JPH07154016A - High speed apc circuit - Google Patents

Abstract

PURPOSE:To provide a high speed APC circuit applicable to transmission of burst while sustaining a constant optical output. CONSTITUTION:The high speed APC circuit comprises a driving section 1 comprising a semiconductor laser (light emitting element) LD, an optical detecting section 2 comprising a photodiode (light receiving element) PD for receiving the light emitted from the semiconductor laser LD and delivering an optical detection signal L3, a section 3 for generating a reference electric signal L4 according to a drive signal L1, and a section for comparing a voltage, obtained by adding the optical detection signal L3 and the reference electric signal L4 under inverted state, with a reference voltage ER. The high speed APC circuit further comprises an operational amplifier 5 generating a driving/amplification control signal for the semiconductor laser LD based on the comparison result, and an analog switch 6 receiving a control signal S for indicating presence/ absence of emission to the semiconductor laser LD and switching the control signal upon interruption of a burst signal being used as a data signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to output control of a light emitting element such as a semiconductor laser, and also for high speed APC (Auto Power Control) for burst transmission.
Automatic output control) circuit.

[0002]

2. Description of the Related Art Conventionally, when optical transmission is performed, the optical output of a light emitting element fluctuates due to temperature and the like. Therefore, a high speed APC circuit is used to keep this optical output constant. Such a high speed APC circuit is disclosed in, for example, Japanese Patent Laid-Open No. 61-94386.
Japanese Patent Laid-Open No. 62-43190 and the like.

FIG. 3 shows an example of a conventional high speed APC circuit. This high-speed APC circuit receives the data signal D and the clock signal CL and inputs the drive signals L ₁ and L.
Flip-flop (FF) unit 4 for outputting ₂ , drive unit 1 including transistors Tr1 and Tr2, semiconductor laser LD as a light emitting element, and photodiode PD as a light receiving element for receiving light emitted from semiconductor laser LD ，
Including a variable resistor and a smoothing capacitor C3 which are grounded,
The light detection unit 20 that outputs the light detection signal L ₃ and the reference voltage generation unit 30 that generates the reference voltage E _R according to the drive signal L ₁ are compared with the light detection signal L ₃ and the reference voltage E _R , and the comparison is made. And a comparison and amplification section 50 that generates a drive amplification signal based on the result.

Among them, in the drive unit 1, the transistors Tr1 and Tr2 are connected to each other by the emitter,
The transistor Tr1 is driven by the drive signal L ₁ , the transistor Tr2 is driven by the drive signal L ₂ , and the semiconductor laser LD is driven by these transistors T 1.
It is driven according to the state of the current flowing through r1 and Tr2. Further, the emitter connection parts of the transistors Tr1 and Tr2 are connected to the collector side of the transistor Tr3, and the emitter side thereof is grounded via a resistor. The base side of the transistor Tr3 is connected to the comparison amplification section 50 via the resistor R1. The base of the transistor Tr3 and the resistor R1 are grounded via a smoothing capacitor C2. Further, the reference voltage generating unit 30 and the positive electrode terminal of the comparison amplification unit 50 are connected via a resistor, and the resistance and the positive electrode terminal of the comparison amplification unit 50 are connected to each other by a smoothing capacitor C1.
Grounded through.

In this high-speed APC circuit, the light output from the semiconductor laser LD of the drive unit 1 is received by the photodiode PD of the light detection unit 20 and photoelectrically converted, and the photocurrent obtained by this is converted into a voltage and converted into light. The detection signal L ₃ is output. The comparison amplification unit 50 compares the voltage of the light detection signal L _{3 with} the voltage of the reference voltage E _R from the reference voltage generation unit 30, and the drive amplification signal generated based on the result of the comparison is transmitted to the transistor T.
By transmitting from the collector side of r3 to the drive unit 1,
The drive current for the semiconductor laser LD is controlled. As a result, feedback control is performed to keep the optical average output constant.

[0006]

However, the amplification control by the drive current in the above-mentioned high-speed APC circuit is as follows.
Since the control is to keep the time average output of light constant based on the input data signal and clock signal, the data signal (drive signal) is a burst signal in which the presence and absence of data alternate. The peak of the optical output fluctuates greatly depending on the cycle. Especially when the no-data state (disconnection state) of the burst signal is long in time,
The control of the drive current for the semiconductor laser (light emitting element) by the drive amplification signal in the comparison amplification unit is continued, and the optical output power is further increased. In such a case, as a result, an excessive current is supplied to the light emitting element, which may damage the light emitting element.

Further, the above-mentioned high-speed APC circuit has a smoothing capacitor C ₁ existing in the feedback loop,
Due to the charging time constants of C ₂ and C ₃ , it is impossible to accurately transmit a signal of an optical output from 1 bit, and therefore, there is a problem that it cannot be used for burst transmission.

The present invention has been made to solve the above problems, and its technical problem is that it can be applied to burst transmission and can maintain a constant optical output at a high speed.
It is to provide a PC circuit.

[0009]

According to the present invention, there are provided a light emitting element, a drive unit for driving the light emitting element according to an input data signal, and a light receiving element for generating a light detection signal when light emitted by the light emitting element is received. A photodetector including the reference electric signal generator for generating a reference electric signal according to the data signal;
Addition means for adding the photodetection signal and the reference electrical signal to generate an addition signal, comparison means for comparing the voltage of the addition signal with the reference voltage, and a control signal for controlling the operation of the drive section based on the result of the comparison. A high-speed APC circuit including a control means for generating is obtained.

Further, according to the present invention, in the above high-speed APC circuit, a burst signal used as a data signal according to the control signal is further inputted to the light emitting element, the control signal instructing the presence or absence of light emission. When there is no data, the high-speed APC circuit including the control suppressing means for suppressing the control signal can be obtained.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The high-speed APC circuit of the present invention will be described in detail below with reference to the accompanying drawings. Figure 1
1 shows a basic configuration of a high speed APC circuit according to an embodiment of the present invention.

This high-speed APC circuit receives a data signal D and a clock signal CL and outputs drive signals L ₁ and L ₂ , a flip-flop (FF) section 4, a semiconductor laser LD as a light emitting element, and a transistor. Tr1, and T
a drive unit 1 including r2, includes a photodiode PD, and a variable resistor as a light receiving element for receiving light emitted by the semiconductor laser LD, the light detecting unit 2 for generating light detection signals L ₃
And the reference electric signal generator 3 for generating the reference electric signal L ₄ according to the drive signal L _1, and the photodetection signal L ₃ and the reference electric signal L ₄ are added in the mutually inverted state, and the result is added. The operational amplifier 5 that compares the voltage of the signal with the DC reference voltage E _R and generates a control signal that controls drive amplification for the semiconductor laser LD based on the result of the comparison, and instructs the semiconductor laser LD whether to emit light. A control signal S to be input is input, and when the burst signal used as the data signal D is in a no-data state (disconnected state), an analog switch 6 that switches and suppresses the control signal for the semiconductor laser LD is provided.

However, here, the drive signals L ₁ and L ₂ are data signals D based on the clock cycle of the clock signal CL.
Is taken out, and can be regarded as one of the data signals D. The control signal S represents the state of the data signal D, and indicates the presence or absence of light emission to the semiconductor laser LD via the analog switch 6 according to the state.

Of these, in the drive section 1, the transistors Tr1 and Tr2 are connected to each other by emitter connection,
Furthermore the transistor Tr1 is driven by the drive signal L _1, transistor Tr2 is driven by the drive signal L _2, the semiconductor laser LD is driven according to the state of the current flowing through the transistors Tr1 and Tr2. Further, the emitter connection part of the transistors Tr1 and Tr2 is connected to the collector side of the transistor Tr3, and the emitter side thereof becomes a negative voltage application end part of -5.2V through a resistor. The base side of the transistor Tr3 is connected to the operational amplifier 5 via the analog switch 6. The output side of the semiconductor laser LD is the positive voltage application end of +5.0.

On the other hand, the control signal S is applied to the terminal connected to the base side of the transistor Tr3 in the analog switch 6. One terminal facing this terminal is connected to the operational amplifier 5 via the resistor R2, and the other terminal is connected to the negative voltage application terminal of -5.2V described above. Also, a capacitor C is provided between one terminal and the resistor R2.
It is grounded through 4. Incidentally, the resistor R2 and the capacitor C4 determine the rising time constant in this high speed APC circuit. In this high-speed APC circuit, the number of resistors and capacitors is smaller than that of the conventional one shown in FIG. 3, and the rise of the optical output can be speeded up by reducing the time constant of these resistors R2 and C4.

That is, the analog switch 6 makes one terminal contact the terminal connected to the base side of the transistor Tr3 when data is present in the burst signal used as the data signal D by the control signal S as described later. When the burst signal has no data, the terminal connected to the base side of the transistor Tr3 is switched to be in contact with the other terminal. Therefore, the analog switch 6 functions as a control suppressing unit that suppresses the control signal when the burst signal is in the no-data state according to the control signal S.

Further, in the operational amplifier 5, the negative terminal is connected to the reference electric signal generator 3 and the photodetector 2, and the positive terminal is a variable resistor inserted in the voltage application line of -5.2V to + 5.0V. Connected. The operational amplifier 5 inputs a photodetection signal L ₃ from the photodetection section 2 and a reference electric signal L ₄ which is the inverse of the photodetection signal L ₃ to the negative inverting input terminal, and outputs these signals. Addition means for adding and outputting an addition signal, comparison means for comparing the voltage of the addition signal and the reference voltage E _R, and amplification control means for generating a control signal for controlling drive amplification for the semiconductor laser LD based on the comparison result. Function as.

FIG. 2 is a timing chart showing the control processing for the photodetection signal L ₃ and the reference electric signal L ₄ by the control signal S when the burst signal B is input in this high speed APC circuit.

Here, it is assumed that the control signal S turns on / off the light emission of the semiconductor laser LD, and there is data in the burst signal B in the ON state with a long cycle, and the relationship of each signal at that time. Is shown. That is, at this time, the photodetection signal L ₃ becomes the same as the data signal D, and the photodetection signal L ₃ and the reference electrical signal L ₄ are inverted with respect to the ground (GND) level as an axis, and their output peaks are different from each other. It is kept constant and has the same amplitude.

This is nothing but the result of the control by the OP amplifier 5. That is, the optical output decreases due to factors such as an increase in ambient temperature, and the amplitude of the reference electrical signal L ₄ changes to the light detection signal L
_When it becomes larger than the amplitude of ₃ , the OP amplifier 5 raises the output potential of the control signal to increase the light output, and makes the amplitude of the reference electric signal L ₄ equal to the amplitude of the light detection signal L ₃ . On the contrary, when the optical output rises and the amplitude of the reference electric signal L ₄ becomes smaller than the amplitude of the light detection signal L ₃ , O
The P amplifier 5 lowers the output potential of the control signal to reduce the light output, and makes the amplitude of the reference electric signal L ₄ equal to the amplitude of the light detection signal L ₃ .

On the other hand, when the burst signal B is in the non-data state, the analog switch 6 switches its contact to the other terminal on the side of the negative voltage application terminal of -5.2 V according to the control signal S and controls the control signal. Therefore, the excessive current is not supplied to the light emitting element even if the data-free state is long.

As described above, this high-speed APC circuit can perform control for always keeping the optical output constant even when the burst signal B is input. The response time in this high-speed APC circuit is determined by the time constant of the resistor R2 and the capacitor C4, but any time may be used as long as it can prevent loop oscillation.

[0023]

As described above, according to the present invention, the voltage of the added signal and the reference voltage obtained by adding the photodetection signal from the photodetector and the reference electric signal inverted from the photodetection signal. Since the control signal for controlling the drive amplification for the semiconductor laser is obtained based on the comparison result with, the CR (capacitor-resistance) that determines the time constant of the circuit is minimized. , High-speed A that can be applied for burst transmission and can keep the optical output constant at all times
It becomes possible to provide a PC circuit. Further, since the amplification control suppressing means for suppressing the control signal is provided when the burst signal is in the no-data state according to the control signal for instructing the light-emitting element to emit light, the time in the no-data state is long. However, excessive current is not supplied to the light emitting element, and damage to the light emitting element can be reliably prevented.

[Brief description of drawings]

FIG. 1 illustrates a high speed APC circuit according to an embodiment of the present invention.

2 is a timing chart showing a control process for a photo detection signal and a reference electric signal by a control signal when a burst signal is input in the high speed APC circuit shown in FIG.

FIG. 3 shows a conventional high speed APC circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 drive part 2, 20 photodetection part 3 reference electric signal generation part 4 flip-flop (FF) part 5 operational amplifier 6 analog switch 30 reference voltage generation part LD semiconductor laser (light emitting element) PD photodiode (light receiving element) L ₁ , L ₂ drive signal L ₃ optical detection signal L ₄ reference electrical signal D data signal S control signal B burst signal

Claims (2)

[Claims] 1. A light emitting device, a drive unit for driving the light emitting device according to an input data signal, a light detecting unit including a light receiving device for generating a light detection signal when light emitted by the light emitting device is received, and the data. A reference electric signal generator for generating a reference electric signal in accordance with the signal; an addition means for adding the photodetection signal and the reference electric signal to generate an addition signal; and a comparison for comparing the voltage of the addition signal with a reference voltage. A high-speed APC circuit comprising: means and a control means for generating a control signal for controlling the operation of the driving unit based on the result of the comparison. 2. The high-speed APC circuit according to claim 1, further comprising: inputting a control signal to the light emitting element, the burst signal being used as the data signal according to the control signal. Is a non-data state, a high-speed APC circuit including control suppressing means for suppressing the control signal.