KR20240051704A - Optical transceiver and method for removing after pulse for the same - Google Patents

Abstract

An optical transceiver and a method for removing an after-pulse of the optical transceiver are provided. The optical transceiver uses an optical transmitter that transmits optical pulses at a preset period and a solid state photon multiplexer (SSPM) equipped with a plurality of SPADs (Single Photon Avalanche Diodes), and receives reflected light corresponding to the optical pulses to produce an optical reception signal. It includes a light receiving unit that outputs and a signal processing unit that performs signal processing on the light receiving signal input from the light receiving unit. The signal processing unit selects a first effective peak from the optical reception signal corresponding to a given optical pulse, and selects the first effective peak based on a peak level ratio relative to the first effective peak and a time interval from the first effective peak. It is configured to remove the after-pulse peak from among the peaks following the peak.

Description

Optical transceiver and after-pulse removal method of optical transceiver {OPTICAL TRANSCEIVER AND METHOD FOR REMOVING AFTER PULSE FOR THE SAME}

The present invention relates to a method for removing peaks caused by after-pulses included in an optical reception signal and an optical transceiver using the same.

The content described in this section simply provides background information about the present invention and does not constitute prior art.

In SPAD (Single Photon Avalanche Diode), which is used to detect reflected light in LiDAR devices, some of the charge carriers generated during the avalanche phenomenon do not disappear immediately. Charge carriers that are not completely annihilated remain inside the avalanche photodiode, generating an avalanche when the next gate signal GS is applied to the avalanche photodiode. This phenomenon is called the after pulse noise effect.

Figure 7 shows the theoretical waveform of the after pulse. After-pulses often occur due to the process characteristics, especially in compound semiconductors using a 1550 nm wavelength. Since the after-pulse can be confused with the pulse caused by the actual input optical signal, it is necessary to reduce the after-pulse phenomenon or remove it from the signal processing process.

In the case of a SPAD that uses only a single cell as shown in (a) of Figure 8, quenching occurs immediately after receiving the first optical signal, and a dead time (dead time) occurs during which the optical signal cannot be received for a certain period of time. It enters a deadtime period and cannot operate as a receiver during this period. To overcome these shortcomings, SSPM (Solid State Photon Multiplexer) is used. SSPM, for example, creates hundreds of SPAD elements in the form of microcells and connects them in parallel with a quenching resistor, as shown in (b) of FIG. 8.

LiDAR or gas sensors using LiDAR are asynchronous systems that do not know when the transmitted optical signal will be received, and there are two main advantages when SSPM is used in such systems. First, when an optical signal is input, it is intended to eliminate dead time by using the fact that not all microcells receive the optical signal and therefore are not quenched in all microcells. Second, using SSPM, the intensity of the input optical signal can be measured.

Looking at the first advantage, which is advantageous in eliminating dead time, we can see that dead time can be controlled by using an actual example of a shape made of an actual semiconductor and a shape in which optical signals are actually received by this semiconductor.

Figure 9(a) is the layout of SSPM with multiple SPADs arranged. The area indicated by a circle in (b) of FIG. 9 is the area where the optical signal according to the distance arrives. As can be seen from the figure, the number of SPAD microcells in the area where light actually reaches is limited. As a result, only the SPADs included in the cells to which the optical signal has arrived are quenched and enter a dead time situation, and the remaining microcells become operable, allowing immediate continuous operation without dead time.

In fact, when an optical signal is input in a system using this, minute light in photon units is often detected, so the stochasticity of light is applied even in situations where there is no extreme change in position as described above, and the optical signal reaches almost the same position. Even though some SPADs are detected, some SPADs are not detected, and continuous operation is possible.

The second advantage is that the output level is detected according to the intensity of the input light. In (b) of FIG. 8, when the optical signal does not reach all SPADs, the reverse voltage is applied to all SPADs, so current does not flow, and as a result, the voltage is maintained at a constant value.

In a situation of constant voltage without any optical signal, if an optical signal (hv) is transmitted to several SPADs (or photo-diodes) as shown in (b) of FIG. 8, where h is Planck constant and v is the optical frequency (photon's) frequency) is reached, the SPAD is in a short state where current flows, and as soon as the short state is reached, it goes into the quenching state again, creating an electrical pulse at the time of input of the optical signal. At this time, the resistor connected to the circuit with the shorted diode or SPAD creates a current path created by the bias voltage, and the resulting pulse becomes the output waveform. According to this principle, assuming that the resistance that appears in the circuit when one microcell, that is, a SPAD, receives an optical signal is the value R, when two SPADs receive an optical signal, two resistances with the value R are A circuit connected in parallel is created, and when N SPADs receive optical signals, an electronic circuit is created in which N resistors with R values are connected in parallel.

Based on this, if the relationship between the generated voltage level and the input photon number (proportional to the intensity of light) is drawn as a graph, the graph is as shown in FIG. 10. Since the output level according to the intensity of the input light is detected in this way, it is used in sensor applications that need to determine the intensity of the received light.

Continuous optical signal detection operation is possible even if some of the microcells of the SSPM are in a dead time situation, but the output signal of the SSPM may have afterpulse noise caused by some of the microcells, and measures to remove this afterpulse noise are required. This is needed.

The purpose of the present invention is to provide a method for removing after-pulse noise from an output signal of an optical transceiver and an optical transceiver using the same.

According to one embodiment of the present invention, the optical transceiver uses an optical transmitter that transmits optical pulses at a preset period and a solid state photon multiplexer (SSPM) having a plurality of SPADs (Single Photon Avalanche Diodes), It includes a light receiver that receives reflected light corresponding to the pulse and outputs a light reception signal. The optical transceiver further includes a signal processor that performs signal processing on the optical reception signal input from the optical receiver, and a control unit that controls the optical transmitter, the optical receiver, and the signal processor. The signal processing unit selects a first effective peak from the optical reception signal corresponding to a given optical pulse, and selects the first effective peak based on a peak level ratio relative to the first effective peak and a time interval from the first effective peak. It is configured to remove the after-pulse peak from among the peaks following the peak.

In some embodiments, the signal processing unit selects a peak whose peak level ratio is less than or equal to a preset first threshold and where the time interval is within a preset first threshold range among peaks following the first effective peak as an after pulse. It may be configured to determine by peak.

In some embodiments, the signal processing unit selects a second effective peak following the first effective peak, and selects the second effective peak based on a peak level ratio relative to the second effective peak and a time interval from the second effective peak. It may be configured to remove the after-pulse peak from among the peaks following the second effective peak. The signal processing unit is configured to determine, among peaks following the second effective peak, a peak whose peak level ratio is less than or equal to a preset first threshold and where the time interval is within a preset first threshold range as the after pulse peak. It can be.

In some embodiments, the control unit may be configured to select the first threshold value that the signal processor will use to remove the after-pulse peak from among a plurality of predefined threshold values.

In some embodiments, the control unit may be configured to select the first threshold range that the signal processor will use to remove the after-pulse peak from among a plurality of predefined threshold ranges.

In some embodiments, the signal processing unit is configured to detect effective peaks among peaks included in the light reception signal, and determine the amount of received light corresponding to the detected effective peak and the distance from the reflector corresponding to the detected peak. It can be.

In some embodiments, signal processing for the optically received signal includes a plurality of processes sequentially performed in the digital domain, and the signal processing unit may be configured to perform the plurality of processes in a pipeline processing method.

According to one embodiment of the present invention, in an optical transceiver using an SSPM with a plurality of SPADs to receive reflected light corresponding to an optical pulse transmitted at a preset period, a method for removing the after-pulse peak from the optical reception signal is provided. do. The method includes selecting a first effective peak from an optically received signal corresponding to a given optical pulse, and selecting the first effective peak based on a peak level ratio relative to the first effective peak and a time interval from the first effective peak. and removing the after-pulse peak from among the peaks following the peak.

The method includes selecting a second valid peak subsequent to the first valid peak, and selecting a second valid peak based on a peak level ratio relative to the second valid peak and a time interval from the second valid peak. It further includes removing the after-pulse peak from the subsequent peaks.

According to embodiments of the present invention, detection performance can be improved by effectively removing peaks caused by the after-pulse from the optical reception signal output from the SSPM.

1 is a block diagram showing the internal configuration of an optical transceiver according to a preferred embodiment of the present invention.
Figure 2 is a block diagram showing the signal processing process in an optical transceiver.
Figure 3 is a block diagram showing the detailed processing of each signal processing process.
Figure 4 is a diagram conceptually showing the relationship between two pulses.
Figure 5 shows an example of continuous pulse reception due to diffuse reflection.
Figure 6 shows an example of continuous pulse reception due to reflected light reflected from a glass window.
Figure 7 is a theoretically simulated waveform diagram of the after pulse.
Figure 8 is a circuit diagram of SPAD and SSPM.
Figure 9 (a) shows the layout of the SSPM with multiple SPADs arranged, and (b) shows the area where the optical signal reaches the SSPM.
Figure 10 is a graph showing the relationship between the number of photons incident on the SSPM and the output voltage level.

Hereinafter, embodiments of the present invention will be described in detail with reference to the exemplary drawings. When adding reference numerals to components in each drawing, it should be noted that identical components are given the same reference numerals as much as possible even if they are shown in different drawings. Additionally, in describing the present embodiments, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present embodiments, the detailed description will be omitted.

Additionally, in describing the components of the present embodiments, terms such as first, second, A, B, (a), and (b) may be used. These terms are only used to distinguish the component from other components, and the nature, order, or order of the component is not limited by the term. Throughout the specification, when a part is said to 'include' or 'have' a certain component, this means that it does not exclude other components but may further include other components, unless specifically stated to the contrary. . In addition, ‘…’ stated in the specification. Terms such as 'unit' and 'module' refer to a unit that processes at least one function or operation, which may be implemented as hardware, software, or a combination of hardware and software.

The detailed description set forth below in conjunction with the accompanying drawings is intended to illustrate exemplary embodiments of the invention and is not intended to represent the only embodiments in which the invention may be practiced.

The technology disclosed in this specification is related to an optical transceiver that uses a solid state photon multiplexer (SSPM) equipped with a plurality of single photon avalanche diodes (SPADs) to receive reflected light corresponding to optical pulses transmitted at a preset period. As explained in detail below, the optical transceiver considers the peak following a given peak as an after-pulse peak and removes it based on the 'time interval' and 'level ratio' between peaks identified in the optical reception signal output from the SSPM. You can decide whether to treat it as another peak caused by the actual reception of an optical signal.

When continuous light detection is performed using SSPM, there are cases where meaningful peaks (i.e., signals resulting from actual light reception) occur continuously within a short period of time in the light reception signal that is their output. These continuous peaks may be noise caused by the after-pulse, but may also be meaningful pulses caused by the reception of an actual optical signal.

Figure 5 shows an example of continuous peak generation due to diffuse reflection. If you want to fire laser light with an optical transmitter and receiver such as LiDAR in a closed space and receive the reflected light, the light is emitted as a red arrow in the same shape as (a), and is also reflected as a red arrow. The return result of transmission and reception is expected. However, in reality, light is not reflected in only one path. This is because the surface of the object is not smooth, causing diffuse reflection. In reality, light is reflected in all directions and is created in various paths, such as the blue path shown as an example in (b) of Figure 5. In Figure 5, only one diffuse reflection path is shown for convenience, but in reality, many light paths can be created. In optical design, it is intended to prevent reflected light from unwanted paths, but in reality, it is impossible to prevent all diffuse reflections, so many optical signals are received.

In the above case, if the lengths of the straight path and the diffuse reflection path are similar, two very close consecutive peaks appear in the optical reception signal. Additionally, when light is transmitted and received in a very open space, there are cases where the reflection of light by the previously emitted transmitted light due to continuous laser transmission is received after the subsequent light is transmitted.

Figure 6 shows another example, where light is reflected from an object beyond a window. The emitted light first reflects off the glass window and then returns to be received. The light that passes through the glass window is then reflected from the object beyond the window and returned again. In this case as well, continuous peaks occur in the optical reception signal, and here both peaks are meaningful information.

Therefore, it is necessary to distinguish between meaningful peaks and after-pulse peaks among continuous peaks that may appear in the optical reception signal. Although there are differences depending on the physical characteristics or operating environment of the SSPM, the after-pulse occurs at a predetermined time interval from the actual pulse generated by reflected light, and the larger the time interval, the smaller the pulse level. According to the experiment, the after-pulse occurred at intervals of about 4 to 8 ns with a time difference from the actual pulse. Additionally, the level occurred at a magnitude of about 50 to 75% of the level of the preceding pulse.

Therefore, considering the statistical time characteristics and level characteristics at which the after-pulse occurs, a peak that occurs within a certain time interval from the first peak in the optical reception signal and shows certain level characteristics can be considered an after-pulse (i.e., noise). You can.

When processing the optical reception signal output from the SSPM, the optical transceiver selects peaks above a certain level through preprocessing such as noise removal, and performs the task of removing peaks caused by the after pulse for the selected peaks. You can. At this time, the first peak among the selected peaks is regarded as a valid peak, and whether the subsequent peaks are peaks caused by the after pulse can be determined in the following manner.

For example, as indicated by the dotted line in FIG. 4, the optical transceiver sets a threshold level having a specific ratio to the level of the first peak, and removes peaks that have a level below the threshold level and occur within a specific time interval. can do. If a peak subsequent to the first peak has a level greater than the threshold level or occurs outside a specific time interval, the optical transceiver may determine that the subsequent peak is another valid peak.

In one embodiment, the optical transceiver may select a threshold ratio to be used to remove peaks caused by the after-pulse from among various predefined level ratios.

ratio combination ratio(%) code R0 100 1111 R1+R2+R3 87.5 1110 R1+R2 75 1101 R1+R2-R3 62.5 1100 R1 50 1011 R1-R3 37.5 1010 R2 25 1001 R3 12.5 1000 NO PASS NO PASS 0000

Table 1 shows the ratio of sizes between peaks in one example. In Table 1, R1 represents 50%, R2 represents 25%, and R3 represents 12.5%, and the ratio of levels is expressed as a combination of these. Since the temporal characteristics and level characteristics of the after pulse may vary depending on the SSPM element actually included in the optical transceiver or the environment within the optical transceiver in which the SSPM element is driven, an appropriate rate and time interval can be set in the calibration step for each optical transceiver. there is.

Among the consecutive peaks that can appear in the optical reception signal, whether each peak following the first peak (i.e., effective peak) is an after-pulse peak is determined by the ratio of the peak level relative to the immediately preceding effective peak and the time interval from the immediately preceding effective peak. It can be decided based on . For example, an after-pulse peak may be determined among peaks following the first effective peak based on the peak level ratio relative to the first effective peak and the time interval from the first effective peak. Additionally, a second effective peak subsequent to the first effective peak (i.e., a peak that is not determined to be an afterpulse peak with respect to the first effective peak) is selected, and the peak level ratio relative to the second effective peak is calculated from the second effective peak. An after-pulse peak may be determined among peaks following the second effective peak based on the time interval of .

In some embodiments, a combination of two or more peak level ratios and time intervals may be used. For example, the optical transceiver may select peaks that satisfy a first time interval (e.g., 4 to 6 ns) and a first peak level ratio (e.g., 75%) in a plurality of peaks following a given effective peak and a first peak level ratio (e.g., 75%). Peaks that satisfy a 2 time interval (eg, 6 to 8 ns) and a second peak level ratio (eg, 50%) may be determined as after-pulse peaks.

Hereinafter, an embodiment of an optical transceiver employing the technique for removing the above-described after-peak will be described with reference to FIG. 1. Figure 1 is a block diagram conceptually showing the configuration of an optical transmitter and receiver. The optical transceiver 100 includes an optical transmitter 120 including a light emitting diode and a lens module, an optical receiver 130 that receives light reflected and incident from a reflector and converts it into an electrical signal, and a signal processor that performs signal processing of the reflected light. (140), and a control unit 110 that controls the optical transmitting unit 120, the optical receiving unit 130, and the signal processing unit 140 to perform laser light emission, reception, and signal processing.

Figure 1 shows a case where the control unit 110 and the signal processing unit 140 are provided separately, but depending on the embodiment, the functions of the control unit 110 and the signal processing unit 140 may be configured to be processed in one device. there is.

The control unit 110 and the signal processing unit 140 may be implemented as a custom very-large-scale integration (VLSI) circuit or a hardware circuit including semiconductors such as a gate array, logic chip, and transistor. The control unit 110 and the signal processing unit 140 may also be implemented as programmable hardware devices such as a field programmable gate array (FPGA), programmable array logic, programmable logic devices, etc.

The light emitting diode of the optical transmitter 120 emits laser light (i.e., optical pulse) having a constant pulse width at a set period. That is, the optical transmitter 120 transmits a train of optical pulses. The light pulse strikes an object, is reflected, and returns to the optical transceiver 100. The optical receiver 130 converts the received optical signal into an electrical optical reception signal. The light receiving unit 130 is equipped with a solid state photon multiplexer (SSPM) using a single photon avalanche diode. The signal processing unit 140 may be configured to detect effective peaks among peaks included in the light reception signal, and determine the amount of received light corresponding to the detected effective peak and the distance from the reflector corresponding to the detected peak.

In addition, the signal processing unit 140 selects a first effective peak from the optical reception signal, and selects a first effective peak following the first effective peak based on the peak level ratio relative to the first effective peak and the time interval from the first effective peak. Among the peaks, it can be configured to distinguish between the after-pulse and the actual pulse. The signal processing unit 140 may be configured to determine, among peaks following the first effective peak, a peak whose peak level ratio is less than or equal to a preset first threshold and whose time interval is within a preset first threshold range as the after pulse peak. You can.

The signal processing unit 140 selects a second effective peak following the first effective peak, and selects a second effective peak following the second effective peak based on the peak level ratio relative to the second effective peak and the time interval from the second effective peak. It may be configured to remove the after-pulse peak among the peaks. The signal processing unit 140 is configured to determine, among peaks following the second effective peak, a peak whose peak level ratio is less than or equal to a preset first threshold and whose time interval is within a preset first threshold range as the after pulse peak. It can be.

The control unit 110 may be configured to select a first threshold value that the signal processing unit 140 will use to remove the after-pulse peak from among a plurality of predefined threshold values. Additionally, the control unit 110 may be configured to select a first threshold range that the signal processing unit 140 will use to remove the after-pulse peak from among a plurality of predefined threshold ranges.

Figure 2 is a flowchart showing the signal processing process for the optical reception signal performed in the optical transceiver 110. As illustrated in FIG. 2, the signal processing unit 140 of the optical transceiver 100 may signal-process data through a plurality of signal processing processes (or a plurality of signal processing blocks). These processes may be performed in a pipelined manner, for example in hardware circuitry.

The analog signal detected by the photo diode is converted into a digital signal by an analog to digital converter (ADC) and input to the signal processing unit 140. The input ADC output signal is subjected to noise removal in the preprocessing step (S10), conversion of the number of bits for parallel processing due to differences in operating clocks (for example, conversion to 64-bit data for parallel processing of eight 8-bit data), etc. It goes through a preprocessing process. In the peak detection step (S20), peaks that satisfy certain conditions are detected from the preprocessed data. In the peak selection step (S30), a predetermined number of peaks are finally selected from among the detected peaks. In the math operation step (S40), operations such as calculating distance values or counting the number of photons are performed on the remaining peaks. In the data packaging step (S50), values calculated for a predetermined number of detected peaks are packetized. Packetized information may include the distance of the final selected peak, intensity of light, information on received photons, information on the material of the reflector, etc. Packetized information can be transmitted to an external application processor.

Although FIG. 2 shows an example in which the signal processing step consists of five steps, it can be composed of various combinations of steps depending on the embodiment. Additionally, each step may be composed of a plurality of small steps.

This example is shown in Figure 3. In the example of FIG. 3, the peak detection step (S20) may include an ADC threshold cutoff step (S21) and a first peak detection step (S22). The ADC threshold cutoff step (S21) is a part that removes electrical noise from the signal input from the ADC (Analog to Digital Converter), and basically removes the ripple of the signal along with the biased electrical constant value. In general, a peak can be judged when there are three consecutive numbers and the value located in the middle is the largest. Conversely, if the value in the middle of three consecutive numbers is the smallest, it can be called a valley. The first peak detection step (S22) detects all peaks without conditions and flags all corresponding positions for use in the next processing.

The peak selection step (S30) may include a peak threshold cutoff step (S31) and a final peak selection step (S32) of selecting final peaks from the remaining peaks. Peak detection step (S20) In order to find meaningful peaks among all detected peaks, peaks recognized as noise must be removed. In the peak threshold cutoff step (S31), peaks due to electrical noise are removed by setting a threshold. That is, peaks below a predetermined threshold are removed. Depending on the embodiment, the threshold value may be determined by referring to a preset look-up table. In the final peak selection step (S32), peaks according to distance and information from previous and adjacent optical reception signals are applied to peaks other than the peaks judged to be noise and excluded, and a final number of peaks, for example, 8, is selected. Select .

The mathematical operation step (S40) includes an adjacent position cutoff step (S41) that cuts off peaks at adjacent positions, a distance calculation step (S42) that calculates the distance to the remaining peaks, and a photon number calculation step (S43). It can be provided. The adjacent position cutoff step (S41) is a step to remove noise in special situations such as after pulse. Among the predetermined number of final peaks selected in the previous step, peaks to be excluded are selected according to a preset time interval and peak level ratio as described above. As a result, for example, up to 4 peaks can be selected. In the distance calculation step (S42), the reflected distance is calculated for the selected final peaks. In the photon number calculation step (S43), the information on the received photons is quantified by referring to the intensity of light along with the distance for the final four selected peaks. In addition, by analyzing the nature of the peak, information on the material of the reflector can also be generated as a result.

The above description is merely an illustrative explanation of the technical idea of the present embodiment, and those skilled in the art will be able to make various modifications and variations without departing from the essential characteristics of the present embodiment. Accordingly, the present embodiments are not intended to limit the technical idea of the present embodiment, but rather to explain it, and the scope of the technical idea of the present embodiment is not limited by these examples. The scope of protection of this embodiment should be interpreted in accordance with the claims below, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of rights of this embodiment.

110: Control unit 120: Optical transmission unit
130: light receiving unit 140: signal processing unit

Claims (12)

An optical transmitter that transmits optical pulses at a preset period;
An optical receiver that uses a solid state photon multiplexer (SSPM) equipped with a plurality of single photon avalanche diodes (SPAD) and receives reflected light corresponding to the optical pulse to output an optical reception signal;
a signal processing unit that performs signal processing on the optical reception signal input from the optical reception unit; and
A control unit that controls the optical transmitter, the optical receiver, and the signal processor
Includes,
The signal processing unit selects a first effective peak from the optical reception signal corresponding to a given optical pulse, and selects the first effective peak based on a peak level ratio relative to the first effective peak and a time interval from the first effective peak. configured to remove the after-pulse peak from among the peaks following the peak,
Optical transmitter receiver. According to paragraph 1,
The signal processing unit
Selecting a second valid peak following the first valid peak, from among the peaks following the second valid peak based on a peak level ratio relative to the second valid peak and a time interval from the second valid peak. configured to eliminate after-pulse peaks,
Optical transmitter receiver. According to paragraph 1,
The signal processing unit
Configured to determine, among peaks following the first effective peak, a peak whose peak level ratio is less than or equal to a preset first threshold and where the time interval is within a preset first threshold range as an after-pulse peak,
Optical transmitter receiver. According to paragraph 3,
The control unit is configured to select the first threshold value to be used by the signal processing unit to remove the after-pulse peak from among a plurality of predefined threshold values,
Optical transmitter receiver. According to paragraph 3,
The control unit is configured to select the first threshold range to be used by the signal processing unit to remove the after-pulse peak from among a plurality of predefined threshold ranges,
Optical transmitter receiver. According to paragraph 1,
The signal processing unit
Configured to detect effective peaks among the peaks included in the light reception signal, and determine the amount of received light corresponding to the detected effective peak and the distance from the reflector corresponding to the detected peak,
Optical transmitter receiver. According to paragraph 1,
Signal processing for the optically received signal includes a plurality of processes performed sequentially in the digital domain, and the signal processing unit is configured to perform the plurality of processes in a pipeline processing method,
Optical transmitter receiver. In an optical transceiver that uses a solid state photon multiplexer (SSPM) equipped with a plurality of single photon avalanche diodes (SPAD) to receive reflected light corresponding to optical pulses transmitted at a preset period, the after-pulse peak is removed from the optical reception signal. As a method,
selecting a first effective peak from the optically received signal corresponding to a given optical pulse; and
Removing an after-pulse peak from peaks following the first effective peak based on a peak level ratio relative to the first effective peak and a time interval from the first effective peak.
Method, including. According to clause 8,
selecting a second effective peak subsequent to the first effective peak; and
Removing an after-pulse peak from peaks following the second effective peak based on a peak level ratio relative to the second effective peak and a time interval from the second effective peak.
A method further comprising: According to clause 8,
Among the peaks following the first effective peak, a peak whose peak level ratio is less than or equal to a preset first threshold and where the time interval is within a preset first threshold range is determined as the after pulse peak,
method. According to clause 10,
further comprising selecting the first threshold to use for removing the after-pulse peak from a plurality of predefined thresholds,
method. According to clause 10,
Further comprising selecting the first threshold range to be used for removing the afterpulse peak from a plurality of predefined threshold ranges,
method.

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