Recharging circuit for digital silicon photomultipliers
By employing a conditional recharge circuit and increasing the duty cycle in the silicon photomultiplier detector array, the problems of dark counting and breakdown domino effect were solved, thereby improving the performance and reliability of the detector.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE LTD
- Filing Date
- 2020-07-16
- Publication Date
- 2026-06-02
AI Technical Summary
Existing silicon photomultiplier (SiPM) detector arrays are prone to dark counting and breakdown domino effects during recharging, leading to false triggering and increased detector dead time.
A conditional recharge circuit is employed to recharge the SPAD by meeting two conditions: a recharge signal is applied and a trigger signal indicates that the SPAD is in a breakdown state. Gated recharge is performed by increasing the duty cycle or using additional circuitry to prevent the SPAD's anode from being grounded unnecessarily.
It effectively prevents the dark counting and breakdown domino effect of SPAD, reduces noise events, improves the spatial resolution and sensitivity of the detector, and reduces dead time.
Smart Images
Figure CN114174781B_ABST
Abstract
Description
Background Technology
[0001] The following describes silicon photomultiplier (SiPM) detector arrays, a type frequently used in digital positron emission tomography (PET) systems, astronomical detectors, and light detection and ranging (LIDAR) systems. In a SiPM used for digital PET, each pixel of the detector array itself comprises an array of cells, where each cell includes a single photoavalanche diode (SPAD) reverse-biased above its breakdown voltage, and a portion of supporting circuitry. The supporting circuitry includes submodules for generating and verifying trigger events when the SPAD enters breakdown, and for counting breakdown events across the array of cells of the pixel during the time interval following the trigger event. After the trigger event (e.g., after breakdown), quenching and refresh circuitry is used to accelerate the recovery of the SPAD. Some illustrative examples of SiPM detector arrays for PET are described in US Patent 9268033 entitled “Digital Silicon Photomultiplier for TOF-PET” by Frach et al. and US Patent Publication 2016 / 0011321A1 entitled “Timestamping Detected Radiation Quanta” by Solf.
[0002] The following discloses specific improvements to address these and other issues. Summary of the Invention
[0003] In one disclosed aspect, an optical detector includes: an array of cells; and a recharge circuit configured to apply a recharge signal to a group of cells in the array. In some embodiments, each cell includes: a single-photon avalanche diode (SPAD) reverse-biased to a voltage above the breakdown voltage of the SPAD; a trigger logic unit connected to the SPAD for outputting a trigger signal indicating whether the SPAD is in a breakdown state; and a conditional recharge circuit configured to recharge the SPAD under two conditions: (i) the recharge circuit applies the recharge signal to the cell and (ii) the trigger signal output by the trigger logic unit of the cell indicates that the SPAD of the cell is in a breakdown state.
[0004] In another disclosed aspect, a method includes: outputting a trigger signal using a trigger logic unit connected to a single-photon avalanche diode (SPAD), the trigger signal indicating that the SPAD is in a breakdown state. The method may further include utilizing a conditional recharge circuit: receiving the trigger signal indicating that the SPAD is in a breakdown state; receiving a recharge signal indicating that the SPAD should be recharged; and recharging the SPAD in response to receiving both the trigger signal indicating that the SPAD is in a breakdown state and the recharge signal indicating that the SPAD should be recharged.
[0005] In another disclosed aspect, an optical detector includes: an array of units, each unit comprising: a single-photon avalanche diode (SPAD) reverse-biased above a breakdown voltage of the SPAD; and a trigger logic unit connected to the anode of the SPAD, configured to output a trigger signal. In some embodiments, each unit in the array is configured to connect the SPAD to ground when a recharge signal is applied, and the recharge signal includes a duty cycle.
[0006] One advantage is that it prevents the SPAD from breaking down due to the "domino effect" in the event of dark counting during recharging.
[0007] Another advantage is the improved recharge circuitry.
[0008] The given embodiments may not provide the aforementioned advantages, may provide one, two, more or all of the aforementioned advantages, and / or may provide other advantages, as will become apparent to those skilled in the art upon reading and understanding this disclosure. Attached Figure Description
[0009] This invention can take the form of various components and their arrangements, as well as various steps and their arrangements. The accompanying drawings are for illustrative purposes only and should not be construed as limiting the invention.
[0010] Figure 1 An embodiment of a PET scanning system is illustrated in the diagram.
[0011] Figure 2 The illustration shows a common example of row recharging.
[0012] Figure 3 The illustration shows a unit embodiment that includes an exemplary conditional recharge circuit to form a row recharge configuration with gated recharge.
[0013] Figure 4 An example conditional recharge circuit is shown.
[0014] Figure 5The illustration shows an example of data from a conventional recharge.
[0015] Figure 6 The illustration shows an example of smart recharge data with a 50% duty cycle.
[0016] Figure 7 A flowchart illustrating an embodiment of the system and method described herein is shown schematically. Detailed Implementation
[0017] However, specific problems can arise due to noise. Specifically, so-called dark counting is SPAD breakdown that is unrelated to photon detection but primarily due to thermally generated carriers in the single-photon avalanche diode junction. This dark counting can lead to false triggering, thereby introducing unwanted detector dead time during handling, rejecting false triggers, and SiPM reset. Furthermore, if breakdown occurs during recharging, a breakdown domino effect can occur, where adjacent SPADs also break down.
[0018] The following relates to silicon photomultiplier tube (SiPM) detector arrays, a type frequently used in medical nuclear imaging systems such as digital positron emission tomography (PET) systems. However, the disclosed methods have numerous applications both within and outside the field of nuclear medicine imaging.
[0019] refer to Figure 1 The radiation emission imaging system 10 includes a scanner 12. The scanner 12 is arranged and sized to receive a prone human object in the examination area.
[0020] Different scanning techniques and variations can be used in medical nuclear imaging. One such technique is PET. In one example of PET, a radiopharmaceutical consisting of a positron-emitting radioisotope is administered to the object. The radiopharmaceutical can be designed to accumulate in an organ or tissue of interest, such as the brain, lungs, tumor, etc. After the radiopharmaceutical is administered, the object is loaded into the area to be examined. Over time, the radiopharmaceutical will emit positrons in a radioactive decay event. The positrons emitted by the radiopharmaceutical travel a very short (usually negligible) distance before interacting with the electron. Once the positron interacts with the electron, both the positron and the electron annihilate each other, producing a pair of gamma photons traveling in opposite directions (sometimes called annihilation photons). The gamma photons travel in opposite directions, and each gamma photon can be detected when it reaches the scintillator 100 in the scanner 12. This example can depend on the simultaneous detection of the pair of gamma photons. Therefore, some algorithms may ignore gamma photons that do not arrive at the same time.
[0021] To detect gamma photons, silicon photomultiplier tube (SiPM) detector arrays are used. In these detectors, each pixel of the detector array itself comprises an array of cells, where each cell includes a single photoavalanche diode (SPAD) reverse-biased above its breakdown voltage, along with a portion of the supporting circuitry. (Hereinafter, the term "pixel" is used to refer to an array of SPAD cells, as in PET applications, this array of cells forms one pixel in a larger PET detector array. However, it should be understood that in some other applications, a single SPAD cell array may be used, such as as a radiation detector in a LIDAR system, in which case there may only be one "pixel.") The supporting circuitry includes submodules for generating and verifying trigger events when SPAD breakdown occurs, counting breakdown events on the pixel cell array over time intervals following the trigger event, and assigning digital timestamps to the events. Quenching and refresh circuitry is used after breakdown to accelerate SPAD recovery. To provide high spatial resolution in the PET detector design, the silicon space occupied by each cell is minimized. While some support circuitry must be located within the cell regions of the array, feasible portions of the support circuitry are placed on the periphery of the pixels and are also designed to serve multiple cells (e.g., an entire row of cells). Some illustrative examples of SiPM detector arrays for PET are described in U.S. Patent 9268033 entitled “Digital Silicon Photomultiplier for TOF-PET” by Frach et al., and U.S. Patent Publication No. 2016 / 0011321 A1 entitled “Timestamping Detected Radiation Quanta” by Solf, both of which are incorporated herein by reference in their entirety.
[0022] The complete PET radiation detector for detecting gamma rays also includes a scintillator 100, which generates a flash (scintillation) when gamma rays are absorbed. SiPM pixels 102 detect the bursts of photons that constitute the scintillation. The total count over the integration time interval is a measure of the photon energy for the detected event, while the timing of the trigger signal provides a timestamp for the event. Furthermore, it is desirable to operate the SiPM at room temperature, or at least limit the amount of cooling required.
[0023] Interestingly, the recharge circuit 104 is positioned on the periphery of the pixel region, and a single recharge circuit is connected to a row of cells of the pixel. In its quiescent state, the SPAD is biased to a few volts higher than its breakdown voltage. When the SPAD breaks down, the voltage on the junction drops below its breakdown voltage and must be restored to above the breakdown voltage to reset the SPAD. The recharge circuit operates by briefly turning on the transistor to connect the anode of the SPAD to ground, thereby applying charge to the anode and bringing the broken-down SPAD above its breakdown voltage, thus returning it to the quiescent state.
[0024] Furthermore, active quenching and recharging circuitry minimizes the dead time of the SPAD. Ideally, these circuits would be designed to quench and recharge each SPAD individually (see Nolet et al., “Quenching Circuit and SPAD Integrated in CMOS 65nm with 7.8ps FWHM Single Photon Timing Resolution”, Instruments, 2018). However, the circuitry required for quenching and recharging a single SPAD is typically large and may require analog components to fine-tune the quenching and recharging times. Therefore, providing a separate recharging circuit for each SPAD cell may be impractical, especially in applications such as PET detectors where high spatial resolution is desired, driving the minimization of SPAD cells.
[0025] Alternatively, a universal row recharge technique can be used to reduce area requirements and offload timing circuitry to the sensor periphery (see Frach et al., “The Digital Silicon Photomultiplier - Principle of Operation and Intrinsic Detector Performance”, IEEE Nuclear Science Symposium conference record, Nuclear Science Symposium, December 2009). In this case, each SPAD is quenched independently, but multiple SPADs (typically in one or more rows) are recharged once. This method significantly reduces the area of the unit electronics and results in higher photon detection efficiency due to the higher fill factor.
[0026] Figure 2An example electrical schematic of two cells in a row of cells in a SPAD is illustrated, which share a common row recharge. Referring to this, each cell 202 includes a single-photon avalanche diode (SPAD) (204) reverse-biased above the SPAD's breakdown voltage, and a trigger logic unit 206 connected to the SPAD 204. The trigger logic unit 206 is configured to output a trigger signal to the pixel's trigger network, indicating whether the SPAD 204 is in a breakdown state. The illustrative trigger logic unit 206 performs additional functions, including generating a readout signal on the readout line and controlling an optional enable transistor 212 that can be used to disconnect the SPAD 204 (e.g., if the SPAD 204 is defective and should be deactivated). Some illustrative examples of suitable trigger logic units are disclosed in U.S. Patent No. 9268033 to Frach et al. and U.S. Patent Publication No. 2016 / 0011321 A1 to Solf.
[0027] As in Figure 2 As can be further seen, each cell 202 also includes a recharge transistor 220 that controls the recharging of the SPAD 204. The recharge transistor 220 of cell 202 is part of a recharge circuit configured to apply a recharge signal to multiple rows of cells in the array. (More generally, the recharge circuit is configured to apply a recharge signal to a group of cells in the array; in the illustrative example, the group is a row of cells in the array, but other groupings are also possible). The recharge circuit also includes a recharge driver 222 that outputs a recharge signal for each row, and an electrical conductor 224 that connects the driver 222 to the recharge transistors 220 of all cells in that row. In this way, the driver 222 that outputs the recharge signal applies the recharge signal to the recharge transistors 220 of all cells in that row. In operation, the pixel controller detects a SPAD breakdown anywhere in the row (e.g., a readout and / or trigger signal output via trigger logic unit 206) and controls the driver 222 to output a recharge signal. In the illustrative example, the recharge signal is an active-high signal (i.e., logic "1"), causing driver 222 to output a low signal (logic "0") until the pixel controller activates driver 222 to output an active-high recharge signal. (The reverse arrangement is expected, where the recharge signal is active-low, as will be discussed below.) The active-high recharge signal applied to the gate of the recharge transistor 220 of each cell 202 causes the anode of SPAD 204 to connect to electrical ground, thereby placing charge on the anode and causing the broken-down SPAD to return to a quiescent state above its breakdown voltage.
[0028] An embodiment employing an "inverted arrangement" is also envisioned, where the recharge signal is active low. In these embodiments, the recharge transistor is of the PMOS type. Figure 2 The recharge transistor 220 shown is an NMOS (because it is turned on when the gate is logic 0 and turned off when the gate is logic 1), and the entire circuit is also "inverted". For background, U.S. Patent Application Publication US2011 / 0079727A1 illustrates some aspects of the two readout methods.
[0029] To further illustrate, in the embodiments disclosed herein, the SPAD is connected to GND when the recharge transistor is closed. With the cathode having a positive bias (= Vbreakdown + Vexcess), the SPAD is biased at Vexcess, which is higher than the breakdown voltage, when the recharge NMOS is turned on. When the SPAD breaks down, current flows in the junction until the anode-cathode voltage drops to Vbreakdown. Since the cathode potential is fixed, only the anode potential can change, and therefore the anode voltage will increase from GND to -Vexcess (assuming the NMOS transistor is open; otherwise, a large current would flow through the SPAD).
[0030] In the PMOS embodiment, the recharge transistor is connected to the cathode to connect to the power supply defining the overvoltage. In this case, the anode is biased to negative V-breakdown, and the PMOS recharge connects the cathode to the power rail defining V-overvoltage. When the recharge switch is turned on and the cathode voltage transitions to GND during breakdown, the SPAD's cathode remains at V-overvoltage. The entire logic of the subsequent cell circuit is thus inverted.
[0031] One advantage of this universal row recharge design is that the only component of the recharge circuit that needs to be located locally within cell 202 is the recharge transistor 220. The recharge driver 222 can be positioned on the periphery of the array 200 of cells 202. This facilitates miniaturization of cells 202, resulting in smaller pixels and PET detectors with higher spatial resolution. Alternatively, the pixel size can remain fixed, and the disclosed method enables an increase in the fill factor of the cells (i.e., a reduction in the area of the light-insensitive portions of the cells), thereby increasing the sensitivity of the sensor. Higher sensitivity leads to better timing resolution of the sensor (and system). It should be noted that when any cell in the row breaks down, the pixel controller activates the recharge driver to apply a recharge signal to the entire row (or other group) of cells, including the cell that broke down. However, connecting the anode of the SPAD, which is in its quiescent state (i.e., reverse-biased above its breakdown voltage), to electrical ground via its recharge transistor 220 does not change the state of the SPAD, as it only slightly increases the magnitude of the reverse bias further above its breakdown voltage. Therefore, the common line recharge design is generally understood to provide a favorable reduction in the total number of components and a corresponding miniaturization of the array 200 without the associated costs.
[0032] As previously described, using a generic row recharge design, the recharge circuit grounds the anodes of all SPADs in the row, regardless of whether any particular SPAD in that row has broken down. This is typically not a problem, as currently unbroken SPADs will remain in a quiescent state. However, this paper recognizes that if such a SPAD is in its quiescent state (i.e., biased above the breakdown voltage but not in a breakdown state), and its anode is connected to electrical ground via its recharge transistor 220, and a breakdown happens, then an excessive current flows through the SPAD's pn junction, and the SPAD effectively becomes a photoemitter. The light emitted by the SPAD can then trigger the breakdown of adjacent SPADs (a breakdown domino effect).
[0033] In other words, a problem arises in the common row recharge circuit when a SPAD breaks down during a recharge cycle for the row containing that SPAD. In some SiPM designs for PET detector pixels, dozens of SPADs are connected to recharge line 224, and not all SPADs discharge at the start of recharge. Therefore, there is a realistic possibility that one of the SPADs in its quiescent state will subsequently break down after its recharge transistor 220 is turned off. In this case, a large current begins to flow through the SPAD, resulting in high light emission. This light emission then triggers breakdown of adjacent SPADs in the same row or other rows (breakdown domino effect). This state ends with the end of recharge and leads to spurious events, where sometimes the initial SPAD emits thousands of photons, causing many other SPADs to break down. This combined "domino effect" produces some events that pass through the energy-based verification threshold, causing "noise" events that increase the sensor's dead time. A small fraction of these events also fall within the system's energy window, thus increasing the random coincidence rate of the PET imaging system.
[0034] The systems and methods disclosed herein implement two solutions to this problem: one solution employs additional circuitry, and the other employs modification of the signal applied to the recharge line. It should be understood that these two solutions can be used in combination or individually. Some embodiments of the first solution include additional circuitry located in a region of the cell; this additional circuitry performs a logical AND operation (involving some buffering) between the recharge line and the trigger line, and applies the output of the logical AND operation to a transistor that is typically activated solely by the recharge line. More generally, the additional circuitry gates the recharge line via the trigger line. Therefore, the SPAD anode is grounded only when two conditions are met: (i) the recharge line is active, and (ii) a particular SPAD has been triggered (and therefore is in a breakdown state). On the other hand, a SPAD in a quiescent state will have a logic "0" on its (buffered) trigger line, and therefore its anode is not grounded.
[0035] In other words, the recharge pulse is only applied to discharged SPADs. While this does not change the probability of SPAD breakdown, it eliminates the large current flowing through the SPAD that could cause breakdown, thus significantly reducing the likelihood of a domino effect. Furthermore, the compact circuitry facilitates cell miniaturization, reduces the load on the row recharge line, thereby accelerating recharge time and reducing the power consumption of the row recharge line driver.
[0036] Figure 3 The illustration shows an example of the electrical schematic of two cells in a row of cells in a SPAD, which share a common row recharging circuit, including additional circuitry 310, which is consistent with the previously referenced... Figure 2 The described recharge transistor 220 together forms conditional recharge circuits 220, 310, which are configured by additional circuit 310 to recharge SPAD 204 under the following two conditions: (i) recharge circuits 222, 224 apply a recharge signal to a row cell including the cell and (ii) trigger logic cell 206 indicates that SPAD 204 of the cell is in a breakdown state. Figure 3 As can be seen, the auxiliary circuit 310 receives the recharge signal 312 as input through conductor 224, and also receives the trigger signal 314 output by the trigger logic unit 206 as a second input. The trigger signal 314 indicates whether the SPAD 204 of the unit is in a breakdown state. The auxiliary circuit 310 outputs a gated recharge signal 316, which is the recharge signal 312 gated by the trigger signal 314.
[0037] In the illustrative example, the recharge signal 312 is active high (i.e., logic "1" indicates that SPAD 204 is recharged through recharge transistor 220) and the trigger signal is also active high (i.e., logic "1" indicates that SPAD 204 is in a breakdown state, and logic "0" indicates that it is not in a breakdown state). In this case, additional circuitry 310 is used as an AND gate to implement the following logic:
[0038] The gated recharge signal (316) = recharge signal (312) AND trigger signal (314). Therefore, when both the recharge signal 312 and the trigger signal are logic "1", the gated recharge signal 316 is only logic "1". It should be understood that the logic implemented by the additional circuit may be different if different activation states are used. For example, if the recharge signal is active high but the trigger signal is active low (i.e., logic "0" indicates that the SPAD is in a breakdown state), the additional circuit appropriately implements the following logic: gated recharge signal = recharge signal (312) AND NOT trigger signal.
[0039] Figure 4 An example implementation of the additional circuit 310 is shown. The additional circuit 310 is implemented in each unit 202 (e.g., Figure 3 As shown), it should therefore be compact in order to maintain a high fill factor of the cells to achieve high photon detection efficiency. Figure 4 The basic function of the example is as follows: The recharge pulse 312 dynamically stores the state output of the flip-flop 314 of the cell on node DN. When the recharge signal 312 is active high, it turns on the p-channel field-effect transistor (P-FET) P1 that connects the flip-flop signal 314 to DN during recharging. The remaining transistors implement a logical AND function between the state stored on node DN and the recharge signal 312, i.e., SPAD recharge = recharge AND DN. To further illustrate the background of DN, the state of the SPAD is stored during the recharge time at the start of the recharge pulse; otherwise, the recharge of the SPAD would stop shortly after the anode reaches the threshold voltage of the attached logic (~V over / 2). By storing the state on DN, the recharge transistor of the SPAD is ensured to be off throughout the recharge process.
[0040] Dynamic memory (where the state is stored on the gate capacitances of N1 and P3) offers advantages such as small area and high speed; however, it has a limited storage time due to leakage. PMOS P1 is half the size of the transmission gate. The NMOS is omitted here to save area, but it can be easily added by adding an NMOS controlled by an inverted recharge signal (requiring an additional NMOS + inverter NMOS / PMOS). Other memory elements (latches, flip-flops) can also be used, at the cost of increased silicon area.
[0041] Advantageously, Figure 4 The additional circuit 310 contains only seven transistors, and therefore can be made very compact.
[0042] The second solution is to increase the duty cycle of the recharge line. In some embodiments, the duty cycle is added as part of the pulse queue of the recharge line 224. As shown in the experiments reported herein (see...). Figure 5 and 6 (and related texts), the method is also very effective in suppressing the breakdown domino effect and can be used alone or in combination with additional circuitry of the first solution.
[0043] The second solution works physically because, in the event of a breakdown during a short recharge pulse, the SPAD has a chance to recover during the OFF state. The recharge pulse width and duty cycle can be adjusted (e.g., 10 ns, 50%). The duration of the ON state is appropriately chosen based on the recharge transistor recharging the excess SPAD capacitance at V, typically in nanoseconds. The duration of the OFF state depends on the time required for the SPAD to remove charge from the junction and discharge any trapped charge in the bandgap (which would otherwise result in an afterpulse). This also depends on the operating temperature, as the trapped charge lifetime is a function of temperature.
[0044] To further explain the second solution, photoemission and the domino effect can be further suppressed by increasing the duty cycle of the recharge pulse. A typical 10 ns long recharge pulse with a 50% duty cycle has been shown to be very effective in suppressing photoemission, such as... Figure 5 and 6 As shown, it reports the experimental results for four sensor pixels. Figure 5 The use of a 10ns long static recharge pulse and Figure 2 The data obtained by the circuit (without additional circuit (310)). Furthermore, Figure 5 The data shown illustrates the expected signals for noisy events (i.e., units of "ph" represent photon counts, with 1000 ph representing a detected noisy "event" and a time-integrated energy of 1000 photons) over a wide energy range up to 1000 ph and for peak photon events in the energy range of 1500-2000 ph. In contrast, Figure 6 The demonstration showed the use of a 10ns recharge pulse with a 50% duty cycle and Figure 3 Data of the circuit (with additional circuitry (310)). For example... Figure 6 As shown, noise events in the 0-1000ph range are effectively eliminated.
[0045] for Figure 5 and 6The data shown indicates that photon peak events are generated by diffuse laser irradiation with a total energy of 1500ph-2000ph (depending on the positions of the four sensor pixels). The dark count rate of the SPAD matrix is generated by thermal noise at 20°C.
[0046] More specifically, it can be seen that, Figure 2 In the case of the circuit, and without pulsed recharge signals (i.e., 100% "duty cycle"), normal line recharge results in low-energy noise events. Figure 5 (), with an energy of several hundred photons. In comparison, such as Figure 6 As shown, with the addition of circuitry (310) and using a 50% duty cycle, noise events are almost completely eliminated. Figure 5 and Figure 6 The comparison shows that the disclosed improved recharge effectively eliminates the possibility of associated SPAD breakdown during the recharge phase.
[0047] Figure 7 A flowchart illustrating an embodiment of the system and method described herein is schematically shown. In step 710, a duty cycle is applied to a recharge signal indicative of recharging the SPAD. In step 720, a trigger signal indicative of the SPAD being in a breakdown state is output using a trigger logic unit connected to the SPAD. In step 730, the trigger signal is received using a conditional recharge circuit. In step 740, the recharge signal indicative of recharging the SPAD is received using the conditional recharge circuit. In step 750, the SPAD is recharged using the conditional recharge circuit in response to receiving both the trigger signal and the recharge signal indicative of recharging the SPAD.
[0048] Beyond PET, the disclosed technology has many other applications, particularly at high temperatures (due to increased SPAD breakdown at higher temperatures). More generally, consider other applications requiring the detection of light pulses with high temporal resolution timestamps. Other applications include, for example, PET / CT, PET / MR, SPECT, high-energy physics, lidar, and fluorescence lifetime imaging microscopy. Of particular interest are LIDAR systems, which perform optical ranging based on the time-of-flight between laser beam emission and reflection detection. LIDAR has applications in multiple industries, including automotive, where it is used, for example, as a trigger device to activate emergency braking.
[0049] It will be further understood that the techniques disclosed herein can be embodied in a non-transient storage medium that stores instructions that can be read and executed by an electronic data processing device to perform the disclosed techniques. Such a non-transient storage medium may include hard disk drives or other magnetic storage media, optical disks or other optical storage media, cloud-based storage media such as RAID disk arrays, flash memory or other non-volatile electronic storage media, and so on.
[0050] The invention has been described with reference to preferred embodiments. Various modifications and variations can be made by those skilled in the art upon reading and understanding the foregoing detailed description. This disclosure is intended to be understood to include all such modifications and variations, provided they fall within the scope of the appended claims or their equivalents.
Claims
1. An optical detector, comprising: Array (200) of cells (202); as well as A recharge circuit (222, 224) is configured to connect a group of cells in the array and to apply a recharge signal (312) to the group of cells in response to a single-photon avalanche diode (SPAD) breakdown occurring at any point in the group of cells. Each unit includes: SPAD (204), which is reverse biased to the breakdown voltage of the SPAD; A trigger logic unit (206), connected to the SPAD (204), is configured to output a trigger signal (314) indicating whether the SPAD (204) is in a breakdown state; and A conditional recharge circuit (220, 310) is configured to recharge the SPAD (204) to restore the voltage on the junction of the broken-down SPAD (204) to a level higher than the breakdown voltage when the following two conditions are met: (i) the recharge signal (312) applied to the unit is received from the recharge circuit and (ii) the trigger signal (314) output by the trigger logic unit (206) of the unit indicates that the SPAD of the unit is in a breakdown state.
2. The optical detector according to claim 1, wherein: The group of cells (202) in the array (200) is a row of cells in the array; and the recharge circuit (222, 224) includes for each row a recharge driver (222) for outputting the recharge signal (312) and an electrical conductor (224) for connecting the output of the recharge driver to the conditional recharge circuit (220, 310) of all cells in the row.
3. The optical detector according to any one of claims 1-2, wherein, The conditional recharge circuit (220, 310) is configured to recharge the SPAD (204) by grounding the anode of the SPAD (204).
4. The optical detector according to any one of claims 1-2, wherein: Each of the units (202) further includes a first p-channel field-effect transistor (P-FET) (P1); the recharge signal (312) is connected to the gate of the first P-FET (P1); and the trigger signal (314) is connected to the source of the first P-FET (P1).
5. The optical detector according to any one of claims 1-2, wherein: The recharge signal (312) is connected to: the gate of the first p-channel field-effect transistor (P-FET) (P1), the gate of the second P-FET (P2), and the gate of the n-channel field-effect transistor (N-FET) (N1); and The trigger signal (314) is connected to the source of the first P-FET (P1).
6. The optical detector according to any one of claims 1-2, wherein, The recharge signal (312) includes a pulse queue with a duty cycle.
7. The optical detector according to any one of claims 1-2, wherein, The recharge signal has a variable pulse width.
8. The optical detector according to claim 6, wherein, The recharge signal (312) includes a 10ns pulse.
9. The optical detector according to claim 6, wherein, The duty cycle is 50%.
10. A method for optical detection, comprising: Using a recharge circuit (222, 224) configured to connect groups of cells in an array, a recharge signal (312) is applied to the group of cells in response to a single-photon avalanche diode (SPAD) breakdown occurring at any point in the group of cells. A trigger signal (314) is output using a trigger logic unit (206) connected to the SPAD (204), the trigger signal indicating that the SPAD (204) is in a breakdown state; and Utilizing the conditional recharge circuit (310): Receive the trigger signal (314) indicating that the SPAD (204) is in a breakdown state. Receive the recharge signal (312) from the recharge circuit indicating that the SPAD (204) should be recharged. In response to receiving the trigger signal (314) indicating that the SPAD (204) is in a breakdown state and receiving the recharge signal (312) from the recharge circuit indicating that the SPAD (204) should be recharged, the SPAD (204) is recharged so that the voltage on the junction of the broken SPAD (204) is restored to a value higher than the breakdown voltage of the SPAD (204).
11. The method according to claim 10, wherein, The conditional recharge circuit (310) recharges the SPAD (204) by grounding the anode of the SPAD (204).
12. The method according to any one of claims 10-11, wherein, The recharge signal (312) is sent to the gate of the first P-FET (P1); and The trigger signal (314) is sent to the source of the first P-FET (P1).
13. The method according to any one of claims 10-11, wherein, The recharge signal (312) is sent to: the gate of the first p-channel field-effect transistor (P-FET) (P1), the gate of the second P-FET (P2), and the gate of the n-channel field-effect transistor (N-FET) (N1); and The trigger signal (314) is sent to the source of the first P-FET (P1).
14. The method according to any one of claims 10-11, wherein, The recharge signal (312) includes a pulse queue with a duty cycle.
15. The method according to claim 14, wherein, The recharge signal (312) includes a 10ns pulse.
16. The method of claim 14, wherein, The duty cycle is 50%.
17. An optical detector, comprising: An array (200) of cells (202), each cell comprising: A single-photon avalanche diode (SPAD) (204), which is reverse biased above the breakdown voltage of the SPAD (204); and A trigger logic unit (206) is connected to the anode of the SPAD (204) and is configured to output a trigger signal (314) indicating whether the SPAD (204) is in a breakdown state. Each cell (202) of the array (200) is configured to connect the SPAD (204) to ground when a recharge signal (312) from the recharge circuit is applied and the trigger signal (314) indicates that the SPAD (204) is in a breakdown state, so that the voltage on the junction of the broken SPAD (204) is restored to a value higher than the breakdown voltage of the SPAD (204), wherein the recharge signal (312) comprises a pulse queue with a duty cycle, and wherein the recharge circuit is configured to connect a group of cells in the array and to apply the recharge signal (312) to the group of cells in response to a SPAD breakdown occurring at any point in the group of cells.
18. The optical detector according to claim 17, wherein, The recharge signal (312) includes a 10ns pulse.
19. The optical detector according to any one of claims 17-18, wherein, The duty cycle is 50%.
20. The optical detector according to any one of claims 17-18, wherein, At least one of the duty cycle and period length of the pulse queue is configurable.