JPS63303503A - Light receiving circuit - Google Patents

Abstract

PURPOSE:To receive desired signal light with an excellent SN ratio by adding a resonance circuit to resonate with a special frequency and amplify selectively the electric signal of the frequency to a negative feed-back amplifier circuit. CONSTITUTION:When the light, in which luminance modulation is executed at a prescribed frequency (f), is propagated in a space and received by a semiconductor light- receiving device 1, the light receiving device 1 converts the light receiving signal to the electric signal and outputs it to a negative feed-back amplifier circuit 2. In this case, a signal component and a disturbance light component are included to an output current ip of the light receiving device 1. At a feed-back circuit 3 of the circuit 2, a resonance circuit 4 to make a resonance frequency f0 coincident to the frequency 1 is provided, the circuit 4 is resonated by the resonance frequency f0 and an impedance Z is significantly increased. As the result, for the circuit 4, the impedance Z is higher to the signal light component of the frequency (f) and the Z is lower to the disturbance light component of other frequency. For this reason, in the circuit 2, the signal light component of the frequency (f) coincident to the resonance frequency f0 is selected, on the other hand, the disturbance light component of the frequency except it is attenuated and the signal light of the excellent SN ratio is outputted.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to, for example, an optical receiving circuit for receiving signal light propagating in space. The present invention provides an optical receiving circuit that receives signal light.

<Prior Art> As shown in FIG. 4, a conventional optical receiving circuit of this kind is known in which a negative feedback amplifier circuit 22 is connected to a semiconductor light receiver 21 such as a photodiode. This negative feedback type amplifier circuit 22 has a configuration in which an operational amplifier 23 is provided with a negative feedback resistor 24, and is configured as shown in FIG. 5, for example. The circuit in the figure consists of two transistors 25.2
6, and a negative feedback resistor 25 is connected between the output terminal of the transistor 26 in the subsequent stage and the input terminal of the transistor 25 in the previous stage.

In this optical receiving circuit, the output current of the semiconductor optical receiver 21 is '? + If the resistance value of the negative feedback resistor 24 is Rf, the input impedance of the operational amplifier 23 is usually high, so most of the current i flows through the negative feedback resistor 24 and is output to the output terminal 27.
An output voltage v0 of 12×Rf appears.

<Problems to be Solved by the Invention> By the way, in the optical space transmission method in which signal light is emitted into space and transmitted, in order to be able to distinguish between the signal light and disturbance light, it is necessary to change the brightness of the signal at a predetermined frequency. A method of modulating and transmitting is adopted.

However, in the case of the conventional optical receiving circuit described above, frequency components other than the predetermined frequency are also amplified with the same amplification factor, so there is a problem that the S/N ratio becomes poor.

This invention was made with attention to the above-mentioned problem, and provides a novel optical receiving circuit that can receive a desired signal light with an excellent signal-to-noise ratio by selecting and amplifying only specific frequency components. The purpose is to provide.

<Means for Solving the Problems> In order to achieve the above object, the present invention includes a semiconductor photoreceptor for receiving light and converting it into an electrical signal, and a semiconductor photodetector for amplifying the electrical signal and extracting an output signal. In the optical receiving circuit comprising a negative feedback amplifier circuit, the negative feedback amplifier circuit is further provided with a resonant circuit that resonates at a specific frequency and selectively amplifies the electrical signal of that frequency. I made it.

Effect> When light whose brightness is modulated at a predetermined frequency propagates through space and is received by a semiconductor photodetector, the semiconductor photodetector converts the received light signal into an electrical signal and outputs it to a negative feedback amplifier circuit. A resonant circuit is added to this negative feedback type amplifier circuit, and the resonant frequency of this resonant circuit is set so that it resonates at the predetermined frequency and its impedance changes.

As a result, the resonant circuit functions to selectively amplify the electric signal of the predetermined frequency with respect to the negative feedback amplifier circuit, thereby removing disturbance light components of frequencies other than the above, and only the signal light component. is selected and retrieved. Therefore, the desired signal light is received with an excellent signal-to-noise ratio.

Embodiment FIG. 1 shows an optical receiving circuit according to an embodiment of the present invention, which includes a semiconductor optical receiver 1, a negative feedback amplifier circuit 2 connected in series with the semiconductor optical receiver 1, and a negative feedback amplifier circuit 7 connected in series with the semiconductor optical receiver 1. The negative feedback amplifier circuit 2 includes a feedback circuit 3 and a resonant circuit 4 provided in place of a negative feedback resistor.

The semiconductor light receiver 1 is for receiving light propagating in space and photoelectrically converting it to obtain an electric signal. In the illustrated example, a photodiode is used as the semiconductor light receiver 1, but it is not limited to this, and a phototransistor or C
It is also possible to use other semiconductor devices such as dS.

The negative feedback amplifier circuit 2 includes an operational amplifier 5 and a feedback circuit 3.
It is configured to amplify the electrical signal and extract an output signal. Now, assuming that the output current of the semiconductor photodetector 1 is tP+the impedance of the feedback circuit 3 is Z, the output voltage v0 of the negative feedback amplifier circuit 2 is given by the following equation.

VO=ip As shown in the figure, the resonance frequency is high at f0, and becomes lower as the resonance frequency f is further away.

Here, the resonant frequency f is made to match the modulation frequency of the spatially transmitted signal light.

FIG. 3 shows another embodiment of the invention, in which a negative feedback amplifier circuit 2 is connected to a semiconductor light receiver 1 made of a photodiode via a resonant circuit 4. In the case of this embodiment, the resonant circuit 4 is a series resonant circuit in which an inductor 7 and a capacitor 6 are connected in series, and its impedance Z is low at the resonant frequency f0 and becomes high when the distance is away from the resonant frequency f0. In the figure, 8 is a negative feedback resistor provided in the feedback circuit 3, and 9 is a resistor for applying a reverse bias to the semiconductor photodetector 1.

Therefore, in the embodiment shown in FIG.
The brightness-modulated light propagates through space and reaches the semiconductor photodetector 1.
When the light is received by the semiconductor light receiver 1, the semiconductor light receiver 1 converts the light reception signal into an electrical signal and outputs it to the negative feedback amplifier circuit 2. In this case, the output current of the semiconductor photodetector 1 is 1. includes a signal light component and a disturbance light component. The feedback circuit 3 of the negative feedback amplifier circuit 2 is provided with a resonant circuit 4 whose resonant frequency f0 is set to the frequency f, and this resonant circuit 4 resonates at the resonant frequency f0 and its impedance Z becomes significantly high (see Figure 2 (1)). As a result, this resonant circuit 4 has a high impedance Z for the signal light component of the frequency f, and a low impedance Z for the disturbance light components of other frequencies.

(Since the output voltage v0 of the negative feedback amplifier circuit 2 is given by the above equation 0, the signal light component of the frequency f that coincides with the resonance frequency f0 is selectively amplified in the negative feedback amplifier circuit 2, and on the other hand, As a result, disturbance light components of other frequencies are attenuated (see FIG. 2 (2)), and a desired signal light is outputted to the output terminal 10 with an excellent signal-to-noise ratio.

In the case of the embodiment shown in FIG. 3, the resonant circuit 4 resonates at its resonant frequency f, and its impedance Z becomes extremely low. As a result, this resonant circuit 4 has a low impedance Z for the signal light component of the frequency f (and a high impedance Z for the disturbance light components of other frequencies. The component easily flows through the resonant circuit 4, while the disturbance light component hardly flows through the resonant circuit 4. Therefore, the negative feedback amplifier circuit 2 selectively amplifies the signal light component, and the output terminal 10 receives the desired signal. Light is extracted with excellent signal to noise ratio.

<Effects of the Invention> As described above, the present invention provides an optical receiving circuit that amplifies an electrical signal obtained by a semiconductor optical receiver using a negative feedback amplifier circuit and extracts an output signal. Since a resonant circuit is added to resonate and selectively amplify the electrical signal of that frequency, it is possible to attenuate disturbance light components other than the specific frequency and selectively extract only the signal light component of the specific frequency. The present invention achieves remarkable effects such as being able to receive desired signal light with an excellent signal-to-noise ratio.

[Brief explanation of the drawing]

FIG. 1 is an electrical circuit diagram of an optical receiver circuit according to an embodiment of the present invention, and FIG. 2 is a characteristic showing the relationship between frequency and impedance of a resonant circuit and the relationship between frequency and output voltage of a negative feedback amplifier circuit. 3 are electrical circuit diagrams of an optical receiving circuit according to another embodiment, and FIGS. 4 and 5 are electrical circuit diagrams of a conventional optical receiving circuit. 1... Semiconductor photoreceiver 2... Negative feedback amplifier circuit 3,... Feedback circuit 4... Resonant circuit patent
Applicant: Tateishi Electric Co., Ltd. Agent, Patent Attorney: Yu Mitsuru Suzuki i4 pay light receiving i wealth r 1i S(toσ)1hi1hii) Ward name hln
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Claims (1)

[Scope of Claims] [1] An optical receiver comprising a semiconductor photodetector for receiving light and converting it into an electrical signal, and a negative feedback amplifier circuit for amplifying the electrical signal and extracting an output signal. An optical receiver circuit, wherein the negative feedback amplifier circuit is further provided with a resonant circuit that resonates at a specific frequency and selectively amplifies an electrical signal at that frequency. [2] The optical receiver circuit according to claim 1, wherein the semiconductor light receiver is a photodiode. [3] Claim 1, wherein the resonant circuit is an LC parallel resonant circuit provided in a feedback circuit of a negative feedback amplifier circuit.
Optical receiver circuit described in section. [4] The optical receiving device according to claim 1, wherein the resonant circuit is an LC series resonant circuit connected in series to the input side of a negative feedback amplifier circuit.