This application claims the benefit of Italian Application No. 102020000016396, filed on Jul. 7, 2020, which application is hereby incorporated herein by reference.
The description relates to pulse generator circuits. One or more embodiments are applicable to pulse generator circuits for driving laser diodes.
Pulse generator circuits may be used in various applications such as power transistors and drivers, laser diode drivers, for instance in LIDAR (LIght Detection And Ranging or Laser Imaging Detection And Ranging) systems as increasingly used in the automotive sector.
In pulse generators as discussed in the foregoing, pulses may be generated using a resonant tank comprising a capacitor which is recharged during operation.
A short recharge time and a limited power dissipated in recharging the resonant tank capacitor are thus desirable features of such pulse generators.
According to one or more embodiments, a pulse generator circuit has the features set forth in the claims that follow.
One or more embodiments may concern a related system. A LIDAR system for use in the automotive sector, for instance, comprising one or more laser diodes may be exemplary of such a system.
One or more embodiments may concern a related method.
The claims form an integral part of the technical teaching of the description provided herein.
In one or more embodiments, a resonant tank capacitor can be charged using a charging inductor, which may significantly reduce power dissipation in comparison with resistive charging.
One or more embodiments may exploit the resonance of a charging inductor, which may involve controlling the value of the capacitor voltage at a certain instant at a voltage which may be lower or higher than the supply voltage.
One or more embodiments facilitate accurate and non-dissipative charging of a resonant tank capacitor as used, for instance, to generate sub-nanosecond current pulses in a laser for LIDAR applications.
One or more embodiments may include a voltage regulation block with the function of charging the resonant tank capacitor in a fast and non-dissipative manner.
In one or more embodiments, the current flowing through the laser diode is linked to the charging voltage of the capacitor.
One or more embodiments may include a circuit topology (somewhat akin to a DC-DC converter) which can be synchronized with resonant tank activations. This is contrast with DC-DC converter topologies which involve a closed loop with feedback on the output current with the purpose of generating a constant current equal to the amplitude of the current flowing through an array of laser diodes (an array of vertical-cavity surface-emitting laser or VCSEL diodes, for instance).
One or more embodiments may provide one or more of the following advantages:
The features and advantages of embodiments will become apparent from the following detailed description of practical implementations thereof, shown by way of non-limiting example in the accompanying figures, wherein:
In the ensuing description, various specific details are illustrated aimed at enabling an in-depth understanding of the embodiments. The embodiments may be provided without one or more of the specific details, or with 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.
Reference to “an embodiment” or “one embodiment” in the framework of this description is meant to indicate that a particular configuration, structure, or characteristic described in relation to the embodiment is comprised in at least one embodiment. Hence, phrases such as “in an embodiment”, “in one embodiment”, or the like that may be present in various points of this description do not necessarily refer to one and the same embodiment. Moreover, particular conformations, structures, or characteristics may be combined in any adequate way in one or more embodiments.
The headings/references used herein are only provided for convenience and hence do not define the sphere of protection or the scope of the embodiments.
Throughout the figures, like parts, elements or components are designated by like reference symbols and a detailed description will not be repeated for each and every figure in order not to burden the present detailed description.
Similarly, throughout this description a same designation may be used for simplicity to indicate a certain circuit node or line and a signal occurring at that node or line.
As illustrated, the pulse generator circuit comprises a high-side electronic drive switch HSD and a low-side electronic drive switch LSD.
These switches may be transistors such as field-effect transistors, advantageously GaN (Gallium Nitride) transistors, as they can have switching times in the 100 ps range.
The laser diode LD is generally exemplary of an electrical load to which a pulse signal is intended to be applied. As such, the load as exemplified by the laser diode LD may be a distinct element from the pulse generator.
As illustrated:
the high-side electronic drive switch HSD is coupled between a first node 10 and a second node 12,
In the exemplary case of the laser diode LD considered herein, the anode and the cathode of the laser diode LD are coupled to the first 10 and to the second node 12, respectively.
Two driver circuits 141, 142 are illustrated coupled to the control electrodes (gates, in the case of field-effect transistors) of the switches HSD and LSD.
An LC resonant tank including an inductor Lr and a capacitor Cr connected in series is provided coupled between the first node 10 and the reference node GND.
As illustrated, the inductor Lr is arranged intermediate the first node 10 and an intermediate node 16 of the resonant tank circuit and the capacitor Cr is arranged intermediate the node 16 and the reference node GND.
A charge resistor Rcharge is coupled between a regulated voltage node at a voltage VCC and the intermediate node 16 in the resonant circuit Lr, Cr.
The two driver circuits 141, 142 are configured to be operated in order to turn the drive switches 141, 142 alternately on (switch closed and conductive) and off (switch open and non-conductive) so that drive pulses are applied to the load (to produce pulsed laser operation of the laser diode LD, for instance) as schematically represented on the left-hand side of
For instance, Italian patent application No. 102019000029132/U.S. patent application Ser. No. 17/123,712 (already cited) discloses a solution wherein the driver circuitry 141, 142 is configured to cyclically repeat during a sequence of switching cycles the following steps:
In a circuit as exemplified in
In a circuit as exemplified in
In a circuit as exemplified in
In a circuit as exemplified in
It will be otherwise appreciated that embodiments herein are primarily concerned with the charge control of the resonant tank Lr, Cr in the pulse generator, rather than with details of operation as recalled previously, thus making it unnecessary to provide a more detailed description herein.
A solution as illustrated in
The current amplitude of the laser pulse is fixed by the energy stored in the resonant tank. An accurate control of the laser current pulse amplitude thus involves controlling the amount of charge on the capacitor Cr at the time when the resonant tank is activated. This in turn involves recharging at a precise voltage value the capacitor of the resonant tank at the time of resonant tank activation.
A fast recharge thus plays a role in facilitating activating the laser LD at a high activation frequency.
A fast capacitor charge in turn militates against a precise voltage control. Also, high frequency charging can result in high power dissipation in the charging circuit.
As illustrated in
The resistance value of Rcharge can be selected high enough to avoid interference with the resonant tank, with Vcc/Rcharge (much) smaller than the peak current Ipeak.
As a consequence, charging Cr may become a critical factor when activating the laser at high frequency is desired: a small resistance value of Rcharge, as beneficial for a fast (re)charge would in fact conflict with countering interference with the resonant tank as discussed previously.
This issue may be addressed as illustrated in
As illustrated in
As illustrated in
The driver 143 can be actuated in a synchronized manner with the drivers 141 and 142 as schematically represented on the left-hand side of
The solution of
Also, when the switch CS is off, Rcharge has no influence on the resonant circuit.
The solution illustrated in
One may otherwise note that, if the solution of
The power dissipation in the switch is equal to these energy losses times the resonant tank activation frequency (or the frequency of the laser pulses).
If a laser activation frequency is envisaged in the range of 500 kHz, the power dissipation in the switch CS can be as high as several watts, with the power dissipation of the laser driver system substantially doubled.
It is noted that high power dissipation may be undesirable for various reasons:
One or more embodiments may address the issues discussed in the foregoing along the lines of a solution for non-dissipative charging of Cr as illustrated in general terms in
In
As noted, the embodiments herein are primarily concerned with the charge control of the resonant tank Lr, Cr in the pulse generator, rather than with other details of circuit operation (opening/closing the switches HSD and LSD): for the purposes herein such circuit operation can be held to correspond to the cyclical operation including subsequent first, second, third and fourth time intervals as recalled previously in connection with
Briefly, a circuit as generally exemplified in
In the solution generally illustrated in
Reference to a DC-DC converter indicates that any DC-DC converter topology known to those of skill in the art (buck, boost, buck boost, resonant, just to mention a few by way of example) can be taken as a model for the circuit 100, being otherwise understood that the circuit 100 embodies a specific topology which can be synchronized with resonant tank activations.
In that respect it is noted that, while certainly advantageous, synchronized operation (that is, synchronizing the PWM signal with the resonant tank activation frequency) is not mandatory; also, the switching frequency can be different from the resonant tank frequency activations. In fact it is possible to generate a charge current for Cr with a frequency different (e.g. higher) than the frequency of resonant tank activations as this would not involve a synchronization with the resonant tank.
For the purposes herein, one may essentially note that the drive circuitry (141, 142—see also 14 in
An approach as considered herein lends itself to being implemented according to different options. These different options can be synchronized with the resonant tank activations in order to facilitate reaching a desired value for the charge voltage V Cr on the capacitor Cr in coordination with the resonant tank (notionally, in the very instant the resonant tank is activated).
In the following, various such options will be discussed:
Turning first to the non-dissipative charge control of Cr in an open loop,
The switches 102a, 102b are driven on and off alternately (see the inverter 102c coupled to the control electrode—gate, in the case of a field-effect transistor—of the switch 102b) to drive with a square voltage Vswitch an inductor (L Charge) coupled between the intermediate point 106 of the bridge and the capacitor Cr.
As illustrated, a (PWM modulated) square wave voltage to drive the switch circuit 102 can be produced by a comparator 104 by comparing the charging voltage of Cr (namely V Cr) with a threshold voltage (a fixed threshold 108 in the case illustrated in
The value of L Charge can be selected so that the average current Icharge through the inductor L Charge is higher than zero 0 with a ripple less than the average value so as to obtain a current control in a continuous mode.
In that way the capacitor Cr is charged with the current Icharge, with the value of Icharge (and hence the charge speed of Cr) being a function of the threshold voltage 108. Since the resonant tank activation frequency is constant, the value of V Cr at the instant when resonant tank is activated (that is the Cr charging voltage) will be a function of the (fixed) voltage threshold 108.
The diagrams of
One may note that after few cycles from start up the charge switch 102 is synchronous with resonant tank activations and the value of V Cr at the times of tank activations remains substantially stable.
In an arrangement as illustrated in
In an arrangement as illustrated in
For instance, the peak current in the recharge inductor may be 1.6 A with an average value of 1.3 A, which is adequate for recharging the resonator Lr, Cr in applications as discussed in the foregoing.
These are of course merely exemplary values, which are mentioned without any limiting intents of the embodiments.
The circuit of
The variable threshold 108′ can be generated (in manner known per se) is such a way to be linked to (closed loop) feedback parameters, generally indicated as FB. These may include, for instance, V Cr itself or a parameter linked to V Cr, such as—by way of example—the current in the resonant tank and/or the power emitted by the laser diode.
A variable threshold such as 108′ facilitates a continuous regulation of Vcr and/or defining calibration procedures.
The diagrams of
In an arrangement as illustrated in
In an arrangement as illustrated in
Here again, the peak current in the recharge inductor may be 1.6 A with an average value of 1.3 A. As noted this is adequate for recharging the resonator Lr, Cr in applications as discussed in the foregoing.
Again, these are merely exemplary values, which are mentioned without any limiting intents of the embodiments.
The inductor L Charge resonates with the capacitor Cr with oscillations generated by the activations of the resonant tank.
In a circuit as illustrated in
Such a choice for the inductance value of the inductor L Charge may be otherwise advantageous also for the other implementations illustrated herein.
The diagrams of
In a configuration as illustrated in
Also in this case, the recharge inductor operates in continuous conduction mode with possible values for the peak current and the average current therein equal to 1.66 and 1.58, again adequate for recharging the resonator.
Once more, these figures are merely exemplary values, mentioned without any limiting intents of the embodiments.
By way direct comparison with
As illustrated in
The clamping diode D2 facilitates recovering the excess energy back to a reference voltage.
The diode D1 facilitates current (re)circulation in the inductor L Charge when the switch CS is off (nonconductive).
In a solution as illustrated in
This facilitates charging the capacitor Cr in a time which substantially ¼ the resonance period (the charging time should desirably be lower or equal to the frequency of activation of the resonant tank).
For instance the value of Vcr can reach Vcro+2×(VCC−Vcro) where Vcro is the value of Vcr when the charge switch CS is activated.
When using a regulated clamping voltage less than Vcro+2×(VCC−Vcro), the charging value of Vcr will reach a regulated value and will be clamped by this value.
The diagrams of
A solution as illustrated in
Therefore this solution can be advantageously used in connection with arrangements where laser activations are not performed at a constant frequency.
In
Italian patent application No. 102019000029132/U.S. patent application Ser. No. 17/123,712 (already repeatedly cited) discloses an arrangement including a resonant tank such as Lr, Cr and two switches. When the two switches are on (conductive), the resonant tank exchange the energy stored in Cr with energy stored in Lr. When Vcr=0 the energy and the current in Lr reach the maximum value. When the HSD switch (in parallel to the load—here the diode LD) is turned off, the current flowing in Lr will flow in the load and the switching speed (di/dt) will be dependent on the inductance in the associated commutation loop.
This topology allows having very low inductance because the commutation loop including (only) the switch and the load can be very short and the associated stray inductances can be reduced below the 100 pH range.
An inductive charge circuitry as exemplified herein was found to reduce the power dissipation related to recharging the resonant tank capacitor Cr by a factor in excess of 10 in comparison with resistive solutions as exemplified in
In fact, a corresponding integrated circuit (IC) can include the control of the resonant tank with the laser activation together with the charge control. This facilitates controlling the amplitude of the current in the laser.
In conventional topologies measuring the current in the laser is hardly feasible due to difficulty of implementing reliable current sensing with 1 ns response time.
An IC as contemplated herein can i) measure the current in the resonant tank at frequencies in the range of 2 MHz (Tr=500 ns) and, based on this measurement, ii) generate a feedback signal to control V Cr that is linked to the maximum value for the current ILr in the inductor Lr (the current is the load LD cannot exceed ILr).
Inductive charge circuitry as exemplified herein may facilitate control of L Charge and Cr resonance and a well-controlled charge voltage of Cr.
Relying on resonance, the controlled voltage can be rendered higher or lower than the supply voltage, with the circuit operating a buck boost converter.
Continuous current operation of L Charge may facilitate reducing the peak current in a charge switch so that such a charge switch can be easily integrated in an IC, which in turn facilitates integrating the Cr charge control circuitry in a laser driver IC.
For instance, circuitry as exemplified herein may facilitate a compact implementation of integrated Gallium nitride (GaN) transistors of a 4 channel laser driver and PCB layout.
A pulse generator circuit as exemplified herein may comprise:
In a pulse generator circuit as exemplified herein, the charge circuitry may consist (only) of a further inductance in a current flow line between the supply node and the intermediate node in the LC resonant circuit.
In a pulse generator circuit as exemplified herein,
In a pulse generator circuit as exemplified herein, the charge circuitry may comprise:
In a pulse generator circuit as exemplified herein, the charge threshold may comprise a variable threshold (for instance, 108′).
In a pulse generator circuit as exemplified herein, the variable threshold may be variable as a function of the charge voltage of the capacitance in the LC resonant circuit or a parameter linked thereto.
In a pulse generator circuit as exemplified herein, the charge circuitry may comprise:
In a pulse generator circuit as exemplified herein the inductance (for instance, Lr) and the capacitance (for instance, Cr) in the LC resonant circuit may be coupled:
A pulsed operation system (that is, a system configured for pulsed operation) as exemplified herein may comprise:
In a pulsed operation system as exemplified herein, the electrical load may comprises one or more laser diodes (for instance, LD).
A method of operating a pulse generator circuit as exemplified herein or a pulsed operation system as exemplified herein may comprise actuating the first electronic switch and the second electronic switch cyclically repeating during a sequence of switching cycles:
Without prejudice to the underlying principles, the details of construction and the embodiments may vary widely with respect to what has been described and illustrated herein purely by way of example, without thereby departing from the scope of the embodiments.
The extent of protection is determined by the annexed claims.
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Number | Date | Country | |
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20220013984 A1 | Jan 2022 | US |