U.S. patent application number 14/477893 was filed with the patent office on 2015-03-12 for driving circuit of a laser diode and driving method of a laser diode.
The applicant listed for this patent is Etron Technology, Inc., TM Technology Inc.. Invention is credited to Jiann-Chyi Sam Shieh, Chih-Yang Wang, Ren-Bang Yeh.
Application Number | 20150071318 14/477893 |
Document ID | / |
Family ID | 52597871 |
Filed Date | 2015-03-12 |
United States Patent
Application |
20150071318 |
Kind Code |
A1 |
Yeh; Ren-Bang ; et
al. |
March 12, 2015 |
DRIVING CIRCUIT OF A LASER DIODE AND DRIVING METHOD OF A LASER
DIODE
Abstract
A driving method of a laser diode includes setting a bias
current, a modulation current, a first target corresponding to a
predetermined average power, and a second target corresponding to a
predetermined average modulation power; executing a first adjusting
current step group; generating a temporary modulation current
according to the modulation current; executing a second adjusting
current step group; and executing the first adjusting current step
group again.
Inventors: |
Yeh; Ren-Bang; (New Taipei
City, TW) ; Shieh; Jiann-Chyi Sam; (San Jose, CA)
; Wang; Chih-Yang; (Kaohsiung City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Etron Technology, Inc.
TM Technology Inc. |
Hsinchu
Hsinchu |
|
TW
TW |
|
|
Family ID: |
52597871 |
Appl. No.: |
14/477893 |
Filed: |
September 5, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61874369 |
Sep 6, 2013 |
|
|
|
Current U.S.
Class: |
372/38.02 |
Current CPC
Class: |
H01S 5/06812 20130101;
H01S 5/0427 20130101; H01S 5/06832 20130101 |
Class at
Publication: |
372/38.02 |
International
Class: |
H01S 5/06 20060101
H01S005/06 |
Claims
1. A driving method of a laser diode, the driving method
comprising: setting a bias current, a modulation current, a first
target corresponding to a predetermined average power, and a second
target corresponding to a predetermined average modulation power;
executing a first adjusting current step group, wherein the first
adjusting current step group comprises: driving a laser diode
according to the bias current and the modulation current;
generating a first monitor value corresponding to an average power
of the laser diode according to light emitted by the laser diode;
comparing the first monitor value with the first target; and
adjusting the bias current or maintaining the bias current
according to a first comparison result; generating a temporary
modulation current according to the modulation current; executing a
second adjusting current step group, wherein the second adjusting
current step group comprises: driving the laser diode according to
the bias current and the temporary modulation current; generating a
second monitor value corresponding to an average modulation power
of the laser diode according to the light emitted by the laser
diode; comparing the second monitor value with the second target;
and adjusting the modulation current or maintaining the modulation
current according to a second comparison result; and executing the
first adjusting current step group again.
2. The driving method of claim 1, wherein when the first comparison
result is the first monitor value greater than the first target,
the bias current is decreased.
3. The driving method of claim 1, wherein when the first comparison
result is the first monitor value less than the first target, the
bias current is increased.
4. The driving method of claim 1, wherein when the first comparison
result is the first monitor value equal to the first target, the
bias current is maintained.
5. The driving method of claim 1, wherein when the second
comparison result is the second monitor value greater than the
second target, the modulation current is decreased.
6. The driving method of claim 1, wherein when the second
comparison result is the second monitor value less than the second
target, the modulation current is increased.
7. The driving method of claim 1, wherein when the second
comparison result is the second monitor value equal to the second
target, the modulation current is maintained.
8. The driving method of claim 1, further comprising: driving the
laser diode according to the bias current, the modulation current,
and a first driving signal.
9. The driving method of claim 8, wherein the first driving signal
is a burst mode driving signal.
10. The driving method of claim 8, wherein the first driving signal
is a continuous mode driving signal.
11. The driving method of claim 1, further comprising: driving the
laser diode according to the bias current, the temporary modulation
current, and a second driving signal.
12. The driving method of claim 11, wherein the second driving
signal is a burst mode driving signal.
13. The driving method of claim 11, wherein the second driving
signal is a continuous mode driving signal.
14. The driving method of claim 1, wherein the temporary modulation
current is a sum of the modulation current and a product of the
modulation current and a predetermined value.
15. A driving method of a laser diode, the driving method
comprising: setting a bias current, a modulation current, a first
target corresponding to a predetermined average power, and a second
target corresponding to a predetermined average modulation power;
repeatedly executing a first adjusting current step group a first
predetermined times, wherein the first adjusting current step group
comprises: driving a laser diode according to the bias current and
the modulation current; generating a first monitor value
corresponding to an average power of the laser diode according to
light emitted by the laser diode; comparing the first monitor value
with the first target; and adjusting the bias current or
maintaining the bias current according to a first comparison
result; generating a temporary modulation current according to the
modulation current; repeatedly executing a second adjusting current
step group a second predetermined times, wherein the second
adjusting current step group comprises: driving the laser diode
according to the bias current and the temporary modulation current;
generating a second monitor value corresponding to an average
modulation power of the laser diode according to the light emitted
by the laser diode; comparing the second monitor value with the
second target; and adjusting the modulation current or maintaining
the modulation current according to a second comparison result; and
executing the first adjusting current step group again the first
predetermined times.
16. A driving circuit of a laser diode, the driving circuit
comprising: a driving unit driving a laser diode according to a
bias current, a modulation current, and a first driving signal, or
according to the bias current, a temporary modulation current, and
a second driving signal, or according to the bias current and the
modulation current, or according to the bias current and the
temporary modulation current; a monitor unit generating a first
monitor value corresponding to an average power of the laser diode
and a second monitor value corresponding to an average modulation
power of the laser diode according to light emitted by the laser
diode; a comparison unit comparing the first monitor value with a
first target corresponding to a predetermined average power to
generate a first comparison result, and comparing the second
monitor value with a second target corresponding to a predetermined
average modulation power to generate a second comparison result; a
first current generation module executing a first corresponding
operation on the bias current according to the first comparison
result; and a second current generation module generating the
temporary modulation current according to the modulation current,
and executing a second corresponding operation on the modulation
current according to the second comparison result.
17. The driving circuit of claim 16, wherein when the first
comparison result is the first monitor value greater than the first
target, the first current generation module decreases the bias
current; when the first comparison result is the first monitor
value less than the first target, the first current generation
module increases the bias current; and when the first comparison
result is the first monitor value equal to the first target, the
first current generation module maintains the bias current.
18. The driving circuit of claim 16, wherein when the second
comparison result is the second monitor value greater than the
second target, the second current generation module decreases the
modulation current; when the second comparison result is the second
monitor value less than the second target, the second current
generation module increases the modulation current; and when the
second comparison result is the second monitor value equal to the
second target, the second current generation module maintains the
modulation current.
19. The driving circuit of claim 16, wherein the first driving
signal and the second driving signal are burst mode driving
signals.
20. The driving circuit of claim 16, wherein the first driving
signal and the second driving signal are continuous mode driving
signals.
21. The driving circuit of claim 16, wherein the temporary
modulation current is a sum of the modulation current and a product
of the modulation current and a predetermined value.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/874,369, filed on Sep. 6, 2013 and entitled
"Dual Closed Loop," the contents of which are incorporated herein
by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a driving circuit of a
laser diode and a driving method of a laser diode, and particularly
to a driving circuit of a laser diode and a driving method of a
laser diode that have dual feedback loop for adjusting current to
make the laser diode maintain a fixed extinction ratio under
different operation temperatures.
[0004] 2. Description of the Prior Art
[0005] Please refer to FIG. 1. FIG. 1 is a diagram illustrating
relationships between output powers, input currents, and operation
temperatures of a laser diode. As shown in FIG. 1, if the operation
temperature of the laser diode is 25.degree. C., when the input
current is a bias current IBIAS1, the bias current IBIAS1 can make
the laser diode output an output power P0, and when the input
current is a sum of the bias current IBIAS1 and a modulation
current IMOD1, the sum of the bias current IBIAS1 and the
modulation current IMOD1 can make the laser diode output an output
power P1, wherein the output power P1 corresponds to a logic value
.left brkt-top.1.right brkt-bot. of a light signal and the output
power P0 corresponds to a logic value .left brkt-top.0.right
brkt-bot. of the light signal, and an average value of the output
power P0 and the output power P1 is an average power PAVE. If the
operation temperature of the laser diode is 85.degree. C., when the
input current is a bias current IBIAS2, the bias current IBIAS2 can
make the laser diode output the output power P0, and when the input
current is a sum of the bias current IBIAS2 and a modulation
current IMOD2, the sum of the bias current IBIAS2 and the
modulation current IMOD2 can make the laser diode output the output
power P1.
[0006] As shown in FIG. 1, because a slope of a characteristic
curve of the laser diode under the operation temperature
(25.degree. C.) is greater than the slope of the characteristic
curve of the laser diode under the operation temperature
(85.degree. C.), the bias current IBIAS2 needs to be greater than
the bias current IBIAS1 and the modulation current IMOD2 also needs
to be greater than the modulation current IMOD1 to maintain an
extinction ratio (P1/P0) of the laser diode. For solving the above
mentioned problem, the prior art adjusts the bias currents and the
modulation currents of the laser diode under different operation
temperatures according to a lookup table, wherein the lookup table
records relationships between the operation temperatures, the bias
currents and the modulation currents. Thus, the prior art may need
a large number of memories to store the lookup table, resulting in
cost being increased. In addition, another prior art provides a
single loop automatic power control to fix an average output power
of the laser diode. Although the single loop automatic power
control can fix the average output power of the laser diode, the
single loop automatic power control cannot make the extinction
ratio of the laser diode unchangeable. Therefore, the above
mentioned prior arts are not good choices for the laser diode when
the laser diode operates under different temperature.
SUMMARY OF THE INVENTION
[0007] An embodiment of the present invention provides a driving
method of a laser diode. The driving method includes setting a bias
current, a modulation current, a first target corresponding to a
predetermined average power, and a second target corresponding to a
predetermined average modulation power; executing a first adjusting
current step group, wherein the first adjusting current step group
includes driving a laser diode according to the bias current and
the modulation current; generating a first monitor value
corresponding to an average power of the laser diode according to
light emitted by the laser diode; comparing the first monitor value
with the first target; and adjusting the bias current or
maintaining the bias current according to a first comparison
result; generating a temporary modulation current according to the
modulation current; executing a second adjusting current step
group, wherein the second adjusting current step group includes
driving the laser diode according to the bias current and the
temporary modulation current; generating a second monitor value
corresponding to an average modulation power of the laser diode
according to the light emitted by the laser diode; comparing the
second monitor value with the second target; and adjusting the
modulation current or maintaining the modulation current according
to a second comparison result; and executing the first adjusting
current step group again.
[0008] Another embodiment of the present invention provides a
driving method of a laser diode. The driving method includes
setting a bias current, a modulation current, a first target
corresponding to a predetermined average power, and a second target
corresponding to a predetermined average modulation power;
repeatedly executing a first adjusting current step group a first
predetermined times, wherein the first adjusting current step group
includes driving a laser diode according to the bias current and
the modulation current; generating a first monitor value
corresponding to an average power of the laser diode according to
light emitted by the laser diode; comparing the first monitor value
with the first target; and adjusting the bias current or
maintaining the bias current according to a first comparison
result; generating a temporary modulation current according to the
modulation current; repeatedly executing a second adjusting current
step group a second predetermined times, wherein the second
adjusting current step group includes driving the laser diode
according to the bias current and the temporary modulation current;
generating a second monitor value corresponding to an average
modulation power of the laser diode according to the light emitted
by the laser diode; comparing the second monitor value with the
second target; and adjusting the modulation current or maintaining
the modulation current according to a second comparison result; and
executing the first adjusting current step group again the first
predetermined times.
[0009] Another embodiment of the present invention provides a
driving circuit of a laser diode. The driving circuit includes a
driving unit, a power generation unit, a comparison unit, a first
current generation module, and a second current generation module.
The driving unit is used for driving a laser diode according to a
bias current, a modulation current, and a first driving signal, or
according to the bias current, a temporary modulation current, and
a second driving signal, or according to the bias current and the
modulation current, or according to the bias current and the
temporary modulation current. The monitor unit is used for
generating a first monitor value corresponding to an average power
of the laser diode and a second monitor value corresponding to an
average modulation power of the laser diode according to light
emitted by the laser diode. The comparison unit is used for
comparing the first monitor value with a first target corresponding
to a predetermined average power to generate a first comparison
result, and comparing the second monitor value with a second target
corresponding to a predetermined average modulation power to
generate a second comparison result. The first current generation
module is used for executing a first corresponding operation on the
bias current according to the first comparison result. The second
current generation module is used for generating the temporary
modulation current according to the modulation current, and
executing a second corresponding operation on the modulation
current according to the second comparison result.
[0010] The present invention provides a driving circuit of a laser
diode and a driving method of a laser diode. The driving circuit
and the driving method utilize a first current generation module of
the driving circuit and an first target to adjust a bias current
driving the laser diode, and utilize a second current generation
module of the driving circuit and a second target to adjust a
modulation current driving the laser diode. Therefore, compared to
the prior art, the present invention has advantages as follows:
first, because the present invention has a feedback loop
corresponding to the first current generation module adjusting the
bias current and a feedback loop corresponding to the second
current generation module adjusting the modulation current, the
present invention does not need an additional memory; and second,
because the present invention has the feedback loop corresponding
to the first current generation module adjusting the bias current
and the feedback loop corresponding to the second current
generation module adjusting the modulation current, the present
invention can make the laser diode maintain a fixed extinction
ratio under different operation temperatures.
[0011] These and other objectives of the present invention will no
doubt become obvious to those of ordinary skill in the art after
reading the following detailed description of the preferred
embodiment that is illustrated in the various figures and
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a diagram illustrating relationships between
output powers, input currents, and operation temperatures of a
laser diode.
[0013] FIG. 2 is a diagram illustrating a driving circuit of a
laser diode according to a first embodiment.
[0014] FIG. 3A and FIG. 3B are flowcharts illustrating a driving
method of a laser diode according to a second embodiment.
[0015] FIG. 4 is a diagram illustrating the bias current, the
modulation current, the temporary modulation current, a first
monitor value, a second monitor value, and corresponding output
powers.
[0016] FIG. 5A and FIG. 5B are flowcharts illustrating a driving
method of a laser diode according to a third embodiment.
[0017] FIG. 6 is a diagram illustrating the bias current, the
modulation current, the temporary modulation current, a first
monitor value, a second monitor value, and the corresponding output
powers.
[0018] FIG. 7 is a diagram illustrating a driving circuit of a
laser diode according to a fourth embodiment.
DETAILED DESCRIPTION
[0019] Please refer to FIG. 2. FIG. 2 is a diagram illustrating a
driving circuit 200 of a laser diode according to a first
embodiment. As shown in FIG. 2, the driving circuit 200 includes a
driving unit 202, a monitor unit 204, a comparison unit 206, a
first current generation module 208, and a second current
generation module 210. As shown in FIG. 2, the comparison unit 206
is coupled to the monitor unit 204, wherein the comparison unit 206
includes a first comparator 2062 and a second comparator 2064. The
first current generation module 208 is coupled between the first
comparator 2062 and the driving unit 202, wherein the first current
generation module 208 includes a first flip-flop 2082, a first
digital filter 2084, a first counter 2086, and a first
digital-to-analog converter 2088. The second current generation
module 210 is coupled between the second comparator 2064 and the
driving unit 202, wherein the second current generation module 210
includes a second flip-flop 2102, a second digital filter 2104, a
second counter 2106, a second digital-to-analog converter 2108, and
a temporary modulation current generator 2110, and the temporary
modulation current generator 2110 includes a multiplier 21102, an
adder 21104, and a switch 21106.
[0020] Please refer to FIGS. 2, 3A, 3B, 4. FIG. 3A and FIG. 3B are
flowcharts illustrating a driving method of a laser diode according
to a second embodiment, and FIG. 4 is a diagram illustrating the
bias current, the modulation current, the temporary modulation
current, a first monitor value, a second monitor value, and output
powers. The method in FIG. 3A and FIG. 3B is illustrated using the
driving circuit 200 in FIG. 2. Detailed steps are as follows:
[0021] Step 300: Start.
[0022] Step 302: A user sets a bias current IB, a modulation
current IM, a first target PAVT corresponding to a predetermined
average power, and a second target PMT corresponding to a
predetermined average modulation power.
[0023] Step 304: The driving unit 202 drives a laser diode 214
according to the bias current IB and the modulation current IM.
[0024] Step 306: The monitor unit 204 generates a first monitor
value PAV corresponding to an average power of the laser diode 214
when the laser diode 214 is driven by the bias current IB and the
modulation current IM according to light emitted by the laser diode
214.
[0025] Step 308: The first comparator 2062 of the comparison unit
206 compares the first monitor value PAV with the first target PAVT
to generate a first comparison result.
[0026] Step 310: The first current generation module 208 executes a
first corresponding operation on the bias current IB according to
the first comparison result.
[0027] Step 312: The temporary modulation current generator 2110 of
the second current generation module 210 generates a temporary
modulation current IMT according to the modulation current IM.
[0028] Step 314: The driving unit 202 drives the laser diode 214
according to the bias current IB and the temporary modulation
current IMT.
[0029] Step 316: The monitor unit 204 generates a second monitor
value PMV corresponding to an average modulation power of the laser
diode 214 when the laser diode 214 is driven by the bias current IB
and the temporary modulation current IMT according to the light
emitted by the laser diode 214.
[0030] Step 318: The second comparator 2064 of the comparison unit
206 compares the second monitor value PMV with the second target
PMT to generate a second comparison result.
[0031] Step 320: The second current generation module 210 executes
a second corresponding operation on the modulation current IM
according to the second comparison result, go to Step 304.
[0032] As shown in FIGS. 2, 4, in Step 302, the user can first set
an initial value (e.g. 3 mA) of the bias current IB, an initial
value (e.g. 5 mA) of the modulation current IM, an initial value of
the first target PAVT corresponding to the predetermined average
power (e.g. 9 mW), and an initial value of the second target PMT
corresponding to the predetermined average modulation power (e.g.
9.6 mW). As shown in FIGS. 2, 4, in Step 304, during a period T1,
the driving unit 202 drives the laser diode 214 according to the
bias current IB (e.g. 3 mA) and the modulation current IM (e.g. 5
mA). But, in another embodiment of the present invention, the
driving unit 202 drives the laser diode 214 according to the bias
current IB (e.g. 3 mA), the modulation current IM (e.g. 5 mA), and
a first driving signal A0, wherein the first driving signal A0 is a
burst mode driving signal. But, the present invention is not
limited to the first driving signal A0 being a burst mode driving
signal, that is, the first driving signal A0 can also be a
continuous mode driving signal. In addition, as shown in FIG. 4,
when the driving unit 202 drives the laser diode 214 according to
the bias current IB (e.g. 3 mA) and the modulation current IM (e.g.
5 mA), the laser diode 214 can emit an output power P1 (e.g. 8 mW)
and an output power P0 (e.g. 3 mW). As shown in FIGS. 2, 4, in Step
306, the monitor unit 204 can generate the first monitor value PAV
(wherein the first monitor value PAV can be a current value or a
voltage value) according to the light emitted by the laser diode
214, wherein the first monitor value PAV corresponds to the average
power (e.g. 5.5 mW) of the laser diode 214 when the laser diode 214
is driven by the bias current IB and the modulation current IM. In
Step 308, the first comparator 2062 of the comparison unit 206
compares the first monitor value PAV (corresponding to the average
power (e.g. 5.5 mW)) with the first target PAVT (corresponding to
power 9 mW) to generate the first comparison result (that is, the
first monitor value PAV is less than the first target PAVT). In
addition, as shown in FIG. 2, the second comparator 2064 of the
comparison unit 206 can also compare the first monitor value PAV
with the second target PMT in fact. But, because clocks CLKB, CLKB'
are disabled, the second comparison result outputted by the second
comparator 2064 is neglected. As shown in FIG. 4, in Step 310, when
clocks CLKA, CLKA' are enabled and the clocks CLKB, CLKB' are
disabled, the first comparison result generated by the first
comparator 2062 can pass the first flip-flop 2082 and be filtered
by the first digital filter 2084, wherein the first flip-flop 2082
is used for storing the first comparison result generated by the
first comparator 2062. Because the first monitor value PAV is less
than the first target PAVT, an output generated by the first
digital filter 2084 can make the first counter 2086 count upward.
Because the first counter 2086 counts upward, the first
digital-to-analog converter 2088 increases the bias current IB
(e.g. 3 mA) to generate a new bias current IB (e.g. 4 mA). In Step
312, when the first digital-to-analog converter 2088 generates the
bias current IB (e.g. 4 mA), the switch 21106 of the temporary
modulation current generator 2110 is turned on, so the temporary
modulation current generator 2110 can utilize the multiplier 21102
and the adder 21104 to generate the temporary modulation current
IMT according to the modulation current IM (e.g. 5 mA), wherein the
temporary modulation current IMT is a sum of the modulation current
IM (e.g. 5 mA) and a product of the modulation current IM (e.g. 5
mA) and a predetermined value (e.g. 0.2), that is, the temporary
modulation current IMT is 5+0.2.times.5=6 mA.
[0033] As shown in FIGS. 2, 4, in Step 314, during a period T2, the
driving unit 202 drives the laser diode 214 according to the bias
current IB (e.g. 4 mA) and the temporary modulation current IMT
(e.g. 6 mA). But, in another embodiment of the present invention,
the driving unit 202 drives the laser diode 214 according to the
bias current IB (e.g. 4 mA), the temporary modulation current IM
(e.g. 6 mA), and a second driving signal B0, wherein the second
driving signal B0 is a burst mode driving signal. But, the present
invention is not limited to the second driving signal B0 being a
burst mode driving signal, that is, the second driving signal B0
can also be a continuous mode driving signal. In addition, as shown
in FIG. 4, when the driving unit 202 drives the laser diode 214
according to the bias current IB (e.g. 4 mA) and the temporary
modulation current IMT (e.g. 6 mA), the laser diode 214 can emit
the output power P1 (e.g. 10 mW) and the output power P0 (e.g. 4
mW). As shown in FIGS. 2, 4, in Step 316, the monitor unit 204 can
generate the second monitor value PMV (wherein the second monitor
value PMV can be a current value or a voltage value) according to
the light emitted by the laser diode 214, wherein the second
monitor value PMV corresponds to the average modulation power (e.g.
7 mW) of the laser diode 214 when the laser diode 214 is driven by
the bias current IB (e.g. 4 mA) and the temporary modulation
current IMT (e.g. 6 mA). In Step 318, the second comparator 2064 of
the comparison unit 206 compares the second monitor value PMV
(corresponding to the average modulation power (e.g. 7 mW)) with
the second target PMT (corresponding to power 9.6 mW) to generate
the second comparison result (that is, the second monitor value PMV
is less than the second target PMT). As shown in FIG. 4, in Step
320, when the clocks CLKA, CLKA' are disabled and the clocks CLKB,
CLKB' are enabled, the second comparison result generated by the
second comparator 2064 can pass the second flip-flop 2102 and be
filtered by the second digital filter 2104, wherein the second
flip-flop 2102 is used for storing the second comparison result
generated by the second comparator 2064. Because the second monitor
value PMV is less than the second target PMT, an output generated
by the second digital filter 2104 can make the second counter 2106
count upward. Because the second counter 2106 counts upward, the
second digital-to-analog converter 2108 increases the modulation
current IMT (e.g. 5 mA) to generate a new modulation current IM
(e.g. 6 mA). In addition, after the second current generation
module 210 generates the modulation current IM (e.g. 6 mA), because
operational principles of the driving circuit 200 during a period
T3, a period T4, and a period T5 are the same as those of the
driving circuit 200 during the period T1 and the period T2, further
description thereof is omitted for simplicity. Further, in another
embodiment of the present invention, the period T3, the period T4,
and the period T5 corresponds to a first driving signal A1, a
second driving signal B1, and a first driving signal A2,
respectively.
[0034] As shown in FIGS. 2, 4, after the period T5, during a period
T6, in Step 314 and Step 316, when the driving unit 202 drives the
laser diode 214 according to the bias current IB (e.g. 6 mA) and
the temporary modulation current IMT (7+0.2.times.7=8.4 mA), the
monitor unit 204 can generate the second monitor value PMV
according to the light emitted by the laser diode 214, wherein the
second monitor value PMV corresponds to the average modulation
power (e.g. 10.2 mW) of the laser diode 214 when the laser diode
214 is driven by the bias current IB (e.g. 6 mA) and the temporary
modulation current IMT (e.g. 8.4 mA). In Step 318, the second
comparator 2064 of the comparison unit 206 compares the second
monitor value PMV (corresponding to the average modulation power
(e.g. 10.2 mW)) with the second target (corresponding to power 9.6
mW) to generate the second comparison result (that is, the second
monitor value PMV is greater than the second target PMT). As shown
in FIG. 4, in Step 320, when the clocks CLKA, CLKA' are disabled
and the clocks CLKB, CLKB' are enabled, the second comparison
result generated by the second comparator 2064 can pass the second
flip-flop 2102 and be filtered by the second digital filter 2104.
Because the second monitor value PMV is greater than the second
target PMT, the output generated by the second digital filter 2104
can make the second counter 2106 count downward. Because the second
counter 2106 counts downward, the second digital-to-analog
converter 2108 decreases the modulation current IMT (e.g. 7 mA) to
generate a new modulation current IM (e.g. 6 mA).
[0035] As shown in FIGS. 2, 4, after the period T6, during a period
T7, in Step 304 and Step 306, the driving unit 202 drives the laser
diode 214 according to the bias current IB (e.g. 6 mA) and the
modulation current IM (e.g. 6 mA), the monitor unit 204 can
generate the first monitor value PAV according to the light emitted
by the laser diode 214, wherein the first monitor value PAV
corresponds to the average power (e.g. 9 mW) of the laser diode 214
when the laser diode 214 is driven by the bias current IB (e.g. 6
mA) and the modulation current IM (e.g. 6 mA). In Step 308, the
first comparator 2062 of the comparison unit 206 compares the first
monitor value PAV (corresponding to the average power (e.g. 9 mW))
with the first target PAVT (corresponding to power 9 mW) to
generate the first comparison result (that is, the first monitor
value PAV is equal to the first target PAVT). As shown in FIG. 4,
in Step 310, when the clocks CLKA, CLKA' are enabled and the clocks
CLKB, CLKB' are disabled, the first comparison result generated by
the first comparator 2062 can pass the first flip-flop 2082 and be
filtered by the first digital filter 2084. However, because the
first monitor value PAV is equal to the first target PAVT, the
output generated by the first digital filter 2084 can make the
first counter 2086 maintain a current count. Because the first
counter 2086 maintains the current count, the first
digital-to-analog converter 2088 maintains to output the current
bias current IB (e.g. 6 mA).
[0036] As shown in FIGS. 2, 4, after the period T7, during a period
T8, in Step 314 and Step 316, when the driving unit 202 drives the
laser diode 214 according to the bias current IB (e.g. 6 mA) and
the temporary modulation current IMT (6+0.2.times.6=7.2 mA), the
monitor unit 204 can generate the second monitor value PMV
according to the light emitted by the laser diode 214, wherein the
second monitor value PMV corresponds to the average modulation
power (e.g. 9.6 mW) of the laser diode 214 when the laser diode 214
is driven by the bias current IB (e.g. 6 mA) and the temporary
modulation current IMT (e.g. 7.2 mA). In Step 318, the second
comparator 2064 of the comparison unit 206 compares second monitor
value PMV (corresponding to the average modulation power (e.g. 9.6
mW) with the second target PMT (corresponding to power 9.6 mW) to
generate the second comparison result (that is, the second monitor
value PMV is equal to the second target PMT). As shown in FIG. 4,
in Step 320, when the clocks CLKA, CLKA' are disabled and the
clocks CLKB, CLKB' are enabled, because the second monitor value
PMV is equal to the second target PMT and the clocks CLKB, CLKB'
are enabled, the second comparison result generated by the second
comparator 2064 can pass the second flip-flop 2102 and be filtered
by the second digital filter 2104. However, because the second
monitor value PMV is equal to the second target PMT, the output
generated by the second digital filter 2104 can make the second
counter 2106 maintains a current count. Because the second counter
2106 maintains the current count, the second digital-to-analog
converter 2108 maintains to output the current modulation current
IM (e.g. 6 mA). In addition, after the second digital-to-analog
converter 2108 maintains to output the current modulation current
IM (e.g. 6 mA), because operational principles of the driving
circuit 200 during a period T9 and a period T10 are the same as
those of the driving circuit 200 during the period T7 and the
period T8, further description thereof is omitted for simplicity.
Further, in another embodiment of the present invention, the period
T9 and the period T10 corresponds to a first driving signal A4 and
a second driving signal B4, respectively.
[0037] Please refer to FIGS. 2, 5A, 5B, 6. FIG. 5A and FIG. 5B are
flowcharts illustrating a driving method of a laser diode according
to a third embodiment, and FIG. 6 is a diagram illustrating the
bias current, the modulation current, the temporary modulation
current, the average power, the modulation power, and the output
powers. The method in FIG. 5A and FIG. 5B is illustrated using the
driving circuit 200 in FIG. 2. Detailed steps are as follows:
[0038] Step 500: Start.
[0039] Step 502: The user sets a bias current IB, a modulation
current IM, a first target PAVT corresponding to a predetermined
average power, and a second target PMT corresponding to a
predetermined average modulation power.
[0040] Step 504: The driving unit 202 drives the laser diode 214
according to the bias current IB and the modulation current IM.
[0041] Step 506: The monitor unit 204 generates a first monitor
value PAV corresponding to an average power of the laser diode 214
when the laser diode 214 is driven by the bias current IB and the
modulation current IM according to light emitted by the laser diode
214.
[0042] Step 508: The first comparator 2062 of the comparison unit
206 compares the first monitor value PAV with the first target PAVT
to generate a first comparison result.
[0043] Step 510: The first current generation module 208 executes a
first corresponding operation on the bias current IB according to
the first comparison result, and the first counter 2086 of the
first current generation module 208 accumulates a comparison number
executed by the first comparator 2062.
[0044] Step 512: If the comparison number accumulated by the first
counter 2086 is equal to a first predetermined value; if yes, go to
Step 514; if no, go to Step 504.
[0045] Step 514: The temporary modulation current generator 2110 of
the second current generation module 210 generates a temporary
modulation current IMT according to the modulation current IM.
[0046] Step 516: The driving unit 202 drives the laser diode 214
according to the bias current IB and the temporary modulation
current IMT.
[0047] Step 518: The monitor unit 204 generates a second monitor
value PMV corresponding to an average modulation power of the laser
diode 214 when the laser diode 214 is driven by the bias current IB
and the temporary modulation current IMT according to the light
emitted by the laser diode 214.
[0048] Step 520: The second comparator 2064 of the comparison unit
206 compares the second monitor value PMV with the second target
PMT to generate a second comparison result.
[0049] Step 522: The second current generation module 210 executes
a second corresponding operation on the modulation current IM
according to the second comparison result, and the second counter
2106 of the second current generation module 210 accumulates a
comparison number executed by the second comparator 2064.
[0050] Step 524: If the comparison number accumulated by the second
counter 2106 is equal to a second predetermined value; if yes, go
to Step 504; if no, go to Step 506.
[0051] A difference between the embodiment in FIG. 5A and FIG. 5B
and the embodiment in FIG. 3A and FIG. 3B is that a second
adjusting current step group (Step 516-524) is executed after a
number of a first adjusting current step group (Step 504-512) being
repeatedly executed is equal to the first predetermined value, and
the first adjusting current step group (Step 504-512) is executed
again after a number of the second adjusting current step group
(Step 516-524) being repeatedly executed is equal to the second
predetermined value, wherein the first predetermined value and the
second predetermined value can be positive integers. In addition,
as shown in FIG. 6, operational principles of the driving circuit
200 during periods T1-T8 are the same as those of the driving
circuit 200 during the periods T1-T10 in FIG. 3A and FIG. 3B, so
further description thereof is omitted for simplicity.
[0052] Please refer to FIG. 7. FIG. 7 is a diagram illustrating a
driving circuit 700 of a laser diode according to a fourth
embodiment. As shown in FIG. 7, differences between the driving
circuit 700 and the driving circuit 200 are that the driving
circuit 700 integrates the first comparator 2062 and the second
comparator 2064 of the driving circuit 200 into a comparator 706,
and integrates the first digital filter 2084 and the second digital
filter 2104 of the driving circuit 200 into a filter 708; a first
current generation module 710 includes a first flip-flop 2082, a
first counter 2086, and a first digital-to-analog converter 2088;
and a second current generation module 712 includes a second
flip-flop 2102, a second counter 2106, a second digital-to-analog
converter 2108, and a temporary modulation current generator 2110.
In addition, operational principles of the driving circuit 700 are
the same as those of the driving circuit 200, so further
description thereof is omitted for simplicity.
[0053] To sum up, the driving circuit of a laser diode and the
driving method of a laser diode utilize the first current
generation module and the first target to adjust the bias current
driving the laser diode, and utilize the second current generation
module and the second target to adjust the modulation current
driving the laser diode. Therefore, compared to the prior art, the
present invention has advantages as follows: first, because the
present invention has a feedback loop corresponding to the first
current generation module adjusting the bias current and a feedback
loop corresponding to the second current generation module
adjusting the modulation current, the present invention does not
need an additional memory; and second, because the present
invention has the feedback loop corresponding to the first current
generation module adjusting the bias current and the feedback loop
corresponding to the second current generation module adjusting the
modulation current, the present invention can make the laser diode
maintain a fixed extinction ratio under different operation
temperatures.
[0054] Those skilled in the art will readily observe that numerous
modifications and alterations of the device and method may be made
while retaining the teachings of the invention. Accordingly, the
above disclosure should be construed as limited only by the metes
and bounds of the appended claims.
* * * * *