Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/481—Constructional features, e.g. arrangements of optical elements
  • G01S7/4816—Constructional features, e.g. arrangements of optical elements of receivers alone
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
  • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
  • G01S17/06—Systems determining position data of a target
  • G01S17/08—Systems determining position data of a target for measuring distance only
  • G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
  • G01S17/88—Lidar systems specially adapted for specific applications
  • G01S17/93—Lidar systems specially adapted for specific applications for anti-collision purposes
  • G01S17/931—Lidar systems specially adapted for specific applications for anti-collision purposes of land vehicles
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/481—Constructional features, e.g. arrangements of optical elements
  • G01S7/4814—Constructional features, e.g. arrangements of optical elements of transmitters alone
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/483—Details of pulse systems
  • G01S7/486—Receivers
  • G01S7/4861—Circuits for detection, sampling, integration or read-out
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
  • G01S17/88—Lidar systems specially adapted for specific applications
  • G01S17/93—Lidar systems specially adapted for specific applications for anti-collision purposes

Definitions

• the present invention relates to the field of lidars performing a measurement by time of flight (“time of flight” in English or TOF), and more particularly lidars having a field of view greater than 5°.
• time of flight in English or TOF
• lidars having a field of view greater than 5°.
• a lidar Light Detection And Ranging is a device used to measure distance by measuring the time of flight of a light pulse.
• the lidar consists of:
• an optical pulse transmitter laser diode or light-emitting diode
• a logic component of the microprocessor, microcontroller or FPGA type -an optoelectronic receiver whose role is to convert the reflected pulse into an electrical signal in compliance with measurement quality, in particular by maximizing the measurement signal-to-noise ratio, denoted S/N
• This device can be a time-distance converter, or “Time to Distance Convert” (TDC), or a digital signal processing system based on a microprocessor, microcontroller or FPGA.
• TDC Time to Distance Convert
• the optical power emitted can be up to a few tens of watts over a period of a few nanoseconds.
• the orders of magnitude of powers received from the echoes are typically from a few nanowatts to a few hundred milliwatts.
• the luminous background can vary from zero power for complete darkness up to 1kW/m 2 (120klux) in case of full sun.
• an illumination of 10W/m 2 corresponding to average artificial lighting illuminating a 5x5mm 2 silicon photodiode will generate a photo generation current of approximately 500 ⁇ A, full sun a current of approximately 20mA (taking into account the entire spectrum solar).
• Lidars are used to measure distances, map surfaces, detect objects. There are several types of lidars:
• the narrow-field 1D lidar presents an emitted pulsed light beam of small aperture (lidar low field of view - Field Of View - FOV). It measures the distance from a specific point, where the object is located.
• the optoelectronic components (beam emission diode, reception photodiode) are then associated with optical components (lenses, filters, etc.) for collimating and focusing the beams.
• FIG. 1 illustrates a lidar 1 D L0 according to the state of the art. It comprises an emission device DE0 for emitting light pulses in the direction of a scene at a low angle (FOV), typically less than 3°.
• the emissive element ELO is for example a laser diode or a light-emitting diode.
• collimating optics (not shown) is coupled to the emitter to obtain low divergence of the illumination beam.
• the lidar L0 also comprises a reception device DR0 (or receiver) comprising a photo-detector PD0 which can receive pulses reflected or backscattered by at least one element (Ei i index of the element) of the scene and for converting the reflected pulses into an electrical signal and a CAD amplification circuit that amplifies the electrical signal.
• the receiver photodetector and amplification circuit
• the receiver has an impulse response hr(t) which can be measured and/or determined by calculation.
• an optic of reception (not shown) is coupled to the photodetector to obtain a low reception solid angle, and thus to recover the useful light as a priority
• a processing unit UTO controls the transmission, typically via a logic component of the microprocessor, microcontroller or FPGA type, digitizes the amplified electrical signal, and processes it so as to extract the useful information, i.e. say the presence of the elements in the detection field and their respective distance.
• the optoelectronic components (beam emission diode, reception photodiode) are then often associated with optical components (lenses, filters, etc.) for collimating and focusing the beams.
• optical components typically less than 3°
• These narrow field (typically less than 3°) and short range 1D lidars are marketed for obstacle detection applications in light applications of autonomous or semi-autonomous moving objects such as drones or robots in the broad sense (vacuum cleaners and autonomous mowers, radio-controlled vehicles with obstacle detection, etc.). They have supplanted the traditional ultrasonic rangefinders whose field is much wider and of which we do not know exactly which object will constitute its first detected obstacle.
• FIG. 2 illustrates a drone D equipped with a 1D lidar L0 according to the state of the art in descent action on uneven terrain: obstacle detection is uncertain due to the narrow field.
• 3D lidars with scan technology are used today.
• the pulsed beam is also of low aperture, but coupled with a mechanical scanning system to irradiate an entire portion of space: several shots directed towards several places are necessary to produce a map.
• 3D lidars make it possible to establish a precise cartography of the environment by the use of more or less complex mechanical systems or even by the use of MEMS (Micro Electro Mechanic Systems). They are effective but have the disadvantage of being oversized with regard to light applications, in terms of:
• the difficulty of detecting thin, small or surface objects - the slowness of measurement is a limit to the detection of obstacles moving relative to the sensor
• a lidar having the wide field properties of ultrasonic sensors which would illuminate a scene according to a cone greater than 5°, see 10° or 20°, would make it possible to scan a large portion of space and detect echoes from different elements/obstacles present in the scene or observation field, with the possibility of a single pulse (no need for scanning anymore).
• a wide FOV lidar almost insensitive to high humidity and/or rain and having the possibility of detecting a smooth painted surface under high incidence, would have a competitive advantage in the fields of anti-collision still reserved for ultrasound. It could also be used for autonomous movement of robots or drones.
• the wide field is not the natural domain of the lidar. Indeed, the backscattered optical flux decreases with the distance (d) in d -4 for small objects instead of decreasing in d -2 for a narrow field, which limits its range. Indeed the difference is made on the density of incident light intensity.
• a so-called "narrow" field it is considered that all the incident energy is included on the surface of the obstacle (in other words, the surface of the obstacle is greater than the illuminated surface according to the solid angle): obstacle receives all the energy from the transmitter. Each point of the obstacle then backscattered energy towards the receiver according to a law in d -2 .
• the obstacle In the case of a wide field, the obstacle is completely included in the cone of illumination: the obstacle receives only part of the energy of the transmitter according to a law in d -2 , and backscattered this energy towards the receiver also according to a law in d -2 , with overall an energy on receiver in d -4 of the energy of the transmitter.
• large objects in the background obscure small ones in the foreground. The centimeter resolution is more difficult to obtain, the costs are a priori higher than for an ultrasonic sensor.
• Transimpedance Amplifier Trans Impedance Amplifier
• TIA Transimpedance Amplifier
• the TIA circuit based on operational amplifiers, can be complex. It is configured to transform the current from the photodetector into electrical voltage.
• the TIA-type CAD amplification circuit consists of a resistor R0 and an operational amplifier Amp0. Its structure is shown in Figure 4. [0022] Considering the ideal components:
• the PD0 photodiode transforms the luminous flux into photo generation current i ph0 .
• V s0 — R 0 i ph0 .
• resistor R 0 sets the gain of the amplifier.
• TIA is tied to this value.
• the most widely used photodetector is a PIN type photodiode, which is more reliable and simpler to implement than an avalanche photodiode.
• the current from the photodiode can be described by the relationship: in which :
• S is the sensitivity of the photodiode, of the order of 0.6A/W, ⁇ e (t) is the light power received,
• I 0 is the sum of the reverse static currents of the photodiode (saturation current, black current), represents the sum of the intrinsic noise of the photodiode (mainly shot noise).
• the captured light power ⁇ e (t) can also consist of a dynamic part ⁇ e (t) such as the reflected pulse and a static part caused by a light background ⁇ e0 , caused by the sun For example.
• a dynamic part ⁇ e (t) such as the reflected pulse
• a static part caused by a light background ⁇ e0 caused by the sun
• a silicon PIN photodiode generates approximately 600mA/W.
• the photodiode is usually followed by a transimpedance amplifier whose gain is generally a compromise between the desired bandwidth and the sensitivity (detection capacity) of the sensor. It can also be limited by the intensity of the reverse static currents of the photodiode.
• the operational amplifier AmpO and the resistor R 0 are sources of noise.
• FET technology is most often used for the operational amplifier because of its attractive characteristics of very low noise current, in the order of femtoA/ ⁇ Hz.
• an optical filter just on the surface of the photodiode. It can be the color filter integrated into the photodiode proposed by the manufacturers (broad spectrum of the order of 300nm), or even an interference filter (narrow spectrum of the order of 10nm and angular tolerance of less than 3°, which presents a major directivity drawback).
• a typical TIA supply voltage is 3 to 5V. Any higher theoretical output voltage VsO will have the effect of saturating it. It follows that:
• the MAX40658 produced by Maxim Integrated, illustrates this method. Its effectiveness is limited by the saturation of the compensation circuit and leads at least to the use of a narrow band optical filter (interference filter) to minimize the power of the sun on the photodiode, without guarantee of operation for the strongest luminosity. . But the interference filter is not compatible with wide field detection, because it only works on an angular zone close to the normal.
• An object of the present invention is to overcome some of the aforementioned drawbacks by proposing a Lidar with a large field of view having improved sensitivity and rendered insensitive to ambient lighting, this being obtained by the addition of a component in the receiving device.
• the subject of the present invention is a lidar system by measuring a time of flight comprising:
• -an emission device configured to emit light pulses in the direction of a scene at an angle greater than or equal to 5°
• a photo-detector configured to receive pulses reflected or backscattered by at least one element (Ei) of the scene and to convert said pulses into an electrical signal
• the amplification circuit comprises a transimpedance amplifier, a transformer comprising a primary and a secondary, a capacitor and an impedance arranged in series with the capacitor, the primary of the transformer being connected to an anode of the photo-detector, the secondary being connected to said capacitor, said capacitor being connected to an input of said transimpedance amplifier.
• the frequency operating range of the transformer includes the band [10 MHz; 350MHz], According to one embodiment, a transformation ratio equal to the ratio of the number of turns of the secondary to the number of turns of the primary is strictly greater than 1.
• the capacitance C and the inductance L satisfy the relationship:
• the inductor verifies the relationship: with: n p and n s number of primary and secondary turns respectively,
• said inductor verifies the relationship:
• the capacitor C verifies the relation [0051] with Cph transition capacity of the photodiode.
• the reception device further comprises a so-called damping resistor between the photodetector and the primary of the transformer.
• FIG. 1 already cited illustrates a low field of view lidar according to the state of the art.
• Figure 2 already cited illustrates a drone equipped with a lidar 1 D according to the state of the art in descent action on rough terrain.
• FIG. 3 already cited illustrates the advantage of a wide-field lidar for the detection of obstacles during the landing of a drone.
• FIG. 4 already cited illustrates a simplified amplification circuit for lidar according to the state of the art.
• FIG. 5 illustrates a wide field of view TOF lidar according to the invention.
• Figure 6 illustrates an amplification circuit according to the invention.
• FIG. 7 illustrates an embodiment of the lidar reception device according to the invention with a basic transimpedance amplifier circuit.
• FIG. 8 illustrates the equivalent diagram of a photodiode.
• FIG. 9 illustrates a circuit illustrating the notion of noise gain.
• FIG. 10 illustrates the equivalent diagram of the reception device according to the invention comprising a photodiode, a transformer, an additional impedance Z and a transimpedance amplifier.
• Figure 11 shows the equivalent diagram of Figure 10 with the elements connected to the primary reported to the secondary of the transformer.
• Figure 12 illustrates an embodiment of the amplification circuit according to the invention in which an inductance L placed in series with the capacitor C is added.
• Figure 13 illustrates an overall diagram with an impedance Z comprising a capacitor C and inductance L.
• Figure 14 illustrates the asymptotic diagram of signal gain (A) and noise gain (B) of the circuit of Figure 13.
• FIG. 15 illustrates the asymptotic diagram of signal gain (A) and noise gain (B) for three values of f M (f M1 , f M2 , f M3 ).
• FIG. 16 illustrates the equivalent diagram of the circuit of FIG. 13 in which the noise voltage source has been deliberately omitted.
• FIG. 17 illustrates an embodiment of the reception device according to the invention comprising a resistor in series with the photodiode.
• Figure 18 illustrates various simulated signals.
• a wide FOV TOF lidar 10 according to the invention is illustrated in FIG. 5. It comprises an emission device DE configured to emit light pulses in the direction of a scene at an angle (FOV) greater than or equal to 5° , preferably 10°.
• the emissive element is for example a laser diode or a light-emitting diode.
• the choice of wavelength for a lidar according to the invention is wider than for a lidar with a narrow field, because for eye safety the fact of using a wide field greatly limits the risks.
• the illumination wavelength close to the maximum sensitivity of the detector is chosen for the purpose of optimizing reception.
• the desired large field of view is obtained by using the natural divergence of the transmitter (approximately ten degrees to a few tens of degrees depending on the components and the emission axes) which has the advantage of eliminate an optic and therefore gain in size and simplicity.
• an optic coupled to the transmitter makes it possible to obtain the desired FOV.
• the lidar 10 also comprises a reception device DR (or receiver) comprising a photo-detector PD configured to receive pulses reflected or backscattered by at least one element (Ei i index of the element) of the scene and to converting the reflected pulses into an electrical signal and an AC amplifier circuit configured to amplify the electrical signal.
• the detector can be used without optics or coupled with detection field adaptation optics.
• a processing unit UT controls the transmission, typically via a logic component of the microprocessor, microcontroller or FPGA type, digitizes the amplified electrical signal, and processes it so as to extract the useful information, i.e. the presence of the elements (Ei i index d of the element) in the detection field and their respective distance (distance di) .
• FIG. 5 there are two elements E1 and E2 in the detection field, respectively a pole P and a vehicle V.
• R 1 the delay related to the distance d 1 between the transmitter and the post P
• R 2 the delay linked to the distance d 2 between the transmitter and the vehicle V.
• the detector also receives ambient light such as sunlight.
• photo 1 illustrates the scene illuminated by the lidar of the vehicle V.
• the lidar according to the invention can be on board any object in movement: automobile, drone, robot, cane for the visually impaired...
• the lidar must detect the presence of the pole P and determine its distance d1 from it without being disturbed by the backscatter of the vehicle V.
• the Lidar is static and detects the presence of static or moving objects.
• a first consequence of the opening of the field is the spatial spreading of the energy emitted leading to less illumination of the obstacles which in return provide lesser echoes, more difficult to measure than in the case of an emission of focused or collimated beam.
• a second consequence of opening the detection field is the greater probability of finding a strong emissive source there, such as the sun.
• lidar signals having a frequency of interest included in the band [10 MHz, 350 MHz].
• This frequency band is linked, among other things, to the shape of the pulse and to the separation of the return pulses that one wishes to measure (for example distinguishing 1 m of spacing).
• the object of the invention is to overcome the parasitic signal generated by the presence of ambient illumination, that is to say the cancellation of the component continuous photogeneration current while maintaining high sensitivity and low noise.
• the CA amplification circuit of the lidar 10 comprises a transimpedance amplifier circuit TIA, a transformer T comprising a primary P and a secondary S and a capacitor C as shown in FIG. 6.
• the photodetector has in a conventional manner an anode An and a cathode Cath.
• the TIA transimpedance amplifier circuit is a circuit suitable for lidar applications known from the state of the art.
• the primary P of the transformer being connected to the anode An of the photo-detector, the secondary S is connected to the capacitor C, itself connected to an input of the transimpedance amplifier. It is recalled that the primary P and secondary S circuits of a transformer are, as a first approximation, linked by the relationship:
• FIG. 7 An example of an amplification circuit according to the invention, with a basic transimpedance amplifier comprising an amplifier Amp and a resistor R, is illustrated in FIG. 7.
• the invention is compatible with any more complex TIA used for detection.
• lidar including several amplification components (operational amplifiers, transistors).
• the principle of operation of the transformer lies in the conversion of a current in its primary, which is here the photodiode current i ph (t) into a magnetic field B(t), itself reconverted into an electric field. E(t), therefore in a voltage Vs(t) at the secondary of the transformer.
• I 0 sum of the reverse static currents of the photodiode (saturation current, black current), sum of the intrinsic noise of the photodiode (mainly shot noise).
• the transimpedance amplifier ideally fulfills its role only if the current source connected to its input is ideal and sees its infinite output impedance.
• a real current source has a finite output impedance. This can be resistive, inductive or capacitive, or a mix of several elements.
• the equivalent diagram of a photodiode is recalled in figure 8.
• the TIA intrinsically generates noise symbolized at its inputs as a single source of voltage noise and a single source of current noise, the spectral densities of which can be considered constants for the frequencies of interest.
• the amplification technology with FET (Field Effect Transistor) elements adding only little current noise, the high value of the resistance against feedback R of the TIA also adding little noise, we are interested here in the voltage noise source e n , referred to the input.
• the TIA whatever its electronic structure, then behaves like an amplifier with respect to its source of noise voltage, of a value conventionally called "noise gain", illustrated in Figure 9.
• the noise gain G is defined as:
• FIG. 10 illustrates the equivalent diagram photodiode PD (i ph , Cph)/transformer T (primary P of inductance Lp, secondary S of inductance Ls)/additional impedance Z/transimpedance amplifier TIA.
• the TIA is represented here according to its basic version but it is understood that the reasoning applies for a more complex TIA circuit.
• FIG. 11 represents the photodiode/transformer/Z/TIA equivalent diagram with the elements connected to the primary connected to the secondary of the transformer.
• the impedance of the transformer loaded by the photodiode is called Zeq. It should be noted that the source i ph does not appear there for the sake of simplification.
• the noise gain formula G for the circuit according to the invention of FIG. 11 is written:
• another constituent element of Z is added, which is an inductance L placed in series with the capacitance C, as shown in FIG. 12.
• This is a means of raising the impedance Z at high frequencies and therefore of lowering the noise gain for these frequencies.
• the impedance L is an additional impedance different from the impedance Ls of the secondary of the transformer. The respective position of the impedance and the capacitance, arranged in series between the input of the amplifier and the secondary of the transformer, is irrelevant.
• the structure of the amplification circuit as claimed therefore solves two problems.
• the sensor is virtually insensitive to ambient light. It is then possible to detect obstacles with the sun in front. It is thus perfectly adapted to the use of a large F.O. lidar. V.
• a fundamental characteristic of the transformer for its use in the circuit according to the invention is the non-saturation of its magnetic circuit by the direct current generated, in particular by the sun. Saturation of the magnetic core would have the effect of deforming the useful signal or even its absence of transmission, the coefficient k then evolving towards 0. The deformation of the useful signal leads to non Linearities leading to limitations in signal processing With the aim of minimizing non-linearities, it is advisable to choose a transformer capable of transporting currents ten times higher than the photogeneration current due to the sun in front. Considering the full sun situation resulting in a photogeneration current of 0.52mA, the nominal operating current of the transformer must be greater than or equal to 5mA.
• the information-carrying phenomena involved in the time-of-flight measurement are at the level of ten nanoseconds. This leads to an equivalent frequency of This frequency very roughly constitutes the limit of low cut-off frequency that the transformer T must have.
• the low cut-off frequency of the transformer is chosen to be lower, of the order of ten MHz or one MHz.
• the frequency of transformer high cutoff is preferably chosen to be greater than this value. Consequently, a so-called radiofrequency transformer is chosen, the bandwidth of which preferably includes the range 10 MHz to 350 MHz. These transformers also have the advantage of being of reduced volume (the volume occupied by a transformer is inversely linked to its working frequencies).
• the transformation ratio is designated as voltage: a voltage step-up transformer sees a transformation ratio n greater than
• the noise gain reveals three resonance frequencies:
• f m is an elbow frequency dependent on R, L, L p , of an order of magnitude greater than GHz, well beyond the frequencies of interest.
• a first element for minimizing Gn is to shift the resonance f LC towards low frequencies, i.e. f LC ⁇ f m , whence:
• a second noise gain reduction factor at the frequencies of interest is the bringing of the frequency f M , partly controlled by L, closer to the frequency determined by L s and C ph . Indeed, the more the frequency f M moves away from f m , the more the noise gain increases in the frequency range of interest, as illustrated in figure 15, B, which schematizes the asymptotic diagram of noise gain for three different values of f M (f M1 , f M2 , f M3 ).
• a third noise gain reduction factor at the frequencies of interest is the positioning of the maximum noise gain at a frequency lower than the minimum frequency of interest.
• the Z dipole comprising L and C decreases the noise gain but also impacts the signal gain. From the diagram of figure 13 can be deduced that of figure 16 called small signals making it possible to describe the circuit by disentangling the primary and secondary of the transformer. We deliberately omitted the source of noise voltage, which makes it possible to calculate the signal gain, and the capacitance C is omitted from the reasoning (resonance frequency generated with L and Ls very low compared to the frequencies of interest).
• the signal-to-noise ratio is even better than the photodiode capacitance C ph . is low and the transformation ratio is high, i.e. n>1.
• the frequency f M corresponding to the maximum noise gain or to the maximum noise spectral density must preferably be located at a value lower than the lowest frequency of interest f i_b .
• the transformation of the formula expressing f M makes it possible to fix:
• the values of the primary and secondary inductances L p and L s respectively are linked by the transformation ratio n by: For optimum operation, it is advisable to take a value of L approaching Ls, so as not to lower the signal gain too much. Thus preferably 0.5 Ls ⁇ L ⁇ 2 Ls.
• the AC amplification circuit according to the invention illustrated in the figure has several resonance modes with the effect of a pseudo-oscillating impulse response. These pseudo oscillations do not pose a problem when the lidar processing unit has a module carrying out an appropriate processing, transforming these oscillations into suitable signals. For other lidar applications that do not include a TF module, these oscillations can be troublesome.
• the reception device DR according to the invention further comprises a resistor, called a damping resistor Rph, placed in series with the photodiode PD, which damps the oscillations.
• resistance Rph adding noise and causing a voltage drop through the static currents crossing it, it is advisable to choose the minimum value to achieve the desired effect while minimizing it.
• this resistance Rph is from a few ohms to a few hundred ohms.
• FIG. 18 illustrates various simulated signals.
• signal 10 is equal to Itia with an amplification circuit comprising the transformer, a capacitance but no inductance. The signal is still noisy.
• signal 20 is equal to Itia with an amplification circuit comprising a capacitor and an inductor. The signal is now very quiet and usable for lidar detection.
• signal 30 is equal to Itia with an amplification circuit comprising a capacitor, an inductor and a damping resistor Rth of 500 Q. The oscillation has almost disappeared.
• the determination of the moment of reception of the echo pulse (20 ns) is carried out by a series of processing operations (not detailed here) carried out on the signals 20 or 30.

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• General Physics & Mathematics (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Electromagnetism (AREA)
• Optical Radar Systems And Details Thereof (AREA)

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• 2021
  • 2021-12-21 FR FR2114176A patent/FR3131004B1/fr active Active
• 2022
  • 2022-12-16 EP EP22835826.3A patent/EP4453604A1/de active Pending
  • 2022-12-16 US US18/722,587 patent/US20250052866A1/en active Pending
  • 2022-12-16 WO PCT/EP2022/086515 patent/WO2023117816A1/fr not_active Ceased

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