JPH08316520A - Photoelectric conversion circuit - Google Patents

Abstract

PURPOSE: To realize the title photoelectric conversion circuit capable of avoiding the decline in the transmission rate and SN ratio using a laser diode as a photodetecting element. CONSTITUTION: The output current O/E conversion element 10 using a laser diode as a photodetecting element is converted into level signals by a current- voltage converting circuit 11. Next, in an inverting amplifier 13 and a non- inverting amplifier 14, the level signals are level shifted to transmit output signal having noise margins. Next, a comparator 15 compares the levels of these output signals having these noise margins to transmit detecting signals. Through these procedures, the decline in transmission rate and the SN ratio can be avoided even if the laser diode is used as a photodetecting element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical / electrical conversion circuit suitable for use in an optical communication device for optical communication in a half-duplex system via a single-core optical fiber.

[0002]

2. Description of the Related Art Conventionally, there has been known an optical communication device for performing optical communication in a half-duplex system via a single-core optical fiber. FIG.
It is a block diagram showing a schematic structure of this kind of optical communication apparatus. In this figure, reference numeral 1 denotes a CPU that controls each part of the device, and sends out transmission data Tx, while receiving reception data Rx transmitted from the opposite device side (not shown).
Reference numeral 2 denotes an LD driver, which generates a drive signal for driving the laser diode 3 according to the transmission data Tx supplied from the CPU 1. The laser diode 3 oscillates light of a predetermined wavelength according to the drive signal supplied from the LD driver 2, and inputs the optical signal to the 3 dB optical coupler 4.

The 3 dB optical coupler 4 includes a laser diode 3
The optical signal output from the optical waveguide is guided to the optical connector LC side, and a part of the optical signal is supplied to the non-reflection end NR.
The optical signal guided to the optical connector LC side is sent to the opposite station side via the one-core optical fiber F connected to this connector LC. Reference numeral 5 denotes a photodiode, which receives an optical signal from the opposite station side supplied via the 3 dB optical coupler 4, converts it into an electric signal, and outputs the electric signal. Reference numeral 6 is a PD detection circuit, which generates received data Rx based on the output of the photodiode 5 and supplies it to the CPU 1 side.

[0004]

In the half-duplex type optical communication device having the above structure, when the reflection component generated by the optical coupler 4 is larger than the intensity of the optical signal supplied from the opposite station side. Since the optical signal cannot be received from the opposite station side, the light receiving signal of the photodiode 5 is ignored while the optical signal is being sent from the laser diode 3. Further, in this optical communication device, while the optical signal is transmitted from the laser diode 3 and the optical signal supplied from the opposite station side is received by the photodiode 5, the 3 dB optical coupler 4 having the non-reflection end NR is essential. This is a factor that causes an increase in signal loss and an increase in product cost.

Therefore, as shown in FIG. 4, the laser diode 3 acts as a light emitting element but also as a light receiving element, that is, the laser diode 3 acts as a light receiving element only in the receiving state. The above-mentioned drawback can be avoided by adopting the configuration of detecting. However, in such a case, the capacitance component of the laser diode 3 is larger than the capacitance component of the photodiode 5, whereby the signal is delayed and the transmission speed (throughput rate) at the time of receiving light is reduced, or the noise component is generated. It has not been put to practical use because there is a problem that it is difficult to obtain a sufficient SN ratio in many cases. Therefore, there is a demand for an optical / electrical conversion circuit that does not cause a reduction in transmission speed or a reduction in SN ratio even if a laser diode is used as a light receiving element. The present invention has been made in view of the above-mentioned circumstances, and even if a laser diode is used as a light receiving element, a decrease in transmission speed or S
It is an object of the present invention to provide an optical / electrical conversion circuit capable of preventing a decrease in N ratio.

[0006]

In order to achieve the above-mentioned object, in the invention described in claim 1, a conversion element for receiving input light, converting it into a light reception signal and outputting it, and outputting from this conversion element. Signal separation means for converting the signal current of the received light signal into a voltage signal and separating the voltage signal into first and second voltage signals whose levels have been shifted, and the first voltage signal and the second voltage signal. And a comparison means for generating a detection signal corresponding to the received light signal when the first voltage signal becomes larger than the second signal.

According to a second aspect of the present invention, which is dependent on the first aspect, the conversion element causes the laser diode to act as a light-receiving element to output the light-receiving signal,
It is characterized in that the signal separating means is composed of a non-inverting amplifier which generates the first voltage signal and an inverting amplifier which generates the second voltage signal.

[0008]

According to the present invention, the signal separating means converts the signal current of the light receiving signal output from the converting element into a voltage signal and separates the voltage signal into first and second voltage signals which are level-shifted. Then, the comparing means compares the first voltage signal and the second voltage signal in magnitude to generate a detection signal corresponding to the light receiving signal when the first voltage signal becomes larger than the second signal. Therefore, even if a laser diode is used as a light receiving element, it is possible to prevent a decrease in transmission speed and a decrease in SN ratio.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an optical / electrical conversion circuit according to an embodiment of the present invention. In this figure, 10 is an O / E conversion element for converting an optical signal into an electric signal, and in this case, the laser diode 3 which is the above-mentioned light emitting element is made to act as a light receiving element. When the laser diode 3 is made to act as a light receiving element, as described above, the transmission speed and the SN ratio are lowered, but in the present invention, the point is to remove them by the circuit element in the subsequent stage.

Reference numeral 11 denotes a current / voltage conversion circuit composed of an operational amplifier, which converts the output current of the O / E conversion element 10 into a level signal and outputs it. This current / voltage conversion circuit 1
1, the smoothing capacitor 11a is interposed between the non-inverting input terminal and the output terminal.
By a, the random noise superimposed on the output current of the O / E conversion element 10 is smoothed and the noise component is suppressed. If the capacitance of the capacitor 11a is small, random noise increases, and if it is too large, the transmission speed of the received light signal decreases, so the capacitance is set to an optimum value. Reference numeral 12 is a coupling capacitor, which cuts a DC component from the output of the current / voltage conversion circuit and outputs it to the next stage.

Reference numeral 13 denotes an inverting amplifier. The output of the coupling capacitor 12 is supplied to the non-inverting input terminal side of the inverting amplifier, while the DC bias generated via the voltage dividing resistor is applied to the inverting input terminal side. . Reference numeral 14 is a non-inverting amplifier, the output of the coupling capacitor 12 is supplied to the inverting input terminal side thereof, and a DC bias generated via a voltage dividing resistor is applied to the non-inverting input terminal side thereof. Here, the inverting amplifier 13
Is adjusted to have an output bias of +20 mV in the absence of signal input, and is adjusted to have an output bias of -20 mV in the absence of signal input even in the non-inverting amplifier 14. Reference numeral 15 is a comparator for comparing the output levels of the amplifiers 13 and 14. As shown in FIG. 2, the comparator 15 generates an L level (0 V) signal when (output of the amplifier 13 <output of the amplifier 14), and otherwise outputs an H level (+5 V) signal. To occur.

In such a configuration, when the O / E conversion element 10 receives an optical signal from the opposite station side and generates a light reception signal, the current / voltage conversion circuit 11 generates a level signal corresponding to the light reception signal. To do. That is, the current / voltage conversion circuit 11 does not depend on the capacitance component of the O / E conversion element 10 and generates a voltage waveform according to the current value. Therefore, even if a laser diode is used as a light receiving element, the transmission speed does not decrease. Moreover, if the smoothing capacitor 11a is set to an optimum value, random noise of the diode can be reduced.

The level signal output from the current / voltage conversion circuit 11 has its direct current component cut through the coupling capacitor 12 and the signal component corresponding to the received data Rx is supplied to the inverting amplifier 13 and the non-inverting amplifier 14. Is entered. The output signals of the amplifiers 13 and 14 are compared in a comparator 15, and a detection signal is generated when (output of the amplifier 13 <output of the amplifier 14). Here, the comparator 15 is an amplifier 13 having a sufficient noise margin,
Since the comparison operation is performed with the 14 output signals, it is possible to secure a sufficient SN ratio.

As described above, according to this embodiment, the output current of the O / E conversion element 10 is converted into a level signal, and the level signal is separated into two level-shifted signals to provide a noise margin. Since the comparison process is performed to generate the detection signal, the transmission speed and the SN ratio are not reduced even if the laser diode is used as the light receiving element. When a high SN ratio is ensured in this way, the effect of inevitably improving the operating characteristics at the time of low temperature / high temperature (minimum light receiving level, maximum light receiving level) is also obtained. In addition, since the optical / electrical conversion circuit according to the present embodiment can be configured with general-purpose components, it can contribute to cost reduction.

[0015]

According to the present invention, the signal separating means converts the signal current of the light receiving signal output from the converting element into a voltage signal, and the first and second voltage signals are level-shifted. And the comparison means compares the first voltage signal and the second voltage signal in magnitude, and when the first voltage signal becomes larger than the second signal, the detection signal corresponding to the received light signal is detected. Therefore, even if a laser diode is used as a light receiving element, it is possible to prevent a decrease in transmission speed and a decrease in SN ratio.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an optical / electrical conversion circuit according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a comparing operation in the embodiment.

FIG. 3 is a diagram for explaining a conventional example.

FIG. 4 is a diagram for explaining a conventional example.

[Explanation of symbols]

Reference numeral 10 ... O / E conversion element (conversion element), 11 ... Current / voltage conversion circuit (signal separation means), 12 ... Coupling capacitor (signal separation means), 13 ... Inversion amplifier (signal separation means), 1
4 ... Non-inverting amplifier (signal separation means), 15 ... Comparator (comparison means)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H04B 10/14 10/04 10/06 // H01L 31/12

Claims (2)

[Claims] 1. A conversion element which receives input light, converts it into a light reception signal and outputs it, and converts a signal current of the light reception signal output from the conversion element into a voltage signal and level-shifts the voltage signal. A signal separating means for separating the first voltage signal and the second voltage signal, and comparing the first voltage signal and the second voltage signal.
An optical / electrical conversion circuit comprising: a comparison unit that generates a detection signal corresponding to the received light signal when the first voltage signal becomes larger than the second signal. 2. The conversion element causes a laser diode to act as a light receiving element to output the light receiving signal, and the signal separating means includes a non-inverting amplifier which generates the first voltage signal, and the second The opto-electric conversion circuit according to claim 1, comprising an inverting amplifier for generating a voltage signal.