A photomultiplier tube gating variable gain system

Abstract

The present invention discloses a novel PMT gating variable gain system for a pulsed lidar. It includes a multi-pixel photon counter, a voltage dividing network, an AGC variable gain unit, a gating pulse unit, a DC high voltage network, and a PMT synchronous control unit. The multi-pixel photon counter converts the received optical signal into an electrical signal; the voltage dividing network preliminarily amplifies the electrical signal generated by the multi-pixel photon counter, one path enters the AGC variable gain unit, and the other path enters the gating pulse unit; the gating pulse unit controls the potential between the first dynode and the photocathode to remain closed before the gating pulse arrives, and the AGC variable gain unit controls the potential difference between the dynodes to achieve variable gain amplification of the circuit; it reaches the PMT synchronous control unit through the DC high voltage network to control the PMT to achieve the purpose of fast gating variable gain. The present invention can effectively reduce the error caused by echo noise and expand the dynamic range.

Description

Technical Field

[0001] The present invention relates to the field of laser measurement, and particularly to a photomultiplier tube gating variable gain system, which is applied to the field of laser ranging. Background Art

[0002] With the booming development of laser technology in various fields, the technology of laser ranging has become relatively perfect and mature. Among them, the pulsed laser technology has gradually matured, and its application directions have also been expanded. Pulsed laser measurement uses a laser as a light source. The emitted laser reaches the surface of the object to be measured, and after reflection, it is received by the rangefinder. The rangefinder simultaneously records the round-trip time of the laser. Half of the product of the speed of light and the round-trip time is the distance between the rangefinder and the object to be measured. It has the advantages of simple structure, low price, high reliability, strong anti-interference performance, and no need for cooperative targets, and has been widely used in civil and military fields.

[0003] In order to detect different moments of laser echo pulses at different distances, generally, the photomultiplier tube measurement method is adopted. The purpose of the photomultiplier tube ranging method is to facilitate the processing of laser signals received at different distances. When measuring the distance, the photomultiplier tube is controlled to receive the laser signal at the corresponding moment, and the optical signal is converted into an electrical signal. The magnitude of the electrical signal reflects the distance of the object to be measured.

[0004] Currently, the main photomultiplier tube measurement methods are the normally closed type and the normally open type. The normally open type photomultiplier tube measurement method has a simple structure, but it is difficult to meet the design requirements for different measurement distances. The normally closed type photomultiplier tube measurement method needs to be externally controlled to open or close, and is often used in measurements under different depth ranges. However, it is difficult to select the opening moment to meet the requirements of ns level or ps level, so it is difficult to control. The invention with the application number 201510200729.8 discloses a study on a dual-channel time discrimination circuit. Its defects are: it is difficult to accurately control the opening and closing of the normally closed photomultiplier tube, provide the selection of the gating pulse width (gate width) and delay time, and it is relatively complex to adjust the gain at different measurement distances. It is often saturated due to excessive amplitude at the gating moment. Therefore, it is necessary to improve and perfect the above gating variable gain system. Summary of the Invention

[0005] The purpose of the present invention is to provide a new PMT gating variable gain system for pulsed lidar, which can effectively avoid the saturation of the photomultiplier tube caused by the echo amplitude, accurately determine the gating moment through a multi-pixel photon counter (MPPC), improve the dynamic range of measurement, and thus further effectively improve the measurement accuracy of pulsed laser ranging.

[0006] To achieve the object of the present invention, the following technical solutions are adopted: A novel PMT gating variable gain system for a pulsed lidar, comprising a multi-pixel photon counter (MPPC), a voltage dividing network, an AGC variable gain unit, a gating pulse unit, a DC high voltage network, and a photomultiplier tube synchronous control unit; in the multi-pixel photon counter (MPPC) and the voltage dividing network, the received laser signal is converted into an electrical signal by the multi-pixel photon counter (MPPC), and the electrical signal enters the voltage dividing network, and the voltage dividing network adjusts and transmits it to the next unit according to the received electrical signal; after receiving the signal, the AGC variable gain unit generates a corresponding gain signal according to the signal strength; after receiving the signal, the gating pulse unit generates a gating signal, and the gain signal and the gating signal are given corresponding control signals to the photomultiplier tube through the DC high voltage network and the photomultiplier tube synchronous control unit.

[0007] The beneficial effects of the present invention are as follows: A novel PMT gating variable gain system for a pulsed lidar is adopted, including an external trigger photoelectric conversion technology in the photomultiplier tube synchronous control unit. The combination of the gating technology and the variable gain technology is used to jointly obtain and determine the arrival time and dynamic range of the laser echo, that is, it improves the dynamic range of laser ranging and effectively provides that the main wave signal of the gating can be controlled and synchronized with the photomultiplier tube; on the other hand, the combination of the gating technology and the variable gain technology effectively solves the opening and closing of the normally closed photomultiplier tube at the gating moment and overcomes the influence caused by the over-saturation problem caused by the change of the laser echo pulse amplitude; the present invention is suitable for the detection of high-energy narrow pulses and large distance ranges, and can overcome the over-saturation caused by time gating and echo amplitude. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is the principle block diagram of the present invention.

[0009] Figure 2 is the circuit structure diagram of the gating pulse unit in the receiving system of the present invention.

[0010] Figure 3 is the circuit structure diagram of the AGC variable gain unit in the receiving system of the present invention.

[0011] Figure 4 is the waveform diagram of the gating implementation principle in the receiving system of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Embodiment:

[0013] Combined with Figure 1A novel PMT gating variable gain system for a pulsed lidar, comprising a multi-pixel photon counter (MPPC), a voltage dividing network, an AGC variable gain unit, a gating pulse unit, a DC high voltage network, and a photomultiplier tube synchronous control unit; in the multi-pixel photon counter (MPPC) and the voltage dividing network, the received laser signal is converted into an electrical signal by the multi-pixel photon counter (MPPC), and the electrical signal enters the voltage dividing network, and the voltage dividing network adjusts and transmits it to the AGC variable gain unit and the gating pulse unit according to the received electrical signal; according to the time delay of the optical pulse and the time delay of the electrical pulse, the AGC variable gain unit and the gating pulse unit are respectively set with an inherent delay. After receiving the signal, the AGC variable gain unit generates a corresponding gain signal according to the signal strength; after receiving the signal, the gating pulse unit generates an ultra-fast, high-voltage, narrow pulse-width gating signal, and the gain signal and the gating signal are given to the photomultiplier tube synchronous control signal through the DC high voltage network and the photomultiplier tube synchronous control unit.

[0014] Combined with Figure 2 , the gating pulse unit includes an avalanche triode and a diode clipping circuit. The avalanche triode generates an ultra-fast step high-voltage pulse, and then the ultra-fast step high-voltage pulse is clipped by the diode clipping circuit to output a gating pulse signal. Preferably, the gating pulse signal is a picosecond gating pulse signal. One end of the output terminal of the voltage dividing network is connected to the first end of the avalanche triode Q1, the second end of the avalanche triode Q1 is connected to the first end of the first diode VD1; the second end of the avalanche triode Q1 is connected to the second end of the second diode VD2; the third end of the avalanche triode Q1 is connected to the second end of the first voltage source E1, and the third end of the avalanche triode Q1 is connected to the first end of the second voltage source E2; the second end of the first diode VD1 is connected to the first end of the first voltage source E1; the first end of the second diode VD2 is connected to the second end of the second voltage source E2; the first end of the differentiator U1 is connected to the avalanche triode Q1; the second end of the differentiator U1 is connected to the third end of the avalanche triode;

[0015] Combined with Figure 3 , the AGC variable gain unit is composed of a transimpedance amplifier circuit, an AGC circuit, a switch, and an output buffer circuit. The main amplifier circuit is divided into three stages of amplification to control the signal gain. The AGC circuit generates a suitable switch control signal. The AGC variable gain unit realizes the preliminary circuit variable gain amplification process by controlling the potential difference between the last dynode and the penultimate dynode. Preferably, the input dynamic range is increased.

[0016] Combined with Figure 3, the third terminal of the differentiator U1 is connected to the first terminal of the second operational amplifier U2; the second terminal of the second operational amplifier U2 is connected to the first terminal of the third operational amplifier U3; the second terminal of the third operational amplifier U3 is connected to the first terminal of the fourth operational amplifier U4; the second terminal of the fourth operational amplifier U4 is connected to the first terminal of the fifth operational amplifier U5; the second terminal of the fifth operational amplifier U5 is connected to the photomultiplier tube strobe variable gain control circuit; the first terminal of the switch SWh1 is connected to the second terminal of the second operational amplifier U2; the second terminal of the switch SWh1 is connected to the second terminal of the 5th operational amplifier U5; the third terminal of the switch SWh1 is connected to the first terminal of the AGC; the first terminal of the switch SWh2 is connected to the second terminal of the third operational amplifier U3; the second terminal of the switch SWh2 is connected to the second terminal of the 5th operational amplifier U5; the third terminal of the switch SWh2 is connected to the second terminal of the AGC; the first terminal of the switch SWh3 is connected to the second terminal of the third operational amplifier U4; the second terminal of the switch SWh3 is connected to the second terminal of the 5th operational amplifier U5; the third terminal of the switch SWh3 is connected to the second terminal of the AGC;

[0017] Combined with Figure 4 , a is the system off state. At this time, the multi-pixel photon counter (MPPC) does not receive the laser signal, and the potential of the photocathode is higher than that of the dynode. There is a potential difference between the photocathode and the dynode, and the system is in the off state at this time. b is the system strobe state. The multi-pixel photon counter receives the laser signal and preliminarily processes the signal and transmits it to the voltage dividing network. The voltage dividing network processes the signal and divides it into two electric pulse signals to trigger strobe and variable gain. Then, the voltage generated by the DC high-voltage network is applied to the control circuit of the photomultiplier tube, and a pulsed negative high voltage is superimposed on the potential of the photocathode. When the potential of the photocathode is lower than that of the dynode, the photomultiplier tube is in the conduction state.

[0018] Combined with Figure 4 , according to theoretical analysis and experimental verification, the schematic diagram of the waveforms of the off and on states in the new PMT strobe variable gain system of the pulsed lidar is as Figure 4 shown. In the figure, V1(t) is the waveform of the photocathode potential, and V2(t) is the dynode potential. When the system is in the off state, the photomultiplier tube is in the off interval when V1(t) < V2(t). The photomultiplier tube is in the strobe interval when V1(t) > V2(t).

[0019] When receiving the target laser signal, the oscilloscope detects whether the target signal can detect a waveform. When the received signal generates a corresponding waveform within the strobe interval, the system is considered effective.

Claims

1. A novel PMT gating variable gain system for pulsed lidar, characterized in that It consists of a multi-pixel photon counter (MPPC), a voltage division network, an AGC variable gain unit, a gating pulse unit, and a photomultiplier tube synchronous control unit; The multi-pixel photon counter (MPPC) converts the signal received by the beam splitter of the laser emission system into an electrical signal. Its main function is to pre-collect the optical signal before the photomultiplier tube receives the optical signal for the control of gated variable gain. The voltage division network preliminarily amplifies the electrical signal generated by the multi-pixel photon counter and splits the electrical signal into two paths. One path enters the AGC variable gain unit, and the other path enters the gating pulse unit. After obtaining the pulse signal, the gating pulse unit controls the potential between the first dynode and the photocathode to remain closed before the gating pulse arrives. The AGC variable gain unit realizes the preliminary circuit variable gain amplification process by controlling the potential difference between the last dynode and the penultimate dynode. It reaches the photomultiplier tube synchronous control unit through the DC high-voltage network to control the photomultiplier tube to achieve its function, thus achieving the purpose of fast gated variable gain of the photomultiplier tube.

Images