Patent Publication Number: US-2020292678-A1

Title: Multi-channel lidar illumination driver

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application for patent claims the benefit of and priority to and is a Continuation from U.S. patent application Ser. No. 16/134,068, entitled “Multi-Channel LIDAR Illumination Driver” filed Sep. 18, 2018, which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The described embodiments relate to LIDAR based 3-D point cloud measuring systems. 
     BACKGROUND INFORMATION 
     LIDAR systems employ pulses of light to measure distance to an object based on the time of flight (TOF) of each pulse of light. A pulse of light emitted from a light source of a LIDAR system interacts with a distal object. A portion of the light reflects from the object and returns to a detector of the LIDAR system. Based on the time elapsed between emission of the pulse of light and detection of the returned pulse of light, a distance is estimated. In some examples, pulses of light are generated by a laser emitter. The light pulses are focused through a lens or lens assembly. The time it takes for a pulse of laser light to return to a detector mounted near the emitter is measured. A distance is derived from the time measurement with high accuracy. 
     Some LIDAR systems employ a single laser emitter/detector combination combined with a rotating mirror to effectively scan across a plane. Distance measurements performed by such a system are effectively two dimensional (i.e., planar), and the captured distance points are rendered as a 2-D (i.e. single plane) point cloud. In some examples, rotating mirrors are rotated at very fast speeds (e.g., thousands of revolutions per minute). 
     In many operational scenarios, a 3-D point cloud is required. A number of schemes have been employed to interrogate the surrounding environment in three dimensions. In some examples, a 2-D instrument is actuated up and down and/or back and forth, often on a gimbal. This is commonly known within the art as “winking” or “nodding” the sensor. Thus, a single beam LIDAR unit can be employed to capture an entire 3-D array of distance points, albeit one point at a time. In a related example, a prism is employed to “divide” the laser pulse into multiple layers, each having a slightly different vertical angle. This simulates the nodding effect described above, but without actuation of the sensor itself. 
     In all the above examples, the light path of a single laser emitter/detector combination is somehow altered to achieve a broader field of view than a single sensor. The number of pixels such devices can generate per unit time is inherently limited due limitations on the pulse repetition rate of a single laser. Any alteration of the beam path, whether it is by mirror, prism, or actuation of the device that achieves a larger coverage area comes at a cost of decreased point cloud density. 
     As noted above, 3-D point cloud systems exist in several configurations. However, in many applications it is necessary to see over a broad field of view. For example, in an autonomous vehicle application, the vertical field of view should extend down as close as possible to see the ground in front of the vehicle. In addition, the vertical field of view should extend above the horizon, in the event the car enters a dip in the road. In addition, it is necessary to have a minimum of delay between the actions happening in the real world and the imaging of those actions. In some examples, it is desirable to provide a complete image update at least five times per second. To address these requirements, a 3-D LIDAR system has been developed that includes an array of multiple laser emitters and detectors. This system is described in U.S. Pat. No. 7,969,558 issued on Jun. 28, 2011, the subject matter of which is incorporated herein by reference in its entirety. 
     In many applications, a sequence of pulses is emitted. The direction of each pulse is sequentially varied in rapid succession. In these examples, a distance measurement associated with each individual pulse can be considered a pixel, and a collection of pixels emitted and captured in rapid succession (i.e., “point cloud”) can be rendered as an image or analyzed for other reasons (e.g., detecting obstacles). In some examples, viewing software is employed to render the resulting point clouds as images that appear three dimensional to a user. Different schemes can be used to depict the distance measurements as 3-D images that appear as if they were captured by a live action camera. 
     Some existing LIDAR systems employ an illumination source and a detector that are not integrated together onto a common substrate (e.g., electrical mounting board). Furthermore, the illumination beam path and the collection beam path are separated within the LIDAR device. This leads to opto-mechanical design complexity and alignment difficulty. 
     In addition, mechanical devices employed to scan the illumination beams in different directions may be sensitive to mechanical vibrations, inertial forces, and general environmental conditions. Without proper design these mechanical devices may degrade leading to loss of performance or failure. 
     To measure a 3D environment with high resolution and high throughput, the measurement pulses must be very short. Current systems suffer from low resolution because they are limited in their ability to generate short duration pulses. 
     Saturation of the detector limits measurement capability as target reflectivity and proximity vary greatly in realistic operating environments. In addition, power consumption may cause overheating of the LIDAR system. Light devices, targets, circuits, and temperatures vary in actual systems. The variability of all of these elements limits system performance without proper calibration of the photon output of each LIDAR device. 
     Improvements in the illumination drive electronics and receiver electronics of LIDAR systems are desired to improve imaging resolution and range. 
     SUMMARY 
     Methods and systems for performing three dimensional LIDAR measurements with a LIDAR measurement system employing a multiple channel, GaN based illumination driver integrated circuit (IC) are described herein. The multiple channel, GaN based illumination driver IC includes field effect transistors (FETs) that offer higher current density than conventional silicon based complementary metal oxide on silicon (CMOS) devices. As a result the GaN based illumination driver is able to deliver relatively large currents to each illumination source with significantly less power loss. 
     In one aspect, an illumination driver of a LIDAR measurement device is a multiple channel, GaN based IC that selectively couples each illumination source associated with each measurement channel to a source of electrical power to generate a measurement pulse of illumination light. The response of each measurement channel is controlled by a pulse trigger signal and a number of control signals received onto the multiple channel, GaN based illumination driver IC. 
     In another aspect, each pulse trigger signal associated with each independent measurement channel is received on a separate node of the multiple channel, GaN based illumination driver IC. In this manner, each measurement channel responds to a trigger signal that is unique to each measurement channel. 
     In another aspect, each of the control signals are received on a separate node of the multiple channel and each of the control signals is communicated to all of the measurement channels of the multiple channel, GaN based illumination driver IC. In this manner, each measurement channel responds to control signals that are shared among all of the measurement channels of the multiple channel, GaN based illumination driver IC. 
     In another aspect, the multiple channel, GaN based illumination driver IC includes a power regulation module. The power regulation module only supplies regulated voltage to various elements of each measurement channel when any pulse trigger signal received by the illumination driver IC is in a state that triggers the firing of an illumination pulse. In this manner, power is not supplied to many circuit elements during periods of time when the illumination driver IC is not required to trigger a pulse emission. 
     The foregoing is a summary and thus contains, by necessity, simplifications, generalizations and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not limiting in any way. Other aspects, inventive features, and advantages of the devices and/or processes described herein will become apparent in the non-limiting detailed description set forth herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified diagram illustrative of one embodiment of a LIDAR measurement system including a multiple channel, GaN based illumination driver in at least one novel aspect. 
         FIG. 2  depicts an illustration of the timing associated with the emission of a measurement pulse and capture of the returning measurement pulse. 
         FIG. 3  depicts a simplified diagram illustrative of a multiple channel, GaN based illumination driver IC in one embodiment. 
         FIG. 4  depicts a simplified diagram illustrative of one embodiment of a power regulation module of the multiple channel, GaN based illumination driver IC depicted in  FIG. 3 . 
         FIG. 5  depicts a simplified diagram illustrative of one embodiment of a power control module of the multiple channel, GaN based illumination driver IC depicted in  FIG. 3 . 
         FIG. 6  depicts a simplified illustration of the changes in various operational signals of the power control module depicted in  FIG. 5 . 
         FIG. 7  depicts a simplified diagram illustrative of one embodiment of a pulse initiation signal generator of the multiple channel, GaN based illumination driver IC depicted in  FIG. 3 . 
         FIG. 8  depicts a simplified diagram illustrative of one embodiment of a pulse termination signal generator of the multiple channel, GaN based illumination driver IC depicted in  FIG. 3 . 
         FIG. 9  depicts a simplified diagram illustrative of one embodiment of a control signal generator of the multiple channel, GaN based illumination driver IC depicted in  FIG. 3 . 
         FIG. 10  depicts a simplified diagram illustrative of one embodiment of a power driver module of the multiple channel, GaN based illumination driver IC depicted in  FIG. 3 . 
         FIG. 11  depicts a simplified diagram illustrative of another embodiment of a power driver module of the multiple channel, GaN based illumination driver IC depicted in  FIG. 3 . 
         FIG. 12  depicts a simplified illustration of the changes in various operational signals of the multiple channel, GaN based illumination driver IC depicted in  FIG. 3 . 
         FIG. 13  is a diagram illustrative of an embodiment of a 3-D LIDAR system  100  in one exemplary operational scenario. 
         FIG. 14  is a diagram illustrative of another embodiment of a 3-D LIDAR system  10  in one exemplary operational scenario. 
         FIG. 15  depicts a diagram illustrative of an exploded view of 3-D LIDAR system  100  in one exemplary embodiment. 
         FIG. 16  depicts a view of optical elements  116  in greater detail. 
         FIG. 17  depicts a cutaway view of optics  116  to illustrate the shaping of each beam of collected light  118 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to background examples and some embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
       FIG. 1  depicts a two channel LIDAR measurement system  120  in one embodiment. LIDAR measurement system  120  includes a master controller  190  and a multiple channel Gallium Nitride (GaN) based illumination driver integrated circuit (IC)  140 . In addition, each channel of LIDAR measurement system  120  includes a return signal receiver IC, a photodetector, and an illumination source. As depicted in  FIG. 1 , LIDAR measurement channel A includes return signal receiver IC  150 A, photodetector  170 A and illumination source  160 A. Similarly, LIDAR measurement channel B includes return signal receiver IC  150 B, photodetector  170 B and illumination source  160 B. In some embodiments, the multiple channel GaN based illumination driver IC  140 , illumination sources  160 A-B, photodetectors  170 A-B, and return signal receiver ICs  150 A-B are mounted, either directly or indirectly, to a common substrate (e.g., printed circuit board) that provides mechanical support and electrical connectivity among the elements. 
     In addition, LIDAR measurement system  120  includes one or more voltage supplies that provide voltage to various electronic elements and electrical power to illumination devices  160 A-B. As depicted in  FIG. 1 , LIDAR measurement system  120  includes a low signal voltage supply  132  configured to supply a relatively low voltage across nodes VDD LV    125  and VSS  124 . In some embodiments, the low signal voltage supply is approximately five volts. This voltage is selected to ensure that the voltage supplied at the gates of one or more of the transistors of multiple channel GaN based illumination driver IC  140  does not exceed the damage threshold. In addition, LIDAR measurement system  120  includes a medium signal voltage supply  133  configured to supply a voltage across nodes VDD MV    127  and VSS  126  that is higher than the voltage supplied by the low signal voltage supply. In some embodiments, the voltage supplied by the medium signal voltage supply is approximately twelve volts. This voltage is selected to ensure fast switching transitions of one or more of the transistors of multiple channel GaN based illumination driver IC  140 . In addition, LIDAR measurement system  120  includes a power voltage supply  131  configured to supply a voltage across nodes VDD HV    122  and VSS  121  that is higher than the voltage supplied by the medium voltage supply. In some embodiments, the voltage supplied by the power voltage supply is approximately fifteen to twenty volts. The power voltage supply is configured to supply high current  123 A and  123 B (e.g., one hundred amperes, or more) to illumination sources  160 A and  160 B, respectively, that causes illumination sources  160 A and  160 B to each emit a pulse of measurement light. 
     Although, preferred output voltages have been described herein, in general, the low signal voltage supply, the medium signal voltage supply, and the power voltage supply may be configured to supply any suitable voltages. In general, any of the power supplies described herein may be mounted to a separate substrate and electrically coupled to the various electronic elements in any suitable manner. Although the power supplies  131 ,  132 , and  133  are described as voltage supplies with reference to  FIG. 1 , in general, any electrical power source described herein may be configured to supply electrical power specified as voltage or current. Hence, any electrical power source described herein as a voltage source or a current source may be contemplated as an equivalent current source or voltage source, respectively. 
     Each illumination source  160 A-B emits a measurement pulse of illumination light  162 A-B in response to a corresponding pulse of electrical current  123 A-B. Each beam of illumination light  162 A-B is focused and projected onto a location in the surrounding environment by one or more optical elements of the LIDAR system. 
     In some embodiments, each illumination source  160 A-B is laser based (e.g., laser diode). In some embodiments, each illumination source is based on one or more light emitting diodes. In general, any suitable pulsed illumination source may be contemplated. 
     As depicted in  FIG. 1 , illumination light  162 A-B emitted from each channel of LIDAR measurement system  120  and corresponding return measurement light  171 A-B directed toward LIDAR measurement system  120  share a common optical path. Each channel of LIDAR measurement system  120  includes a photodetector  170 A-B. As depicted in  FIG. 1 , an overmold lens  172 A-B is mounted over each photodetector  170 A-B, respectively. Each overmold lens  172 A-B includes a conical cavity that corresponds with the ray acceptance cone of return light  171 A-B, respectively. Return light  171 A-B is reflected from mirrors  161 A-B to corresponding photodetectors  170 A-B, respectively. As depicted in  FIG. 1 , each illumination source  160 A-B is located outside the field of view of each photodetector. Illumination light  162 A-B from illumination sources  160 A-B is injected into the corresponding detector reception cone through an opening in mirrors  161 A-B, respectively. 
     As depicted in  FIG. 1 , return light  171 A-B reflected from the surrounding environment is detected by photodetectors  170 A-B, respectively. In some embodiments, each photodetector is an avalanche photodiode. Each photodetector generates an output signal  173 A-B that is communicated to corresponding return signal receiver ICs  150 A-B. Each receiver IC  150 A-B includes timing circuitry and a time-to-digital converter that estimates the time of flight of each measurement pulse from each illumination source  160 A-B, to reflective objects in the three dimensional environment, and back to each corresponding photodetector  170 A-B. Signals  152 A-B indicative of the estimated times of flight are communicated to master controller  190  for further processing and communication to a user of the LIDAR measurement system  120 . In addition, each return signal receiver IC  150 A-B is configured to digitize segments of each corresponding return signal  173 A-B that include peak values (i.e., return pulses), and communicate signals  153 A-B indicative of the digitized segments to master controller  190 . In some embodiments, master controller  190  processes these signal segments to identify properties of detected objects. 
     Master controller  190  is configured to generate pulse command signals  191 A-B communicated to receiver ICs  150 A-B, respectively. In general, LIDAR measurement system  120  includes any number of LIDAR measurement channels. In these embodiments, master controller  190  communicates a pulse command signal to each different LIDAR measurement channel. In this manner, master controller  190  coordinates the timing of LIDAR measurements performed by any number of LIDAR measurement channels. 
     Each pulse command signal is a digital signal generated by master controller  190 . Thus, the timing of each pulse command signal is determined by a clock associated with master controller  190 . In some embodiments, each pulse command signal  191 A-B is directly used to trigger pulse generation by multiple channel GaN based illumination driver IC  140  and data acquisition by each corresponding receiver IC  150 A-B. However, illumination driver IC  140  and each receiver IC  150 A-B do not share the same clock as master controller  190 . For this reason, precise estimation of time of flight becomes much more computationally tedious when a pulse command signal is directly used to trigger pulse generation and data acquisition. 
     In one aspect, each receiver IC  150 A-B receives a pulse command signal  191 A-B and generates corresponding pulse trigger signals  151 A and  151 B, in response to pulse command signals  191 A-B, respectively. Each pulse trigger signal  151 A-B is communicated to illumination driver IC  140  and directly triggers illumination driver IC  140  to electrically couple each illumination source  160 A-B to power supply  131  and generate a corresponding pulse of illumination light  162 A-B. In addition, each pulse trigger signal  151 A-B directly triggers data acquisition of return signals  173 A-B and associated time of flight calculations. In this manner, pulse trigger signals  151 A-B generated based on the internal clock of receiver ICs  150 A-B, respectively, is employed to trigger both pulse generation and return pulse data acquisition for a particular LIDAR measurement channel. This ensures precise synchronization of pulse generation and return pulse acquisition which enables precise time of flight calculations by time-to-digital conversion. 
       FIG. 2  depicts an illustration of the timing associated with the emission of a measurement pulse from channel A of LIDAR measurement system  120  and capture of the returning measurement pulse. As depicted in  FIG. 2 , a measurement is initiated by the rising edge of pulse trigger signal  191 A generated by receiver IC  150 A. As depicted in  FIGS. 1 and 2 , a return signal  173 A is received by receiver IC  150 A. As described hereinbefore, a measurement window (i.e., a period of time over which collected return signal data is associated with a particular measurement pulse) is initiated by enabling data acquisition at the rising edge of pulse trigger signal  191 A. Receiver IC  150 A controls the duration of the measurement window, T measurement , to correspond with the window of time when a return signal is expected in response to the emission of a measurement pulse sequence. In some examples, the measurement window is enabled at the rising edge of pulse trigger signal  191 A and is disabled at a time corresponding to the time of flight of light over a distance that is approximately twice the range of the LIDAR system. In this manner, the measurement window is open to collect return light from objects adjacent to the LIDAR system (i.e., negligible time of flight) to objects that are located at the maximum range of the LIDAR system. In this manner, all other light that cannot possibly contribute to useful return signal is rejected. 
     As depicted in  FIG. 2 , return signal  173 A includes three return measurement pulses (e.g., MP 1 , MP 2 , and MP 3 ) that correspond with the emitted measurement pulse. In general, signal detection is performed on all detected measurement pulses. Further signal analysis may be performed to identify the closest valid signal P 1  (i.e., first valid instance of the return measurement pulse), the strongest signal, and the furthest valid signal P 3  (i.e., last valid instance of the return measurement pulse in the measurement window). Any of these instances may be reported as potentially valid distance measurements by the LIDAR system. 
     Internal system delays associated with emission of light from the LIDAR system (e.g., signal communication delays and latency associated with the switching elements, energy storage elements, and pulsed light emitting device) and delays associated with collecting light and generating signals indicative of the collected light (e.g., amplifier latency, analog-digital conversion delay, etc.) contribute to errors in the estimation of the time of flight of a measurement pulse of light. Thus, measurement of time of flight based on the elapsed time between the rising edge of the pulse trigger signal  191 A and each return pulse (i.e., MP 1 , MP 2 , and MP 3 ) introduces undesirable measurement error. In some embodiments, a calibrated, pre-determined delay time is employed to compensate for the electronic delays to arrive at a corrected estimate of the actual optical time of flight. However, the accuracy of a static correction to dynamically changing electronic delays is limited. Although, frequent re-calibrations may be employed, this comes at a cost of computational complexity and may interfere with system up-time. 
     In another aspect, each receiver IC  150 A-B measures time of flight based on the time elapsed between the detection of a detected pulse (e.g., MP 1 ) due to internal cross-talk between each illumination source  160 A-B and corresponding photodetector  170 A-B and a valid return pulse (e.g., MP 2  and MP 3 ). In this manner, systematic delays are eliminated from the estimation of time of flight. Pulse MP 1  is generated by internal cross-talk with effectively no distance of light propagation. Thus, the delay in time from the rising edge of the pulse trigger signal and the instance of detection of pulse MP 1  captures all of the systematic delays associated with illumination and signal detection. By measuring the time of flight of valid return pulses (e.g., return pulses MP 2  and MP 3 ) with reference to detected pulse MP 1 , all of the systematic delays associated with illumination and signal detection due to internal cross-talk are eliminated. As depicted in  FIG. 2 , receiver IC  150 A estimates the time of flight, TOF 1 , associated with return pulse MP 2  and the time of flight, TOF 2 , associated with return pulse MP 3  with reference to return pulse MP 1 . 
     In some embodiments, the signal analyses are performed by receiver ICs  150 A-B, entirely. In these embodiments, signals  152 A-B communicated include an indication of the time of flight determined by receiver IC  150 A-B, respectively. In some embodiments, signals  153 A-B include digitized segments of return signals  173 A-B generated by receiver ICs  150 A-B, respectively. These raw measurement signal segments are processed further by one or more processors located on board the 3-D LIDAR system, or external to the 3-D LIDAR system to arrive at another estimate of distance, an estimate of one of more physical properties of the detected object, or a combination thereof. 
     In one aspect, a LIDAR measurement system includes a multiple channel GaN based illumination driver IC that selectively couples an illumination source corresponding to each measurement channel to a source of electrical power to generate a measurement pulse of illumination light in response to a pulse trigger signal. The multiple channel GaN based illumination driver includes field effect transistors (FETs) that offer higher current density than conventional silicon based complementary metal oxide on silicon (CMOS) devices. As a result the GaN based illumination driver is able to deliver relatively large currents to an illumination source with significantly less power loss than a silicon based driver. 
     As depicted in  FIG. 1 , multiple channel GaN based illumination driver IC  140  is coupled to a voltage node  121  of power voltage supply  131  and nodes of illumination sources  160 A-B, each corresponding to a different LIDAR measurement channel. Another node of each illumination source  160 A-B is coupled to voltage node  122  of power voltage supply  131 . In response to each pulse trigger signal  151 A-B, one or more field effect transistors (FETs) of illumination driver IC  140  becomes substantially conductive, and effectively couples each corresponding illumination source  160 A-B to node  121 . This induces high current flows  123 A-B through illumination sources  160 A-B, respectively, which stimulates the emission of measurement pulses of illumination light  162 A-B. 
       FIG. 3  depicts multiple channel GaN based illumination driver IC  140  in one embodiment. In the embodiment depicted in  FIG. 3 , illumination driver IC  140  includes two independently controlled illumination driver channels, drivers  220 A and  220 B. However, in general, a multiple channel GaN based illumination driver IC as described herein may include any number of independently controlled illumination driver channels. 
     In one aspect, many input signals provided to illumination driver IC  140  are shared by both drivers  220 A and  220 B. This reduces the size of illumination driver IC  140  by minimizing chip and routing area that would be required to accommodate a larger number of separate control signals. In the embodiment depicted in  FIG. 3 , pulse width control signal  192 , selection signal  194 , and amplitude control signal  193  are all shared by drivers  220 A and  220 B (i.e., each of these signals is received on chip on a node and distributed to various elements of drivers  220 A and  220 B on chip). 
     In the embodiment depicted in  FIG. 3 , the pulse trigger signals  151 A and  151 B provided to drivers  220 A and  220 B are the only signals received onto illumination driver IC  140  that are individually provided to drivers  220 A and  220 B, respectively, and thus are not shared by drivers  220 A and  220 B. 
     In some examples, master controller  190  communicates pulse trigger signals to each measurement channel of the LIDAR measurement system  100  such that only one channel of the LIDAR measurement system is firing at a given time. In some of these examples, master controller  190  updates the shared control signals supplied to all of the measurement channels (e.g., pulse width control signal  192 , selection signal  194 , and amplitude control signal  193 ) to desired values for each firing instance of each measurement channel. In this manner, master controller  190  independently controls the pulse emission parameters of each LIDAR measurement channel with control signals shared by all LIDAR measurement channels. 
     In some other examples, master controller  190  communicates pulse trigger signals to a subset of measurement channels of the LIDAR measurement system  100  such that only the subset of measurement channels are firing at a given time. In some of these examples, master controller  190  updates the shared control signals supplied to all of the measurement channels (e.g., pulse width control signal  192 , selection signal  194 , and amplitude control signal  193 ) to desired values for each firing instance of each subset of measurement channels. In this manner, master controller  190  independently controls the pulse emission parameters of each subset of LIDAR measurement channels with control signals shared by all LIDAR measurement channels. 
     In some other embodiments, pulse width control signal  192 , selection signal  194 , and amplitude control signal  193  are communicated to multi-channel GaN based illumination driver IC  140  from a return signal receiver IC of illumination driver IC  140 , rather than master controller  190 . 
     In another aspect, an illumination driver IC includes a power regulation module that supplies a regulated voltage to various elements of each measurement channel when any pulse trigger signal received by the illumination driver IC is in a state that triggers the firing of an illumination pulse. In this manner, power is not supplied to many circuit elements during periods of time when illumination driver IC  140  is not required to trigger a pulse emission. As depicted in  FIG. 3 , illumination driver IC  140  includes a power regulation module  260  that supplies a regulated voltage  261  to various elements of drivers  220 A and  220 B when pulse trigger signal  151 A, pulse trigger signal  151 B, or both, are in a state (e.g., high state or low state) that triggers the firing of an illumination pulse. In the embodiment depicted in  FIG. 3 , regulated voltage  261  is supplied to power drivers  290 A-B, control signal generators  280 A-B, pulse termination signal generators  230 A-B, and power control modules  210 A-B only when either, or both, pulse trigger signals  151 A-B are in a state that triggers the firing of an illumination pulse. 
     As depicted in  FIG. 3 , each illumination driver includes a pulse termination signal generator, a pulse initiation signal generator, a power control module, a control signal generator, and a power driver. For example, illumination driver  220 A includes a pulse initiation signal generator  250 A that generates pulse initiation signal  251 A based on pulse trigger signal  151 A. Pulse initiations signal  251 A is communicated to pulse termination signal generator  230 A and control signal generator  280 A. Pulse termination signal generator  230 A generates a pulse termination signal  231 A based on pulse width control signal  192  and pulse initiation signal  251 A. Power control module  210 A generates a channel amplitude control signal  211 A based on pulse trigger signal  151 A. Control signal generator  280  generates gate control signal  293 A, gate charge control signal  281 A, and gate discharge control signal  282 A based on pulse initiation signal  251 A, pulse termination signal  231 A, and channel amplitude control signal  211 A. Power driver  290 A includes a number of field effect transistors (FETS) that control the flow of current through illumination source  160 A based on gate control signal  293 A, gate charge control signal  281 A, and gate discharge control signal  282 A. 
     Similarly, illumination driver  220 B includes a pulse initiation signal generator  250 B that generates pulse initiation signal  251 B based on pulse trigger signal  151 B. Pulse initiations signal  251 B is communicated to pulse termination signal generator  230 A and control signal generator  280 B. Pulse termination signal generator  230 B generates a pulse termination signal  231 B based on pulse width control signal  192  and pulse initiation signal  251 B. Power control module  210 B generates a channel amplitude control signal  211 B based on pulse trigger signal  151 B. Control signal generator  280  generates gate control signal  293 B, gate charge control signal  281 B, and gate discharge control signal  282 B based on pulse initiation signal  251 B, pulse termination signal  231 B, and channel amplitude control signal  211 B. Power driver  290 B includes a number of field effect transistors (FETS) that control the flow of current through illumination source  160 B based on gate control signal  293 B, gate charge control signal  281 B, and gate discharge control signal  282 B. 
     In another aspect, the number of FETS employed to generate electrical current flow through an illumination source is controlled by selection signal  194 . By controlling the number of FETS employed to generate electrical current flow through an illumination source, the amount of current flow generated through the illumination source for a given set of transistor control signals (e.g., gate control signals  293 A-B, gate charge control signals  281 A-B, and gate discharge control signals  282 A-B) is controlled. 
       FIG. 4  depicts a power regulation module  260  in one embodiment. As depicted in  FIG. 3 , illumination driver IC  140  includes a power regulation module  260  that controls the power supplied to a portion of the circuitry of multiple channel GaN based illumination driver IC  140  to reduce power consumption. In operation, the illumination driver IC  140  spends a relatively short amount of time generating a measurement pulse and a relatively long amount of time waiting for a trigger signal to generate the next measurement pulse. During these idle periods, it is desirable to reduce or eliminate power supplied to circuit components that do not need to be active for the entire waiting period. As depicted in  FIG. 4 , power regulation module  260  is coupled between voltage nodes VDD MV  and VSS of signal voltage supply  132  depicted in  FIG. 1 . In addition, power regulation module  260  receives pulse trigger signals  151 A and  151 B from master controller  190  and, in response, generates a regulated voltage, REG, that is supplied to various portions of illumination driver IC  140 . For example, REG is provided to power control module  210  depicted in  FIG. 5 , pulse termination signal generator  230  depicted in  FIG. 8 , control signal generator  280  depicted in  FIG. 9 , and the main FET groups  491 A-N depicted in  FIG. 11 . 
       FIG. 4  depicts power regulation module  260  in one embodiment. As depicted in  FIG. 4 , power regulation module  260  includes a logical AND circuit module  268  that receives pulse trigger signals  151 A and  151 B and generates an input signal to regulator module  269 . The value of the input signal is determined by the values of pulse trigger signals  151 A and  151 B. If either or both of pulse trigger signals  151 A and  151 B is in a low state (i.e., indicating a trigger to fire one or both illumination channels), the value of the input signal is low. In this scenario FET  264  is “off” and FET  266  is diode connected. As a result a non-zero regulated voltage  261  is provided by regulator module  269 . If pulse trigger signals  151 A and  151 B are both in a high state (i.e., indicating no trigger to fire either of the illumination channels), the value of the input signal is high. In this scenario FET  264  is “on” and the gate voltage of FET  266  is driven to VSS. As a result zero regulated voltage  261  is provided by regulator module  269 . In this scenario, no electrical power is supplied by power regulation module  260 . 
     As depicted in  FIG. 4 , logic circuit  268  is an active circuit coupled to voltage nodes  124  and  125  of low voltage supply  132  depicted in  FIG. 1 . In addition, regulator module  269  is coupled to voltage nodes  126  and  127  of medium voltage supply  133  depicted in  FIG. 1 . As depicted in  FIG. 4 , VDD MV  is provided to one node of resistor  265  and the drain of FET  266 . The other node of resistor  265  is coupled to the drain of FET  264  and the gate of FET  266 . VSS is provided to the source of FET  264 , one node of capacitor  263  and one node of capacitor  267 . The other node of capacitor  263  is coupled to the gate of FET  264  and a node of resistor  262 . The other node of resistor  262  is coupled to the output of logic circuit  268 . The other node of capacitor  267  is coupled to the source of FET  266 , where the output of power regulation module  260  is provided. 
     Resistor  262  and capacitor  263  create an RC network that introduces a delay at the gate of FET  264 . This introduces a delay (I D-SLEEP  depicted in  FIG. 12 ) between the rising edge of TRG 1  and the time when REG drops to VSS during sleep mode. 
       FIG. 12  depicts a simplified illustration of the changes in the regulated voltage, REG, generated by the power regulation module  260  in response to any of the pulse trigger signals, TRG 1  and TRG, being in a state that triggers the firing of an illumination pulse. As depicted in  FIG. 12 , at the rising edge of one, or both, of the pulse trigger signals, the regulated voltage remains high for a period of time, I D-SLEEP . This length of time is determined by the values of resistor  262  and capacitor  263 . After this period of time, the REG drops quickly. At the falling edge of TRG 1 , the regulated voltage remains low for a period of time and then ramps up to a relatively high voltage value, so that the illumination driver IC  140  is ready to generate a measurement pulse in response to the subsequent rising edge of TRG 1 . 
     In another aspect, each channel of an illumination driver IC includes a power control module that generates a channel amplitude control signal and communicates the signal to the corresponding control signal generator. When the pulse trigger signal associated with a particular measurement channel is in a state that triggers the firing of an illumination pulse, the power control module generates a channel amplitude control signal having a value of the amplitude control signal received from the master controller. However, when the pulse trigger signal associated with the particular measurement channel is in a state that does not trigger the firing of an illumination pulse, the power control module generates a channel amplitude control signal having a zero value. In this manner, power is not supplied to circuit elements of the corresponding control signal generator and power driver during periods of time when the particular LIDAR measurement channel is not required to trigger a pulse emission. 
       FIG. 5  depicts a power control module  210  in one embodiment. Power control module  210  is replicated as power control module  210 A and  210 B in illumination driver IC  140  depicted in  FIG. 3 . As depicted in  FIG. 5 , power control module  210  is implemented as power control module  210 A depicted in  FIG. 3  for explanatory purposes. Power control module  210  includes a delay module  220  that receives a pulse trigger signal (e.g., pulse trigger signal  151 A) and generates a delayed pulse trigger signal  227 . Power save module  217  receives the delayed pulse trigger signal  227  and generates channel pulse amplitude signal  211 A based on the delayed pulse trigger signal  227  and pulse amplitude control signal  193  shared among all measurement channels of illumination driver IC  140 . 
     As depicted in  FIG. 5 , delay module  220  includes resistors  221  and  222 , capacitors  224  and  226 , and FETS  223  and  225 . VSS is supplied to the source of FET  225 , the source of FET  223 , a first node of capacitor  224  and a first node of capacitor  226 . Pulse trigger signal  151 A is provided at the gate of FET  225 . The drain of FET  225  is coupled to a second node of capacitor  224 , the gate of FET  223  and a first node of resistor  221 . The drain of FET  223  is coupled to a second node of capacitor  226  and a first node of resistor  222 . Delayed pulse trigger signal  227  is provided at the drain of FET  223 . VDD LV  is provided at the second node of resistors  221  and  222 . Power save module  217  includes resistor  213  and FETS  214 ,  215 , and  216 . VSS is supplied to the source of FET  214  and the source of FET  215 . The gate of FET  214  and the gate of FET  215  are coupled to the drain of FET  223 . In this manner, delayed pulse trigger signal  227  at node  212  is supplied to the gates of FETS  214  and  215 . Regulated voltage  261  is provided at a first node of resistor  213 . The second node of resistor  213  is coupled to the gate of FET  216 . Amplitude control signal  193  is provided at the drain of FET  216 . The source of FET  216  is coupled to the drain of FET  215 , where the channel amplitude control signal  211 A is present. 
     As depicted in  FIG. 6 , delay module  220  generates a delayed pulse trigger signal  227  having a time delay, T DEL , from pulse trigger signal  151 A. Power save module  217  generates a channel amplitude control signal  211 A having an amplitude value, AMP, that matches the amplitude value of the amplitude control signal  193  at the falling edge of delayed pulse trigger signal  227 . Channel amplitude control signal  211 A maintains the amplitude value, AMP, until the rising edge of delayed pulse trigger signal  227 . At this instance, the channel amplitude control signal  211 A drops to a zero value. Due to the time delay, T DEL , the firing of an illumination pulse from channel A occurs at a time, T FIREA , when the amplitude value of channel amplitude control signal  211 A is at the amplitude value, AMP, of the amplitude control signal  193 . In this manner, the amplitude value, AMP, of the amplitude control signal  193  is effectively transmitted to the control signal generator  280  around the period of time when control signal generator  280  generates control signals that cause an illumination pulse to be emitted from the corresponding LIDAR measurement channel. However, at other times, when the LIDAR measurement channel is idle, a zero valued signal is transmitted to the control signal generator  280 . 
       FIG. 7  depicts a pulse initiation signal generator  250  in one embodiment. Pulse initiation signal generator  250  is replicated as pulse initiation signal generators  250 A and  250 B in illumination driver IC  140  depicted in  FIG. 3 . As depicted in  FIG. 7 , pulse initiation signal generator  250  is implemented as pulse initiation signal generator  250 A depicted in  FIG. 3  for explanatory purposes. Pulse initiation signal generator  250  generates a pulse initiation signal  251 A based on the pulse trigger signal  151 A. Pulse initiation signal generator  250  includes a FET  252  and a resistor  253 . Pulse trigger signal  151 A is provided on the gate of FET  252 . VSS is provided to the source of FET  252 . VDD MV  is provided to a first node of resistor  253  and a second node of resistor  253  is coupled to the drain of FET  252 . Pulse initiation signal  251 A is provided at the drain of FET  252 . 
       FIG. 12  depicts a simplified illustration of the changes in the pulse initiation signal, INIT1, generated by the pulse initiation signal generator  250  in response to the pulse trigger signal, TRG 1 . As depicted in  FIG. 12 , at the rising edge of the pulse trigger signal, INIT1, drops to a low voltage value, VSS, very quickly. At the falling edge of TRG1, INIT1 ramps up to the value of VDD MV , so that the illumination driver IC  140  is ready to generate a falling pulse initiation signal in response to the subsequent rising edge of TRG1. 
       FIG. 8  depicts a pulse termination signal generator  230  in one embodiment. Pulse termination signal generator  230  is replicated as pulse termination signal generators  230 A and  230 B in illumination driver IC  140  depicted in  FIG. 3 . As depicted in  FIG. 8 , pulse termination signal generator  230  is implemented as pulse termination signal generator  230 A depicted in  FIG. 3  for explanatory purposes. Pulse termination signal generator  230  is configured to generate a pulse of programmable duration based on a value of an analog input signal. As depicted in  FIG. 1 , master controller  190  generates an analog pulse width control signal  192 , and communicates PWC  192  to illumination driver IC  140 . In response, illumination driver IC  140  changes the pulse duration based on the received value of PWC  192 . In the embodiment depicted in  FIG. 8 , pulse termination signal generator  230  receives, PWC  192  and INIT1  251 A and generates a pulse termination signal, TERM1  231 A, having a delay from INIT1  251 A programmed in accordance with a value of PWC  192 . 
     As depicted in  FIG. 8 , pulse termination signal generator  230  includes resistor  238  and FETs  236 - 237  configured as an operational amplifier. The output of the operational amplifier is coupled to the gate of FET  243 . The operational amplifier receives PWC  192  as input at the gate of FET  236 . In addition, the operational amplifier receives an input voltage  249  at the gate of FET  237 . When the input voltage  249  exceeds the value of PWC  192 , the value of output voltage  248  switches transitions to a low value. When the value of PWC  192  exceeds the value of input voltage  249 , the value of output voltage  248  transitions to a high value. Input voltage  249  is the voltage of the RC circuit formed by resistor  241  and capacitor  242 . INIT1  251 A is received at the gate of FET  240 . When INIT1  251 A transitions to a low value (at the start of pulse), FET  240  effectively disconnects the RC circuit from VSS. This allows the RC circuit to begin to charge. FET  239  provides a nonzero starting voltage for the RC circuit. As the voltage of the RC circuit rises, eventually it exceeds the value of PWC  192 , thus triggering the transition of output node  248 . Since the voltage ramp rate of the RC circuit is constant, the delay until the transition of output voltage  248  is determined in part by the value of PWC  192 . The larger the value of PWC  192 , the longer the delay from pulse initiation before the generation of the termination signal, TERM1  231 A. In this manner, the value of PWC  192  determines the pulse duration. Pulse termination signal generator  230  includes resistor  232  and FETs  233 - 235  configured as a current source for the operational amplifier structure. FETS  243  and  244  are configured to scale down the value of output voltage  248 . Resistors  245  and  247  and FET  246  are configured to invert the scaled value of output voltage  248 . The pulse termination signal, TERM1  231 A, is provided at the drain of FET  246 . 
       FIG. 12  depicts a simplified illustration of the changes in the pulse termination signal, TERM1  231 A, generated by the pulse termination signal generator  230  in response to the pulse initiation signal, INIT1  251 A and the pulse width control signal, PWC  192 . As depicted in  FIG. 12 , when INIT1 goes low, the voltage of the RC circuit begins to ramp up. At the point in time when the voltage of the RC circuit exceeds PWC, TERM1 goes high, holds for a period of time and then ramps down again. Note that the period of time, T D-PULSE  between pulse initiation and the rising edge of TERM1 determines the relative duration of the measurement pulse. At the falling edge of TRG1, TERM1 ramps down again so that the illumination driver IC  140  is ready to generate a pulse termination signal for the subsequent pulse. As depicted, in  FIG. 12 , the gate voltage, GATE 1 , of main FET  141 , or group of FETS, is also depicted. 
     As depicted in  FIG. 3 , illumination driver IC  140  includes pulse termination signal generators  230 A-B that generate pulse termination signals, TERM1 and TERM2, based on corresponding pulse initiation signals. Together, the pulse initiation signals and the pulse termination signals directly determine the timing of each pulse generated by illumination driver IC  140 . In these embodiments, rather than having a pulse trigger signal (e.g., TRG1, TRG2) directly determine the timing of a pulse generated by illumination driver IC  140 , a pulse trigger signal is employed to trigger the generation of a pulse initiation signal. The pulse initiation signal, in turn, directly initiates the pulse generation, and also initiates the generation of the pulse termination signal. The pulse termination signal, in turn, directly terminates the pulse generation. 
       FIG. 9  depicts a control signal generator  280  in one embodiment. Control signal generator  280  is replicated as control signal generators  280 A and  280 B in illumination driver IC  140  depicted in  FIG. 3 . As depicted in  FIG. 9 , control signal generator  280  is implemented as control signal generator  280 A depicted in  FIG. 3  for explanatory purposes. Control signal generator  280  generates gate control signal  283 A, gate charge control signal  281 A and gate discharge control signal  282 A based on the pulse initiation signal  251 A, pulse termination signal  231 A, and channel amplitude control signal  211 A. The control signals generated by control signal generator  280  directly control the FETS that control the flow of current through an illumination source coupled to illumination driver  140 . 
     Control signal generator  280  includes a pulse amplitude control circuit  255 , FETS  284 ,  286 ,  287 ,  288 , and resistor  285 . 
     In another aspect, pulse termination signal generator  230  is configured to generate a pulse of programmable amplitude based on a value of an analog input signal. As depicted in  FIG. 1 , receiver IC  150  generates an analog amplitude control signal, V AMP    153 , and communicates V AMP  to illumination driver IC  140 . In response, illumination driver IC  140  changes the pulse amplitude based on the received value of V AMP . 
     In the embodiment  140 C of portions of illumination driver IC  140  depicted in  FIG. 11 , pulse amplitude control circuit  250  receives, V AMP , that controls the amplitude of the pulse generated by illumination source  160 . 
     When INIT1  251 A goes low (signaling the start of a measurement pulse), FET  286  quickly releases the gate of a charge FET (e.g., charge FET  393  depicted in  FIG. 10 ) from VSS via gate charge control signal  281 A, allowing the charge FET to quickly charge. Similarly, FET  287  quickly releases the gate of the main FET (e.g., main FET  391  depicted in  FIG. 10 ) from VSS, allowing the main FET to charge via gate control signal  283 A. 
     When TERM1  231 A goes high (signaling the end of a measurement pulse), FET  288  shorts the gate of the charge FET to VSS. Similarly, a discharge FET (e.g., discharge FET  394  depicted in  FIG. 10 ) shorts the gate of the main FET to VSS via gate discharge control signal  282 A as quickly as possible to shut off current flow through illumination source  160 . FET  285  and resistor  285  provide a quick turn-on of the discharge FET and FET  288 . 
     In addition, pulse amplitude control circuit  255  includes resistors  256  and  259 , capacitor  257 , and FET  258 . Channel amplitude control signal, AMP1  211 A, is received on a first node of resistor  256 . The second node of resistor  256  is coupled to the gate of FET  258  and to a first node of capacitor  257 . The drain of FET  258  is coupled to the regulated voltage supply, VREG, and receives regulated voltage  261 . The source of FET  258  is coupled to a first node of resistor  259 . The second node of resistor  259  is coupled to the second node of capacitor  257 , where gate charge control signal  281 A is provided. In this manner, the pulse amplitude control circuit  255  controls the charge at the gate of a charge FET (e.g., charge FET  393  depicted in  FIG. 10 ). 
     As depicted in  FIG. 12 , the value of AMP1 controls the ramp rate of the pulse amplitude control circuit  255 . As AMP1 increases, the rate of charge accumulation at the gate of FET  258  increases. In turn, this increases rate of charge accumulation on the gate of a charge FET via gate charge control signal  281 A. This, in turn, increases the rate of charge accumulation on the gate of a main FET, which accelerates the ramp rate of the resulting illumination pulse generated by illumination source  160 A. In this manner, AMP1, controls the peak amplitude of the illumination pulse for a given pulse duration. 
       FIG. 10  depicts a power driver  390  in one embodiment. In some embodiments, power driver  390  is replicated as power drivers  290 A and  290 B in illumination driver IC  140  depicted in  FIG. 3 . As depicted in  FIG. 10 , power driver  390  is implemented as power driver  290 A depicted in  FIG. 3  for explanatory purposes. In the depicted embodiment, power driver  390  includes three FETs  391 ,  393 , and  394  integrated onto GaN based IC  140 . In the example depicted in  FIG. 10 , main FET  391  controls the flow of current  123 A through illumination source  160 A (e.g., laser diode  160 A). Gate control signal  283 A contributes to the gate voltage of main FET  393 . In addition, charge FET  393  and discharge FET  394  also contribute to the gate voltage of main FET  391  and accelerate the transitions and minimize power losses. 
     As depicted in  FIG. 10 , the drain of charge FET  393  is coupled to voltage node  125  of low voltage supply  132  depicted in  FIG. 1 . The source of charge FET  393  is coupled to the drain of discharge FET  394  and to the gate of main FET  391 . The source of discharge FET  394  is coupled to voltage node  124  of low voltage supply  132 . In addition, a resistor  392  is coupled between the gate of main FET  391  and voltage node  124  of low voltage supply  132 . A gate charge control signal  281 A is provided at the gate of charge FET  393 , and a gate discharge control signal  282 A is provided at the gate of discharge FET  394 . In this manner, gate charge control signal  281 A, gate discharge control signal  282 A, and gate control signal  283 A determine the charge at the gate of main FET  391 , and thus the conductive state of main FET  391 . 
     Although  FIG. 10  depicts embodiment  390  implemented as power driver  290 A depicted in  FIG. 3 , in general, embodiment  390  may be implemented as a power driver of any LIDAR measurement channel (e.g., power driver  290 A,  290 B, or both). 
     The embodiment  390  of power driver module  290 A depicted in  FIG. 10  includes a single main FET  391  that determines the current flow through illumination source  160 A. In another aspect, a power driver includes a number of different FETs configured to control the current flow through an illumination source. Moreover, the number of FETs coupled to each illumination source is programmable. This enables a programmable maximum current flow through each illumination source, and thus a programmable maximum illumination pulse amplitude. 
       FIG. 11  depicts a power driver  490  in another embodiment. In some embodiments, power driver  490  is replicated as power drivers  290 A and  290 B in illumination driver IC  140  depicted in  FIG. 3 . As depicted in  FIG. 11 , power driver  490  is implemented as power driver  290 A depicted in  FIG. 3  for explanatory purposes. Like numbered elements are described with reference to  FIG. 10 . As depicted in  FIG. 11 , N groups of one or more FETs are coupled in parallel with illumination source  160 A, where N is any positive, integer number. A drain of each main FET of each FET group  491 A- 491 N is coupled to a node of illumination source  160 A. Similarly, a source of each main FET of each FET group  491 A- 491 N is coupled to node  121  of power voltage supply  131 . The gates of each main FET of each FET group  141 A- 141 N are selectively coupled to the source of a charge FET and the drain of a discharge FET as described with reference to  FIG. 10 . Whether each main FET of a particular group of FETs is electrically coupled to the source of a charge FET and the drain of a discharge FET is determined by the state of selection signal, SEL  194 , received from master controller  190 . In the example depicted in  FIG. 11 , SEL is an N-bit word. Each bit corresponds with a particular main FET group. If a particular bit is in a high state, each main FET associated with the corresponding main FET group is coupled to the source of a charge FET and the drain of a discharge FET. In this state, gate control signal  283 A, gate charge control signal  281 A, and gate discharge control signal  282 A determine the charge at the gate of each main FET of the corresponding main FET group. In this manner, the state of each bit of the N-bit word determines which main FET groups will participate in pulse generation by illumination source  160 A. 
     Master controller  190  determines which FET groups should participate in the next measurement pulse by generating and communicating the SEL signal to illumination driver IC  140 . In some examples, the determination is based on the return signal received from the prior measurement pulse. For example, if the received return signal is saturated, master controller  190  generates and communicates a selection signal, SEL, to illumination driver  140  with a larger number of zero valued bits to reduce the number of participating main FET groups. In this manner, the number of photons emitted in the next illumination pulse is reduced. 
     In some embodiments, the number of FETS in each main FET group is different. In this manner, different combinations of FET groups can be activated to achieve a wide range of participating FETs with uniform resolution. 
     Although  FIG. 11  depicts embodiment  490  implemented as power driver  290 A depicted in  FIG. 3 , in general, embodiment  490  may be implemented as a power driver of any LIDAR measurement channel (e.g., power driver  290 A,  290 B, or both). 
       FIGS. 13-15  depict 3-D LIDAR systems that include one or more multiple channel GaN based illumination driver ICs. In some embodiments, a delay time is set between the firing of each LIDAR measurement channel. In some examples, the delay time is greater than the time of flight of the measurement pulse to and from an object located at the maximum range of the LIDAR device. In this manner, there is no cross-talk among any of the LIDAR measurement channels. In some other examples, a measurement pulse is emitted from one LIDAR measurement channel before a measurement pulse emitted from another LIDAR measurement channel has had time to return to the LIDAR device. In these embodiments, care is taken to ensure that there is sufficient spatial separation between the areas of the surrounding environment interrogated by each beam to avoid cross-talk. 
       FIG. 13  is a diagram illustrative of an embodiment of a 3-D LIDAR system  100  in one exemplary operational scenario. 3-D LIDAR system  100  includes a lower housing  101  and an upper housing  102  that includes a domed shell element  103  constructed from a material that is transparent to infrared light (e.g., light having a wavelength within the spectral range of 700 to 1,700 nanometers). In one example, domed shell element  103  is transparent to light having a wavelengths centered at 905 nanometers. 
     As depicted in  FIG. 13 , a plurality of beams of light  105  are emitted from 3-D LIDAR system  100  through domed shell element  103  over an angular range, a, measured from a central axis  104 . In the embodiment depicted in  FIG. 13 , each beam of light is projected onto a plane defined by the x and y axes at a plurality of different locations spaced apart from one another. For example, beam  106  is projected onto the xy plane at location  107 . 
     In the embodiment depicted in  FIG. 13 , 3-D LIDAR system  100  is configured to scan each of the plurality of beams of light  105  about central axis  104 . Each beam of light projected onto the xy plane traces a circular pattern centered about the intersection point of the central axis  104  and the xy plane. For example, over time, beam  106  projected onto the xy plane traces out a circular trajectory  108  centered about central axis  104 . 
       FIG. 14  is a diagram illustrative of another embodiment of a 3-D LIDAR system  10  in one exemplary operational scenario. 3-D LIDAR system  10  includes a lower housing  11  and an upper housing  12  that includes a cylindrical shell element  13  constructed from a material that is transparent to infrared light (e.g., light having a wavelength within the spectral range of 700 to 1,700 nanometers). In one example, cylindrical shell element  13  is transparent to light having a wavelengths centered at 905 nanometers. 
     As depicted in  FIG. 14 , a plurality of beams of light  15  are emitted from 3-D LIDAR system  10  through cylindrical shell element  13  over an angular range, β. In the embodiment depicted in  FIG. 14 , the chief ray of each beam of light is illustrated. Each beam of light is projected outward into the surrounding environment in a plurality of different directions. For example, beam  16  is projected onto location  17  in the surrounding environment. In some embodiments, each beam of light emitted from system  10  diverges slightly. In one example, a beam of light emitted from system  10  illuminates a spot size of 20 centimeters in diameter at a distance of 100 meters from system  10 . In this manner, each beam of illumination light is a cone of illumination light emitted from system  10 . 
     In the embodiment depicted in  FIG. 14 , 3-D LIDAR system  10  is configured to scan each of the plurality of beams of light  15  about central axis  14 . For purposes of illustration, beams of light  15  are illustrated in one angular orientation relative to a non-rotating coordinate frame of 3-D LIDAR system  10  and beams of light  15 ′ are illustrated in another angular orientation relative to the non-rotating coordinate frame. As the beams of light  15  rotate about central axis  14 , each beam of light projected into the surrounding environment (e.g., each cone of illumination light associated with each beam) illuminates a volume of the environment corresponding the cone shaped illumination beam as it is swept around central axis  14 . 
       FIG. 15  depicts an exploded view of 3-D LIDAR system  100  in one exemplary embodiment. 3-D LIDAR system  100  further includes a light emission/collection engine  112  that rotates about central axis  104 . In the embodiment depicted in  FIG. 15 , a central optical axis  117  of light emission/collection engine  112  is tilted at an angle, θ, with respect to central axis  104 . As depicted in  FIG. 15 , 3-D LIDAR system  100  includes a stationary electronics board  110  mounted in a fixed position with respect to lower housing  101 . Rotating electronics board  111  is disposed above stationary electronics board  110  and is configured to rotate with respect to stationary electronics board  110  at a predetermined rotational velocity (e.g., more than 200 revolutions per minute). Electrical power signals and electronic signals are communicated between stationary electronics board  110  and rotating electronics board  111  over one or more transformer, capacitive, or optical elements, resulting in a contactless transmission of these signals. Light emission/collection engine  112  is fixedly positioned with respect to the rotating electronics board  111 , and thus rotates about central axis  104  at the predetermined angular velocity, ω. 
     As depicted in  FIG. 15 , light emission/collection engine  112  includes an array of LIDAR measurement devices  113 . In some embodiments, each LIDAR measurement device is a multiple channel LIDAR measurement device such as LIDAR measurement device  120  illustrated in  FIG. 1 . 
     Light emitted from each LIDAR measurement device passes through a series of optical elements  116  that collimate the emitted light to generate a beam of illumination light projected from the 3-D LIDAR system into the environment. In this manner, an array of beams of light  105 , each emitted from a different LIDAR measurement device are emitted from 3-D LIDAR system  100  as depicted in  FIG. 13 . In general, any number of LIDAR measurement devices can be arranged to simultaneously emit any number of light beams from 3-D LIDAR system  100 . Light reflected from an object in the environment due to its illumination by a particular LIDAR measurement device is collected by optical elements  116 . The collected light passes through optical elements  116  where it is focused onto the detecting element of the same, particular LIDAR measurement device. In this manner, collected light associated with the illumination of different portions of the environment by illumination generated by different LIDAR measurement devices is separately focused onto the detector of each corresponding LIDAR measurement device. 
       FIG. 16  depicts a view of optical elements  116  in greater detail. As depicted in  FIG. 16 , optical elements  116  include four lens elements  116 A-D arranged to focus collected light  118  onto each detector of the array of LIDAR measurement devices  113 . In the embodiment depicted in  FIG. 16 , light passing through optics  116  is reflected from mirror  124  and is directed onto each detector of the array of LIDAR measurement devices  113 . In some embodiments, one or more of the optical elements  116  is constructed from one or more materials that absorb light outside of a predetermined wavelength range. The predetermined wavelength range includes the wavelengths of light emitted by the array of integrated LIDAR measurement devices  113 . In one example, one or more of the lens elements are constructed from a plastic material that includes a colorant additive to absorb light having wavelengths less than infrared light generated by each of the array of integrated LIDAR measurement devices  113 . In one example, the colorant is Epolight 7276A available from Aako BV (The Netherlands). In general, any number of different colorants can be added to any of the plastic lens elements of optics  116  to filter out undesired spectra. 
       FIG. 16  depicts a cutaway view of optics  116  to illustrate the shaping of each beam of collected light  118 . 
     In this manner, a LIDAR system, such as 3-D LIDAR system  10  depicted in  FIG. 14 , and system  100 , depicted in  FIG. 13 , includes a plurality of LIDAR measurement devices each emitting multiple pulsed beams of illumination light from the LIDAR device into the surrounding environment and measuring return light reflected from objects in the surrounding environment. 
     In some embodiments, such as the embodiments described with reference to  FIG. 13  and  FIG. 14 , an array of LIDAR measurement devices is mounted to a rotating frame of the LIDAR device. This rotating frame rotates with respect to a base frame of the LIDAR device. However, in general, an array of LIDAR measurement devices may be movable in any suitable manner (e.g., gimbal, pan/tilt, etc.) or fixed with respect to a base frame of the LIDAR device. 
     In some other embodiments, each LIDAR measurement device includes a beam directing element (e.g., a scanning mirror, MEMS mirror etc.) that scans the illumination beams generated by the LIDAR measurement device. 
     In some other embodiments, two or more LIDAR measurement devices each emit beams of illumination light toward a scanning mirror device (e.g., MEMS mirror) that reflects the beams into the surrounding environment in different directions. 
     In a further aspect, one or more LIDAR measurement devices are in optical communication with an optical phase modulation device that directs the illumination beams generated by the LIDAR measurement devices in different directions. The optical phase modulation device is an active device that receives a control signal that causes the optical phase modulation device to change state and thus change the direction of light diffracted from the optical phase modulation device. In this manner, the illumination beam generated by the LIDAR measurement devices are scanned through a number of different orientations and effectively interrogate the surrounding 3-D environment under measurement. The diffracted beams projected into the surrounding environment interact with objects in the environment. Each respective LIDAR measurement channel measures the distance between the LIDAR measurement system and the detected object based on return light collected from the object. The optical phase modulation device is disposed in the optical path between the LIDAR measurement device and an object under measurement in the surrounding environment. Thus, both illumination light and corresponding return light pass through the optical phase modulation device. 
     A computing system as described herein may include, but is not limited to, a personal computer system, mainframe computer system, workstation, image computer, parallel processor, or any other device known in the art. In general, the term “computing system” may be broadly defined to encompass any device having one or more processors, which execute instructions from a memory medium. 
     Program instructions implementing methods such as those described herein may be transmitted over a transmission medium such as a wire, cable, or wireless transmission link. Program instructions are stored in a computer readable medium. Exemplary computer-readable media include read-only memory, a random access memory, a magnetic or optical disk, or a magnetic tape. 
     In one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. 
     Although certain specific embodiments are described above for instructional purposes, the teachings of this patent document have general applicability and are not limited to the specific embodiments described above. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.