Light emitting element driving apparatus

Details Light emitting element driving apparatus Light emitting element driving apparatus

1998-10-19

2001-09-18

Pascal, Leslie (Department: 2633)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S199200, C359S199200, C359S199200

Reexamination Certificate

active

06292284

ABSTRACT:

BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a light emitting element driving apparatus, and more particularly one for performing automatic light power control (APC control; Automatic Power Constant control) for a light output from a light emitting element.
(2) Description of the Related Art
In recent years, we have seen active efforts made to develop subscriber exclusive optical communication devices in the field of optical communications. In an optical communication device used in an optical subscriber system, a semiconductor circuit based on a CMOS type field effect transistor has been put to frequent use in order to satisfy requests for reductions in costs, power consumption, and so on.
Not only in the foregoing optical communication device of the optical subscriber system but also in the optical transmission device of a trunk system, a function unit for transmitting light signals via optical fibers transmits signals containing data information, for instance burst signals, by driving a light emitting element such as a laser diode (LD).
In such a situation, a light emitting element driving apparatus for driving the light emitting element such as an LD must have a function for dealing with burst signals and, more importantly, a function for accurately maintaining light power constant even if there is a long time interval between burst signals. These functions must be provided also for securing reliability of the light emitting element itself.
In a driving apparatus for driving a magneto-optic disk (MO) or a laser printer, an LD or the like is used as a light emitting element for emitting laser lights. For the magneto-optic disk driving apparatus or the laser printer, functional improvements can be expected by providing a function for accurately maintaining light power constant even if a long time interval occurs between burst signals.
FIG. 22
is a block diagram showing a light emitting element driving apparatus where a conventional automatic light power control circuit is applied. A light emitting element
100
and a light emitting element driving apparatus
110
shown in
FIG. 22
can be applied to an optical communication device for transmitting/receiving light signals via not-shown optical fibers.
The light emitting element
100
converts electric signals into light signals, supplies output signals to a not-shown optical transmission line and outputs monitoring lights. The light emitting element driving apparatus
110
performs control so as to maintain constant light power of a light signal outputted from the light emitting element
100
. The light emitting element driving apparatus
110
includes a data receiving unit
101
, an LD driving unit
102
, a reference voltage generation unit
103
, a light receiving element
104
, a monitoring voltage conversion unit
105
, a difference voltage generation unit
106
and a control signal generation unit
107
.
The data receiving unit
101
receives data and a clock to produce a signal for driving the light emitting element
100
. The LD driving unit
102
receives an output from the data receiving unit
101
. The LD driving unit
102
is controlled by a control signal produced by the control signal generation unit
106
for automatic light power control so as to drive the light emitting element (LD)
100
. The data receiving unit
101
and the LD driving unit
102
constitute a main signal unit
108
together.
The reference voltage generation unit
103
generates a reference voltage for automatic light power control from a reference signal as an output signal from the data receiving unit
101
. The light receiving element (PD; Photo Diode)
104
converts a monitoring light outputted from the light emitting element
100
into an electric signal again. The monitoring voltage conversion unit
105
voltage-converts a monitoring signal as an output current from the light receiving element
104
so as to produce a monitoring voltage for automatic light power control.
The difference voltage generation unit
106
produces a difference in output voltages between the reference voltage generation unit
103
and the monitoring voltage conversion unit
105
. The control signal generation unit
107
produces an LD driving control signal for automatic light power control according to the output of the difference voltage generation unit
106
. The reference voltage generation unit
103
, the monitoring voltage conversion unit
105
, the difference voltage generation unit
106
and the control signal generation unit
107
constitute an automatic light power control unit (APC unit)
109
together.
Detailed configuration of each of the LD driving unit
102
, the difference voltage generation unit
106
and the control signal generation unit
107
is shown in FIG.
23
.
Specifically, the difference voltage generation unit
106
includes a differential amplifier. The control signal generation unit
107
includes a field effect transistor (T
1
)
107
a
, a capacitor (C
1
)
107
b
, a field effect transistor (T
2
)
107
c
and a resistor (R
2
)
107
d.
The field effect transistor
107
a
supplies a current according to the output of the difference voltage generation unit
106
. The capacitor
107
b
is connected to the field effect transistor
107
a
via a connector
107
e
. The capacitor
107
b
charges a current supplied from the field effect transistor
107
a
. A terminal voltage of the capacitor
107
b
is outputted as a control signal for the LD driving unit
102
.
The field effect transistor
107
c
is placed in a conductive condition when a transmitting signal is ON. The resistor
107
d
causes the capacitor
107
b
to discharge excessive electric charges when a transmitting signal is ON.
In other words, the field effect transistor
107
a
and the capacitor
107
b
produce a control signal for the LD driving unit
102
according to an output from the difference voltage generation unit
106
.
The LD driving unit
102
includes three field effect transistors (T
11
to T
13
)
102
a
to
102
c
and a resistor (RL)
102
d
. An APC control signal from the control signal generation unit
107
is received by the transistor
102
c
. Data transmitted from the data receiving unit
101
is received by the transistors
102
a
and
102
b
. Then, a driving current signal having been subjected to automatic light power control is supplied to the light emitting element
100
.
With the foregoing configuration, the light emitting element driving apparatus
110
shown in
FIG. 22
controls a driving current of the light emitting element
100
based on a difference voltage between a reference voltage produced from a signal outputted from the data receiving unit
101
and a monitoring voltage produced from a monitoring signal outputted from the light receiving element
104
, controls an output light of the light emitting element
100
to a constant level and outputs the output light to the optical transmission line.
In the control signal generation unit
107
, if a transmitting signal (burst signal) is in an ON condition (transmission condition) [e.g., see points of time (t2) to (t4) of FIGS.
24
(
b
) and
24
(
c
)] after power input [see a point of time (t1) of FIG.
24
(
a
)], the transistor
107
c
is switched ON. Accordingly, a control signal V
PCNT
for the LD driving unit
102
is controlled according to the light output control of a loop gain including the resistor
107
d
[see points of time (t2) to (t3) of FIG.
24
(
d
)].
On the other hand, if the transmitting signal is in an OFF condition (non-transmission condition) [e.g., see points of time (t4) to (t5) of FIG.
24
(
b
)], the transistor
107
c
is switched OFF. Accordingly, a control signal V
PCNT
produced during transmission [see points of time (t2) to (t4) of FIG.
24
(
b
)] is held until a next burst transmission section [see a point of time (t5) and after of FIG.
24
(
b
)] is reached.
FIG. 25
is a block diagram showing a light emitting element driving apparatus
110
A where an APC loop is

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