Bias generator connected to a sipm

Abstract

A switched mode power supply includes a microcontroller, an interface circuit connected to the controller, and a boost circuit connected to the controller. A feedback circuit is connected to the controller, and a SiPM is connected to the boost circuit and the feedback circuit.

Description

[0001] Related Applications Cross Reference To Related Applications

[0002] This application claims priority to U.S. Application No. 62 / 941,154, filed on November 27, 2019, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] Aspects of the present disclosure relate generally to switched-mode power supplies, and more particularly to switched-mode power supplies that provide high efficiency for SiPM bias generation. Background Art

[0004] For example, silicon photomultipliers (SiPMs) are used in various industries to detect radiation and light. In some areas, SiPMs can be used to detect thermoluminescence by measuring infrared light. SiPMs can also be used in gamma-ray detectors or dosimeters to determine radiation levels in hazardous environments, which can be used to help protect users from exposure to such radiation. Gamma-ray detectors utilize the excitation of atoms or molecules caused by radiation passing through a scintillation material. Subsequent de-excitation produces photons that can be measured to obtain an indication of the energy deposited in the detector by the radiation. The detector can include a scintillation material, such as sodium iodide (NaI), cesium iodide (CsI), or certain plastics, coupled to a silicon device that acts as a photomultiplier tube. When the detector is exposed to radiation, the scintillation material is excited, producing photons of visible light. This light then shines on a photomultiplier tube, which amplifies the result and produces a measurable signal.

[0005] Portable versions of these devices, often carried by individuals, include electronic personal dosimeters (EPDs), personal radiation detectors (PRDs), and radioisotope identifiers (RIIDs). These devices require batteries in the remote environments in which they operate, and, therefore, providing long battery life under these operating conditions is highly advantageous.

[0006] SiPMs require a bias voltage, typically in the range of 25-35V, and a very low current, ranging from nA to a maximum of about 1mA. For battery-powered devices, this voltage must be generated from a much lower battery voltage, typically in the range of 1.0-5.0V. Most commercially available boost electronic integrated circuits (ICs) are designed for lower voltages (e.g., from 1.0V to 3.3V) and / or higher currents (e.g., specified for loads from 10mA to several amperes) and do not perform the task of providing SiPM bias in an efficient manner that conserves battery power. Known boost circuits often have too low an output current and may draw more power to convert the voltage required by the SiPM's load, resulting in very low efficiency.

[0007] Additionally, the bias voltage of SiPMs often needs to be adjusted to compensate for changes in the operating temperature of the device. This adjustment is sometimes only supported by commercial boost ICs and often requires the addition of components such as digital-to-analog converters or digital potentiometers, which add cost, power consumption, and size to the design.

[0008] It would be desirable to provide a bias generator that reduces or overcomes some or all of the difficulties in previously known designs. Particular objects and advantages will be apparent to those skilled in the art, that is, to those persons who have the skill and experience in the field of technology to which this technology pertains, in view of the following disclosure and the detailed description of certain embodiments. SUMMARY

[0009] According to a first aspect, a switched mode power supply includes a microcontroller, an interface circuit connected to the controller, a boost circuit connected to the controller, and a feedback circuit connected to the controller. A SiPM is connected to the boost circuit and the feedback circuit.

[0010] The aspects disclosed herein provide a low cost and efficient device that can provide voltage biasing for SiPMs and other devices. These and additional features and advantages will be further understood from the following detailed disclosure of certain embodiments, together with the drawings, and from the claims. BRIEF DESCRIPTION OF DRAWINGS

[0011] The foregoing and other features and advantages of the embodiments of the application will be more fully understood from the following detailed description of illustrative embodiments taken in conjunction with the accompanying drawings, in which:

[0012] Figure 1 is a schematic diagram of elements of a bias generator.

[0013] Figure 2 is an embodiment of a circuit of a bias generator of Figure 1

[0014] Figure 3 is a graph of current draw for an embodiment of a bias generator of Figure 1

[0015] Figure 4 is a circuit diagram of a boost topology of a boost circuit for a bias generator of Figure 2

[0016] Figure 5 is a circuit diagram of an alternative topology of a boost circuit for a bias generator of Figure 2

[0017] Figure 6 is a circuit diagram of another alternative topology of a boost circuit for a bias generator of Figure 2

[0018] ​​​​​The figures mentioned above are not necessarily drawn to scale and should be understood as providing representations of specific embodiments and are merely conceptual in nature and illustrative of the principles involved. To facilitate explanation and understanding, some features depicted in the figures have been enlarged or distorted relative to others. The same reference numerals are used in the figures for similar or identical components and features shown in the various alternative embodiments. The bias generator disclosed herein will have a configuration and components determined in part by the intended application and the environment in which it will be used. DETAILED DESCRIPTION

[0019] Embodiments disclosed herein provide an interactive, high-efficiency bias generator for use with a SiPM that (a) very efficiently provides the voltage and current required by the SiPM from a battery source; (b) allows voltage adjustment without additional components; (c) provides the ability to read out the average current or total charge over an interval in a manner that can be used as part of a higher-level measurement; and (d) can be switched between different operating modes that can be optimized for different conditions. For example, these conditions might include low-current "background" radiation, high-current "pulsed" radiation, or high-precision "spectroscopy" measurements. Thus, this type of bias generator allows for efficient generation of the SiPM's bias voltage, direct control of the output voltage, and the ability to measure the SiPM's current or power consumption.

[0020] The bias generators as discussed herein can be used with small SiPMs, such as those used in EPDs and PRDs. It will be appreciated that the bias generators as discussed herein can also be used with higher power level devices, such as spectroscopy devices.

[0021] like Figure 1 As shown, bias generator 30 may include a power supply 32 and a controller 34, as well as a boost circuit 36 ​​and a feedback circuit 38 connected to SiPM 40. Bias generator 30 may also include an interface circuit 42 and a readout circuit 44 connected to SiPM 40. In some embodiments, power supply 32 may be a battery. For example, the voltage of power supply 32 may be between approximately 1.0V and approximately 4.2V. In other embodiments, power supply 32 may be a mains-powered DC power supply. Other suitable power supplies will become apparent to those skilled in the art, given the benefit of this disclosure.

[0022] The controller 34 can be a low-power microcontroller unit ("MCU"). An exemplary MCU is a C8051F980-GM 8-bit microcontroller available from Silicon Labs of Austin, TX. In other embodiments, the controller 34 can instead or additionally include a field programmable gate array ("FPGA") or an application-specific integrated circuit ("ASIC"). The controller 34 can also include a measurement device, such as an analog-to-digital converter ("ADC"), a comparator such as an analog comparator, or a combination of these. The controller 34 can also additionally include an event counting device, which can be an interrupt signal or a counter responsive to SiPM photon detection, such as a digital counter. In some embodiments, the measurement device is an ADC and the event counting device is a digital counter integrated into the same commercially available module with the interface, MCU, and potentially other peripheral functionality. The use of a low-power MCU and its components allows for measurement of the performance and real-time control of the bias generator 30 while providing the boost functionality.

[0023] The boost circuit 36 ​​that provides a bias voltage between approximately 25V and approximately 35V to the SiPM 40 may include one or more inductors, capacitors, transistors, diodes, and other discrete components. In some embodiments, the boost circuit 36 ​​may be a conventional "asynchronous boost" circuit that includes an inductor, an N-channel logic-level field-effect transistor ("FET"), a diode, input and output capacitors, and possibly a current-limiting resistor. In other embodiments, the boost circuit 36 ​​may be a "synchronous boost" circuit that uses two or more transistors; a "flyback" circuit that uses a transformer, a FET, and a diode; or a "voltage doubler" circuit that uses four or more diodes and four or more capacitors.

[0024] Feedback circuit 38 may include one or more resistors. In some embodiments, feedback circuit 38 may include two resistors having high resistance values, and a buffer amplifier that provides an output that is sent to the control circuit.

[0025] Interface circuitry 42 can provide control of the bias voltages to be formed, as well as monitoring of the SiPM's performance (e.g., voltage, current, power, etc.). Interface circuitry 42 can include one or more connections to controller 34, according to a standards organization, such as a Serial Peripheral Interconnect (SPI), a System Management Bus (SMB), asynchronous RS-232 or RS-485 serial, or other public or proprietary standards. In some embodiments, this interface is an SPI interface including a data input line, a data output line, a clock line, and a select line.

[0026] The components of the exemplary circuit of the bias generator 30 are shown in FIG. Figure 2As indicated above, controller 34 can be a low-power MCU having multiple pins. In some embodiments, fewer than all of controller 34's pins are in use. For example, controller 34 may include 20 pins, with only 13 pins being used. As shown here, pins 3, 12, and 21 of controller 34 can be connected to ground. Pin 4 of controller 34 can be an IC power input. Pins 5 and 6 of controller 34 can be programming pins, which can be used to load firmware for controller 34. Pin 11 of controller 34 can be connected to feedback circuit 38 and receive voltage feedback of the adjustable voltage of bias generator 30. Pin 16 of controller 34 can be an SPI ready-to-receive signal for waking controller 34 from sleep mode. Pin 17 of controller 34 can be an SPI chip select, which provides a selection mechanism for controller 34 to communicate with. Pin 18 of controller 34 can be an SPI master-out slave-in ("MOSI") data output line. Pin 19 of controller 34 may be the SPI master-in slave-out (“MISO”) data input line. Pin 20 of controller 34 may be the SPI clock pin.

[0027] Controller 34 may include a pair of resistors R7 and R8 that hold the programming lines at pins 5 and 6 of controller 34, respectively, in a known low-power state. In some embodiments, resistor R7 may be a 1K ohm resistor, while R8 may be a 1M ohm resistor. A pair of bypass capacitors C5 and C6 may be connected near pin 4 of controller 14. In some embodiments, capacitor C5 may be a 0.1 μF capacitor, while capacitor C6 may be a 1 μF capacitor. Resistor R3 may be located near pin 14 and used to pull down the gate of the FET of boost circuit 36 ​​(described in more detail below) to ensure that it does not turn on when controller 34 is initialized.

[0028] The boost circuit 36 ​​may include an inductor L1, a diode D1, and a FET Q1, as shown in FIG. Figure 2 . In some embodiments, the inductor L1 can be a 100 μH inductor. In some embodiments, the diode D1 can be a Schottky barrier diode with a low forward voltage drop. An exemplary FET Q1 can be an N-channel FET, model RTF016N05T1, available from Rohm Semiconductor of Kyoto, Japan. In some embodiments, the boost circuit 36 ​​can include a first filter 46, which can include a resistor R1 positioned between the capacitor C1 and the capacitor C2 and can be used to reduce the voltage applied to the boost circuit 36 ​​from the supply voltage V 入 In some embodiments, resistor R1 may be a 10 ohm resistor, capacitor C1 may be a 10 μF capacitor, and C2 may be a 10 μF capacitor.

[0029] The boost circuit 36 ​​may include a second filter 48, which may include a resistor R2 positioned between capacitor C3 and capacitor C4 and may be used to help stabilize the output voltage V 偏置 In some embodiments, resistor R2 may be a 10 ohm resistor, capacitor C1 may be a 3.3 μF capacitor, and C2 may be a 0.1 μF capacitor.

[0030] Feedback circuit 38 may include a high-resistance voltage divider 50 formed by resistors R6 and R9, followed by a low-power, low-bandwidth operational amplifier U2. An exemplary amplifier is a TLV8541DBVR operational amplifier, available from Texas Instruments in Dallas, TX. In some embodiments, resistor R6 may be a 100M ohm resistor and resistor R9 may be a 4.99M ohm resistor. Amplifier U2 may also be provided with a bypass capacitor C7. In some embodiments, capacitor C7 may be a 0.1 μF capacitor. Amplifier U2 may also include a diode D2 and resistors R10, R5, and R4. An exemplary diode is a ZXRE1004 diode available from Diodes Incorporated in Plano, TX. In some embodiments, resistor R10 may be a 220k ohm resistor, resistor R5 may be a 100k ohm resistor, and resistor R4 may be a 220k ohm resistor. In some embodiments, feedback circuit 38 may draw a load that is less than the amount of power used by SiPM 40. Feedback circuit 38 may use an offset to increase the accuracy of voltage measurements within the useful range of SiPM 40.

[0031] Figure 3 The current draw of the bias generator 30 is shown. The bias generator 30 can be operated by moving in and out of a sleep state, for example, at a boost rate of 3 Hz. The system wakes up from the sleep state, takes a reading and determines whether the boost circuit 36 ​​needs to provide a bias voltage, if so, provides a boost voltage and takes a reading to assess the effectiveness of the boost, and then returns to the sleep state. When the controller 34 is awakened from the sleep state, it can sample the feedback voltage using its ADC and compare the value of the feedback voltage to the voltage set point to determine whether a voltage boost is needed. The controller 34's internal algorithm can then be used to adjust the pulse frequency to match the output load. It should be understood that the controller 34 can include non-volatile memory that can be changed to implement different algorithms.

[0032] It will be appreciated that various topologies may be used for the boost circuit 36. Figure 2 The boost circuit topology used in the described embodiments is found inFigure 4 , shows the voltage source V s and voltage output V o , and includes inductor L1, diode D1, FET Q1 and capacitor C8.

[0033] Another embodiment that can be used is the Cuk topology, such as Figure 5 This embodiment of the boost circuit 36 ​​is shown with a voltage source V s and voltage output V o , including a pair of inductors L2, L3, a pair of conductors C9, C10, FET Q1 and diode D3.

[0034] Another embodiment of the boost circuit 36 ​​is a flyback topology, such as Figure 6 This embodiment of the boost circuit 36 ​​is shown with a voltage source V i and the voltage output V across the resistor R o , including transformer T1, switch S, diode D4 and capacitor C11.

[0035] It will be appreciated that other topologies may be used with the boost circuit 36 ​​, and other suitable topologies will become apparent to those skilled in the art, given the benefit of this disclosure.

[0036] The bias generator 30 can be used to provide a boosted voltage for a variety of devices, including small SiPMs with low current requirements (e.g., on the order of a few hundred nA) to spectrum-on-demand devices that require high performance and bias voltage ripple stability. For example, when implementing the bias generator 30 in a PRD mode that only provides a count of detection events, efficiency may be a primary concern. When implementing the bias generator 30 with a spectrum PRD, higher power requirements may result due to the more complex operating mode that not only counts detection events but also determines what is actually detected. In such embodiments, the performance of the circuit is modified by the higher level requirements of the application of the bias generator 30. It should be understood that in some embodiments, for example, when used with an EPD, the bias generator 30 can continue to operate, whether the dose rate is low (where the current requirement is low) or the dose rate is high (where the current requirement is increased), without changing the operating mode of the bias generator 30.

[0037] The current consumption of the SiPM 40 provides a feedback signal that can provide additional information about the operation of the bias generator 30. If the SiPM 40 is used in counting mode, the total integrated coulombs of charge are generally very linearly coupled to the total number of events and their cumulative intensity. Therefore, in instances where the SiPM 40 is used as part of a radiation detector, the current (nA) is a very good indicator of the dose exposure rate (μSv / h) and can be used as an alternative measurement at dose exposure rates where the ability to count single photons is no longer possible.

[0038] When the SiPM 40 is used in applications with low background event rates (one / minute or less at background dose exposure in radiation measurements), the occurrence of a photon event can be used as a trigger to move the bias generator 30 to a more active control state. Because these events are infrequent, they have little impact on average power consumption; however, when non-background conditions occur, they provide a mechanism to switch the bias generator 30 to a more tightly coupled regulation regime. Thus, when used with a spectral PRD, the bias generator 30 can switch back and forth between a background or low power mode and a more active or low ripple mode. For example, a switch between background mode and a more active mode can be triggered when photon event activity rises above a preselected level or rate, or when the user selects a specific operation (such as a spectral measurement).

[0039] Embodiments of the bias generator 30 disclosed herein can provide significant advantages. The controller 34, using a low-cost MCU, can provide extensive operational and monitoring capabilities, which can increase the performance of the bias generator 30 while reducing the overall cost of the system. In certain embodiments, the bias generator 30 can be far more efficient than other power supplies not designed for this purpose. For example, a typical commercial off-the-shelf ("COTS") "ultra-low power" boost converter draws over 500uW at no load. Embodiments of the bias generator 30 described herein can draw less than 20% of this power at no load.

[0040] Because the boost frequency and duty cycle can be controlled by any of many possible algorithms implemented in controller 34, it is not limited to fixed switching frequency (pulse width modulation or "PWM"), fixed on-time (pulse frequency modulation or "PFM"), or other methods typically implemented with purely analog control loops, and the best algorithm can be selected for different operating points. Specifically, the selected algorithm allows for an event count input that allows it to switch from the lowest power background mode to the higher power active mode in response to one or more photons detected by the SiPM.

[0041] The bias generator 30 can be adjusted directly without the need for additional components. For SiPMs that need to adjust the bias voltage to correct for operating temperature, this reduces cost, circuit complexity, and power consumption compared to circuits that explicitly control the bias voltage through temperature-dependent resistors or through DACs or digital potentiometers used to control COTS boost converters.

[0042] As an added benefit of using common components, multiple different products can be built around the same components, even if the products require different algorithms. By replacing the control software while retaining the same controller components, manufacturing inventory remains smaller, more flexible, and therefore costs can be reduced.

[0043] Using the knowledge gained from this disclosure, those skilled in the art will recognize that various changes can be made to the disclosed apparatus and methods to obtain these and other advantages without departing from the scope of the present invention. Therefore, it should be understood that the features described herein are susceptible to modification, change, alteration or substitution. For example, all combinations of those elements and / or steps that are explicitly intended to perform substantially the same function in substantially the same manner to achieve the same results are within the scope of the present invention. The replacement of elements from one described embodiment to another is also fully anticipated and contemplated. The specific embodiments illustrated and described herein are for illustrative purposes only and do not limit the present invention as set forth in the appended claims. Other embodiments will be apparent to those skilled in the art. It should be understood that the foregoing description is provided for clarity only and is exemplary only. The spirit and scope of the present invention are not limited to the above examples, but are covered by the appended claims.

Claims

1. A switching mode power supply comprising: Microcontroller; an interface circuit connected to the microcontroller; a voltage boost circuit connected to the microcontroller; a feedback circuit connected to the microcontroller; a readout circuit connected to the microcontroller; and a SiPM connected to the boost circuit, the readout circuit, and the feedback circuit, wherein the microcontroller is configured to control the boost circuit to switch between a first operating mode and a second operating mode, wherein said switching between the first mode of operation and the second mode of operation is initiated when said SiPM detects photon event activity greater than a preselected level, and The preselected level is the background dose exposure in radiation measurements.

2. The switched mode power supply of claim 1, wherein the microcontroller contains non-volatile memory that can be changed to implement different algorithms.

3. The switched mode power supply of claim 1, wherein the microcontroller includes an ADC.

4. The switched mode power supply of claim 1, wherein the microcontroller includes an analog comparator.

5. The switched-mode power supply of claim 1 , wherein the feedback circuit draws a load that is less than the amount of power used by the SiPM.

6. The switched-mode power supply of claim 1 , wherein the feedback circuit utilizes an offset to increase the accuracy of voltage measurements within a useful range of the SiPM.

7. The switched-mode power supply of claim 1, wherein the boost circuit comprises an inductor, a diode, and a FET.

8. The switched-mode power supply of claim 7, wherein the boost circuit further comprises a first filter connected to the inductor, the first filter comprising a resistor positioned between a pair of capacitors.

9. The switched-mode power supply of claim 7, wherein the boost circuit further comprises a second filter connected to the diode, the second filter comprising a resistor positioned between a pair of capacitors.

10. The switched mode power supply of claim 1, wherein the feedback circuit comprises a high voltage divider including a pair of resistors, and an amplifier.

11. The switched-mode power supply of claim 10, wherein the amplifier is a low-power, low-bandwidth operational amplifier.

12. The switched mode power supply of claim 10, wherein the feedback circuit comprises a bypass capacitor.

13. The switched mode power supply of claim 1, wherein the first and second operating modes comprise a background mode and an active mode.

14. The switched mode power supply of claim 1, wherein the background dose is one event per minute.

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