Pulse generator circuit, related system and method

Abstract

Embodiments of the present disclosure relate to pulse generator circuits, related systems, and methods. According to an embodiment, the pulse generator circuit includes: an LC resonant circuit coupled between a first node and a reference node; a first switch coupled between the first node and the reference node; a switch network including a second switch coupled between the first node and a reference drive node; and a drive circuit whose output is coupled to the first switch and the second switch of the switch network. The drive circuit is configured to, in a repeated cycle, during a resonant cycle, close the first electronic switch when the current flowing through the inductor of the LC resonant circuit increases, open the first electronic switch when the current flowing through the inductor reaches a threshold, close the second electronic switch of the switch network for a pulse duration when the first electronic switch is opened, wherein the current flowing through the inductor is commutated toward the second electronic switch and the corresponding drive node, and open the second electronic switch when the pulse duration expires.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Italian Patent Application No. 102020000016423, filed on Jul. 7, 2020, which is incorporated herein by reference. Technical Field

[0003] The present description relates to pulse generator circuits. One or more embodiments may be applied, for example, in pulse generator circuits for driving laser diode arrays. Background Art

[0004] Due to their 3D capabilities and ability to operate in adverse weather conditions / darkness, LIDAR (Light Detection and Ranging or Laser Imaging Detection and Ranging) systems are increasingly being used, possibly in combination with radar systems and cameras, for environmental mapping and other safety applications such as emergency braking, pedestrian detection and collision avoidance in the automotive field.

[0005] Ultrashort high current pulses, such as having intensities in the tens of amperes and with rise and fall times in the (sub) nanosecond range, e.g. of the order of 100 ps, ​​are desirable for laser diodes for use in LiDAR systems that utilize time-of-flight (ToF) technology to detect distances in the medium and short range.

[0006] Laser diode arrays comprising laser diodes activated sequentially or in parallel are also used to improve the signal-to-noise ratio (S / N) in the received return signal.Multi-channel drivers offer the possibility to select diode(s) to be activated with high intensity narrow current pulses.

[0007] The generation of such high intensity narrow pulses presents a challenge in the design of laser diode drivers.

[0008] Precise control of the pulse duration cannot be achieved by acting on the switching time of the power switches alone: ​​for example, parasitic inductances of the interconnects limit the di / dt during current rise and fall and strongly influence the pulse duration. Additional problems arise when driving multiple laser diodes in an array connected with a common cathode. Summary of the invention

[0009] According to an embodiment, a pulse generator circuit includes: an LC resonant circuit coupled between a first node and a reference node; a charging circuit coupled to the LC resonant circuit; a first electronic switch coupled between the first node and the reference node, the first electronic switch being connected in parallel with the LC resonant circuit; a switch network including a second electronic switch coupled between the first node and a corresponding drive node of the switch network, the corresponding drive node being configured to be coupled to a corresponding electrical load; and a driver circuit having an output coupled to the first electronic switch and the second electronic switch of the switch network. The driver circuit is configured to: during the resonant cycle, when the current flowing through the inductor of the LC resonant circuit increases, close the first electronic switch, when the current flowing through the inductor reaches a threshold, open the first electronic switch, when the first electronic switch is opened, close the second electronic switch of the switch network for a pulse duration, wherein the current flowing through the inductor is commutated toward the second electronic switch and the corresponding drive node, and open the second electronic switch when the pulse duration expires in a repeated cycle.

[0010] According to another embodiment, a laser diode system includes: a pulse generator including: an LC resonant circuit coupled between a first node and a reference node, a first electronic switch coupled between the first node and the reference node, the first electronic switch being connected in parallel with the LC resonant circuit, and a plurality of switch networks, each of the plurality of switch networks including a second electronic switch coupled between the first node and a respective drive node of the switch network, wherein the respective drive node is configured to be coupled to a respective laser diode of a plurality of laser diodes; and a driver circuit. The driver circuit is configured to: during a resonant period, when a current flowing through an inductor of the LC resonant circuit increases, close the first electronic switch, sequentially close the second switches of the plurality of switch networks for respective pulse durations, wherein during each respective pulse duration, the second electronic switch of one of the plurality of switch networks is closed while the second electronic switches of the other switch networks of the plurality of switch networks are opened, and open each second switch of the plurality of switch networks after expiration of its respective pulse duration.

[0011] According to another embodiment, a method of operating a pulse generator circuit includes multiple steps. The pulse generator circuit includes: an LC resonant circuit, coupled between a first node and a reference node, a first electronic switch, coupled between the first node and the reference node, and the first electronic switch is connected in parallel with the LC resonant circuit, and a plurality of switch networks, wherein each switch network includes a second electronic switch coupled between the first node and a corresponding drive node, the drive node is associated with its corresponding switch network, and the drive node is configured to be coupled to a corresponding electrical load in a plurality of electrical loads. The method includes the following steps: during a resonant period, when a current flowing through an inductor of the LC resonant circuit increases, closing the first electronic switch; for corresponding pulse durations, sequentially closing the second switches of the plurality of switch networks, wherein during each corresponding pulse duration, the second electronic switch of one of the plurality of switch networks is closed, while the second electronic switches of other switch networks in the plurality of switch networks are opened; and after the expiration of its corresponding pulse duration, opening each second switch of the plurality of switch networks. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The characteristics and advantages of the embodiment will become apparent from the following detailed description of a practical embodiment thereof, illustrated by way of non-limiting example in the accompanying drawings, in which:

[0013] Figure 1 is an exemplary block diagram of a conventional system including a laser diode array and an associated pulse generator;

[0014] Figure 1A is Figure 1 Circuit diagram of the equivalent circuit of the commutation circuit in the system;

[0015] Figure 2 is a block diagram of an embodiment of the present description;

[0016] FIG. 2A to FIG. 2E is a graphical representation of possible temporal behavior of various signals that may occur in embodiments of the present description;

[0017] Figure 3 is an exemplary operational block diagram of an embodiment of the present description;

[0018] FIG. 3A to FIG. 3E is a block diagram of possible temporal behavior of various signals that may occur in embodiments of the present description;

[0019] Figure 4 is a block diagram of an embodiment of the present description;

[0020] Figure 5 is a general representation of a system according to an embodiment of the present description;

[0021] Figure 6is a diagram of possible system integration according to embodiments of the present description; and

[0022] Figure 7 is a description of a possible system architecture for an automotive LiDAR system that includes embodiments of the present description. DETAILED DESCRIPTION

[0023] In the following description, various specific details are described in order to enable a deep understanding of the embodiments. The embodiments may not provide one or more specific details, or provide other methods, components, materials, etc. In other cases, known structures, materials, or operations are not shown or described in detail, so that various aspects of the embodiments will not be obscured.

[0024] In the framework of this description, references to "an embodiment" or "one embodiment" are intended to indicate that a particular configuration, structure or characteristic related to the embodiment is included in at least one embodiment. Thus, phrases such as "in an embodiment," "in one embodiment," or similar phrases may appear at different points in this description and do not necessarily refer to the same implementation. Furthermore, particular configurations, structures or characteristics may be combined in any appropriate manner in one or more embodiments.

[0025] The headings / references used herein are provided for convenience only and do not define the scope of protection or the scope of the embodiments.

[0026] Throughout the drawings, like parts, elements or components are designated by like reference numerals, and a detailed description will not be repeated for each figure in order not to burden the present detailed description.

[0027] Similarly, throughout this description, for simplicity, the same name may be used to refer to a certain circuit node or line and a signal occurring at the node or line.

[0028]

[0046] With the method described in detail with respect to illustrative embodiments, it is noted that generating high current narrow pulses presents a challenge in designing drivers for pulse operated systems (ie, systems that operate in a pulsed manner).

[0029] For example, a laser diode driver with rise and fall times in the 100 ps range is desirable because minimizing the pulse duration helps keep the energy emitted by the laser below safe limits.

[0030] At the laser driver level, this translates into providing very high values ​​for di / dt, i.e. the time derivative of the current generated by the driver, which is expected to be able to commutate (switch) high currents in very short times. This problem does not arise in low-power systems, where high di / dt is hardly a consideration.

[0031] In drives where continuous high current operation is not the goal, current generation may involve a DC-DC converter.

[0032] It is worth noting that managing high DC currents requires expensive high power dissipation DC-DC converters; in contrast, pulsed current generators using resonant tanks are simple, inexpensive, controllable, and have low power consumption.

[0033] In order to limit the power dissipation in the laser diode, the laser can be activated with a limited frequency.

[0034] A pulsed current can be generated using a resonant tank (LC resonant circuit), where the inductor of the resonant tank is used as a current generator during a time window during which the current can be considered constant.

[0035] The laser diodes in the array can be activated sequentially, in a "ring" activation sequence, so that one diode is (always) activated at a time.

[0036] It is worth noting that this approach can be combined for high di / dt values, where there is a current deviation in one of the laser diodes in the array. This generates a commutation loop that can be physically very short, with no passive components in the commutation loop. This helps to achieve (very) high di / dt values, for example, if fast electronic switches (such as gallium nitride or GaN transistors) are used.

[0037] As discussed, the generation of high intensity narrow pulses is a challenge for designing laser diode drivers with rise and fall times in the 100ps range. The switching time of the power switch may not be sufficient to provide precise control of the pulse duration because parasitic inductance in the interconnect can limit the di / dt during current rise and fall and adversely affect pulse duration generation.

[0038] Various additional problems arise when generating high intensity narrow pulses. These problems can include, for example:

[0039] A supply voltage (very) higher than the laser diode voltage drop may be desirable to facilitate the generation of the desired high di / dt; a supply voltage higher than the laser diode voltage drop may in turn generate safety issues in case the laser diode is accidentally and permanently connected to the supply voltage (which may be the result of an actuator malfunctioning in the "on" state);

[0040] Inductor voltage overshoot may damage the laser diode;

[0041] The generation of several pulses within a short time frame can be critical, since in conventional systems the "next" pulse can only be generated after recharging the capacitor used as a fast energy source; and

[0042] The amplitude of the pulse current may be difficult to control.

[0043] Additionally, driving an array comprising a plurality of laser diodes in a common cathode configuration may involve driving each laser diode via a switch (eg, a FET) having its drain connected to a supply voltage Vcc, and

[0044] Parasitic capacitance can generate spurious pulses in a temporarily inactive laser diode.

[0045] It is also important to note that in driver systems intended for use with electrical loads other than laser diodes, at least some of the issues discussed above will arise.

[0046] Therefore, although reference will be made to laser diodes for exemplary purposes in the remainder of this description, the present embodiments are not limited to use in laser drivers.

[0047] Figure 1 is a general representation of a conventional system comprising a plurality (eg four) of laser diodes D1, D2, D3, D4 in a common anode-common cathode configuration, which are powered (at their anodes) via a power bus with a VBUS voltage (referring to ground GND) via an RC circuit.

[0048] The cathodes of the laser diodes D1 , D2 , D3 , D4 are commonly coupled to an associated electronic switch, such as a field effect transistor or FET.

[0049] The switch SW is selectively activatable to a closed state (switch conducting) to pull the cathodes of the laser diodes D1 , D2 , D3 , D4 to ground, causing light to be emitted through the positively polarized diodes D1 , D2 , D3 , D4 .

[0050] The operation of the switch SW is controlled via a driver stage D coupled to a control terminal (gate in case of a field effect transistor) of the switch SW.

[0051] The operation of the driver stage D receiving the input voltage VIN (referring to the ground line GND) is controlled by the narrow pulse generator NP.

[0052] Figure 1A The figure shows the equivalent circuit of the corresponding commutation loop.

[0053] exist Figure 1A In FIG. 1 , the symbol LD generally denotes a laser diode, which is illustrated together with an associated series parasitic inductance.

[0054] SW is an electronic switch (eg implemented as a FET) which is illustrated together with an associated output capacitance OC (in parallel) and an associated series parasitic inductance.

[0055] As shown, a ceramic capacitor C can be used as a fast energy storage to drive a pulsed current in the laser diode LD using a fast power switch SW connected in series with the capacitor C and the laser diode in the commutation loop.

[0056] exist Figure 1A The parasitic (stray) inductance of the interconnects of the commutation loop is illustrated in FIG and accumulated as Lc, which can exceed 1 nH.

[0057] like Figure 1 and 1A The solution shown has some disadvantages:

[0058] The stray inductance(s) cannot be reduced as desired to obtain higher di / dt values ​​(e.g. 100ps rise and fall times for high amplitude current pulses) because the length of the commutation loop is affected by the capacitor size;

[0059] A (much) higher supply voltage than the laser voltage is beneficial for obtaining higher di / dt values ​​(V=Ldi / dt), but on the other hand may lead to (very) high power dissipation in case of high laser activation frequency: at each commutation, the switch SW will dissipate the energy E of its output capacitance OC, where E=1 / 2COC*VOC2, COC is the capacitance value of OC, VOC is the voltage across OC;

[0060] The value of the laser diode current is difficult to control solely via the capacitor discharge process: in fact, the current will ultimately depend on the impedance of the commutation circuit;

[0061] Since the laser diode array includes laser diodes in a common cathode configuration, Figure 1 The overall architecture of a multi-channel driver for laser diode selection (i.e., capable of activating each diode D1, D2, D3 and D4 separately) involves a corresponding number (e.g., four) of switches in a HS configuration; and,

[0062] Counteracting the undesired stray activation of the non-selected laser diode (which may be generated by the resonance of stray inductance and capacitance in the commutation loop) would involve placing an additional switch in parallel with the laser diode.

[0063] In one or more embodiments, the issues discussed above can be addressed by Figure 2 , Figure 3 and Figure 4 The pulse generator circuit shown is solved.

[0064] Throughout these drawings (as well as in other drawings), similar parts, elements or components are denoted by similar reference numerals, and for the sake of brevity, the corresponding detailed description will not be repeated.

[0065] In such Figure 2 , Figure 3 and Figure 4 In FIG. 1 , reference numerals LD_1 , LD_2 , ..., LD_n denote n-th (n=1, 2, ...) laser diodes, which may form an array as described above. For example, by way of non-limiting example, n=4.

[0066] Additionally, depending on the embodiment, the electrical loads represented here by the laser diodes LD_1, LD_2, ..., LD_n may be different elements relative to the pulse generator circuit 100. For example, the laser diodes LD_1, LD_2, ..., LD_n or other electrical loads that may be intended to be coupled to the pulse generator circuit 100 may be determined solely by the end customer / user.

[0067] As noted, although reference will be made to laser diodes for exemplary purposes in the remainder of this description, the present embodiments are not limited to use in laser drivers.

[0068] As shown (and to some extent conventional in the art), the laser diodes LD_1, LD_2, ..., LD_n are configured to be selectively activated (in a pulsed manner) via corresponding half-bridges S2_1, S3_1 (laser diode LD_1), ..., S2_n, S3_n (laser diode LD_n), which are driven by corresponding driver circuits 101, ..., 10n coupled to the control terminals (gates in the case of field effect transistors) of the switches in the half-bridges S2_1, S3_1, ..., S2_n, S3_n. Driver circuits 101, ..., 10 n This can be achieved using a half-bridge driver circuit known in the art.

[0069] As shown, the half-bridges S2_1, S3_1, ..., S2_n, S3_n include electronic switches, such as field effect transistors, wherein each half-bridge includes:

[0070] Switches S2_1, ..., S2_n, coupled between a first node or line 12 (common to all half-bridges) and a second node 121, ..., 12n

[0071] The switches S3_1, ..., S3_n are coupled between the second nodes 121, ..., 12n and a reference node or line (eg, ground GND).

[0072] As shown, the laser diodes LD_1, ..., LD_n are coupled (at their anodes) to the second nodes 121, ..., 12n of the respective half bridges S2_1, S3_1, ..., S2_n, S3_n, and are arranged in a common cathode configuration between the second nodes 121, ..., 12n and a reference node or line (here ground GND).

[0073] Designations such as S2_j, s3_j and LD_j, 10j, 12j (assuming j=1, ..., n) will be used below to avoid making the description too complicated.

[0074] The LC resonant tank includes an inductor Lr and a capacitor Cr connected in series, and is provided between a first node or line 12 and a reference node GND. As shown, the inductor Lr is arranged between the first node or line 12 and an intermediate node 14 of the resonant tank circuit, and the capacitor Cr is arranged between the node 14 and the reference node GND.

[0075] Node 14 is coupled to a charging circuit (regulator) which receives a supply voltage VCC.

[0076] A switch S1 - an electronic switch, such as a gallium nitride (GaN) field effect transistor - is coupled intermediate the first node or line 12 and a reference node GND.

[0077] The (first) switch S1 and the switches S2_j, S3_j are driven in response to a supplied enable signal, as discussed below, designated as a whole by the control circuit arrangement 18.

[0078] For ease of description and understanding only, the control circuit device 18 may be regarded as comprising:

[0079] The corresponding control circuits 182_1, ..., 182_n (182_j) for the half-bridges S2_1, S3_1, ..., S2_n, S3_n are configured to send corresponding enable signals Ton_S2_1, ..., Ton_S2_n (Ton_S2_j) to the half-bridges S2_1, S3_1, ..., S2_n, S3_n to enable the corresponding laser diodes LD_1, ..., LD_n to be powered (and thus emit light),

[0080] Two additional control circuits 201 , 202 are configured to control the switch S1 (eg, via its control electrode, such as the gate in the case of a field effect transistor as illustrated herein) via an AND gate 203 .

[0081] As mentioned above, the control circuits 182_j, 201, 202 and 203 are represented as different entities only for the convenience of description and understanding. In fact, these control circuits can be integrated into a single unit 18 (see also Figure 5 and Figure 6 The control circuits 182_j, 201, 202, and 203 may be implemented using digital logic circuit design techniques known in the art. For example, one or more state machine circuits may be used to implement digital logic circuits, and / or synthesized logic may be used to perform the functions described herein.

[0082] It can also be understood that the embodiments of the present invention mainly involve the coordination of the operation of the "first" switch S1 with the operation of the "second" switch S2_j and the "third" switch S3_j to achieve the generation of high di / dt (ultra) short pulses, which are switched to the laser diode LD_j to obtain selective individual activation and thereby luminescence.

[0083] One or more embodiments illustrated herein may actually include at least one switch (i.e., S1, common to all laser diodes LD_1, ..., LD_n in the array) to energize the resonant slot Lr, Cr to define the energy content and peak current of the laser diode pulse, and at least one second switch, i.e., s2_j (j=1, ..., n), connected in series with the corresponding laser diode LDj for selection (with regard to the activation and thereby the emission of the laser diode).

[0084] As described herein by way of example, laser diodes LD_j (j=1, ..., n) are in a common cathode configuration with:

[0085] At least one "second" switch S2_j, arranged in series with the anode of the corresponding laser diode LD_j,

[0086] At least one “third” switch S3_j (j=1, . . . , n) is arranged in parallel to the anode of the corresponding laser diode LD_j.

[0087] Thus, each group of second switch S2_j, third switch S3_j and corresponding laser diode LD_j provides a j-th laser channel activatable by an associated half-bridge driver 10j (j=1, . . . , n).

[0088] The regulator 16 can be implemented in a manner known per se, charging the capacitor Cr in the resonant tank with a voltage sufficient to obtain a peak current in the resonant tank Lr, Cr being equal to or higher than the desired laser diode pulse current. In some embodiments, the regulator 16 can be implemented, for example, using a resistor coupled between VCC (or a regulated voltage source) and the node 14.

[0089] Italian Patent Application No. 102019000029132 and corresponding US Patent Application No. 17 / 123,712, as well as Italian Patent Application No. 102020000016396 (filed on the same date as the application from which this application claims priority) provide exemplary descriptions of such charging circuit arrangements. US Application No. 17 / 123,712 is incorporated herein by reference.

[0090] For example, in Figure 2 In the exemplary embodiment shown, the second switch S2_j and the third switch S3_j can be driven by the control circuit device 18 in a half-bridge configuration so as to:

[0091] When S2_j is turned on (ie, conductive), S3_j is turned off (non-conductive), and when S2_j is turned on (conductive), the laser diode LD_j can be activated so that current is injected into the laser diode LD_j in the corresponding light emission channel;

[0092] When S2_j is off, switch S3_j is turned on, thereby canceling the undesirable stray current flowing through the laser diode LD_j.

[0093] The switch S1 is common to all light emission channels, and is connected to the resonant tanks Lr, Cr circuits (in parallel), which are also common to all light emission channels, and are connected to S1 (in parallel to each other), and therefore also to the resonant tanks Lr, Cr.

[0094] FIG. 2A to FIG. 2E is a possible exemplary sequence that results in the generation of pulses in selected laser diodes in an array comprising four laser diodes LD_1 , LD_2 , LD_3 and LD_4 .

[0095] Specifically, Figures 2A to 2E Indicates that, relative to the general time (abscissa) scale, the possible time behaviors are:

[0096] Resonance tank current - Figure 2A ;

[0097] Laser emission command signal provided to switch S2_j -- Figure 2B ;

[0098] Laser channel enable signal Enable LD_j from block 182_j (j=1, ..., n) Figure 2C ;

[0099] The laser current in LD_1, LD_2, LD_3 and LD_4 is - Figure 2D ;as well as

[0100] VDS (drain-source) voltage in switch S2_j -- Figure 2E.

[0101] For clarity, in Figure 2C and Figure 2D In the accompanying drawings, different representation methods are used for the signals of various LD channels in different intervals of these signals (solid line ____________, dotted line ----, chain line -.-.-.-, cross line --+--+--).

[0102] In such Figure 2 In the arrangement shown, FIG. 2A to FIG. 2E Exemplary, non-limiting values ​​for the illustrated parameters may include those reported in Table I below.

[0103] Table I - Exemplary Parameters

[0104]

[0105]

[0106] exist FIG. 2A to FIG. 2E In the illustrated operation, the laser current pulses are generated with a delay between pulses (e.g., 3 ns, which is Figure 2 The left side of the box 182_j is also highlighted), and for the resonant slots Lr, Cr in the same resonant period (see Figure 2A in almost "flat" behavior).

[0107] The capacitor Cr is charged with a voltage value which is sufficient to obtain the required current in the resonance tank Lr,Cr.

[0108] When S1 is turned on (closed or made conductive), the resonant tank Lr,Cr starts to resonate and the current in the inductor Lr rises.

[0109] The "second" switch S2 The selected one of the "second" switches in j corresponds to the laser LD_j that is desired to be activated, and this switch is turned on (made conductive) in response to the laser diode enable signal issued by the corresponding block 182_j.

[0110] In response to the current in the resonant tank Lr, Cr reaching a threshold, S1 is turned off (becomes non-conductive), and the off time corresponds to the desired laser pulse length (duration) (eg, 1 ns).

[0111] During this time, the inductor Lr essentially behaves as a current generator and current will continue to flow in the laser LD_j activated by the switch S2_j, placing it in the on (conductive) state.

[0112] At the end of the pulse duration, switch S2_j is turned off (becomes non-conductive).

[0113] Another laser diode (in those arrangements comprising a plurality of laser diodes, ie n>1) or even the same laser diode may be activated during the same pulse generated by the resonant circuit Lr, Cr via a subsequence comprising:

[0114] S2_j is turned on (becomes conductive);

[0115] S1 is off (non-conductive) for a duration equal to the pulse time of the laser diode;

[0116] S2_j is off (non-conductive).

[0117] Such a subsequence can be repeated multiple times, compatible with a progressive discharge or resonant tank Lr, Cr, wherein the switch S1 remains on (conductive) until the resonant period of Lr, Cr ends.

[0118] When such a moment is reached, with zero crossing current, S1 can be switched off and the voltage on Cr will rise to a value defined by the residual energy of the resonant tank Lr,Cr.

[0119] Figure 3 and FIG. 3A to FIG. 3E is an exemplary embodiment in which the laser diodes LD_j (j=1, ..., n) are activated in adjacent sequence (actually in contact) without delays between pulses (which are Figure 3 The block 182_j on the left is also highlighted in the representation).

[0120] FIG. 3A to FIG. 3E is an example of a possible corresponding sequence that generates pulses in an array comprising four laser diodes LD_1 , LD_2 , LD_3 and LD_4 .

[0121] Specifically, FIG. 3A to FIG. 3E Indicates that, compared to the usual time (abscissa) scale, possible time behaviors are as follows:

[0122] The oscillator current and the total laser current Figure 3A ;

[0123] S1 Command (inverted: when command is high, S1 is off; see box 201, box 202 and box 203) - Figure 3B .

[0124] Laser channel command, i.e., enable signal Enable LD_j from block 182_j (j=1, ..., n) Figure 3C .

[0125] The laser current in LD_1, LD_2, LD_3 and LD_4 is - Figure 3D ;as well as

[0126] The drain-source voltage across switch S1 is Figure 2E .

[0127] Here, in such Figure 3C and Figure 3D In the figure, different representation methods are used for the signals of various LD channels only within different intervals of these signals (solid line ________, dotted line ----, chain line -.-.-.-.-, cross line --+--+--).

[0128] In such an activation sequence, the "first" switch S1 is turned off (non-conductive) so as to generate a current pulse having a duration equal to the sum of the total pulse durations.

[0129] The capacitor Cr is charged with a voltage value which is sufficient to obtain the required current in the resonance tanks Lr, Cr.

[0130] In response to S1 being turned on (making it conductive), the resonant tank Lr,Cr begins to oscillate and the current in the inductor Lr rises.

[0131] The switch S2_j corresponding to the laser LD_j to be activated is first turned on (made conductive), and in response to the current of the resonant tank Lr, Cr reaching the threshold current, S1 is turned off (made non-conductive), and the turn-off time of S1 corresponds to the sum of the times of all pulses expected to be generated.

[0132] The previously conducting switch S2_j is turned off (non-conducting) and the (consecutive) switch S2_j+1 is turned on (conducting), so that current will be diverted from laser diode LD_j to laser diode LD_j+1, ie another (eg adjacent) laser diode in the array is activated.

[0133] The same operation discussed previously may be repeated with S2_j+1 turning off (non-conductive) and following switch S2_j+2 turning on (becoming conductive) and so on.

[0134] In response to the sequence having almost reached the last laser diode in the array, switch S1 is turned on again (becomes conductive) so that current will no longer flow in the laser diode LD_j (j=1, ..., n), and after a certain delay (or even at the same time) all switches S2_j (j=1, ..., n) are turned off (non-conductive).

[0135] When the resonance time is reached (ended), at the zero current crossing, S1 is switched off (non-conducting) as described before, and the voltage on Cr will rise to a value defined by the residual energy of the resonance tank Lr,Cr.

[0136] exist Figure 3 and FIG. 3A to FIG. 3E In the illustrated sequence, the commutation loop "migrates" in an almost seamless manner from S1 to S2_1, LD_1 with a first commutation CL1 and to S2_2, LD_2 with a second commutation CL2 and so on for activation of the other laser diodes up to CLn.

[0137] This approach helps to shorten the length of the commutation loop (thus reducing stray inductance), combined with Figure 2 The circuit topologies discussed are the same.

[0138] Figure 4 (wherein parts, elements or components similar to those already discussed in the preceding figures are designated by similar figure marks without repeating the corresponding detailed description) illustrates possible options in the implementation of switches (transistors) S2_j and S3_j (j=1,…,n).

[0139] In one or more of the embodiments discussed herein, switches (transistors) S1 and S2_j (J=1, . . . , n) may advantageously be implemented as GaN transistors.

[0140] This facilitates monolithic solutions, for example using existing GaN technology.

[0141] The size of transistor S1 can be determined according to the root mean square and peak current values ​​in the resonance tanks Lr, Cr, and the size of transistor S2_j can be determined according to the root mean square and peak current values ​​of the laser diode LD_j.

[0142] The transistors S3_j (which may be conventional field effect transistors, such as MOSFET transistors) may be integrated in the associated driver circuit 10j, since these transistors only draw a (very) low current, namely the parasitic current flowing in the output capacitance of the associated transistor S2_j.

[0143] like Figure 5 As illustrated, such an embodiment may be advantageously integrated in an integrated circuit (IC), such as a system on package 1000, for drivers of high current, short pulse (ns range) laser diodes LD_1, ..., LDn for LiDAR applications, where switches S1 and S2_j are implemented by GaN transistors.

[0144] This further indicates that the laser diodes LD_1 , LD_2 , . . . , LD_n may be distinct components with respect to the integrated system 1000 , wherein the laser diodes LD_1 , LD_2 , . . . , LD_n are only coupled to the IC 1000 by the end customer / user.

[0145] like Figure 5As shown, the system 1000 can perform additional functions for pulse timing and current control (setting C for overall) and diagnostics (setting D). It should be noted that such a configuration is not inherently specific to multi-channel laser drivers and laser arrays, and can also be used for single-channel configurations, including a single laser diode (n=1).

[0146] Figure 6 is an illustration of a possible integrated circuit implementation, which is a 4-channel laser driver 1000, including GaN transistors integrated in a 4-layer PCB layout.

[0147] exist Figure 6 SS1 denotes the source for S1, SS2_j (j=1, ..., 4) denotes the sources of S2_1, S2_2, S2_3, and S2_4. The common cathode of the lasers is designated as LDCC, and the ground is designated as GND.

[0148] Figure 7 For a possible use of embodiments herein in a LiDAR equipment for a vehicle V such as a motor vehicle, the equipment comprises an emitter path EP and a receiver path RP.

[0149] As shown in the figure, the transmitter path EP includes:

[0150] The laser illumination module, in turn, comprises a laser diode (array) designated as LD and an associated driver system, such as 1000 described above.

[0151] A LiDAR mirror module 1002 (e.g., a MEMS mirror module), receives a drive signal A from a mirror driver (e.g., an ASIC) 1003 and provides a sensing signal S thereto, e.g., having the ability to illuminate the surrounding scene with a vertical laser beam and perform horizontal scanning as needed, so as to detect pedestrians at a distance of several meters in a reliable manner.

[0152] As shown in the figure, the receiver path RP includes:

[0153] a photodiode module 1004, which is sensitive to a reflection signal generated as a result of reflection of optical radiation from the emitter path EP on an object illuminated by this radiation, and

[0154] An associated receiving circuit arrangement 1005 is coupled to the photodiode module 1004 .

[0155] exist Figure 7 Reference numeral 1006 in the figure denotes a controller (e.g., a multi-core microcontroller architecture, possibly including an FPGA / dedicated LiDAR hardware accelerator 1006A), configured to:

[0156] Issue a trigger and laser power setting signal TPS to the system 1000 in the laser irradiator;

[0157] exchanging driving information DI with the driver 1003 of the LiDAR mirror module 1002; and

[0158] The raw data RD is received from the receiving circuitry 1005 coupled to the photodiode module 1004 , and the trigger and gain setting information TGS is sent to the receiver circuitry 1005 coupled to the photodiode module 1004 .

[0159] It should be noted that in addition to the features of the laser illumination module discussed in this article, Figure 7 The structures illustrated in FIG. 1 may be regarded as other conventional structures in the art, which makes it unnecessary to provide a more detailed description here.

[0160] For example, the application applies to Figure 7 Coordination of the operation of the LiDAR equipment with the operation of other equipment in the vehicle V (such as configuration data received from the controller 1006 and status point cloud information published from the controller 1006).

[0161] In summary, the circuits exemplified herein have rise and fall times in the range of 100 ps, ​​which facilitates fast switching, which in turn facilitates the generation of controlled pulses in the 1 ns range with current amplitudes in the range of tens of amperes.

[0162] In the circuit shown in this article:

[0163] Facilitates control of pulse current amplitude by reducing parasitic inductance in the commutation loop;

[0164] The supply voltage can be lower than the laser diode voltage drop;

[0165] Common cathode configuration can be used in multi-channel laser diode arrangements to avoid undesired spurious turn-on of inactive laser diodes;

[0166] The stray inductance in the commutation loop is reduced (e.g. below 0.1 nH) because of the presence of a single common switch such as S1 and a (very) short interconnect to the laser diode: As mentioned earlier, conventional circuit arrangements may include additional capacitors in the commutation loop and the associated interconnects may exhibit parasitic inductances of up to 1 nH (or more) as a result of the connection length being related to the size of the capacitor.

[0167] Switches such as S1 and S2_j can be implemented with a monolithic common-drain GaN transistor arrangement, which is beneficial for optimizing the commutation loop and reducing the value due to possible integration;

[0168] Switches such as S3_j (which counteract stray laser turn-on) can be integrated in standard IC technology because both the magnitude and duration of stray currents are limited;

[0169] The voltage across switch S1 is limited to the (maximum) voltage drop across the laser diode, which helps reduce commutation delays due to the stray capacitive charge of the switch;

[0170] The amplitude of the current pulse can be set by the resonant circuit and does not depend on the impedance of the commutation loop;

[0171] The laser diode can be driven by a current generator using the inductive energy stored in a resonant circuit, unlike conventional circuits based on the discharge of a storage capacitor, where the current may depend on various parameters (capacitance value, impedance of the storage capacitor plus the laser diode plus interconnects) that are almost impossible to control;

[0172] The resonant Lr, Cr circuit facilitates the use of a low voltage source for inductor pre-charging; the inductor behaves as an ideal current generator and the voltage drop across the laser diode can be higher than the supply voltage; and

[0173] The energy storage capacitor is excluded from the commutation loop, so the interconnection length and stray inductance in the commutation loop can be greatly reduced (less than 0.1nH).

[0174] Additional advantages of the circuits illustrated herein include easy control of the amplitude of the pulsed current via the resonant circuit, and recovery of energy generated due to the resonant operation.

[0175] The driver circuit illustrated herein includes three types of switches, namely S1, S2_j and S3_j, having different functions.

[0176] Switch S1 drives the resonant circuit and generates a sinusoidal current wave with well-controlled amplitude and frequency. During resonance, switch S1 is turned off (non-conductive) for a short period of time, so the current flowing in the resonant tank can be diverted to the laser diode to be activated in a very short time.

[0177] Switch S2_j is directly connected in series with the laser diode LD_n, and when S1 is turned off, the resonant current is forced to flow through the laser diode LD_n when switch S2_j is turned on (made conductive): this facilitates extremely fast commutation with di / dt>500A / ns.

[0178] Additionally, since S1 is connected in parallel with the laser diode (plus S2_j being on), the voltage across S1 is limited, so the delay associated with charging its output capacitance is also reduced.

[0179] As mentioned previously, switches such as S3_j can effectively cancel stray laser turn-on and can be integrated in standard IC technology as long as these stray currents are limited in magnitude and duration.

[0180] The corresponding topology can be integrated in a system package, embedding fast power transistors (eg GaN transistors) as well as drive and diagnostic circuitry.

[0181] The pulse generator circuit (eg, 100) exemplified herein may include:

[0182] An LC resonant circuit (e.g., Lr, Cr), including a series connection of an inductor (e.g., Lr) and a capacitor (e.g., Cr) having an intermediate node (e.g., 14) therebetween, is coupled between a first node (e.g., 12) and a reference node (e.g., GND).

[0183] A charging circuit (e.g., 16) is coupled between a power supply node (e.g., VCC) and a middle node of the LC resonant circuit, and the charging circuit charges a capacitor in the LC resonant circuit;

[0184] A first electronic switch (e.g., S1) coupled between the first node and a reference node;

[0185] at least one second electronic switch (e.g., S2_1, ..., S2_n) coupled between the first node and the corresponding driving node (e.g., 121, ..., 12n), and at least one second electronic switch is configured to be coupled to the corresponding electrical load (e.g., LD_1, ..., LD_n); and

[0186] A driving circuit arrangement (e.g., 18, 182_1, ..., 182_n; 201, 202, 203) of a first electronic switch and at least one second electronic switch, the driving circuit arrangement being configured to repeat a pulse generation cycle, comprising:

[0187] The first electronic switch is closed, wherein the LC resonant circuit is able to oscillate as the current flowing in the inductance of the LC resonant circuit increases.

[0188] In response to the current flowing in the inductor of the LC resonant circuit reaching a threshold value, opening the first electronic switch, wherein due to the at least one second electronic switch being turned off within the corresponding pulse duration (e.g., Ton_S2_1, ..., Ton_S2_n), the current flowing in the inductor of the LC resonant circuit (within the corresponding pulse duration) is commutated toward the at least one second electronic switch and the corresponding driving node (which is coupled to the at least one second electronic switch), and

[0189] When the corresponding pulse duration has expired, at least one second electronic switch is opened.

[0190] The pulse generator circuit exemplified herein may include a plurality of second electronic switches (e.g., S2_1, ..., S2_n), the plurality of second electronic switches being coupled between the first node and corresponding driving nodes (e.g., 121, ..., 12n), the driving nodes being configured to be coupled to corresponding electrical loads, wherein the driver circuit device is configured to repeat a pulse generation cycle, including:

[0191] in response to a current flowing in the inductor of the LC resonant circuit reaching a threshold, opening the first electronic switch, wherein the current flowing in the inductor of the LC resonant circuit sequentially commutates (e.g., see CL1, CL2, ..., CLn) toward a corresponding second electronic switch in the plurality of second electronic switches and a corresponding driving node to which the second electronic switch is coupled, which is a result of the corresponding second electronic switch in the plurality of second electronic switches being sequentially closed, and

[0192] A second electronic switch of the plurality of second electronic switches is opened when the corresponding pulse duration expires.

[0193] In the pulse generator circuits exemplified herein, the drive circuit device may be configured to sequentially close the second electronic switches of the plurality of second electronic switches for respective pulse durations with separation delays between the pulse durations (e.g., see FIG. 2A to FIG. 2E ).

[0194] In the pulse generator circuits illustrated herein, the drive circuit device may be configured (eg, 201, 202, 203) to alternately open and close the first electronic switch at each of the respective pulse durations with a separation delay between the respective pulse durations.

[0195] In the pulse generator circuit exemplified herein, the driving circuit device may be configured to sequentially close the second electronic switches (eg, see FIG. 3A to FIG. 3E ).

[0196] In the pulse generator circuits exemplified herein, the drive circuit arrangement may be configured to keep the first electronic switch open for a cumulative time (ie including the sum) of adjacent pulse durations.

[0197] In the pulse generator circuit shown in this article:

[0198] At least one second electronic switch may have a corresponding third electronic switch coupled between a corresponding drive node and a reference node (eg, S3_1, ..., S3_n), and

[0199] The drive circuit arrangement may be configured to selectively close the third electronic switch to couple the respective drive node to the reference node, wherein stray currents therebetween are short-circuited.

[0200] In the pulse generator circuit exemplified herein, the driving circuit device may be configured as:

[0201] closing the first electronic switch to allow the LC resonant circuit to resonate as the current flowing in the inductance of the LC resonant circuit increases, and

[0202] In response to a reduction in current flowing in the LC resonant circuit, the first electronic switch is opened as a result of current being commutated towards the at least one second electronic switch and the respective drive node to which the at least one second electronic switch is coupled (and thus applied to the electrical loads LD_1 to LD_n provided thereby).

[0203] In the pulse generator circuits illustrated herein, the first electronic switch and the at least one second electronic switch may include gallium nitride, GaN transistors.

[0204] In the pulse generator circuit illustrated in this article, the inductor and capacitor in the LC resonant circuit can be coupled respectively at:

[0205] between the first node and the intermediate node, and

[0206] Between the intermediate node and the reference node.

[0207] A system as exemplified herein (e.g., 1000, LD) may include:

[0208] A pulse generator circuit as exemplified herein, and

[0209] At least one electrical load (eg, LD_1, . . . , LD_n) is coupled to at least one second electronic switch at a corresponding driving node.

[0210] In the pulse generator circuits illustrated herein, at least one electrical load may include at least one laser diode.

[0211] In the pulse generator circuits illustrated herein, at least one laser diode has its anode coupled to a respective drive node and has its cathode coupled to a reference node.

[0212] The pulse generator circuits illustrated herein may include a plurality of laser diodes having anodes coupled to respective drive nodes and having cathodes coupled to a reference node in a common cathode configuration.

[0213] A method of operating a pulse generator circuit or system as exemplified herein (wherein the circuit comprises a plurality of second electronic switches having associated respective third electronic switches) may comprise:

[0214] sequentially closing a second electronic switch of the plurality of second electronic switches for respective pulse durations (e.g., Ton_S2_1, ..., Ton_S2_n), wherein during each respective pulse duration of the respective pulse durations, a respective second electronic switch of the plurality of second electronic switches is closed, while other second electronic switches of the plurality of second electronic switches are opened, and

[0215] During each pulse duration in the corresponding pulse duration, the third electronic switch associated with other second electronic switches among the plurality of second electronic switches (which are open) is closed, and the third electronic switch associated with one second electronic switch among the plurality of second electronic switches (which are closed) is closed.

[0216] In various embodiments, a LiDAR system used in the automotive field, for example including a laser diode array, may be an example of such a system.

[0217] One or more embodiments include a storage capacitor and a driver that excludes the storage capacitor from the commutation loop, so the interconnect length and stray inductance in the commutation loop can be significantly reduced (eg, below 0.1 nH).

[0218] In one or more embodiments, the driver circuit may include various switches having different functions.

[0219] The first switch drives the resonant circuit or tank and generates a sinusoidal current wave with well-controlled amplitude and frequency. The switch is briefly turned off (opened) during the resonant period, and the current flowing in the resonant tank can be commutated (deflected) to the laser diode to be activated in a very short time.

[0220] One or more embodiments may contemplate the use of multiple laser diodes in an array. These laser diodes may be selected to be activated via a corresponding second switch in series with the corresponding laser diode so that when the first switch is turned off, the resonant current is forced to flow through the selected laser diode. This facilitates fast commutation with di / dt>500A / ns.

[0221] Furthermore, since the first switch is connected in parallel with the selected laser diode, the voltage across the first switch is limited, thereby reducing the delay generated by charging its output capacitance.

[0222] One or more embodiments facilitate controlling pulse current amplitude via a resonant circuit and energy recovery due to resonant operation.

[0223] One or more embodiments may provide one or more of the following advantages:

[0224] Fast switches with rise and fall times in the order of 100ps facilitate controlled generation of pulses in the 1ns range with current amplitudes in the tens of amperes; this contrasts with the 1ns rise and fall times of conventional solutions, which can only achieve similar current amplitudes with pulse lengths of 2 to 5ns;

[0225] Facilitates control of pulse current amplitude;

[0226] Reduce parasitic inductance in the commutation circuit;

[0227] The supply voltage can be lower than the voltage drop of the laser diode;

[0228] Multi-channel driver operation also facilitates laser diode arrays including laser diodes in a common cathode configuration;

[0229] Spurious switching on of inactive laser diodes can be suppressed and virtually eliminated.

[0230] Without affecting the underlying principles, the details of the construction and the embodiments may vary significantly from what is described and illustrated herein purely by way of example, without thereby departing from the scope of the embodiments.

[0231] The scope of protection is determined by the appended claims.

Claims

1. A pulse generator circuit, comprising: An LC resonant circuit coupled between the first node and a reference node; a charging circuit coupled to the LC resonant circuit; A first electronic switch is coupled between the first node and the reference node, the first electronic switch being connected in parallel with the LC resonant circuit; a switch network comprising a second electronic switch coupled between the first node and a respective drive node of the switch network, the respective drive node being configured to be coupled to a respective electrical load; as well as A drive circuit having an output coupled to the first electronic switch and the second electronic switch of the switch network, the drive circuit being configured to: During the resonance period, when the current flowing through the inductor of the LC resonant circuit increases, the first electronic switch is closed, When the current flowing through the inductor reaches a threshold value, turning off the first electronic switch, closing the second electronic switch of the switch network for a pulse duration when the first electronic switch is open, wherein the current flowing through the inductor is commutated towards the second electronic switch and the corresponding drive node, and opening the second electronic switch when the pulse duration expires; wherein the switch network comprises a third electronic switch coupled between the drive node and the reference node; as well as The drive circuit is configured to selectively close the third electronic switch to short-circuit a stray current between the drive node and the reference node.

2. The pulse generator circuit according to claim 1, wherein: The switch network includes a plurality of switch networks configured to be coupled to a corresponding plurality of electrical loads; and In each of the repeated cycles, the drive circuit is configured to sequentially perform the steps of closing the second electronic switch and opening the second electronic switch for each switch network, wherein each second electronic switch is sequentially closed for the pulse duration and then opened after the pulse duration expires, wherein the current flowing in the inductor is sequentially commutated to each second electronic switch of each of the multiple switch networks.

3. The pulse generator circuit of claim 2 , wherein the drive circuit is configured to provide a separation delay between a first time and a second time, the first time being when the second electronic switch of the first electronic switch network among the multiple switch networks is opened, and the second time being when the second electronic switch of the second electronic switch network among the multiple switch networks is closed.

4. The pulse generator circuit of claim 3 , wherein the drive circuit is configured to alternately open and close the first electronic switch while opening and closing the second electronic switch in the plurality of switch networks, wherein the first electronic switch is opened during the pulse duration and the first electronic switch is closed during the separation delay. 5 . The pulse generator circuit of claim 2 , wherein the drive circuit is configured to sequentially close the second electronic switches of the plurality of switch networks for adjacent pulse durations. 6 . The pulse generator circuit of claim 5 , wherein the drive circuit is configured to keep the first electronic switch open for a cumulative duration of the adjacent pulse durations.

7. The pulse generator circuit according to claim 1, wherein the driving circuit is configured to: closing the first electronic switch to enable the LC resonant circuit to resonate as the current flowing in the inductor increases; and The first electronic switch is opened in response to a decrease in the current flowing in the inductor as a result of the current being commutated toward the second electronic switch of the switch network and the drive node.

8. The pulse generator circuit of claim 1, wherein the first electronic switch and the second electronic switch each comprise a gallium nitride (GaN) transistor.

9. The pulse generator circuit of claim 1, wherein the LC resonant circuit comprises a capacitor coupled between the reference node and an intermediate node, and the inductor is coupled between the intermediate node and the first node.

10. The pulse generator circuit of claim 9, wherein the charging circuit is coupled to the middle node of the LC resonant circuit.

11. A laser diode system comprising: The pulse generator circuit according to claim 1; as well as The corresponding electrical load.

12. The system of claim 11, wherein the corresponding electrical load comprises a laser diode.

13. The system of claim 12, wherein the laser diode comprises an anode and a cathode, the anode being coupled to the drive node and the cathode being coupled to the reference node.

14. A laser diode system comprising: Pulse generator, including: An LC resonant circuit, coupled between the first node and the reference node, a first electronic switch coupled between the first node and the reference node, the first electronic switch being connected in parallel with the LC resonant circuit; and a plurality of switch networks, each of the plurality of switch networks comprising a second electronic switch coupled between the first node and a respective drive node of the switch network, wherein the respective drive node is configured to be coupled to a respective laser diode of a plurality of laser diodes; and The drive circuit is configured as: During the resonance period, when the current flowing through the inductor of the LC resonant circuit increases, the first electronic switch is closed, sequentially closing the second electronic switches of the plurality of switch networks for respective pulse durations, wherein during each respective pulse duration, the second electronic switch of one of the plurality of switch networks is closed while the second electronic switches of other switch networks of the plurality of switch networks are opened, and opening each second electronic switch of the plurality of switch networks after expiration of its corresponding pulse duration; wherein the switch network comprises a third electronic switch coupled between the drive node and the reference node; and The drive circuit is configured to selectively close the third electronic switch to short-circuit a stray current between the drive node and the reference node.

15. The laser diode system of claim 14, further comprising a charging circuit coupled to the LC resonant circuit. 16 . The laser diode system of claim 14 , further comprising the plurality of laser diodes configured to be coupled to a corresponding drive node of each of the plurality of switch networks.

17. A method of operating a pulse generator circuit, the pulse generator circuit comprising: an LC resonant circuit coupled between the first node and a reference node; a first electronic switch, the first electronic switch being coupled between the first node and the reference node, and the first electronic switch being connected in parallel with the LC resonant circuit; and a plurality of switch networks, each of the plurality of switch networks comprising a second electronic switch coupled between the first node and a respective drive node associated with its respective switch network, the drive node being configured to be coupled to a respective one of a plurality of electrical loads, the method comprising: During a resonance period, when a current flowing through an inductor of the LC resonant circuit increases, closing the first electronic switch; Sequentially closing the second electronic switches of the plurality of switch networks for respective pulse durations, wherein during each respective pulse duration, the second electronic switch of one of the plurality of switch networks is closed while the second electronic switches of other switch networks of the plurality of switch networks are opened; and opening each second electronic switch of the plurality of switch networks after expiration of its corresponding pulse duration; wherein each switch network further comprises a third electronic switch coupled between the corresponding drive node and ground; and The method further includes, for each switch network, closing the third electronic switch when the second electronic switch is open, and opening the third electronic switch when the second electronic switch is closed.

18. The method of claim 17, further comprising charging the LC resonant circuit using a charging circuit.

19. The method of claim 17, wherein the plurality of electrical loads comprises a plurality of laser diodes, and the method further comprises driving the laser diodes via the second electronic switch in the plurality of switch networks.

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