Pre-amplifier and detector

Abstract

The invention provides a pre-amplifier and a detector comprising the pre-amplifier, belongs to the field of radiation detection, and solves the defect that a pre-amplifier in the prior art cannot be effectively reset or cannot fully discharge charges. The preamplifier comprises a charge sensitive structure, a comparator and a reset circuit, wherein the charge sensitive structure comprises a common source amplifier, an operational amplifier and a feedback capacitor. The reset circuit comprises a switch control module, a multi-stable circuit and a charge discharge module. Wherein a control unit in the switch control module controls a switch unit to connect or disconnect a circuit between the charge discharge module and the multi-stable circuit according to the level output by the comparator. And the charge discharge module intermittently pulls down the voltage of the source electrode of the common-source amplifier when receiving the pulse signal of the rectangular wave generated by the multistable circuit, so that the grid electrode and the source electrode of an input tube in the common-source amplifier are conducted to realize discharge reset. According to the invention, the effectiveness and timeliness of capacitor reset can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of radiation detection and relates to the field of electronics, in particular to a preamplifier and a detector comprising the preamplifier. Background Art

[0002] Pulse feedback preamplifiers are widely integrated and used in radiation detectors due to their low noise and high count rate characteristics. During operation, the preamplifier needs to discharge and reset the feedback capacitor.

[0003] Traditional preamplifier pulse feedback reset schemes such as Figure 1 As shown, the front-end electronics circuit utilizes a charge-sensitive structure 10 and is divided into two stages. The first stage is a common-source amplifier 101 composed of field-effect transistors (such as junction field-effect transistors (JFETs). This amplifier circuit has an extremely low noise level and can meet most radiation measurement requirements. The second stage, an operational amplifier 102, performs non-inverting amplification on the first stage. This non-inverting amplification is added to increase the open-loop gain of the entire circuit, thereby ensuring circuit linearity. This front-end electronics circuit implements charge-sensitive amplification by connecting a feedback capacitor Cf between the input (the gate input of the common-source amplifier 101 in the figure) and the output (the output of the operational amplifier 102 in the figure). During long-term operation, the charge accumulated on the feedback capacitor Cf due to signal flow will gradually increase or decrease the output voltage. To prevent output saturation, the charge on the feedback capacitor Cf needs to be discharged to achieve a reset.

[0004] Figure 1 The conventional feedback reset scheme shown uses a comparator 12 to compare the output signal of the front-end electronics circuit with a threshold signal to control a discharge device 11 (typically an active device) to discharge and achieve reset. The introduction of discharge device 11 in this scheme adds parasitic parameters to the input of common-source amplifier 101, which can degrade the performance of the front-end electronics circuit. Furthermore, the dynamic range of the output signal of the front-end electronics circuit in this scheme is limited by the hysteresis of comparator 12, limiting it to a narrow range. This results in increased count loss in the detector connected to the front-end electronics circuit, reducing overall system efficiency. Summary of the Invention

[0005] In view of this, the present invention provides a preamplifier that does not use an additional discharge device and can effectively improve the effectiveness and timeliness of reset, and a detector including the preamplifier.

[0006] According to a first aspect of an embodiment of the present invention, a preamplifier is provided, which includes a charge-sensitive structure, a comparator, and a reset circuit.

[0007] The charge-sensitive structure includes a common-source amplifier, an operational amplifier and a feedback capacitor, wherein the operational amplifier is used to perform in-phase amplification on the output of the common-source amplifier, and the feedback capacitor is connected across the gate of the common-source amplifier and the output terminal of the operational amplifier.

[0008] One input terminal of the comparator is connected to the output terminal of the operational amplifier, and the other input terminal is connected to the threshold signal. The comparator is used to compare the signal output by the operational amplifier with the threshold signal and output a high level or a low level according to the comparison result.

[0009] The reset circuit includes a switch control module, a multistable circuit and a charge discharge module, wherein the switch control module includes a switch unit and a control unit, the multistable circuit is connected in series with the charge discharge module through the switch unit, and the charge discharge module is connected in series to the source of the common-source amplifier.

[0010] The control unit is connected to the output of the comparator and is configured to control the switch unit to turn on or off the circuit based on the level of the comparator output. The multistable circuit is configured to generate a rectangular wave signal. The charge discharge module is configured to lower the voltage at the source of the common-source amplifier upon receiving a pulse signal of the rectangular wave signal, thereby conducting the gate and source of the input transistor JFET in the common-source amplifier.

[0011] According to an embodiment of the present invention, the multistable circuit includes: a timer circuit, configured to control the pulse width of the rectangular wave signal and output the rectangular wave signal.

[0012] According to an embodiment of the present invention, the timer circuit includes a 555 timer.

[0013] According to an embodiment of the present invention, the common-source amplifier is composed of a junction field effect transistor (JFET).

[0014] According to an embodiment of the present invention, the charge discharge module includes a diode and a transistor. The anode of the diode is connected to the source of the common-source amplifier, and the cathode of the diode is connected to the collector of the transistor. The base of the transistor is connected to the charge discharge module via the switch unit, and the emitter of the transistor is connected to a low potential.

[0015] According to a second aspect of the embodiments of the present invention, a detector is provided, wherein the detector includes the preamplifier as described above.

[0016] According to an embodiment of the present invention, the detector is a high-purity germanium detector.

[0017] One or more of the above embodiments of the present invention have the following advantages or beneficial effects:

[0018] First, no additional discharge device is used at the input end of the preamplifier according to the embodiment of the present invention, thereby avoiding the influence of additional parasitic parameters on the performance of the preamplifier.

[0019] Secondly, in the mode where the switch control module is combined with the multi-stable circuit, the switch control module is connected or disconnected by the level control circuit of the comparator, and the multi-stable circuit can generate a periodic rectangular wave signal with controllable pulse width. When the switch unit of the switch control module is connected to the circuit, the periodic rectangular wave signal generated by the multi-stable circuit can trigger the front-end amplifier to discharge intermittently according to the pulse change of the rectangular wave signal. In this way, on the one hand, the switch control module using level control can ensure that during operation, the reset will not occur due to the failure to pick up the signal jump edge output by the comparator; on the other hand, it can also avoid the situation where a single reset is insufficient to meet the circuit reset requirements when the system state suddenly changes and too much charge accumulates on the feedback capacitor; on the other hand, when a reset is required, the intermittent discharge reset with the pulse change of the rectangular wave signal of the multi-stable circuit can also reduce the situation where the reset time is too long when relying solely on a single reset, which will interfere with the processing of the external detection signal input to the preamplifier during this period.

[0020] Third, the control level of the comparator is not directly related to the amplitude of the rectangular wave output by the multi-stable circuit. The control level of the comparator only controls the on and off of the switch unit in the switch control module (that is, the circuit is connected or disconnected). The pulse width and amplitude of the rectangular wave output by the multi-stable circuit can be set as needed (such as setting the amplitude according to the maximum discharge charge and pulse width, etc.), rather than being determined by the hysteresis of the comparator (the level of the comparator output directly controls the discharge of the circuit), thereby ensuring that the rectangular wave output by the multi-stable circuit can have a signal amplitude close to the full power supply voltage, which can improve the efficiency of discharge reset. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0022] Figure 1 The schematic diagram shows the circuit structure of a traditional preamplifier pulse feedback reset scheme;

[0023] Figure 2 A schematic diagram illustrating the structure of a preamplifier according to an embodiment of the present invention; and

[0024] Figure 3 The figure schematically shows a structure diagram of a multistable circuit according to an embodiment of the present invention. DETAILED DESCRIPTION

[0025] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of the concept of the present invention.

[0026] Given that Figure 1 The traditional preamplifier pulse feedback reset scheme shown has defects such as the introduction of parasitic capacitance and the narrow dynamic range of the output signal of the front-end electronic circuit. The related art has proposed a mode of realizing feedback reset by using a monostable pulse signal to control the conduction of the source and gate of the field effect transistor constituting the common source amplifier 101 instead of using an additional discharge device. In this mode, the output signal of the front-end electronic circuit can also be compared with a threshold signal by the comparator 12. When the output signal exceeds the threshold signal, the comparator 12 outputs a jump edge. However, the next step is similar to Figure 1 The processing method is different, in which the jump edge will be input into a monostable circuit, which will generate a gate pulse signal with a fixed width. The gate pulse signal can be used to lower the source voltage of the field effect tube, so that the source and gate of the field effect tube are turned on, and the charge accumulated on the feedback capacitor Cf is discharged through the conduction loop.

[0027] However, this model needs to be improved in at least two aspects:

[0028] 1) In this mode, the generation of the monostable pulse signal is triggered by the monostable circuit capturing the rising or falling edge of the comparator 12 output. However, in the presence of external interference or system instability, this edge may be lost or the monostable circuit may not effectively detect it. As a result, the monostable circuit cannot properly output the monostable pulse signal, resulting in a failure to properly reset the circuit. If a reset fails, the front-end electronics circuit will not function properly again without external intervention.

[0029] 2) Even if the monostable circuit correctly detects the transition edge of the comparator 12 output signal, it only generates a gate pulse signal with a fixed width. If the feedback capacitor Cf accumulates a larger charge than usual during operation, such as when the detector leakage current suddenly increases or a large interference signal is coupled from the high voltage through the detector to the front-end electronics, a single gate pulse signal with a fixed width will not be sufficient to discharge the charge accumulated on the feedback capacitor Cf. Furthermore, if the width of the gate pulse output by the monostable circuit is increased, the reset dead time will be increased, resulting in a large error in the count rate measurement.

[0030] In view of this, an embodiment of the present invention provides a new type of preamplifier, which can use a multi-stable circuit to generate a rectangular wave signal to control the on and off of the source and gate of the field-effect transistor to achieve the discharge and reset of the feedback capacitor, and use the output level of the comparator to control the switching action of a switch control module to disconnect or connect the multi-stable circuit. In this way, on the one hand, the level control avoids the hidden danger of failure to reset due to unsuccessful capture of the jump edge, and on the other hand, it avoids the defect that a single gate pulse signal is not sufficient to fully discharge the charge, thereby ensuring that the preamplifier can be effectively reset under any circumstances.

[0031] The following will be combined Figure 2 and Figure 3 The structure of the preamplifier according to the embodiment of the present invention is exemplarily described.

[0032] like Figure 2 As shown, the preamplifier 200 of an embodiment of the present invention may include a charge sensitive structure 10, a comparator 12 and a reset circuit. The structure and connection method of the charge sensitive structure 10 and the comparator 12 are similar to those of FIG. Figure 1 The charge-sensitive structure 10 is a front-end electronic circuit comprising two stages of amplification. One input of the comparator 12 is connected to the output signal of the operational amplifier 102, and the other input is connected to the threshold signal. The comparator 12 is used to compare the output signal of the operational amplifier 102 with the threshold signal and output a high or low level based on the comparison result.

[0033] The reset circuit includes a switch control module 201, a multistable circuit 202, and a charge discharge module 203. The switch control module 201 includes a switch unit and a control unit. The multistable circuit 202 is connected in series with the charge discharge module 203 via the switch unit, and the charge discharge module 203 is connected in series to the source of the common-source amplifier 101.

[0034] The control unit of the switch control module 201 is connected to the output terminal of the comparator 12 and is used to control the switch unit to connect or disconnect the circuit according to the level output by the comparator 12. The switch control module 201 can be a level-controlled switch, or can be designed as a switch circuit controlled by a level, and the specific selection can be made according to actual needs.

[0035] The multi-stable circuit 202 is used to generate a periodic rectangular wave signal with adjustable pulse width. In one embodiment, the multi-stable circuit 202 may include a voltage-stabilized power supply and a timer circuit. The voltage-stabilized power supply may be used to provide a power supply voltage for generating a rectangular wave signal. The timer circuit is connected to the voltage-stabilized power supply to control the pulse width of the rectangular wave signal and output a rectangular wave signal. In one embodiment, the circuit structure of the multi-stable circuit 202 may be as follows: Figure 3As shown, the timer circuit can be a 555 timer, wherein the regulated power supply VCC can power the 555 timer. The 555 timer is connected to a periodic rectangular wave generating circuit, and the low-level and high-level times of the periodic rectangular wave can both be adjusted by the 555 timing circuit. In another embodiment, the multistable circuit 202 can include only a timer circuit, wherein the regulated power supply VCC can be the regulated power supply of the system in which the preamplifier 200 is deployed.

[0036] The charge discharge module 203 is used to pull down the voltage of the source of the common source amplifier when receiving a pulse signal of a rectangular wave signal, so as to turn on the gate and source of the input tube in the common source amplifier. Figure 2 The charge discharge module 203 shown may include a diode and a transistor, wherein the anode of the diode is connected to the source of the common-source amplifier, and the cathode of the diode is connected to the collector of the transistor. The base of the transistor is connected to the charge discharge module 203 via a switch unit, and the emitter of the transistor is connected to a low potential.

[0037] The specific working process of the preamplifier is as follows:

[0038] In the first step, the output signal of the charge-sensitive structure 10 is still compared with a threshold signal through the comparator 12. When the output signal exceeds the threshold signal, the output level of the comparator 12 is flipped (assuming it is flipped from a low level to a high level);

[0039] The second step is to use the high level signal to control the switch unit in the switch control module 201 to close. Specifically, the high level signal is input to the control unit of the switch control module 201, and the control unit controls the switch unit to close the circuit after receiving the high level signal.

[0040] In the third step, the switch control module 201 is connected to the multi-stable circuit 202 and the charge discharge module 203. When the switch of the switch control module 201 is closed, the multi-stable circuit 202 and the charge discharge module 203 (such as the level conversion circuit therein) are connected;

[0041] In the fourth step, the multi-stable circuit 202 generates a periodic rectangular wave signal with adjustable pulse width.

[0042] In the fifth step, the periodic rectangular wave signal is used to control the on / off of the gate and source of the common source amplifier 101 (taking JFET as an example) through the charge discharge module 203. For example, Figure 2When the pulse signal in the rectangular wave signal triggers the transistor to turn on, the transistor's emitter is connected to a low potential, which can pull down the JFET's source voltage, thereby turning on the JFET's gate and source. This allows the charge signal of the feedback capacitor Cf to be discharged through the conduction circuit between the JFET's gate and source. Because the high and low level pulses in the rectangular wave signal change periodically, the JFET's gate and source can be triggered to turn on and off periodically, thus preventing the JFET's gate and source from being on for too long each time.

[0043] In the sixth step, when the charge signal of the feedback capacitor Cf is discharged and the output signal of the operational amplifier 102 is less than the threshold signal of the comparator 12, the output of the comparator 12 is flipped again (combined with the above assumption, the high level is flipped to the low level at this time). After the output of the comparator 12 is low, the switch unit of the switch control module 201 disconnects the circuit, disconnecting the multi-stable circuit 202 from the charge discharge module 203, and the reset is also completed. The circuit is in normal working state.

[0044] In this embodiment, the JFET itself can be used as a discharge device to discharge the feedback capacitor Cf. The specific principle is that when the JFET's source voltage is set to an extremely low level, the JFET's gate and source will conduct, and the charge accumulated on the feedback capacitor Cf will be discharged through this conduction loop. This avoids the parasitic parameters caused by the use of an additional discharge device at the input of the preamplifier. In addition, the charge discharge module 203 in this embodiment of the present invention is not directly connected to the input electrode, thereby preventing the introduction of additional noise at the input.

[0045] In the preamplifier 200 of the embodiment of the present invention, the switch control module 201 is combined with the multistable circuit 202. The switch control module 201 is connected or disconnected by the level control circuit of the comparator 12, and the multistable circuit 202 can generate a periodic rectangular wave signal with controllable pulse width. When the switch unit of the switch control module 201 is connected to the circuit, the periodic rectangular wave signal generated by the multistable circuit 202 can trigger the front-end amplifier to intermittently discharge according to the pulse variation of the rectangular wave signal. In this way, on the one hand, the switch control module 201 using level control can ensure that during operation, the reset failure will not occur due to the failure to pick up the signal transition edge output by the comparator 12; on the other hand, it can also avoid the situation where a single reset is insufficient to meet the circuit reset requirement when the system state suddenly changes and the amount of charge accumulated on the feedback capacitor Cf is too much; on the other hand, when a reset is required, the intermittent discharge reset is carried out according to the pulse variation of the rectangular wave signal of the multistable circuit 202, which can also reduce the situation where the reset time is too long when relying on a single reset, which will interfere with the processing of the detection signal of the detector input to the preamplifier during this period.

[0046] In the preamplifier 200 of the embodiment of the present invention, the control level of the comparator 12 is not directly associated with the amplitude of the rectangular wave output by the multi-stable circuit 202, wherein the control level of the comparator 12 only controls the on-off of the switch unit in the switch control module 201 (i.e., the connection or disconnection of the circuit). The pulse width and amplitude of the rectangular wave output by the multi-stable circuit 202 can be set as needed (such as setting the amplitude according to the maximum discharge charge and pulse width, etc.), rather than being determined by the hysteresis of the comparator 12 (the level output by the comparator 12 directly controls the discharge condition of the circuit), thereby ensuring that the rectangular wave output by the multi-stable circuit 202 can have a signal amplitude close to the full power supply voltage, which can improve the efficiency of discharge reset.

[0047] When applied to a detector (such as a high-purity germanium detector), the preamplifier 200 of the present invention embodiment exhibits high reset efficiency and timeliness, strong anti-interference capabilities, and minimal impact on normal operating signals. On one hand, the preamplifier 200 of the present invention embodiment overcomes the problem in related art where a monostable signal discharge reset method may fail due to external interference or changes in the detector's own performance. Once a reset fails, the front-end electronics cannot function normally again without external intervention. This ensures effective reset in any complex environment. On the other hand, the preamplifier 200 of the present invention embodiment does not use an additional discharge device at the preamplifier input, which can prevent the impact of additional parasitic parameters on the circuit performance of the preamplifier electronics, thereby improving detector performance.

[0048] It will be understood by those skilled in the art that the features described in the various embodiments of the present invention may be combined and / or coupled in various ways, even if such combinations or couplings are not explicitly described in the present invention. In particular, the features described in the various embodiments of the present invention may be combined and / or coupled in various ways without departing from the spirit and teachings of the present invention. All such combinations and / or couplings fall within the scope of the present invention.

[0049] The above describes embodiments of the present invention. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Although each embodiment has been described separately above, this does not mean that the measures in each embodiment cannot be advantageously used in combination. Without departing from the scope of the present invention, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present invention.

Claims

1. A preamplifier, characterized in that: include: A charge-sensitive structure, comprising a common-source amplifier, an operational amplifier, and a feedback capacitor, wherein the operational amplifier is used to perform in-phase amplification on the output of the common-source amplifier, and the feedback capacitor is connected across the gate of the common-source amplifier and the output terminal of the operational amplifier; a comparator having one input terminal connected to the output terminal of the operational amplifier and another input terminal connected to a threshold signal, for comparing the signal output by the operational amplifier with the threshold signal and outputting a high level or a low level according to the comparison result; A reset circuit, comprising a switch control module, a multistable circuit and a charge discharge module, wherein the switch control module comprises a switch unit and a control unit, the multistable circuit is connected in series with the charge discharge module via the switch unit, and the charge discharge module is connected in series to the source of the common-source amplifier; The control unit is connected to the output terminal of the comparator and is used to control the switch unit to connect or disconnect the circuit according to the level output by the comparator; The multistable circuit is used to generate a periodic rectangular wave signal with adjustable pulse width; The charge discharge module is used to pull down the voltage of the source of the common-source amplifier when receiving the pulse signal of the rectangular wave signal, so as to turn on the gate and source of the input tube in the common-source amplifier.

2. The preamplifier according to claim 1, wherein: The multi-stable circuit comprises: The timer circuit is used to control the pulse width of the rectangular wave signal and output the rectangular wave signal.

3. The preamplifier according to claim 1, wherein: The common source amplifier is composed of a junction field effect transistor (JFET).

4. The preamplifier according to claim 1, wherein: The charge discharge module includes a diode and a triode; wherein, The anode of the diode is connected to the source of the common-source amplifier, and the cathode of the diode is connected to the collector of the transistor; The base of the transistor is connected to the charge discharge module through the switch unit, and the emitter of the transistor is connected to a low potential.

5. A detector, characterized in that: include: The preamplifier according to any one of claims 1 to 4.

6. The detector according to claim 5, characterized in that The detector is a high-purity germanium detector.

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