JPS6133732Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved binary optical signal receiving device.

Conventionally, a photoelectric conversion element such as an APD (avalanche photo diode) or a PiN diode has been used in a light receiving section of a binary optical signal receiving device for high speed. These elements are expensive and are not easy to handle. Therefore, when a low speed is acceptable, devices such as a photo transistor with a built-in amplifier element or a Darlington photo transistor are used, which are inexpensive and have a large signal output.
However, these low-speed photoelectric conversion elements have a drawback of very poor temperature characteristics. FIG. 1 shows the temperature characteristics of a phototransistor with a built-in amplifier element, where the horizontal axis shows temperature and the vertical axis shows output. The broken line shows the dark current value, the solid line shows the photocurrent value, and the three solid lines A, B, and C each show the photocurrent value when the received light power is used as a parameter. As shown in FIG. 1, this device had the disadvantage that it could not be used in places where there were large temperature fluctuations, since both the photocurrent value and the dark current value increased as the temperature rose.

In addition, in such a photoelectric conversion element, when the received light power increases, the element becomes saturated, and when the received light power increases further, the falling speed of the element becomes slower, so the element does not operate normally with short-cycle binary signals. do not. FIG. 2 shows the output waveform of the element when the received light power is used as a parameter, where the vertical axis shows the output voltage and the horizontal axis shows time. Here, K indicates a reference voltage for determining level "1" or "0". In FIG. 2, A is the output waveform when the received light power is small, and although there is a time delay, the level "1" or "0" can be correctly determined. As the received light power is increased, the output waveform becomes as shown in (b), and the time at level "1" becomes longer and the time at level "0" becomes shorter. If the received light power is further increased, the output voltage will always be higher than the reference voltage K as shown in C, making it impossible to determine level "0". For this reason, when these photoelectric conversion elements are used, there is a drawback that the reference voltage must be adjusted according to the received light power. Furthermore, the photoelectric conversion element with a built-in amplification element has a drawback in that the current amplification rate of the amplification element differs depending on the element.

The present invention forms the light receiving section with a low-speed photoelectric conversion element that is inexpensive and has a large signal output, and compensates for the above-mentioned drawbacks of this element using a temperature compensation circuit and a level detection/voltage generation circuit. The present invention provides a binary optical signal receiving device that can be used over a wide temperature range, can operate without adjustment even if the received light power changes greatly, and is simple and inexpensive to produce.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 3 is a block diagram showing the configuration of the present invention. The binary optical signal L is photoelectrically converted by the photoelectric conversion element 1 . Then, the output of the photoelectric conversion element 1 is input as a comparison input to a voltage comparator 4 for binarization, and a level detection/voltage generation circuit consisting of a level detection circuit and a voltage generation circuit that generates a voltage according to the detection level. Input to circuit 2. The output of the level detection/voltage generation circuit 2 is added to the output of the temperature compensation circuit 3 to become a reference voltage for the comparator 4.

Here, the output characteristics of the temperature compensation circuit 3 will be explained using FIG. 1.

Now, assuming that the output current for the minimum received light power is the solid line A, the output of the temperature compensation circuit 3 changes as shown by the dashed-dotted line D in FIG. 1 when converted to current. The current at the bottom is determined to have a reception level of "0", and the current above this dashed-dotted line D is determined to have a reception level of "1". 1st
As shown in the figure, the temperature change characteristics of the output of the temperature compensation circuit 3 are the same as those of the photoelectric conversion element 1 at the minimum receiving power.
Set so that the temperature characteristics and change ratio of the output current are almost the same. Further, the output value of the temperature compensation circuit 3 at the maximum operating temperature is set to be the geometric mean value of the dark current value at that temperature and the output current at the minimum received light power. By doing so, it is possible to prevent the influence of temperature changes on the photoelectric conversion sensitivity of the photoelectric conversion element, and at the same time, it is possible to reduce the sudden increase in dark current due to temperature rise.

Moreover, by doing this, when considering variations in the elements and variations due to other factors, the temperature characteristics as described above can provide the highest reliability and the greatest margin.

In addition, since the level detection/voltage generation circuit 2 outputs a voltage according to the force applied to the photoelectric conversion element 1, the received light power increases and the output of the photoelectric conversion element 1 becomes as shown in FIG. In this case, the reference voltage key is increased by the output of the level detection/voltage generation circuit 2, so that it is possible to accurately judge whether the reception level is "0" or "1". Next, a specific circuit will be shown and explained.

FIG. 4 is a circuit diagram showing an embodiment of the present invention. In FIG. 4, 5 is a phototransistor which is a photoelectric conversion element with a built-in amplification element, 6 is a load resistor, 7 is a current limiting resistor, and 8 is a bypass capacitor. Here, since the speed of a photoelectric conversion element with a built-in amplifier element varies widely depending on the load resistance, the speed is increased by decreasing the value of the load resistance. In this case, if the operating temperature is high and the received light power increases, the power consumption of the photoelectric conversion element will exceed the rated value, so connect a power limiting resistor like this in series with the power supply to reduce the power consumption to the rated value. I try not to exceed.

9 is an amplifier 10, 11, a diode 12, 1
3. A level detection/voltage generation circuit consisting of a capacitor 14. Here, the amplifier 10 is a buffer amplifier, and its output passes through a diode 12 and charges a capacitor 14. The amplifier 11 is a buffer amplifier with high input resistance, and slowly discharges the charge stored in the capacitor 14. diode 13
becomes conductive when the output voltage of the amplifier 11 becomes larger than the minimum reference voltage output from the temperature compensation circuit 15. Further, the gain of the amplifier 10 or the amplifier 11 is set to 1 or less so that the output voltage of the level detection/voltage generation circuit 9 does not exceed the maximum value of the output voltage of the photo transistor 5.
Temperature compensation circuit 15 includes a thermistor 16 and a resistor 1
It consists of 7, 18, and 19. A comparator 20 compares the output of the photo transistor 5 with the voltage obtained by adding the output of the level detection/voltage generation circuit 9 to the output (minimum reference voltage) of the temperature compensation circuit 15.

The operation of this embodiment configured as above will be explained.

First, when the received light power is small, the comparator 20
The reference voltage is thermistor 16, low resistance resistor 17, 1
This is the minimum reference voltage determined by 8 and 19. This minimum reference voltage is the first
It changes as shown by the dashed line in the figure. When the received light power increases and the output of the phototransistor 5 increases, the voltage of the capacitor 14 increases and the amplifier 1
When the output voltage of amplifier 1 exceeds the minimum reference voltage, diode 13 becomes conductive, and the output of amplifier 11 is connected to resistor 19.
Since the reference voltage of the comparator 20 is added to the minimum reference voltage, the reference voltage of the comparator 20 increases.

In this embodiment, the reference voltage of the comparator 20 changes continuously as the output of the photo transistor 5 increases, but if the amplifier 10 is used as a voltage comparator, it changes discretely.

As explained above, according to the present invention, the conversion sensitivity and dark current of the photoelectric conversion element are not affected by changes in temperature, so it can be used over a wide temperature range and can operate without adjustment even if there are large changes in received light power. and
It has the remarkable advantage of being simple and having low production costs over conventional methods.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the temperature characteristics of a photoelectric conversion element.
Fig. 2 is a diagram showing changes in the received light power of a photoelectric conversion element, Fig. 3 is a block diagram showing the basic configuration of the present invention, and Fig. 4 is a circuit diagram showing an embodiment of the present invention. . 1...Photoelectric conversion element, 2, 9...Level detection/
Voltage generation circuit, 3, 15...Temperature compensation circuit, 4,
20... Comparator.

Claims (1)

[Claims for Utility Model Registration] A photoelectric conversion element that receives a binary optical signal, a level detection/voltage generation circuit that detects the output of the photoelectric conversion element and outputs a voltage according to the output, and a temperature change rate. is a voltage equal to the rate of change of the photoelectric conversion sensitivity of the photoelectric conversion element, and the geometric mean of the dark current value of the photoelectric conversion element at the maximum temperature of use and the current value corresponding to the minimum received light power at the maximum temperature of use. A temperature compensation circuit that generates a voltage corresponding to the value, and a reference voltage created by adding the output of the temperature compensation circuit and the output of the level detection/voltage generation circuit, and the output voltage of the photoelectric conversion element are compared. 1. A binary optical signal receiving device comprising: a comparator;