Coherent light generators – Particular component circuitry – For driving or controlling laser
Reexamination Certificate
2002-06-11
2004-09-28
Wong, Don (Department: 2828)
Coherent light generators
Particular component circuitry
For driving or controlling laser
C372S038040, C372S038070, C327S110000, C327S112000
Reexamination Certificate
active
06798802
ABSTRACT:
Pursuant to 35 U.S.C. §119(a)-(d), this application claims priority from Taiwanese application no. 91104506, filed on Mar. 11, 2002.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser driver, and especially to a high-speed laser driver including wave shaping and dynamic control circuits, which uses a source degeneration resistor instead of a prior constant current source to increase the operating speed, a buffer with a dynamic loading source resistor to buffer the output differential signals to the next circuit, and a tunable device to control output gain and prevent overshoot.
2. Description of Related Art
FIG. 1
is a block diagram of a typical laser driver
10
. As shown in
FIG. 1
, the laser circuit
10
includes a wave-shaping circuit
11
to receive and shape signals Sdp and Sdn externally, an output control circuit
12
to adjust signals Sdp and Sdn to desired signals Swu and Swl, and an output stage circuit
13
to convert signals Swu and Swl into a desired output I for the laser diode
14
by externally inputting the signal CG to set the desired modulation current. As such, the laser circuit
10
drives the modulation current Im of a laser diode
14
. When the laser diode
14
functions, the required bias voltage is provided by a bias current source
15
. However, for high-speed and broadband (NRZ signal) requirements of laser drivers, such a conversional MOS constant current source differential pair structure cannot meet the design specification because the speed limitation comes from the parasitic capacitance and some physical behavior of MOS devices. Thus, the laser drive with the conversional structure has poor performance. For example,
FIG. 2
is an example of the wave-shaping circuit
11
of FIG.
1
. As shown in
FIG. 2
, the wave-shaping circuit
11
has constant current source differential pairs. These constant current source differential pairs serve as gain stages and limit the output swing to a desired level. For simplification, only the last differential stage
111
consisting of resistors R
1
, R
2
, MOSs M
1
, M
2
, and a constant current source CS
1
is shown. Further, circuit
112
serves as an output stage to drive the next circuit and adjusts the output voltage level to a desired swing. A wave-shaping circuit like
11
can convert a differential sine wave pair Sdp, Sdn into a differential square wave pair Swu, Swl or a single-end signal into a differential pair (not shown). However, as mentioned above, the operating speed of a constant current source differential pair is limited by the non-ideal characteristics and of MOS current source. Thus, as shown in
FIG. 3
, a parasitic capacitance Cp is formed due to the junction voltage difference Vd−Vb between the drain D and bulk B of the MOS, for example M
1
(
FIG. 2
) when an external current Iext is input to the drain D of M
1
. The parasitic capacitance Cp causes the current source CS
1
, CS
2
and CS
3
in
FIG. 2
to be non-ideal current sources such that the operating speed of the differential pair M
1
, M
2
is limited. When operating at high speed, the total current of NMOSs M
1
and M
2
is equal to the current of CS
1
in ideal. However, the parasitic capacitance Cp in the non-ideal constant current sources can cause signal distortion. For example, when a 0.35 &mgr;m CMOS manufacturing process is used to shape a 1.25G clock pulse, as shown in
FIG. 4
, the signal such as Swu may change the waveform from V
1
to V
2
and cause a signal distortion. If the signals Swu, Swl are unchanged, and sent to the next output control circuit
12
, as shown in
FIG. 5
, the circuit
12
also includes MOSs M
51
-
53
, causing output signal distortion. That is, the MOS M
53
becomes a non-ideal constant current source and the signals Sout
1
, Sout
2
sent to the next output stage circuit
13
(
FIG. 1
) change the waveform from V
1
to V
2
(
FIG. 4
) so as to cause output signal distortion. Likewise, the waveform distortion may present in the output stage circuit
13
consisting of, for example, a resistor R
53
, MOSs M
54
-M
56
as mentioned above.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to provide a high-speed laser driver including a wave-shaping circuit, which performs wave shaping for the laser driver at high speeds.
Another object of the invention is to provide a high-speed laser driver including wave-shaping and dynamic control circuits, which performs the wave shaping and the dynamic control for the laser driver at high speed.
The invention provides a high-speed laser driver including wave-shaping circuits, which performs wave shaping for driving the laser at high speed. The laser driver includes a wave-shaping circuit having a source degeneration resistor instead of a prior constant current source to increase the operating speed and a buffer with a dynamic loading source resistor to buffer the output differential signals to the next circuit. The laser driver further includes a dynamic control circuit having a tunable device to control output gain and prevent overshoot.
REFERENCES:
patent: 5563898 (1996-10-01), Ikeuchi et al.
patent: 5739707 (1998-04-01), Barraclough
patent: 5828247 (1998-10-01), Moller et al.
patent: 6021143 (2000-02-01), Ransijn et al.
patent: 6130562 (2000-10-01), Bosch et al.
patent: 6590914 (2003-07-01), Tanase et al.
patent: 6597209 (2003-07-01), Iguchi et al.
patent: 2003/0002551 (2003-01-01), Kwon et al.
patent: 2003/0086455 (2003-05-01), Ciubotaru et al.
patent: 2003/0156609 (2003-08-01), Tsai
Industrial Technology Research Institute
Jackson Cornelius H.
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