RU210345U1 - Pulse code modulation laser ranger - Google Patents

Abstract

The utility model relates to optical instrumentation and is intended for use in devices for measuring the distance to objects on the ground using laser radiation. A laser range meter with pulse-code modulation is proposed, consisting of a transmitting channel containing pulsed semiconductor lasers installed in series with lenses, circuits for generating current pulses, a radiation pulse sensor, as well as a receiving channel, at the input of which an interference filter and an objective of the receiving channel and four avalanche photodiode, while additionally introduced reverse bias voltage generators, transimpedance amplifiers, pulse counters, FPGA1 for controlling lasers and processing optical signals, RAM with M-memory cells and FPGA2 for comparing voltages in memory cells with a threshold voltage, moreover, to the inputs of pulsed semiconductor lasers the output of the current pulse formation circuit is connected, the input of which is connected to the first output, and the input signal and noise pulse counters are connected to the second and third inputs of the FPGA1, while the amplified signal of the avalanche photodiodes in the form of a pulse sequence n is fed to the RAM input and after summation is recorded in the memory cells, the electrical output of the radiation sensor is connected to the first input, and the RAM output to the second input of the FPGA2, its output is connected to the inputs of the reverse bias voltage generators, the outputs of the formers are connected to the cathodes of avalanche photodiodes. The technical result is the creation of a laser range meter with pulse code modulation, which provides distance measurement up to 10-15 kilometers, increased noise immunity and secrecy, reduced average power consumption, reduced harmful effects on the eyes of observers.

Description

The utility model relates to optical instrumentation, and specifically to technical means for measuring the distance to objects on the ground using laser radiation.

A pulsed laser rangefinder is known (Patent for utility model No. 22386, G01C 3/00, 03/27/2002, Bull. No. 9), consisting of a pulsed solid-state laser, an optical sighting system, an optical system for reading information about the range, a photodetector, a meter time intervals, a digital display and a power supply, a p-i-n photodiode based on A3B5 compounds was used as a photodetector. The disadvantages of rangefinders based on solid-state lasers with pulse modulation are high power consumption, danger to vision, low secrecy of operation, insufficient distance measurement accuracy, and low noise immunity from external pulsed laser radiation.

Known laser rangefinder with increased range resolution (Utility model patent No. 167276, G01C 3/00, 12/27/2016, Bull. No. 36), consisting of receiving and phase channels, in which a pulsed semiconductor laser, a photodiode, a pulse formation circuit are installed current, a pulse generator, a receiving device, a control and information processing circuit, a radiation pulse sensor, a display, a frequency semiconductor laser, a modulation frequency generator, a frequency signal amplifier and a phase measurement circuit. The advantages of the utility model are higher accuracy and better noise immunity. The disadvantages of this device are high power consumption, danger to eyesight, low secrecy of work, complication of the design due to the additional phase channel.

The task is to increase stealth and noise immunity, reduce the laser radiation power.

The technical result of the proposed utility model is to increase the noise immunity and secrecy, reduce the average power consumption of the laser rangefinder through the use of pulse-code modulation of the laser radiation, while the amplitude of the pulses can be below the noise level.

To achieve the above technical result, a laser range meter with pulse code modulation is proposed, containing a transmitting channel consisting of pulsed semiconductor lasers installed in series with lenses, a circuit for generating laser current pulses, a radiation pulse sensor, as well as a receiving channel, at the input of which an interference detector is installed. filter and receiving channel lens and four avalanche photodiodes, while the device additionally includes reverse bias voltage generators, transimpedance amplifiers, total signal and noise pulse counters, FPGA1 for controlling lasers and processing optical signals, RAM with M-memory cells and FPGA2 for comparing voltages in memory cells with a threshold voltage, and the output of the current pulse shaping circuit is connected to the inputs of the pulsed semiconductor lasers, the input of which is connected to the first output, and the counters of the input signal and noise pulses are connected to the second and third to the inputs of FPGA1, while the amplified total signal of avalanche photodiodes in the form of a pulse sequence is fed to the input of the RAM and after summation is recorded in the memory cells, the electrical output of the radiation sensor is connected to the first input, and the output of the RAM to the second input of the FPGA2, its output is connected to the inputs of the shapers reverse bias voltage, the outputs of the shapers are connected to the cathodes of the avalanche photodiodes.

Figure 1 shows a block diagram of a laser range meter with pulse code modulation, where Roman numerals indicate the hardware modules of the range finder:

I - transmitting channel;

II - receiving channel;

III - control unit and signal conversion;

IV - block of correlation and recording of signals;

V - block for determining the range and sensitivity correction.

Wherein:

1, 2 - lenses of laser diodes;

3, 4 - semiconductor lasers (laser diodes);

5 - radiation sensor;

6 - diagram of the formation of laser current pulses;

7 - interference filter;

8 - lens of the photoreceiving channel;

9, 10, 11, 12 - avalanche photodiodes;

13, 14, 15, 16 - limiting resistors;

17, 18 - devices for generating bias voltages of photodiodes;

19, 20, 21, 22 - transimpedance amplifiers;

23, 24 - schemes "OR";

25, 26 - pulse counters;

27 - FPGA1;

28, 29 - schemes of coincidences "AND";

30, 31 - pulse adders;

32, 33 - shift registers;

34 - random access memory "RAM" with memory cells from 1 to M;

35 - FPGA2.

The device works as follows.

The laser rangefinder with pulse-code modulation of the signal is built on the principle of the optimal code. The master oscillator in the FPGA1 (27) generates pulses of the code sequence, which are fed to the input of the circuit for generating laser current pulses (6). In this case, the rangefinder lasers (3, 4) emit bursts of pulses encoded by a certain optimal code with a minimum divergence of beams focused by the lenses (1, 2) of the transmitting channel.

These code sequences can consist of many single pulses, but the uniqueness of these codes is that if you calculate the correlation function of this sequence, you can find that the side components of this function have a value of no more than the energy of one pulse.

When pulses are emitted by high-speed lasers, part of the pulse energy is reflected from the surfaces of the lenses and enters the radiation sensor (5), which converts the optical signal into electrical strobe pulses and starts the time interval measurement unit as part of the FPGA2 (35). The emitted signal, the amplitude of which does not exceed the average level of optical noise and backgrounds, encoded by the optimal code, reaches the object, after reflection from it, it enters the input of the receiving channel. After passing through the interference filter (7) and lens (8), the noise-like signal irradiates the receiving area of the avalanche photodiode (9), which, depending on the reverse bias voltage generated by the shapers (17, 18), can be in the photon counting mode or in the counter mode Geiger. The Geiger counter mode is implemented by applying a high reverse voltage to detect small optical signals from distant objects until the input pulse sequence (IPS) code is fixed. In order to reduce the "dead" time of the counters, limiting resistors (13-16) are connected in series with the photodiodes. In addition, at this time, with some delay, the same voltage is applied to the photodiode (11), which halves the pause caused by saturation of the diode (9). ), which is supplied with the same bias as the photodiodes (9, 11). However, the photoreceiving pads of these diodes are deployed with respect to the pads of the diodes (9) and (11) and they receive mainly background and noise signals. As soon as the input of the receiving channel receives a signal that differs in amplitude from the background, the bias voltage across the diodes decreases. With a decrease in the reverse voltage, the avalanche photodiode switches to the mode of counting individual pulses, the amplitude of which depends on the number of registered photons. In the future, despite the fact that the bias voltage is reduced, the amplitude of the pulses increases due to the summation of the EIT pulses. In this mode, the range finder is operational even when the amplitude of individual pulses is below the noise level, since the noise signals are random, and the signals of the optimal code are deterministic and are recorded at specified time intervals.

Electrical signals from all avalanche photodiodes are fed to the inputs of transimpedance amplifiers (19-22). Amplified pulses of signals from the object and noise through the "OR" circuits (23, 24) are normalized by voltage and fed to the inputs of electrical impulse counters (25, 26), from where they are sent in binary code to the second and third inputs of FPGA1 (27). At the same time, the normalized signal at the output of circuit (23) is an input pulse sequence containing the optimal code mixed with noise signals. To restore the VIP code, the amplitude-normalized pulse signal from the output of the circuit (23) is fed to the input of the RAM (34). The RAM implements M virtual correlators, the signals of which are recorded in the memory cells.

To restore the TIP from M pulses, it is necessary to apply the strobe pulse signal and the TIP signal delayed by the shift registers (32 or 33) to the “I” circuits (28 or 29), if the pulses coincide in time, the output of the coincidence circuits (28 and 29) will be generated pulses, which in the adders (30,31) are added to the RAM signal and are recorded in memory cells with numbers from 1 to M.

Next, the digital signal enters the FPGA2 (35), where, as a result of comparison with the threshold level voltage, the likelihood ratio is found and the reverse bias voltage of the avalanche diodes is adjusted in order to maximize the detection probability, and the number of objects (targets) and their range are determined.

The advantages of a range finder with pulse code modulation are the ability to control the radiation power not only by changing the amplitude and duration of laser pulses, but also by changing the number of pulses of optimal codes. In addition, it is possible to set the effective code length for the estimated range in order to increase the resolution of the meter.

Thus, the proposed useful model of a laser range meter with pulse code modulation has advantages over analogues, provides increased noise immunity and secrecy, reduced average power consumption, and reduced harmful effects on the eyes of observers.

Claims (1)

Laser range meter with pulse-code modulation, consisting of a transmitting channel containing pulsed semiconductor lasers installed in series with lenses, circuits for generating laser current pulses, a radiation pulse sensor, as well as a receiving channel, at the input of which an interference filter and an objective of the receiving channel and four avalanche photodiode, characterized in that it additionally introduced reverse bias voltage generators, transimpedance amplifiers, pulse counters, FPGA1 for controlling lasers and processing optical signals, RAM with M-memory cells and FPGA2 for comparing voltages in memory cells with a threshold voltage, and to The inputs of the pulsed semiconductor lasers are connected to the output of the current pulse shaping circuit, the input of which is connected to the first output, and the counters of the input signal and noise pulses are connected to the second and third inputs of the FPGA1, while the amplified total signal of the avalanche photodiodes in the form and the pulse sequence is fed to the RAM input and after summation is recorded in the memory cells, the electrical output of the radiation sensor is connected to the first input, and the RAM output to the second input of the FPGA2, its output is connected to the inputs of the reverse bias voltage generators, the outputs of the formers are connected to the cathodes of avalanche photodiodes.

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