CN110361716B - Human eye protection circuit for optical detection and ranging system - Google Patents

Abstract

The invention discloses a human eye protection circuit that can be used in light detection and ranging systems. The human eye protection circuit includes: a digital-to-analog converter, which converts an input sampling signal into an output DC level. signal, the sampling signal is sampled from the light detection and ranging system; and a comparator, the comparator receives the DC level signal and the threshold voltage signal as input, and outputs a protection signal at the same time, and the protection signal is fed back to the The light detection and ranging system is used to shut down the light detection and ranging system when the pulse intensity of the light detection and ranging system exceeds the endurance of the human eye; wherein the DC level signal is higher than the threshold voltage When the DC level signal is lower than the threshold voltage signal, the protection signal is at a high level; conversely, when the DC level signal is lower than the threshold voltage signal, the protection signal is at a low level. The invention has the beneficial effect of automatically shutting down problematic laser driving circuits to protect human eyes.

Description

A human eye protection circuit that can be used in light detection and ranging systems

Technical field

The invention belongs to the field of light detection and ranging, and specifically relates to a human eye protection circuit that can be used in light detection and ranging systems.

Background technique

Many applications cannot measure distance to a target by establishing actual contact with the target. Possible options for non-contact distance measurement include millimeter waves, lasers and ultrasound. Light detection and ranging (LIDAR) systems use the time it takes for light to travel between objects to try to measure the distance to this target, and flash LIDAR systems use pulsed lasers and a pulsed time-of-flight (TOF) algorithm to calculate target distance. The system emits extremely narrow pulses, with widths ranging from a few ns to tens of ns, and peak powers ranging from hundreds of mW to 70W or more. For the human eye, the accumulated thermal effects of higher peak power laser irradiation in continuous mode or wider pulses can cause damage. But with the pulse mode and lower duty cycle it is acceptable to the human eye. The commonly used pulse laser drive circuits today do not take into account the personal injury that may be caused when the pulse laser fails or is misoperated.

Contents of the invention

In view of the problems existing in the prior art, the present invention provides a human eye protection circuit that can be used in light detection and ranging systems. Some embodiments of the present invention can use multiple safety designs to avoid hazards to the human body when problems occur in the driving circuit. It is compatible with existing sampling circuits and will not affect the normal operation of existing driving circuits. This circuit considers both purely analog circuits and solutions when controlled by digital circuits.

In order to achieve the above objects, the present invention adopts the following technical solutions:

A human eye protection circuit that can be used in light detection and ranging systems, the human eye protection circuit includes: a digital-to-analog converter, the digital-to-analog converter converts an input sampling signal into an output DC level signal, the The sampling signal is sampled from the light detection and ranging system; and

A comparator that receives the DC level signal and the threshold voltage signal as input and outputs a protection signal at the same time. The protection signal is fed back to the light detection and ranging system for use in the light detection and ranging system. When the system pulse intensity exceeds the endurance of the human eye, the light detection and ranging system is shut down; when the DC level signal is higher than the threshold voltage signal, the protection signal is high level; otherwise, the DC level signal is high. When the signal is lower than the threshold voltage signal, the protection signal is low level.

Preferably, the human eye protection circuit further includes: a latch, a first end of the latch receives the protection signal as an input, a second end of the latch outputs a conversion signal, the conversion signal Feedback to the light detection and ranging system is used to shut down the light detection and ranging system when the pulse intensity of the light detection and ranging system exceeds the endurance of the human eye. When the protection signal is converted to a high level, The conversion signal then converts to a high level.

Preferably, the third terminal of the latch is connected to the second terminal through an inverter, and the third terminal receives the reversed conversion signal. When the third terminal is at a low level, the The conversion signal output from the second terminal is locked.

Preferably, the latch has a fourth terminal for receiving a reset signal.

Preferably, the light detection and ranging system includes a laser drive circuit and an arithmetic unit. The arithmetic unit receives a trigger signal and an inverted conversion signal as input, and the arithmetic unit combines the trigger signal and the inverted converted signal. The converted signal is subjected to logical AND operation and then output to the laser driving circuit.

Preferably, the second end of the latch is connected to a single-chip computer, and the single-chip computer is connected to the light detection and ranging system. When the conversion signal received by the single-chip computer is at a high level, the single-chip computer turns off all Described light detection and ranging system.

Preferably, the sampling signal is sampled from a laser driving circuit in the light detection and ranging system.

Preferably, the sampling signal is sampled from a laser receiving circuit in the light detection and ranging system.

Preferably, the laser receiving circuit is connected to one end of a transimpedance amplifier for converting the received laser pulse signal into an electrical pulse signal, and the other end of the transimpedance amplifier is connected to one end of a cascade amplifier for amplifying The electrical pulse model serves as the sampling signal, and the other end of the cascade amplifier is connected to the digital-to-analog converter for inputting the sampling signal.

Compared with the prior art, the beneficial effects of the present invention are:

1. This invention can automatically shut down problematic laser driving circuits to protect human eyes;

2. The present invention can adjust different thresholds according to the width of the pulse to apply to different situations where pulse width needs to be limited;

3. Multiple safety designs are used to avoid harm to the human body when problems occur in the drive circuit. It is also compatible with existing sampling circuits and will not affect the normal operation of the existing drive circuit. This circuit considers both pure analog circuits and active circuits. Solutions for digital circuit control.

Description of the drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without exerting creative efforts.

Figure 1 is the circuit block diagram of Lidar application.

Figure 2 is a schematic diagram of the principle of an embodiment of the present invention.

Figure 3 is a schematic block diagram of the sampling signal coming from the laser driving circuit in the embodiment of the present invention.

Figure 4 is a schematic block diagram of the sampling signal coming from the laser receiving circuit in the embodiment of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without exerting creative efforts fall within the scope of protection of the present invention.

In the description of the present invention, it should be understood that the terms "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", The orientations or positional relationships indicated by "horizontal", "top", "bottom", "inner", "outer", etc. are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and are not Any indication or implication that the referred device or element must have a specific orientation, be constructed and operate in a specific orientation should not be construed as a limitation on the invention.

As shown in Figure 1-4, this embodiment provides a human eye protection circuit that can be used in light detection and ranging systems. The human eye protection circuit includes: a digital-to-analog converter 1. The digital-to-analog converter 1 converts the input sampling signal 11 is converted into an output DC level signal 21, and the sampling signal 11 is sampled from the light detection and ranging system; and

Comparator 2. The comparator 2 receives the DC level signal 21 and the threshold voltage signal 22 as input, and at the same time outputs a protection signal 23. The protection signal 23 is fed back to the light detection and ranging system, and is used when the pulse intensity of the light detection and ranging system exceeds When the human eye can bear it, the light detection and ranging system is turned off; when the DC level signal 21 is higher than the threshold voltage signal 22, the protection signal 23 is high level; conversely, when the DC level signal 21 is lower than the threshold voltage signal 22, the protection signal 23 is at a high level. Signal 23 is low.

The human eye protection circuit also includes: a latch 3, a first end 31 of the latch 3 receives the protection signal 23 as an input, a second end 32 of the latch 3 outputs a conversion signal, and the conversion signal is fed back to light detection and ranging. The system is used to shut down the light detection and ranging system when the pulse intensity of the light detection and ranging system exceeds the endurance of the human eye. When the protection signal 23 is converted to a high level, the conversion signal follows and is converted to a high level.

The third terminal 33 of the latch 3 is connected to the second terminal 32 through the inverter 9. The third terminal 33 receives the reversed conversion signal. When the third terminal 33 is low level, the conversion signal output by the second terminal 32 Signal lock.

The latch 3 has a fourth terminal 34 for receiving the reset signal.

The light detection and ranging system includes a laser drive circuit 4 and an arithmetic unit 5. The arithmetic unit 5 receives the trigger signal 51 and the reversed conversion signal as input, and the arithmetic unit 5 performs a logical AND on the trigger signal 51 and the reversed conversion signal. After calculation, it is output to the laser driving circuit 4.

The second end 32 of the latch 3 is connected to the microcontroller, and the microcontroller is connected to the light detection and ranging system. When the conversion signal received by the microcontroller is high level, the microcontroller turns off the light detection and ranging system.

The sampling signal 11 is sampled from the laser driving circuit 4 in the light detection and ranging system.

The sampling signal 11 is sampled from the laser receiving circuit 6 in the light detection and ranging system.

The laser receiving circuit 6 is connected to one end of the transimpedance amplifier 7 to convert the received laser pulse signal into an electrical pulse signal. The other end of the transimpedance amplifier 7 is connected to one end of the cascade amplifier 8 to amplify the electrical pulse model. As the sampling signal 11, the other end of the cascade amplifier 8 is connected to the digital-to-analog converter 1 for inputting the sampling signal 11.

TOF is the abbreviation of Time of flight, which literally means flight time. The so-called time-of-flight 3D imaging is to continuously send light pulses to the target, and then use a sensor to receive the light returned from the object, and obtain the target distance by detecting the flight (round-trip) time of the light pulse. Because the TOF algorithm must sample the transmission time and reception time of the transmitting module for comparison, it usually samples the switching circuit of the laser-driven circuit or collects the emitted pulse laser through a detector. The sampled signal will be a periodic signal, equivalent to a PWM (Pulse Width Modulation) wave with a very low duty cycle. The PWM wave can be converted into a DC level that is linearly related to the duty cycle through a 1-bit DAC (digital-to-analog conversion). The 1-bit DAC consists of a low-pass filter and a follower amplifier. When the pulse period remains unchanged but the pulse width changes, the level of the DAC output will become higher as the pulse width becomes wider. We can set a threshold level to compare with the level through the analog comparator. When the level exceeds the threshold, a shutdown signal will be triggered to shut down the laser drive circuit to ensure that no pulses harmful to the human body are emitted. If the sampled signal is not a PWM but a DC signal, it is equivalent to a PWM with a 100% duty cycle, which will cause the 1-bitDAC to output a very high DC level or be saturated, and will also trigger a shutdown signal.

An additional consideration is that using a detector to sample the emitted light pulse requires a TIA (transimpedance amplifier) to reduce the light pulse to an electrical pulse signal. Because the signal will be very small, it needs a multi-stage amplification circuit to amplify it and then compare it with a 1-bit DAC. The circuit that collects the emitted laser through the detector will have a TIA circuit. This invention can use the same TIA to extract the sampling signal.

Considering that after the shutdown circuit is triggered, the laser pulse disappears, and the level of the 1-bitDAC output will become 0V, which is significantly lower than the threshold, causing the comparator to think that the pulse has cleared the shutdown signal normally. Once the circuit has been in an abnormal state, it will continue to enter the shutdown state like a hiccup, so the logic circuit is required to maintain the shutdown signal.

The protection circuit needs to sample the PWM wave on the Laser trigger and send it to the 1-bit DAC. The 1-bitDAC consists of a low-pass filter and an op amp. A simple RC filter is used here to illustrate. If the PWM period will change, you can consider using an adjustable low-pass filter. The 1-bitDAC converts the PWM into a DC level, and then compares it with the threshold voltage through a comparator. When the DC level is higher than the threshold voltage, it is considered that the input pulse is abnormal, and the comparator will output a high level, indicating that the laser drive circuit needs to be turned off at this time. The prompt status needs to be latched to prevent the prompt status from being cleared to re-trigger the laser drive circuit to turn on after the drive circuit is turned off. The latch of the high-level state can be achieved through a combination of D latch and inverter. The output of the Q terminal will be selected according to the state of LE: when LE is high, Q will follow the change of D; when LE is ground, Q will latch the state and is not affected by the D input. So add an inverter between the Q output and LE: when the D input is low, LE will be pulled high to keep Q consistently low; when the D input is high, the LE output will be inverted as Low, thereby latching the high-level signal, and thereafter the input at the D terminal will no longer affect the output of Q. When the external CLR signal is high, the lock state will be cleared. At this time we have obtained two mutually opposite levels to indicate that the laser drive circuit needs to be turned off at this time: the high level can be given to the MCU (single chip microcomputer) to trigger the protection interrupt; the low level can be ANDed with the laser drive trigger signal The operation to turn off the laser pulse is shown in the figure above, and can also be used to turn off the laser's PMIC (power management chip). If latch shutdown is not required, the D latch and inverter can be omitted, in which case the hiccup protection will be triggered. You can consider adding a delay to open the circuit to lengthen the hiccup time, thereby ensuring that the distance between problematic lasers emitted is widened and reducing heat accumulation.

The back-end of the detector sampling circuit scheme and the direct sampling drive circuit level are basically the same. The main difference between the two schemes is that the optical signal needs to be restored through a TIA (transimpedance amplifier), and a cascade amplifier is required for appropriate amplification. The amplified signal is still a fixed period PWM signal. This signal can then undergo normal 1-bitDAC conversion.

Although the above embodiments have specifically described the present invention, those of ordinary skill in the art should understand that modifications or improvements can be made based on the disclosed content of the present invention without departing from the spirit and scope of the present invention. These modifications and improvements are within the spirit and scope of the invention.

Claims (7)

1. An eye protection circuit for use in a light detection and ranging system, the eye protection circuit comprising:

-a digital-to-analog converter (1), said digital-to-analog converter (1) converting an input sampling signal (11) into an output dc-level signal (21), said sampling signal (11) being sampled from said light detection and ranging system; and

-a comparator (2), said comparator (2) receiving as inputs said dc level signal (21) and a threshold voltage signal (22) while outputting a protection signal (23);

wherein the protection signal (23) is high when the DC level signal (21) is higher than the threshold voltage signal (22); conversely, when the DC level signal (21) is lower than the threshold voltage signal (22), the protection signal (23) is at a low level;

a latch (3), a first end (31) of the latch (3) receiving the protection signal (23) as input, a second end (32) of the latch (3) outputting a switching signal, the switching signal being fed back to the light detection and ranging system for switching off the light detection and ranging system when the light detection and ranging system pulse strength exceeds the human eye tolerance capability, the switching signal being followed by a high level when the protection signal (23) is switched to a high level,

the third end (33) of the latch (3) is connected with the second end (32) through the inverter (9), the third end (33) receives the inverted conversion signal, and when the third end (33) is in a low level, the conversion signal output by the second end (32) is locked.

2. Eye protection circuit for light detection and ranging systems according to claim 1, characterized in that the latch (3) has a fourth terminal (34) for receiving a reset signal.

3. The eye protection circuit according to claim 2, wherein the light detection and ranging system comprises a laser driving circuit (4) and an operator (5), the operator (5) receives a trigger signal (51) and a converted signal after inversion as inputs, and the operator (5) logically and-calculates the trigger signal (51) and the converted signal after inversion and outputs the result to the laser driving circuit (4).

4. A human eye protection circuit applicable to a light detection and ranging system according to any one of claims 2-3, characterized in that the second end (32) of the latch (3) is connected to a single-chip microcomputer, the single-chip microcomputer is connected to the light detection and ranging system, and when the conversion signal received by the single-chip microcomputer is at a high level, the single-chip microcomputer turns off the light detection and ranging system.

5. Eye protection circuit for a light detection and ranging system according to claim 1, characterized in that the sampling signal (11) is sampled from a laser driver circuit (4) in the light detection and ranging system.

6. Eye protection circuit usable in a light detection and ranging system according to claim 1, characterized in that the sampling signal (11) is sampled from a laser receiving circuit (6) in the light detection and ranging system.

7. The eye protection circuit for an optical detection and ranging system according to claim 6, wherein the laser receiving circuit (6) is connected to one end of a transimpedance amplifier (7) for converting a received laser pulse signal into an electrical pulse signal, the other end of the transimpedance amplifier (7) is connected to one end of a cascode amplifier (8) for amplifying the electrical pulse signal as the sampling signal (11), and the other end of the cascode amplifier (8) is connected to the digital-analog converter (1) for inputting the sampling signal (11).