Laser diode drive circuit

Details Laser diode drive circuit Laser diode drive circuit

2000-09-27

2003-01-21

Ip, Paul (Department: 2828)

Coherent light generators

Particular component circuitry

For driving or controlling laser

C372S031000, C315S149000, C315S151000

Reexamination Certificate

active

06510168

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser diode drive circuit utilized in an optical communication system, and more specifically, a laser diode drive circuit utilized in an optical transmission system that converts an electrical signal to an optical signal by using a laser diode.
2. Description of the Related Art
FIG. 5
shows a laser diode drive circuit
501
in the related art. The laser diode drive circuit
501
comprises drive sources (V+) and (V−), a switch buffer
503
, a switch circuit
507
, a laser diode LD, resistors R
5
and R
505
and the like. The continuity of transistors Q
5
and Q
6
at the switch circuit
507
is switched by switch control input signals Vin
1
(positive phase) and Vin
2
(negative phase) to achieve electrical continuity for a drive current IP either with the laser diode LD-side or with the resistor R
5
-side. The laser diode LD generates an optical signal corresponding to an input signal by emitting
ot emitting light. In addition, the level of the drive current Ip which determines the light output power of the laser diode LD is controlled by a base potential Vb of a transistor Q
503
which is connected in cascade to the switch circuit
507
.
The lower limit of source voltage (V+)−(V−) at this laser diode drive circuit
501
is expressed as follows:
(
V+
)−(
V−
)≧i Vf+Vsw/2+
Vce
5
+
Vce
503
+
Ip·R
505
  (expression 1)
with Vf representing the forward voltage of the laser diode LD, Vsw representing the output amplitude of the switch buffer
503
and Vce
5
and Vce
503
respectively representing minimum values of the collector-emitter voltages at the transistors Q
5
and Q
503
. More specifically, Vf is approximately 1.5V, Vsw is approximately 0.3V, Vce
5
and Vce
503
are both approximately 0.45V, and Ip·R
505
is approximately 0.35V. Thus, the lower limit of the source voltage in the circuit in the related art is calculated by using (expression 1) as; (V+)−(V−)≧2.9V, and a 3.3V single source which is normally used in communication systems at present is utilized for the source voltage.
However, in the circuit structure in the related art achieved by connecting in cascade the current control transistor Q
503
to the switch circuit
507
, the source voltage lower limit cannot be reduced, and therefore, it cannot support the 2.5V single source expected to become the mainstream source in the future.
SUMMARY OF THE INVENTION
An object of the present invention, which has been completed by addressing the problem discussed above, is to achieve low voltage drive and low power consumption in a laser diode drive circuit.
In order to achieve the object described above, the present invention provides a laser diode drive circuit comprising a level shift circuit connected to a drive source, which reduces the drive source voltage by a specific degree, a current switch that turns on/off a laser diode connected to the drive source and a switch buffer connected to the level shift circuit, which implements control on the current switch.


REFERENCES:
patent: 5349595 (1994-09-01), Ogawa et al.
patent: 5883910 (1999-03-01), Link
patent: 5991320 (1999-11-01), Nakayama
patent: 6097159 (2000-08-01), Mogi et al.
patent: 6249178 (2001-06-01), Umeda

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