JPH02143640A - Optical receiver - Google Patents

Abstract

PURPOSE:To keep the width of a voltage signal constant and to obtain an optical receiver without malfunction by separating a voltage signal from a current-voltage conversion means into a positive signal and other inverting signal, smoothing them respectively and adding the difference signals. CONSTITUTION:An optical current from a photoelectric conversion element 1 is converted into a voltage by a current voltage amplifier means 11 and inputted to a separation means 21. The means 21 divides the signal into a positive signal and an inverting signal caused in a period without the positive signal and the result is outputted to smoothing means 31,41. The means 31,41 smooth the positive signal and the inverting signal respectively and a differential means 51 adds the differences between the positive signals and the inverting signals. Then the added voltage signal and the identification level are compared and binarized via a comparator circuit 61. Thus, the amplitude of the voltage signal is increased/decreased up to a prescribed value in response to the quantity of voltage signal width distortion, the width distortion of a digital signal is made proper without being affected by the output of the optical signal and malfunction is reduced.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an optical receiver of an optical signal transmission system using an optical transmission path, and particularly relates to an output waveform shaping circuit of an optical receiver. Regarding.

(Prior art) In recent years, optical signal transmission systems using optical fiber cables have been widely used in audio equipment, as they have advantages such as less signal deterioration during optical signal transmission and no external noise. It has also come to be used for connecting products. Under these circumstances, the light emitting characteristics and light receiving characteristics of optical transmitters and optical receivers were put on the market based on the ideas of each manufacturer, and this had a particularly large impact on optical receivers.

For example, if an optical transmitter with a large optical signal output is used as a transmitter, the amplifier of the optical receiver may become saturated, or the width of the transmitted signal may change, making it impossible to output a normal rectangular pulse. Ivy.

Furthermore, the connection between optical transmitters or optical receivers manufactured according to the ideas of each manufacturer and optical fiber cables is not always good, and the received optical signal output and this depend on the connection state with the optical fiber cable. The voltage signal width associated with this changes greatly.

Under these circumstances, it has become possible to prevent signal saturation by using optical receivers with large amplification ranges. Various optical receivers have also been invented that can compensate for changes in voltage signal width.

For example, the optical receiver described in Japanese Patent Publication No. 63-25738 determines the discrimination level of the comparison circuit based on the peak value of the voltage signal from the amplifier that amplifies the output of the photodetector and a preset voltage. , the discrimination level was increased or decreased in proportion to the increase or decrease in the peak value.

Normally, when the voltage signal is large, the voltage signal width also tends to become large. In this case, the optical receiver increases the discrimination level and decreases the voltage signal width as the peak value increases. Conversely, when the voltage signal is small, the voltage signal width tends to be small, so as the peak value decreases, the discrimination level is decreased and the voltage signal width is increased to output a digital waveform with suppressed distortion.

In this way, in conventional optical receivers, by providing a reference voltage generation circuit that changes in proportion to the magnitude of the input optical signal,
This suppressed distortion in the voltage signal width.

l+= (Problem to be Solved by the Invention) In the optical receiver described above, the discrimination level is determined by comparing a preset voltage with a peak value, and the voltage signal is determined by comparing this discrimination level with the voltage signal. This was to eliminate the wide jump.

For this reason, since correction was made based on the magnitude of the voltage signal regardless of the magnitude of the voltage signal width jump, distortion was not sufficiently eliminated. For example, when the voltage signal output is large but the voltage signal width is smaller than usual, the discrimination level is set large, and the voltage signal width becomes smaller, making it impossible to eliminate the voltage signal width jump.

In addition, it is very difficult to use it in optical transmission systems with a wide variety of combinations, as the set voltage must be adjusted for each.

Furthermore, for example, if the rise of the voltage signal is slow due to the characteristics of the photoelectric conversion element, but the fall is steep,
If the amplitude of the voltage signal is constant, conventional optical receivers cannot eliminate voltage signal width jumps.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical receiver that can be used in optical transmission systems with a wide variety of combinations and can maintain a constant voltage signal width regardless of the size of the input waveform and will not malfunction during signal processing at the edge of a pulse signal. The optical receiver of the present invention includes a light receiving element that converts an optical signal from an optical transmission path into a current signal, a current-voltage conversion amplification means that converts the current signal into a voltage signal and amplifies it, and the current-voltage conversion amplification device. separating means for dividing the voltage signal from the means into a first voltage signal and a second voltage signal;
a smoothing means that smoothes the first voltage signal and the second voltage signal, respectively; and a differential differential that outputs the difference between the first voltage signal and the second voltage signal smoothed by the smoothing means. and an addition means for adding the difference between the smoothed first voltage signal and the second voltage signal and the voltage signal to output a third voltage signal.

(Function) Currently, the optical signal used for transmitting digital audio signals is a pi-phase signal with a duty ratio of about 50%. A voltage signal corresponding to the input optical signal is output from the current-voltage conversion amplification means, and this output voltage signal is used as a first voltage signal, and the area where the first voltage signal is not generated is used as a second voltage signal. In this case, in the pi-phase signal, the smoothed first voltage signal and the smoothed second voltage signal are the same. When a voltage signal with a voltage signal width wider than the voltage signal width at the time of transmission (hereinafter referred to as positive voltage signal width jump) is output from the current-voltage conversion amplification means, the smoothed first voltage signal is smoothed. the second voltage signal.

Conversely, if a voltage signal with a voltage signal width narrower than the voltage signal width at the time of transmission (hereinafter referred to as negative voltage signal width distortion) is output from the current-voltage converter, the smoothed first voltage signal is smaller than the smoothed second voltage signal.

Therefore, in the optical receiver of the present invention, by having the above-described configuration, the smoothed first voltage signal and the smoothed second voltage signal are compared, and if a positive voltage signal width distortion occurs, a negative voltage signal is detected. The difference voltage signal is added to the voltage signal from the current-voltage converter to output a third voltage signal. Conversely, when negative voltage signal width distortion occurs, a positive differential voltage signal is added to the voltage signal from the current-voltage converter to output a third voltage signal. This third voltage signal is obtained by increasing or decreasing the imaging width of the voltage signal to a predetermined value according to the magnitude of voltage signal width distortion, and is a digital signal that is finally reproduced without being affected by the output of the optical signal. The width can be optimized.

(Example) Hereinafter, an optical receiver according to an example of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an optical receiver according to an embodiment of the present invention, and the optical receiver has the following configuration. A photoelectric conversion element (1) to which a reverse bias is applied and outputs a current proportional to the magnitude of the optical signal from the optical transmission path, and a photoelectric conversion element (1) that is connected to the anode of the photoelectric conversion element (1) and converts the electrical signal into a voltage signal. A current-voltage conversion amplification means (11) for amplifying the current-to-voltage conversion amplification means, and a positive signal which is a first voltage signal from the current-voltage conversion amplification means (11) and a second voltage signal which is a positive signal without the first voltage signal. a separating means (21) for separating the inverted signal generated in the region; and a smoothing means (3) for smoothing the positive signal and the inverted signal, respectively, separated by the separating means (21).
1), (41), and differential means (51) that outputs the difference between the positive signal and the inverted signal smoothed by the smoothing means (31) and (41) and adds it to the voltage signal, and Third
The identification means (61) compares the voltage signal with the identification level and converts it into a binary value.

FIG. 2 is a schematic circuit diagram of this optical receiver, and specifically has the following configuration.

The current-voltage conversion amplification means (11) includes a photoelectric conversion element (1
) is connected to the input of an amplifier (3), a resistor R1 (5) is connected in parallel with this amplifier (3), and a capacitor CI (7) is connected to the output of the amplifier. . The current signal from the photodiode (1) is converted into a voltage signal by the resistor R1 (5), and the current signal from the photodiode (1) is converted to a voltage signal by the amplifier (3).
), and the DC component of the voltage signal is removed by a capacitor CI (7) and output.

It is connected to separation means (21) which separates the voltage signal from this current-voltage conversion amplification means (11) into a positive signal and an inverted signal. The positive signal and the inverted signal from this separation means (21) are connected to smoothing means (31) and (41), respectively. Various types of smoothing means (31) and (41) can be considered, but here, the resistance R3 (35)
.

R4 (45) and capacitor C2 (37), C3 (4
7) and diodes (33) and (43). This capacitor C2 (
37).

It is possible to change the time constant of the integrating circuit by changing the capacitance of C3 (47), but here the time constant is set to 10.
It was set to about 0 pulse time.

The positive signal and the inverted signal smoothed by the smoothing means (31) and (41) are transferred to the differential means (52).
An inverted signal is input to the negative side of the differential means (52).

The output of this differential means (52) is the addition resistor R9 (71
), connected to the input of the separation means (21) through the RIO (72), and furthermore -゛ identification means (
61). The identification means (61) is made up of a comparator (63) and a set voltage power source (65) connected to one terminal of the comparator (63) which applies a voltage of a set voltage VTH as a discrimination level to be input.

Next, the operation of this optical receiver will be explained with reference to FIG.

When the optical signal shown in FIG. 3(a) is transmitted from the optical transmitter, the optical signal becomes dull due to the characteristics of the optical transmitter/receiver or deterioration during transmission, and the output side of the current-voltage conversion amplification means (11) ( 101), a distorted voltage signal is output as shown in FIG. 3(b). The dotted line in the figure shows the case where the optical input signal is small and has negative signal voltage width distortion, and the solid line shows the case where the optical input signal is large and has positive signal voltage width distortion. .

This voltage signal is separated by a separating means (21) into a positive signal which is a first voltage signal and an inverted signal which is a second voltage signal.
Separate into two signal components. Positive signal output section (103)
(C) in Figure 3 shows the signal at the inverted signal output section (10
The signal at step 5) is shown in (d).

These positive signals and inverted signals are respectively smoothed by smoothing means (
31) and (41) and output section (107).

(109) respectively. The output from the output section (107) is shown in (e) in Figure 3, and the output from the output section (109) is shown in the third
It is shown in (f) in the figure. If the signal voltage has positive signal voltage width distortion, the positive signal will be larger than the inverted signal. Therefore, the output signal from the differential means (51) has a negative voltage waveform at the output section (111) as shown in FIG. 3(a). Therefore, the voltage signal and the output signal from the differential means (51) are added together, and the third voltage signal input to the identification means (61) becomes a signal as shown in (h) in FIG. It is possible to reduce signal voltage width distortion to a greater extent than the signal voltage width.

Conversely, when a voltage signal with negative signal voltage width distortion is output from the photoelectric conversion element (1), the voltage signal width distortion is smaller than usual ((b) in FIG. 3), and the differential amplification means ( The output from 51) becomes a positive signal ((g) in FIG. 3), and the third voltage signal input to the identification means (61) is set to be larger than the voltage signal width at the time of input.

Then, a comparator (6
3) and outputs a digital signal.

In this way, in the optical receiver of this embodiment, since the digital signal is outputted by the identification means (61) after sufficiently correcting the voltage signal width distortion, malfunction will not occur even if signal processing is performed on the edge portion of the digital signal. There is no.

In this way, the signal voltage width width of the voltage signal is adjusted according to the magnitude of the voltage signal width distortion regardless of the magnitude of the optical signal, and the voltage signal is adjusted so that the voltage signal width is always constant.
61), it has become possible to create an optical receiver that does not malfunction.

Furthermore, although a simple integrating circuit is used as the smoothing means in this embodiment, a sampling circuit may also be used.

Moreover, although the voltage signal width distortion that changes depending on the magnitude of the voltage signal has been described here, it is also sufficiently effective in eliminating voltage signal width distortion caused by the characteristics of photoelectric conversion elements and the like.

[Effects of the Invention] As described above in detail, the optical receiver of the present invention is capable of suppressing distortion of various signal voltage widths regardless of the size of the optical signal in an optical receiver that handles signals with a duty ratio of about 50%. It can be corrected, and even if used in combination with various optical transmission systems, it will operate differentially without malfunction.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an optical receiver according to an embodiment of the present invention, FIG. 2 is a schematic circuit diagram of an optical receiver according to an embodiment of the present invention, and FIG. 3 is a schematic diagram of an optical receiver according to an embodiment of the present invention. It is a voltage waveform diagram at each part inside. 1)...Photoelectric conversion element 11)...Current-voltage conversion amplification means 21...Separation means 31...Smoothing means 41...Smoothing means 51...Differential means 61... identification means

Claims (1)

[Scope of Claims] A light-receiving element that converts an optical signal from an optical transmission path into a current signal, a current-voltage conversion amplification means that converts the current signal into a voltage signal and amplifies it, and from this current-voltage conversion amplification means. separation means for dividing the voltage signal into a first voltage signal and a second voltage signal; a smoothing means for smoothing the first voltage signal and the second voltage signal, respectively; and this smoothing means. differential means for outputting the difference between the first voltage signal and the second voltage signal smoothed by the first voltage signal; and the difference between the first voltage signal and the second voltage signal smoothed. An optical receiver comprising an adding means for adding the voltage signal and outputting a third voltage signal.