JP2019007803A - Light detector - Google Patents

Abstract

To provide a light detector with which it is possible to adjust noise processing on the output signal of a photo multiplier and suppress the leakage of pulse counts by a counter.SOLUTION: The light detector comprises a photo multiplier (12), an amplification circuit (20), a peak value discrimination circuit (30) and a pulse width setting circuit (42). The photo multiplier (12) photoelectrically converts light from a light-emitting source (11) and outputs an electric signal. The amplification circuit (20) amplifies the output signal of the photo multiplier (12). The peak value discrimination circuit (30) discriminates an output signal, out of the output signals of the amplification circuit (20), whose peak value is greater than or equal to a threshold and outputs the discriminated output signal. A threshold adjuster (31) is capable of adjusting the threshold. The pulse width setting circuit (42) extends the pulse width of the output signal of the peak value discrimination circuit (30) on the basis of a previously adjusted pulse width and outputs the extended signal to a counter that counts the number of pulses.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a photodetection device that detects photons.

  With regard to the technology for accurately measuring faint light, the importance in the medical field, the environmental field, the astronomical observation field, etc. is not limited. FIG. 1 shows a circuit configuration of a conventional chemiluminescence detector used in an immunoassay technique using chemiluminescence.

  A counting unit 1 for detecting photons includes a sensor module 2, an amplifier 3, and a discriminator (wave height discriminator) 4. The sensor module 2 includes, for example, a photomultiplier tube, a high voltage power supply circuit, and a voltage dividing circuit. Photons to be detected are converted into photoelectrons amplified through a photomultiplier tube in the sensor module 2 of the counting unit 1, and then converted into a pulse waveform amplified by the amplifier 3.

  Normally, this pulse waveform contains electrical noise (dark count) that does not originate from photons. After the signal below a predetermined peak value is discarded through the discriminator 4, the pulse waveform is guided to the counter 5 and photometric data is obtained. Get. In Patent Document 1, a photon counting circuit corresponding to the above-described counting unit 1 is used for weak light, and a direct current component derived from photons is measured for relatively strong light (C -P converter), and a technique of properly using a circuit according to the amount of light is disclosed.

JP-A-3-181825

  Since the counting unit 1 shown in FIG. 1 is packaged, the discriminator 4 in the counting unit 1 lacks versatility. For this reason, the discriminating process of the discriminator 4 cannot be easily changed in consideration of individual differences in the sensitivity of the photomultiplier tube and the purpose of use. Also, as the pulse width of the output signal of the discriminator 4 is smaller, there is a possibility that a part of the pulse signal input to the counter 5 cannot be counted depending on the count performance of the counter 5.

  An object of the present invention is to provide a photodetector that can adjust noise processing for an output signal of a photomultiplier tube and can suppress leakage of the number of pulses by a counter.

  The photodetector according to the present invention includes a photomultiplier tube, an amplifier circuit, a peak value discriminating circuit, a threshold adjuster, and a pulse width setting circuit. The photomultiplier tube photoelectrically converts light from the light source and outputs an electrical signal. The amplifier circuit amplifies the output signal of the photomultiplier tube. The peak value discriminating circuit discriminates and outputs an output signal having a peak value equal to or greater than a threshold value among the output signals of the amplifier circuit. The threshold adjuster can adjust the threshold. The pulse width setting circuit expands the pulse width of the output signal of the peak value discriminating circuit based on the pulse width adjusted in advance, and outputs the expanded signal to a counter that counts the number of pulses.

  The counter counts the number of pulses based on the output signal of the pulse width setting circuit. The counter can be arranged outside the light detection device or can be built in the light detection device. When the counter is arranged outside the photodetection device, the counter and the photodetection device may be connected by wire or wirelessly.

  The amplifier circuit can be composed of a plurality of operational amplifiers connected in series. For example, by connecting two operational amplifiers having high slew rate characteristics (for example, 500 V / μs) in series, a desired gain can be easily secured. Specifically, if an operational amplifier with a gain of 4 and an operational amplifier with a gain of 6 are connected in series, the gain of the amplifier circuit can be increased to 24 times.

  The peak value discriminating circuit can be constituted by a comparator and an LVDS receiver connected to each other. The comparator compares the output signal of the amplifier circuit with the threshold adjusted by the threshold adjuster. Specifically, the peak value discriminating circuit can be composed of a high-speed comparator that supports LVDS (low voltage differential signal) output and an operational amplifier for LVDS receiver. By using an LVDS-compatible high-speed comparator and an LVDS receiver operational amplifier, high-speed data transmission is possible, and radiated electromagnetic noise can be reduced.

  The photodetection device according to the present invention can be provided with a pulse width adjuster for adjusting the pulse width expanded by the pulse width setting circuit. By using the pulse width adjuster, the pulse width can be arbitrarily changed in consideration of the count performance of the counter.

  According to the present invention, since the peak value discriminating circuit can adjust the threshold value, the threshold value can be adjusted in consideration of individual differences in the sensitivity of the photomultiplier tube, the purpose of use, and the like. Thereby, an appropriate noise process can be performed with respect to the output signal of a photomultiplier tube. Further, since the pulse width setting circuit extends the pulse width of the output signal of the peak value discriminating circuit, the output signal of the pulse width setting circuit (in other words, the input signal of the counter) becomes a signal that the counter can easily count. , Leakage of the pulse count by the counter can be suppressed.

It is a block diagram which shows the circuit structure of the conventional chemiluminescence detector. It is a block diagram which shows the circuit structure of the photon detection apparatus which is this embodiment. It is an enlarged view which shows the waveform of the input signal of an amplifier circuit. It is a figure which shows the waveform of the output signal of an amplifier circuit. It is a figure which shows the waveform of the output signal of a peak value discrimination circuit. It is the figure which expanded the time width rather than FIG. 4A about the waveform of the output signal of an amplifier circuit. It is the figure which expanded time width about the waveform of the output signal of a crest value discrimination circuit rather than Drawing 4B.

  A photodetecting device according to an embodiment of the present invention will be described. The photodetection device of this embodiment detects photons, and FIG. 2 shows a circuit configuration example of the photodetection device 10 of this embodiment.

  Photons generated from the chemiluminescence source 11 are received by a photomultiplier tube 12 that operates by receiving electric power from a high-voltage power supply 13, and is converted into an electric signal by photoelectric conversion processing. An amplifying circuit 20 is connected to the photomultiplier tube 12, and an output signal of the photomultiplier tube 12 is input to the amplifying circuit 20. Here, one end of the termination resistor element 14 is connected to the connection line between the photomultiplier tube 12 and the amplifier circuit 20, and the other end of the termination resistor element 14 is grounded.

  By using the termination resistance element 14, the current value of the output signal of the photomultiplier tube 12 can be converted into a voltage value. Therefore, the voltage value of the output signal of the photomultiplier tube 12 is input to the amplifier circuit 20. FIG. 3 shows an enlarged view of the waveform of the input signal of the amplifier circuit 20. In FIG. 3, the vertical axis represents voltage values, and the horizontal axis represents time. According to FIG. 3, a waveform derived from photons (a peak waveform having a peak height of approximately 20 mV and a peak width of approximately 2 ns) can be observed in a state including a noise peak.

  The amplifier circuit 20 amplifies the input signal (voltage value). The operational amplifier used in the amplifier circuit 20 is required to have a high slew rate characteristic (for example, 500 V / μs), but the gain is limited. Therefore, in this embodiment, the amplifier circuit 20 is configured as a two-stage operational amplifier (the first-stage operational amplifier 21 and the post-stage operational amplifier 22), so that the gain of the amplifier circuit 20 is secured while ensuring high slew rate characteristics.

  The input terminal of the first stage operational amplifier 21 is connected to the photomultiplier tube 12, and the output terminal of the first stage operational amplifier 21 is connected to the input terminal of the subsequent stage operational amplifier 22. For example, by setting the gain of the first stage operational amplifier 21 to 4 times and the gain of the subsequent stage operational amplifier 22 to 6 times, the amplification circuit 20 including the first stage operational amplifier 21 and the subsequent stage operational amplifier 22 can secure a gain of 24 times.

  In the present embodiment, the two operational amplifiers 21 and 22 are connected in series, but the present invention is not limited to this. Specifically, the amplifier circuit 20 can be configured by connecting three or more operational amplifiers in series.

  FIG. 4A shows a waveform obtained by observing the output signal (amplified signal) of the amplifier circuit 20 with an oscilloscope in a time period of about 14 μs. In FIG. 4A, the vertical axis represents voltage values, and the horizontal axis represents time. In the present embodiment, since the gain of the amplifier circuit 20 is set to a negative gain, the signal polarity is different between the input signal of the amplifier circuit 20 (see FIG. 3) and the output signal of the amplifier circuit 20 (see FIG. 4A). (Plus or minus) is inverted, and in FIG. 4A, an upward peak is mainly obtained.

  A crest value discriminating circuit 30 is connected to the amplifying circuit 20, and an output signal of the amplifying circuit 20 is input to the crest value discriminating circuit 30. The peak value discriminating circuit 30 outputs a signal equal to or higher than a threshold value (voltage value) among the input signals as a pulse signal. The peak value discriminating circuit 30 includes a threshold adjuster 31 for adjusting a threshold, a comparator 32 corresponding to LVDS (Low Voltage Differential Signaling) output, and an operational amplifier 33 for LVDS receiver. By using the comparator 32 and the operational amplifier 33, high-speed data transmission can be performed between the comparator 32 and the operational amplifier 33, and radiated electromagnetic noise can be reduced. The peak value discriminating circuit 30 only needs to be able to output (discriminate) a signal equal to or higher than the threshold value as described above, and a circuit different from the circuit described in the present embodiment can also be used.

  The output terminal of the amplifier circuit 20 (specifically, the post-stage operational amplifier 22) is connected to the first input terminal of the comparator 32, and the output signal of the amplifier circuit 20 is input to the first input terminal of the comparator 32. . A threshold adjuster 31 is connected to the second input terminal of the comparator 32, and the threshold adjusted by the threshold adjuster 31 is input to the second input terminal of the comparator 32. The comparator 32 compares the output signal (voltage value) of the amplifier circuit 20 with the threshold value (voltage value) adjusted by the threshold adjuster 31 and outputs a signal equal to or higher than the threshold value. The operational amplifier 33 generates a pulse signal based on the output signal of the comparator 32.

  Here, the pulse width of the signal output from the peak value discriminating circuit 30 is the same as the peak width of the signal input to the amplifier circuit 20 (specifically, the peak width (approximately 2 ns shown in FIG. 3)). . When the pulse width is short as described above, when the pulse signal output from the peak value discriminating circuit 30 is counted by the counter 43 described later, a part of the pulse signal may not be counted depending on the count performance of the counter 43.

  Therefore, in the present embodiment, a pulse width setting circuit 42 is provided between the peak value discriminating circuit 30 and the counter 43 in order to suppress pulse signal count leakage. Specifically, the input terminal of the pulse width setting circuit 42 is connected to the output terminal of the peak value determination circuit 30, and the output terminal of the pulse width setting circuit 42 is connected to the input terminal of the counter 43.

  The pulse width setting circuit 42 sets the pulse width of the output signal (pulse signal) of the peak value discriminating circuit 30. Here, a pulse width adjuster 41 is connected to the pulse width setting circuit 42, and information on the pulse width adjusted by the pulse width adjuster 41 is input to the pulse width setting circuit 42. The pulse width setting circuit 42 changes the pulse width of the output signal of the peak value discriminating circuit 30 to the pulse width adjusted by the pulse width adjuster 41. The pulse width adjuster 41 is adjusted to a pulse width (for example, several tens to 100 ns, preferably 20 ns) according to the count performance of the counter 43 so that the pulse signal can be counted without omission. In the present embodiment, the pulse width of the output signal of the peak value discriminating circuit 30 is extended by the pulse width adjuster 41 and the pulse width setting circuit 42 so that the counter 43 can count the pulse signal without omission.

  An output signal (pulse signal) of the pulse width setting circuit 42 is input to the counter 43. The counter 43 counts the number of pulses based on the pulse signal output from the pulse width setting circuit 42.

  FIG. 4B shows the waveform of the output signal of the pulse width setting circuit 42. In the waveform shown in FIG. 4B, only three signals exceeding the threshold are extracted from the signals shown in FIG. 4A. Here, the waveform shown in FIG. 4A and the waveform shown in FIG. 4B have the same phase. Although not recognized in FIG. 4B, the pulse width of the waveform shown in FIG. 4B is expanded compared to the waveform shown in FIG. 4A.

  Here, FIGS. 5A and 5B are diagrams showing the waveforms shown in FIGS. 4A and 4B when the time axis of FIGS. 4A and 4B is enlarged 10 times, respectively. The waveform shown in FIG. 5A corresponds to the waveform of the region R1 shown in FIG. 4A, and the waveform shown in FIG. 5B corresponds to the waveform of the region R2 shown in FIG. 4B. In the waveform shown in FIG. 5A, the pulse width (peak width) is several ns, whereas in the waveform shown in FIG. 5B, the pulse width (peak width) is extended to about 60 ns. By extending the pulse width (peak width) in this way, it is possible to prevent the counting performance of the counter 43 from counting a part of the pulse signal and improve the accuracy of the counting process.

  In the present embodiment, as shown in FIG. 2, the light detection device 10 includes the counter 43, but this is not a limitation. Specifically, a counter 43 can be provided outside the light detection device 10 and the light detection device 10 and the counter 43 can be connected by wire or wirelessly. In this case, the output signal of the pulse width setting circuit 42 is transmitted to the counter 43 via wired or wireless.

DESCRIPTION OF SYMBOLS 1 Counting unit 2 Sensor module 3 Operational amplifier 4 Discriminator 5 Counter 10 Photodetection device 11 Chemiluminescence source 12 Photomultiplier tube 13 High voltage power supply 14 Termination resistor element 20 Amplifying circuit 21 First stage operational amplifier 22 Later stage operational amplifier 30 Crest value discrimination circuit 31 Threshold value Adjuster 32 Comparator (LVDS output compatible)
33 Operational amplifier (LVDS receiver)
41 Pulse width adjuster 42 Pulse width setting circuit 43 Counter

Claims (5)

A photomultiplier tube that photoelectrically converts light from the light source and outputs an electrical signal;
An amplifier circuit for amplifying the output signal of the photomultiplier;
Among the output signals of the amplifier circuit, a peak value discriminating circuit for discriminating and outputting an output signal whose peak value is equal to or greater than a threshold value;
A threshold adjuster for adjusting the threshold;
A pulse width setting circuit that expands the pulse width of the output signal of the peak value discriminating circuit based on a pre-adjusted pulse width, and outputs the expanded signal to a counter that counts the number of pulses;
A photodetection device comprising:   The photodetecting device according to claim 1, comprising the counter.   The photodetecting device according to claim 1, wherein the amplifier circuit includes a plurality of operational amplifiers connected in series. The peak value discrimination circuit is:
A comparator that compares the output signal of the amplifier circuit with the threshold adjusted by the threshold adjuster;
An LVDS receiver connected to the comparator;
The photodetection device according to claim 1, wherein the photodetection device includes:   5. The photodetection device according to claim 1, further comprising a pulse width adjuster that adjusts a pulse width expanded by the pulse width setting circuit.

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