U.S. patent application number 13/717413 was filed with the patent office on 2013-05-02 for projector systems with light beam alignment.
This patent application is currently assigned to INTERSIL AMERICAS INC.. The applicant listed for this patent is INTERSIL AMERICAS INC.. Invention is credited to Daryl Chamberlin, Dong Zheng.
Application Number | 20130107133 13/717413 |
Document ID | / |
Family ID | 44277373 |
Filed Date | 2013-05-02 |
United States Patent
Application |
20130107133 |
Kind Code |
A1 |
Chamberlin; Daryl ; et
al. |
May 2, 2013 |
PROJECTOR SYSTEMS WITH LIGHT BEAM ALIGNMENT
Abstract
Embodiments of the present invention generally relate to
circuits, systems and methods that can be used to detect light beam
misalignment, so that compensation for such misalignment can be
performed. In accordance with an embodiment, a circuit includes a
photo-detector (PD) having a plurality of electrically isolated PD
segments. Additionally, the circuit has circuitry, including
switches, configured to control how currents indicative of light
detected by the plurality of electrically isolated PD segments are
arithmetically combined. When the switches are in a first
configuration, a signal produced by the circuitry is indicative of
vertical light beam alignment. When the switches are in a second
configuration, the signal produced by the circuitry is indicative
of horizontal light beam alignment. The signals indicative of
vertical light beam alignment and horizontal light beam alignment
can be used detect light beam misalignment, so that compensation
for such misalignment can be performed.
Inventors: |
Chamberlin; Daryl; (San
Jose, CA) ; Zheng; Dong; (San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INTERSIL AMERICAS INC.; |
Milpitas |
CA |
US |
|
|
Assignee: |
INTERSIL AMERICAS INC.
Milpitas
CA
|
Family ID: |
44277373 |
Appl. No.: |
13/717413 |
Filed: |
December 17, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12868343 |
Aug 25, 2010 |
8357889 |
|
|
13717413 |
|
|
|
|
61296987 |
Jan 21, 2010 |
|
|
|
Current U.S.
Class: |
348/750 |
Current CPC
Class: |
G03B 21/14 20130101;
G03B 21/28 20130101; H04N 5/74 20130101; H04N 9/3129 20130101; H04N
9/3194 20130101 |
Class at
Publication: |
348/750 |
International
Class: |
H04N 5/74 20060101
H04N005/74 |
Claims
1. A projector system, comprising: a first light emitting element
that emits light of a first color; a second light emitting element
that emits light of a second color; a third light emitting element
that emits light of a third color; a controller configured to
produce first, second and third pixel data in dependence on a video
signal received from a video source; a driver configured to drive
the first, second and third light emitting elements in dependence
on the first, second and third pixel data produced by the
controller; one or more micro-mirror(s) that project an image in
dependence on light beams produced in dependence on the light of
the first, second and third colors emitted by the first, second and
third light emitting elements; and an opto-electronics circuit
including a plurality of electrically isolated photodetector (PD)
segments; and circuitry configured to control how currents
indicative of light detected by the plurality of electrically
isolated PD segments are arithmetically combined; wherein the
controller is also configured to detect vertical and/or horizontal
light beam misalignment(s) in dependence on signals produced by the
opto-electronics circuit, and compensate for detected vertical
and/or horizontal light beam misalignment(s); wherein each of the
plurality of electrically isolated PD segments produces a
corresponding current indicative an amount of light detected by the
PD segment; wherein the circuitry, configured to control how
currents indicative of light detected by the plurality of
electrically isolated PD segments are arithmetically combined,
comprises switches, trans-impedance amplifiers (TIAs), and summing
circuitry; wherein when the switches are in a first configuration,
a signal produced by the opto-electronics circuit is used by the
controller to detect vertical light beam misalignment; and wherein
when the switches are in a second configuration, a signal produced
by the opto-electronics circuit is used by the controller to detect
horizontal light beam misalignment.
2. (canceled)
3. The projector system of claim 1, wherein when the switches are
in a third configuration, a signal produced by the opto-electronics
circuit is used by the controller to perform at least one of
automatic power control (APC) or color calibration.
4. The projector system of claim 3, wherein the controller is
configured to compensate for a detected change in output power by
changing an amplitude and/or pulse width of one or more drive
signals produced by the driver to drive the light emitting
elements.
5. The projector system of claim 1, wherein: the first color is
red; the second color is green; the third color is blue; the first
pixel data is red pixel data; the second pixel data is green pixel
data; and the third pixel data is blue pixel data.
6. The projector system of claim 5, wherein the controller is
configured to compensate for detected vertical and/or horizontal
light beam misalignment(s) by adjusting timing of at least one of
the red pixel data, the green pixel data or the blue pixel
data.
7. The projector system of claim 1, wherein the controller is
configured to compensate for detected vertical and/or horizontal
light beam misalignment(s) by adjusting timing of at least one of
the first, second or third pixel data.
8. The projector system of claim 1, wherein: the plurality of
electrically isolated PD segments comprises four electrically
isolated PD segments; each of the four electrically isolated PD
segments produces a corresponding current indicative an amount of
light detected by the PD segment; the equation Y_Offset=(A+B)-(C+D)
is used to produce the signal indicative of vertical light beam
alignment for each of the light emitting elements; and the equation
X_Offset=(A+C)-(B+D) is used to produce the signal indicative of
horizontal light beam alignment for each of the light emitting
elements, where A is indicative of the current produced by a first
one of the four electrically isolated PD segments, B is indicative
of the current produced by a second one of the four electrically
isolated PD segments, C is indicative of the current produced by a
third one of the four electrically isolated PD segments, and D is
indicative of the current produced by a fourth one of the four
electrically isolated PD segments.
9. The projector system of claim 8, wherein the equation
Power=A+B+C+D is used to produce a signal indicative of light beam
power for each of the light emitting elements.
10. A projector system, comprising: a first light emitting element
that emits light of a first color; a second light emitting element
that emits light of a second color; a third light emitting element
that emits light of a third color; a controller configured to
produce first, second and third pixel data in dependence on a video
signal received from a video source; a driver configured to drive
the first, second and third light emitting elements in dependence
on the first, second and third pixel data produced by the
controller; one or more micro-mirror(s) that project an image in
dependence on light beams produced in dependence on the light of
the first, second and third colors emitted by the first, second and
third light emitting elements; and an opto-electronics circuit
including a plurality of electrically isolated photodetector (PD)
segments; and circuitry configured to control how currents
indicative of light detected by the plurality of electrically
isolated PD segments are arithmetically combined; wherein the
controller is configured to detect vertical and/or horizontal light
beam misalignment(s) in dependence on signals produced by the
opto-electronics circuit; the controller is configured to
compensate for detected vertical and/or horizontal light beam
misalignment(s); each of the plurality of electrically isolated PD
segments produces a corresponding current indicative an amount of
light detected by the PD segment; the circuitry, configured to
control how currents indicative of light detected by the plurality
of electrically isolated PD segments are arithmetically combined,
comprises switches, trans-impedance amplifiers (TIAs) and a current
mirror; when the switches are in a first configuration, the TIAs
and the current mirror are used to produce a signal that is
indicative of vertical light beam alignment; when the switches are
in a second configuration, the TIAs and the current mirror are used
to produce a signal that is indicative of horizontal light beam
alignment; and when the switches are in a third configuration, the
TIAs are used to produce a signal indicative of light beam
power.
11. A method for use with a projector system, comprising: receiving
a video signal; producing first, second and third pixel data in
dependence on the received video signal; driving first, second and
third light emitting elements, in dependence on the first, second
and third pixel data, to thereby emit light of first, second and
third colors; producing light beams of the first, second and third
colors in dependence on the emitted light of the first, second and
third colors; controlling one or more micro-mirror(s) to thereby
project an image in dependence on the light beams of the first
color, the second color and the third color; using a plurality of
electrically isolated photodetector (PD) segments to detect
portions of the light beams of the first color, the second color
and the third color, wherein each of the PD segments produces a
current indicative of light detected by the PD segment; for each of
the light beams of the first color, the second color and the third
color, arithmetically combining the currents indicative of light
detected by the plurality of electrically isolated PD segments in
at least two different manners; detecting vertical and/or
horizontal light beam misalignment(s) in dependence on results of
the arithmetically combining the currents; and compensating for
detected vertical and/or horizontal light beam misalignment(s);
wherein the arithmetically combining is performed using switches,
trans-impedance amplifiers (TIAs) and a current mirror, and
includes for each of the light beams of the first color, the second
color and the third color, configuring the switches in a first
configuration that causes the TIAs and the current mirror to
produce a signal that is indicative of vertical light beam
alignment; and for each of the light beams of the first color, the
second color and the third color, configuring the switches in a
second configuration that causes the TIAs and the current mirror to
produce a signal that is indicative of horizontal light beam
alignment.
12. (canceled)
13. The method of claim 11, further comprising: for each of the
light beams of the first color, the second color and the third
color, configuring the switches in a third configuration that
causes the TIAs to produce a signal indicative of light beam
power.
14. The method of claim 13, further comprising: performing
automatic power control (APC) in dependence on the signal
indicative of light beam power that is produced for each of the
light beams of the first color, the second color and the third
color.
15. The method of claim 14, wherein performing APC includes
compensating for a detected change in output power by changing an
amplitude and/or pulse width of one or more signals used for
driving the first, second and third light emitting elements.
16. The method of claim 14, further comprising: performing color
calibration in dependence on the signal indicative of light beam
power that is produced for each of the light beams of the first
color, the second color and the third color.
17. A method for use with a projector system, comprising: receiving
a video signal; producing first, second and third pixel data in
dependence on the received video signal; driving first, second and
third light emitting elements, in dependence on the first, second
and third pixel data, to thereby emit light of first, second and
third colors; producing light beams of the first, second and third
colors in dependence on the emitted light of the first, second and
third colors; controlling one or more micro-mirror(s) to thereby
project an image in dependence on the light beams of the first
color, the second color and the third color; using a plurality of
electrically isolated photodetector (PD) segments to detect
portions of the light beams of the first color, the second color
and the third color, wherein each of the PD segments produces a
current indicative of light detected by the PD segment; for each of
the light beams of the first color, the second color and the third
color, arithmetically combining the currents indicative of light
detected by the plurality of electrically isolated PD segments in
at least two different manners; detecting vertical and/or
horizontal light beam misalignment(s) in dependence on results of
the arithmetically combining the currents; and compensating for
detected vertical and/or horizontal light beam misalignment(s);
wherein the arithmetically combining is performed using switches,
trans-impedance amplifiers (TIAs) and a current mirror, and
includes for each of the light beams of the first color, the second
color and the third color, while the light beam is being scanned
vertically, configuring the switches in a first configuration that
causes the TIAs and the current mirror to produce a signal that is
indicative of vertical light beam alignment; and for each of the
light beams of the first color, the second color and the third
color, while the light beam is being scanned horizontally,
configuring the switches in a second configuration that causes the
TIAs and the current mirror to produce a signal that is indicative
of horizontal light beam alignment.
18. A projector system, comprising: a first light emitting element
that emits light of a first color; a second light emitting element
that emits light of a second color; a third light emitting element
that emits light of a third color; a controller configured to
produce first, second and third pixel data in dependence on a video
signal; a driver configured to drive the first, second and third
light emitting elements in dependence on the first, second and
third pixel data produced by the controller; one or more
micro-mirror(s) that project an image in dependence on light beams
produced in dependence on the light of the first, second and third
colors emitted by the first, second and third light emitting
elements; a plurality of electrically isolated photodetector (PD)
segments, each of which produces a corresponding current indicative
an amount of light detected by the PD segment; switches,
trans-impedance amplifiers (TIAs) and a current mirror that are
collectively configured to control how currents indicative of light
detected by the plurality of electrically isolated PD segments are
arithmetically combined; wherein when the switches are in a first
configuration, a signal indicative of vertical light beam
misalignment is produced; wherein when the switches are in a second
configuration, a signal indicative of horizontal light beam
misalignment is produced; and wherein the controller is also
configured to detect and compensate for vertical and/or horizontal
light beam misalignment(s) in dependence on the produced signals
indicative of vertical light beam misalignment and horizontal light
beam misalignment.
19. The projector system of claim 18, wherein: when the switches
are in a third configuration, a signal indicative of light beam
power is produced; and the controller is also configured to
performing automatic power control (APC) in dependence on the
produced signal indicative of light beam power.
20. The projector system of claim 19, wherein: the controller is
also configured to performing color calibration in dependence on
the produced signal indicative of light beam power.
Description
CLAIM OF PRIORITY
[0001] This application is a Divisional Application of U.S. patent
application Ser. No. 12/868,343, filed Aug. 25, 2010, which claims
priority under 35 U.S.C. 119(e) to U.S. Provisional Patent
Application No. 61/296,987, filed Jan. 21, 2010, both of which are
incorporated herein by reference.
BACKGROUND
[0002] FIG. 1 illustrates an exemplary miniature projector display
device 100, sometimes referred to as a picoprojector. The miniature
projector device 100 can be integrated with or attached to a
portable device, such as, but not limited to, a mobile phone, a
smart phone, a portable computer (e.g., a laptop or netbook), a
personal data assistant (PDA), or a portable media player (e.g.,
DVD player). The miniature projector device 100 can alternatively
be integrated with or attached to a non-portable device, such as a
desktop computer or a media player (e.g., a DVD player), but not
limited thereto. The miniature projector device 100 can
alternatively be a stand alone device.
[0003] Referring to FIG. 1, the projector display device 100 is
shown as including a video source 102, a controller 104 (e.g., an
application specific integrated circuit and/or a micro-controller),
a laser diode driver (LDD) 108 and a voltage regulator 110.
Depending on the type of video source, a video analog-font-end
(AFE) can be included between the video source and controller, and
the video AFE may include, e.g., one or more analog-to-digital
converters (ADCs). For example, if the input is a Video Graphics
Array (VGA) input, then a video AFE may be included. However, a
video AFE may not be needed where the video source is a digital
video source.
[0004] The controller 104 can perform scaling and/or pre-distortion
of video signals before such signals are provided to the LDD 108.
The voltage regulator 110 (e.g., a quad-output adjustable DC-DC
buck-boost regulator) can convert a voltage provided by a voltage
source (e.g., a battery or AC supply) into the various voltage
levels (e.g., four voltage levels V1, V2, V3 and V4) for powering
the various components of the projector display device 100.
[0005] The LDD 108 is shown as including three digital-to-analog
converts DACs 109.sub.1, 109.sub.2 and 109.sub.3 (which can be
collectively referred to as DACs 109). The LDD is also shown as
including a serial interface 122 which may receive, via a serial
bus 103, a serial enable (SEN) signal and a serial clock signal
(SClk) from a serial interface of the controller 104. Additionally,
a bi-directional serial data input/output (SDIO) line of the serial
bus 103 allows the controller 104 to write data to and read data
from registers within the LDD 108. Alternative serial buses and
interfaces can be used, such as, but not limited to, an
Inter-Integrated Circuit (I2C) or an Serial Peripheral Interface
(SPI) bus and interface. The LDD 108 also includes registers, and
the like, which are not shown.
[0006] The DACs 109 of the LDD 108 drive laser diodes 112, which
can include, e.g., a red, a green and a blue laser diode, but are
not limited thereto. Where the LDD 108 is used to drive a red (R),
a green (G) and a blue (B) laser diode, the LDD can be referred to
as a RGB triple laser diode driver.
[0007] The light produced by the laser diodes 112 can be provided
to beam splitters 114, which can direct a small percentage of the
light toward one or more calibration photo-detectors (PDs) 120, and
direct the remainder of the light toward projector optics 116,
which include lenses, mirrors, reflection plates and/or the like.
The light output by the optics 116 can be provided to one or more
micro mirror(s) 118. The mirror(s) 118 can be controlled by the
controller 104, or another portion of the system, to raster-scan
reflected light onto a surface, e.g., a screen, a wall, the back of
a chair, etc. Because of the scanning of laser beams performed
using the mirror(s) 118, the projector 100 can be referred to as a
laser based scanning projector 100. In one configuration, a single
mirror 118 that can be controlled in both the X and Y directions is
used for scanning of the laser beams. In another configuration, a
first mirror 118 is used for controlling horizontal scanning (i.e.,
scanning in the X direction), and a second mirror 118 is used for
controlling vertical scanning (i.e., scanning in the Y direction).
These are just two exemplary configurations, which are not meant to
be limiting. It is also possible that more than two mirrors 118 be
used.
[0008] In a laser based scanning projector, at each clock cycle,
the R, G, and B lasers diodes output a pixel intensity at a
location set by the linear speed of the scanning mirror(s) 118 and
a clock time base, as can be appreciated from the exemplary timing
diagram of FIG. 2A. In the exemplary timing diagram of FIG. 2A,
there are only 8 pixels per horizontal line, and there is no output
during each blanking period (B). However, it is noted that there
are typically many more pixels per line in a normal display. At
each clock cycle, each color data pixel intensity can be either
controlled using a pulse width modulation (PWM) scheme, where the
R, G and B lasers diodes are turned on for different durations, or
by amplitude modulation (AM), where the R, G and B laser diodes may
all be driven at the same time but with different current
levels.
[0009] Over time, a laser beam pointing direction might shift for
various reasons, which causes misalignment among pixel colors. This
is illustrated in timing diagram of FIG. 2B, which represents the
observed timing relative to the image being displayed (as opposed
to the timing of the data being sent from the controller 104 to the
LDD 108). FIG. 2B attempts to illustrate that the blue laser shifts
to the right hand side (RHS) by one pixel (or close to one pixel),
resulting in a color offset in the displayed image, which is
undesirable.
[0010] The laser beams produced by the R, G and B laser diodes can
be or become misaligned for various reasons. For example, there
will be some inherent misalignment that results from imperfect
mechanical manufacturing of a projector system. Further,
misalignment can occur due to mechanical modifications that occur
to a projector system, e.g., if the projector system is dropped.
Additionally, misalignment can also result from the thermal changes
to the laser diodes, as well as aging of the laser diodes.
SUMMARY
[0011] Embodiments of the present invention generally relate to
circuits, systems and methods that can be used to detect light beam
misalignment, so that compensation for such misalignment can be
performed. Such light beams are produced by light emitting
elements, such as, but not limited to, laser diodes or light
emitting diodes (LEDs). Where the light beams are produced by laser
diodes, the light beams can be referred to as laser beams.
[0012] In accordance with an embodiment, an opto-electronics
circuit includes a plurality of electrically isolated PD segments.
Additionally, the opto-electronics circuit has circuitry, including
switches, configured to control how currents indicative of light
detected by the plurality of electrically isolated PD segments are
arithmetically combined. When the switches are in a first
configuration, a signal produced by the opto-electronics circuit is
indicative of vertical light beam alignment. When the switches are
in a second configuration, a signal produced by the
opto-electronics circuit is indicative of horizontal light beam
alignment. When the switches are in a third configuration, a signal
produced by the opto-electronics circuit is indicative of light
beam power. The circuitry, configured to control how the currents
are arithmetically combined, can also include trans-impedance
amplifiers (TIAs) and summing circuitry. In a specific embodiment,
only two TIAs are required, reducing the power and complexity of
the opto-electronics circuit.
[0013] In accordance with an embodiment, the plurality of
electrically isolated PD segments includes four electrically
isolated PD segments. Each of the four electrically isolated PD
segments produces a corresponding current indicative an amount of
light detected by the PD segment.
[0014] In accordance with an embodiment, the equation
Y_Offset=(A+B)-(C+D) is used to produce the signal indicative of
vertical light beam alignment, where A is indicative of the current
produced by a first one of the four electrically isolated PD
segments, B is indicative of the current produced by a second one
of the four electrically isolated PD segments, C is indicative of
the current produced by a third one of the four electrically
isolated PD segments, and D is indicative of the current produced
by a fourth one of the four electrically isolated PD segments. In
accordance with an embodiment, the equation X_Offset=(A+C)-(B+D) is
used to produce the signal indicative of horizontal light beam
alignment. Additionally, the equation Power=A+B+C+D can be used to
determine a measure of power of a light beam, which can be used,
e.g., for automatic power control (APC) and/or color
calibration.
[0015] In dependence on the signals indicative of vertical light
beam alignment and the signals indicative of horizontal light beam
alignment, a controller can detect when one of the light beams
produced by the light emitting elements is misaligned relative to
the other light beams produced by the other light emitting
elements. Additionally, the controller can compensate for the
detected misalignment by controlling timing of color data that is
used to produced the signals that drive the light emitting
elements. In dependence on the signals indicative of light beam
power, the controller can detect when an output power of one or
more light beams produced by one or more of the light emitting
elements changes. Additionally, the controller can compensate for
the detected change in output power by changing an amplitude and/or
pulse width of one or more signals that drive the light emitting
elements.
[0016] Embodiments of the present invention are also directed to
projector systems that include the opto-electronics circuit
described above. Such a projector system can also include, e.g., a
first laser diode that emits light of a first color, a second laser
diode that emits light of a second color, and a third laser diode
that emits light of a third color. Additionally, the projector
system can also included a controller, a laser diode driver (LDD),
and one or more micro-mirror(s). The controller can be configured
to output first, second and third pixel data in dependence on a
video signal received from a video source. The LDD can be
configured to drive the first, second and third laser diodes in
dependence on the first, second and third pixel data received from
the controller. The one or more micro-mirror(s) can be controlled
by the controller and can be configured to project an image in
dependence on laser beams produced by the first, second and third
laser diodes. Additionally, the controller can be configured to
detect vertical and/or horizontal laser beam misalignment(s) in
dependence on signals produced by the opto-electronics circuit, as
well as to compensate for detected vertical and/or horizontal laser
beam misalignment(s) so that laser beam misalignment(s) do not
adversely affect the image projected by the one or more
micro-mirror(s).
[0017] This summary is not intended to summarize all of the
embodiments of the present invention. Further and alternative
embodiments, and the features, aspects, and advantages of the
embodiments of invention will become more apparent from the
detailed description set forth below, the drawings and the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 illustrates an exemplary miniature projector display
device, sometimes referred to as a picoprojector.
[0019] FIG. 2A illustrates an exemplary timing diagram for a laser
based scanning projector, wherein at each clock cycle, red, green
and blue lasers diodes output a pixel intensity at a location set
by the linear speed of the scanning mirror(s) and a clock time
base.
[0020] FIG. 2B is an exemplary timing diagram that is used to show
a shift in laser beam pointing direction, which causes misalignment
among pixel colors.
[0021] FIG. 2C illustrates exemplary signals indicative of the
horizontal laser beam alignment produced in accordance with an
embodiment of the present invention.
[0022] FIG. 3 illustrates an opto-electronics integrated circuit
(OEIC), according to an embodiment of the present invention, which
is used to monitor alignment of the red, green and blue laser
beams, which enables laser beam re-alignment to be performed when
necessary.
[0023] FIG. 4A illustrates details of the OEIC introduced in FIG.
3, according to an embodiment of the present invention, wherein the
OEIC includes a photodetector (PD) having four electrically
isolated PD segments and four transimpedance amplifiers (TIAs).
[0024] FIG. 4B shows an alternative embodiment of the OEIC, that
reduces power and complexity by using only 2 TIAs.
[0025] FIG. 5 is a high level flow diagram that is used to
summarize methods in accordance with embodiments of the present
invention.
DETAILED DESCRIPTION
[0026] Various reason for laser beam (and more generally, light
beam) misalignment were described above. Embodiments of the present
invention described herein can be used to detect and compensate for
all of the above causes for misalignment.
[0027] An exemplary laser beam misalignment was described above
with reference to the timing diagram of FIG. 2B, which represents
the observed timing relative to the image being displayed (as
opposed to the timing of the data being sent from the controller
104 to the LDD 108). More specifically, FIG. 2B attempts to
illustrate that the blue laser shifted to the right hand side (RHS)
by one pixel (or close to one pixel), resulting in a color offset
in the displayed image. This can also be appreciated from FIG. 2C,
which shows exemplary signals indicative of the horizontal laser
beam alignment for each of the red, green and blue laser diodes,
e.g., using the equation X_Offset=(A+C)-(B+D), which equation, and
other equations, are explained in more detail below.
[0028] Referring to FIG. 3, in accordance with an embodiment of the
present invention, an opto-electronics integrated circuit (OEIC)
330 is used to monitor alignment of the red, green and blue laser
beams, which enables laser beam re-alignment to be performed when
necessary (such laser beam re-alignment can also be referred to as
compensation for laser beam misalignment). Referring to FIG. 4A, in
accordance with a specific embodiment, the OEIC 330 includes a
photodetector (PD) 402 that includes four electrically isolated PD
segments (referred to and shown as segments A, B, C and D). Still
referring to FIG. 4A, the four PD segments are arranged in two rows
and two columns, such that the PD segments are generally arranged
in a checkerboard manner. Due to its four segments, the PD 402 can
be referred to herein as a quad PD 402. The quad PD 402 can be
positioned relative to the mirror(s) 118 (e.g., at the end of a
scan line), and/or addition optics and/or beam splitters can be
used so that laser beams are incident on the quad PD when alignment
(and/or automatic power control) is being performed, which is
discussed in more detail below. Regardless of where the quad PD 402
(and more generally, the OEIC 330) is located, it should not
adversely affect the image being projected.
[0029] In accordance with an embodiment, the size of each segment
of the quad PD 402 is slightly larger than the size of the laser
beam that is being aligned using the quad PD 402. For example, each
of the four segments of the quad PD can be approximately
350.times.350 micrometers (.mu.m), and the diameter of the laser
beam can be approximately 300 .mu.m. The gap between the adjacent
PD segments can be, e.g., 10 .mu.m. Exemplary shapes of each PD
segment are shown in FIG. 4A, but alternative shapes are possible
and within the scope of the present invention. For example, each
segment can be shaped like a square, a rectangle, or a quarter of a
circle, but is not limited thereto.
[0030] By placing the quad PD 402 at an appropriate location
relative to the laser beams being scanned (e.g., such that the quad
PD 402 detects beams projected near a center of the projector
output), currents generated by the four PD segments (which can be
referred to as currents A, B, C and D) can be combined in various
manners to monitor the vertical and horizontal alignment of the R,
G and B laser beams generated by the laser diodes 112. Such
currents can also be used to monitor the power of each of the R, G
and B laser beams, and thus, the quad PD 402 can also be used for
automatic power control (APC). APC can be used to control the
intensity output of the laser diodes to compensate for changes in
characteristics of the laser diodes, e.g., due to environmental
(e.g., thermal) variations and/or aging of the laser diodes
112.
[0031] Referring to FIG. 4A, in accordance with an embodiment, to
determine a vertical offset of a laser beam (also referred to as
the Y_Offset), the following equation can be used:
Y_Offset=(A+B)-(C+D) {Equation 1}.
[0032] Still referring to FIG. 4A, in accordance with an
embodiment, to determine a horizontal offset of a laser beam (also
referred to as the X_Offset), the following equation can be
used:
X_Offset=(A+C)-(B+D) {Equation 2}.
[0033] Additionally, in accordance with an embodiment, to determine
the power of a laser beam for use with automatic power control
(APC) and color calibration, the following equation can be
used:
Power=A+B+C+D {Equation 3}.
[0034] Such power measurements can be used to ensure that the power
of the laser beams produced by each of the laser diodes (or more
generally, the power of the light beams produced by each of the
light emitting elements) can be consistently maintained at desired
levels. This enables there to always be a known ratio between the
red, blue and green color intensities, to provide for proper color
calibration (the color calibration can include white balancing and
gamma correction, but is not limited thereto). Additionally, this
enables the power of each of the light beams to remain the same
over time to provide for consistent operation as output power of a
light emitting element changes due to changes in temperature and/or
degrades over time due to long term drift (e.g., due to aging).
[0035] In these equations: A is a current indicative of the
intensity of the light detected by PD segment A; B is a current
indicative of the intensity of the light detected by PD segment B;
C is a current indicative of the intensity of the light detected by
PD segment C; and D is a current indicative of the intensity of the
light detected by PD segment D. Such currents may be amplified
prior to or after being combined, but their intensities relative to
one another should remain the same.
[0036] Each of the four electrically isolated PD segments produces
a corresponding current indicative an amount of light detected by
the PD segment. In FIG. 4A the current produced by each PD segment
is provided to a corresponding transimpedance amplifier (TIA),
which provides amplification and coverts the current produced by
each PD section to a corresponding voltage. At the output of each
TIA is a resistor (R) which converts the voltage at the output of
the TIA back to a current. More specifically, TIA_1 converts the
current produced by PD segment A to a voltage, and resistor R1
converts the voltage at the output of TIA_1 back to a current;
TIA_2 converts the current produced by PD segment B to a voltage,
and resistor R2 converts the voltage at the output of TIA_2 back to
a current; TIA_3 converts the current produced by PD segment D to a
voltage, and resistor R3 converts the voltage at the output of
TIA_3 back to a current; and TIA_4 converts the current produced by
PD segment C to a voltage, and resistor R4 converts the voltage at
the output of TIA_4 back to a current.
[0037] The OEIC 330 also includes current a summing stage 410
(e.g., implemented using current mirrors and summing nodes), a gain
stage 412 (which can be adjustable) and an output driver 414. The
summing stage 410 (also referred to as summing circuitry) can
perform subtraction, depending on how it is implemented, as can be
appreciated from FIG. 4A (and FIG. 4B discussed below). The gain
stage 412 can increase the amplitude of the current resulting from
the summing stage 410 before the current is provided to the output
driver 414. The voltage output (vout) of the output driver 414,
which can be single ended or differential, can be provided to the
controller 104 (see FIG. 3). The switches S1 through S6 can be
controlled by an OEIC controller 422 so that the output of the OEIC
is selectively a voltage indicative of: (A+B)-(C+D); (A+C)-(B+D);
or A+B+C+D. For example, assuming a "0" is used to represent an
open switch, and a "1" is used to represent a closed switch, then
the following functions can be implemented by the OEIC controller
422:
[0038] to achieve (A+B)-(C+D): S1=1, S2=1, S3=1, S4=0, S5=0,
S6=0;
[0039] to achieve (A+C)-(B+D): S1=0, S2=0, S3=1, S4=1, S5=1, S6=0;
and
[0040] to achieve (A+B+C+D): S1=1, S2=1, S3=0, S4=0, S5=0,
S6=1.
[0041] The voltage signal(s) output by the output driver 414 can be
provided directly back to the controller 104 (in FIG. 3), or first
converted from analog to digital by an analog-to-digital converter
(ADC). Such an ADC can be part of the OEIC 330, or external the
OEIC 330. The OEIC controller 422 can be, e.g., an application
specific integrated circuit, a micro-controller, a decoder or a
state machine, but is not limited thereto.
[0042] FIG. 4B shows an alternative embodiment that reduces power
and complexity of the OEIC by using only 2 TIAs (instead of 4). In
a similar manner as in FIG. 4A, the switches 51 through S6 are
controlled by the OEIC controller 422 so that the output of the
OEIC is selectively a voltage indicative of: (A+B)-(C+D);
(A+C)-(B+D); or A+B+C+D. Again, assuming a "0" is used to represent
an open switch, and a "1" is used to represent a closed switch,
then the following functions can be implemented by the OEIC
controller 422:
[0043] to achieve (A+B)-(C+D): S1=0, S2=1, S3=1, S4=0, S5=0,
S6=1;
[0044] to achieve (A+C)-(B+D): S1=1, S2=0, S3=0, S4=1, S5=0, S6=1;
and
[0045] to achieve (A+B+C+D): S1=0, S2=1, S3=1, S4=0, S5=1,
S6=0.
[0046] FIG. 4B also shows that buffers 420 can be used to isolate
that TIAs from portion(s) of the current summing stage 410 (e.g.,
implemented using a current mirror). In an embodiment, the
controller 104 (in FIG. 3) can perform the functions of the OEIC
controller 422, eliminating the need for the separate OEIC
controller 422. In other embodiments, the controller 104 (in FIG.
3) communicates with the OEIC controller 422.
[0047] When performing laser beam alignment, both vertical
alignment and horizontal alignment can be performed. For horizontal
alignment, Equation 1 (i.e., Y_Offset=(A+B)-(C+D)) can be used. For
vertical alignment, Equation 2 (i.e., X_Offset=(A+C)-(B+D)) can be
used. In accordance with an embodiment, the laser beam alignment
can be performed during initialization of the projector system,
e.g., each time the projector system is turned from off to on, or
more frequently if desired. For vertical alignment each laser beam
is scanned vertically using the mirror(s) 118 (while the other
laser beams are turned off) so that the beam vertically crosses the
center of the quad PD 402. For horizontal alignment each laser beam
is scanned horizontally using the mirror(s) 118 (while the other
laser beams are turned off) so that the beam horizontally crosses
the center of the quad PD 402. The controller 104 records the
location and/or timing data indicative of when the laser beam
crosses the center of the quad PD 402, which is when there is a
zero crossing resulting from the equation (A+B)-(C+D) for vertical
alignment, and when there is a zero crossing resulting from the
equation (A+C)-(B+D) for horizontal alignment. Based on the signals
received from the OEIC 330, the controller 104 can recognize when a
laser beam is misaligned relative to the other laser beams, and the
controller 104 can control when it outputs specific color pixel
data signals to compensate for the laser misalignment. For example,
referring to the exemplary signals in FIG. 2C, illustrative of
(A+C)-(B+D), the controller 104 can recognize that the blue laser
beam is horizontally misaligned relative to the red and green laser
beams, and the controller 104 can output blue signal one horizontal
scan clock cycle earlier, to compensate for the blue laser beam
horizontal misalignment. Vertical misalignment can be compensated
for in a similar manner. For example, if the controller 104
recognizes that the blue laser beam is vertically misaligned
relative to the red and green laser beam, the controller 104 can
output the blue signal one vertical scan clock cycle early or
late.
[0048] Embodiments of the present invention can be used to detect
laser beam misalignment (and compensate for such) as often as
desired. For example, a system can be designed such that laser beam
misalignment is only checked for relatively infrequently, e.g.,
upon power up of a projector system, as mentioned above. For
another example, a system can be designed such that laser beam
misalignment is checked for more frequently, e.g., once per scan
line, once per frame, or once per period of time (e.g., once every
5 minutes), but is not limited thereto.
[0049] As mentioned above, Equation 3 (i.e., A+B+C+D) can be used
for automatic power control (APC), to calibrate for changes in
efficiency of laser diodes due to changing in temperature, aging,
etc. Such use of the OEIC 330 in this manner can negate the need
for the separate calibration PD 120 shown in FIG. 3.
[0050] While the laser diodes described herein were described as
being red, green and blue in color, it is within the scope of the
present invention that the laser diodes emit light of colors other
than red, green and blue, such as, but not limited to, cyan,
magenta and yellow. It is also within the scope of the present
invention that more three colors are produced per pixel by the
laser diodes, e.g., red, green, blue and yellow (e.g., if four
laser diodes are used, the LDD 108 could include four DACs).
[0051] While the OEIC 330 and its quad PD 402 were described as
being used to detect and compensate for laser beam misalignment,
the OEIC 330 and its quad PD 402 can alternatively be used to
detect and compensate for misalignment of light beams produced by
other types of light emitting element, including, but not limited
to, light emitting diodes (LEDs). As the term light beam is used
herein, it can be a beam produced by a laser diode (i.e., a laser
beam), a beam produced by an LED, or a beam produced by some other
light emitting element.
[0052] In the above discussion of FIGS. 4A and 4B, it was noted
that the size of each PD segment of the quad PD 402 should be
slightly larger than the size of the laser beam that is being
aligned using the quad PD 402. LEDs produce light beams that are
less focused, and thus, larger than light beams produced by laser
diodes. Accordingly, where the quad PD 402 is to be used with LEDs
(or other light emitting elements), the PD segments should be sized
accordingly. For example, each PD segment size would likely need to
be increased if LEDs were used instead of laser diodes.
[0053] FIG. 5 will now be used to summarize methods in accordance
with embodiments of the present invention. Such methods are for use
with light emitting elements, such as, but not limited to laser
diodes or LEDs, each of which produces a light beam when
driven.
[0054] As indicated at step 502, a light beam produced by one of a
plurality of light emitting elements is scanned vertically across a
photo-detector (PD), including a plurality of electrically isolated
PD segments, wherein each PD segment is used to detect light
produced by the light emitting element, and wherein each PD segment
produces a current indicative of light detected by the PD segment.
The quad PD 402, shown in FIGS. 4A and 4B, is an example of the PD
that can be used to perform step 502.
[0055] As indicated at step 504, the currents produced by the
plurality of PD segments are combined in a first manner, e.g.,
using Equation 1, to produce a signal indicative of vertical light
beam alignment.
[0056] As indicated by step 506, steps 502 and 504 are repeated for
each of a plurality of light beams, to thereby produce the signal
indicative of vertical light beam alignment for each of the light
emitting elements (e.g., each of a red, green and blue laser
diode).
[0057] Referring now to step 512, a light beam produced by one of
the plurality of light emitting elements is scanned horizontally
across the same photo-detector (PD) including the plurality of
electrically isolated PD segments, wherein each PD segment is used
to detect light produced by the light emitting element, and wherein
each PD segment produces a current indicative of light detected by
the PD segment. As indicated at step 514, the currents produced by
the plurality of PD segments are combined in a second manner, e.g.,
using Equation 2, to produce a signal indicative of horizontal
light beam alignment. FIG. 2C illustrates examples of signals
indicative of horizontal light beam alignment for each of a red,
green and blue laser diode.
[0058] At step 522 the currents are optionally combined in a third
manner, e.g., using Equation 3, to produce a signal indicative of
power of the light beam produced by the light emitting element.
[0059] As indicated by step 526, steps 512 and 514 (and optionally
522) are repeated for each of the plurality of light beams, to
thereby produce the signal indicative of horizontal light beam
alignment for each of the light emitting elements (e.g., each of a
red, green and blue laser diode), and optionally to also produce
the signal indicative of power for each of the light emitting
elements. As described above, the power measurements can be used
for APC and/or color calibration, but is not limited thereto.
[0060] At step 532, vertical light beam misalignment and/or
horizontal light beam misalignment can be detected, if such
misalignment exists. More specifically, the signals indicative of
vertical light beam alignment can be used to detect vertical light
beam misalignment, and the signals indicative of horizontal light
beam alignment can be used to detect horizontal light beam
misalignment (e.g., as described above with reference to FIG.
2C).
[0061] At step 534, if vertical light beam misalignment and/or
horizontal light beam misalignment is detected, compensation for
such misalignment is performed by controlling the timing of color
data. An example of this was described above.
[0062] The various steps of FIG. 5 can be performed in a different
order than shown, while still being within the scope of the present
invention. For example, the light beam produced by one of the light
emitting elements can be scanned both vertically and horizontally,
to thereby produce both the signal indicative of vertical light
beam alignment and the signal indicative of horizontal light beam
alignment, before doing the same for the other light emitting
elements. It is also possible that optional step 522 be performed
between steps 502 and 504, between steps 504 and 506, or between
steps 512 and 514. Further, horizontal light beam alignment may be
determined prior to vertical light beam alignment (e.g., steps 512
and 514 can be performed prior to steps 502 and 504). These are
just a few examples of how the order of the steps can be changed.
One of ordinary skill in the art reading this description would
realize that other variations are possible and within the scope of
the present invention. An additional step can include detecting, in
dependence on the signals indicative of light beam power produced
at step 522, when an output power of one or more light beams
produced by one or more of the light emitting elements changes.
Further, the detected change in output power can be compensated for
by changing an amplitude and/or pulse width of one or more signals
that drive the light emitting elements.
[0063] The foregoing description is of the preferred embodiments of
the present invention. These embodiments have been provided for the
purposes of illustration and description, but are not intended to
be exhaustive or to limit the invention to the precise forms
disclosed. Many modifications and variations will be apparent to a
practitioner skilled in the art.
[0064] Embodiments were chosen and described in order to best
describe the principles of the invention and its practical
application, thereby enabling others skilled in the art to
understand the invention. Slight modifications and variations are
believed to be within the spirit and scope of the present
invention. It is intended that the scope of the invention be
defined by the following claims and their equivalents.
* * * * *