JPH02280442A - Optical reception circuit - Google Patents

Abstract

PURPOSE:To ensure the waveform shaping of an optical signal and to enhance the sensitivity of a reception circuit by increasing the time constant of a capacitor coupling circuit more than the pulse width of a burst optical signal and decreasing the time constant less than the length of the burst signal. CONSTITUTION:A photodetection 7 is provided to set the time constant of a capacitor coupling circuit, thereby increasing the length of the time constant more than the pulse width and decreasing it less than the width of the burst signal in a digital optical receiver in which the burst optical signal whose non- signal state and data part take place alternately is converted into an electric signal by a photodetector 1, amplified by a preamplifier circuit 2 and the resulting signal is coupled in terms of AC by a capacitive element 3 to a main amplifier circuit 4. Thus, the waveform shaping is surely implemented from the initial pulse waveform of the burst signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital optical receiving circuit, and more particularly to an optical receiving circuit suitable for waveform shaping of a digital optical signal.

[Conventional technology] FIG. 2(a) shows an example of a conventional optical receiving circuit.

In FIG. 2(a), an optical input is received by the light receiving element 1, converted into a current, and converted into a voltage by the #J amplifier 2. In FIG. The output of the preamplifier 2 is then coupled to the main amplifier 4 via a capacitor 3, and the waveform is shaped by a comparator to obtain an output. In FIG. 1(a), since the time constant of the condenser coupling circuit is conventionally set large, the burst signal received by the preamplifier 2 is
As shown in waveform 8 in b), a gradual DC level fluctuation is generated at the input of the main amplifier 3. This waveform 8 is amplified by the main amplifier 4 and input to the comparator 5. Since the comparison level of the comparator 5 is set relatively to the level indicated by the dotted line 9 in FIG. 2(b), there is a drawback that the beginning part of the burst waveform 8 cannot be compared.

In order to improve this drawback, the capacitor 3 shown in Fig. 2(a) is
When is replaced with the differentiating circuit 6 as shown in Fig. 3(a), the output waveform of the differentiating circuit 6 becomes as shown in 10 in Fig. 3(b), so the burst signal can be detected from the first pip 1. However, since the waveform 10 is a sharp pulse waveform, there is a problem in that, for example, the frequency bandwidth of the main amplifier 4 blunts the waveform and reduces its amplitude, reducing the sensitivity of the optical receiving circuit.

[Problems to be Solved by the Invention] The conventional circuit described using FIGS. 2 and 3 has a problem in that the waveform shaping of the burst signal becomes uncertain.

An object of the present invention is to provide an optical receiving circuit that can always reliably shape the waveform of the burst signal.

[Means for Solving the Problems] In order to achieve the above object, the present invention converts a burst-like optical signal in which a no-signal state and a data portion occur alternately into an electrical signal using a light-receiving element. The time constant of the capacitor coupling circuit of the digital optical receiver, which is amplified by a width circuit and AC coupled to the main amplification circuit by an element, is set to be larger than the pulse width of the burst-like optical signal; Make it shorter than the length of the signal.

[Function 1] The optical receiving circuit configured as described above can perform waveform shaping with sufficient accuracy from the first pulse of the burst optical signal.

[Embodiment] Hereinafter, an embodiment of the present invention will be described using FIG. 1. 1st
In the figure, a resistive element 7 is inserted to set the above-mentioned time constant of the capacitor coupling circuit. If the above-mentioned time constant is smaller than the pulse width, the same drawback as explained in Fig. 3 will occur, and if it is too large, the fault explained in Fig. 2 will occur1. Therefore, a good range of the above-mentioned time constant 1 is larger than the above pulse width and is within a range smaller than the width of the burst signal. 11 in Fig. 1(b) is the resistor 7 terminal when the above time constant is set to approximately twice the pulse width. This is the voltage waveform of Since the first pulse waveform of the burst signal clearly exceeds comparison level 9, it can be seen that the above-described waveform shaping operation is reliably performed.

[Effects of the Invention] When the present invention is applied as described in detail above, the waveform shaping operation of a bust-shaped optical signal can be ensured, and at the same time, the sensitivity of the optical receiving circuit can be increased.

[Brief explanation of drawings]

FIG. 1(a) is a circuit diagram showing one embodiment of the optical receiving circuit of the present invention, and FIG. 1(b) is a circuit diagram showing one embodiment of the optical receiving circuit of the present invention.
1-width amplifier input waveform diagrams, Figures 2(a) and 3(a) are circuit diagrams of conventional optical receiver circuits, Figures 2(b) and 3(b)
) is a main amplifier input waveform diagram of a conventional optical receiving circuit. 1: Photodetector, 2: Preamplifier circuit, 3: Capacitor, 4: Main amplifier, 5: Comparator, 6: Differential circuit. Agent Patent Attorney Susuki 11 Published by Yuki

Claims (1)

[Claims] 1. Optical reception in which a burst optical signal in which a no-signal state and a data portion occur alternately is converted into an electrical signal by a light receiving element, amplified by a preamplifier circuit, and AC coupled to the main amplifier circuit by a capacitor element. An optical receiving circuit characterized in that the time constant of the capacitor coupling circuit is larger than the pulse width of the burst-like optical signal and shorter than the length of the burst signal.