JPH03214917A - optical receiver - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] 11↓pBJ minutes! The present invention relates to an optical receiver. More specifically, the present invention relates to a circuit configuration of an optical receiver that converts an optical signal into an electrical signal.

2. Description of the Related Art FIGS. 2 and 3 are block diagrams of typical conventional optical receivers, respectively. The optical receiver shown in FIG. 2 includes a preamplifier 2 that amplifies received signals received by a photodetector 1 such as a photodiode and converted into electrical signals, and a main amplifier 3 connected in series to the preamplifier 2. A comparator 5 is connected in series to the main amplifier 3 and outputs a signal to an output terminal 6 when a voltage higher than the reference voltage is input. Further, the optical receiver shown in FIG. 3 includes a filter circuit 4 between the front stage amplifier 2 and the main amplifier 3 of the optical receiver shown in FIG. The filter circuit 4 is provided to remove high frequency noise, and is composed of, for example, a passive filter circuit such as an RC filter.

? Problems to be Solved by Akira Akira In the above-mentioned conventional optical receiver, jitter sometimes increases when the temperature rises during use. This is because, for example, if the preamplifier 2 has a temperature characteristic in which the peaking of the frequency characteristic becomes noticeable at high temperatures as shown in FIG. 4, it will be affected by this peaking.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical receiver that solves the problems of the prior art and does not increase jitter even at high temperatures.

Means for Solving the Problems According to the present invention, there are provided a light receiving element that receives an optical signal and converts it into an electrical signal, an amplifier that amplifies the electrical signal, and a filter circuit that removes noise from the electrical signal amplified by the amplifier. An optical receiver is provided, characterized in that the filter circuit is given a temperature characteristic that corrects the temperature characteristic of the gain of the amplifier.

The main feature of the optical receiver of the present invention is that the filter circuit has temperature characteristics that cancel out the temperature characteristics of the amplifier. In the optical receiver of the present invention, for example, when an amplifier with temperature characteristics in which beaking appears in the frequency characteristics at high temperatures as described above is used, the filter circuit is provided with temperature characteristics in which the band becomes narrower at high temperatures. It is preferable that When an amplifier with such characteristics is combined with a filter circuit, the temperature characteristics of the filter circuit cancel out the temperature characteristics of the amplifier, which is effective in suppressing deterioration in reception sensitivity and increase in jitter of the optical receiver.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the following disclosure is merely an example of the present invention and does not limit the technical scope of the present invention in any way.

Embodiment FIG. 1 shows a block diagram of an optical receiver of the present invention. 1st
The optical receiver shown in the figure has the same configuration as the conventional optical receiver shown in FIG. 3, except that the configuration of the filter circuit 4 is different. Therefore, the explanation will focus on the configuration of the filter circuit 4.

The filter circuit 4 of the optical receiver of the present invention shown in FIG.
Depletion type n-channel MOSFET Q. This is an RC filter using a drain-source resistance RDS. FETQ has a drain connected to the output terminal of the preamplifier 2 and a source connected to the input terminal of the main amplifier 3. Further, the gate of FETQ+ is connected to the collector of bipolar transistor Q2. The collector of the bipolar transistor Q2 is further connected to the high voltage side V through a resistor R1. C, and its emitter is grounded via a resistor R2. The base of the bipolar transistor Q2 is grounded via a constant current source I0, and further connected to the high voltage side Vcc via a diode D whose forward direction is the direction of the constant current I0. The source of FETQ is also connected to the high voltage side Vcc via a resistor R,
It is also grounded via a parallel circuit to a resistor R and a capacitor C. In this way, FETQ. The drain-source resistance RDS and the capacitor C basically constitute a high frequency cutoff RC filter.

FETQ. The drain-source resistance Rns of the FET
It can be controlled as shown in FIG. 5 by the gate-source voltage Vcs of Q. In the filter circuit of the optical receiver of the present invention, the constant current I.

The gate potential of FET Q1 is determined by the forward voltage of diode D through which the current flows. Here, when the current flowing through the diode D is constant, the forward voltage VF of the diode D is as follows: VF(TI) VF(To) = k (Tt
It has a temperature characteristic given by To), and the higher the temperature, the lower the forward voltage. In the filter circuit of the optical receiver mentioned above, the temperature characteristics of this diode D are used to
When the temperature rises, the base potential of transistor Q2 rises, and the collector potential of transistor Q2, that is, the FET
Q. The gate potential of FETQ. The drain of
The structure is such that the source-to-source resistance RDS is large.

Therefore, in the optical receiver of the present invention, the filter circuit 4 has a characteristic that the band becomes narrower as the temperature rises. This characteristic functions in the direction of suppressing peaking when the preamplifier has frequency characteristics in which peaking becomes noticeable at high temperatures. Therefore, the optical receiver of the present invention has high performance without deterioration of receiving sensitivity due to peaking at high temperatures and without increase in jitter.

Effects of the Invention As described above, the optical receiver of the present invention maintains constant sensitivity and jitter even if the temperature rises during use. Therefore, it is effective in the field of optical communications, especially when used in optical receivers that require small size and high performance.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an example of the optical receiver of the present invention, FIGS. 2 and 3 are block diagrams of conventional optical receivers, and FIG. 4 is a block diagram of a pre-stage amplifier of the optical receiver. FIG. 5 is a graph showing changes in frequency characteristics due to temperature, and FIG. 5 is a graph showing gate-source voltage-drain-source voltage characteristics of an FET used in the filter circuit of the optical receiver of the present invention. . [Main reference numbers] 1...Light receiving element, 2...Pre-stage amplifier, 3...Main amplifier, 4...Filter circuit, 5...Comparator patent author Sumitomo Electric Industries, Ltd.

Claims (1)

[Claims] An optical receiver comprising a light receiving element that receives an optical signal and converts it into an electrical signal, an amplifier that amplifies the electrical signal, and a filter circuit that removes noise from the electrical signal amplified by the amplifier, the filter circuit is provided with temperature characteristics that correct the temperature characteristics of the gain of the amplifier.