Light source system

Abstract

This disclosure relates to light source systems. Specifically, it relates to light source driving systems, such as laser driving systems. The system is configured to include an extremely low inductance current loop for an initial portion of a drive current signal to turn on the light source. By implementing the system with a very low inductance current loop, very fast light source turn-on times can be achieved, which is particularly useful for time-of-flight systems requiring very fast turn-on responses from the light source.

Description

Technical Field

[0001] This invention relates to light source systems, which can be used, for example, as light sources in time-of-flight camera systems. Background Technology

[0002] Time-of-flight (ToF) camera systems are range imaging systems that resolve the distance between a camera and an object by measuring the round-trip time of a light signal emitted from the ToF camera system. These systems typically include a light source (e.g., a laser or LED), a light source driver that controls the light emitted from the light source, an image sensor that images the light reflected from the object, an image sensor driver that controls the operation of the image sensor, optics for shaping the light emitted from the light source and focusing the light reflected from the object onto the image sensor, and a computational unit configured to determine the distance to the object by determining the amount of time between light emission from the light source and the corresponding reflection from the object.

[0003] ToF camera systems can measure distances from a few centimeters to 100 or 1000 meters. Considering the high speed of light, the mere 16.66 ns time difference between the emission of light and the reception of reflected light corresponds to an object 2.5 meters away from the camera system. Therefore, ToF camera systems require a high level of time accuracy and control to accurately measure distances. Summary of the Invention

[0004] This disclosure relates to a light source driving system, such as a laser driving system. The system is configured to include an initial portion of a drive current signal for turning the light source on and off using an extremely low inductance current loop. By implementing the system with a very low inductance current loop, the light source can achieve a very fast turn-on time, which is particularly useful for time-of-flight systems requiring a very fast turn-on response or modulation frequency from the light source.

[0005] In a first aspect of this disclosure, a light source system is provided, comprising: a substrate; a light source mounted on a surface of the substrate, wherein the light source includes: an upper surface having an upper terminal; and a mounting surface electrically fixed to the surface of the substrate and having a lower terminal, the light source being configured to be turned on by a current flowing between the upper terminal and the lower terminal; a vertical capacitor for providing a first portion of current to drive the light source, wherein the vertical capacitor includes: an upper surface including an upper terminal to a first plate of the vertical capacitor, wherein the upper terminal of the vertical capacitor is electrically coupled to the upper terminal light source; and a mounting surface electrically fixed to the surface of the substrate and including a lower terminal to a second plate of the vertical capacitor; and a current driver mounted on the surface of the substrate and coupled to the light source and the vertical capacitor for controlling the current flow from the vertical capacitor to the light source to control the operation of the light source, wherein the substrate includes a voltage terminal electrically coupled to the vertical capacitor for providing a second portion of the current required to drive the light source.

[0006] The voltage terminals of the substrate can be electrically coupled to the upper terminals of the vertical capacitor via a first interconnect.

[0007] The distance between the substrate surface and the upper terminal of the light source can be substantially the same as the distance between the light source surface and the upper terminal of the vertical capacitor (e.g., within 25%).

[0008] The light source can be mounted on the surface of a substrate using a conductive base, the conductive base having a thickness such that the distance between the substrate surface and the upper terminal of the light source is substantially the same as the distance between the substrate surface and the upper terminal of the vertical capacitor.

[0009] The current driver may be a low-side driver, and the lower terminal of the light source may be electrically coupled to the lower terminal of the vertical capacitor via the current driver. The upper terminal of the vertical capacitor may be electrically coupled to the upper terminal of the light source via a second interconnect, such that when the light source is turned on, current flows from the upper terminal of the vertical capacitor to the upper terminal of the light source, and then from the lower terminal of the light source back to the vertical capacitor via the current driver.

[0010] The first interactor may include one or more bond lines.

[0011] The substrate may include: a first conductive path (e.g., a first conductive trace) that is conductively fixed between the lower terminal of the light source and the first terminal of the current driver, such that when the light source is turned on, current flows through the first conductive path from the lower terminal of the light source to the first terminal of the current driver; and a second conductive path (e.g., a second conductive trace) that is conductively fixed between the lower terminal of the vertical capacitor and the second terminal of the current driver, such that when the light source is turned on, current flows through the second conductive path from the second terminal of the driver to the lower terminal of the vertical capacitor.

[0012] The second conductive path can be maintained at a reference potential, such as ground.

[0013] The current driver can be a high-side driver, and the upper terminal of the vertical capacitor can be electrically coupled to the upper terminal of the light source through the current driver.

[0014] The substrate may include a reference voltage conductive path that is electrically fixed between the lower terminal of the light source and the lower terminal of the vertical capacitor, such that when the light source is turned on, current flows from the lower terminal of the light source to the lower terminal of the vertical capacitor through the first conductive path.

[0015] A portion of the reference voltage conductive path can flow below the current driver, such that when the light source is turned on, current flows through the reference voltage conductive path from the lower terminal of the light source to the lower terminal of the vertical capacitor, substantially in the opposite direction to the direction of current flow from the upper terminal of the vertical capacitor to the upper terminal of the light source below the current driver.

[0016] The high-side current driver may include: a first surface having a third terminal and a fourth terminal; and a second surface fixed to the surface of the substrate, wherein the upper terminal of the vertical capacitor is coupled to the third terminal of the current driver via a third interconnector, and the fourth terminal of the current driver is coupled to the upper terminal of the light source via a fourth interconnector.

[0017] The third interconnect may include one or more bonding wires, and the fourth interconnect may include one or more bonding wires.

[0018] The upper terminal of the light source, the upper terminal of the vertical capacitor, and the third and fourth terminals of the current driver can all be at approximately the same distance from the surface of the substrate.

[0019] In all aspects of this disclosure, the first interconnect may include: a conductive platform having a mounting surface conductively fixed to a voltage terminal and an upper surface at a distance substantially the same as the upper terminal of the vertical capacitor from the base surface; and at least one conductive element fixed to the upper surface of the conductive platform and the upper terminal of the vertical capacitor.

[0020] In all aspects of this disclosure, the substrate may be a non-conductive substrate of a PCB.

[0021] The light source system may also include a third portion of current for driving the light source, wherein the third capacitor has a larger capacitance than the vertical capacitor, and wherein the vertical capacitor, the light source and the current driver are coupled together to form a first current loop, and wherein the third capacitor, the light source and the current driver are coupled together to form a second current loop.

[0022] The light source system may further include a second vertical capacitor, wherein the second vertical capacitor includes: an upper surface including an upper terminal to a first plate of the second vertical capacitor, wherein the upper terminal of the second vertical capacitor is electrically coupled to a second upper terminal of the light source, wherein the first upper terminal of the light source is located on a first side of the upper surface of the light source, and the second upper terminal of the light source is located on a second opposite side of the upper surface of the light source; and a mounting surface, conductively fixed to the surface of the substrate and including a lower terminal to the second plate of the vertical capacitor, wherein the second vertical capacitor is electrically coupled to a voltage terminal of the substrate and is located on the side of the light source opposite to the position of the first vertical capacitor, such that when the light source is turned on, the direction of current flowing from the first vertical capacitor to the light source is substantially opposite to the direction of current flowing from the second vertical capacitor to the light source.

[0023] In a second aspect of this disclosure, a light source system is provided, comprising: a driver IC including a current driver; a light source mounted on a surface of the driver IC, wherein the light source includes: a first terminal; and a second terminal on the mounting surface of the light source, the second terminal of the light source being conductively coupled to the first terminal of the current driver on the surface of the driver IC; and a capacitor mounted on the surface of the driver IC, wherein the capacitor includes: a first terminal to a first plate of the capacitor, the first terminal being conductively coupled to a power supply voltage and the first terminal of the light source, such that when the light source is turned on, current flows from the first plate of the capacitor to the first terminal of the light source; and a second terminal to a second plate of the capacitor, the second end of the capacitor being on the mounting surface of the capacitor and conductively coupled to the second terminal of the current driver on the surface of the driver IC, such that when the light source is turned on, current flows through the current driver from the second terminal of the light source to the second plate of the capacitor.

[0024] The capacitor may be a vertical silicon capacitor, wherein the first terminal of the capacitor is located on the upper surface of the capacitor. The first terminal of the capacitor may be coupled to the first terminal of the light source using a bonding wire.

[0025] Alternatively, the capacitor may be a lateral silicon capacitor, wherein the second terminal of the capacitor is on the mounting surface of the capacitor and is electrically coupled to the conductive path of the driver IC, the conductive path of the driver IC being electrically coupled to the first terminal of the light source. The first terminal of the light source may be on the upper surface of the light source, and the conductive path of the driver IC is electrically coupled to the first terminal of the light source using a bonding wire. Alternatively, the first terminal of the light source may be on the mounting surface of the light source, and the conductive path of the driver IC is electrically coupled to the first terminal of the light source using a conductive bonding wire.

[0026] In a third aspect of this disclosure, a laser driver circuit is provided, comprising: a laser; a first capacitor coupled to the laser for providing current to drive the laser, wherein the first capacitor has a first capacitance; a second capacitor coupled to the laser for providing current to drive the laser, wherein the second capacitor has a second capacitance greater than the first capacitance; and a current driver coupled to the laser, the first capacitor, and the second capacitor for controlling current flow between the laser and the first and second capacitors, wherein the laser, the current driver, and the first capacitor together form a first current circuit, and wherein the laser, the current driver, and the second capacitor together form a second current circuit, and wherein the inductance of the first current circuit is relatively smaller than the inductance of the second current circuit.

[0027] The first capacitor may be a vertical silicon capacitor, with its lower surface electrically bonded to conductive traces on the capacitor surface.

[0028] The laser can be mounted on the surface of a substrate, wherein the upper terminal on the upper surface of the first capacitor is electrically coupled to the upper terminal on the upper surface of the laser, such that when the laser is turned on, the driving current flows from the upper terminal of the first capacitor to the upper terminal of the laser.

[0029] The first capacitor can be coupled to the current driver by mounting the first capacitor on the surface of an integrated circuit, in which the current driver is formed and conductively bonded to the terminals of the first capacitor, to a first terminal on the surface of the integrated circuit. The laser can be coupled to the current driver by mounting the laser on the surface of the integrated circuit and conductively bonding the laser's terminals to a second terminal on the surface of the integrated circuit. Attached Figure Description

[0030] Aspects of this disclosure are described with reference to the following figures, in which:

[0031] Figure 1A and 1B An example representation of a packaged light source module is shown;

[0032] Figure 1C Showing mounted on the PCB Figure 1A and 1B The encapsulated light source module;

[0033] Figure 1D It shows the representative Figure 1A and 1B The circuit diagram of the light source module;

[0034] Figure 1E It shows the representation of the ideal drive current signal and the ideal light source optical power signal;

[0035] Figure 2A A light source system according to one aspect of this disclosure is shown;

[0036] Figure 2B It shows Figure 2A The circuit diagram representing the system configuration;

[0037] Figure 3A It shows Figure 2A A side view of the system's first capacitor and light source;

[0038] Figure 3B It shows Figure 2A The system has a first capacitor and a light source on the other side, which has a platform for raising the height of the light source;

[0039] Figure 3CIt shows Figure 2A The system's first capacitor and light source are further apart on the side, with an additional platform to increase the height of the voltage terminals;

[0040] Figure 3D It shows Figure 2A The first capacitor of the system is on the other side of the light source, where a conductive bridge is used to form an electrical coupling;

[0041] Figure 4A Another light source system according to one aspect of this disclosure is shown;

[0042] Figure 4B express Figure 4A The system's circuit diagram.

[0043] Figure 5A Another light source system according to one aspect of this disclosure is shown;

[0044] Figure 5B express Figure 5A The system's circuit diagram.

[0045] Figure 6 Another light source system according to one aspect of this disclosure is shown;

[0046] Figure 7A Another light source system according to one aspect of this disclosure is shown;

[0047] Figure 7B Showing Figure 7A A side view of the system;

[0048] Figure 8A Another light source system according to one aspect of this disclosure is shown;

[0049] Figure 8B express Figure 8A The system's circuit diagram.

[0050] Figure 9 Another light source system according to one aspect of this disclosure is shown;

[0051] Figure 10A Another light source system according to one aspect of this disclosure is shown;

[0052] Figure 10B express Figure 10A The system's circuit diagram.

[0053] Figure 10C Showing Figure 10A A side view of the system;

[0054] Figure 11A Another light source system according to one aspect of this disclosure is shown;

[0055] Figure 11B express Figure 11A The system's circuit diagram.

[0056] Figure 12 Another light source system according to one aspect of this disclosure is shown;

[0057] Figure 13A Another light source system according to one aspect of this disclosure is shown;

[0058] Figure 13B Showing Figure 13A A side view of the system;

[0059] Figure 13C Another light source system according to one aspect of this disclosure is shown;

[0060] Figure 13D It shows Figure 13C A side view of the first capacitor of the system;

[0061] Figure 13E Showing Figure 13C A side view of the system;

[0062] Figure 13F Another light source system according to one aspect of this disclosure is shown;

[0063] Figure 13G Showing Figure 13F A side view of the system;

[0064] Figure 14A and 14B A representation of a conductive clip that can be used to couple a first capacitor to a power supply voltage terminal is shown. Detailed Implementation

[0065] Many factors can affect the accuracy of ToF camera systems in measuring object distances. One of these factors is the nature of the light emitted from the light source. For example, ambient light interference can affect the accuracy of distance / depth determination. Generally, modulating the emitted light with a relatively high-frequency modulation signal can reduce ambient light interference. However, the maximum achievable frequency may be limited by the rise and fall times of the signal driving the light source.

[0066] Furthermore, the range of accurate distance / depth measurements may be limited by the peak power of the emitted light. Increasing the peak power of the emitted light, while remaining within eye-safe limits, can increase the maximum depth that the system can accurately measure.

[0067] The relationship between noise, light source modulation frequency, and the number of detected signal photons in depth measurement can be seen from the following formula:

[0068]

[0069] in:

[0070] σ = Depth noise

[0071] c = light catch

[0072] A 信号 = The average number of detected signal photons

[0073] B 背景 = Average number of detected background photons

[0074] f mod =Modulation frequency

[0075] MC = Modulated Contrast

[0076] Increasing the peak power of the emitted light should increase A. signal Increasing the modulation frequency of the emitted light should also reduce the uncertainty of the overall depth noise. By way of example only, the inventors have recognized that if the light source is a vertical-cavity surface-emitting laser (VCSEL), then if the light source drive signal can provide a peak current in the range of 4 A, then a good depth measurement range can be achieved and σ can be kept within the desired level, with rise and fall times around 600 ps. For imaging objects within a range of several meters, the modulation frequency may be in the range of 50 to 400 MHz, and multiple frequencies can be used on multiple capture frames to handle phase unwrapping at different distances. The modulated light bursts in the range of 10 microseconds (µs) per frame; for short-range applications, bursts are typically in the range of 10 µs every 1–2 milliseconds; and for longer projection applications, bursts are typically in the range of 100 µs. However, it should be understood that the aspects disclosed herein are not limited to these specific parameters, and the system can be configured to deliver other levels of peak current, rise / fall time, modulation frequency, and burst period.

[0077] Therefore, to improve accuracy and measurement range, it is desirable to emit a high peak power optical signal modulated by a relatively high frequency modulation signal from the light source. This requires transmitting a high current drive signal to the light source to achieve a high peak current within a relatively short rise and fall time.

[0078] However, driving a light source with a large current and short rise and fall times presents many challenges. In particular, the inherent resistance and inductance in the light source driver circuit not only cause electrical losses (thus increasing the amount of current required to achieve a specific optical power output from the light source), but also slow down the circuit transitions between current levels, resulting in slow on and off cycles.

[0079] To address this challenge, the inventors devised various light source system designs suitable for ToF camera systems. In these designs, the system includes a low-inductance current loop / circuit designed to provide the first portion of the light source drive current with very short rise and / or fall times. The low-inductance loop includes a first capacitor positioned close to the light source and coupled to both the light source and driver circuitry. Due to this proximity, the current loop / circuit formed by the first capacitor, the light source, and the light source driver is very small, minimizing inductance. The first capacitor provides the initial current for turning on the light source, and the rise time of this initial current can be very short due to the loop's low inductance. Furthermore, the required margin for driver current and power supply can be lower, resulting in a more energy-efficient solution.

[0080] Optionally, a second, higher-inductance loop may also exist, comprising a second capacitor larger than the first capacitor and capable of replenishing the charge on the first capacitor and / or driving the light source after initial power-on. The second capacitor is not so tightly coupled to the light source and the light source driver. Thus, the inductance of the current loop / circuit formed by the second capacitor, the light source, and the light source driver is greater than the inductance formed by the first capacitor, the light source, and the light source driver. Alternatively, the second capacitor can be omitted, and the first capacitor can be replenished, allowing the light source to be driven by the supply voltage after initial power-on. In this way, the light source can initially be supplied with current in the lower-inductance current loop, thereby improving the current signal rise time, and then supplied with current in the higher-inductance current loop during the “steady state” of the drive signal, thereby maintaining a high peak current throughout the duration of the drive signal. Since the achieved rise time is initially most affected by the inductance of the drive circuit, a fast rise time and high peak current can be achieved. The supply voltage can provide the current required to recharge both capacitors and maintain a longer current burst period.

[0081] Various design details for minimizing the inductance of the first current loop are also disclosed. For example, the first capacitor is implemented as a vertical capacitor such that a portion of the vertical translation of the current between the substrate plane of the mounting element and the plane containing the upper terminal of the light source is performed by the first capacitor. This reduces / eliminates the need for any features purely dedicated to conducting current between these two planes, such as conductive vias, thereby further reducing inductance. In a further example, the light source and the first capacitor can be mounted on the surface of an integrated circuit (IC) containing drive circuitry, thereby minimizing the physical size of the formed current loop, which further reduces inductance.

[0082] Figure 1A and 1BAn example of a previously packaged light source module 110 is shown, which suffers from relatively high inductance driving circuitry and therefore relatively slow rise and fall times. The light source is a VCSEL, and the packaged light source module 110 includes a VCSEL 120 and a photodiode 130 (which can be used to measure optical power output for eye safety reasons). The anode terminal 122 of the VCSEL 120 is coupled to a bonding pad 140 via a wire bond 142, and the cathode terminal is on the underside of the VCSEL 110 (and therefore not visible).

[0083] Figure 1C A packaged light source module 110 mounted on a PCB 160 is shown. The pads 140 and cathode terminals of the light source module 110 are coupled to a driver IC 150 via the PCB 160.

[0084] Figure 1D A circuit diagram representing system 100 is shown, including representations of parasitic inductance, resistance, and capacitance. It should be understood that the packaged VCSEL module 110 contains a relatively high equivalent series inductance, which, combined with PCB wiring parasitism, can suppress the rise time of the current-driven signal. These can also lead to unwanted electrical resonance. When the current changes rapidly, the voltage drop across the inductor during drive reduces the available voltage compliance / headroom of the driver. To compensate for this, the supply voltage could be increased, but this would increase power consumption during laser drive. Therefore, it is desirable to reduce the circuit inductance to minimize power consumption during laser operation.

[0085] Figure 1E The ideal drive current signal and the ideal optical power signal are shown, as well as the signal transmitted through the optical circuit. Figure 1C The actual optical power and driver current achieved with the 1D arrangement are represented. It can be seen that the rise and fall times of the driver current, and therefore the optical power output from the VCSEL 120, are slower than ideal. The VCSEL's drive signal is not limited to a square wave. In particular, pre-emphasis or waveform shaping can be added to attempt to control and improve the optical edge speed or spectral content, but these all struggle with loop inductance.

[0086] Figure 2AA light source system 200 according to one aspect of this disclosure is shown. System 200 includes a light source 210, in this case a VCSEL, a light source driver 220, a first capacitor 230, and a second capacitor 240. In this example, the first capacitor 230 is a low-inductance wire-bonded vertical capacitor. For example, it can be a silicon capacitor, such as the wire-bonded vertical silicon capacitor manufactured by Murata - https: / / www.murata.com / - / media / webrenewal / products / capacitor / silicon capacitors / pdf / silicon-capacitors-cataloguev15murata.ashx?la=en&cvid=20200227020954000000.

[0087] These vertical silicon capacitors can be made of silicon and incorporate some form of trench to increase the effective capacitive surface area in a given region. The trench can be lined with an electrode coated with an insulator, followed by a second electrode. The first electrode can then be attached to the bottom surface of the capacitor via heavily doped silicon, which is then coated with a good metallic conductor to form terminals, allowing it to be used for connection to a system via solder or equivalents. An upper electrode can be formed on the upper surface of the capacitor in a similar manner to allow for wire bonding or other connection methods. However, other methods exist for manufacturing such capacitors.

[0088] The upper surface of the first capacitor 230 includes an upper terminal for connection to a first (top) plate of the first capacitor 230. The upper terminal is coupled to a voltage terminal, which in this example is a power supply voltage trace via connection line 232 (which can be any suitable voltage, such as 3.3V, 5V, or 11V, etc.). The upper terminal of the first capacitor 230 is also coupled via connection line 234 to an upper terminal (in this case, the anode terminal) on the upper surface of the VCSEL 210, thus providing two distinct connections to the upper terminal of the first capacitor 230. Here, when the VCSEL is turned on, current can be supplied from the first capacitor 230 and the power supply voltage (as explained later) to the anode terminal.

[0089] The mounting (lower) surface of the first capacitor 230 includes a second (bottom) plate for connecting to the first capacitor 230. Figure 2AThe lower terminal (not visible in the image) is the mounting surface of the first capacitor. The mounting surface of the first capacitor is electrically connected to the reference voltage conduction path by any suitable means (e.g., solder / bump bonding or conductive adhesive, etc.), in this case, the reference voltage conduction path being a ground trace on the PCB by any suitable means such as solder / bump bonding or conductive adhesive, etc. The mounting (lower) surface of the VCSEL 210 includes a lower terminal (in this case, a cathode terminal). The lower terminal is electrically connected to the cathode conduction path (in this example, a PCB trace) by any suitable means (e.g., metal-to-metal bonding or conductive adhesive, etc.). The lower terminals of VCSEL 210 and the first capacitor 230 are coupled to each other by the current driver 220 through conductively joining (e.g., solder / bump bonding, conductive adhesive, etc.) the first (current input) terminal of the driver 220 to the cathode trace and conductively joining (e.g., chip bonding, solder / bump bonding, conductive adhesive, etc.) the second (current output) terminal of the driver 220 to the reference voltage trace, such that when the VCSEL is turned on, the current from the cathode of the VCSEL drives the driver 220 and returns to the bottom plate of the first capacitor 230, whose top plate transmits the current to the anode of the same VCSEL 210.

[0090] In this example, all represented components / elements are mounted on an insulating substrate of the PCB. However, it should be understood that other non-PCB types of substrates, such as ceramic substrates, can be used in this example implementation and all other example implementations below. It can be seen that the conductive paths (e.g., traces) are all on the same side of the substrate, eliminating the need for interconnects such as conductive vias, which helps reduce circuit length and circuit inductance.

[0091] Figure 2BA circuit diagram representation of the configuration of system 200 is shown. Driver 220 is shown as including a current source / sink, but for simplicity, other components of driver 220 (e.g., for turning the VCSEL drive current on and off) are not shown. Driver 220 may include a transistor device such as a FET having a controlled gate voltage to bias the transistor for use as a current source / sink. The transistor may also act as a switch to turn the circuit current on and off, thereby controlling VCSEL 210. Alternatively, driver 220 may include a second transistor device that may be connected in series with the current source and VCSEL, located on either side of the current source, which may act as a switch to turn the circuit current on or off. Optionally, multiple drive transistors may be present to form a digitally controlled current, and the current may be modulated from one non-zero level to another non-zero level by multiple drive transistors or otherwise to produce the light source modulation required to transition from one level to another, rather than simply moving the driver current between on and off. It can be seen that in this example, since driver 220 is located on the cathode side of VCSEL 210, driver 220 operates as a low-side driver. Therefore, it should be understood that the driver / current driver 220 can alternatively be referred to as a controller / current controller configured to control the on and off of current in a control circuit.

[0092] The first capacitor 230 is located very close to the VCSEL 210 and the driver 220. Therefore, the current loop formed by the first capacitor 230, VCSEL 210, and driver 220 is relatively short. The first capacitor 230 and VCSEL 210 can be located in regions spaced 100μm, 200μm, 500μm, 1mm, or 2mm apart. Furthermore, the first capacitor 230 is a vertical capacitor, allowing for a low-inductance design, such as a silicon vertical capacitor. The closer the first capacitor 230 is to the VCSEL 210 in height, the closer the components can be positioned together, and the shorter and fewer the loops can be in the connection method. Therefore, the current loop formed by the first capacitor 230, VCSEL 210, and driver 220 is shorter and has lower inductance. However, due to the desire for a very compact design, the capacitance value of the first capacitor 230, and therefore the amount of energy (current over a short period) that the first capacitor 230 can transfer to the VCSEL 210, can be relatively small. The second capacitor 240 is located further away from the VCSEL 210 and the driver 240 and can have a relatively high inductance design (compared to the vertical capacitor). As a result, the current loop formed by the second capacitor 240, VCSEL 210, and driver 220 can be relatively long and have a relatively high inductance (compared to the first loop). However, the second capacitor 240 can have a relatively high capacitance compared to the first capacitor 230, and is therefore able to deliver a relatively large current to the VCSEL 210 with a relatively low rate of current change, since the first capacitor 230 already meets the high-frequency requirements. The second capacitor 240 can be any suitable design or type or combination of capacitors, such as ceramic capacitors, polymer capacitors, and / or combinations of multiple types of capacitors. In one example, it can be an SMD capacitor mounted on a substrate on which the VCSEL 210 is mounted, or mounted elsewhere and connected via cable or flex cable.

[0093] When driver 220 initiates the drive current, the first capacitor 230 should initially provide the first portion of the drive current to VCSEL 210 due to the relatively low inductance of the first loop. The relatively low loop inductance results in a short rise time for this current, allowing the high-frequency components of the drive current to be supplied by the first capacitor 230. The second capacitor 240 should provide the second portion of the drive current to the VCSEL, and the power supply voltage should provide the third portion of the drive current to the VCSEL, while also supplementing the first capacitor 230 and / or the second capacitor 240. Because the loop inductance of the circuit including the second capacitor 240 and the power supply voltage is large, and the impedance of the power supply voltage is high, the rise time may be longer than the first portion of the current supplied by the first capacitor 230. However, the relatively large current that the second capacitor 240 can provide and the power supply voltage should enable the circuit to maintain a large peak current throughout the duration of the drive signal. Therefore, this arrangement means that for the entire lighting operation cycle of 10s or 100s, high drive current (e.g., 4A, such as 3.5A or 4.5A, or higher) can be achieved at high modulation frequencies (e.g., in sequence from 10MHz to 500MHz or higher) with relatively fast switching / rise times (e.g., in sequence of 500ps, such as 460ps, or 520ps, etc.).

[0094] The first capacitor may be in the range of 10's-100's nF to provide current for a portion of several cycles of the modulation frequency with a ripple of only a few hundred mV, while the second capacitor may be much larger (uFs to 100'suF) to maintain current transfer for 10's or 100'suS and / or smooth the current drawn from the power source for many cycles of the modulation frequency within the pulse train.

[0095] Optionally, the height of the first capacitor 230 (i.e., the distance between the upper surface of the first capacitor 230 and the surface of the substrate on which it is mounted) can be selected to be substantially the same as the height of the VCSEL 210 (i.e., the distance between the upper surface of the VCSEL 210 and the surface of the substrate on which it is mounted) (e.g., within 5%, or within 10%, or within 25%). Typically, the thickness of the VCSEL can be in the range of 100 μm or 120 μm. They are typically within this range to minimize thickness to improve heat transfer from the VCSEL and reduce its series impedance, while maintaining thickness to maintain the stiffness required for handling and reliability. However, it is possible now or in the future to have thinner or thicker VCSELs and other light-emitting devices. Furthermore, this thickness may be affected by manufacturing tolerances within the range of 5% or 10%. Therefore, it should be understood that the term "substantially" does not mean that the heights of the two components are exactly the same. Rather, it means that they are at least close to being at the same height, within the manufacturing tolerance range and / or within a reasonable approximation range considering the limitations of the physical device size selection. In particular, significant benefits can be achieved if the device heights are the same and differ from each other by no more than 20-30%, for example, no more than 25%. For example, if the VCSEL has a nominal thickness of 100 μm, the upper terminal of the first capacitor 210 can be at approximately the same height as the upper terminal of the VCSEL, with its nominal thickness at any location in the range of 70-130 μm (i.e., within + / -30%), or in the range of 80-120 μm (i.e., within + / -20%). In particular, the length of the bonding wire 234 can be minimized due to the reduced vertical distance the bonding wire must travel, and also because it allows the first capacitor 230 and VCSEL 210 to be positioned closer to each other. This minimizes the parasitic inductance and resistance associated with the bonding wire. Furthermore, the number of “loops” in the bonding wire 234 can be reduced, which further reduces the inductance associated with the bonding wire 234. This can be further understood with reference to Figure 3. In addition, the capacitor can perform most (if not all) of the current required to initially drive the VCSEL 210 vertically, eliminating the need for components dedicated to vertical current conduction and further reducing inductance.

[0096] Although the vertical capacitor 230 described above is a silicon design, other types of vertical capacitors can be used alternatively. For example, vertical capacitors can be coated onto the surface of a substrate, such as onto the reference voltage trace in the example of Figure 2A, and in accordance with the aforementioned reference... Figure 2AThe same three conductive conditions are applied to both boards. Compared to the VCSEL 210, such capacitors can be relatively thin, allowing them to be at substantially different heights. However, this design still means that a portion of the vertical translation of current from the substrate surface to the upper terminals of the VCSEL is performed by the first capacitor 230, which helps reduce inductance compared to an arrangement where all vertical translation is done by components that only perform current conduction (e.g., vias). Furthermore, this design allows the first capacitor 230 to be positioned very close to the VCSEL 210, minimizing the size of the current loop and reducing inductance. Therefore, even when the first capacitor 230 is a vertical capacitor with a height substantially different from that of the VCSEL 210, the system can still achieve reduced inductance and thus perform a portion of the required vertical current conversion with the vertical capacitor and / or achieve a more compact circuit layout with faster current conversion / change.

[0097] Further alternatively, depending on the dimensions of the first capacitor 230 and VCSEL 210, a base (also referred to as a "block") may be used to elevate the upper surfaces of the first capacitor 230 and / or VCSEL 210 so that their upper surfaces are substantially coplanar. Figure 3A The diagram illustrates an arrangement with a height difference Δh between the upper surfaces of the first capacitor 230 and the upper surface of the VCSEL 210. The VCSEL 210 can be mounted on a conductive material, such as copper, to form a conductive coupling between the cathode of the VCSEL 210 and the conductive traces on the PCB. The first capacitor 230 and the VCSEL 210 can be selected such that any possible height difference Δh between them is small enough that they can be considered to be at substantially the same height. However, in cases where the height difference Δh is large, a platform or metal block can be used to make the heights of the components (i.e., the distance between the PCB surface and the upper terminals of the components) substantially the same.

[0098] Figure 3B An example is shown where a platform 310 (or "block" or "pad") is used to raise the height of the first capacitor 230 of the VCSEL 210 such that its upper surface is at substantially the same height as the top surface of the first capacitor 230. The base can be made of any suitable conductive material, such as copper, thus similar to the reference above. Figure 3A The conductive material described has a height specifically chosen to reduce or eliminate the height difference Δh. The surface area of ​​platform 310 can be similar to that of the component it is raising, in this case VCSEL 210, with the platform located on the substrate surface between the substrate surface and VCSEL 210. As a result, the length of wire bonding 234 can be reduced, which reduces parasitic inductance and resistance. Furthermore, it can be seen that... Figure 3BThe junction line 234 is compared to Figure 3A The bonding line 234 in the middle has fewer "loops" (i.e., the radius of the loop formed by the bonding line 234 is effectively reduced) and thus further reduces the inductance.

[0099] It should be understood that, depending on the geometry of the first capacitor 230 and VCSEL 210, the base 310 can alternatively be used to raise the height of the first capacitor 230, for example, where the height of the VCSEL 210 is greater than the height of the first capacitor 230, such that the base 310 can be positioned below the first capacitor 230 to raise its top surface to be substantially coplanar with the upper surface of the VCSEL 210. In any case, it should be understood that the use of techniques such as... may be employed in any aspect disclosed herein. Figure 3B Platform 310, etc., so that the terminals of the first capacitor 230 and VCSEL 210 coupled to the bonding line 234 reach a substantially coplanar height.

[0100] Figure 3C A further configuration is shown, in which an additional conductive base 320 is used to increase the height of the bonding point between the bonding wire 232 and the conductive trace on the PCB. The conductive base 320 can be made of any suitable conductive material, such as copper. By increasing the height of the point where the bonding wire 232 is electrically coupled to the power trace on the PCB, the number of “loops” in the bonding wire 232 can be reduced, thereby further reducing the inductance of the bonding wire 232. The mesa 320 can be used as a complement to or alternative to the mesa 310.

[0101] Figure 3D An alternative configuration is shown where, instead of using bonding wires for coupling between the power supply terminals, the first capacitor 230, and the VCSEL 210, conductive coupling can be achieved using a conductive "bridge" 330 (e.g., a sheet of any suitable conductive material, such as copper). The bridge 330 can be fixed to the anode terminals of the first capacitor 230 and the VCSEL 210 using conductive adhesive. By doing so, not only is the current loop minimized, as the surfaces of the first capacitor 230 and the VCSEL 210 are substantially coplanar, thus reducing the loop inductance, other inductances associated with the bonding wires (e.g., inductance caused by the "ring" shape) can potentially be reduced or eliminated. Furthermore, the coupling impedance can be reduced due to the increased conductive area compared to bonding wires. Other example alternatives using bonding wires are given later.

[0102] Figure 4AAnother light source system 400 according to one aspect of this disclosure is shown. It is similar to the first system 200, but includes a third capacitor 430 having the same design as the first capacitor 230 and a fourth capacitor 440 having the same design as the second capacitor 420. The VCSEL 210 has two upper terminals on its upper surface, to which the first capacitor 230 is coupled via bonding wire 234, and to the other terminal via bonding wire 434. The third capacitor 430 is also coupled to a power supply voltage conduction path via bonding wire 432.

[0103] Figure 4B A circuit diagram representation of the configuration of system 400 is shown. It can be seen that the first capacitor 230 and the third capacitor 430 are each part of a relatively low-inductance current loop (the first loop and the third loop). The second capacitor 240 and the fourth capacitor 440 are both part of a higher-inductance current loop (the second loop and the fourth loop). The operation of system 400 is very similar to that of system 200. However, compared to system 200, by doubling the number of bonding pads connected on the VCSEL 210, the bonding wire inductance can be reduced by approximately half, thereby further reducing the inductance of the current loop and improving the rise time of the drive current. Furthermore, it may be possible to deliver the same current by using more capacitors and / or smaller capacitors, which can then be physically closer to the VCSEL 210 and the driver 220, thereby further reducing the inductance of the current loop and even further reducing the rise / fall time of the current. Moreover, due to the symmetry of the layout, the current flows in substantially the opposite direction in the first loop compared to the third loop, and in the second loop compared to the fourth loop. Therefore, there may be some magnetic field cancellation, which can reduce electromagnetic radiation and reduce the effective inductance seen in each part of the system.

[0104] Figure 5A Another light source system 500 according to one aspect of this disclosure is shown. It is very similar to system 400, but does not include the fourth capacitor 440. Figure 5B A circuit diagram representation of the configuration of system 500 is shown. In this example, the same benefit of doubling the pad connections as explained in reference system 400 can be achieved. From Figure 5A and 5B It is understandable that, due to the symmetry of the layout, the current in the first loop flows in the opposite direction to that in the third loop. Furthermore, two current loops are effectively formed between the second capacitor 240 and the other components of the circuit, resulting in second and fourth loops again with current flowing in substantially opposite directions. Therefore, there may be some magnetic field cancellation, which can reduce electromagnetic radiation and reduce the effective inductance seen in each part of the system.

[0105] Figure 6 Another light source system 600 according to one aspect of this disclosure is shown. System 600 is very similar to system 500, but instead of including the third capacitor 430, it includes a junction line 610 for coupling the second upper terminal of VCSEL 610 to a power supply voltage. Thus, the second capacitor 240 is coupled to VCSEL 210 via two paths: one through the first plate of the first capacitor 230, and the second through the junction line 610. Alternatively, a conductive plateau can be used to raise the point where the junction line 610 is coupled to the power supply voltage trace (similar to...). Figure 3D This ensures that the two ends of the bonding wire 610 are at approximately the same distance from the substrate surface, and that all components are mounted on this surface.

[0106] Figure 7A Another light source system 700 according to one aspect of this disclosure is shown. System 700 is very similar to the system described above, but includes a second VCSEL 710 driven by the same driver 220 as the first VCSEL 210, but with separate low-inductance and high-inductance current loops formed by a third capacitor 430 and a fourth capacitor 440. Optionally, the driver 220 can be configured to drive both VCSELs simultaneously to increase the light output power, or it can be configured to drive only one at a time, for example, they are configured to perform two different functions (e.g., as referenced). Figure 7B The above).

[0107] Figure 7B A side view of system 700 is shown, in which two different light sources are configured to perform different functions. Optionally, two different optical elements can be used for two VCSELS. In this example, optical element 720 is a diffuser and optical element 730 is a diffractive optical element for generating patterned light sources. It should be understood that for each VCSEL, any suitable / desirable optical element can be used, or no optical element may be used at all.

[0108] Figure 8A Another light source system 800 according to one aspect of this disclosure is shown. Figure 8B A circuit diagram representation of the configuration of system 800 is shown. System 800 is very similar to the previously described system 200, except that it includes a VCSEL bypass 810 and the driver 220 includes bypass circuitry. In this configuration, the driver 220 can maintain a continuous current flow by switching between the bypass loop and the VCSEL 210 drive loop to turn the VCSEL 210 on and off. By doing so, a continuous current flow through some parasitic inductance can be maintained, thereby reducing the effects of those parasitic inductances and reducing the rise and fall times of the VCSEL drive current. Figure 8A As can be seen, the upper terminal of the first capacitor 230 is connected to the bypass 810 by a lead wire.

[0109] In each of the examples above, the first capacitor 230 is a vertical capacitor. Using a vertical capacitor in a light source system significantly reduces loop inductance compared to previous circuits using other types of capacitors. In particular, it should be understood that the VCSEL is a vertical structure because current flows between the terminals on its upper and lower surfaces when it is turned on. Therefore, the circuit must also have a second reverse current return path.

[0110] In many traditional systems, VCSELs may be mounted on a multilayer substrate, with a vertical layer for each voltage potential, thus potentially three layers: one for the ground terminal, another for the cathode voltage, and a third carrying the supply terminal. Circuit components can be mounted on the top surface of the substrate, with conductive vias providing appropriate vertical connections to the lower surface of the substrate. However, these vias affect the overall inductance of the circuit.

[0111] from Figures 3A to 3D As can be seen from this disclosure, by using a vertical capacitor for the first capacitor 230, the first capacitor 230 can perform at least some of the required vertical current conversion in the direction opposite to the current flowing through the VCSEL 210, that is, to transfer the current to the level of the anode terminal of the VCSEL 210. Therefore, the first capacitor 230 effectively performs two functions: providing some drive current and providing vertical current conversion. As a result, component features such as vias used solely for vertical current conversion purposes can be avoided, and loop inductance is reduced.

[0112] This characteristic is for Figure 3B to 3D The implementation of the "platform" can be particularly beneficial. As can be seen from these diagrams, there are now effectively two lateral or horizontal planes: a high-voltage plane on the anode surface of the VCSEL 210 and a low-voltage plane on the PCB for the cathode terminal and ground. There are also effectively two vertical or translational current paths between the lateral planes: one formed by the VCSEL 210 and the platform 210 to transfer current from the higher voltage level / plane to the lower voltage level / plane, and another formed by the first capacitor 230 to transfer current from the lower voltage level / plane to the higher voltage level / plane. This results in a significantly shorter overall current loop and reduced inductance compared to other solutions that require only conductive paths (e.g., vias) to move between different levels / layers of the system.

[0113] It should be understood that Figures 3A to 3DThe current path shown is simplified because the current will also flow through the driver 220, which is mounted on the PCB but not shown in the figure for simplicity. However, it should be understood that since the driver 220 is mounted on the PCB, which serves as the low-voltage plane of the system, the current will flow from the cathode trace of the PCB where the VCSEL 210 is mounted, through the driver 220, to the ground trace of the PCB, and then through the first capacitor 230 to the high-voltage plane of the system. Therefore, the current is switched from the low-voltage plane to the high-voltage plane via the first capacitor 230, thus avoiding the need to provide a conductive path to perform this function.

[0114] In an alternative configuration, the first capacitor 230 (and optionally the third capacitor 430) can be a lateral capacitor instead of a vertical capacitor. For example, it can be an interdigitated silicon lateral capacitor. This type of capacitor is generally structurally similar to the vertical capacitor described earlier because it utilizes trenches or other means (e.g., pillars) through the electrodes and insulating layers to increase the effective surface density of the capacitor. However, unlike a vertical capacitor, both terminals extend through the same surface for easy connection to the two plates of the capacitor. These capacitors can optionally cross the rows of electrode connections to reduce parasitic resistance and inductance.

[0115] Figure 9 An example representation of such a capacitor implemented in a system 900 similar to system 200 is shown. It can be seen that the first plate 935 of the first capacitor 930 is wire-bonded to the power supply voltage trace via bonding line 932 and to the anode of the VCSEL 210 via bonding line 234. The second plate 936 of the first capacitor 930 crosses the first plate 935 and is wire-bonded to the ground trace via wire bond 942 (opposite to the bottom bonding used in the vertical capacitor design described earlier). As a result, as in the implementation of a vertical capacitor, the capacitor has three distinct connections at both ends. Making the plates cross helps eliminate inductance between the wire bond 932 to the power supply voltage and the wire bond 942 to ground, since the corresponding wire bonds are also cross and have currents flowing in opposite directions. Therefore, arranging the plates of the first capacitor 930 in such a way that the bonding lines to the power supply voltage of the first plate and to the ground of the second plate cross each other helps reduce the inductance of the lower inductance current loop of the drive circuit.

[0116] Furthermore, the inductance of the current loop can be further reduced by placing the different couplings within the loop at substantially the same height. For example, the height of the first board 935 terminal can be substantially coplanar with the anode terminal of the VCSEL 210, and the PCB traces are all on one surface, making the couplings between the VCSEL's cathode, driver, and ground traces substantially coplanar. Therefore, essentially only two current planes flow around the low-inductance loop, and the current moves between the two planes only through the VCSEL and through junction lines 932 and 942. Similarly, one or both of the platforms described above can be used if desired. Figure 3B and 3C .

[0117] Figure 10A Another light source system 1000 configured according to this disclosure is shown. Figure 10B A circuit diagram representation of the configuration of system 1000 is shown. In this system, driver 1020 is configured as a high-side driver of VCSEL 210 (therefore, the driving transistor of driver 1020 can be a PMOS transistor, rather than an NMOS transistor typically used for low-side drivers), such that the upper terminal of the first capacitor 230 is coupled to the upper terminal of VCSEL 210 through driver 1020. Specifically, the upper terminal of VCSEL 210 is coupled to the second (output current) terminal of driver 1020 via bonding line 1050, and the upper terminal of the first capacitor 230 is coupled to the first (input current) terminal of driver 1020 via bonding line 1014, such that when VCSEL 210 is turned on, current flows from the first capacitor 230 to the first terminal of driver 1020, and then from the second terminal of driver 1020 to VCSEL 210. Figure 10A Other terminals of the driver coupled to additional terminals on the PCB are also shown, but these are only optional connections for purposes such as controlling the driver and are not described further. The lower terminals of VCSEL 210 and the first capacitor 230 can be electrically coupled to each other by any suitable form of electrical coupling, securing them to a reference voltage conduction path (e.g., ground trace) on the PCB 160, for example in... Figure 10AThe metal-to-metal bonding or conductive adhesive is not visible in the representation. This arrangement helps reduce ground loop inductance, thereby further reducing the rise time of the VCSEL drive current. In particular, the size of the current loop can be minimized by limiting the current to travel in essentially two planes—the first plane is the ground trace on the PCB substrate, and the second plane is the plane containing the terminals on the upper surface of the first capacitor 230, driver 1020, and VCSEL 210. In a low-inductance loop, current flows from the ground plane through the first capacitor 230 to the terminal connection plane, and from the terminal connection plane through the VCSEL 210 back to the ground plane. The benefits of using the first capacitor 230 not only as a charge supply but also to connect the ground plane to the terminal connection plane have been described above. Furthermore, in this particular arrangement, the driver is mounted above a portion of the reference voltage trace on the substrate through which current returns from the VCSEL 210 to the first capacitor 230. For example, it can be insulated to the substrate so that current can pass under the driver 1020. This means that in both high-inductance and low-inductance current loops, the current flows essentially in one direction in the ground plane, but in the opposite direction in the terminal connection plane. Therefore, a degree of loop inductance cancellation can be achieved, thereby further reducing the inductance of each loop.

[0118] Figure 10C A side view of system 1000 is shown, in which the current flow in the two current planes can be more easily understood.

[0119] Optionally, the heights of the upper surfaces of the first capacitor 230, driver 1020, and VCSEL 210 from the substrate surface can be substantially the same. This can be achieved by component selection and / or by making the driver 1020 IC relatively thinner to reduce the height of the driver 1020. Additionally or alternatively, one or more conductive platforms can be used to raise the height of one or more of the first capacitor 230, VCSEL 210, and / or driver 1020 so that their terminals are substantially at the same height as the PCB surface. Additionally or alternatively, one or more conductive platforms can be used to raise the height of the power supply voltage bonding wire terminals such that bonding wire 232 bonds to a conductive platform substantially coplanar with the bonding wire terminals on the surface of the first capacitor 230. As can be understood from the foregoing description, these features can help and even further reduce loop inductance.

[0120] The lower terminal of VCSEL 210 is coupled to PCB substrate 160, which improves heat dissipation of VCSEL 210. The first capacitor 230 in this example is a vertical capacitor, although it should be understood that... Figure 9 The lateral capacitor implementation can also be used in conjunction with a high-side driver.

[0121] Figure 11A Another light source system 1100 according to one aspect of this disclosure is shown. Figure 11B A circuit diagram representation of the configuration of system 1100 is shown. This system is very similar to system 1000, but driver IC 1120 also includes an integrated photodiode 1130. Photodiode 1130 is coupled to the upper terminal of VCSEL 210 via internal electrical connections and bonding wires within driver IC 1020. Alternatively, it can be coupled to the first capacitor 230 and / or an internal route for the reference voltage in driver 1020. For eye safety reasons, photodiode 1130 is used to measure the intensity of light emitted from VCSEL 210, absorbing light reflected back from any optical components (e.g., diffusers) in the light output path. It can be seen that driver IC 1120 includes additional components, such as a buffer / amplifier and an ADC for measuring light intensity. Photodiode 1130 can be embedded inside the driver IC because it also faces upwards, which allows for a simpler, lower-cost solution without the need for additional components. It should also be noted that there are several different ways to configure the photodiode 1130 and use it to detect representative light from the VCSEL 210. For example, it can be referenced to another supply voltage, or it can be used to discharge a capacitor during an illumination cycle to create a low-pass filtered version of the captured light energy. In this particular example, the driver IC 1120 also includes a switch that can be used to switch between measuring light intensity and measuring the voltage on the anode of the VCSEL 210. The configuration of system 1100 results in a compact, low parasitic inductance design with built-in safety features.

[0122] Figure 12 Another light source system 1200 configured according to this disclosure is shown. In this example, system 1200 includes another safety monitoring IC 1210 with lead bonding. Safety monitoring IC 1210 includes an integrated photodetector configured to measure the intensity of light emitted from VCSEL 210. Safety monitoring IC 1210 includes an integrated switch to disconnect power to system 1200 or shunt the voltage of driver 1120 to 0V, thereby shutting down the system in the event of a dangerous level of light emission. By having safety monitors in two different dies, system 1200 provides additional redundancy in system safety monitoring, as a fault detected by either safety monitoring IC 1210 or driver IC 1120 could shut down the system, thus stopping light emission. While safety monitoring IC 1210 and... Figure 11A This system layout can be used in conjunction with other system designs disclosed herein, but it should be understood that it can be used in conjunction with any other system design disclosed herein.

[0123] Figure 13A Another light source system 1300 according to a configuration of this disclosure is shown. The system includes a module or package 1350 (shown in dashed lines) with a driver IC 1330, a VCSEL 210, a first capacitor 230, and a third capacitor 430 directly mounted on its upper surface. The cathode of the VCSEL 210 may be chip-to-chip bonded to the driver 1330. The first capacitor 230 and the third capacitor 430 are vertical capacitors of the type previously described. The die of the driver IC 1330 may optionally be thinned to improve heat dissipation. Multiple terminals for coupling the module or package 1350 to external components (e.g., SDA, SCL, etc.) are shown. These are optional controls for configuring, powering, and controlling the driver and are not described further. A second capacitor 240 is external to the module or package 1350. A fourth capacitor 440 is not shown in this figure, but it should be understood that the fourth capacitor 440 may optionally be included as part of the light source system 1300. Note that in this example, the driver IC 1330 includes a photodiode 1030 embedded inside as described above.

[0124] The driver IC 1330 can be electrically coupled to a reference voltage (GND) trace on the substrate / PCB on which it is mounted. Alternatively, the ground terminal of the driver IC 1330 can be coupled to a terminal of the ground trace via an interconnect, such as bonding wire 1340. The power supply voltage terminal of the driver IC 1330 can also be coupled to a terminal of the power supply voltage trace via an interconnect, such as bonding wire 1340.

[0125] Figure 13B A side view of a portion of module or package 1350 is shown, providing a clearer understanding of the component arrangement and interconnections. It can be seen that the upper terminals of both the first capacitor 230 and the third capacitor 430 are electrically coupled to the power supply voltage via bonding wire 1320. In this example, bonding wire 1320 couples the upper terminals of the capacitors to provide voltage terminals on the upper surface of the driver IC 1330. However, in an alternative arrangement, interconnects such as bonding wire 1320 could directly couple the upper terminals of the capacitors to provide voltage terminals on the surface of the substrate / PCB on which the driver IC 1330 is mounted.

[0126] The upper terminals of capacitors 230 and 430 are also electrically coupled to the upper terminal of VCSEL 210 via interconnect 1310, which in this example is a bonding wire. It can be seen that in this example, the upper terminals of capacitors 230 and 430, as well as the VCSEL, are located at substantially the same height from the surface of driver IC 1320, thereby minimizing the length and "loop" of bonding wire 1310 and also allowing the capacitors to be positioned closer to VCSEL 210.

[0127] The lower terminals of capacitors 230 and 430, as well as VCSEL 210, are electrically bonded to terminals on the upper surface of driver IC 1310 using conductive bonding agent 1360. In this manner, the lower terminals of VCSEL 210 are electrically connected to the terminals of the driver IC 1310 via a current driver (in...). Figure 13B The lower terminals of capacitors 230 and 430 are coupled to the lower terminals of the VCSEL 210 (represented by the current source symbol). Specifically, the lower terminal of the VCSEL 210 can be conductively coupled to the first (current input) terminal of the current driver, and the lower terminals of the first and third capacitors 230 and 430 are coupled to the second (current output) terminal of the current driver, such that when the VCSEL is turned on, current flows from the first terminal of the current driver through the current driver to the second terminal of the current driver.

[0128] from Figure 13A and 13B It is understandable that the current loop formed by the first and third capacitors 230 and 430, VCSEL 210, and the current driver is very compact. Furthermore, the current flows effectively in two planes—the first plane including capacitors 230 and 430 and the upper terminal of VCSEL 210, and the second plane serving as the driver IC—moving up and down between the planes through capacitors 230 and 430 and through VCSEL 210. Therefore, the inductance of the circuit can be minimized, allowing for a very fast initial turn-on speed using the current stored in capacitors 230 and 430. Additionally, the physical size of the module or package 1350 is made very small, making it easier to use in the light source system 1300.

[0129] Figure 13C It shows the relationship with Figure 13A Another alternative implementation of the very similar light source system 1300 shown in the figure, except that the first and third capacitors 230 and 430 are lateral silicon design capacitors.

[0130] Figure 13D This image shows one side of a lateral silicon design capacitor, illustrating the two bump terminal connections between the capacitor's two plates. These two bump terminal connections can be conductively bonded to appropriate conductive paths within the driver IC circuitry via semiconductor processing.

[0131] Figure 13E Showing Figure 13CThe implementation is shown in the side view. It can be seen that one terminal of each of capacitors 230 and 430 is conductively connected to the reference voltage (in this case, ground) conductive path in the IC circuit. The other terminal of each of capacitors 230 and 430 is conductively connected to the power supply voltage conductive path in the IC circuit, which is also coupled to the upper terminal of VCSEL 210 via interconnect 1320 (in this example, a bonding wire).

[0132] Lateral silicon capacitors are relatively low-inductance devices, and coupling the first and third capacitors 230 and 430 to the current driver and VCSEL 210 via terminals conductively bonded to the surface of the driver IC minimizes the inductance in the current loop. Therefore, a very fast initial turn-on speed for the VCSEL can be achieved using the current stored in the first and third capacitors 230 and 430.

[0133] Figure 13F It shows the relationship with Figure 13C Another alternative implementation of the very similar light source system 1300 is that only the anode and cathode terminals of the VCSEL 210 are on the mounting surface of the VCSEL 210. Figure 13G This shows where it might be easier to understand this difference.

[0134] In this alternative, instead of interconnect 1320, VCSEL 1370 includes an internal through-hole 1370 that routes current from the anode terminal on its mounting surface to the upper surface of VCSEL 1370. The cathode and anode terminals of VCSEL 210 can be conductively bonded to appropriate terminals on the driver IC surface via conductive bonding material 1360. Similarly, with Figures 13C to 13E Similar to the implementation method, this arrangement can have very low loop inductance, thereby enabling a very fast VCSEL 210 turn-on speed using the current stored in the first and third capacitors 230 and 430.

[0135] In this method, the VCSEL 210 uses through-silicon vias or similar means to bring the anode terminal to a different area from the cathode terminal on the mounting surface of the VCSEL 210, while the emitter aperture of the VCSEL emitter array remains on the upper surface, allowing light to be emitted from that surface. This is sometimes referred to as backlighting or BSI.

[0136] It should be understood that Figures 13A to 13G Some features indicated are optional. For example, in an alternative, PD 1030 can be omitted, the third capacitor 430 can be omitted, and / or the fourth capacitor 440 can be used.

[0137] Optionally, the height of the voltage supply and / or reference voltage (ground) terminals on substrate 160 can be effectively raised to substantially the same height as the surface of driver IC 1330. This allows the bonding wire 1340 to be fabricated as short as possible with the smallest possible loop. Additionally or alternatively, in embodiments where there is an interconnect between the upper surface of driver IC 1330 and the upper surfaces of capacitors 230 and 430 (e.g. Figure 13A and 13B ) or between the upper surface of driver IC 1330 and the upper surface of VCSEL 210 (e.g. Figure 13C and 13E In this implementation, the height of the associated driver IC terminal can be raised to be substantially the same as the height of the capacitor / VCSEL. For example, this can be achieved by growing a conductive layer (e.g., copper) on the bonding terminals on the chip surface using any suitable semiconductor processing technique. Alternatively, a conductive material (e.g., copper) can be fixed to the die surface above the bonding terminals using a suitable conductive epoxy resin. In both cases, this can achieve... Figure 3C Similar results were shown in the diagram, which allowed for a reduction in the length of the bonding wires that couple the VCSEL 210 to the driver 1330, and also reduced the amount of “loops” that were already present, thereby further reducing inductance and resistance.

[0138] In all the systems disclosed above, one or more capacitors are arranged to form a relatively low inductance loop with the VCSEL and driver to provide an initial driver current with low parasitic inductance and therefore a shorter rise time. One or more additional capacitors are also coupled to the VCSEL and driver in a relatively high inductance loop to supply peak current to the VCSEL, thereby achieving a relatively high peak drive current (although, as mentioned above, one or more additional capacitors can be omitted, and the peak current can be provided solely by the supply voltage). Thus, a system can be implemented that simultaneously achieves short rise and fall times as well as high-frequency operation, which can improve the accuracy and depth range of ToF systems using light source systems. Furthermore, the capacitor design for the capacitors used to carry the initial current can be selected to have very low parasitic inductance, even if their capacitance / density is small. The capacitor design for the capacitors used to carry later currents can be selected to have high capacitance / density to carry high peak currents, even if their inductance is relatively high. Therefore, the advantages of low inductance and high capacitance can be achieved in the same system to provide short current rise time and high peak current.

[0139] In each of the above examples, at least one coupling terminal of the first capacitor 230 (and optionally a third capacitor 430) may be substantially coplanar / at the same height as the terminals of the device to which it is coupled (e.g., VCSEL 210 or a driver). In some cases, this can be achieved through component selection or circuit design (e.g., Figure 13A (As shown). In other cases, one or more conductive platforms may be used to raise the height of the first capacitor 230 and / or the devices coupled thereto, such that their respective terminals are substantially coplanar. Optionally, other surfaces coupled to the first capacitor 230 (and optionally a third capacitor 430) may be substantially coplanar / at the same height as the elements to which the capacitors are coupled. For example, if the upper surface of the capacitor is wire-bonded to a power or ground trace on a mounting substrate, a platform may be used to raise the height of the trace bonding surface to be substantially coplanar with the upper surface of the capacitor.

[0140] Various example systems have been disclosed above, in which the first capacitor 230 (and optionally the third capacitor 430) is a vertical capacitor. In those examples, one of the capacitor plates (on the upper or top side of the capacitor) has two couplings, such as bond wire couplings or conductive clips. Typically, one of these couplings is a pad / trace on the substrate on which the capacitor is mounted, for example, a power supply voltage, while the other coupling is a component of the laser drive circuitry, such as a light source or driver. The other capacitor plate (on the lower or bottom side of the capacitor) is typically conductively attached to a contact pad / trace (e.g., ground) on the substrate on which the capacitor is mounted. By coupling the vertical capacitor within the laser drive circuitry in this three-coupling arrangement, the loop inductance of the circuitry can be reduced, thereby improving the turn-on speed. Figure 9 Similar to lateral interdigitated capacitors, wire bonding (or conductive clip coupling) is used to connect two capacitor plates to three different components / assemblies. Specifically, one capacitor plate is wire-bonded to the VCSEL and also wire-bonded to a power supply voltage trace on the substrate. The second capacitor plate is wire-bonded to a ground trace on the substrate. Again, this three-coupling arrangement helps minimize loop impedance in the circuit.

[0141] In each of the above examples, the VCSEL, driver, and first capacitor (and third capacitor) can be included in a single package / module, such that the current loop formed by these components is small and has a small inductance. One or more (e.g., two, three, four, etc.) capacitors can be used for this fast rise time purpose. The second capacitor (and fourth capacitor) can be part of the package / module or can be external to the package / module, wherein the package / module is configured to couple one or more external capacitors. One or more (e.g., two, three, four, etc.) capacitors can be used for this high peak current purpose. Furthermore, while each of the above examples includes at least one relatively low-capacitance capacitor (e.g., first capacitor 230) and at least one relatively high-capacitance capacitor (e.g., second capacitor 240), in alternatives, the circuit may have only one or more low-capacitance capacitors. In this case, the first capacitor 230 can provide the initial, first portion of the drive current to quickly turn on the VCSEL 210. The remaining portion of the drive current required to maintain the VCSEL in the on-state for the desired duration can be provided by a voltage source. This implementation can be particularly useful when the power supply voltage is capable of providing the remainder of the required drive current, in which case circuit cost and physical size can be reduced by omitting the second capacitor 240. However, in cases where the power supply voltage is not suitable for providing the full remainder of the required drive current, the second capacitor 240 may be included, and the remainder of the required drive current may be provided by both the power supply voltage and the second capacitor 240.

[0142] Those skilled in the art will readily understand that various changes or modifications can be made to the foregoing aspects of this disclosure without departing from the scope of this disclosure.

[0143] The various aspects described herein include wire bonding. Wherever wire bonding is used, any other suitable form of surface electrical coupling can be used. For example, strip bonding and conductive clip coupling can be used alternatively. Figure 14A An example representation of a conductive clip 1410 (e.g., a copper clip) for coupling the first plate of the first capacitor 230 to a PCB trace instead of using wire bonding is shown. Figure 14B shows another example of how the conductive clip can be extended to also couple the first plate of the first capacitor 230 to the VCSEL 210. In this example, it can be seen that even without wire bonding, it is still beneficial for the terminal connection between the first capacitor 230 and the VCSEL 210 to be substantially on the same plane (achieved in this example using a platform / tablet 310) to reduce the current path length. The conductive clip can be fixed to the first capacitor 230 and / or VCSEL 210 using any suitable material such as conductive epoxy.

[0144] Although the above-described light source systems are specifically referenced in conjunction with ToF camera systems, the light source systems are not limited to this purpose and can be used for any other purpose. Furthermore, while each of the above-described light source systems has a VCSEL as a light source, any suitable type of light source, such as any other type of laser or LED, can be used alternatively.

[0145] In most of the examples given here, the light source 210 has an anode terminal on its upper surface and a cathode terminal on its lower surface. However, it can also be reversed by making appropriate minor reconfigurations to the component connections in the rest of the circuit. For example, in Figure 2A In this arrangement, the upper terminal of the first capacitor 230 can be coupled to the reference voltage (GND) trace via interconnect 232, instead of being coupled to the power supply voltage trace. The lower terminal can be conductively connected to the power supply voltage trace together with the terminal of the driver 202, and another terminal of the driver 220 and the lower anode terminal of the light source 210 are conductively connected to the anode trace (with...). Figure 2A The traces marked "cathode" are essentially the same. In this case, driver 220 will be a high-side driver. In other words, the trace marked "supply voltage" will become the reference voltage trace (ground), the trace marked "GND" will become the supply voltage trace, and the trace marked "cathode" will become the anode trace. Similarly, for... Figure 11A In this configuration, the trace marked "Power Supply Voltage" will become the reference voltage trace (ground), the trace marked "GND" will become the power supply voltage trace, and driver 1120 will become the low-side driver.

[0146] The terms “coupled” and “connected” are used throughout this disclosure to cover both direct electrical connection between two components / devices and indirect electrical coupling between two components / devices, wherein one or more intermediate components / devices are present in the electrical coupling path between the two components / devices.

Claims

1. A light source system, comprising: substrate; A light source mounted on the surface of the substrate, wherein the light source includes: The upper surface having the upper terminal; and A mounting surface, electrically fixed to the surface of the substrate and having a lower terminal, is provided. The light source is configured to be turned on by a current flowing between the upper and lower terminals. A vertical capacitor is used to provide a first portion of the current to drive the light source, wherein the vertical capacitor comprises: The upper surface includes the upper terminal of the first plate of the vertical capacitor, wherein the upper terminal of the vertical capacitor is electrically coupled to the upper terminal of the light source; and Mounting surface, electrically fixed to the surface of the substrate and including a lower terminal to the second plate of the vertical capacitor; and A current driver, mounted on the surface of the substrate and coupled to the light source and the vertical capacitor, is used to control the current flow from the vertical capacitor to the light source, thereby controlling the operation of the light source. The substrate includes a voltage terminal electrically coupled to the vertical capacitor for providing a second portion of the current required to drive the light source. The distance between the surface of the substrate and the upper terminal of the light source is substantially the same as the distance between the surface of the substrate and the upper terminal of the vertical capacitor.

2. The light source system according to claim 1, wherein the voltage terminal of the substrate is electrically coupled to the upper terminal of the vertical capacitor via a first interconnect.

3. The light source system of claim 1, wherein the light source is mounted on the surface of the substrate using a conductive base, the conductive base having a thickness such that the distance between the surface of the substrate and the upper terminal of the light source is substantially the same as the distance between the surface of the substrate and the upper terminal of the vertical capacitor.

4. The light source system of claim 1, wherein the current driver is a low-side driver, and the lower terminal of the light source is electrically coupled to the lower terminal of the vertical capacitor via the current driver; and The upper terminal of the vertical capacitor is electrically coupled to the upper terminal of the light source via a second interconnect, such that when the light source is turned on, current flows from the upper terminal of the vertical capacitor to the upper terminal of the light source, and then from the lower terminal of the light source back to the vertical capacitor via the current driver.

5. The light source system according to claim 4, wherein the substrate comprises: The lower terminal of the light source and the first terminal of the current driver are electrically fixed to a first conductive path, such that when the light source is turned on, current flows from the lower terminal of the light source to the first terminal of the current driver through the first conductive path; and The lower terminal of the vertical capacitor and the second terminal of the current driver are electrically fixed to a second conductive path, such that when the light source is turned on, current flows from the second terminal of the driver to the lower terminal of the vertical capacitor through the second conductive path.

6. The light source system of claim 5, wherein the second conductive path is maintained at a reference potential.

7. The light source system of claim 1, wherein the current driver is a high-side driver, and the upper terminal of the vertical capacitor is electrically coupled to the upper terminal of the light source through the current driver.

8. The light source system according to claim 7, wherein the substrate comprises: The lower terminal of the light source and the lower terminal of the vertical capacitor are electrically fixed to a reference voltage conductive path, such that when the light source is turned on, current flows from the lower terminal of the light source to the lower terminal of the vertical capacitor through the reference voltage conductive path.

9. The light source system of claim 8, wherein a portion of the reference voltage conductive path passes below the current driver, such that when the light source is turned on, current flows through the reference voltage conductive path from the lower terminal of the light source to the lower terminal of the vertical capacitor, below the current driver in a direction substantially opposite to the current flow from the upper terminal of the vertical capacitor to the upper terminal of the light source.

10. The light source system according to claim 7, wherein the current driver comprises: The first surface has a third terminal and a fourth terminal; and A second surface fixed to the surface of the substrate. The upper terminal of the vertical capacitor is coupled to the third terminal of the current driver via a third interconnect, and the fourth terminal of the current driver is coupled to the upper terminal of the light source via a fourth interconnect.

11. The light source system according to claim 10, wherein the upper terminal of the light source, the upper terminal of the vertical capacitor, and the third and fourth terminals of the current driver are all located at substantially the same distance from the surface of the substrate.

12. The light source system of claim 2, wherein the first interconnector comprises: A conductive platform has a mounting surface that is conductively fixed to a voltage terminal, and an upper surface that is located at a substantially the same distance from the surface of the substrate as the upper terminal of the vertical capacitor. and At least one conductive element is fixed to the upper surface of the conductive platform and the upper terminal of the vertical capacitor.

13. The light source system of claim 1, further comprising a third portion of the current for driving the light source, and an additional capacitor. The additional capacitor mentioned therein has a larger capacitance than the vertical capacitor, and The vertical capacitor, the light source, and the current driver are coupled together to form a first current loop. The additional capacitor, the light source, and the current driver are coupled together to form a second current loop.

14. The light source system of claim 1, wherein the vertical capacitor is a first vertical capacitor, and the light source system further comprises a second vertical capacitor, wherein the second vertical capacitor comprises: The upper surface includes an upper terminal to a first plate of the second vertical capacitor, wherein the upper terminal of the second vertical capacitor is electrically coupled to a second upper terminal of the light source, wherein the first upper terminal of the light source is located on a first side of the upper surface of the light source, and the second upper terminal of the light source is located on a second opposite side of the upper surface of the light source; and A mounting surface, electrically fixed to the surface of the substrate, and including a lower terminal to the second plate of the first vertical capacitor. The second vertical capacitor is electrically coupled to the voltage terminal of the substrate and is located on the side of the light source opposite to the position of the first vertical capacitor, such that when the light source is turned on, the current flows from the first vertical capacitor to the light source in a direction substantially opposite to the current flowing from the second vertical capacitor to the light source.

15. A light source system, comprising: Driver ICs, including current drivers; A light source mounted on the surface of the driver IC, wherein the light source comprises: First terminal; and The second terminal on the mounting surface of the light source is electrically connected to the first terminal of the current driver on the surface of the driver IC; and A capacitor mounted on the surface of the driver IC, wherein the capacitor comprises: A first terminal of the first plate of the capacitor is electrically coupled to a power supply voltage and a first terminal of the light source, such that when the light source is turned on, current flows from the first plate of the capacitor to the first terminal of the light source; and The second terminal of the second plate of the capacitor is electrically connected to the second terminal of the current driver on the surface of the capacitor mounting surface, such that when the light source is turned on, current flows through the current driver from the second terminal of the light source to the second plate of the capacitor. The first terminal of the light source and the first terminal of the capacitor are located at approximately the same height from the surface of the driver IC.

16. The light source system of claim 15, wherein the capacitor is a vertical silicon capacitor, and The first terminal of the capacitor is located on the upper surface of the capacitor.

17. The light source system of claim 15, wherein the capacitor is a lateral silicon capacitor; and The second terminal of the capacitor is located on the mounting surface of the capacitor and is electrically coupled to the conductive path of the driver IC, which is electrically coupled to the first terminal of the light source.

18. A laser driving circuit, comprising: Laser; A first capacitor is coupled to the laser to provide current to drive the laser, wherein the first capacitor has a first capacitance; A second capacitor is coupled to the laser to provide current to drive the laser, wherein the second capacitor has a second capacitance greater than that of the first capacitor; A current driver, coupled to the laser, the first capacitor, and the second capacitor, is used to control the current flow between the laser and the first and second capacitors. The laser, the current driver, and the first capacitor together form a first current circuit. The laser, the current driver, and the second capacitor together form a second current circuit. The inductance of the first current circuit is relatively smaller than the inductance of the second current circuit, and The upper terminal of the laser is located at substantially the same height as the upper terminal of the first capacitor.

19. The laser driving circuit of claim 18, wherein the first capacitor is coupled to the current driver by mounting the first capacitor on the surface of an integrated circuit in which the current driver is formed and conductively bonding the terminals of the first capacitor to a first terminal on the surface of the integrated circuit.

Images