# Patent

## Title
Devices and methods for adjustable resolution depth mapping

## Abstract

Devices and methods are described that provide for scanning surfaces and generating 3-dimensional point clouds that describe the depth of the measured surface at each point. In general, the devices and methods utilize scanning mirror(s) that reflect a laser beam into a pattern of scan lines. When the raster pattern of scan lines is directed at a surface, reflections of the laser beam from the surface are received and used to the generate 3-dimensional point clouds that describe the measured surface depth at each point. The motion of the scanning mirror(s) can be dynamically adjusted to modify the characteristics of the resulting 3-dimensional point cloud of the surface. For example, the adjustment of the scanning mirror motion can modify the resolution or data density of the resulting 3-dimensional point cloud that describes the measured depths of the surface.

## Background
FIELD
The present disclosure generally relates to depth mapping, and more particularly relates to depth mapping with scanning lasers.
BACKGROUND
Depth mapping sensors have been developed to generate 3D maps of surfaces, where the 3D maps describe the variations in depth over the surface. One limitation in typical depth mapping sensors is their limited flexibility. For example, typical depth mapping sensors may be limited to generating 3D maps with specific resolutions.
For example, some depth mapping sensors use CMOS imaging sensors to receive light reflected from the surface, and then generate the 3D map from that received light. However, such CMOS imaging sensors typically have a fixed horizontal and vertical resolution. Thus, depth mapping sensors that use such CMOS imaging sensors are limited to providing 3D maps with resolutions that are less than or equal to the horizontal and vertical resolution of the CMOS imaging sensors.
As such, there remains a need for improved devices and methods for depth mapping, and in particular a need for depth mapping with improved flexibility.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a schematic diagram of a laser depth sensing device in accordance with various embodiments of the present invention;
FIG. 2. shows a schematic view of a depth mapping device in accordance with various embodiments of the present invention;
FIGS. 3A, 3B, 3C, and 3D are graphical representations of raster patterns in accordance with various embodiments of the present invention;
FIG. 4 is a graphical representation of an expanded portion of a raster pattern in accordance with various embodiments of the present invention;
FIG. 5 shows a schematic view of a scanning laser projector in accordance with various embodiments of the present invention;
FIG. 6 shows a plan view of a microelectromechanical system (MEMS) device with a scanning mirror in accordance with various embodiments of the present invention;
FIG. 7 shows a block diagram of a mobile device in accordance with various embodiments of the present invention;
FIG. 8 shows a perspective view of a mobile device in accordance with various embodiments of the present invention;
FIG. 9 shows a perspective view of a head-up display system in accordance with various embodiments of the present invention;
FIG. 10 shows a perspective view of eyewear in accordance with various embodiments of the present invention;
FIG. 11 shows a perspective view of a robotic apparatus in accordance with various embodiments of the present invention; and
FIG. 12 shows a perspective view of a gaming apparatus in accordance with various embodiments of the present invention.



DESCRIPTION OF EMBODIMENTS
The embodiments described herein provide devices and methods for scanning surfaces and generating 3-dimensional point clouds that describe the depth of the measured surface at each point. In general, the devices and methods utilize scanning mirror(s) that reflect a laser beam into a pattern of scan lines. When the raster pattern of scan lines is directed at a surface, reflections of the laser beam from the surface are received and used to the generate 3-dimensional point clouds that describe the measured surface depth at each point (e.g., provide a depth map of the surface).
In accordance with the embodiments described herein, the motion of the scanning mirror(s) can be dynamically adjusted to modify the characteristics of the resulting 3-dimensional point cloud of the surface. For example, the horizontal scan rate, horizontal scan amplitude, vertical scan rate, vertical scan amplitude and/or vertical scan waveform shape of the scanning mirror motion can be dynamically adjusted. This adjustment of the scanning mirror motion is configured to modify the characteristics of the resulting 3-dimensional point clouds. For example, the adjustment of the scanning mirror motion can modify the resolution or data density of the resulting 3-dimensional point cloud that describes the measured depths of the surface.
Thus, the embodiments described herein can provide increased flexibility over systems that have fixed horizontal and vertical resolution (e.g., systems that use CMOS imaging sensors with defined horizontal and vertical resolutions).
Turning now to FIG. 1, a schematic diagram of a laser depth sensing device 100 is illustrated. The laser depth sensing device 100 includes a laser light source 102, scanning mirror(s) 104, a drive circuit 106, and a depth mapping device 108. During operation, the laser light source 102 generates a beam of laser light that is reflected by the scanning mirror(s) 104 into a pattern 114 of scan lines inside a scanning region 112. In the example of FIG. 1, the pattern 114 of scan lines comprises a raster pattern. However, this is just one example, and in other embodiments other patterns of scan lines can be generated as used. For example, spiral patterns and Lissajous patterns could instead be used. To facilitate the generation of the pattern 114, the drive circuit 106 controls the movement of the scanning mirror(s) 104. Specifically, the drive circuit 106 provides excitation signal(s) to excite motion of the scanning mirror(s) 104 in a way that results in the generation of the pattern 114 of scan lines.
In accordance with the embodiments described herein, the depth mapping device 108 is configured to receive reflections of the laser beam from the surface and generate a 3-dimensional point cloud of the surface based at least in part on the received reflections of the laser beam. For example, the laser light source 102 can be configured to generate pulses in the laser beam. The reflection of those pulses is received by the depth mapping device 108, and the depth mapping device 108 calculates a time of flight for the return of each received pulse. From this, the depth mapping device 108 generates the 3-dimensional point cloud of the surface.
The horizontal motion of the beam of laser light in this pattern 114 defines rows of data points in the 3-dimensional point cloud, while the vertical motion of the beam of laser light in the pattern 114 defines a vertical scan rate and thus the number of rows in the 3-dimensional point cloud.
As noted above, the scanning mirror(s) 104 are configured to reflect the laser beam, and the drive circuit 106 is configured to provide an excitation signal to excite motion of the scanning mirror(s) 104. Specifically, the motion is excited such that the scanning mirror(s) 104 reflect the laser beam in the raster pattern 114 of scan lines. And in accordance with the embodiments described herein the drive circuit 106 is further configured to dynamically adjust the motion of the scanning mirror(s) 104 to modify the characteristics of the resulting 3-dimensional point cloud of the surface. For example, the drive circuit 106 can be configured to provide dynamic adjustment of the horizontal scan rate, horizontal scan amplitude, horizontal scan waveform shape, vertical scan rate, vertical scan amplitude, and/or vertical scan waveform shape of the scanning mirror motion. This adjustment of the scanning mirror motion modifies the characteristics of the resulting 3-dimensional point clouds generated by the depth mapping device 108. For example, the adjustment of the scanning mirror motion can modify the resolution or data density of the resulting 3-dimensional point cloud that describes the measured depths of the surface generated by the depth mapping device 108. Thus, the laser depth sensing device 100 can provide increased flexibility over systems that have fixed horizontal and vertical resolution.
In one specific embodiment, the drive circuit 106 is configured to dynamically decrease the vertical scan rate of the scanning mirror 104 motion to provide increased vertical resolution in the 3-dimensional point cloud of the surface. In another specific embodiment, the drive circuit 106 is configured to dynamically decrease the vertical scan amplitude of the scanning mirror 104 motion to provide increased vertical data density in the 3-dimensional point cloud of the surface.
In another specific embodiment, the drive circuit 106 is configured to dynamically decrease the horizontal scan amplitude of the scanning mirror 104 motion to provide increased horizontal resolution in the 3-dimensional point cloud of the surface. Specifically, the decrease in the horizontal scan amplitude results in a decrease in spacing between adjacent pulses generated by the laser light source 102 as they impact the surface.
In another specific embodiment, the drive circuit 106 is configured to dynamically change the vertical scan rate during each vertical scan of the scanning mirror 104 motion to provide variable horizontal data resolution in the 3-dimensional point cloud of the surface. In another specific embodiment, the drive circuit 106 is configured to dynamically change the vertical scan waveform shape of the scanning mirror 104 motion to provide increased horizontal and decreased resolution in the 3-dimensional point cloud of the surface. In yet another specific embodiment, the drive circuit 106 is configured to dynamically change the horizontal scan waveform shape of the scanning mirror 104 motion.
In another specific embodiment, the laser light source 102 is configured to stagger the pulses of laser light in adjacent lines of the raster pattern of scan lines. Turning now to FIG. 2, a more detailed embodiment of a depth mapping device 200 is illustrated. In FIG. 2, the depth mapping device 200 includes an optical sensor 202 and a processor 204. In general, the optical sensor 202 is configured to receive laser light reflected from a surface and generate signals proportional to the received laser light reflections. Those signals are the passed to the processor 204.
In some embodiments those signals can be filtered, synthesized or otherwise processed prior to sending to the processor 204, while in other embodiments those signals can be processed by the processor 204. The processor 204 also receives light timing data from the light source (e.g., laser light source 102). This light timing data describes the timing of the depth mapping pulses projected on to the surface. Likewise, the processor 204 receives mirror position data from the drive circuit (e.g., drive circuit 106). The mirror position data describes the position of the mirror as it relates to each depth mapping pulse. The processor 204 receives the signals from the optical sensor 202, the light timing data and mirror position data, and generates a 3-dimensional point cloud of the surface.
In one embodiment, the laser light source 102 can be configured to generate pulses of infrared laser light during the pattern scan over a surface (e.g., raster pattern). Each pulse of infrared laser light is reflected off the surface and received by the optical sensor 202, and each pulse of reflected laser light can then correspond to one point in the 3-dimensional point cloud. In such an embodiment the optical sensor 202 can comprise any suitable sensor. For example, the optical sensor 202 could be implemented with a suitable photodiode implemented to be sensitive to infrared light, including silicon photodiodes and avalanche photodiodes. In other embodiments the optical sensor 202 could be implemented with a silicon photomultiplier or photomultiplier tubes. It should finally be noted that in some embodiments other types of laser may be used to generate the pulses, including visible light lasers.
The processor 204 is coupled to the optical sensor 202 and generates 3-dimensional point clouds that describe the surface depth. In one embodiment, the processor 204 generates the 3-dimensional point cloud by calculating a time of flight for each pulse that is reflected back and received by the optical sensor. Specifically, the time of flight for each pulse to travel from the light source to the surface, and back to the optical sensor 202 can be determined at least in part by light timing data and the signals from the optical sensor 202. The location on the surface corresponding to each pulse can be determined at least in part from the mirror position data. Because the time of flight of each pulse is proportional to the distance to the surface at that point, the time of flight can be used to calculate the surface depth at that point of reflection. And when a composite of the determined surface depths from each point in the raster pattern scan is made, the resulting content can provide a 3-dimensional point cloud describing the surface depth of the scanned surface.
To facilitate this, the processor 204 can be implemented with any suitable type of processing system or device. For example, the processor 204 can be implemented with software implemented programs that are loaded into memory and executed on hardware, where the hardware utilizes integrated circuits designed to execute such programs. In other embodiments, the processor 204 can be implemented exclusively in hardware or in combinations of hardware and software. For example, the processor 204 can be implemented to include application-specific integrated circuits (ASICs) designed for this specific application, or general purpose Central processing units (CPUs) that commonly provide processing functionality on computing devices. Furthermore, system on Chip (SoC) processors can integrate a variety of system components into a single integrated device, and may include digital, analog, optical, and other functions on a single semiconductor substrate.
As was noted above, during operation of a laser depth sensing device a laser beam is reflected off scanning mirror(s) to generate a pattern of scan lines (e.g., a raster pattern). This raster pattern of scan lines determines the resolution of the scan and the resulting 3-dimensional point cloud describing the surface depth. In general, the “slow axis” of the raster pattern is the vertical axis, while the “fast axis” is the horizontal axis, recognizing that the terms “vertical” and “horizontal” are essentially arbitrary in this context as they are determined by the orientation of the laser depth sensing device. To generate such a raster pattern, the vertical scan motion of the mirror can follow a relatively slow, sawtooth-like pattern, while the horizontal scan motion follows a relatively fast, sinusoidal-like pattern.
Turning now to FIG. 3A, a first vertical scan pattern 302, a first raster pattern 304, a modified vertical scan pattern 306, and a modified raster pattern 308 are illustrated. In general, these graphs illustrate how a dynamic decrease in the vertical scan rate can be used to increase the vertical resolution of the resulting 3-dimensional point cloud of the surface.
Specifically, the first vertical scan pattern 302 is a relatively fast sawtooth pattern, and this relatively fast pattern results in the first raster pattern 304. Conversely, the modified vertical scan pattern 306 is a relatively slow sawtooth pattern, and that relatively slow pattern results in the second raster pattern 308. It should be noted that in these examples, the vertical scan patterns 302 and 306 include a relatively short vertical retrace period (occurring during the steep downward slopping portion of the sawtooth pattern) and a relatively long active display period (occurring during the relatively shallow upward slopping section of the sawtooth pattern). In such embodiments the raster patterns 304 and 308 would be generated during the active display periods, while the relatively short vertical retrace period is used to return the mirror to the original vertical position after each raster pattern.
As can be seen in FIG. 3A, reducing the vertical scan rate to a relatively slower sawtooth pattern results in the reduced spacing between the horizontal lines of the resulting raster pattern. This reduced spacing results in more horizontal scan lines over a given vertical distance, and thus increases the vertical resolution and vertical data density of the scan. Conversely, increased spacing between horizontal lines results in less horizontal scan lines over a given vertical distance, and thus decreases the vertical resolution of the scan. It should also be noted that this reduction in the vertical scan rate also changes the horizontal scan waveform shape.
Thus, in accordance with an embodiment described herein, a drive circuit (e.g., drive circuit 106) can be configured to selectively decrease the vertical scan rate to increase the vertical resolution of the resulting of the resulting 3-dimensional point cloud of the surface. Conversely, the drive circuit can be configured to selectively increase the vertical scan rate to decrease the vertical resolution of the resulting 3-dimensional point cloud. This provides an increased flexibility in depth mapping, as the vertical resolution is not limited to that provided by a fixed resolution sensor.
It should be noted that FIG. 3A illustrates examples where the vertical scan rate is relatively constant during the generation of the raster pattern. Stated another way, the vertical position changes in a substantially linear fashion over the saw tooth pattern. It should be noted that this is just one example, and in other embodiments the vertical scan rate could be variable over each raster pattern.
Turning now to FIG. 3B, a variable rate, vertical scan pattern 309 and resulting raster pattern 310 are illustrated graphically. The vertical scan pattern 309 has a shape such that the rate of vertical motion varies over each raster pattern. This results in portions of the raster pattern having decreased vertical resolution and other portions of the raster pattern having increased vertical resolution. Such an arrangement can facilitate more detailed scanning of selected portions of a surface.
Thus, in accordance with an embodiment described herein, a drive circuit (e.g., drive circuit 106) can be configured to dynamically change the vertical scan waveform shape of the scanning mirror motion to provide increased horizontal resolution in a first portion of the 3-dimensional point cloud of the surface and provide decreased horizontal resolution in a second portion of the 3-dimensional point cloud of the surface.
Turning now to FIG. 3C, a first vertical scan pattern 312, a first raster pattern 314, a modified vertical scan pattern 316, and a modified raster pattern 318 are illustrated. In general, these graphs illustrate how a dynamic decrease in the vertical scan amplitude can provide increased vertical data density in the 3-dimensional point cloud of the surface.
Specifically, the first vertical scan pattern 312 has a relatively large amplitude, and this large amplitude results in the first raster pattern 314. Conversely, the modified vertical scan pattern 316 has a relatively small amplitude, and that relatively small amplitude results in the second raster pattern 318. As can be seen in FIG. 3C, reducing the vertical scan amplitude results in less vertical distance being scanned with the same number of horizontal scan lines, and this again reduces the spacing between the horizontal lines of the resulting raster pattern. This reduced spacing again results in more horizontal scan lines over a given vertical distance, and thus increases the vertical data density in the scan. Conversely, increased spacing between horizontal lines results in more horizontal scan lines over a given vertical distance, and thus decreases the vertical data density in the scan.
Thus, in accordance with an embodiment described herein, a drive circuit (e.g., drive circuit 106) can be configured to selectively decrease the vertical scan amplitude to increase the vertical data density of the resulting of the resulting 3-dimensional point cloud of the surface. Conversely, the drive circuit can be configured to selectively increase the vertical scan amplitude to decrease the vertical data density of the resulting 3-dimensional point cloud. This again provides an increased flexibility in depth mapping.
The embodiments illustrated in FIGS. 3A, 3B and 3C illustrate techniques that increase the vertical resolution and/or the vertical data density of the resulting 3-dimensional point cloud. Variations on these embodiments can also increase the horizontal resolution and/or horizontal data density. Specifically, by controlling the timing of the pulses in the laser beam while also reducing the spacing between horizontal lines, a staggered pulse arrangement that increases the horizontal data density can be generated.
Turning to FIG. 3D, an expanded portion of a raster pattern 322 is illustrated. The expanded portion of the raster pattern 322 illustrates exemplary pulse strike locations 324, with the locations 324 illustrated as black dots. It should be noted that these locations are merely illustrative, and are not necessarily drawn to scale. As can be seen in FIG. 3D the timing of the pulses is configured to stagger pulses in adjacent horizontal lines of the raster scan pattern. When adjacent line spacing is sufficiently close, adjacent lines of pulses will interleave together to fill the gaps and effectively form one horizontal line with twice the resolution. Thus, this technique can increase the horizontal resolution of the resulting 3-dimensional point cloud of the surface.
Turning now to FIG. 4, a first raster pattern 422 and modified raster pattern 424 are illustrated. Also illustrated is an expanded portion 426 of the first raster pattern 422, and an expanded portion 428 of the modified raster pattern 434. The expanded portion 426 and expanded portion 428 both illustrate exemplary pulse strike locations 430, with the locations 430 illustrated as black dots. Again, it should be noted that these locations are merely illustrative, and are not necessarily drawn to scale.
In general, these graphs illustrate how a dynamic decrease in the vertical scan amplitude can provide increased horizontal resolution and horizontal data density in the 3-dimensional point cloud of the surface. Specifically, the decrease in the horizontal scan amplitude results in a decrease in spacing between adjacent pulses generated by the laser light source as they impact the surface.
Specifically, the first raster pattern 422 has a relatively large horizontal amplitude, and this horizontal amplitude results in relatively wide spacing between pulses. Conversely, the modified raster pattern 424 has a relatively small horizontal amplitude, and assuming an equal pulse rate this relatively small amplitude results in relatively close spacing between pulses. As can be seen in FIG. 4, reducing the horizontal spacing between pulses increases the horizontal data density in the scan. Conversely, increasing the horizontal scan amplitude would result in increased spacing between pulses and decreased horizontal data density.
Thus, in accordance with an embodiment described herein, a drive circuit (e.g., drive circuit 106) can be configured to selectively decrease the horizontal scan amplitude to increase the horizontal resolution and data density of the resulting of the resulting 3-dimensional point cloud of the surface. Conversely, the drive circuit can be configured to selectively increase the horizontal scan amplitude to decrease the horizontal resolution and data density of the resulting 3-dimensional point cloud.
Thus, the embodiments described herein provide for dynamically adjusting the motion of scanning mirror(s) to modify the characteristics of the resulting 3-dimensional point cloud of the surface. While these techniques have been described in the context of a standalone laser depth sensing device, in other embodiments these devices and techniques can be implemented together with a scanning laser projector. In scanning laser projectors, the laser light is encoded with pixel data to generate image pixels. That encoded laser light is reflected off the scanning mirror(s) to project an image.
In these embodiments the scanning laser projector can be configured to operate in at least two modes, with a first mode for image projection, and a second mode for depth scanning. In such a scanning laser projector, the drive circuit can be configured to drive the scanning mirrors differently depending upon the mode. Thus, the scanning laser projector can create a first raster pattern optimized for projecting an image when operating in a first mode, and the scanning laser projector can create a second raster pattern optimized for depth scanning when operating in a second mode. Specifically, the drive circuit can be configured to modify the motion of the at least one scanning mirror to change at least one of the horizontal scan rate, horizontal scan amplitude, horizontal scan waveform shape, vertical scan rate, vertical scan amplitude, and vertical scan waveform shape when operating during the second mode. Thus, the scanning laser projector can provide both desired image quality in one mode and desired scanning resolutions and/or data densities in another mode.
In other embodiments the scanning laser projector can operate in one mode both image projection and depth scanning. Specifically, in such embodiments, the drive circuit can be configured to generate the same scanning patterns during both image projection and depth scanning. Furthermore, in such embodiments the image projection and depth scanning can be temporally coincident, in phase or out of phase.
Turning now to FIG. 5, a schematic view of a scanning laser projector 700 is illustrated. The scanning laser projector 700 is a more detailed example of the type of system that can be used in accordance with various embodiments of the present invention. Specifically, the scanning laser projector 700 can be implemented to provide both laser depth scanning and laser image projection. Scanning laser projector 700 includes an image processing component 702, a pixel drive generator 704, an infrared laser module 705, a red laser module 706, a green laser module 708, and a blue laser module 710. In such an embodiment the red, green and blue light can be used for image projection, while the infrared light can be used for depth scanning. Light from the laser modules is combined with dichroics 712, 714, 716 and 717. Scanning laser projector 700 also includes fold mirror 718, drive circuit 720, a MEMS device 722 with scanning mirror 724, and a depth mapping device 740. It should be noted that this illustrated arrangement for combing the outputs from the various laser modules is just one example implementation, and other implementations using different techniques for combing laser light of different wavelengths can instead be used.
In operation, image processing component 702 processes video content at using two dimensional interpolation algorithms to determine the appropriate spatial image content for each scan position at which an output pixel is to be displayed by the pixel drive generator 704. For example, the video content may represent a grid of pixels at any resolution (e.g., 640×480, 848×480, 1280×720, and 1920×1080). The input light intensity encoding typically represents the light intensity in 8, 10, 12 bit or higher resolutions.
This content is then mapped to a commanded current for each of the red, green, and blue laser sources such that the output intensity from the lasers is consistent with the input image content. In some embodiments, this process occurs at output pixel rates in excess of 150 MHz. The laser beams are then directed onto an ultra-high speed gimbal mounted 2 dimensional bi-axial laser scanning mirror 724. In some embodiments, this bi-axial scanning mirror is fabricated from silicon using MEMS processes. The vertical axis of rotation is operated quasi-statically and creates a vertical sawtooth raster trajectory. The vertical axis is also referred to as the slow-scan axis. The horizontal axis is operated on a resonant vibrational mode of the scanning mirror. In some embodiments, the MEMS device uses electromagnetic actuation, achieved using a miniature assembly containing the MEMS die and small subassemblies of permanent magnets and an electrical interface, although the various embodiments are not limited in this respect. For example, some embodiments employ electrostatic or piezoelectric actuation. Any number of mirrors and type of mirror actuation may be employed without departing from the scope of the present invention.
The pixel drive generator 704 also generates pulses with the infrared laser module 705 for depth scanning. As described above, this can include the staggering of adjacent pulses for increased horizontal scan resolution.
In some embodiments, the horizontal axis is driven in a resonant mode, and as such is commonly referred to as the fast-scan axis. In some embodiments, raster pattern 726 is formed by combining a sinusoidal component on the horizontal axis and a sawtooth component on the vertical axis. In these embodiments, output beam 728 sweeps back and forth left-to-right in a sinusoidal pattern, and sweeps vertically (top-to-bottom) in a sawtooth pattern with the display blanked during flyback (bottom-to-top).
It should be noted that FIG. 5 illustrates the sinusoidal pattern as the beam sweeps vertically top-to-bottom, but does not show the flyback from bottom-to-top. In other embodiments, the vertical sweep is controlled with a triangular wave such that there is no flyback. In still further embodiments, the vertical sweep is sinusoidal. The various embodiments of the invention are not limited by the waveforms used to control the vertical and horizontal sweep or the resulting raster pattern 726.
The drive circuit 720 provides a drive signal to MEMS device 722. The drive signal includes an excitation signal to control the resonant angular motion of scanning mirror 724 on the fast-scan axis, and also includes slow scan drive signal to cause deflection on the slow-scan axis. The resulting mirror deflection on both the fast and slow-scan axes causes output beam 728 to generate a raster scan 726 in an image region 730. In operation, the laser light sources produce light pulses for each output pixel and scanning mirror 724 reflects the light pulses as beam 728 traverses the raster pattern 726. Drive circuit 720 also receives a feedback signal from MEMS device 722. The feedback signal from the MEMS device 722 can describe the maximum deflection angle of the mirror, also referred to herein as the amplitude of the feedback signal. This feedback signal is provided to the drive circuit 720, and is used by the drive circuit 720 to accurately control the motion of the scanning mirror 724.
In operation, drive circuit 720 excites resonant motion of scanning mirror 724 such that the amplitude of the feedback signal is constant. This provides for a constant maximum angular deflection on the fast-scan axis as shown in raster pattern 726. The excitation signal used to excite resonant motion of scanning mirror 724 can include both amplitude and a phase. Drive circuit 720 includes feedback circuit(s) that modifies the excitation signal amplitude to keep the feedback signal amplitude substantially constant. Additionally, the drive circuit 720 can modify the excitation signal to control the horizontal phase alignment and vertical position of the raster pattern 726.
The drive circuit 720 is further configured to dynamically adjust the motion of the scanning mirror 724 during depth scanning to modify the characteristics of the resulting 3-dimensional point cloud of the surface. For example, the drive circuit 720 can be configured to drive the scanning mirror 724 to generate one raster pattern during a first mode for image projection, and selectively change to drive of the scanning mirror 724 to generate a second raster pattern for depth scanning. For example, the drive circuit 720 can be configured to provide dynamic adjustment of the horizontal scan rate, horizontal scan amplitude, horizontal scan waveform shape, vertical scan rate, vertical scan amplitude and/or vertical scan waveform shape of the scanning mirror motion when operating in the second mode. As was described above, this adjustment of the scanning mirror 724 motion modifies the characteristics of the resulting 3-dimensional point clouds compared to how they would be generated during the first mode. For example, the adjustment of the scanning mirror 724 motion can modify the resolution or data density of the resulting 3-dimensional point cloud that describes the measured depths of the surface generated by the depth mapping device 740.
To facilitate this, drive circuit 720 may be implemented in hardware, a programmable processor, or in any combination. For example, in some embodiments, drive circuit 720 is implemented in an application specific integrated circuit (ASIC). Further, in some embodiments, some of the faster data path control is performed in an ASIC and overall control is provided by a software programmable microprocessor.
Next, it should be noted that while FIG. 5 shows both the laser light for the depth scanning (e.g., light from the infrared laser module 705) and the laser light for image projection (e.g., laser light from the red laser module 706, green laser module 708, and blue laser module 710) all projected into the same region 730, that this is just one example implementation. In other embodiments, the laser light pulses for depth mapping can be directed to one field or region, while the pixels for image projection are directed to another field or region. Such a redirection of pulses or pixels can be accomplished through the use of wavelength dependent optical elements, where these wavelength dependent optical elements are configured to direct light of some component wavelengths to a first region and direct light of other component wavelengths to another region. These wavelength dependent components can include both transmissive and reflective components, including various beam splitters and various combinations thereof. Such a technique would allow for depth mapping to be performed over one region, while an image is being projected into another region.
It should be noted that while FIG. 5 illustrates an embodiment with a single MEMS device 722 and a single scanning mirror 724, that this is just one example implementation. As another example, a scanning laser projector could instead be implemented with scanning mirror assembly that includes two scanning mirrors, with one mirror configured to deflect along one axis and another mirror configured to deflect along a second axis that is largely perpendicular to the first axis.
Such an embodiment could include a second MEMS device, a second scanning mirror, and a second drive circuit. The first scanning mirror could be configured to generate horizontal scanning motion, and the second scanning mirror configured to generate vertical motion. Thus, the motion of one scanning mirror determines the horizontal scan amplitude and the motion of the other scanning mirror determines the vertical scan amplitude.
Finally, although red, green, blue and infrared laser light sources are shown in FIG. 5, the various embodiments are not limited by the wavelength of light emitted by the laser light sources.
In accordance with the embodiments described herein, the depth mapping device 740 is provided to generate the 3-dimensional point cloud of the surface. To facilitate this, the depth mapping device 740 can include an optical sensor to receive laser light reflected from a surface and generate signals proportional to the received laser light reflections. The depth mapping device 740 can also receive light timing data from the pixel drive generator 704 and/or infrared laser module 705. The depth mapping device can also receive mirror position data from the drive circuit 720. From those signals and data, the depth mapping device 740 generates the 3-dimensional point cloud of the surface. In one embodiment, depth mapping device 740 generates the 3-dimensional point cloud by calculating a time of flight for each pulse that is reflected back and received by the optical sensor. Specifically, the time of flight for each pulse to travel from the infrared laser module 705 to the surface, and back to the optical sensor can be determined at least in part by light timing data and the signals from the optical sensor. The location on the surface corresponding to each pulse can be determined at least in part from the mirror position data. Because the time of flight of each pulse is proportional to the distance to the surface at that point, the time of flight can be used to calculate the surface depth at that point of reflection. And when a composite of the determined surface depths from each point in the raster pattern scan is made, the resulting content can provide a 3-dimensional point cloud describing the surface depth of the scanned surface.
Turning now to FIG. 6, a plan view of a microelectromechanical system (MEMS) device with a scanning mirror is illustrated. MEMS device 800 includes fixed platform 802, scanning platform 840, and scanning mirror 816. Scanning platform 840 is coupled to fixed platform 802 by flexures 810 and 812, and scanning mirror 816 is coupled to scanning platform 840 by flexures 820 and 822. Scanning platform 840 has a drive coil connected to drive lines 850, which are driven by a drive signal provided from a drive circuit (e.g., drive circuit 720). The drive signal includes an excitation signal to excite resonant motion of scanning mirror 816 on the fast-scan axis, and also includes a slow-scan drive signal to cause non-resonant motion of scanning platform 840 on the slow-scan axis. Current drive into drive lines 850 produces a current in the drive coil. In operation, an external magnetic field source (not shown) imposes a magnetic field on the drive coil. The magnetic field imposed on the drive coil by the external magnetic field source has a component in the plane of the coil, and is oriented non-orthogonally with respect to the two drive axes. The in-plane current in the coil windings interacts with the in-plane magnetic field to produce out-of-plane Lorentz forces on the conductors. Since the drive current forms a loop on scanning platform 840, the current reverses sign across the scan axes. This means the Lorentz forces also reverse sign across the scan axes, resulting in a torque in the plane of and normal to the magnetic field. This combined torque produces responses in the two scan directions depending on the frequency content of the torque.
The long axis of flexures 810 and 812 form a pivot axis. Flexures 810 and 812 are flexible members that undergo a torsional flexure, thereby allowing scanning platform 840 to rotate on the pivot axis and have an angular displacement relative to fixed platform 802. Flexures 810 and 812 are not limited to torsional embodiments as shown in FIG. 6. For example, in some embodiments, flexures 810 and 812 take on other shapes such as arcs, “S” shapes, or other serpentine shapes. The term “flexure” as used herein refers to any flexible member coupling a scanning platform to another platform (scanning or fixed), and capable of movement that allows the scanning platform to have an angular displacement with respect to the other platform.
Scanning mirror 816 pivots on a first axis formed by flexures 820 and 822, and pivots on a second axis formed by flexures 810 and 812. The first axis is referred to herein as the horizontal axis or fast-scan axis, and the second axis is referred to herein as the vertical axis or slow-scan axis. In some embodiments, scanning mirror 816 scans at a mechanically resonant frequency on the horizontal axis resulting in a sinusoidal horizontal sweep. Further, in some embodiments, scanning mirror 816 scans vertically at a nonresonant frequency, so the vertical scan frequency can be controlled independently.
In a typical embodiment the MEMS device 800 will also incorporates one or more integrated piezoresistive position sensors. For example, piezoresistive sensor 880 can be configured to produces a voltage that represents the displacement of mirror 816 with respect to scanning platform 840, and this voltage can be provided back to the drive circuit. Furthermore, in some embodiments, positions sensors are provided on one scan axis while in other embodiments position sensors are provided for both axes.
It should be noted that the MEMS device 800 is provided as an example, and the various embodiments of the invention are not limited to this specific implementation. For example, any scanning mirror capable of sweeping in two dimensions to reflect a light beam in a raster pattern or other suitable pattern may be incorporated without departing from the scope of the present invention. Also for example, any combination of static and dynamic/scanning mirrors (e.g., two mirrors: one for each axis) may be utilized to reflect a light beam in a raster pattern. Further, any type of mirror drive mechanism may be utilized without departing from the scope of the present invention. For example, although MEMS device 800 uses a drive coil on a moving platform with a static magnetic field, other embodiments may include a magnet on a moving platform with drive coil on a fixed platform. Further, the mirror drive mechanism may include an electrostatic drive mechanism.
The laser depth sensing devices described above (e.g., laser depth sensing device 100 of FIG. 1) can be implemented in a wide variety of devices and for a wide variety of applications. Several specific examples of these types of devices will not be discussed with reference to FIGS. 7-12. In each case, the various embodiments described above can be implemented with or as part of such a device.
Turning to FIG. 7, a block diagram of a mobile device 900 in accordance with various embodiments is illustrated. Specifically, mobile device 900 is an example of the type of device in which a standalone laser depth sensing device (e.g., laser depth sensing device 100 of FIG. 1) or a combination scanning laser projector/laser depth sensing device (e.g., scanning laser projector 700 of FIG. 5) can be implemented. As shown in FIG. 7, mobile device 900 includes wireless interface 910, processor 920, memory 930, and laser projector 902. In accordance with the embodiments described herein the laser projector 902 can implement a standalone laser depth sensing device or a combination scanning laser projector with laser depth sensing device
Laser projector 902 may receive image data from any image source. For example, in some embodiments, laser projector 902 includes memory that holds still images. In other embodiments, laser projector 902 includes memory that includes video images. In still further embodiments, scanning laser projector 902 displays imagery received from external sources such as connectors, wireless interface 910, a wired interface, or the like.
Wireless interface 910 may include any wireless transmission and/or reception capabilities. For example, in some embodiments, wireless interface 910 includes a network interface card (NIC) capable of communicating over a wireless network. Also for example, in some embodiments, wireless interface 910 may include cellular telephone capabilities. In still further embodiments, wireless interface 910 may include a global positioning system (GPS) receiver. One skilled in the art will understand that wireless interface 910 may include any type of wireless communications capability without departing from the scope of the present invention.
Processor 920 may be any type of processor capable of communicating with the various components in mobile device 900. For example, processor 920 may be an embedded processor available from application specific integrated circuit (ASIC) vendors, or may be a commercially available microprocessor. In some embodiments, processor 920 provides image or video data to scanning laser projector 902. The image or video data may be retrieved from wireless interface 910 or may be derived from data retrieved from wireless interface 910. For example, through processor 920, scanning laser projector 902 may display images or video received directly from wireless interface 910. Also for example, processor 920 may provide overlays to add to images and/or video received from wireless interface 910, or may alter stored imagery based on data received from wireless interface 910 (e.g., modifying a map display in GPS embodiments in which wireless interface 910 provides location coordinates).
Turning to FIG. 8, a perspective view of a mobile device 1000 in accordance with various embodiments is illustrated. Specifically, mobile device 1000 is an example of the type of device in which a standalone laser depth sensing device or combination scanning laser projector with laser depth sensing device can be implemented. Mobile device 1000 may be a hand held scanning laser projector with or without communications ability. For example, in some embodiments, mobile device 1000 may be a laser projector with little or no other capabilities. Also for example, in some embodiments, mobile device 1000 may be a device usable for communications, including for example, a cellular phone, a smart phone, a tablet computing device, a global positioning system (GPS) receiver, or the like. Further, mobile device 1000 may be connected to a larger network via a wireless (e.g., cellular), or this device can accept and/or transmit data messages or video content via an unregulated spectrum (e.g., WiFi) connection.
Mobile device 1000 includes laser projector 1020, touch sensitive display 1010, audio port 1002, control buttons 1004, card slot 1006, and audio/video (A/V) port 1008. Again, the laser projector 1020 can implement a standalone laser depth sensing device or combination scanning laser projector with laser depth sensing device. In some embodiments the mobile device may only include only the laser projector 1020 without any of touch sensitive display 1010, audio port 1002, control buttons 1004, card slot 1006, or A/V port 1008. Some embodiments include a subset of these elements. For example, an accessory projector may include scanning laser projector 1020, control buttons 1004 and A/V port 1008. A smartphone embodiment may combine touch sensitive display device 1010 and projector 1020.
Touch sensitive display 1010 may be any type of display. For example, in some embodiments, touch sensitive display 1010 includes a liquid crystal display (LCD) screen. In some embodiments, display 1010 is not touch sensitive. Display 1010 may or may not always display the image projected by laser projector 1020. For example, an accessory product may always display the projected image on display 1010, whereas a mobile phone embodiment may project a video while displaying different content on display 1010. Some embodiments may include a keypad in addition to touch sensitive display 1010. A/V port 1008 accepts and/or transmits video and/or audio signals. For example, A/V port 1008 may be a digital port, such as a high definition multimedia interface (HDMI) interface that accepts a cable suitable to carry digital audio and video data. Further, A/V port 1008 may include RCA jacks to accept or transmit composite inputs. Still further, A/V port 1008 may include a VGA connector to accept or transmit analog video signals.
In some embodiments, mobile device 1000 may be tethered to an external signal source through A/V port 1008, and mobile device 1000 may project content accepted through A/V port 1008. In other embodiments, mobile device 1000 may be an originator of content, and A/V port 1008 is used to transmit content to a different device.
Audio port 1002 provides audio signals. For example, in some embodiments, mobile device 1000 is a media recorder that can record and play audio and video. In these embodiments, the video may be projected by laser projector 1020 and the audio may be output at audio port 1002.
Mobile device 1000 also includes card slot 1006. In some embodiments, a memory card inserted in card slot 1006 may provide a source for audio to be output at audio port 1002 and/or video data to be projected by scanning laser projector 1020. Card slot 1006 may receive any type of solid state memory device, including for example secure digital (SD) memory cards.
Turning to FIG. 9, a perspective view of a head-up display system 1100 in accordance with various embodiments is illustrated. Specifically, head-up display system 1100 is an example of the type of device in which a laser projector as described above can be implemented. The head-up display system 1100 includes a laser projector 1102. The laser projector 1102 can again implemented as a standalone laser depth sensing device or combination scanning laser projector with laser depth sensing device. The laser projector 1102 is shown mounted in a vehicle dash to project the head-up display. Although an automotive head-up display is shown in FIG. 9, this is not a limitation and other applications are possible. For example, various embodiments include head-up displays in avionics application, air traffic control applications, and other applications.
Turning to FIG. 10, a perspective view of eyewear 1200 in accordance with various embodiments is illustrated. Specifically, eyewear 1200 is an example of the type of device in which a laser projector as described above can be implemented. Eyewear 1200 includes scanning laser projector 1202 to project a display in the eyewear's field of view. In some embodiments, eyewear 1200 is see-through and in other embodiments, eyewear 1200 is opaque. For example, eyewear 1200 may be used in an augmented reality application in which a wearer can see the display from projector 1202 overlaid on the physical world. Also for example, eyewear 1200 may be used in a virtual reality application, in which a wearer's entire view is generated by projector 1202.
Although only one projector 1202 is shown in FIG. 10, this is not a limitation and other implementations are possible. For example, in some embodiments, eyewear 1200 includes two projectors 1202, with one for each eye.
Turning to FIG. 11, a perspective view of a robotic apparatus 1300 in accordance with various embodiments is illustrated. The robotic apparatus 1300 is exemplary of the type of devices that can be implemented with a scanning laser projector 1302. Again, as described above, the scanning laser projector 1302 can be implemented to provide both image projection and depth mapping capabilities.
In the illustrated example, the robotic apparatus 1300 is a self-guiding mobile robot that can perform a variety of functions. For example, the robotic apparatus 1300 can be implemented to provide cleaning services, delivery services, media services, gaming, or otherwise act as entertainment device. In each case the depth mapping provided by the scanning laser projector 1302 can be used to provide a variety of functions, including navigation, interactivity, object recognition, etc.
As one example, the depth mapping provided by the scanning laser projector 1302 can be used to guide the robotic apparatus 1300 during cleaning or other navigation. As another example, the depth mapping provided by the scanning laser projector 1302 can be used to locate and identify objects. As another example, the image projection and depth mapping provided by the scanning laser projector 1302 can be used to provide a user interface with the robotic apparatus 1300, for example, by projecting images and allowing a user to control the apparatus with gestures that interact with those images. As another example, the robotic apparatus 1300 can use the scanning laser projector 1302 to display visual media to user, such as by identifying the location of a surface using the depth mapping and then projecting images on that located surface. Finally, it should be noted that these various embodiments could also apply to animatronic robotic devices that emulate human, animal or other such life-like characteristics.
It should be noted that to facilitate this robotic apparatus 1300 could include a variety of other features. For example, in addition to the scanning laser projector 1302, other sensor devices can be included to contribute to navigation. Furthermore, other human interfaces can be provided to facilitate interactions and control of the robotic device 1300. As other examples, the robotic apparatus 1300 may also include audio output devices and other such communication devices.
Turning to FIG. 12, a perspective view of a gaming apparatus 1400 in accordance with various embodiments is illustrated. Again, gaming apparatus 1400 can be implemented with a standalone laser depth sensing device or combination scanning laser projector with laser depth sensing device. Gaming apparatus 1400 includes buttons 1404, display 1410, and projector 1402. In some embodiments, gaming apparatus 1400 is a standalone apparatus that does not need a larger console for a user to play a game. For example, a user may play a game while watching display 1410 and/or the projected content. In other embodiments, gaming apparatus 1400 operates as a controller for a larger gaming console. In these embodiments, a user may watch a larger screen tethered to the console in combination with watching display 1410 and/or projected content.
In one embodiment, a laser depth sensing device is provided, comprising: at least one source of laser light configured to generate a laser beam; at least one scanning mirror configured to reflect the laser beam; a depth mapping device configured to receive reflections of the laser beam from a surface and generate a 3-dimensional point cloud of the surface based at least in part on timing of the received reflections of the laser beam from the surface; and a drive circuit configured to provide an excitation signal to excite motion of the at least one scanning mirror to reflect the laser beam in a pattern of scan lines on the surface, the motion of the at least one scanning mirror having a horizontal scan rate, a horizontal scan amplitude, a vertical scan rate, a vertical scan amplitude and a vertical scan waveform shape, and wherein the drive circuit is configured to dynamically adjust at least one of the horizontal scan rate, the horizontal scan amplitude, horizontal scan waveform shape, the vertical scan rate, the vertical scan amplitude and the vertical scan waveform shape to modify characteristics of the 3-dimensional point cloud of the surface.
In another embodiment, a scanning laser projector is provided, comprising: at least one source of laser light, the at least one source of laser light configured to generate a laser beam; at least one scanning mirror configured to reflect the laser beam; a depth mapping device configured to receive reflections of the laser beam from a surface and generate a 3-dimensional point cloud of the surface based at least in part on timing of the received reflections of the laser beam from the surface; and a drive circuit configured to provide an excitation signal to excite motion of the at least one scanning mirror, the motion of the at least one scanning mirror configured to reflect the laser beam in a pattern of scan lines on the surface, the motion of the at least one scanning mirror having a horizontal scan rate, a horizontal scan amplitude, horizontal scan waveform shape, a vertical scan rate, a vertical scan amplitude, and a vertical scan waveform shape, and wherein the drive circuit is configured to operate in a first mode for projecting an image and in a second mode for generating the 3-dimensional point cloud, and wherein the drive circuit is further configured to adjust at least one the horizontal scan rate, the horizontal scan amplitude, the vertical scan rate, the vertical scan amplitude, and the vertical scan waveform shape when operating in the second mode.
In another embodiment, a method of generating a 3-dimensional point cloud of a surface, the method comprising: generating a laser beam; reflecting the laser beam with at least one scanning mirror; exciting motion of the at least one scanning mirror to reflect the laser beam in a pattern of scan lines on the surface, the motion of the at least one scanning mirror having a horizontal scan rate, a horizontal scan amplitude, a vertical scan rate, a vertical scan amplitude and a vertical scan waveform shape; receiving reflections of the laser beam from a surface and generating the 3-dimensional point cloud of the surface based at least in part on timing of the received reflections of the laser beam from the surface; and dynamically adjusting at least one of the horizontal scan rate, the horizontal scan amplitude, horizontal scan waveform shape, the vertical scan rate, the vertical scan amplitude and the vertical scan waveform shape to modify characteristics of the 3-dimensional point cloud of the surface.
In the preceding detailed description, reference was made to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments were described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that the various embodiments of the invention, although different, are not necessarily mutually exclusive. For example, a particular feature, structure, or characteristic described herein in connection with one embodiment may be implemented within other embodiments without departing from the scope of the invention. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the scope of the invention. The preceding detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, appropriately interpreted, along with the full range of equivalents to which the claims are entitled. In the drawings, like numerals refer to the same or similar functionality throughout the several views.
Although the present invention has been described in conjunction with certain embodiments, it is to be understood that modifications and variations may be resorted to without departing from the scope of the invention as those skilled in the art readily understand. Such modifications and variations are considered to be within the scope of the invention and the appended claims.

## Claims

1. A laser depth sensing device comprising:
at least one source of laser light configured to generate a laser beam;
at least one scanning mirror configured to reflect the laser beam;
a depth mapping device configured to receive reflections of the laser beam from a surface and generate a 3-dimensional point cloud of the surface based at least in part on timing of the received reflections of the laser beam from the surface; and
a drive circuit configured to provide an excitation signal to excite motion of the at least one scanning mirror to reflect the laser beam in a pattern of scan lines on the surface, the motion of the at least one scanning mirror having a horizontal scan rate, a horizontal scan amplitude, a vertical scan rate, a vertical scan amplitude and a vertical scan waveform shape, and wherein the drive circuit is configured to dynamically adjust at least one of the horizontal scan rate, the horizontal scan amplitude, horizontal scan waveform shape, the vertical scan rate, the vertical scan amplitude and the vertical scan waveform shape to modify characteristics of the 3-dimensional point cloud of the surface.

2. The laser depth sensing device of claim 1, wherein the drive circuit is configured to dynamically decrease the vertical scan rate of the at least one scanning mirror motion to provide increased vertical resolution in the 3-dimensional point cloud of the surface.

3. The laser depth sensing device of claim 1, wherein the drive circuit is configured to dynamically decrease the vertical scan amplitude of the at least one scanning mirror motion to provide increased vertical data density in the 3-dimensional point cloud of the surface.

4. The laser depth sensing device of claim 1, wherein the drive circuit is configured to dynamically decrease the horizontal scan amplitude of the at least one scanning mirror motion to provide increased horizontal data density in the 3-dimensional point cloud of the surface.

5. The laser depth sensing device of claim 4, wherein the at least one source of laser light is configured to generate pulses in the laser beam, and wherein the depth mapping device generates the 3-dimensional point cloud of the surface by calculating a time of flight for a return of the pulses in the laser beam, and wherein the decrease in the horizontal scan amplitude further decreases spacing between adjacent pulses.

6. The laser depth sensing device of claim 1, wherein the drive circuit is configured to dynamically change the vertical scan rate during each vertical scan of the at least one scanning mirror motion to provide variable horizontal data resolution in the 3-dimensional point cloud of the surface.

7. The laser depth sensing device of claim 1, wherein the drive circuit is configured to dynamically change the vertical scan waveform shape of the at least one scanning mirror motion to provide increased horizontal resolution in a first portion of the 3-dimensional point cloud of the surface and provide decreased horizontal resolution in a second portion of the 3-dimensional point cloud of the surface.

8. The laser depth sensing device of claim 1, wherein the at least one source of laser light is configured to generate pulses in the laser beam, and wherein the depth mapping device generates the 3-dimensional point cloud of the surface by calculating a time of flight for a return of the pulses in the laser beam.

9. The laser depth sensing device of claim 8, wherein the at least one source of laser light is configured to stagger the pulses in the laser beam in adjacent lines of the pattern of scan lines to improve horizontal data density in the 3-dimensional point cloud of the surface.

10. The laser depth sensing device of claim 1, wherein the at least one laser light source comprises an infrared laser.

11. The laser depth sensing device of claim 10, wherein the at least one laser light source additionally comprises a red laser, a blue laser, and a green laser.

12. A scanning laser projector, comprising:
at least one source of laser light, the at least one source of laser light configured to generate a laser beam;
at least one scanning mirror configured to reflect the laser beam;
a depth mapping device configured to receive reflections of the laser beam from a surface and generate a 3-dimensional point cloud of the surface based at least in part on timing of the received reflections of the laser beam from the surface; and
a drive circuit configured to provide an excitation signal to excite motion of the at least one scanning mirror, the motion of the at least one scanning mirror configured to reflect the laser beam in a pattern of scan lines on the surface, the motion of the at least one scanning mirror having a horizontal scan rate, a horizontal scan amplitude, horizontal scan waveform shape, a vertical scan rate, a vertical scan amplitude, and a vertical scan waveform shape, and wherein the drive circuit is configured to operate in a first mode for projecting an image and in a second mode for generating the 3-dimensional point cloud, and wherein the drive circuit is further configured to adjust at least one the horizontal scan rate, the horizontal scan amplitude, the vertical scan rate, the vertical scan amplitude, and the vertical scan waveform shape when operating in the second mode.