JPH0685508B2 - Optical receiver circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical receiving circuit for converting a received optical signal into an electric signal. In particular, the present invention relates to an optical receiver circuit in which correction of frequency characteristics is taken into consideration.

〔Overview〕

According to the present invention, in an optical receiving circuit having an impedance conversion circuit including an active semiconductor element, the impedance between the ground electrode of the active semiconductor element and the common potential exhibits an extremely low value with respect to the repetition frequency of the optical signal reaching the light receiving element. By making such settings, the impedance conversion circuit is provided with a differential characteristic and the gain is not lowered.

[Prior Art] As shown in FIG. 2, a conventional optical receiver circuit includes a light receiving element D1 for converting an optical signal into an electric signal and a gate for the light receiving element D1.
It is connected to the anode of D1, the drain is connected to the power supply via the first resistor R1, the source is connected to the common potential via the second resistor R2 and to the common potential via the first capacitor C1. Field-effect transistor FET to be connected, the emitter is connected to the drain of the field-effect transistor FET, the base is connected to the reference voltage, the collector is connected to the common potential via the third resistor R3 first PNP type A transistor TR1 and an NPN type whose pace is connected to the collector of the first PNP type transistor TR1, the collector is connected to the power supply, and the emitter is connected to a common potential via the fifth resistor R5 and the sixth resistor R6. Second transistor TR2 and fifth resistor R5
A transformer composed of a second capacitor C2 connected in parallel with the seventh resistor R7 connected between the contacts of the fifth resistor R5 and the sixth resistor R6 and the gate of the field effect transistor FET. Impedance type amplifier circuit is used. In this circuit, when the frequency characteristic is not sufficiently wide, the band is widened by connecting the differentiating circuit composed of the fourth capacitor C4, the eighth resistor R8, and the ninth resistor R9.

[Problems to be solved by the invention]

In such a conventional circuit, since the differentiating circuit is connected to the latter stage of the amplifying circuit, the gain of the differentiating circuit is considerably reduced, and the amplifying circuit is connected to the latter stage of the differentiating circuit in order to increase the minimum light receiving level. However, there is a drawback that the circuit scale becomes large.

The present invention solves the above-mentioned drawbacks, and an object of the present invention is to provide an optical receiving circuit that can obtain a band equivalent to that of a conventional differentiating circuit without lowering the gain.

[Means for solving problems]

The present invention provides a light receiving element that converts an incoming optical signal into an electric signal, a comparison amplification circuit to which an output of the light reception element is connected to an input, and an active semiconductor element to which an output of the comparison amplification circuit is connected to an input. In a light receiving circuit including an impedance conversion circuit including, a parallel circuit of a resistor and a capacitor is connected between the ground electrode of the active element and a common potential, and the parallel circuit is used for the light arriving at the light receiving element. It is characterized by being set to a constant exhibiting an extremely low impedance at the signal repetition frequency.

Here, the active semiconductor element may be any of a MOS type transistor, a bipolar type transistor and a FET type transistor.

[Action]

The incoming optical signal is converted into an electric signal by the light receiving element, and this is amplified by the comparison and amplification circuit. This output is input to the active semiconductor element of the impedance conversion circuit. The impedance of the parallel circuit of the resistor and the capacitor inserted between the ground electrode of the active semiconductor element and the common potential has an extremely low value with respect to the repetition frequency of the optical signal reaching the light receiving element. This is an effect equivalent to the high pass filter effect by the differentiating circuit in the conventional circuit, and the bandwidth can be expanded.

〔Example〕

 An embodiment circuit of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit connection diagram showing a configuration of an embodiment circuit of the present invention.

The circuit of this embodiment includes a light receiving element D1 such as an avalanche photodiode and a PIN junction type photodiode for converting an optical signal into an electric signal, a gate connected to an anode of the light receiving element D1, and a drain via a first resistor R1. A field effect transistor FET connected to a power source, a source connected to a common potential via a second resistor R2 and a common potential connected via a first capacitor C1, and an emitter connected to a drain of the field effect transistor FET. Connected, the base is connected to the reference voltage terminal V _Ref , and the collector is connected to the common potential via the third resistor R3, the first transistor TR1 of the PNP type
And the base is connected to the collector of the first transistor TR1, the collector is connected to the power supply, and the emitter is the fifth resistor.
NPN connected to common potential via R5 and sixth resistor R6
-Shaped second transistor TR2, a second capacitor C2 connected in parallel with the fifth resistor R5, a fifth resistor R5 and a sixth resistor R6.
Between the contact of and the gate of the field effect transistor FET, a seventh resistor R7, a third capacitor C3 connected in parallel with the sixth resistor R6, and between the collector of the second transistor and the power supply. With the inserted fourth resistor R4, the collector of the second transistor TR2 is connected to the output terminal OUT. The part surrounded by a broken line in the figure shows a comparison amplifier circuit.

In this circuit configuration, the high frequency component is mainly the third capacitor C3.
, The gain is low for low frequency components and high for high frequency components.

〔The invention's effect〕

As described above, the present invention is composed of the eighth resistor R8, the ninth resistor R9 and the fourth capacitor C4 used in the conventional example by adding the fourth resistor R4 and the third capacitor C3. Since it can be obtained without lowering the gain in the same band as that of the differentiating circuit, it is not necessary to add an amplifier circuit after the differentiating circuit in order to obtain sufficient gain, which has the effect of reducing the circuit scale. .

[Brief description of drawings]

FIG. 1 is a circuit connection diagram showing a configuration of an embodiment circuit of the present invention. FIG. 2 is a circuit connection diagram showing a configuration of a conventional circuit. D1 ... Light receiving element, FET ... Field effect transistor, TR1 ...
… PNP type transistor, TR2 …… NPN type transistor, R1
~ 9: resistor, C1 ~ 4 ... battery, V _Ref ... reference voltage input terminal, OUT ... output terminal, V _CC ... power supply terminal.

Claims (1)

[Claims] 1. A light receiving element for converting an incoming optical signal into an electric signal, a comparison amplifier circuit to which an output of the light receiving element is connected to an input, and an active semiconductor element to which an output of the comparison amplifier circuit is connected to an input. In an optical receiver circuit including an impedance conversion circuit including a resistor, a parallel circuit of a resistor and a capacitor is connected in series between the ground electrode of the active element and a common potential, and the amplifier is connected from a connection point of the parallel circuit. A return path to the circuit is provided, and the parallel circuit is set to a constant exhibiting an extremely low impedance at the repetition frequency of the optical signal reaching the light receiving element.