JPH07264142A - Optical reception circuit - Google Patents

Abstract

PURPOSE:To provide an output of a signal without pulse width distortion and missing of a reception signal even when a level of an input signal is fluctuated. CONSTITUTION:An optical input 1 is a burst signal whose level is fluctuated and converted into an electric signal by a light receiving element 2. This signal is amplified by an amplifier 3 and given to a comparator 4 and a reference signal generating circuit 6. The reference signal generating circuit 6 generates a reference signal fluctuated in interlocking with the amplitude of a received pulse signal based on the pulse signal with a different amplitude level and gives the voltage to the comparator 4. As a result, an output of the comparator 4 is a signal reproduced from a burst signal of the optical input 1 with fidelity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver circuit used in an optical communication system, and more particularly, to a fluctuation in the amplitude of a received signal within the same frame due to a fluctuation in the power level of an optical input. The present invention relates to an optical receiver circuit that receives a burst signal.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing a configuration example of a conventional optical receiving circuit. In FIG. 4, 1 is an optical signal, 2 is a light receiving element, 3 is an amplifier, and 4 is a comparator.

In the optical receiving circuit according to the prior art shown in the drawing, a light receiving element 2 for converting an optical signal 1 into an electric signal, an amplifier 3 for amplifying the converted electric signal, and an output signal of the amplifier 3 is applied to one input end. And a comparator 4 to which a reference voltage Vref having a constant potential is applied to the other input terminal.

In the optical receiving circuit according to this prior art, the received signal received by the light receiving element 2 and converted into an electric signal is amplified by the amplifier 3 with a predetermined amplification degree, and the output of the amplifier 3 and the reference voltage Vref are obtained. The comparator 4 compares and outputs a signal exceeding the reference voltage Vref as a burst signal reception output signal.

As another conventional technique of the optical receiving circuit,
In order to cope with the deterioration of the receiving sensitivity due to the fluctuation of the input level of the optical signal, the automatic gain control circuit is used to control and amplify the amplifier to amplify the optical signal of different levels with different gains according to the input level. A technique is known in which the subsequent signal level is kept constant.

As a conventional technique for improving the transmission efficiency of optical communication, for example, the technique described in Japanese Patent Laid-Open No. 4-342325 is known. This prior art relates to an optical receiver for burst optical transmission, in which the signal waveform level and the discrimination level are raised near the beginning of the burst signal, and these levels are returned to their original set levels as they go backwards. By making it possible to identify the signal near the beginning of the burst signal, the length of the preamble is shortened and the transmission efficiency is improved.

[0007]

In the prior art described with reference to FIG. 4, it is necessary to set a reference voltage as a discrimination level to a constant potential for received signals having different amplitudes. For this reason, in the above-mentioned conventional technique, when the rise time and the fall time of the received signal are so long that they cannot be ignored, the ratio between the discrimination level and the signal amplitude becomes indefinite depending on the magnitude of the signal amplitude, and pulse width distortion is generated in the received signal. It has a problem that it causes a lot. Further, this conventional technique has a problem that the signal cannot be discriminated when a signal smaller than the discrimination level is input, and in order to avoid this, the discrimination level is set to a value close to the base level. When set, when a signal with a large amplitude is input,
Even the noise when there is no signal is identified as a signal, which causes a problem that a malfunction occurs.

Further, in the prior art of the optical receiving circuit using the above-mentioned automatic gain control circuit, the fluctuation range of the optical input level is large and the input level is immediately after the frame with the minimum input level (gain maximum) is input. When the frame with the maximum (gain minimum) is input, or vice versa, the frame with the minimum input level (gain maximum) is input immediately after the frame with the maximum input level (gain minimum) is input. Assuming that, the number of bits of the preamble inserted between frames must be increased until the gain control (AGC) becomes stable, which causes a problem of deteriorating transmission efficiency in optical communication. There is.

Further, in the prior art in which the discrimination level and the signal level are raised near the beginning of the burst signal in order to shorten the preamble, many bits for the preamble are required before the discrimination level rises, and thus optical communication is required. However, there is a problem that the transmission efficiency in the above is deteriorated. Further, this conventional technique has a problem that a signal amplitude waveform is deteriorated by inserting a capacitor, and when used in a communication system with a large optical input level difference, a lot of pulse width distortion occurs in a received signal. Will cause it.

The object of the present invention is to solve the above-mentioned problems of the prior art and to output a signal without pulse width distortion without losing the received signal even when the level of the input signal fluctuates. Another object of the present invention is to provide an optical receiving circuit that can be used.

[0011]

According to the present invention, the above object is to amplify a received signal received by a light receiving element and converted into an electric signal by an amplifier with a predetermined amplification degree, and to output an output signal of the amplifier and a reference signal. This is achieved by changing the reference signal in synchronism with the amplitude of the output signal of the amplifier in the optical receiving circuit that outputs the received signal by comparing with.

That is, the object is to include a comparator for comparing an output signal of an amplifier and a reference signal, and a reference signal generating circuit for generating a reference signal, wherein the reference signal generating circuit uses the output signal of the amplifier. A reference signal that has a fixed base level and that varies in accordance with the amplitude of a pulse signal having a different pulse amplitude is generated as a reference voltage, and the comparator has:
This is achieved by applying the output signal from the amplifier to one input terminal and applying the reference voltage from the reference signal generating circuit to the other input terminal.

[0013]

The reference signal generating circuit receives a pulse signal having a fixed base level and different pulse amplitude, and generates a reference signal whose amplitude is controlled at a preset ratio with respect to the amplitude of the input pulse signal. An output signal obtained by integrating the reference signal is generated and output as a reference voltage. The above-mentioned pulse signal having a fixed base level and different pulse amplitudes is input to one input terminal of the comparator, and the reference voltage from the reference signal generating circuit is input to the other input terminal. As a result, in the optical receiving circuit of the present invention, the discrimination level is always at a constant ratio of the signal amplitude with respect to the input signal to the comparator having a fixed base level and different pulse amplitudes. Even when the signal level fluctuates, a signal without pulse width distortion can always be output.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical receiving circuit according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an optical receiving circuit for burst signals according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing the configuration of a reference signal generating circuit, and FIG. 3 is an embodiment of the present invention. It is a figure which shows the signal waveform of each part explaining operation | movement. In FIGS. 1 and 2, 6 is a reference signal generation circuit, R1 to R5.
Is a resistor, C1 is a capacitor, and other symbols are the same as in FIG.

An optical receiving circuit according to an embodiment of the present invention includes a light receiving element 2 for converting an optical signal 1 into an electric signal, an amplifier 3 for amplifying the converted electric signal, and one of the two branched amplifiers 3. An output signal is input, a reference signal generation circuit 6 that generates a reference voltage based on the amplitude of this signal, and the other output signal of the amplifier 3 which is branched into two is applied to one input terminal and the other input terminal is applied. And a comparator 4 to which the reference voltage from the reference signal generating circuit 6 is applied.

The optical signal 1 is, for example, a signal of time division multiplex communication between a main device and a plurality of slave devices which are point / multipoint connected by an optical fiber, and are the same because of variations in their power levels. It is a burst signal in which the amplitude of the received signal varies within the frame. Therefore, the output signal amplified by the amplifier 3 becomes a pulse signal having a fixed base level and different pulse amplitudes.

As shown in FIG. 2, the reference signal generating circuit 6 is composed of resistors R1 to R5, a capacitor C1 and a power source V2, and the received signal amplitude fluctuates due to the fluctuation of the power level of the optical input from the terminal A. The output signal of the amplifier 3, which is a burst signal, is input. In this circuit, the resistors R1, R2, and R3 are controlled based on the amplitude of the input burst signal so that a signal having an amplitude of a predetermined proportion of the amplitude is output as a reference signal. There is. Further, the resistor R3, the resistor R4, the power source V2
Controls the base level of the input burst signal to be the base level of the output reference signal. The controlled reference signal is integrated by the resistor R5 and the capacitor C1, output as a reference voltage from the terminal B, and input to the comparator 4.

The comparator 4 compares the input output signal of the amplifier 3 with the reference voltage from the reference signal generating circuit 6,
The optical signal 1 is output as a received signal. The output signal from the amplifier 3 is a burst signal in which the amplitude of the received signal fluctuates in the same frame due to fluctuations in the power level of the optical signal 1. For example, as shown in FIG. The pulse signals have different amplitude levels, and the pulse signals are input to one input terminal of the comparator 4. Further, the reference voltage signal output from the reference signal generation circuit 6 based on this pulse signal is a pulse signal having a certain proportion of the pulse signal level of the output signal of the amplifier 3 as shown in FIG. 3B. And this signal is input to the other input terminal of the comparator 4.

As a result, the output signal of the optical receiver according to the embodiment of the present invention output from the comparator 4 is controlled in accordance with the amplitude of the optical input 1 so that the reference level which is the discrimination level is variably controlled. As shown in FIG. 3C, the burst signal of the optical input 1 is faithfully reproduced.

[0021]

As described above, according to the present invention, the optical input power level, which is multiplexed and input from a plurality of slave devices having different transmission distances, fluctuates, and the amplitude of the optical reception signal fluctuates. Since the optimum reference signal can be set for the generated burst signal to identify the signal, the received signal is not lost and a signal having a uniform pulse width with no pulse width distortion is output. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a burst signal optical receiving circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a reference signal generation circuit.

FIG. 3 is a diagram showing a signal waveform of each part for explaining the operation of the embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration example of a conventional optical receiving circuit.

[Explanation of symbols]

 1 Optical signal 2 Light receiving element 3 Amplifier 4 Comparator 6 Reference signal generating circuit R1 to R5 Resistor C1 Capacitor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H04B 10/06 H04L 25/03 E 9199-5K 25/06 9199-5K (72) Inventor Hitoshi Hashimoto 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (3)

[Claims] 1. A reference signal for comparison for detecting a received signal in an optical receiving circuit for receiving a burst signal in which the amplitude of the received signal fluctuates because the power level of an optical input fluctuates. An optical receiving circuit, wherein the optical receiving circuit is changed in association with the amplitude of the burst signal. 2. A burst signal having a fixed base level is applied to one input terminal of a comparator, and a reference signal that varies in conjunction with the amplitude of the burst signal is applied to the other input terminal of the comparator as a reference voltage. The light receiving circuit according to claim 1, wherein 3. An optical receiver circuit for receiving a burst signal in which the amplitude of a received signal varies due to a change in the power level of an optical input, and a reference signal which varies in conjunction with the amplitude of the burst signal is used. A reference signal generating circuit for generating a reference voltage; and a comparator for applying the burst signal having a fixed base level to one input terminal and applying the reference voltage to the other input terminal. Optical receiver circuit.