阅读说明：本技术 Lidar数据获取与控制 (LIDAR data acquisition and control ) 是由 D.S.霍尔 R.利欧 O.米尔格罗姆 A.戈帕兰 P.K.文卡特桑 于 2018-05-08 设计创作，主要内容包括：本文中描述了用于使用集成LIDAR测量设备来执行三维LIDAR测量的方法和系统。在一方面,返回信号接收器生成脉冲触发信号,所述脉冲触发信号触发照明光的脉冲的生成以及返回信号的数据获取,并且还通过时间到数字转换触发飞行时间的计算。此外,返回脉冲接收器还估计每个返回脉冲的宽度以及峰值幅度,并且在包括每个返回脉冲波形的峰值幅度的采样窗口上单独地对每个返回脉冲波形进行采样。在另外的方面,基于粗略定时估计和精细定时估计来估计与每个返回脉冲相关联的飞行时间。在另一方面,从由于内部光学串扰导致的测量脉冲以及有效返回脉冲来测量飞行时间。(Methods and systems for performing three-dimensional LIDAR measurements using an integrated LIDAR measurement device are described herein. In one aspect, the return signal receiver generates a pulse trigger signal that triggers generation of a pulse of illumination light and data acquisition of the return signal, and also triggers calculation of time of flight by time-to-digital conversion. In addition, the return pulse receiver also estimates the width and peak amplitude of each return pulse and samples each return pulse waveform individually over a sampling window that includes the peak amplitude of each return pulse waveform. In a further aspect, a time of flight associated with each return pulse is estimated based on the coarse and fine timing estimates. On the other hand, the time of flight is measured from the measurement pulse due to internal optical crosstalk and the effective return pulse.)

1. An integrated LIDAR measurement device, comprising:

an illumination source mounted to the printed circuit board;

an illumination driver Integrated Circuit (IC) mounted to a printed circuit board, the illumination driver IC selectively coupling an illumination source to an electrical power source in response to a pulse trigger signal such that the illumination source emits a measurement pulse of illumination light;

a photodetector mounted to the printed circuit board, the photodetector configured to detect an amount of return light received by the photodetector in response to a measurement pulse of the illumination light, and to generate an output signal indicative of the detected return light;

a return signal receiver IC mounted to a printed circuit board, the return signal receiver IC configured to:

receiving the output signal during the duration of a measurement window;

identifying one or more return pulses of the detected return light;

determining a time of flight associated with each identified return pulse; and

one or more attributes of the segments of each identified return pulse segment are determined.

2. The integrated LIDAR measurement apparatus of claim 1, wherein the return signal receiver IC generates the pulse trigger signal in response to receiving a pulse command signal on the return signal receiver IC.

3. The integrated LIDAR measurement apparatus of claim 1, wherein the return signal receiver IC comprises a return signal analysis module, wherein the return signal analysis module comprises:

a constant fraction discriminator module having a first input node, a second input node, and an output node, wherein the output signal is received on the first input node, and wherein a hit signal at the output node switches to a different value when the output signal exceeds a threshold voltage value on the second input node.

4. The integrated LIDAR measurement apparatus of claim 3, wherein the return signal analysis module further comprises:

a coarse timing module having a first input node coupled to an output node of the constant fraction discriminator, a second input node, and an output node, wherein the pulse trigger signal is present on the second input node, and wherein the coarse timing module generates a digital value at the output node that indicates an elapsed time between a transition of the pulse trigger signal and a transition of the hit signal.

5. The integrated LIDAR measurement apparatus of claim 4, wherein the digital value is a count of a number of transitions of a digital clock signal that occur between transitions of the pulse trigger signal and transitions of the hit signal.

6. The integrated LIDAR measurement apparatus of claim 5, wherein the return signal analysis module further comprises:

a fine timing module having a first input node, a first output node, and a second output node, wherein the hit signal is present on the first input node, wherein the fine timing module generates a first electrical signal at the first output node indicating a time difference between a transition of the hit signal and a subsequent transition of the digital clock signal and generates a second electrical signal at the second output node indicating a time difference between a transition of the digital hit signal and a subsequent transition of the inversion of the digital clock signal.

7. The integrated LIDAR measurement device of claim 5, wherein the coarse timing module generates a metastable signal, wherein the metastable signal is a digital clock signal shifted by one-half of a period of the digital clock signal.

8. The integrated LIDAR measurement device of claim 7, further comprising:

a time-of-flight module configured to estimate a time-of-flight value of a measurement pulse of illumination light based at least in part on a digital value indicative of an elapsed time between a transition of the pulse trigger signal and a transition of the hit signal, a time difference between a transition of the hit signal and a subsequent transition of the digital clock signal, a time difference between a transition of the hit signal and a subsequent transition of an inversion of the digital clock signal, and the metastable state signal.

9. The integrated LIDAR measurement apparatus of claim 3, the return signal analysis module further comprising:

a pulse width detection module comprising:

a first input node on which the hit signal is present,

a second input node on which an enable signal is present, an

An output node, wherein the pulse width detection module generates an electrical signal at the output node that indicates a time difference between a transition of the enable signal and a time when the amplitude of the hit signal falls below a threshold.

10. The integrated LIDAR measurement apparatus of claim 3, the return signal analysis module further comprising:

a return pulse sample and hold module configured to generate an output signal indicative of a peak amplitude of the output signal after a transition of the hit signal.

11. The integrated LIDAR measurement device of claim 10, wherein the return pulse sample and hold module is further configured to generate a plurality of output signal values, each indicative of an amplitude of the output signal before and after the peak amplitude.

12. The integrated LIDAR measurement apparatus of claim 11, wherein a number of output signal samples before and after the peak amplitude is programmable.

13. The integrated LIDAR measurement apparatus of claim 1, wherein a first one of one or more return pulses of the detected return light is due to optical crosstalk of the illumination source and the photodetector, and wherein a time-of-flight associated with each subsequent one of the one or more return pulses is determined with reference to the first return pulse.

14. The integrated LIDAR measurement apparatus of claim 1, wherein a duration of a measurement window is approximately a time of flight of light from the LIDAR measurement apparatus to a maximum range of the LIDAR measurement apparatus and back to the LIDAR measurement apparatus.

15. A method, comprising:

generating a pulse trigger signal in response to receiving a pulse command signal on a return signal receiver IC mounted to the printed circuit board;

selectively electrically coupling an illumination source to an electrical power source in response to the pulse trigger signal such that the illumination source emits a measurement pulse of illumination light;

detecting an amount of return light received by a photodetector in response to a measurement pulse of illumination light, wherein the illumination source and photodetector are mounted to the printed circuit board;

generating an output signal indicative of the detected return light;

receiving the output signal onto the return signal receiver IC during the duration of a measurement window;

identifying one or more return pulses of the detected return light;

determining a time of flight associated with each identified return pulse; and

one or more properties of the segment of each identified return pulse are determined.

16. The method of claim 15, further comprising:

generating a hit signal that switches to a different value when the output signal exceeds a threshold voltage value;

generating a digital value indicative of time elapsed between a transition of the pulse trigger signal and a transition of the hit signal, wherein the digital value is a count of a number of transitions of a digital clock signal that occurred between the transition of the pulse trigger signal and the transition of the hit signal.

17. The method of claim 16, further comprising:

generating a first electrical signal indicative of a time difference between a transition of the hit signal and a subsequent transition of the digital clock signal and a second electrical signal indicative of a time difference between a transition of the digital hit signal and a subsequent transition of an inversion of the digital clock signal; and

generating a metastable signal, wherein the metastable signal is a digital clock signal shifted by half a period of the digital clock signal.

18. The method of claim 17, further comprising:

estimating a value of a time of flight of a measurement pulse of illumination light based at least in part on a digital value indicative of elapsed time between a transition of the pulse trigger signal and a transition of the hit signal, a time difference between a transition of the hit signal and a subsequent transition of the digital clock signal, a time difference between a transition of the hit signal and a subsequent transition of an inversion of the digital clock signal, and the metastable state signal.

19. The method of claim 16, further comprising:

an electrical signal is generated that indicates a time difference between a transition of an enable signal and a time when an amplitude of the hit signal falls below a threshold.

20. The method of claim 16, further comprising:

after the transition of the hit signal, an output signal is generated that indicates a peak amplitude of the output signal.

21. The method of claim 20, further comprising:

generating a plurality of output signal values, each output signal value being indicative of an amplitude of the output signal before and after a peak amplitude, wherein a number of output signal samples before and after the peak amplitude is programmable.

22. An integrated LIDAR measurement device, comprising:

an illumination source mounted to the printed circuit board;

an illumination driver Integrated Circuit (IC) mounted to the printed circuit board, the illumination driver IC selectively coupling the illumination source to an electrical power source in response to a pulse trigger signal such that the illumination source emits a measurement pulse of illumination light;

a photodetector mounted to the printed circuit board, the photodetector configured to detect a first amount of measurement pulses of illumination light caused by crosstalk between the illumination source and the photodetector, and a valid return pulse of light reflected from a location in the ambient environment illuminated by a second amount of the measurement pulses; and

a return pulse receiver IC mounted to the printed circuit board, the return pulse receiver IC configured to estimate a time between an instance when a first amount of measurement pulses of illumination light due to crosstalk is detected and an instance when a valid return pulse of light is detected.

Technical Field

The described embodiments relate to a LIDAR based 3-D point cloud measurement system.

Background

LIDAR systems employ light pulses to measure distances to objects based on the time of flight (TOF) of each light pulse. Light pulses emitted from a light source of the LIDAR system interact with remote objects. A portion of the light reflects off the object and returns to the detector of the LIDAR system. The distance is estimated based on the time elapsed between the emission of the light pulse and the detection of the returned light pulse. In some examples, the light pulses are generated by a laser emitter. The light pulses are focused by a lens or lens assembly. The time taken for a laser pulse to return to a detector mounted near the emitter is measured. The distance is derived from a time measurement with high accuracy.

Some LIDAR systems employ a single laser emitter/detector combination in conjunction with a rotating mirror to effectively scan the entire plane. The distance measurements performed by such systems are two-dimensional (i.e., planar) in nature, and the captured distance points are rendered as a 2-D (i.e., single planar) point cloud. In some examples, the rotating mirror rotates at a very fast speed (e.g., thousands of revolutions per minute).

In many operational scenarios, a 3-D point cloud is required. Several schemes have been employed to interrogate the surrounding environment in three dimensions. In some examples, the 2-D instrument is actuated up and down and/or back and forth, typically on a gimbal. This is commonly referred to in the art as "blinking" or "nodding" the sensor. Thus, a single beam LIDAR unit may be employed to capture the entire 3-D array of range points, albeit one point at a time. In a related example, a prism is employed to "divide" the laser pulse into multiple layers, each with a slightly different vertical angle. This simulates the nodding effect described above, but without the actuation sensor itself.

In all of the above examples, the optical path of a single laser emitter/detector combination is altered in some way to obtain a wider field of view than a single sensor. The number of pixels that such devices can generate per unit time is inherently limited due to limitations on the pulse repetition rate of a single laser. Any modification of the path of light speed, whether by mirrors, prisms, or actuating devices to achieve a larger coverage area, comes at the expense of reduced point cloud density.

As described above, 3-D point cloud systems exist in several configurations. However, in many applications, it is necessary to view in a wide 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 car. Furthermore, in the event that the vehicle enters a dip in the road, the vertical field of view should extend above the horizon. Furthermore, it is necessary to minimize the delay between actions occurring in the real world and the imaging of those actions. In some examples, it is desirable to provide a full image update at least five times per second. To address these needs, 3-D LIDAR systems have been developed that include multiple laser emitters and detector arrays. This system is described in U.S. patent No. 7,969,558 issued on 28/6/2011, the subject matter of which is incorporated herein by reference in its entirety.

In many applications, a sequence of pulses is transmitted. The direction of each pulse is sequentially changed in rapid succession. In these examples, the distance measurements associated with each individual pulse may be considered pixels, and a set of pixels (i.e., a "point cloud") emitted and captured in rapid succession may be rendered into an image or analyzed for other reasons (e.g., to detect obstacles). In some examples, the resulting point cloud is rendered with viewing software as an image that presents three dimensions to the user. Different schemes may be used to depict the distance measurements as 3-D images that appear as if captured by a live camera.

Some existing LIDAR systems employ illumination sources and detectors that are not integrated together on a common substrate (e.g., an electrical mounting board). Additionally, the illumination beam path and the collection beam path are separate within the LIDAR device. This leads to opto-mechanical design complexity and alignment difficulties.

In addition, mechanical devices employed to scan the illumination beam in different directions may be sensitive to mechanical vibrations, inertial forces, and general environmental conditions. Without proper design, these mechanical devices may degrade, resulting in a loss of performance or failure.

In order 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 their ability to generate short duration pulses and resolve short duration return pulses is limited.

The saturation of the detector limits the measurement capability because the target reflectivity and proximity vary greatly in real operating environments. Furthermore, power consumption may cause the LIDAR system to overheat.

The light devices, targets, circuits and temperatures vary in the actual system. Without proper calibration of the signals detected from each LIDAR device, the variability of all of these elements limits system performance.

Improvements to the illumination drive electronics as well as the receiver electronics of LIDAR systems are desired to increase imaging resolution and range.

Disclosure of Invention

Methods and systems for performing three-dimensional LIDAR measurements using an integrated LIDAR measurement device are described herein.

In one aspect, a return signal receiver of the LIDAR measurement device generates a pulse trigger signal that causes the illumination driver to provide electrical power to the illumination source, which causes the illumination source to generate a pulse of illumination light. Furthermore, the pulsed trigger signal directly triggers data acquisition of the return signal and associated time-of-flight calculations. In this way, the pulse trigger signal is employed to trigger both pulse generation and return pulse data acquisition. This ensures accurate synchronization of pulse generation and return pulse acquisition, which enables accurate time-of-flight calculations through time-to-digital conversion.

In another aspect, the return signal receiver identifies one or more return pulses of light reflected from one or more objects in the surrounding environment in response to the pulses of illumination light, and determines a time of flight associated with each return pulse. The return signal receiver also estimates the width of each return pulse, the peak amplitude of each return pulse, and samples each return pulse waveform individually over a sampling window that includes the peak amplitude of each return pulse waveform. These signal attributes and timing information are communicated from the integrated LIDAR measurement device to the master controller.

In a further aspect, a time of flight associated with each return pulse is estimated by the return signal receiver based on the coarse timing module and the fine timing module. In a further aspect, a meta-stable bit is employed to determine the correct count of the coarse timing block when the hit signal is near a clock transition. The value of the meta-stable bit determines whether the hit signal comes near a high-to-low transition of the counter signal or near a low-to-high transition of the counter signal, thereby determining the correct count value.

In another further aspect, the return pulse receiver IC measures time-of-flight based on the time elapsed between detection of a pulse and a valid return pulse caused by internal crosstalk between an illumination source and a photodetector of the integrated LIDAR measurement device. In this way, the delay of the system is eliminated from the estimation of the time of flight.

In another aspect, the master controller is configured to generate a plurality of pulse command signals, each pulse command signal being communicated to a different integrated LIDAR measurement device. Each return pulse receiver IC generates a corresponding pulse trigger signal based on the received pulse command signal.

The foregoing is a summary and thus contains, by necessity, simplifications, generalizations, and omissions of detail; accordingly, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. 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.

Drawings

Fig. 1 is a simplified diagram illustrating one embodiment of a LIDAR measurement system that includes at least on an integrated LIDAR measurement device in at least one novel aspect.

Fig. 2 depicts a graphical representation of the timing associated with the transmission of measurement pulses from the integrated LIDAR measurement device 130 and the capture of return measurement pulses.

Fig. 3 depicts a simplified diagram illustrating one embodiment of a portion of a return signal receiver IC that includes a return signal analysis module 160 in one embodiment.

Fig. 4 depicts a simplified diagram illustrating one embodiment of a portion of a return signal receiver IC including a constant fraction discriminator module 170 in one embodiment.

Fig. 5 depicts a simplified diagram illustrating one embodiment of a portion of a return signal receiver IC including a coarse timing module in one embodiment.

Fig. 6 depicts a simplified diagram illustrating one embodiment of a portion of a return signal receiver IC including a fine timing module in one embodiment.

Fig. 7 depicts a simplified diagram illustrating one embodiment of a portion of a return signal receiver IC including a pulse width detection module in one embodiment.

Fig. 8 is a diagram illustrating an embodiment of the 3-D LIDAR system 100 in one exemplary operational scenario.

Fig. 9 is a diagram illustrating another embodiment of the 3-D LIDAR system 10 in one exemplary operational scenario.

Fig. 10 depicts a diagram illustrating an exploded view of the 3-D LIDAR system 100 in an exemplary embodiment.

Fig. 11 depicts a view of the optical element 116 in more detail.

Fig. 12 depicts a cross-sectional view of the optics 116 to illustrate the shaping of each beam of collected light 118.

Fig. 13 depicts a flow diagram illustrating a method 300 of performing LIDAR measurements with an integrated LIDAR measurement device in at least one new aspect.

Detailed Description

Reference will now be made in detail to background examples of the invention, examples of which are illustrated in the accompanying drawings, and some embodiments.

Fig. 1 depicts a LIDAR measurement system 120 in one embodiment. The LIDAR measurement system 120 includes a master controller 190 and one or more integrated LIDAR measurement devices 130. The integrated LIDAR measurement device 130 includes a return signal receiver Integrated Circuit (IC) 150, a gallium nitride based illumination driver Integrated Circuit (IC) 140, an illumination source 132, a photodetector 138, and a transimpedance amplifier (TIA) 141. Each of these components is mounted to a common substrate 144 (e.g., a printed circuit board) that provides mechanical support as well as electrical connectivity between the components.

Further, in some embodiments, the integrated LIDAR measurement device includes one or more power supplies that provide electrical power to the electronic components mounted to the substrate 144 and to the illumination device 132. The power supply may be configured to supply any suitable voltage or current. In some embodiments, one or more power supplies are mounted to the substrate 144. In general, however, any of the power sources described herein may be mounted to separate substrates and electrically coupled to the various elements mounted to the substrate 144 in any suitable manner.

The master controller 190 is configured to generate a pulsed command signal 191, the pulsed command signal 191 being communicated to the receiver IC150 of the integrated LIDAR measurement device 130. Generally, a LIDAR measurement system includes a plurality of different integrated LIDAR measurement devices 130. In these embodiments, the master controller 190 communicates a different pulsed command signal 191 to each different integrated LIDAR measurement device. In this manner, the master controller 190 coordinates the timing of LIDAR measurements performed by any number of integrated LIDAR measurement devices.

The pulse command signal 191 is a digital signal generated by the main controller 190. Thus, the timing of the pulse command signal 191 is determined by a clock associated with the master controller 190. In some embodiments, the pulse command signal 191 is used directly to trigger pulse generation by the lighting driver IC140 and data acquisition by the receiver IC 150. However, the lighting driver IC140 and the receiver IC150 do not share the same clock with the master controller 190. For this reason, when the pulse command signal 191 is used directly to trigger pulse generation and data acquisition, an accurate estimate of time-of-flight becomes much more computationally burdensome.

In an aspect, the receiver IC150 receives the pulse command signal 191 and generates a pulse trigger signal V in response to the pulse command signal 191_TRG143. Pulse trigger signal 143 is transmitted to illumination driver IC140 and directly triggers illumination driver IC140 to provide electrical pulse 131 to illumination source 132, which causes illumination source 132 to generate a pulse of illumination light 134. In addition, the pulse trigger signal 143 directly triggers data acquisition of the return signal 142 and associated time-of-flight calculations. In this wayIn this way, both pulse generation and return pulse data acquisition are triggered with a pulse trigger signal 143 generated based on the internal clock of the receiver IC 150. This ensures accurate synchronization of pulse generation and return pulse acquisition, which enables accurate time of flight calculations.

The illumination source 132 emits a measurement pulse of illumination light 134 in response to a pulse of electrical energy 131. The illumination light 134 is focused and projected by one or more optical elements of the LIDAR system onto a particular location in the surrounding environment.

In some embodiments, the illumination source 132 is laser-based (e.g., a laser diode). In some embodiments, the illumination source is based on one or more light emitting diodes. In general, any suitable pulsed illumination source may be considered.

As depicted in fig. 1, the illumination light 134 emitted from the integrated LIDAR measurement device 130 and the corresponding return measurement light 135 reflected back toward the integrated LIDAR measurement device 130 share a common optical path. The integrated LIDAR measurement device 130 includes a photodetector 138 having an active sensor region 137. As depicted in fig. 1, the illumination source 132 is located outside the field of view of the active area 137 of the photodetector. As depicted in fig. 1, an overmolded lens 136 is mounted over the photodetector 138. The overmolded lens 136 includes a tapered cavity corresponding to the ray acceptance cone of the return light 135. Illumination 134 from an illumination source 132 is injected through a fiber optic waveguide into the detector cone of acceptance. An optical coupler optically couples the illumination source 132 with the fiber waveguide. At the end of the fiber optic waveguide, a mirror element 133 is oriented at an angle (e.g., 45 degrees) with respect to the waveguide to inject the illumination light 134 into the cone of return light 135. In one embodiment, the end face of the fiber optic waveguide is cut at a 45 degree angle and the end face is coated with a highly reflective dielectric coating to provide a mirrored surface. In some embodiments, the waveguide comprises a rectangular-shaped glass core and a lower-diffraction-index polymer cladding. In some embodiments, the entire optical assembly is encapsulated with a material having a diffraction index closely matched to that of the polymer cladding. In this manner, the waveguide injects the illumination light 134 into the cone of acceptance of the return light 135 with minimal obstruction.

The placement of the waveguide within the cone of acceptance of the return light 135 projected onto the active sensing area 137 of the detector 138 is selected to ensure that the illumination spot and the detector field of view have maximum overlap in the far field.

As depicted in fig. 1, return light 135 reflected from the surrounding environment is detected by a photodetector 138. In some embodiments, the photodetector 138 is an avalanche photodiode. The photodetector 138 generates an output signal 139, which output signal 139 is transmitted to the return signal receiver IC 150.

Output signal 139 is received and amplified by TIA 141. The amplified signal 142 is transmitted to a return signal analysis module 160. In general, the amplification of the output signal 139 may include multiple amplifier stages. In this sense, an analog transimpedance amplifier is provided by way of non-limiting example, as many other analog signal amplification schemes are contemplated within the scope of this patent document. As depicted in fig. 1, although TIA 141 is integrated with return signal receiver IC150, in general, TIA 141 may be implemented as a discrete device separate from receiver IC 150. In some embodiments, it is preferable to integrate the TIA 141 with the receiver IC150 to save space and reduce signal contamination.

The return signal receiver IC150 performs several functions. In one aspect, the receiver IC150 identifies return pulses of light reflected from one or more objects in the ambient environment in response to the pulses of illumination light 134 and determines a time of flight associated with each of these return pulses. In general, the output signal 139 is processed by the return signal receiver IC150 for a period of time corresponding to the time of flight of light from the LIDAR measurement device 130 to a distance equal to the maximum range of the device 130 and back to the device 130. During this time, the illumination pulse 134 may encounter several objects at different distances from the integrated LIDAR measurement device 130. Thus, the output signal 139 may include several pulses, each pulse corresponding to a portion of the illumination beam 134 reflected from a different reflective surface located at a different distance from the device 130. In another aspect, receiver IC150 determines various attributes of each return pulse. As depicted in fig. 1, receiver IC150 determines an indication of the width of each return pulse, determines the peak amplitude of each return pulse, and samples each return pulse waveform individually over a sampling window that includes the peak amplitude of each return pulse waveform. These signal attributes and timing information are communicated from the integrated LIDAR measurement device 130 to the master controller 190. The master controller 190 may further process the data or transfer the data directly to an external computing device for further image processing (e.g., by a user of the LIDAR measurement system 120).

Fig. 2 depicts an illustration of timing associated with transmission of a measurement pulse and capture of a return measurement pulse(s) from the integrated LIDAR measurement device 130. As depicted in fig. 2, the measurement is initiated by the rising edge of the pulsed trigger signal 134 generated by the receiver IC 150. As depicted in fig. 1 and 2, an amplified return signal 142 is generated by TIA 141. As previously described herein, the measurement window (i.e., the period of time that the collected return signal data is associated with a particular measurement pulse) is initiated by enabling data acquisition at the rising edge of the pulse trigger signal 143. Receiver IC150 controls the duration T of the measurement window_measurementTo correspond to a window of time when a return signal is expected in response to transmission of the measurement pulse sequence. In some examples, the measurement window is enabled at the rising edge of the pulse trigger signal 143 and disabled at a time corresponding to the time of flight of light over a distance of approximately twice the range of the LIDAR system. In this manner, the measurement window is opened to collect return light from objects adjacent to the LIDAR system (i.e., negligible time-of-flight) to objects located at the maximum range of the LIDAR system. In this way, all other light that cannot contribute to a useful return signal is rejected.

As depicted in fig. 2, return signal 142 includes three return measurement pulses corresponding to the transmitted measurement pulses. In general, signal detection is performed on all detected measurement pulses. In one example, signal analysis may be performed to identify the nearest valid signal 142B (i.e., the first valid instance of the return measurement pulse), the strongest signal, and the farthest valid signal 142C (i.e., the last valid instance of the return measurement pulse in the measurement window). Any of these instances may be reported by the LIDAR system as a potentially valid range measurement.

Internal system delays associated with the emission of light from the LIDAR system (e.g., signal communication delays and latencies associated with the switching elements, energy storage elements, and pulsed light emitting devices) and delays associated with collecting light and generating signals indicative of the collected light (e.g., amplifier latencies, analog-to-digital conversion delays, etc.) result in errors in the estimation of the time of flight of the measured pulses of light. Therefore, measurement of time-of-flight based on the rising edge of the pulse trigger signal 143 and the elapsed time between each valid return pulse (i.e., 142B and 142C) introduces undesirable measurement errors. In some embodiments, a calibrated, predetermined delay time is employed to compensate for the electronic delay to obtain a corrected estimate of the actual optical time of flight. However, the accuracy of static correction to dynamically changing electronic delays is limited. Although frequent recalibration may be employed, this is at the cost of computational complexity and may interfere with the runtime of the system.

In another aspect, receiver IC150 measures time-of-flight based on the time elapsed between detection of detected pulse 142A and valid return pulses (e.g., 142B and 142C) caused by internal crosstalk between illumination source 132 and photodetector 138. In this way, system delays are eliminated from the time-of-flight estimation. The pulse 142A is generated by internal crosstalk with virtually no distance for light to travel. Thus, the time delay from the rising edge of the pulse trigger signal and the detected instance of pulse 142A captures all of the system delays associated with illumination and signal detection. By measuring the time of flight of the valid return pulses (e.g., return pulses 142B and 142C) with reference to detected pulse 142A, all system delays associated with illumination and signal detection due to internal crosstalk are eliminated. As depicted in FIG. 2, receiver IC150 references return pulse 142ATo estimate the time of flight TOF associated with the return pulse 142B₁And time of flight TOF associated with return pulse 142C₂。

In some embodiments, the signal analysis is performed entirely by receiver IC 150. In these embodiments, the time-of-flight signal 192 transmitted from the integrated LIDAR measurement device 130 includes an indication of the time-of-flight of each return pulse determined by the receiver IC 150. In some embodiments, signal 155-. The waveform information may be further processed by one or more processors located on-board the 3-DLIDAR system or external to the 3-DLIDAR system to obtain another estimate of the distance, an estimate of one or more physical properties of the detected object, or a combination thereof.

Return signal receiver IC150 is a hybrid analog/digital signal processing IC. In the embodiment depicted in fig. 1, return signal receiver IC150 includes TIA 141, return signal analysis module 160, time-of-flight calculation module 159, and analog-to-digital conversion module 158.

Fig. 3 depicts a return signal analysis module 160 in one embodiment. In the embodiment depicted in fig. 3, the return signal analysis module 160 includes a Constant Fraction Discriminator (CFD) circuit 170, a coarse timing module 180, a fine timing module 190, a pulse width detection module 200, and a return pulse sample and hold module 210.

Amplified return signal V _TIA142 and a threshold signal V _THLD145 are received by CFD 170. When the return signal 142 exceeds a threshold value (i.e., the value of the threshold signal 145), the CFD 170 identifies a valid return pulse. In addition, CFD 170 may repeatedly determine when a valid return pulse is detected and generate a hit signal V that transitions sharply at the detection time _HIT178. Hit signal 178 signals the detection of a valid return pulse and triggers each of the timing and waveform acquisition and analysis functions of return signal analysis module 160.

For example, the coarse timing module 180 determines a digital signal (i.e., range 151) indicative of a number of digital clock cycles that have passed the transition of the pulse trigger signal 143 that triggers the illumination pulse 134 and the transition of the hit signal 178 associated with the particular valid return pulse. The coarse timing module 180 also generates a digital signal (i.e., the MS 152) that is a digital clock signal that is time-shifted by one-half of the period of the digital clock signal.

Further, the fine timing module 190 determines the analog signal (i.e., V) having a voltage value indicative of the elapsed time between a transition of the hit signal 178 associated with a particular valid return pulse and the next transition of the digital clock signal CLK_CLK153). Similarly, the fine timing module 190 determines an analog signal (i.e., V) having a voltage value indicative of the time elapsed between a transition of the hit signal 178 associated with a particular valid return pulse and the next transition of the inversion of the digital clock signal CLKB_CLKB154). Time of flight module 159 employs range 151, MS152, V _CLK153 and V _CLKB154 to determine the time of flight associated with each detected return pulse.

The return pulse sample and hold module 210 generates an analog signal (i.e., V) having a signal value (e.g., voltage) indicative of the peak amplitude of each valid return pulse_PEAK156). In addition, the return pulse sample and hold module 210 generates a set of analog signals (i.e., V)_WIND155) Each having a signal value (e.g., voltage) indicative of the amplitude associated with the sampling point of each valid return pulse waveform. In some embodiments, the number of sample points before and after the peak amplitude of the waveform is programmable.

Pulse width detection module 200 generates an analog signal (i.e., V) having a signal value (e.g., voltage) indicative of the width of each valid return pulse waveform_WIDTH157). In the depicted embodiment, V _WIDTH157 indicates when the return pulse signal 142 exceeds V _THLD145 and the time elapsed between the time of the transition of hit signal 178 associated with the particular valid return pulse. V _WIND155、V _PEAK156 and V _WIDTH157 are each converted to a digital signal by an analog-to-digital converter (ADC) 158 of the return signal receiver IC150 before being communicated from the return signal receiver IC to the main controller 190.

Fig. 4 depicts a constant score discriminator 170 in one embodiment. As depicted in fig. 4, the constant fraction discriminator 170 includes a signal delay module 171, a signal divider module 172, an enable module 173, and a comparator module 174. The analog output signal 142 generated by TIA 141 is passed to signal delay module 171, signal splitter module 172, and enable module 173. Signal delay module 171 introduces a fixed delay into signal 142 and generates V_DELAY175. Also, the signal splitter module 172 includes a voltage divider circuit that divides V _TIA142 by a constant fraction (e.g., by 2) to generate V_FRACT176。V_DELAY175 and V_FRACTThe value of 176 is compared by comparator 174. In one example, when V_DELAY175 greater than V_FRACTHit signal V at 176_HIT178 are driven to a high state, and when V is_DELAY175 less than V_FRACTAt 176, V _HIT178 are driven to a low state. In this way, V _HIT178 indicate when the return pulse has arrived and when it has passed in a consistent manner. If an arbitrary threshold is used to determine the arrival of a return pulse, the arrival times will not be consistent because the different return pulse shapes are not similar. However, by employing a constant fraction discriminator, the timing of the arrival and passage of return pulses is consistently identified among the return pulses. The enabling module 173 receives the threshold voltage value V _THLD145, and when a signal V is returned_TIA142 exceeds V _THLD145 time generation of enable signal V _ENABLE177. In this manner, the comparator module 174 is enabled only when the return signal 142 exceeds the threshold. This ensures that spurious spikes in the return signal 142 are ignored and valid return pulses are processed by the comparator module 174. In general, CFD 170 is configured to generate a hit signal 178 associated with each valid return pulse that arrives during a measurement window. Thus, V _HIT178 include a plurality of hit signals that are,each associated with a different return pulse.

Fig. 5 depicts an embodiment of a coarse timing module 180. As depicted in FIG. 5, the coarse timing module 180 includes a binary counter module 181, a binary-to-Gray code converter 182, a metastable bit generator 183, and one or more latch modules 184A-N. As depicted in fig. 5, the digital clock signal CLK and an inverted CLKB of the digital clock signal are received by the coarse timing module 180. In one embodiment, the digital clock signal is generated by a Phase Locked Loop (PLL) on board the return signal receiver IC 150. In one embodiment, the digital clock signal has a frequency of one gigahertz. Thus, in this particular embodiment, the coarse timing module 180 is able to determine the time of flight associated with a particular return pulse to be the closest one nanosecond.

The binary counter module 181 receives the pulse trigger signal 143 and starts counting in response to the pulse trigger. The digital signals BIN [0:10]186 indicating the running count are passed to the binary to gray code converter 182. Binary to gray code converter 182 converts binary COUNT signal BIN [0:10]186 to gray code equivalent digital signal COUNT [0:10 ]. COUNT [0:10] is passed to each of the latch modules 184A-N. In addition, the first bit of the running binary count BIN [0] is passed to meta-stable bit generator 183. Metastable bit generator 183 generates metastable bit MS 188 by introducing a half-cycle shift into BIN [0 ]. MS 188 is also conveyed to each of latch modules 184A-N.

In addition, each hit signal 178 associated with a different return pulse is communicated to a different latch module (i.e., one of latch modules 184A-N). Each of the latch modules 184A-N latches the last known value of COUNT [0:10] and MS at the transition of the corresponding hit signal indicating the identification of a return pulse. The resulting latched values RANGE [0:10]151 and MS152 are each passed to a time-of-flight module 159 depicted in FIG. 1.

Fig. 6 depicts the fine timing module 190 in one embodiment. The fine timing module 190 includes two pulse width generators 191 and 193 and two time-to- voltage converters 192 and 194. Pulse of lightWidth generator 191 receives each hit signal 178 and clock signal CLK. Similarly, pulse width generator 193 receives each hit signal 178 and clock signal CLKB. The pulse width generator 191 generates a pulse having a duration that matches the time between the rising edge of the hit signal 178 and the next rising edge of the clock signal CLK. The pulse signal V _PULSE195 to the time-to-voltage converter 192. In response to V _PULSE195, the time-to-voltage converter 192 generates a current ramp through the capacitor for the duration of the pulse. The voltage across the capacitor indicates the duration of the pulse. The voltage signal V _CLK153 are sent to ADC 158 for conversion to digital signals and on to time of flight module 159. Similarly, the pulse width generator 193 generates pulses having a duration that matches the time between the rising edge of the hit signal 178 and the next rising edge of the clock signal CLKB. The pulse signal V _PULSE-B196 are transmitted to the time-to-voltage converter 194. In response to V_PULSE-BThe time-to-voltage converter 194 generates a current ramp through the capacitor for the duration of the pulse 196. The voltage across the capacitor indicates the duration of the pulse. The voltage signal V _CLKB154 are sent to an ADC 158 for conversion to a digital signal and on to a time of flight module 159. Since the pulse width generators 191 and 193 and the time-to- voltage converters 192 and 194 are analog modules, the uncertainty associated with the estimation of the time elapsed between the rising edge of the hit signal and the next clock signal is less than 10 picoseconds. Thus, the fine timing module enables a high accuracy estimate of the time of flight associated with a particular return pulse.

In another aspect, the determination of the time of flight associated with each return pulse is determined based on the outputs of both the coarse and fine timing modules. In the embodiment depicted in fig. 1, the time-of-flight module 159 is implemented digitally. Time-of-flight module 159 estimates RANGE [0:10] based on the coarse time associated with the return pulse]And fine time estimation to determine the time of flight associated with a particular return pulse. The time of flight module 159 based on whether the hit signal is on the CLK signal orThe proximity of the transition of the CLKB signal determines whether to place V on_CLKOr V_CLKBUsed as a fine time estimate. For example, if the hit signal comes near a transition of the CLK signal, then V_CLKBWill be used as the basis for a fine time estimate since the CLKB signal is stable at that time. Similarly, if the hit signal comes near a transition of the CLKB signal, then V_CLKWill be used as a basis for a fine time estimation since the CLK signal is stable at that time. In one example, the estimated time of flight is the sum of the coarse time estimate and the selected fine time estimate.

In a further aspect, the transition of counter block 181 is determined using the meta-stable bit MS [0] to determine the correct count of RANGE [0:10] when the hit signal is near a clock transition. For example, if hit signal 178 transitions near the transition of counter 181, it is unclear which count is associated with the hit signal. For a 1 gigahertz clock, the error may be one count or one nanosecond. In these scenarios, the value of the metastable bit is used to distinguish which count is associated with a particular bit. The value of the meta-stable bit determines whether the hit signal comes around a high-to-low transition of the counter signal or a low-to-high transition of the counter signal, thereby determining the correct count value.

Fig. 7 depicts the pulse width detection module 200 in one embodiment. The pulse width detection module 200 includes a pulse width generator 201 and a time-to-voltage converter 202. Pulse width generator 201 generates a pulse having an enable signal V as depicted in FIG. 4_ENABLE177, and the falling edge of hit signal 178, for a time matching the duration of the pulse. The pulse signal V _PULSE203 are transmitted to the time-to-voltage converter 202. In response to V_PULSEThe time-to-voltage converter 202 generates a current ramp through the capacitor for the duration of the pulse 203. The voltage across the capacitor indicates the duration of the pulse. The voltage signal V _WIDTH155 are transmitted to ADC 158 for conversion to a digital signal.

Pulse width detection module 200 is depicted by way of non-limiting exampleAnd (6) drawing. In general, the pulse width detection module 200 may be configured to operate on different input signals to generate V _PULSE203 and V _WIDTH155. In one example, pulse width generator 201 generates a pulse having a rising edge in conjunction with hit signal 178 and when V _TIA142 down to V _THLD145 below, and a time between times that match. When V is_TIA142 down to V_THLDThe time below 145 may be determined by a separate comparator or may be determined by the output of the comparator module 174 without having a V-like image_HITAs well as the latched output. In another example, the pulse width generator 201 generates a pulse having a pulse width of V _TIA142 is raised to V_THLDTime above 145 and when V _TIA142 down to V _THLD145 below, and a time between times that match. In one example, V is employed_ENABLE177 instead of pulse width generator 201, and V _ENABLE177 is provided as an input to the time-to-voltage converter 202. The time-to-voltage converter 202 generates a current ramp through the capacitor for the duration of the pulse. Voltage indication V across capacitor_ENABLEThe duration of the pulse.

In another aspect, the master controller is configured to generate a plurality of pulse command signals, each pulse command signal being communicated to a different integrated LIDAR measurement device. Each return pulse receiver IC generates a corresponding pulse control signal based on the received pulse command signal.

Fig. 8-10 depict a 3-D LIDAR system including multiple integrated LIDAR measurement devices. In some embodiments, a delay time is set between the firing of each integrated LIDAR measurement device. In some examples, the delay time is greater than a time of flight of the measurement pulse sequence to and from an object located at a maximum range of the LIDAR device. In this way, there is no crosstalk between any integrated LIDAR measurement devices. In some other examples, measurement pulses are transmitted from one integrated LIDAR measurement device before the measurement pulses transmitted from another integrated LIDAR measurement device have had time to return to the LIDAR device. In these embodiments, care is taken to ensure that there is sufficient spatial separation between the regions of the surrounding environment interrogated by each beam to avoid cross talk.

Fig. 8 is a diagram illustrating an embodiment of the 3-D LIDAR system 100 in one exemplary operational scenario. The 3-DLIDAR system 100 includes a lower housing 101 and an upper housing 102, the upper housing 102 including a dome element 103 composed of a material transparent to infrared light (e.g., light having a wavelength in the spectral range of 700 to 1,700 nanometers). In one example, the dome element 103 is transparent to light having a wavelength centered at 905 nanometers.

As depicted in FIG. 8, a plurality of light beams 105 are emitted from the 3-DLIDAR system 100 through the dome element 103 over an angular range α measured from the central axis 104. in the embodiment depicted in FIG. 8, each light beam is projected onto a plane defined by the x and y axes at a plurality of different locations spaced apart from each other. for example, light beam 106 is projected onto the xy plane at location 107.

In the embodiment depicted in fig. 8, the 3-D LIDAR system 100 is configured to scan each of the plurality of light beams 105 about the central axis 104. Each beam of light projected onto the xy plane delineates a circular pattern centered on the intersection of the central axis 104 and the xy plane. For example, over time, the beam 106 projected onto the xy-plane describes a circular trajectory 108 centered on the central axis 104.

Fig. 9 is a diagram illustrating another embodiment of the 3-D LIDAR system 10 in one exemplary operational scenario. The 3-DLIDAR system 10 includes a lower housing 11 and an upper housing 12, the upper housing 12 including a cylindrical cap element 13 constructed of a material transparent to infrared light (e.g., light having a wavelength in the spectral range of 700 to 1,700 nanometers). In one example, the cylindrical cage element 13 is transparent to light having a wavelength centered at 905 nanometers.

As depicted in FIG. 9, over an angular range β, a plurality of light beams 15 are emitted from the 3-D LIDAR system 10 through the cylindrical cap element 13. in the embodiment depicted in FIG. 9, the chief ray of each light beam is illustrated.

In the embodiment depicted in fig. 9, the 3-D LIDAR system 10 is configured to scan each of the plurality of light beams 15 about the central axis 14. For purposes of illustration, the illustrated light beam 15 is oriented at one angle relative to a non-rotating coordinate system of the 3-D LIDAR system 10, and the illustrated light beam 15' is oriented at another angle relative to the non-rotating coordinate system. As the light beam 15 rotates about the central axis 14, each light beam projected into the ambient environment (e.g., each cone of illumination light associated with each light beam) illuminates the volume of the environment corresponding to the cone of illumination light beams as it sweeps about the central axis 14.

Fig. 10 depicts an exploded view of the 3-D LIDAR system 100 in an exemplary embodiment. The 3-D LIDAR system also includes a light emission/collection engine 112 that rotates about the central axis 104. In the embodiment depicted in fig. 10, the central optical axis 117 of the light emission/collection engine 112 is tilted at an angle θ relative to the central axis 104. As depicted in fig. 10, the 3-DLIDAR system 100 includes a fixed electronic board 110 mounted in a fixed position relative to the lower housing 101. The rotating electronic board 111 is placed above the stationary electronic board 110 and is configured to rotate at a predetermined rotation speed (e.g. greater than 200 revolutions per minute) with respect to the stationary electronic board 110. The electric power signals and the electronic signals are transmitted between the fixed electronic board 110 and the rotating electronic board 111 by means of one or more transformers, capacitive or optical elements, thus obtaining a contactless transmission of these signals. The light emission/collection engine 112 is fixedly positioned with respect to the rotating electronic board 111 and thus rotates around the central axis 104 at a predetermined angular velocity ω.

As depicted in fig. 10, the light emission/collection engine 112 includes an array of integrated LIDAR measurement devices 113. In one aspect, each integrated LIDAR measurement device includes a light emitting element, a light detecting element, and associated control and signal conditioning electronics integrated onto a common substrate (e.g., a printed circuit board or other electronic circuit board).

The light emitted from each integrated LIDAR measurement device passes through a series of optical elements 116, which optical elements 116 collimate the emitted light to generate a beam of illumination that is projected from the 3-D LIDAR system into the environment. In this manner, as depicted in fig. 11, an array of light beams 105, each emitted from a different LIDAR measurement device, is emitted from the 3-D LIDAR measurement system 100. In general, any number of LIDAR measurement devices may be arranged to simultaneously emit any number of light beams from the 3-D LIDAR system 100. Light reflected from objects in the environment due to illumination by a particular LIDAR measurement device is collected by the optical element 116. The collected light passes through the optical element 116 where it is focused onto the detection element of the same, particular LIDAR measurement device. In this way, collected light associated with illumination of different portions of the environment by illumination generated by different LIDAR measurement devices is focused onto the detector of each corresponding LIDAR measurement device, respectively.

Fig. 11 depicts a view of the optical element 116 in more detail. As depicted in fig. 11, the optical element 116 includes four lens elements 116A-D arranged to focus the collected light 118 onto each detector of the array of integrated LIDAR measurement devices 113. In the embodiment depicted in fig. 11, light passing through the optics 116 is reflected from the mirror 124 and directed onto each detector of the array of integrated LIDAR measurement devices 113. In some embodiments, one or more of the optical elements 116 are constructed of one or more materials that absorb light outside of a predetermined wavelength range. The predetermined wavelength range includes wavelengths of light emitted by the array of integrated LIDAR measurement devices 113. In one example, the one or more lens elements are composed of a plastic material that includes a coloring additive that absorbs light having a wavelength less than the infrared light generated by each array of the integrated LIDAR measurement device 113. In one example, the colorant is Epolight 7276A available from Aako BV (the netherlands). In general, any number of different colorants may be added to any plastic lens element of optics 116 to filter out undesired spectra.

Fig. 12 depicts a cross-sectional view of the optics 116 to illustrate the shaping of each beam of collected light 118.

In this manner, a LIDAR system, such as the 3-D LIDAR system 10 depicted in fig. 9 and the system 100 depicted in fig. 8, includes multiple integrated LIDAR measurement devices that each emit a pulsed beam of illumination light from the LIDAR device into the surrounding environment and measure return light reflected from objects in the surrounding environment.

In some embodiments, such as the embodiments described with reference to fig. 8 and 9, the array of integrated LIDAR measurement devices is mounted to a rotating frame of the LIDAR device. The rotating frame rotates relative to a base frame of the LIDAR device. In general, however, the array of integrated LIDAR measurement devices may be movable or fixed relative to the base frame of the LIDAR device in any suitable manner (e.g., gimbal, pan/tilt, etc.).

In some other embodiments, each integrated LIDAR measurement device includes a beam-directing element (e.g., a scanning mirror, a MEMS mirror, etc.) that scans an illumination beam generated by the integrated LIDAR measurement device.

In some other embodiments, two or more integrated LIDAR measurement devices each emit a beam of illumination light toward a scanning mirror device (e.g., a MEMS mirror) that reflects the beam in different directions into the surrounding environment.

In a further aspect, the one or more integrated LIDAR measurement devices are in optical communication with an optical phase modulation device that directs the illumination beam(s) generated by the one or more integrated 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, thereby changing the direction of light diffracted from the optical phase modulation device. In this manner, the illumination beam(s) generated by the one or more integrated LIDAR devices scan through a plurality of different orientations and effectively interrogate the surrounding 3-D environment being measured. The diffracted beam projected into the surrounding environment interacts with objects in the environment. Each respective integrated LIDAR measurement device measures a distance between the LIDAR measurement system and the detected object based on the collected return light from the object. An optical phase modulation device is placed in the optical path between the integrated LIDAR measurement device and the object being measured in the surrounding environment. Thus, both the illumination light and the corresponding return light pass through the optical phase modulation device.

Fig. 13 illustrates a flow diagram of a method 300 suitable for implementation by the integrated LIDAR measurement system described herein. In some embodiments, the integrated LIDAR measurement device may operate in accordance with the method 300 illustrated in fig. 13. In general, however, performance of the method 300 is not limited to the embodiment of the integrated LIDAR measurement device 130 described with reference to fig. 1. These illustrations and corresponding explanations are provided by way of example, as many other embodiments and examples of operation are contemplated.

In block 301, a pulsed trigger signal is generated in response to receiving a pulsed command signal on a return signal receiver IC mounted to a printed circuit board.

In block 302, in response to a pulse trigger signal, an illumination source is selectively electrically coupled to an electrical power source such that the illumination source emits a measurement pulse of illumination light.

In block 303, an amount of return light received by the photodetector is detected in response to the measurement pulse of the illumination light. The illumination source and photodetector are mounted to a printed circuit board.

In block 304, an output signal indicative of the detected return light is generated.

In block 305, an output signal is received onto the return signal receiver IC during the duration of the measurement window.

In block 306, one or more return pulses of the detected return light are identified.

In block 307, a time of flight associated with each of the identified return pulses is determined.

In block 308, one or more attributes of the segments of each of the identified return pulses are determined.

A computing system as described herein may include, but is not limited to, a personal computer system, a mainframe computer system, a workstation, an image computer, a 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 that execute instructions from a memory medium.

Program instructions implementing methods such as those described herein may be transmitted over transmission media such as wire, cable or wireless transmission links. The program instructions are stored in a computer readable medium. Exemplary computer readable media include read-only memory, random-access memory, magnetic or optical disks or tape.

In general, any of the power sources described herein may be configured to supply power specified as a voltage or current. Thus, any electrical power source described herein as a voltage source or current source may be considered an equivalent current source or voltage source, respectively. Similarly, any electrical signal described herein may be designated as a voltage signal or a current signal. Thus, any electrical signal described herein as being a voltage signal or a current signal may be considered an equivalent current signal or voltage signal, respectively.

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 which can be used to carry or store desired program code means in the form of instructions or data structures and which 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 the various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.