CN114236494B

CN114236494B - Echo signal optimizing system for single-frequency laser radar water depth measurement

Info

Publication number: CN114236494B
Application number: CN202111450763.2A
Authority: CN
Inventors: 周国清; 赵大为
Original assignee: Guilin University of Technology
Current assignee: Guilin University of Technology
Priority date: 2021-11-30
Filing date: 2021-11-30
Publication date: 2023-05-05
Anticipated expiration: 2041-11-30
Also published as: CN114236494A

Abstract

The invention discloses a single-frequency laser radar water depth measurement echo signal optimization system. The device comprises a solid laser (532 nm), an optical receiving module, a photomultiplier tube (PMT), a radio frequency amplifier, a linear voltage stabilizing module and a direct current power supply. The laser emits 532nm blue-green laser with strong water penetration to pass through the water surface to reach the water bottom. The laser light reaches the water bottom and returns to the optical receiving module. The optical receiving module outputs laser to the PMT. PMTs convert the optical signal into a weak current signal. The radio frequency amplifying circuit receives the current signal and effectively amplifies the signal. The linear voltage stabilizing module supplies power to the radio frequency amplifier, and the direct current power supply supplies power to all parts. The invention can overcome the defect of gain bandwidth product of the transconductance amplifier, realize amplifying PMT output current signals in a large frequency range, better acquire laser echo signals, expand dynamic range and increase water measuring depth.

Description

Echo signal optimizing system for single-frequency laser radar water depth measurement

Technical Field

The invention relates to the field of laser measurement, in particular to a single-frequency laser radar water depth measurement echo signal optimization system which is applied to the field of laser ranging.

Background

In order to detect different moments of laser echo pulses at different distances, a photomultiplier is generally used for measurement, and the purpose of the photomultiplier is to process laser signals received at different distances. When the distance is measured, the photomultiplier is controlled to receive the laser echo signals at corresponding moments and convert the laser echo signals into electric signals, and the amplitude of the electric signals reflects the distance of the measured object.

The existing main photomultiplier measuring methods are two measuring methods which are normally closed and normally open. The normally open photomultiplier measuring method is simple in structure, but is difficult to match with the requirements of different measuring distances. The normally closed photomultiplier measuring method needs to be externally controlled to be opened or closed and is often applied to measurement in different depth ranges, but the opening time is difficult to meet the requirements of ns level or ps level, so that the normally closed photomultiplier measuring method is difficult to control. The invention with application number 202110848299.6 discloses a research of a transconductance type amplifying circuit, which has the following defects: the signal output by the photomultiplier tube (PMT) is very weak and is difficult to identify by the acquisition circuit, the gain bandwidth product of the transimpedance amplification circuit determines that the method is difficult to meet the requirement of ensuring the bandwidth while simultaneously giving attention to the gain, and the dynamic range is smaller.

Disclosure of Invention

Aiming at the defects that echo signals are weak and a transimpedance amplification circuit is difficult to achieve both gain and bandwidth, the invention provides a single-frequency laser radar water depth measurement echo signal optimization system, when a photomultiplier tube (PMT) receives weak laser signals, weak current signals are generated and sent to a radio frequency amplification circuit, an isolated direct current signal is sent to a radio frequency amplifier in a special AC coupling mode, and the radio frequency amplifier achieves both gain and bandwidth to effectively amplify the signals to a suitable receiving range, so that the water surface signals are clear and discernable.

The invention comprises two parts of system composition and workflow.

The single-frequency laser radar water depth measurement echo signal optimization system consists of a solid laser (532 nm), an optical receiving module, a photomultiplier tube (PMT), a radio frequency amplifier, a linear voltage stabilizing module and a direct current power supply.

The solid-state laser emits a blue-green laser light having a wavelength of 532nm, which has high transmittance.

The optical receiving system is mainly used for receiving laser signals reflected back after laser emitted by the solid laser reaches an object;

a photomultiplier tube (PMT) receives the weak laser signal returned by the optical receiving module and converts the weak laser signal into an electrical signal;

the radio frequency amplifier receives and amplifies a current signal generated by a photomultiplier tube (PMT) and is conveniently identified by a subsequent acquisition circuit. The radio frequency amplifier can realize current amplification within the bandwidth of 800-1500 MHz through the excellent bandwidth characteristic; the radio frequency amplifying circuit effectively isolates the direct current component in the input signal by adopting a cascades structure and a resistance-capacitance coupling mode, and the design of setting a direct current bias network is to provide a proper static working point for the amplifier. A discharge resistor is placed between the capacitor and the input signal to form a ground loop to prevent output offset. The front and back of the radio frequency amplifier are required to keep 50 ohms impedance matching, and the matching network adopts a pi-type resistance network structure.

The linear voltage stabilizing module supplies power to the radio frequency amplifier, and the direct current power supply supplies power to all parts. The linear voltage stabilizing module selects an ultralow noise linear voltage stabilizer. The internal of the power supply is composed of a CMOS transistor and an error amplifier, and excess voltage is subtracted from the input voltage of the front end to generate regulated output voltage to provide heating overload protection, safety current limiting and other value-added performances, and the power consumption can be greatly reduced in the turn-off mode. For a radio frequency amplifier, noise is very sensitive to signal waveforms, and a linear regulator with very low output voltage ripple can suppress power supply noise to the maximum.

The working flow of the single-frequency laser radar water depth measurement echo signal optimization system is as follows:

(1) the upper computer issues instructions to trigger the laser, and the laser emits blue-green laser to reach the water surface, and passes through the water surface to reach the water bottom.

(2) The laser returns a laser echo signal through the water bottom, is received by an optical receiving module and is transmitted to a photomultiplier tube (PMT).

(3) Photomultiplier tubes (PMTs) convert the light signals into weak current signals.

(4) The weak current signal is transmitted to the radio frequency amplifying circuit to effectively amplify the signal.

The beneficial effects of the invention are as follows: on one hand, a weak optical signal is converted into an amplified signal through a radio frequency amplifier, so that the dynamic range of laser ranging is improved. On the other hand, the radio frequency circuit isolates the direct current signal through a special AC coupling mode, and the radio frequency circuit gives consideration to gain and bandwidth, so that the underwater surface signal is clear and distinguishable. In addition, the invention is suitable for the water depth detection of high-energy narrow pulses and large-distance ranges, can effectively amplify echo signals and expands the dynamic range.

Drawings

Fig. 1 is a functional block diagram of the present invention.

Fig. 2 is a block diagram of a radio frequency amplifier circuit in the system of the present invention.

Fig. 3 is a circuit configuration diagram of a linear voltage stabilizing module in the system of the present invention.

Fig. 4 is a system PCB design of the present invention.

FIG. 5 is a view of a circuit board shielding cavity of the system of the present invention

FIG. 6 is a schematic diagram of a system experiment of the present invention.

Fig. 7 is a waveform comparison chart of the system of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, preferred embodiments are described below, and the detailed description of the present invention is further described with reference to the accompanying drawings.

Examples:

referring to fig. 1, the system for optimizing the echo signals of the single-frequency laser radar water depth measurement consists of a solid laser (532 nm), an optical receiving module, a photomultiplier tube (PMT), a radio frequency amplifier, a linear voltage stabilizing module and a direct current power supply.

Referring to fig. 2, the rf amplifying circuit includes a resistor-capacitor coupling, a dc bias network, an amplifier body, and a matching network. The radio frequency amplifying circuit adopts a cascades structure, and the resistance-capacitance coupling mode is a capacitor C ₂ In phase with an operational amplifierThe inputs are connected in series, preferably isolating the dc component of the input signal. The MMIC low noise silicon transistor radio frequency amplifier INA-02184 produced by hp company is selected as the core amplifier of the component, the 3dB bandwidth is 800MHz, the INA-02184 low noise amplifier can provide 31dB gain at the bandwidth of 0.5GHz, and the INA-02184 can provide 26dB gain at the bandwidth of 1.5GHz, so the INA-02184 can stably provide 30dB gain within 500MHz-800 MHz. The design of the dc bias network is chosen to provide a proper static operating point for the amplifier, preferably to ensure constant operating characteristics of the amplifier. The front and back of the radio frequency circuit maintains 50 ohms impedance match, better connecting the front and back parts. The output end of the PMT is connected with the first end of a first resistor R1, the first end of the first resistor R1 is connected with the first end of a first capacitor C1, and the second end of the first resistor R1 is grounded; the first end of the amplifier is connected with the second end of the first capacitor, and the second end, the third end and the fifth end of the amplifier are all grounded; the first end of the first inductor L1 is connected with the fourth end of the amplifier, and the second end of the first inductor L1 is connected with the output end of the linear voltage stabilizing module; the first end of the second capacitor C2 is connected with the first end of the first inductor L1; the first end of the second resistor R2 is connected with the second end of the second capacitor C2, and the second end of the second resistor R2 is grounded; the first end of the third resistor R3 is connected with the first end of the second resistor R2; the second end of the third resistor R3 is connected with the first end of the fourth resistor R4; the second end of the fourth resistor R4 is grounded, and the first end of the fourth resistor R4 is connected with output.

Referring to fig. 3, a circuit diagram of the linear voltage stabilizing module provides a required +12v dc power supply for a radio frequency amplifying circuit (fig. 2) on the system through a power supply input port. The ultra-low noise linear voltage stabilizer P1TPS7A4901 is selected, has enough input voltage margin, is internally composed of a CMOS transistor and an error amplifier, subtracts excess voltage from the input voltage at the front end to generate regulated output voltage, has smaller package and can provide heating overload protection, safe current limiting and other value-added performances, and the turn-off mode can also greatly reduce the power consumption. D1 is a rectifier diode, which has unidirectional conductivity to prevent reverse connection of power supply. R5 and R6 are sampling resistors, and the ratio of the sampling resistors controls the output voltage. D2 represents normal power supply of the linear voltage stabilizing circuit for the light emitting diode, the voltage drop of the light emitting diode is set to 2V, the current is about 150ma according to technical documents, and r4 is a current limiting resistor which is allocated to the light emitting diode. C7 and C8 are filter capacitors, and are used for filtering most of alternating current components in the output voltage to obtain smoother direct current voltage. The noise is very sensitive to the signal waveform and the linear regulator P1 has a very low output voltage ripple, preferably to suppress the supply noise to a maximum.

Referring to fig. 3, the dc power supply supplies a dc voltage of +12v to the linear voltage regulator P1; the first end of the rectifying diode D1 is connected with the output end of the direct-current power supply, and the second end of the rectifying diode D1 is connected with the first end of the third capacitor C3; the first end of the linear voltage stabilizer P1 is connected with the first end of the seventh resistor R7, the second end of the linear voltage stabilizer P1 is connected with the first end of the fifth capacitor C5, the third end of the linear voltage stabilizer P1 is empty, the fourth end of the linear voltage stabilizer P1 is grounded, the fifth end of the linear voltage stabilizer P1 is connected with the first end of the third capacitor C3, the sixth end of the linear voltage stabilizer P1 is connected with the first end of the fourth capacitor C4, and the seventh end of the linear voltage stabilizer P1 is connected with the first end of the third capacitor C3; the second end of the third capacitor C3 and the second end of the fourth capacitor C4 are grounded; the second end of the fifth capacitor C5 is connected with the first end of the linear voltage stabilizer P1; the first end of the sixth capacitor C6 is grounded, and the second end of the sixth capacitor C6 is connected with the first end of the seventh resistor R7; the first ends of the seventh capacitor C7 and the eighth capacitor C8 are connected with the second end of the light-emitting diode D2, and the second ends of the seventh capacitor C7 and the eighth capacitor C8 are grounded; the first end of the fifth resistor R5 is grounded, the second end of the fifth resistor R5 is connected with the first end of the sixth capacitor C6, and the second end of the sixth capacitor C6 is connected with the second end of the sixth capacitor C6; the first end of the light emitting diode D2 is connected with the second end of the seventh resistor R7, and the second end of the light emitting diode D2 is the output end of the linear voltage stabilizing module.

With reference to fig. 4, the PCB design is performed according to the design rules such as the routing direction control, the routing matching rule, the routing resonance rule, etc., in order to make the amplifier operate well, a large number of vias are configured and connected with GND to the bottom layer, so as to have the shortest path to the ground for the interference signal, and meanwhile, a certain distance is kept between the vias and the radio frequency signal line, so as to prevent EMI from affecting the quality of the radio frequency signal.

With reference to fig. 5, the design of the shielding cavity is that the shielding cover is connected with the ground wire of the circuit board, and the screw is fastened in the shielding cavity. The shielding cavity inhibits the propagation of alternating magnetic field and alternating electromagnetic field interference in space, and has the functions of static electricity prevention and circuit board protection.

Referring to fig. 6, after laser is emitted from the system, the laser passes through the optical receiving module and reaches the water bottom, and after receiving a laser echo signal, a photomultiplier tube (PMT) obtains a waveform through processing of a laser echo circuit.

With reference to fig. 7, two sets of contrast without a radio frequency amplifier are respectively provided, and two sets of water surface and water bottom echo signals are displayed through an oscilloscope. In fig. 7, examples a1, a2, a3 are waveforms of laser echoes collected by the rf-free circuit. Examples b1, b2, b3 in fig. 7 are graphs of laser echo waveforms acquired by adding the rf circuits designed herein. Under the requirement of 500MHz-800MHz bandwidth required by the system, the pumping current of the laser is set to be 1A, 2A and 3A respectively. As can be seen from the comparison between the corresponding digital legends of examples a and b of fig. 7, the amplitude of the shipboard laser echo system added with the radio frequency circuit is obviously improved, and the amplification factor is about 30dB.

When a target laser signal is received, the oscilloscope detects whether the target signal can detect the waveform, and when the received signal generates a corresponding waveform in a gating interval, the system is considered to be effective.

The above embodiments are merely for illustrating the present invention and not for limiting the present invention, and various changes and modifications may be made by one of ordinary skill in the related art without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions are also within the scope of the present invention, which is defined by the claims.

The technical content that is not described in detail in the invention is known in the prior art.

Claims

1. The single-frequency laser radar water depth measurement echo signal optimizing system; the device is characterized by comprising a 532nm solid laser, an optical receiving module, a photomultiplier tube (PMT), a radio frequency amplifier, a linear voltage stabilizing module and a direct current power supply; the upper computer sends a triggering instruction, and the solid laser sends out laser with 532nm wavelength after receiving the instruction; the laser penetrates through the water body to reach the water bottom and then is reflected back to the laser echo signal; the optical receiving system receives the laser echo signals and transmits the laser echo signals to a photomultiplier tube (PMT); a photomultiplier tube (PMT) receives the weak laser signal sent by the optical receiving module and converts the optical signal into an electric signal; a radio frequency amplifier is adopted to receive and amplify a current signal generated by a photomultiplier tube (PMT), so that the current signal is convenient for a subsequent acquisition circuit to identify; the linear voltage stabilizing module supplies power to the radio frequency amplifier, and the direct current power supply supplies power to each part;

the radio frequency amplifying circuit effectively isolates the direct current component in the input signal by adopting a cascades structure and a resistance-capacitance coupling mode, and the design of setting a direct current bias network is to provide a proper static working point for the amplifier; a discharge resistor is arranged between the capacitor and the input signal to form a ground loop to prevent output offset; the front and back of the radio frequency amplifier are required to keep 50 ohms impedance matching, and a pi-type resistance network structure is adopted as a matching network;

the radio frequency amplifying circuit comprises a resistor-capacitor coupling, a direct-current bias network, an amplifier body and a matching network, wherein the radio frequency amplifying circuit adopts a capacitor C2 and an operational amplifier in-phase input end are connected in series in a resistor-capacitor coupling mode, direct-current components in input signals are isolated, an MMIC low-noise silicon transistor radio frequency amplifier INA-02184 produced by hp company is selected as a core of the radio frequency amplifier, 30dB gain can be stably provided by INA-02184 in 500MHz-800MHz, proper static working points are provided for the radio frequency amplifier by adopting the design of the direct-current bias network, the constant working characteristics of the radio frequency amplifier are guaranteed, and the front and rear parts of the radio frequency circuit are better connected through 50-ohm impedance matching;

the linear voltage stabilizing module is characterized in that an ultralow noise linear voltage stabilizer is selected; the internal of the power supply is composed of a CMOS transistor and an error amplifier, and excess voltage is subtracted from the input voltage at the front end to generate regulated output voltage to provide heating overload protection and safe current limiting value-added performance, and the power consumption can be greatly reduced in the turn-off mode; for the radio frequency amplifier, noise is very sensitive to signal waveforms, and the linear voltage regulator has very low output voltage ripple so as to furthest suppress power supply noise;

the direct current power supply is characterized in that the direct current power supply adopts a linear voltage-stabilizing direct current power supply which can supply power for a 532nm solid laser, a Photomultiplier (PMT) and a linear voltage-stabilizing module;

the system is characterized in that the workflow of the system comprises an upper computer sending down a command to trigger a laser, and the laser emits laser to reach the water surface and penetrate through the water surface to reach the water bottom; the laser returns a laser echo signal through the water bottom; the laser echo signal returns to reach a photomultiplier tube (PMT) after passing through the optical receiving module; photomultiplier tubes (PMTs) convert the light signals into weak current signals; transmitting the current signal to a radio frequency amplifying circuit; the radio frequency amplifying circuit receives the current signal and effectively amplifies the signal.