JPH01149558A - Light transmitting data receiving circuit - Google Patents

Abstract

PURPOSE:To enlarge the dynamic range of a detectable level without increasing the supply voltage of a receiving amplifying circuit and, simultaneously, to surely detect data regardless of single data and successive data by providing a non-linear amplifying circuit and a detecting circuit, etc. CONSTITUTION:When a photodetector 11 light-receives a transmitting light, the element 11 generates a sawtooth wave current signal, the signal is converting-amplified to a voltage signal e0 by a current-voltage converting amplifier 121 of a non-linear amplifying circuit 12, and it is inputted to a non- linear converter 122. At the converter 122, first, the voltage e0 and a first reference voltage e1 are compared by a first compressing circuit (a), next, a voltage ea and a second reference voltage E2 are compared by a second compressing circuit (b), and an input signal is outputted by being compressed at two stages according to the comparison results. An output signal eb of the converter 122 is inputted to a detecting circuit 13 and a threshold control circuit 14, the circuit 13 outputs the signal of an H level when the input signal eb is at the threshold or above, the circuit outputs the signal of an L level when the signal eb is at the threshold or below, and digital data are reproduced. Thus, the dynamic range of the receivable level can be enlarged, and the data are surely detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an optical transmission data receiving circuit that receives and detects digital data transmitted by light.

(Prior Art) In general, an optical transmission data receiving circuit receives transmitted light with a light receiving element to generate a current signal, amplifies this current signal in a receiving amplifier circuit using a linear amplifier, and then uses a detection circuit to identify a threshold value. It is configured to detect data by comparing it with the data, and its detection method consists of the following methods alone or in combination.

(1) AGC (Automatic Gain Control) Method This is a method in which the level of a received signal is detected and the gain of the receiving amplifier circuit is controlled according to this detected level.

(2) ATC (Automatic Threshold Control) Method This is a method in which the threshold value for detecting 1 and 0 data is controlled in accordance with the level of the received signal so that it is close to the optimum value according to the signal level.

(3) AC coupling method The output end of the receiving amplifier circuit and the input end of the detection circuit are AC coupled by a capacitor or the like. For example, the output of the amplifier is passed through the capacitor to form a differential waveform, and this differential signal is sent to the detection circuit. In this method, the data is played back by inputting it into the .

(4) Direct coupling method This is a method in which the output terminal of the reception amplifier circuit and the input terminal of the detection circuit are directly coupled, and the amplification degree and detection threshold are not controlled.

Here, the above AGC method and ATC method are control methods assuming that data is transmitted continuously. However, although such a system is effective in a data transmission line between points, the response speed of AGC and ATC becomes a problem in a line where the reception level changes rapidly. Further, although the AC coupling method has the feature of being strong against sudden changes in the reception level, it is weak against noise and has the problem of requiring complicated circuits such as differential processing. The direct coupling method has drawbacks such as deterioration in detection performance due to temperature changes in the offset voltage of the amplifier and the dark current of the light receiving element, and changes in the phase and width of the reproduced pulse due to the magnitude of the reception level.

Therefore, in either method, in order to expand the dynamic range of the detectable level, it is necessary to increase the circuit power supply voltage of the linear amplifier, which is disadvantageous in terms of circuit configuration.

(Problems to be Solved by the Invention) As described above, in the conventional optical transmission data receiving device,
In either method, in order to expand the dynamic range of the detectable level, it is necessary to increase the circuit power supply voltage of the receiving amplifier circuit, making the circuit configuration disadvantageous.

This invention was made to solve the above problem.
Provides an optical transmission data receiving circuit that can expand the dynamic range of detectable levels without the need to increase the circuit power supply voltage of the receiving amplifier circuit, and that can reliably detect data regardless of whether it is single data or continuous data. The purpose is to

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, an optical transmission data receiving circuit according to the present invention includes: a light receiving element that receives light indicating transmission data and generates a signal; A non-linear amplifier amplifies the signal generated by this light-receiving element with a high gain when the signal is below a set level and a low gain when the signal is above the set level, and data is detected from the output signal of this non-linear amplifier. and a detection circuit.

(Function) The optical transmission data receiving circuit with the above configuration uses a nonlinear amplifier to amplify the low level signal and compress and amplify the high level signal of the signal obtained by the light receiving element, so the detectable dynamic range is is dramatically expanded, and the reception performance of transmission data signals having sharp level changes over time is also dramatically improved.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

Figure 1 shows the configuration when the present invention is applied to an ATC type optical transmission data receiving circuit.
N photodiode) 11 receives light from the transmission destination,
Generates a current signal in response to light. This current signal is supplied to the nonlinear amplifier circuit 12. This nonlinear amplifier circuit 12 includes a current-voltage conversion amplifier 121 and a nonlinear conversion S 122.
The current signal is voltage amplified by the current-voltage conversion amplifier +21 and then input to the nonlinear converter 122. This nonlinear converter 122 includes a first compression circuit a consisting of resistors RO, R1, a diode D1, and a first reference voltage source El, and a first compression circuit a consisting of resistors RO, R2, a diode D3, and a second reference voltage source E2. The second compression circuit is
It compresses human input signals in two stages and outputs them.

The output signal of this nonlinear converter 122 is inputted to the detection circuit 13 and the threshold mirror control circuit 14 . The threshold mirror control circuit 14 controls the threshold value of the detection circuit 13 according to the level change of the input voltage, and the detection circuit 13 compares the input signal with the threshold value and determines whether the input signal is equal to or higher than the threshold value. When H
(high) level, and when the human input signal is below a threshold value, an L (low) level signal is output, thereby reproducing digital data.

In the above configuration, its operation will be explained below with reference to FIG. It is assumed that this is occurring.

First, when the sawtooth wave current signal shown in FIG. 2(a) is generated in the light receiving element 11, this current signal is converted to the Ov level at the bottom as shown in FIG. 2(b) in the current-voltage conversion amplifier 121. The signal is converted and amplified into a fixed voltage signal eO, and then input to the nonlinear converter 122.

This nonlinear conversion circuit 122 first compares the input voltage eO and the first reference voltage El in the first compression circuit a. Here, while eo<El, the diode DI is in the off state, so the signal is output as is, and when eO>El, the diode DI is in the on state, and the signal is compressed and output using the resistance ratio of the resistors RO and R1. Next, the voltage signal ea that has passed through the first compression circuit is input to the second compression circuit. Here, while ea > R2, the diode D2 is in the off state, so the output is output as is, and when ea > R2, the diode D2 is in the on state and the resistor RO is output.

It is compressed and output according to the resistance ratio of R1 and R2. That is,
As shown in FIG. 2(C), the output signal eb of the nonlinear converter 122 has a relatively high level part compressed in two stages compared to a low level part.

The voltage signal non-linearly converted in this way is input to the detection circuit 13 and the threshold control circuit 14, and digital data is reproduced by well-known processing. Incidentally, each input impedance of the detection circuit 13 and the threshold control circuit 14 must naturally be higher than the output impedance of the nonlinear converter 121.

Figure 3 shows the actual response waveform. The dotted line in the figure is the waveform during linear amplification, and the solid line is the waveform during nonlinear amplification. As is clear from the figure, when the amplitude value of the input pulse is high, the amplitude value of the output pulse is compressed, and when it is low, it is expanded, so that pulses that could not be detected during linear amplification can also be detected.

Therefore, the optical transmission data receiving circuit configured as described above can amplify the received signal with high gain when the received signal is low level and with low gain when the received signal level is high with a relatively small number of circuit elements. The detectable dynamic range can be easily expanded without increasing the circuit power supply voltage of the amplifier circuit, and thereby digital data can be reliably detected regardless of whether it is single data or continuous data.

It is desirable that the nonlinear characteristics of the nonlinear amplifier circuit change logarithmically as shown in Figure 4, but to achieve this the circuit would become complicated, so it is It is sufficient to compress it with If necessary, it may be set to three or more stages.

Furthermore, if compression is performed at another stage, the level of the output signal will drop, but in this case, if a DC coupling amplifier is placed following the nonlinear converter 122 to perform DC amplification, the detection circuit 13 and threshold control circuit 14 can be operated stably.

Other embodiments are shown in FIGS. 5 to 7. However, in FIGS. 5 to 7, the same parts and the same parts as in FIG. 1 are denoted by the same reference numerals. Figure 5 shows the AGC method, Figure 6
The figure shows the configuration when the present invention is applied to the AC coupling method, and FIG. 7 shows the configuration when the present invention is applied to the direct coupling method.
After the signal obtained in step 1 is logarithmically amplified by a nonlinear amplifier circuit 12, digital data is reproduced.

In addition, in FIGS. 5 to 7, 15 is the nonlinear amplifier 1.
16 is a reference voltage source that generates a detection threshold; 17 is a level control circuit that controls the gain of 2 according to its output level;
is an AC coupling capacitor. The response waveforms of each circuit are shown in FIGS. 8 to 10. In each figure, the dotted line indicates the case of linear amplification, and the solid line indicates the case of nonlinear amplification. In both cases, the detectable dynamic range has been expanded, making it possible to detect pulses that could not be detected with linear amplification.

[Effects of the Invention] As described above, according to the present invention, the dynamic range of the receivable level can be expanded without the need to increase the circuit power supply voltage of the receiving amplifier circuit, and it is possible to reliably receive data regardless of whether it is single data or continuous data. An optical transmission data receiving circuit capable of detecting data can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing an embodiment of an ATC type optical transmission data receiving circuit according to the present invention, FIG. 2 is a waveform diagram for explaining nonlinear conversion of the embodiment, and FIG. 3 is the same. FIG. 4 is a characteristic diagram showing ideal nonlinear amplification characteristics of the embodiment, and FIGS. 5 to 7 are block circuits showing other embodiments according to the present invention. 8 to 10 are diagrams showing the response waveforms of FIGS. 5 to 7, respectively. 11... Light receiving element, 12... Nonlinear amplifier circuit, 12
DESCRIPTION OF SYMBOLS 1... Current-voltage conversion amplifier, 122... Nonlinear converter, 13... Detection circuit, 14... Threshold control circuit, 15... Level control circuit, 1B... AC coupling capacitor, 17... reference voltage source. Applicant's agent Patent attorney Takehiko Suzue Figure 4

Claims (1)

[Claims] A light receiving element that receives light indicating transmission data and generates a signal, and a non-light receiving element that amplifies the signal generated by this light receiving element with a high gain when the signal is below a set level and with a low gain when the signal is above the set level. An optical transmission data receiving circuit comprising a linear amplifier and a detection circuit that detects data from an output signal of the nonlinear amplifier.