, and a feedback signal is input to the integrating circuit 210.
  • the integration circuit 210 also receives a current signal from the sensor unit.
  • the flow directions of the current signal and the feedback signal are opposite. For example, if the current signal flows from the integrating circuit 210 to the sensor unit, the feedback signal can be set to flow from the negative feedback circuit 240 to the integrating circuit 210. Therefore, for the integrating circuit 210, the difference between the current signal and the feedback signal is actually finally input, and the integrating circuit 210 can integrate the difference between the two.
  • the direction of the arrow shown in Fig. 2 is the direction of transmission of the signal, not necessarily the direction of flow of the signal.
  • the integration circuit 210 can be implemented using an analog integration circuit, such as a filter circuit composed of a resistor and a capacitor.
  • one input of the comparison circuit 220 is coupled to the output of the integration circuit 210 and the other input of the comparison circuit 220 is coupled to the reference level.
  • Comparison circuit 220 is operative to compare the integrated signal to a reference level and generate a comparison result. For example, when the amplitude of the integrated signal is greater than the reference level, the comparison circuit 220 may output a high level, and when the amplitude of the integrated signal is equal to or less than the reference level, the comparison circuit 220 may output a low level. Therefore, only the high level and low level states can exist in the comparison result output by the comparison circuit 220.
  • the current signal output by the sensor unit is a pulsed current signal that varies over time, in which case the integrated signal is also a time varying signal. Therefore, the comparison result output by the comparison circuit 220 is a signal that switches between the high level and the low level state with time.
  • An input of the transmission control circuit 230 is coupled to the output of the comparison circuit 220.
  • the transmission control circuit 230 is for controlling the transmission of the comparison result with a clock signal to output a digital signal.
  • the comparison result is a signal that switches between the high level and the low state over time.
  • the duration of the high level and the low level may be changed in real time, and it is impossible to confirm Fixed. Therefore, the comparison result can be temporally quantized by the transmission control circuit 230 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.
  • the comparison circuit 220 and the transmission control circuit 230 can be regarded as a 1-bit ADC.
  • each high level and each low level have the same duration, which is equal to the period of the clock signal.
  • a high level can represent a logic level "1” and a low level can represent a logic level "0”, then the digital signal is a sequence of logic levels "1" and "0". 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.
  • the transmission control circuit 230 may be a register or a switching circuit controlled by a clock signal or the like.
  • the input of negative feedback circuit 240 is coupled to the output of transmission control circuit 230.
  • the negative feedback circuit 240 is for converting the digital signal into a feedback signal and feeding back the feedback signal to the integrating circuit 210.
  • the negative feedback circuit 240 can include a digital to analog converter (DAC) for digital to analog conversion of the digital signal to convert it to an analog signal.
  • the DAC may be a 1-bit DAC to convert a sequence consisting of "1" and "0" output from the transmission control circuit 230 into an analog signal, for example, a voltage signal whose amplitude changes with time.
  • the negative feedback circuit 240 can further include a resistor. The DAC is connected to the input of the integrating circuit 210 via the resistor.
  • the above voltage signal will generate a current signal flowing through the resistor, that is, a feedback signal.
  • the feedback signal can cancel a portion of the current signal from the sensor unit to prevent the integrated signal output by the integrating circuit 210 from being excessively large to keep the circuit stable.
  • the feedback signal is constantly canceling the current signal from the sensor unit, the accumulated value of the feedback signal induced by the current signal can be regarded as the accumulated value of the current signal from the sensor unit.
  • the amplitude of the feedback signal is proportional to the amplitude of the digital signal.
  • the digital signal can be utilized to calculate the energy of the photon.
  • the feedback signal should not be too large or too small. If the feedback signal is too large, the offset speed of the current signal 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 cancellation speed of the current signal will be too slow, which will make it impossible to reduce the value of the integrated signal in time, which will also affect the measurement accuracy.
  • the magnitude of the feedback signal can be determined according to actual needs, and the present invention does not limit this.
  • FIG. 3 shows a circuit schematic of current sensing circuit 300 in accordance with one embodiment of the present invention.
  • the current detecting circuit 300 may include an integrating circuit 310, a comparing circuit 320, a transmission control circuit 330, and a negative feedback circuit 340.
  • the integrating circuit 310 can be implemented using an operational amplifier, a resistor Rin, and a capacitor C.
  • the comparison circuit 320 can be implemented with a comparator whose reference level is a ground level.
  • the transmission control circuit 330 can be implemented by a register composed of a D flip-flop whose frequency of the clock signal is f s '.
  • the negative feedback circuit 340 can be implemented using a DAC and a resistor Rf.
  • the DAC can be a pin of a Field Programmable Gate Array (FPGA).
  • the entire current detecting circuit 300 can be implemented by an analog circuit portion and an FPGA portion, as shown in FIG. Diodes, or voltage dividers, can be added to the circuit to reduce or isolate the bias DC current that may be present in the circuit, as needed. Those skilled in the art can understand the principle and working mode of the current detecting circuit 300 according to the above description of the current detecting circuit 200, and will not be described again.
  • Generating a digital detection signal facilitates subsequent calculation of the energy of an active event or a dark event.
  • the processing circuit 124 may calculate the energy of the dark event occurring in the sensor unit 110 by determining whether a pulse event occurs according to the occurrence rule of the high level and the low level in the digital signal; when determining that the pulse event occurs Begin to use the digital signal to calculate the energy of the pulse event until the pulse event is determined according to the occurrence pattern of the high level and the low level in the digital signal; and determine whether the pulse event is a valid event or a dark event according to the energy of the pulse event, if the pulse event If it is a dark event, the energy of the pulse event is determined as the energy of the dark event.
  • a pulse event is an event that produces a pulsed current signal in a sensor unit, which may be a valid event or a dark event.
  • the digital signal is a sequence of "0" and "1".
  • the current detecting circuit 122, 200 or 300 outputs a series of consecutive "0"s, and when an active event or a dark event occurs, the current detecting circuit 122, 200 or 300
  • the output signal should contain several "1”s. It is possible to summarize the occurrence rules of "1" and "0" when the pulse event occurs and the pulse event does not occur, and distinguish between the occurrence of the pulse event and the occurrence of the pulse event according to the summarized rule.
  • a pulse event For example, if a "1" appears after a large number (for example, 10) of consecutive "0"s in a digital signal, it indicates that a pulse event has occurred at this time, which may be a valid event or a dark event. . Subsequently, the energy of the pulse event can be calculated using "1" in the digital signal. For example, "1" in a digital signal can be accumulated or counted. When five “0"s appear consecutively in the digital signal, the description When the pulse event ends, it is possible to stop accumulating or counting "1" at this time. In this way, the relative energy of the pulse event can be finally obtained, which can reflect the magnitude of the absolute energy of the pulse event.
  • the energy of an effective event differs greatly from the energy of a dark event, so that energy can be used to distinguish between the two. For example, if the relative energy of the last obtained pulse event is several thousand, then the pulse event can be considered a valid event, at which point the calculated energy can be discarded. If the relative energy of the last obtained pulse event is several hundred, then the pulse event can be considered a dark event, at which point the calculated energy can be used as the energy of the dark event and used to generate the energy spectrum.
  • This way of measuring the energy of a dark event can be seen as a triggering method, that is, measuring the energy of a dark event when a dark event is triggered.
  • the horizontal axis of the energy spectrum represents the energy of the dark event
  • the vertical axis of the energy spectrum represents the number of times the energy of the dark event is calculated.
  • the processing circuit 124 can calculate the gain of the sensor unit 110 by calculating the gain from the abscissa of the first peak corresponding to the energy of the single dark event in the energy spectrum, or according to the abscissa of the first peak The gain is calculated from the difference between the abscissas of the second peak corresponding to the energy of the two dark events in the energy spectrum.
  • a relative energy value of the dark event can be calculated each time a dark event occurs.
  • the detection of dark events and the calculation of energy can be performed continuously during the measurement period (for example, 5 seconds), and spectral analysis is performed for all dark events detected during the measurement period to obtain an energy spectrum.
  • 4 shows an energy spectrum of a dark event in accordance with one embodiment of the present invention.
  • the energy spectrum shown in Figure 4 has two distinct peaks, the left peak is the energy spectrum peak of the ordinary dark event (the first peak), and the right peak is the cross talk.
  • the energy spectrum peak of the dark event ie the second peak).
  • the horizontal axis of the second peak is almost twice as large as the first peak.
  • the first peak is at a position where the energy is about 40, and 40 represents the energy of a single dark event, and therefore, the first peak corresponds to the energy of a single dark event.
  • the second peak is at an energy of about 80 and 80 represents the energy of two dark events, so the second peak corresponds to the energy of the two dark events.
  • the processing circuit 124 calculates the energy of the dark event based on the digital signal from the start of the dark event to the end of the dark event each time the energy is calculated, so that each time it is obtained is basically a single dark event. energy.
  • the gain of the dark event energy represents the gain of the sensor unit.
  • the energy of the current single dark event can be known by the abscissa of the first peak or the difference between the abscissa of the first peak and the abscissa of the second peak.
  • the gain can be calculated by the difference between the energy of the current single dark event and the energy of the standard dark event. For example, suppose the energy of a standard dark event is 30 and the standard gain is 100. According to the spectrum as shown in Figure 4, the energy of the current single dark event is known to be close to 40. In this way, the sensor unit
  • the current gain can be considered to be approximately 1.33 times the standard gain, ie the current gain is 133.
  • the positions of the first peak and the second peak may be inaccurate due to factors such as interference, for example, may move to the left or right.
  • the difference between the abscissas of the two is always constant, and thus the way of calculating the gain directly using the abscissa of the first peak is The accuracy of calculating the gain using the difference between the abscissa of the first peak and the abscissa of the second peak is higher.
  • the processing circuit 124 may calculate the energy of the dark event occurring in the sensor unit 110 by determining the time period during which the effective event does not occur according to the occurrence rule of the high level and the low level in the digital signal; The digital signal generated within the predetermined time period is selected among the digital signals generated during the period in which the event does not occur; and the energy of the dark event is calculated based on the digital signal generated within the predetermined time period.
  • the time period in which the effective event occurs may be determined according to the occurrence rules of "1" and "0" in the digital signal, and then the time period in which the valid event does not occur may be determined. For example, if a "1" in a digital signal appears 5000 times, a valid event can be considered to occur. A “1" in another digital signal adjacent thereto appears 4000 times, and an effective event can also be considered to occur. Between these two valid events, several dark events may occur. Thus, one or more predetermined time periods can be selected between two active events and a digital signal generated during the predetermined time period can be selected.
  • the predetermined time period may be any suitable time period, such as 10 microseconds, which is not limited by the present invention.
  • the 1 millisecond can be divided into 100 10 microseconds.
  • 100 dark event energy values can be obtained.
  • Such effective event detection and dark event energy calculations can be continued for a gain measurement period (eg, 5 seconds).
  • the triggering mode is not employed to initiate the energy measurement of the dark event, but the energy of all dark events within a predetermined time period in which no valid event (only dark events) has occurred is calculated for generating the energy spectrum.
  • the predetermined time period is set such that the number of average dark events within the predetermined time period satisfies the first preset condition.
  • the horizontal axis of the energy spectrum represents the energy of the dark event.
  • the vertical axis of the energy spectrum represents the number of times the energy of the dark event is calculated.
  • the energy spectrum includes multiple peaks and the Nth peak and N of the energy spectrum.
  • the energy of the dark event corresponds.
  • the processing circuit 124 can calculate the gain of the sensor unit by calculating the gain from the difference between the abscissas of any two adjacent spectral peaks in the energy spectrum.
  • the first preset condition is that the number of average dark events is less than 20.
  • the number of average dark events is less than 20
  • a plurality of discrete peaks may appear in the energy spectrum, that is, The spectrum shows a Poisson distribution.
  • the number of average dark events that cause the energy spectrum to exhibit a Poisson distribution may also have other suitable selection ranges, which is not limited by the present invention. This is described in detail below.
  • the processing circuit 124 calculates the energy of the dark event for a predetermined period of time each time. If the predetermined time period is set appropriately, a plurality of dark events may occur in each predetermined time period, such that the energy of the dark event calculated each time is equal to the sum of the energy of the plurality of dark events.
  • Figure 5 shows an energy spectrum of a dark event in accordance with another embodiment of the present invention. As shown in FIG. 5, the energy spectrum has more peaks than that of FIG. 4, and the highest peak is no longer the first peak. This is because the time period is set longer, so that the probability of the energy of multiple dark events occurring in each time period is much greater than the probability of only a single dark event occurring, so that the energy of the dark event is calculated each time. Always greater than the energy of a single dark event.
  • the number of average dark events refers to an average of the number of dark events occurring in all of the predetermined time periods selected (within the gain measurement period) with respect to the predetermined number of time slots.
  • the energy spectrum depicted in Figure 5 includes the following peaks.
  • the abscissa of the first peak represents the energy of a dark event (which occurs during a predetermined period of time);
  • the abscissa of the second peak represents the energy of two dark events (which occur during a predetermined period of time);
  • the abscissa of the Nth peak represents the energy of N dark events (occurring during a predetermined time period).
  • the abscissa of the Nth peak is substantially N times the first peak.
  • the gain of the dark event energy is the gain of the sensor unit. When the temperature change causes a change in gain, it may cause all the peaks shown in Fig. 5 to move to the right.
  • the change in gain of the sensor unit can be known by tracking the positional change of one (or several) of the peaks.
  • the advantages of this gain measurement method are as follows. Since the abscissa of the Nth peak is N times the abscissa of the first peak, the movement of the abscissa of the Nth peak caused by the change in temperature is shifted from the abscissa of the first peak. It must be N times larger. Therefore, by measuring the movement of the abscissa of the Nth peak, the gain change caused by the temperature is measured, and the gain change caused by the temperature is measured by measuring the movement of the abscissa of the first peak, and the sensitivity and accuracy are required. Higher.
  • the gain can also be calculated from the difference between the abscissas of any two adjacent peaks. This manner is similar to the manner in which the gain is calculated by the difference between the abscissa of the first peak and the abscissa of the second peak as described above, and will not be described again.
  • the predetermined time period is set such that the number of average dark events within the predetermined time period satisfies the second preset condition.
  • the horizontal axis of the energy spectrum represents the energy of the dark event, and the vertical axis of the energy spectrum represents the number of times the energy of the dark event is calculated.
  • Processing circuit 124 can calculate the sensor in the following manner Gain of the unit: Gaussian fitting the energy spectrum to obtain the variance and mean of the energy spectrum, and dividing the variance by the mean to obtain the gain.
  • the second preset condition is that the number of average dark events is greater than 20. When the number of average dark events is greater than 20, the energy spectrum can be approximated to exhibit a Gaussian distribution.
  • the number of average dark events that cause the energy spectrum to exhibit a Gaussian distribution may also have other suitable selection ranges, which is not limited by the present invention. This is described in detail below.
  • Figure 6 shows an energy spectrum of a dark event in accordance with yet another embodiment of the present invention.
  • the energy accumulation time of the embodiment shown in FIG. 6 (the so-called predetermined time period) is much longer than the embodiment shown in FIG. 5, so that the obtained energy spectrum no longer appears.
  • the entire energy spectrum exhibits an approximately normal distribution (ie, Gaussian distribution) as shown in FIG.
  • the number of dark events in a predetermined period of time is essentially a discrete Poisson distribution
  • the Poisson distribution When the number of dark events in a predetermined period of time is large, the Poisson distribution gradually approaches a normal distribution.
  • the number of average dark events ⁇ in a predetermined period of time is greater than a certain value (for example, 20), it can be considered that the Poisson distribution has a normal distribution N( ⁇ , ⁇ ), which can be processed in a normal distribution;
  • the horizontal axis of the energy spectrum measured according to the present embodiment does not correspond to the number of average dark events ⁇ within a predetermined period of time, but corresponds to ⁇ G (G is the gain of the sensor unit). Therefore, after the Poisson distribution has a normal distribution N( ⁇ , ⁇ ), the normal distribution reflected on the energy spectrum is N( ⁇ G, ⁇ G 2 ). Therefore, the gain of the sensor unit can be obtained by dividing the variance of this normal distribution by its mean value.
  • the gain thus calculated is actually the product of the gain G, "1 + crosstalk rate” and “1 + single photon detection resolution squared”.
  • the product of "1 + crosstalk rate” and “1 + single photon detection resolution squared” is very close to 1. Therefore, it is generally considered that the product of the gain G, "1 + crosstalk rate” and “1 + single photon detection resolution squared” is approximately equal to the gain G.
  • the single photon detection resolution is about 0.05, and the "1+ single photon detection resolution square” is approximately 1. Therefore, the calculated gain can also be approximated by the product of the gain G and the "1 + crosstalk rate”.
  • the gain compensation needs to simultaneously compensate for the effect of the temperature on the gain G and the "1 + crosstalk rate”. Therefore, calculating the product of the gain G and the "1 + crosstalk rate" is more practical than simply calculating the true gain.
  • the implementation of calculating the gain of the sensor unit is actually very simple and easy to implement, and the basic steps are as follows:
  • Figure 7a shows the gain versus overvoltage for a particular model of SiPM measured according to the embodiment of Figure 6.
  • Figure 7b shows the dark event rate versus overvoltage for this particular model of SiPM measured according to the embodiment of Figure 6 (dark event rate is approximately equal to dark current divided by gain). It can be seen from Fig. 7a and Fig. 7b that the gain measurement results of the embodiment shown in Fig. 6 are relatively accurate.
  • the embodiment shown in Figure 5 generally requires a current sensing circuit that detects current (or charge) generated by dark events with high accuracy. This is often at the expense of the dynamic range (or dead time) of the entire current sensing circuit.
  • the embodiment shown in Figure 6 requires less accuracy for the current sensing circuit.
  • the gain G of the sensor unit can be calculated in real time, which can be an amount that varies over time.
  • G 0 can also have any suitable value, which is not limited herein.
  • G 0 can be equal to, for example, the standard gain described above.
  • the difference between the energy of the effective event measured at the current time and the energy at the standard gain can be known, so that the energy measured at the current time can be corrected to Energy at standard gain. If such energy is corrected for the energy of the plurality of sensor units, it is equivalent to placing the energy of the plurality of sensor units under the same standard, so that their energy can be compared with each other. For example, if the standard gain is 100 and the gain G measured at the current time is 200, the current gain is increased by a factor of 1. Therefore, the measured energy will also be doubled compared to the energy at standard gain. If the measured energy E 0 is 2000, the corrected energy E may be 1000.
  • the energy of the sensor unit can also be corrected to the actual energy.
  • G 0 can be set to 1. It is assumed that if the current gain of the sensor unit is found to be 1.5 according to the embodiments described herein, and the current energy of the detected valid event is 3000, the energy 3000 can be divided by the gain of 1.5 to obtain the valid event. Corrected energy 2000.
  • the energy of the active or dark event calculated by processing circuit 124 may be relative energy rather than absolute energy, and thus the gain of the sensor unit may also be represented by a relative gain rather than an absolute gain.
  • the absolute gain of the sensor unit during the first gain measurement period can be considered to be approximately 1.33 times the standard gain, ie, the absolute gain during the first gain measurement period is 133. In the preset time range before and after the first gain measurement period, the gain can be considered to be constant.
  • the energy 10000 can be divided by the absolute gain 133 to obtain the corrected energy 75. Then, in another gain measurement period (represented by the "second gain measurement period" for convenience of description), if the energy spectrum is shifted to the right, resulting in a calculated single dark event in the second gain measurement period The energy is close to 50.
  • the absolute gain of the sensor unit during the second gain measurement period can be considered to be approximately 1.67 times the standard gain, i.e., the absolute gain during the second gain measurement period is 167. In the preset time range before and after the second gain measurement period, the gain can be considered to be constant.
  • the energy 10000 can be divided by the absolute gain 167 to obtain the corrected energy 60.
  • the corrected energy 75 can be compared to the corrected energy 60 to know the difference in energy between the two active events.
  • 40 can also be directly considered as the gain of the sensor unit during the first gain measurement period. That is, there is no need to calculate absolute gain based on standard dark events and standard gain.
  • the energy 10000 can be divided by the gain 40 to obtain a corrected energy of 250.
  • 50 can also be directly regarded as the gain of the sensor unit in the second gain measurement period.
  • the energy 10000 can be divided by the gain 50 to obtain a corrected energy of 200.
  • the corrected energy 250 can be compared to the corrected energy 200 to know the difference in energy between the two active events.
  • the results of 75/60 and 250/200 are the same, so it can be seen that whether the absolute gain or the relative gain is calculated correctly reflects the relative magnitude of the energy of each valid event.
  • the above two gain calculation methods can be considered to adopt two different normalization methods, which can Make a selection as needed.
  • the energy based on the gain corrected effective event can make the last obtained energy value more accurate.
  • the processing circuit 124 can be implemented using any suitable digital circuit, such as an FPGA, a Complex Programmable Logic Device (CPLD), a Digital Signal Processor (DSP), a Micro Control Unit (MCU), or a Central Processing Unit (CPU). And so on.
  • CPLD Complex Programmable Logic Device
  • DSP Digital Signal Processor
  • MCU Micro Control Unit
  • CPU Central Processing Unit
  • the circuit provided by the embodiment of the invention has a simple structure, and the current detecting circuit can be implemented by using an analog circuit, and the processing circuit can be implemented by using a digital circuit, and the whole does not require too much hardware, so the cost is low.
  • the present invention can detect and analyze the current (charge) generated by a dark event that is generally considered to be noise without interfering with the normal operating state of the sensor unit, and calculate the gain of the sensor unit.
  • the dark event rate in the sensor unit is typically greater than 300 kHz. This makes it possible to acquire enough data in a sufficiently short time to ensure the accuracy of the spectrum analysis, and to measure and compensate for the gain variation caused by the temperature in real time with high precision.
  • the reaction rate is very fast.
  • an apparatus for measuring sensor gain includes a plurality of the above-described means for measuring sensor gain in one-to-one correspondence with a plurality of sensor units in the sensor array.
  • Figure 8 shows a schematic block diagram of a sensor array and apparatus for measuring sensor gain, in accordance with one embodiment of the present invention.
  • the sensor array includes N sensor units 810, namely, sensor unit 1, sensor unit 2, ... sensor unit N.
  • the apparatus for measuring sensor gain includes N means 820 for measuring sensor gain in one-to-one correspondence with N sensor units.
  • Each device 820 is identical to device 120 described above, and includes current detection circuit 822 and processing circuit 824.
  • the structure, operation mode, and advantages of the apparatus for measuring the sensor gain can be understood by those skilled in the art based on the above description of the apparatus for measuring the sensor gain and the accompanying FIGS. 1 to 7b, and will not be described again.
  • each processing circuit 824 can be implemented using a digital circuit such as an FPGA as described above. It will be appreciated that any number of processing circuits 824 in the device for measuring sensor gain may be integrated in the same digital circuit, such as an FPGA.
  • G 0 is the standard gain of the corresponding sensor unit of each processing circuit 824. For a sensor array, the standard gain of each sensor unit is usually the same.
  • the gain of a SiPM cell is usually proportional to its bias overvoltage.
  • the bias overvoltage is equal to the difference between the bias voltage and the breakdown voltage. Due to the microelectronics process, the breakdown voltage of different SiPM cells has a certain difference. When the same series of SiPM cells form a SiPM array, the same bias (operating) voltage is usually used. Since the breakdown voltages of the various SiPM cells are slightly different, their gains are also different. The difference in gain between the various SiPM cells in the SiPM array affects the performance of the front end detector consisting of the SiPM array.
  • the SiPM cells that make up the SiPM array In general, it is necessary to test and screen the SiPM cells that make up the SiPM array, and select the SiPM cells with small difference in breakdown voltage to form the SiPM array. This aspect increases the fabrication cost of the SiPM array.
  • the gain between the SiPM cells in the SiPM array is also difficult to achieve. Therefore, the gain of each SiPM cell in the SiPM array can be measured in real time, and the gain of each SiPM cell is ensured by the gain compensation method.
  • the gain of three sensor units in the same sensor array may be 1, 1.5, and 0.8, respectively. Therefore, for an effective event with equal energy, the energy detected by each sensor unit will be different. However, it is desirable that the energy detected by the three sensor units is the same. Therefore, when the energy is subsequently corrected (that is, the gain variation is compensated), a constant G 0 is first divided by 1, 1.5, and 0.8, which is equivalent to gain normalization. G 0 can be determined as needed. After energy correction, the effect of the difference in gain between the various sensor units on the energy measurement has been eliminated for the entire sensor array.
  • FIG. 9 shows a flow chart of a method 900 for measuring sensor gain, in accordance with one embodiment of the present invention. As shown in FIG. 9, method 900 includes the following steps.
  • Step S910 detecting a current signal output by the sensor unit and generating a corresponding detection signal.
  • Step S920 calculating the energy of the dark event occurring in the sensor unit according to the detection signal.
  • Step S930 generating an energy spectrum of the dark event.
  • Step S940 calculating the gain of the sensor unit based on the energy spectrum.
  • the detection signal is a digital signal consisting of a high level and a low level of equal duration, and the sum of all high levels in the digital signal is proportional to the integral of the current signal over time.
  • step S920 may include: determining whether a pulse event occurs according to an occurrence rule of a high level and a low level in the digital signal; and starting to determine a pulse event energy using the digital signal when determining that the pulse event occurs, until according to the digital signal
  • the occurrence of high and low levels determines the end of the pulse event; and whether the pulse event is a valid event or a dark event based on the energy of the pulse event, and if the pulse event is a dark event, the energy of the pulse event is determined to be a dark event energy.
  • Step S940 may include: calculating a gain according to an abscissa of the first peak corresponding to the energy of the single dark event in the energy spectrum, or according to the abscissa and the energy spectrum of the first peak, and two The gain is calculated as the difference between the abscissa of the second peak corresponding to the energy of the dark event.
  • step S920 may include: determining a time period in which an effective event does not occur according to an occurrence rule of a high level and a low level in the digital signal; selecting a predetermined one of the digital signals generated in a time period in which the valid event does not occur a digital signal generated during the time period; and calculating the energy of the dark event based on the digital signal generated during the predetermined time period.
  • the predetermined time period is set such that the number of average dark events in the predetermined time period satisfies the first preset condition, the horizontal axis of the energy spectrum represents the energy of the dark event, and the vertical axis of the energy spectrum represents the calculated dark event.
  • the number of times of energy the energy spectrum includes a plurality of spectral peaks and the Nth spectral peak in the energy spectrum corresponds to the energy of the N dark events, and step S940 may include: according to any two phases in the energy spectrum The difference between the abscissas of the neighbor peaks is used to calculate the gain.
  • the first preset condition is that the number of average dark events is less than 50.
  • the predetermined time period is set such that the number of average dark events in the predetermined time period satisfies the second preset condition, the horizontal axis of the energy spectrum represents the energy of the dark event, and the vertical axis of the energy spectrum represents the calculated dark event.
  • the number of times of energy, step S940 may include: performing a Gaussian fitting on the energy spectrum to obtain a variance and an average of the energy spectrum; and dividing the variance by the mean to obtain a gain.
  • the second preset condition is that the number of average dark events is greater than 50.
  • the existing gain compensation methods for SiPM usually include the following:
  • the method of temperature compensation that is, adjusting the bias voltage according to the temperature change to stabilize the gain of the SiPM. For example, when the temperature rises, the bias voltage can be increased to stabilize the gain.
  • this approach requires the design of temperature measurement and voltage control circuitry for each SiPM cell in the SiPM array. In practical applications, a set of SiPM units with close physical space can share a set of temperature measurement and voltage control circuits. This method is the most widely used, but at a higher cost.
  • This method automatically calibrates the gain by finding and tracking the photopeak peak position of the energy spectrum detected by the SiPM at the time of the active event.
  • the accuracy of this method depends on the speed of temperature drift and the effective event rate. To achieve accurate positioning of the peak at a certain temperature, more events are needed to overcome statistical errors. Under normal circumstances (for example, PET human imaging), the effective event rate is very low, and it is difficult to track the photopeak peak in real time.
  • the circuit provided by the method for measuring the gain of the sensor unit by the dark current and further compensating the gain is simple in structure, low in cost, and easy to implement. Moreover, since the dark event rate in the sensor unit is high, a large amount of reference data can be obtained in a short time, so that the gain of the sensor unit can be determined quickly, accurately, and efficiently, which is advantageous for subsequent sensor units. Gain changes are compensated.

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Abstract

一种用于测量传感器增益的装置、设备及方法。该装置包括电流检测电路（122）和处理电路（124）。电流检测电路（122）的输入端连接传感器单元（110）的输出端。电流检测电路（122）用于检测传感器单元输出的电流信号并生成相应的检测信号。处理电路（124）的输入端连接电流检测电路（122）的输出端。处理电路（124）用于根据检测信号计算在传感器单元（110）中发生的暗事件的能量，生成暗事件的能量谱图，并基于能量谱图计算传感器单元（110）的增益。所述用于测量传感器增益的装置、设备及方法通过传感器单元（110）中的暗事件的能量来确定传感器单元（110）的增益，可以快速、准确、高效地确定传感器单元（110）的增益，有利于后续对传感器单元（110）的增益变化进行补偿。

Description

用于测量传感器增益的装置、设备及方法 技术领域
本发明涉及电路领域，具体地，涉及一种用于测量传感器增益的装置、设备及方法。
背景技术
在高能光子(X射线、伽玛光子等)测量系统中，经常采用诸如硅光电倍增管(Silicon Photomultipliers，SiPM)的光电传感器。SiPM是一种基于硅的光电传感器。SiPM由边长10～100微米左右的小的传感器微元(cell)组成。每个传感器微元都是工作在盖革(Geiger)模式下的雪崩式光电二极管。每个传感器微元每次都只能检测一个可见光子。成百上千的传感器微元组成传感器单元(pixel)。传感器单元的尺寸通常为1平方毫米至几十平方毫米。很多传感器单元组合在一起，又可以组成更大的传感器阵列(例如16x16个3毫米x3毫米的传感器单元组成的阵列)。SiPM阵列和闪烁晶体阵列通过光导层耦合在一起，就构成了基于SiPM的前端检测器。基于SiPM的前端检测器广泛应用于高能光子的检测。相比于传统的光电倍增管(Photomultipliers，PMT)，SiPM具有尺寸小、偏置电压低、时间分辨率高、与核磁共振(MRI)磁场兼容等优点。SiPM的一个缺点是其增益受温度影响较大。SiPM增益的变化，对基于SiPM的前端检测器的许多性能有很大影响，并且会影响高能光子的测量结果。为了补偿SiPM的增益变化带来的影响，可以首先测量出SiPM的增益，以获知当前SiPM的增益变化情况。
因此，需要提供一种用于测量传感器增益的装置，以至少部分地解决现有技术中存在的上述问题。
发明内容
为了至少部分地解决现有技术中存在的问题，根据本发明的一个方面，提供一种用于测量传感器增益的装置。该装置包括电流检测电路和处理电 路。电流检测电路的输入端连接传感器单元的输出端。电流检测电路用于检测传感器单元输出的电流信号并生成相应的检测信号。处理电路的输入端连接电流检测电路的输出端。处理电路用于根据检测信号计算在传感器单元中发生的暗事件的能量，生成暗事件的能量谱图，并基于能量谱图计算传感器单元的增益。
根据本发明的另一方面，提供一种用于测量传感器增益的设备。该设备包括与传感器阵列中的多个传感器单元一一对应的多个如上所述的用于测量传感器增益的装置。
根据本发明的另一方面，提供一种用于测量传感器增益的方法。该方法包括：检测传感器单元输出的电流信号并生成相应的检测信号；根据检测信号计算在传感器单元中发生的暗事件的能量；生成暗事件的能量谱图；以及基于能量谱图计算传感器单元的增益。
根据本发明提供的用于测量传感器增益的装置、设备及方法，通过传感器单元中的暗事件的能量来确定传感器单元的增益，由于传感器单元中的暗事件率很高，因此可以在较短的时间内获得较大的参考数据量，从而可以快速、准确、高效地确定传感器单元的增益，有利于后续对传感器单元的增益变化进行补偿。
在发明内容中引入了一系列简化的概念，这些概念将在具体实施方式部分中进一步详细说明。本发明内容部分并不意味着要试图限定所要求保护的技术方案的关键特征和必要技术特征，更不意味着试图确定所要求保护的技术方案的保护范围。
以下结合附图，详细说明本发明的优点和特征。
附图说明
本发明的下列附图在此作为本发明的一部分用于理解本发明。附图中示出了本发明的实施方式及其描述，用来解释本发明的原理。在附图中，
图1示出根据本发明一个实施例的传感器单元以及用于测量传感器增益的装置的示意性框图；
图2示出根据本发明一个实施例的电流检测电路的示意性框图；
图3示出根据本发明一个实施例的电流检测电路的电路示意图；
图4示出根据本发明一个实施例的暗事件的能量谱图；
图5示出根据本发明另一个实施例的暗事件的能量谱图；
图6示出根据本发明又一个实施例的暗事件的能量谱图；以及
图7a示出根据图6所示实施例测量得到的某特定型号的SiPM的增益随过压的变化曲线；
图7b示出根据图6所示实施例测量得到的该特定型号的SiPM的暗事件率随过压的变化曲线；
图8示出根据本发明一个实施例的传感器阵列以及用于测量传感器增益的设备的示意性框图；以及
图9示出根据本发明一个实施例的用于测量传感器增益的方法的流程图。
具体实施方式
在下文的描述中，提供了大量的细节以便能够彻底地理解本发明。然而，本领域技术人员可以了解，如下描述仅涉及本发明的较佳实施例，本发明可以无需一个或多个这样的细节而得以实施。此外，为了避免与本发明发生混淆，对于本领域公知的一些技术特征未进行描述。
根据本发明的一个方面，提供一种用于测量传感器增益的装置。图1示出根据本发明一个实施例的传感器单元110以及用于测量传感器增益的装置120的示意性框图。如图1所示，装置120包括电流检测电路122和处理电路124。
电流检测电路122的输入端连接传感器单元110的输出端。电流检测电路122用于检测传感器单元110输出的电流信号并生成相应的检测信号。
电流检测电路122可以是任何合适的能够检测传感器单元110输出的电流信号的电路。例如，电流检测电路122可以包括示波器，用于检测电流信号并对电流信号进行一些期望处理。可以理解的是，电流检测电路122检测的是传感器单元110在增益测量时段内输出的电流信号。在该增益测量时段内，可能发生有效事件或暗事件，也可能未发生任何事件。在没有事件发生的时段内，传感器单元输出的电流信号为0，电流检测电路122生成的检测信号也是0。
在本文中，有效事件是指高能光子(例如伽玛光子等)在与传感器单元相连的闪烁晶体中作用而引起的在传感器单元中产生电流信号的事件， 暗事件是指噪声(通常是热电子)引起的在传感器单元中产生电流信号的事件。在发生有效事件或暗事件时，传感器单元110可以输出一个脉冲电流信号。为了描述方便，在本文中，将在发生有效事件时传感器单元110输出的脉冲电流信号称为有效电流信号，将在发生暗事件时传感器单元110输出的脉冲电流信号称为暗电流信号。有效电流信号的能量远大于暗电流信号的能量，前者通常是后者的几十至几千倍。因此，通过分析传感器单元110输出的电流信号的能量可以确定在传感器单元110中发生的是有效事件还是暗事件。
处理电路124的输入端连接电流检测电路122的输出端。处理电路124用于根据检测信号计算在传感器单元中发生的暗事件的能量，生成暗事件的能量谱图，并基于能量谱图计算传感器单元的增益。
光电传感器(尤其是SiPM)的增益(或增益及串扰率(Crosstalk rate))与温度以及施加到光电传感器上的偏置电压相关。在光电传感器正常工作时，偏置电压通常是不变的，因此其增益(或增益及串扰率)主要受温度影响。以SiPM为例，温度升高时，SiPM的增益(或增益及串扰率)降低，单位时间内暗事件的个数(暗电流的大小)增大。可以通过检测单个暗事件的能量来直接确定SiPM的增益变化情况。在一个示例中，可以根据经验或理论预先设定一个标准暗事件能量。例如，可以将在25度温度以及30V偏置电压下在SiPM内发生的一个暗事件的平均能量设定为标准暗事件能量，将该情况下的增益设定为标准增益。处理电路124通过分析暗事件的能量谱图可以获知在增益测量时段内发生的一个暗事件的能量相对于标准暗事件能量的变化，从而获知在增益测量时段内SiPM的增益相对于标准增益的变化。之后，可以基于增益的变化情况制定合适的补偿策略，以补偿增益变化带来的影响。
根据本发明提供的用于测量传感器增益的装置，通过传感器单元中的暗事件的能量来确定传感器单元的增益，由于传感器单元中的暗事件率很高，因此可以在较短的时间内获得较大的参考数据量，从而可以快速、准确、高效地确定传感器单元的增益，有利于后续对传感器单元的增益变化进行补偿。
可选地，检测信号是数字信号。数字信号由持续时间相等的高电平和低电平组成，数字信号中的所有高电平之和与电流信号对时间的积分成正 比。在一个示例中，电流检测电路可以实现为图2所示的形式，以生成上述数字信号。图2示出根据本发明一个实施例的电流检测电路200的示意性框图。
电流检测电路200可以包括积分电路210、比较电路220、传输控制电路230和负反馈电路240。
积分电路210连接传感器单元(如图1所示的传感器单元110)的输出端和负反馈电路240的输出端。积分电路210用于接收来自传感器单元的电流信号和来自负反馈电路240的反馈信号，对电流信号和反馈信号的差进行积分并且输出积分信号。
电流检测电路200是包括负反馈环节的电路，反馈信号被输入到积分电路210。同时，积分电路210还接收来自传感器单元的电流信号。电流信号和反馈信号的流动方向是相反的。例如，如果电流信号是从积分电路210流向传感器单元的，则可以将反馈信号设定为从负反馈电路240流向积分电路210。因此，对于积分电路210来说，实际上最终输入的是电流信号与反馈信号的差，积分电路210可以对二者的差进行积分。应该注意，图2中示出的箭头方向是信号的传输方向，而不一定是信号的流动方向。积分电路210可以采用模拟积分电路实现，例如通过电阻和电容组成的滤波器电路实现。
如图2所示，比较电路220的一个输入端连接积分电路210的输出端并且比较电路220的另一输入端接入参考电平。比较电路220用于将积分信号与参考电平进行比较并生成比较结果。例如，当积分信号的幅度大于参考电平时，比较电路220可以输出高电平，当积分信号的幅度等于或小于参考电平时，比较电路220可以输出低电平。因此，比较电路220输出的比较结果中可以只存在高电平和低电平两种状态。通常，传感器单元输出的电流信号是随时间变化的脉冲电流信号，在这种情况下，积分信号也是随时间变化的信号。因此，比较电路220输出的比较结果是随时间变化而在高电平和低电平两种状态之间切换的信号。
传输控制电路230的输入端连接比较电路220的输出端。传输控制电路230用于利用时钟信号控制比较结果的传输以输出数字信号。如上所述，比较结果是随时间变化而在高电平和低电平两种状态之间切换的信号。在该比较结果中，高电平和低电平的持续时间可能是实时变化的，是无法确 定的。所以可以通过传输控制电路230对比较结果进行时间上的量化，使得每段连续的高电平或低电平的持续时间都是时钟信号的周期的整数倍。这种时间上的量化相当于模数转换过程中的时间离散化，因此，从功能性上来看，可以将比较电路220和传输控制电路230这二者视作一个1位的ADC。在传输控制电路230输出的数字信号中，每个高电平和每个低电平的持续时间相等，均等于时钟信号的周期。在一个示例中，高电平可以代表逻辑电平“1”，低电平可以代表逻辑电平“0”，则数字信号是由逻辑电平“1”和“0”组成的序列。假设时钟信号的频率为100Hz，即周期为0.01s，则在数字信号中，单个“1”或“0”的持续时间是0.01s。另外，可以理解的是，当多个“1”或多个“0”连续出现时，该多个“1”或多个“0”的持续时间是0.01s的整数倍。传输控制电路230可以是寄存器或受时钟信号控制的开关电路等。
负反馈电路240的输入端连接传输控制电路230的输出端。负反馈电路240用于将数字信号转换为反馈信号并且将反馈信号反馈给积分电路210。负反馈电路240可以包括数模转换器(DAC)，用于对数字信号进行数模转换以将其转换为模拟信号。具体地，该DAC可以是1位的DAC，以将传输控制电路230输出的由“1”和“0”组成的序列转换为模拟信号，例如转换为幅度随时间变化的电压信号。负反馈电路240可以进一步包括电阻。DAC经由该电阻连接到积分电路210的输入端。因此，上述电压信号将产生流经该电阻的电流信号，即反馈信号。反馈信号可以抵消来自传感器单元的电流信号的一部分，避免积分电路210所输出的积分信号过大，以保持电路稳定。此外，由于反馈信号在不断抵消来自传感器单元的电流信号，所以电流信号引发的反馈信号的累加值可以视作来自传感器单元的电流信号的累加值。同时，反馈信号的幅度与数字信号的幅度成正比。因此，当电流信号的持续时间已经结束并且反馈信号的幅度稳定在零(即针对电流信号的负反馈作用已经停止)时，可以利用数字信号来计算光子的能量。应该注意，反馈信号不宜过大或过小。反馈信号过大会导致电流信号的抵消速度过快，使得数字信号包含的误差增大，影响测量精度。相反，反馈信号过小会导致电流信号的抵消速度过慢，使得无法及时减小积分信号的值，从而也会影响测量精度。反馈信号的幅度可以根据实际需要来确定，本发明不对此进行限制。
图3示出根据本发明一个实施例的电流检测电路300的电路示意图。电流检测电路300可以包括积分电路310、比较电路320、传输控制电路330和负反馈电路340。
积分电路310可以采用运算放大器、电阻Rin和电容C来实现。比较电路320可以采用比较器实现，其参考电平是地电平。传输控制电路330可以采用D触发器构成的寄存器来实现，其时钟信号的频率是fs’。负反馈电路340可以采用一个DAC和一个电阻Rf来实现。该DAC可以是现场可编程门阵列(FPGA)的一个引脚。整个电流检测电路300可以由模拟电路部分和FPGA部分来实现，如图3所示。根据需要，电路中也可以加入二极管，或者分压电路来减少或者隔绝电路中可能存在的偏置直流电流。本领域技术人员根据以上对电流检测电路200的描述，可以理解电流检测电路300的原理和工作方式，不再赘述。
生成数字化的检测信号可以方便后续对有效事件或暗事件的能量进行计算。
可选地，处理电路124可以通过以下方式计算在传感器单元110中发生的暗事件的能量：根据数字信号中的高电平和低电平的出现规律确定脉冲事件是否发生；当确定脉冲事件发生时开始利用数字信号计算脉冲事件的能量，直至根据数字信号中的高电平和低电平的出现规律确定脉冲事件结束为止；以及根据脉冲事件的能量判断脉冲事件是有效事件还是暗事件，如果脉冲事件是暗事件，则将脉冲事件的能量确定为暗事件的能量。
脉冲事件是指在传感器单元中产生脉冲电流信号的事件，其可能是有效事件，也可能是暗事件。如上文所述，数字信号是“0”和“1”组成的序列。当传感器单元中未发生有效事件或暗事件时，电流检测电路122、200或300输出的是一系列连续的“0”，而在发生有效事件或暗事件时，电流检测电路122、200或300输出的信号中应当包含若干个“1”。可以总结脉冲事件发生和脉冲事件未发生时的“1”和“0”的出现规律，并根据总结出的规律来区分脉冲事件发生和脉冲事件未发生这两种情况。例如，如果在数字信号中，在很多个(例如10个)连续的“0”后面出现了一个“1”，则说明此时发生了脉冲事件，其有可能是有效事件，也有可能是暗事件。随后，可以开始利用数字信号中的“1”计算脉冲事件的能量。例如，可以对数字信号中的“1”进行累加或对其进行计数。当数字信号中连续出现5个“0”时，说明 脉冲事件结束，此时可以停止对“1”进行累加或计数。这样，最后可以获得脉冲事件的相对能量，其可以反映脉冲事件的绝对能量的大小。如上文所述，有效事件的能量与暗事件的能量相差较大，因此可以通过能量来区分两者。例如，如果最后获得的脉冲事件的相对能量是几千，则可以认为脉冲事件是有效事件，此时可以将计算出的能量丢弃。如果最后获得的脉冲事件的相对能量是几百，则可以认为脉冲事件是暗事件，此时可以将计算出的能量作为暗事件的能量并将其用于生成能量谱图。这种测量暗事件能量的方式可以视为是触发方式，即当有暗事件触发时才测量暗事件的能量。
可选地，能量谱图的横轴表示暗事件的能量，能量谱图的纵轴表示计算得到暗事件的能量的次数。处理电路124可以通过以下方式计算传感器单元110的增益：根据能量谱图中的、与单个暗事件的能量相对应的第一谱峰的横坐标计算增益，或根据第一谱峰的横坐标和能量谱图中的、与两个暗事件的能量相对应的第二谱峰的横坐标之间的差计算增益。
根据上文所述的方法，可以在每次有暗事件发生时，都计算获得该暗事件的一个相对能量值。可以在测量时段(例如5秒钟)内，不停地进行暗事件的检测和能量计算，并针对在该测量时段内检测到的所有暗事件，进行谱分析，得到能量谱图。图4示出根据本发明一个实施例的暗事件的能量谱图。图4所示的能量谱图中具有两个较明显的谱峰，左边的谱峰是普通暗事件的能量谱峰(即第一谱峰)，右边的谱峰是存在串扰(cross talk)的暗事件的能量谱峰(即第二谱峰)。第二谱峰的横轴位置差不多是第一谱峰的两倍。具体地，第一谱峰在能量为大约40的位置处，40代表单个暗事件的能量，因此，第一谱峰与单个暗事件的能量相对应。第二谱峰在能量为大约80的位置处，80代表两个暗事件的能量，因此，第二谱峰与两个暗事件的能量相对应。根据上文描述可知，处理电路124在每次计算能量时，基于从暗事件开始至暗事件结束的时间内的数字信号来计算暗事件的能量，因此其每次获得的基本是单个暗事件的能量。
暗事件能量的增益即代表传感器单元的增益。通过第一谱峰的横坐标或第一谱峰的横坐标与第二谱峰的横坐标之间的差可以获知当前单个暗事件的能量。通过当前单个暗事件的能量与标准暗事件能量的差异可以计算增益。例如，假设标准暗事件的能量是30，标准增益是100。根据如图4所示的谱图，已知当前单个暗事件的能量为接近40。这样，传感器单元的 当前增益可以认为是标准增益的接近1.33倍，即当前增益为133。可以理解的是，由于干扰等因素存在，第一谱峰和第二谱峰的位置可能不准确，例如可能向左或向右移动。然而，由于第一谱峰与第二谱峰是同步移动的，因此二者的横坐标之间的差始终是不变的，因此与直接利用第一谱峰的横坐标来计算增益的方式相比，利用第一谱峰的横坐标与第二谱峰的横坐标之间的差来计算增益的方式的准确度更高。
可选地，处理电路124可以通过以下方式计算在传感器单元110中发生的暗事件的能量：根据数字信号中的高电平和低电平的出现规律确定有效事件未发生的时间段；从在有效事件未发生的时间段内生成的数字信号中选择在预定时段内生成的数字信号；以及根据在预定时段内生成的数字信号计算暗事件的能量。
可以首先根据数字信号中的“1”和“0”的出现规律确定有效事件发生的时间段，进而可以确定有效事件未发生的时间段。例如，如果一段数字信号中的“1”出现了5000次，可以认为有效事件发生。在与其相邻的另一段数字信号中的“1”出现了4000次，也可以认为有效事件发生。在这两个有效事件之间，可能发生了多次暗事件。因此，可以在两个有效事件之间，选择一个或多个预定时段，并选择在该预定时段内生成的数字信号。该预定时段可以是任何合适的时间段，例如10微秒，本发明不对此进行限制。例如，如果两个有效事件之间的整个时间段长度是1毫秒，则可以将这1毫秒分为100个10微秒。分别计算每个10微秒内包含的暗事件的能量，可以得到100个暗事件能量值。可以在增益测量时段(例如5秒)内持续进行这样的有效事件检测和暗事件能量计算。在这种方式中，不采用触发方式来启动暗事件的能量测量，而是计算未发生有效事件(仅有暗事件)的预定时段内所有暗事件的能量，以用于生成能量谱图。
可选地，预定时段设定为使得在预定时段内的平均暗事件个数满足第一预设条件。能量谱图的横轴表示暗事件的能量，能量谱图的纵轴表示计算得到暗事件的能量的次数，能量谱图包括多个谱峰并且能量谱图中的第N个谱峰与N个暗事件的能量相对应。处理电路124可以通过以下方式计算传感器单元的增益：根据能量谱图中的、任意两个相邻谱峰的横坐标之间的差计算增益。可选地，第一预设条件是平均暗事件个数小于20。当平均暗事件个数小于20时，可以使得能量谱图中出现多个离散的谱峰，即能 量谱图呈现泊松分布。当然，可以理解的是，使能量谱图呈现泊松分布的平均暗事件个数也可以具有其他合适的选值范围，本发明不对此进行限制。下面对此进行详细描述。
根据以上描述可知，处理电路124每次计算预定时段内的暗事件的能量。如果该预定时段设定得合适，则可以使得在每个预定时段内发生多个暗事件，也就使得每次计算得到的暗事件的能量等于多个暗事件的能量之和。图5示出根据本发明另一个实施例的暗事件的能量谱图。如图5所示，该能量谱图中具有比图4更多的谱峰，并且高度最高的谱峰也不再是第一谱峰。这是因为，时间段设定得较长，使得每个时间段内发生多个暗事件的能量的可能性远大于只发生单个暗事件的可能性，从而使得每次计算得到的暗事件的能量总是大于单个暗事件的能量。平均暗事件个数是指在(增益测量时段内的)所选择的所有预定时段内发生的暗事件个数相对预定时段个数的平均。
图5所述的能量谱图包括如下几个谱峰。第一个谱峰的横坐标代表的是(预定时段内发生的)一个暗事件的能量；第二个谱峰的横坐标代表的是(预定时段内发生的)两个暗事件的能量；依此类推，第N个谱峰的横坐标代表的是(预定时段内发生的)N个暗事件的能量。第N个谱峰的横坐标基本是第一个谱峰的N倍。暗事件能量的增益即为传感器单元的增益。当温度变化引起增益变化时，可能导致图5所示的所有谱峰向右侧移动。通过跟踪谱峰中的一个(或者几个)的位置变动，可以获知传感器单元的增益变化。这种增益测量方式的优点如下所述。由于第N个谱峰的横坐标是第一个谱峰的横坐标的N倍，因此温度的变化导致的第N个谱峰的横坐标的移动，比第一个谱峰的横坐标的移动要大N倍。因此，通过测算第N个谱峰的横坐标的移动，来测算温度导致的增益变化，比通过测算第一个谱峰的横坐标的移动，来测算温度导致的增益变化，灵敏度和准确度要高一些。另外，由于第一个谱峰不太明显，因此也可以根据任意两个相邻谱峰的横坐标之间的差计算增益。这种方式与上文所述的通过第一谱峰的横坐标与第二谱峰的横坐标之间的差来计算增益的方式类似，不再赘述。
可选地，预定时段设定为使得在预定时段内的平均暗事件个数满足第二预设条件。能量谱图的横轴表示暗事件的能量，能量谱图的纵轴表示计算得到暗事件的能量的次数。处理电路124可以通过以下方式计算传感器 单元的增益：对能量谱图进行高斯拟合以获得能量谱图的方差和均值，并且将方差除以均值以获得增益。可选地，第二预设条件是平均暗事件个数大于20。当平均暗事件个数大于20时，可以使得能量谱图近似呈现高斯分布。当然，可以理解的是，使能量谱图呈现高斯分布的平均暗事件个数也可以具有其他合适的选值范围，本发明不对此进行限制。下面对此进行详细描述。
图6示出根据本发明又一个实施例的暗事件的能量谱图。与图5所示实施例不同的是，图6所示实施例的能量累积时间(即所谓的预定时段)比图5所示实施例长很多，从而导致得到的能量谱图中，不再出现离散的谱峰，整个能量谱图呈现如图6所示的近似正态分布(即高斯分布)。
产生这一现象的基本原理如下：
(1)预定时段内的暗事件个数本质上是一个离散的泊松分布；
(2)当预定时段内的暗事件个数较少时，可能出现离散的谱峰，但由于测量误差，实际的能量谱图中的谱峰会有一定的宽度；
(3)当预定时段内的暗事件个数较多时，泊松分布逐步接近正态分布。当预定时段内的平均暗事件个数λ大于一定的数值(例如20)时，可以认为泊松分布呈正态分布N(λ,λ)，其可以按正态分布处理；
(4)根据本实施例测量得到的能量谱图的横轴不对应于预定时段内的平均暗事件个数λ，而对应于λG(G是传感器单元的增益)。因此，泊松分布呈正态分布N(λ,λ)后，反映在能量谱图上的正态分布为N(λG,λG2)。因此，把这一正态分布的方差除以其均值即可得到传感器单元的增益G。
需要指出的是，这样计算出来的增益实际上是增益G，“1+串扰率”和“1+单光子检测分辨率平方”三项的乘积。在实际情况中，“1+串扰率”和“1+单光子检测分辨率平方”两项的乘积非常接近于1。因此，通常可以认为，增益G、“1+串扰率”和“1+单光子检测分辨率平方”三项的乘积近似等于增益G。另外，需要指出的是，通常情况下，单光子检测分辨率约为0.05左右，“1+单光子检测分辨率平方”近似为1。因此，计算出来的增益也可以近似为增益G和“1+串扰率”的乘积。由于SiPM测量得到的有效事件的能量正比于增益G和“1+串扰率”的乘积，增益补偿需要同时补偿温度对增益G和“1+串扰率”的影响。因此，计算增益G和“1+串扰率”的乘积比单纯地计算真正的增益更有实际价值。
因此，根据本实施例，计算传感器单元的增益的实施方式实际上非常简单和易于实现，基本步骤如下：
(1)对能量谱进行高斯拟合，计算其均值μ及方差σ2。
(2)计算传感器单元的增益G＝σ2/μ。
图7a示出根据图6所示实施例测量得到的某特定型号的SiPM的增益随过压的变化曲线。图7b示出根据图6所示实施例测量得到的该特定型号的SiPM的暗事件率随过压的变化曲线(暗事件率约等于暗电流除以增益)。从图7a和图7b可以看出图6所示实施例的增益测量结果比较准确。
图5所示的实施例一般要求检测暗事件产生的电流(或者电荷)的电流检测电路具备较高的精度。这往往是以牺牲整个电流检测电路的动态范围(或者死区时间)为代价的。图6所示的实施例对电流检测电路的精度要求较低。
可选地，处理电路124可以进一步用于根据检测信号计算在传感器单元中发生的有效事件的能量E0，并且根据以下公式对有效事件的能量E0进行校正：E＝E0*G0/G，其中，E为经校正的能量，G为所述增益，G0为预定常数。
虽然本实施例描述的是利用处理电路124以及电流检测电路122、200或300来测量有效事件的能量的方法，但可以理解的是，也可以利用其他任何合适的装置测量有效事件的能量。
在本文中，传感器单元的增益G可以实时计算获得，其可以是随时间变化的量。G0也可以具有任何合适的值，本文不对此进行限制。
例如，G0可以等于例如上文所述的标准增益。通过将在当前时刻测量得到的传感器单元的增益与标准增益进行比较，可以获知当前时刻测量得到的有效事件的能量与在标准增益下的能量的差异，从而可以将当前时刻测量得到的能量校正为在标准增益下的能量。如果对多个传感器单元的能量均进行这样的校正，则相当于将这多个传感器单元的能量放在同一标准下，因此它们的能量可以进行相互比较。例如，如果标准增益是100，而当前时刻测量得到的增益G为200，说明当前的增益增大了1倍。因此测量得到的能量也会比在标准增益下的能量增大1倍。如果测量得到的能量E0是2000，则经校正的能量E可以是1000。
另外，也可以将传感器单元的能量校正为实际的能量。在这种情况下， G0可以设定为1。假设，如果已根据本文所描述的实施例获知传感器单元的当前增益是1.5，所检测到的某一有效事件的当前能量是3000，则可以将能量3000除以增益1.5，以得到该有效事件的经校正的能量2000。
可以理解的是，处理电路124计算出的有效事件或暗事件的能量可能是相对能量而非绝对能量，因此传感器单元的增益也可以用相对增益而非绝对增益来表示。
例如，返回参考图4。如上文所述，假设标准暗事件的能量是30，标准增益是100。假设在某一增益测量时段(为描述方便，用“第一增益测量时段”来表示)内获得的能量谱图如图4所示，则在第一增益测量时段内的单个暗事件的能量为接近40。这样，在第一增益测量时段内传感器单元的绝对增益可以认为是标准增益的接近1.33倍，即在第一增益测量时段内的绝对增益为133。在第一增益测量时段前后的预设时间范围内，可以认为增益是不变的。在该时间范围内，如果检测到的有效事件的能量为10000，则可以用能量10000除以绝对增益133，获得校正后的能量75。随后，在另一增益测量时段(为描述方便，用“第二增益测量时段”来表示)内，如果能量谱图向右移动，导致计算得出的在第二增益测量时段内的单个暗事件的能量为接近50。在第二增益测量时段内传感器单元的绝对增益可以认为是标准增益的接近1.67倍，即在该第二增益测量时段内的绝对增益为167。在第二增益测量时段前后的预设时间范围内，可以认为增益是不变的。在该时间范围内，如果检测到的有效事件的能量为10000，则可以用能量10000除以绝对增益167，获得校正后的能量60。这样，可以将校正后的能量75与校正后的能量60相比较，可知两个有效事件之间的能量差异。
可选地，也可以直接将40视作在第一增益测量时段内传感器单元的增益。也就是说，无需基于标准暗事件和标准增益来计算绝对增益。在这种情况下，可以用能量10000除以增益40，获得校正后的能量为250。随后，也可以直接将50视作在第二增益测量时段内传感器单元的增益。在这种情况下，可以用能量10000除以增益50，获得校正后的能量为200。可以将校正后的能量250与校正后的能量200相比较，可知两个有效事件之间的能量差异。75/60与250/200的结果是一样的，因此可见无论是计算绝对增益还是相对增益，都可以正确反映各有效事件的能量之间的相对大小。以上两种增益计算方法可以认为是采用了两种不同的归一化方式，它们可以 根据需要进行选择。基于增益校正有效事件的能量可以使得最后获得的能量值能够更准确。
可选地，处理电路124可以采用任何合适的数字电路实现，例如采用FPGA、复杂可编程逻辑器件(CPLD)、数字信号处理器(DSP)、微控制单元(MCU)或中央处理单元(CPU)等实现。
本发明具有如下优点：
(1)较低的硬件成本。本发明实施例提供的电路结构简单，电流检测电路可以采用模拟电路实现，处理电路可以采用数字电路实现，整体不需要过多硬件，因此成本较低。
(2)不干扰传感器单元的正常工作。本发明可以在不干扰传感器单元的正常工作状态的情况下，对通常被认为是噪声的暗事件产生的电流(电荷)进行检测和分析，计算传感器单元的增益。
(3)实时和高精度的增益测量和补偿。传感器单元中的暗事件率一般大于300kHz。这使得能够在足够短的时间内采集足够多的数据，保证谱分析的精度，做到实时高精度地测量和补偿温度导致的增益变化。反应速度非常快。
根据本发明的另一方面，提供一种用于测量传感器增益的设备。该设备包括与传感器阵列中的多个传感器单元一一对应的多个上文所述的用于测量传感器增益的装置。图8示出根据本发明一个实施例的传感器阵列以及用于测量传感器增益的设备的示意性框图。
如图8所示，传感器阵列包括N个传感器单元810，即传感器单元1、传感器单元2……传感器单元N。用于测量传感器增益的设备包括与N个传感器单元一一对应的N个用于测量传感器增益的装置820。每个装置820与上文所述的装置120相同，均包括电流检测电路822和处理电路824。本领域技术人员根据以上关于用于测量传感器增益的装置的描述以及结合图1至7b能够理解用于测量传感器增益的设备的结构、运行方式和优点等，不再赘述。
需要注意的是，在用于测量传感器增益的设备中，各处理电路824均可以采用如上所述的诸如FPGA的数字电路来实现。可以理解，用于测量传感器增益的设备中的任意数量的处理电路824可以集成在同一诸如FPGA的数字电路中。
可选地，处理电路824进一步用于根据检测信号计算在对应传感器单元中发生的有效事件的能量E0，并且根据以下公式对有效事件的能量E0进行校正：E＝E0*G0/G，其中，E为经校正的能量，G为对应传感器单元的增益，G0为预定常数。可选地，G0为每个处理电路824的对应传感器单元的标准增益。对某一传感器阵列来说，各传感器单元的标准增益通常相同。
下面结合SiPM进行描述。SiPM单元的增益通常正比于其偏置过压。偏置过压等于偏置电压与击穿电压之差。由于微电子工艺上的原因，不同SiPM单元的击穿电压都有一定的差异。同一系列SiPM单元组成SiPM阵列时，通常采用同一偏置(工作)电压。由于各SiPM单元的击穿电压略有不同，它们的增益也不一样。SiPM阵列中的各SiPM单元之间的增益差异会影响由SiPM阵列组成的前端检测器的性能。通常情况下，需要对组成SiPM阵列的SiPM单元进行测试和筛选，选择击穿电压差异较小的SiPM单元来组成SiPM阵列。这一方面加大了SiPM阵列的制作成本，另一方面SiPM阵列中的各SiPM单元之间的增益也很难做到完全一致。因此，可以实时地测量SiPM阵列中的各SiPM单元的增益，并通过增益补偿的方法，保证各SiPM单元的增益一致。
以上公式E＝E0*G0/G中的“G0/G”实现了对同一传感器阵列中的各传感器单元的增益的归一化，从而可以保证各传感器单元的增益一致。例如，同一传感器阵列中的三个传感器单元的增益可能分别是1，1.5和0.8。因此，对于能量相等的有效事件来说，每个传感器单元检测到的能量将是不同的。然而，所期望的是，这三个传感器单元检测到的能量相同。因此，可以在后续对能量进行校正(也就是对增益变化进行补偿)时，首先利用一个常数G0分别除以1，1.5和0.8，这相当于进行了增益归一化。G0可以根据需要而定。经过能量校正之后，对于整个传感器阵列来说，已经消除了各传感器单元之间的增益差异对能量测量带来的影响。
根据本发明的另一方面，提供一种用于测量传感器增益的方法。图9示出根据本发明一个实施例的用于测量传感器增益的方法900的流程图。如图9所示，方法900包括以下步骤。
步骤S910，检测传感器单元输出的电流信号并生成相应的检测信号。
步骤S920，根据检测信号计算在传感器单元中发生的暗事件的能量。
步骤S930，生成暗事件的能量谱图。
步骤S940，基于能量谱图计算传感器单元的增益。
可选地，检测信号是数字信号，数字信号由持续时间相等的高电平和低电平组成，数字信号中的所有高电平之和与电流信号对时间的积分成正比。
可选地，步骤S920可以包括：根据数字信号中的高电平和低电平的出现规律确定脉冲事件是否发生；当确定脉冲事件发生时开始利用数字信号计算脉冲事件的能量，直至根据数字信号中的高电平和低电平的出现规律确定脉冲事件结束为止；以及根据脉冲事件的能量判断脉冲事件是有效事件还是暗事件，如果脉冲事件是暗事件，则将脉冲事件的能量确定为暗事件的能量。
可选地，能量谱图的横轴表示暗事件的能量，能量谱图的纵轴表示计算得到暗事件的能量的次数。步骤S940可以包括：根据能量谱图中的、与单个暗事件的能量相对应的第一谱峰的横坐标计算增益，或根据第一谱峰的横坐标和能量谱图中的、与两个暗事件的能量相对应的第二谱峰的横坐标之间的差计算增益。
可选地，步骤S920可以包括：根据数字信号中的高电平和低电平的出现规律确定有效事件未发生的时间段；从在有效事件未发生的时间段内生成的数字信号中选择在预定时段内生成的数字信号；以及根据在预定时段内生成的数字信号计算所述暗事件的能量。
可选地，预定时段设定为使得在预定时段内的平均暗事件个数满足第一预设条件，能量谱图的横轴表示暗事件的能量，能量谱图的纵轴表示计算得到暗事件的能量的次数，能量谱图包括多个谱峰并且能量谱图中的第N个谱峰与N个暗事件的能量相对应，步骤S940可以包括：根据能量谱图中的、任意两个相邻谱峰的横坐标之间的差计算增益。
可选地，第一预设条件是平均暗事件个数小于50。
可选地，预定时段设定为使得在预定时段内的平均暗事件个数满足第二预设条件，能量谱图的横轴表示暗事件的能量，能量谱图的纵轴表示计算得到暗事件的能量的次数，步骤S940可以包括：对能量谱图进行高斯拟合以获得能量谱图的方差和均值；以及将方差除以均值以获得增益。
可选地，第二预设条件是平均暗事件个数大于50。
可选地，方法900可以进一步包括：根据检测信号计算在传感器单元中发生的有效事件的能量E0；以及根据以下公式对有效事件的能量E0进行校正：E＝E0*G0/G，其中，E为经校正的能量，G为所述增益，G0为预定常数。
本领域技术人员根据以上关于用于测量传感器增益的装置的描述以及附图1至8，能够理解本文所公开的用于测量传感器增益的方法900的实施方式及其优点等，为了简洁，本文不对此进行赘述。
现有的针对SiPM的增益补偿方法通常包括如下几种：
(1)温度控制的方法，即通过温度测量和控制系统来直接稳定SiPM的温度，进而稳定SiPM的增益。这种方法需要构建恒温系统，成本高昂。很多情况下，由于物理空间的限制，这种方法可行性不高。
(2)温度补偿的方法，即根据温度变化来调控偏置电压，以稳定SiPM的增益。例如，温度升高时，可以提高偏置电压，以稳定增益。理想情况下，这种方法需要对SiPM阵列中的每一个SiPM单元，设计温度测量和电压控制电路。实际应用中，一组物理空间接近的SiPM单元，可以共用一套温度测量和电压控制电路。这种方法应用最为广泛，但成本较高。
(3)谱峰跟踪的方法。这种方法通过寻找和跟踪在有效事件发生时SiPM检测到的能量谱的光峰(photopeak)谱峰位置，来自动校准增益。这种方法的精度，取决于温度漂移的速度，及有效事件率。要在某一温度实现谱峰的精确定位，需要较多的事件来克服统计误差。通常情况下(例如，PET人体成像)，有效事件率非常低，很难实现实时地跟踪photopeak谱峰。
与上述现有的增益补偿方法相比，本发明提供的通过暗电流测量传感器单元的增益进而对增益进行补偿的方式所采用的电路结构简单，成本低，易于实现。并且，由于传感器单元中的暗事件率很高，因此可以在较短的时间内获得较大的参考数据量，从而可以快速、准确、高效地确定传感器单元的增益，有利于后续对传感器单元的增益变化进行补偿。
虽然本文以SiPM为例描述了本发明的原理和应用，但是应该理解的是，本发明并不局限于此。本发明所提供的用于测量传感器增益的装置及方法还可以应用于PMT或任何其他合适的光电传感器。
本发明已经通过上述实施例进行了说明，但应当理解的是，上述实施 例只是用于举例和说明的目的，而非意在将本发明限制于所描述的实施例范围内。此外本领域技术人员可以理解的是，本发明并不局限于上述实施例，根据本发明的教导还可以做出更多种的变型和修改，这些变型和修改均落在本发明所要求保护的范围以内。本发明的保护范围由附属的权利要求书及其等效范围所界定。

Claims (22)

  1. 一种用于测量传感器增益的装置，包括电流检测电路和处理电路，其中：
    所述电流检测电路的输入端连接传感器单元的输出端，所述电流检测电路用于检测所述传感器单元输出的电流信号并生成相应的检测信号；
    所述处理电路的输入端连接所述电流检测电路的输出端，所述处理电路用于根据所述检测信号计算在所述传感器单元中发生的暗事件的能量，生成所述暗事件的能量谱图，并基于所述能量谱图计算所述传感器单元的增益。
  2. 根据权利要求1所述的装置，其特征在于，所述检测信号是数字信号，所述数字信号由持续时间相等的高电平和低电平组成，所述数字信号中的所有高电平之和与所述电流信号对时间的积分成正比。
  3. 根据权利要求2所述的装置，其特征在于，所述处理电路通过以下方式计算在所述传感器单元中发生的暗事件的能量：
    根据所述数字信号中的高电平和低电平的出现规律确定脉冲事件是否发生；
    当确定所述脉冲事件发生时开始利用所述数字信号计算所述脉冲事件的能量，直至根据所述数字信号中的高电平和低电平的出现规律确定所述脉冲事件结束为止；以及
    根据所述脉冲事件的能量判断所述脉冲事件是有效事件还是暗事件，如果所述脉冲事件是暗事件，则将所述脉冲事件的能量确定为所述暗事件的能量。
  4. 根据权利要求3所述的装置，其特征在于，所述能量谱图的横轴表示所述暗事件的能量，所述能量谱图的纵轴表示计算得到所述暗事件的能量的次数，
    所述处理电路通过以下方式计算所述传感器单元的增益：
    根据所述能量谱图中的、与单个暗事件的能量相对应的第一谱峰的横坐标计算所述增益，或根据所述第一谱峰的横坐标和所述能量谱图中的、与两个暗事件的能量相对应的第二谱峰的横坐标之间的差计算所述增益。
  5. 根据权利要求2所述的装置，其特征在于，所述处理电路通过以下 方式计算在所述传感器单元中发生的暗事件的能量：
    根据所述数字信号中的高电平和低电平的出现规律确定有效事件未发生的时间段；
    从在有效事件未发生的时间段内生成的数字信号中选择在预定时段内生成的数字信号；以及
    根据所述在预定时段内生成的数字信号计算所述暗事件的能量。
  6. 根据权利要求5所述的装置，其特征在于，所述预定时段设定为使得在所述预定时段内的平均暗事件个数满足第一预设条件，所述能量谱图的横轴表示所述暗事件的能量，所述能量谱图的纵轴表示计算得到所述暗事件的能量的次数，所述能量谱图包括多个谱峰并且所述能量谱图中的第N个谱峰与N个暗事件的能量相对应，
    所述处理电路通过以下方式计算所述传感器单元的增益：
    根据所述能量谱图中的、任意两个相邻谱峰的横坐标之间的差计算所述增益。
  7. 根据权利要求6所述的装置，其特征在于，所述第一预设条件是所述平均暗事件个数小于20。
  8. 根据权利要求5所述的装置，其特征在于，所述预定时段设定为使得在所述预定时段内的平均暗事件个数满足第二预设条件，所述能量谱图的横轴表示所述暗事件的能量，所述能量谱图的纵轴表示计算得到所述暗事件的能量的次数，
    所述处理电路通过以下方式计算所述传感器单元的增益：
    对所述能量谱图进行高斯拟合以获得所述能量谱图的方差和均值，并且将所述方差除以所述均值以获得所述增益。
  9. 根据权利要求8所述的装置，其特征在于，所述第二预设条件是所述平均暗事件个数大于20。
  10. 根据权利要求1至9任一项所述的装置，其特征在于，所述处理电路进一步用于根据所述检测信号计算在所述传感器单元中发生的有效事件的能量E0，并且根据以下公式对所述有效事件的能量E0进行校正：
    E＝E0*G0/G，
    其中，E为经校正的能量，G为所述增益，G0为预定常数。
  11. 一种用于测量传感器增益的设备，包括与传感器阵列中的多个传 感器单元一一对应的多个如权利要求1至9任一项所述的用于测量传感器增益的装置。
  12. 根据权利要求11所述的设备，其特征在于，所述处理电路进一步用于根据所述检测信号计算在对应传感器单元中发生的有效事件的能量E0，并且根据以下公式对所述有效事件的能量E0进行校正：
    E＝E0*G0/G，
    其中，E为经校正的能量，G为所述对应传感器单元的增益，G0为预定常数。
  13. 一种用于测量传感器增益的方法，包括：
    检测所述传感器单元输出的电流信号并生成相应的检测信号；
    根据所述检测信号计算在所述传感器单元中发生的暗事件的能量；
    生成所述暗事件的能量谱图；以及
    基于所述能量谱图计算所述传感器单元的增益。
  14. 根据权利要求13所述的方法，其特征在于，所述检测信号是数字信号，所述数字信号由持续时间相等的高电平和低电平组成，所述数字信号中的所有高电平之和与所述电流信号对时间的积分成正比。
  15. 根据权利要求14所述的方法，其特征在于，所述计算在所述传感器单元中发生的暗事件的能量包括：
    根据所述数字信号中的高电平和低电平的出现规律确定脉冲事件是否发生；
    当确定所述脉冲事件发生时开始利用所述数字信号计算所述脉冲事件的能量，直至根据所述数字信号中的高电平和低电平的出现规律确定所述脉冲事件结束为止；以及
    根据所述脉冲事件的能量判断所述脉冲事件是有效事件还是暗事件，如果所述脉冲事件是暗事件，则将所述脉冲事件的能量确定为所述暗事件的能量。
  16. 根据权利要求15所述的方法，其特征在于，所述能量谱图的横轴表示所述暗事件的能量，所述能量谱图的纵轴表示计算得到所述暗事件的能量的次数，
    所述计算所述传感器单元的增益包括：
    根据所述能量谱图中的、与单个暗事件的能量相对应的第一谱峰 的横坐标计算所述增益，或根据所述第一谱峰的横坐标和所述能量谱图中的、与两个暗事件的能量相对应的第二谱峰的横坐标之间的差计算所述增益。
  17. 根据权利要求14所述的方法，其特征在于，所述计算在所述传感器单元中发生的暗事件的能量包括：
    根据所述数字信号中的高电平和低电平的出现规律确定有效事件未发生的时间段；
    从在有效事件未发生的时间段内生成的数字信号中选择在预定时段内生成的数字信号；以及
    根据所述在预定时段内生成的数字信号计算所述暗事件的能量。
  18. 根据权利要求17所述的方法，其特征在于，所述预定时段设定为使得在所述预定时段内的平均暗事件个数满足第一预设条件，所述能量谱图的横轴表示所述暗事件的能量，所述能量谱图的纵轴表示计算得到所述暗事件的能量的次数，所述能量谱图包括多个谱峰并且所述能量谱图中的第N个谱峰与N个暗事件的能量相对应，
    所述计算所述传感器单元的增益包括：
    根据所述能量谱图中的、任意两个相邻谱峰的横坐标之间的差计算所述增益。
  19. 根据权利要求18所述的方法，其特征在于，所述第一预设条件是所述平均暗事件个数小于20。
  20. 根据权利要求17所述的方法，其特征在于，所述预定时段设定为使得在所述预定时段内的平均暗事件个数满足第二预设条件，所述能量谱图的横轴表示所述暗事件的能量，所述能量谱图的纵轴表示计算得到所述暗事件的能量的次数，
    所述计算所述传感器单元的增益包括：
    对所述能量谱图进行高斯拟合以获得所述能量谱图的方差和均值；以及
    将所述方差除以所述均值以获得所述增益。
  21. 根据权利要求20所述的方法，其特征在于，所述第二预设条件是所述平均暗事件个数大于20。
  22. 根据权利要求13至21任一项所述的方法，其特征在于，所述方 法进一步包括：
    根据所述检测信号计算在所述传感器单元中发生的有效事件的能量E0；以及
    根据以下公式对所述有效事件的能量E0进行校正：
    E＝E0*G0/G，
    其中，E为经校正的能量，G为所述增益，G0为预定常数。
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