JPH0563274A - Ld driving system - Google Patents

Abstract

PURPOSE:To provide an LD driving system for an optical transmitter wherein LD driving capability is improved and DUTY variations of an optical output waveform due to temperature variations are prevented. CONSTITUTION:An LD driving system for an optical transmitter comprises an FF1, a buffer amplifier 2, a differential amplifier 3, a buffer amplifier 4, a laser diode 5, a photodiode 6, a bias circuit 7, an identification level adjuster circuit 8, a DUTY control part 9, and a temperature compensation circuit 10. The identification level adjuster circuit 8 lowers an identification level of an input pulse waveform to the buffer amplifier 4. Hereby, the amplitude of an output pulse waveform from the buffer amplifier 4 is increased about two times compared with prior art to improve an LD driving capability, and variations of the amplitude of an optical output waveform and variations of the DUTY of the same are prevented by correcting temperature with the aid of the temperature compensation circuit 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser diode (hereinafter referred to as LD) driving method in an optical transmission device.

In the conventional LD driving method, the LD driving ability is low and the LD driving current varies depending on the temperature.
Improvement was requested.

[0003]

2. Description of the Related Art FIG. 5 shows an example of a conventional LD driving method, and FIG. 3A shows an output waveform of a flip-flop (hereinafter referred to as FF) 1 and an input of a buffer amplifier 4 in the conventional LD driving method. Figure 3 shows the LD drive current waveform for each point.
(B) shows the LD drive current waveform and the LD output waveform at the output point of the conventional buffer amplifier 4. In FIG. 3, ~ indicates that it is an input or output waveform at the position of ~ in FIG.

To explain the circuit operation, the data signal and the clock signal are input to D and CK of FF1 and waveform-shaped, and the Q and XQ outputs are resistors 11, 19, diodes 15, 16 and resistors 12, respectively. It is sent to the respective bases of the transistor 13 and the transistor 14 which form the buffer amplifier 2 together with 20, the diodes 16 and 18. F
An example of the data signal waveform output from F1 is shown in FIG.

The data signal sent to the base of the transistor 13 is DU by the control current from the DUTY controller 9.
TY is adjusted to a predetermined value, amplified by transistor 13 to a predetermined level, and sent to the base of transistor 23.

The data signal sent to the base of the transistor 14 is amplified to a predetermined level like the transistor 13, and then sent to the base of the transistor 24. Here, the resistors 21 and 22 and the transistors 23 and 24 constitute a differential amplifier circuit, and the resistors 27, 28 and 29 are also included.
And the transistors 25 and 26 constitute a constant current source.

The difference between the output signal waveforms of the transistors 13 and 14 is symmetrically amplified by the transistors 23 and 24 of the differential amplifier circuit 3, and the center of the data signal waveform is set to the DC level by the constant current source. Given constant current.

Further, the light output is received by the photo diode 6, the output is input to the bias circuit 7, and the bias current is automatically controlled so that the light output of the laser diode 5 maintains a predetermined value. It is superimposed on the bias current generated by the bias circuit 7. The data signal waveform (LD drive current waveform) superimposed on the bias current has a waveform as shown in FIG. 3A, which is almost the same as the waveform at the output point of the FF1 but impedance-matched. ..

The two signal currents having opposite polarities generated in this way are sent to the buffer amplifier 4 as currents for driving the LD, waveform-amplified, and supplied to the LD 5.
In the LD5, an optical signal is generated by this LD drive current and sent to the receiving side. The LD drive current waveform and the optical signal output waveform are basically the same as the output signal waveform of the FF1, as shown in and of FIG.

[0010]

However, the conventional LD driving method has a problem that the driving capacity is lowered and the optical waveform is deteriorated because the DUTY variable range of the LD driving circuit is narrow. Also, due to temperature fluctuations, the DU of the optical output waveform
There is also a problem that TY varies and the error rate characteristic deteriorates.

The present invention solves such a problem, and provides an LD driving method for improving the LD driving capability and suppressing the DUTY fluctuation of the optical output waveform due to the temperature fluctuation.

[0012]

FIG. 1 is a block diagram showing the principle of an LD drive system according to the present invention. According to the present invention, the FF1 for shaping the waveform of the input data signal, and the FF
A buffer amplifier 2 that amplifies two data signals whose waveforms are shaped by 1 and whose polarities are opposite to each other; a differential amplifier 3 that amplifies the difference between the two data signals that are amplified by the buffer amplifier 2 whose polarities are opposite; DU that keeps signal DUTY constant
A TY control unit 9, a photo diode 6 that receives an optical output signal, a bias circuit 7 that receives the output of the photo diode 6 and generates a bias current that makes the optical output waveform constant, and the differential circuit In the optical transmitter including a buffer amplifier 4 for amplifying the data signal amplified by the amplifier 3 as an LD drive current, and a laser diode 5 for generating an optical output signal by the output signal current of the buffer amplifier 4, the difference The constant current source section of the dynamic amplifier 3 is changed to the discrimination level adjusting section 8 which varies the discrimination level of the output data signal.

Further, D for controlling the DUTY of the data signal
The UTY control unit 9 is connected from the buffer amplifier 2 so as to act on the discrimination level adjusting unit 8 which functions as the differential amplifier 3 having higher stability, and temperature compensation for compensating the variation of the discrimination level of the data signal due to the temperature variation. A circuit 10 is provided to temperature-compensate the discrimination level of the discrimination level adjusting section 8.

[0014]

[Operation] As described above, by changing the constant current source section of the differential amplifier 3 to the discrimination level adjusting circuit 8 which varies the discrimination level of the output data signal, the signal waveform having a constant DC level is obtained. On the other hand, since the discrimination level of the LD drive current can be lowered by changing the direct current level, the two LD drive currents having opposite polarities of the buffer amplifier 4 have the discrimination level as shown in FIG. One drive current has a high value and the other drive current has a low signal waveform by the lowered value. These two drive currents are amplified by the buffer amplifier 4, and the output LD drive current can have a large amplitude as shown in FIG. 3D, so that the drive efficiency is improved and the optical output power is increased. Can be increased.

When the DC level fluctuates due to temperature fluctuation, the amplitude and waveform width of the output waveform of the buffer amplifier 4 fluctuate,
That is, although the DUTY varies, the temperature compensating circuit 10 is provided and the discrimination level of the input signal of the buffer amplifier 4 is temperature-compensated to suppress the amplitude variation and the DUTY variation of the optical signal output power waveform due to the temperature variation. Therefore, a stable optical signal power waveform can be transmitted.

[0016]

EXAMPLE An example will be described with reference to FIGS. 2, 3 and 4. FIG. 2 is a diagram showing an example of the LD driving method according to the present invention. FIG. 3 is a diagram showing the relationship between the data input signal, the LD drive current waveform, and the discrimination level. FIGS. 3C and 3D are diagrams relating to the present invention, and FIG. 3C is a buffer. 3D shows the relationship between the LD drive current waveform at the input point of the amplifier 4 and the discrimination level, and FIG. 3D shows the LD drive current waveform and L at the output point of the buffer amplifier 4 corresponding to FIG. 3C.
3 shows a D output power waveform. In FIG. 3, symbols .about. Indicate input or output waveforms at the positions where the respective symbols in FIG. 2 are located. FIG. 4 is a diagram showing temperature compensation for keeping the DUTY constant with respect to the temperature change according to the present invention.

In FIG. 2, the same reference numerals as those in FIG. 5 indicate the same components, 8 indicates a discrimination level adjusting circuit, and 10 indicates a temperature compensating circuit. The circuit operation will be described below. The data signal and the clock signal input to the FF1, the operation of the FF1 and the operation of the buffer amplifier 2 are the same as the conventional one. The data signal and the clock signal are input to FF1, the waveform is shaped, and Q
And XQ terminals and further amplified by the transistors 13 and 14 of the buffer amplifier 2.

The two amplified data signals whose polarities are opposite to each other are differentially amplified by the transistors 23 and 24 of the differential amplifier circuit 3, respectively. The discrimination level adjusting circuit 8 compares the direct current level with that of the conventional example. Significantly lower than the conventional discrimination level shown in FIG.
It is sent to the buffer amplifier 4 in a state where the discrimination level is greatly lowered as shown in FIG. Here, the buffer amplifier 4 has an ECL
Since the (Emitter Coupled Level) amplifier is used, the output waveform of the buffer amplifier 4 is
With respect to the input waveform shown in FIG. 3C, the amplitude becomes constant as shown in FIG. 3D, and it is about twice as large as the output waveform of the conventional buffer amplifier 4 shown in FIG. 3B. Amplitude.

Since the LD 5 is driven by the LD drive current which is the output of the buffer amplifier 4, L having a large amplitude is used.
The D optical signal output waveform can be obtained. Moreover, as shown in FIG. 4, since the DC level rises in proportion to the temperature,
A correction for the temperature change is obtained from the temperature compensation circuit 10 that uses a resistor having a temperature coefficient that cancels this and acts so as to have a constant level, and the DUTY control unit 9 receives the correction from the temperature compensation circuit 10. DUTY of output waveform
Control the DC level so that is always constant, and keep the output waveform of the buffer amplifier 4 constant.

[0020]

According to the present invention, in the LD drive system of the present invention, the drive waveform amplitude can be doubled as compared with the conventional LD drive system, so that the LD drive capability can be improved. Light output is stable.

Further, by compensating the discrimination level with temperature, it is possible to suppress the DUTY variation of the optical output power waveform due to the temperature, so that the optical output power waveform can be stabilized.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of an LD drive system according to the present invention.

FIG. 2 is a diagram showing an example of an LD driving method according to the present invention.

FIG. 3 is a diagram showing a relationship between a data input signal, an LD drive current waveform, and a discrimination level.

FIG. 4 is a diagram showing temperature compensation for keeping DUTY constant with respect to temperature changes according to the present invention.

FIG. 5 is a diagram showing an example of a conventional LD driving method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 flip-flop (FF) 2,4 buffer amplifier 3 differential amplifier circuit 5 laser diode (LD) 6 bias circuit 7 photo diode 8 discrimination level adjustment circuit 9 temperature compensation circuit 10 DUTY control unit 11, 12, 19, 20 , 21, 22, 27, 28, 2
9 resistors 13, 14, 23, 24, 25, 26 transistors 15, 16, 17, 18 diodes

Claims (2)

[Claims] 1. A flip-flop (1) for shaping the waveform of an input data signal, and the flip-flop (1).
A buffer amplifier (2) that amplifies two data signals whose waveforms have been shaped by (1) and whose polarities are opposite to each other, and a differential amplifier (amplifies the difference between the two data signals whose polarities are opposite to each other and is amplified by the buffer amplifier (2) 3), a DUTY control unit (9) for keeping the DUTY of the data signal constant, a photo diode (6) for receiving an optical output signal, and an output of the photo diode (6), and an optical output waveform A bias circuit (7) for generating a constant bias current, a buffer amplifier (4) for amplifying the data signal amplified by the differential amplifier (3) as a laser diode drive current, and the buffer amplifier ( In the optical transmitter comprising a laser diode (5) which generates an optical output signal by the laser diode drive current which is the output of 4), the constant current source section of the differential amplifier (3) is A laser diode drive system characterized in that a discrimination level adjusting circuit (8) for varying the discrimination level of the output data signal is used. 2. The discrimination level adjustment circuit (8) according to claim 1, wherein a DUTY control section (9) for controlling the DUTY of the data signal is connected to compensate the variation of the discrimination level of the data signal due to the temperature variation. Temperature compensation circuit (10)
Is provided, and the discrimination level of the discrimination level adjusting circuit (8) is temperature-compensated, and a laser diode drive system.