Hardware manual

US 7,915,570 B2
9
FIG. 5B). The one or more image buffers 722 may be a part of
an FPGA/processing unit 206. The data from the image buff
ers may then be used by a separate processor, such as the
processor 212 of FIG. SE, to perform an algorithm/image
processing/machine vision application.
In some embodiments, the processing unit 206 may include
an exposure generation unit 710 that is operable to generate
an exposure generation signal 750. The exposure generation
unit 710 may generate the exposure generation signal 750 in
response to an external or internal trigger input 758 (such as
a digital input or crossing of an analog threshold), as well as
from a software generated event. The trigger input 758 may
immediately trigger an exposure generation signal 750 or a
strobe generation signal 752, or there may be a built-in delay
prior to the exposure signal and/or the strobe generation sig
nal 752.
A light strobe control generation unit 712 may receive the
exposure generation signal 750 and generate a strobe genera
tion signal 752. In some embodiments, the light strobe control
generation unit 712 may directly receive the trigger signal
758 instead of receiving the exposure generation signal 750.
The light strobe control generation unit 712 may generate the
strobe generation signal 752 to turn on the one or more light
sources 606 for the exposure time of the camera (e.g., the
imager 282). Since it is desirable for the light (e.g., from the
one or more light sources 606) to be at full brightness before
the exposure starts, the strobe generation signal 752 may
slightly precede the actual exposure.
The strobe generation signal 752 may start activation of an
active circuit 708. The active circuit may be operable to
almost instantaneously activate the switching power supply
718 (which may be a part of the active circuit) and supply a
control and power pulse (i.e., a current pulse) 770 to the one
or more light sources 606. As mentioned above, the lighting
current controller 290 offers the advantage of minimiZing
power and current usage, and thus may provide suf?cient
power to the one or more light sources 606 without using any
additional external power supplies and with suf?ciently low
heat dissipation.
In some embodiments, the active circuit 708 may contain a
control loop compensation network 730 that, in conjunction
with the power supply 718, is able to almost instantaneously
create the current pulse. The control loop compensation net
work 730 may be necessary to supply control values to the
switching power supply 718. In some embodiments the con
trol loop compensation network may supply the control val
ues directly to the switching power supply 718.
The active circuit 708 may receive a pulse width modulated
(PWM) signal 756 from a light current setpoint generation
unit 720, which may be included in the processing unit/FPGA
206, or it may be a separate element from the processing unit.
The PWM signal 756 may be ?ltered and eventually trans
mitted to the power supply 718. Since the power supply 718
may be a switching power supply, it may use the PWM signal
to control how much current to supply (as a percentage of full
scale). Thus, the ?ltered PWM signal (see FIGS. 7A-B) may
be received by the power supply 718, which then generates
the current pulse 770 as indicated. The PWM signal may be
generated from the processing unit 206, and thus may be
user/ application programmable to a desired output current.
In some embodiments, the compensation sample control
generation unit 714 may generate a compensation sample
signal 754 to indicate to the ADC in the microcontroller 716
when to sample the voltage in the compensation network 73 0.
This voltage may be the value that determines where the
control loop picks up the next time that the output (i.e., the
current signal 770) is turned on. Without the sample and hold
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circuit, this voltage may decay with time, and may cause an
incorrect current to be sent through the light source, which in
turn may cause a bad exposure and/or damage the light source
606.
Furthermore, this decay may result in an unwanted
delayia period of time when the power supply 718, while
turned on, would need to adjust its output (i.e., the current
signal 770) because of the lost charge. Thus the microcon
troller’ s 716 ADC may sample the voltage, such as instructed
by the FPGA 206 (e.g., using the sample control generation
signal 754). The PWM output of the microcontroller 716 may
be operable to continually refresh the value (i.e., one of the
control values of the control loop) until the next time that the
power supply 718 may need to turn on, such as when the next
strobe generation signal 752 arrives at the active circuit 708
from the processing unit 206.
One way to implement this is through a microcontroller
with integrated multichannel ADC and PWM DAC. The ADC
is used to sample these voltages when turning off the light, for
which the microcontroller is instructed to do so. The PWM
DAC may be used to create a replica of these voltages and
feed reactive components, such as loop capacitors, to keep
them charged at the desired level. Since this state is kept by
using active circuitry, the loop memory can be maintained for
an arbitrarily long time interval.
FIGS. 7A and 7BiBlock Diagrams of the Lighting current
controller
FIG. 7A illustrates some embodiments of the integrated
lighting current controller, and especially the control loop. It
should be noted that this embodiment is meant to be illustra
tive only, and is not intended to limit the architecture, com
ponents, or form of the lighting current controller.
The active circuit 708 may use a control loop, as mentioned
above, to properly regulate the switching power supply. How
ever, control loops may take signi?cant time to establish their
?nal control value after starting from their initial state; in
other words, when all the reactive components of the system
may be discharged. Adjustments to some of the one or more
control variables may occur faster because they represent a
smaller percent variation of the output signal. In some cases,
it may be necessary to have a memory of the state of the
control loop so it can be stopped and restarted without going
through the complete establishment time. In other words, the
values of the one or more control variables may need to be
acquired and stored for future use. The reactive components
of the system may need to be charged to a given energy to
remember the last control loop setting, so the control loop can
reach the ?nal value in the minimum amount of time possible
after an arbitrarily long idle time.
Lighting current controllers for a smart camera can be built
using switching power supplies, which may be used as an
implementation of a control loop. In some embodiments, a
switching supply with a single inductor buck-boost topology
can be used. In other embodiments, other topologies of
switching supplies may be used. In order to adjust the current
pulse 890 to one or more arbitrary values, the current value
may be programmed to a speci?c intensity level (usually by
setting the light current).
Alternatively the power supply can provide continuous
power to the light sources. Although this would solve any
settling time issues, this solution has drawbacks. Many light
sources may have the ability to be overdriven at a higher
strobing current level. The strobing current level may be
higher than a continuous current level, most likely making
strobing current levels incompatible with continuous current
levels. The use of a switching power supply (e.g., a current
regulator) facilitates overdriving of the one or more lighting