JPS62115902A - Optical receiving circuit - Google Patents

Abstract

PURPOSE:To expand a dynamic range with respect to the optical input level of an optical signal by detecting an optical input level to a light receiving element and providing a selection signal alternately deriving the outputs of the 1st and 2nd preamplifier in accordance with said level. CONSTITUTION:The 1st and 2nd preamplifiers 2 and 3 amplifying a light reception output by a light receiving element are provided with a constitution to alternately derive the outputs of both preamplifiers in accordance with the optical input level to the light receiving element. A light receiving part 1 has a light receiving element D and a resistance R, which converts the output of the light receiving element D into voltage from current. The preamplifier 2 uses the anode output of the light receiving element D as an input, and is the trans-impedance type preamplifier of a reverse phase with a feedback resistance Rf, while the preamplifier 3 is a phase output preamplifier employing the cathode output of the light receiving element D as an input. The preamplifiers 2 and 3 generate outputs with reverse phases, and the polarities of signals appearing on the output of a selection circuit 5 are the same. Thus the dynamic range of the optical input level can be substantially expanded.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to an optical receiving circuit, and more particularly to an optical receiving circuit configured to expand the dynamic range.

Prior Art As shown in the block diagram of FIG. 3, a conventional optical receiving circuit consists of a light receiving section 1 that converts an optical signal into an electrical signal, and a preamplifier 2 that amplifies the light output from the light receiving section 1. That's it. An optical receiving circuit having such a configuration has a drawback that the dynamic range is narrow, and therefore, when the optical input level becomes large, the preamplifier 2 operates in saturation, making reception impossible.

Purpose of the Invention Therefore, the present invention has been made to eliminate the drawbacks of the conventional ones, and its purpose is to expand the dynamic range of the optical input level of the optical signal to be received. The purpose of the present invention is to provide an optical receiving circuit.

Structure of the Invention The optical receiving circuit according to the present invention is provided with first and second preamplifiers for amplifying the received light output to the light receiving element, and the optical receiving circuit is provided with first and second preamplifiers for amplifying the light receiving output to the light receiving element. The output amplifier is configured to alternatively derive the output of the amplifier. These preamplifiers are designed in advance to amplify large and small level regions, respectively, with a predetermined threshold level as the boundary for the optical input level, thereby increasing the overall dynamic range. This makes it possible to expand.

Example Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention, and 1 is a light receiving section including a light receiving element such as an avalanche photodiode or a PIN photodiode that converts an optical signal into an electrical signal. Reference numerals 2 and 3 denote first and second preamplifiers, which amplify the light receiving output of the light receiving section 1, respectively.

Reference numeral 4 denotes a level detection circuit for detecting the level of light input to the light receiving section 1, and generates a selection control signal for the selection circuit 5 when the light input level reaches a predetermined threshold. This selection circuit 5 is configured to selectively derive the amplified outputs of both advance amplifiers 2 and 3 in accordance with the selection control signal.

In this configuration, an optical signal received by the light receiving section 1 is converted into an electrical signal and guided to the first and second preamplifiers 2 and 3, respectively. Here, for example, the first preamplification 2
! 82 is used when the optical input level is small, and the second preamplifier 3 is used when the optical input level is large.

That is, when the optical input level is low, the output of the first preamplifier 2 is selected by the level detection circuit 4 and the selection circuit 5 as the circuit output, and when the optical input level is high, the output of the first preamplifier 2 is selected as the circuit output. The output of No. 3 is selected and used as the circuit output.

In other words, the first preamplifier 2 carries out amplification in the region where the optical input level is lower than the predetermined threshold value, and the second preamplifier 3 performs the amplification in the region where the optical input level is higher than the predetermined threshold value. This is to share and amplify the Therefore, both ground breadboards 2
and 3 are designed in advance exclusively for amplification of each optical input level region, and as a result, it becomes possible to expand the received light level range.

FIG. 2 is a circuit diagram showing a specific example of the embodiment shown in FIG.
The light receiving section 1 has a light receiving element and a resistor R, and this resistor R is for converting the output of the light receiving element from current to voltage. The preamplifier 2 receives the anode output of the light receiving element as an input, and is a 1 to lance impedance type preamplifier with a negative phase output and a feedback resistor R[. The other preamplifier 3 is a positive phase output preamplifier which receives the cathode output of the light receiving element as an input. The reason why the double width dividers 2 and 3 generate outputs with opposite phases to each other is that the outputs of the anode and cathode of the light receiving element are in a relationship with opposite phases to each other, so that the signal appearing at the output of the selection circuit 5 This is to make the polarities the same.

The optical input level detection circuit 4 is configured to detect the optical input level based on the DC component of the cathode voltage of the light receiving element.

In the above embodiment, the first preamplifier 2 is used as an amplifier that serves a region where the optical input level is low, and the second preamplifier 3 is used as an amplifier that serves a region where the optical input level is low. However, it is clear that it is also possible to use characteristics that share opposite areas.

Effects of the Invention As described above, according to the present invention, preamplifiers designed in advance to be suitable for areas where the optical input level is small and areas where the optical input level is large are prepared independently of each other, and By appropriately selecting and using both advance amplifiers accordingly, it is possible to substantially expand the dynamic range of the optical input level.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a circuit diagram of a specific example of the embodiment of FIG. 1, and FIG. 3 is a block diagram of a conventional optical receiving circuit. Explanation of symbols of main parts 1... Light receiving section 2.3... Preamplifier 4... Optical input level detection circuit 5... Selection circuit

Claims (2)

[Claims] (1) First and second amplification of the light receiving output by the light receiving element
a preamplifier; and selection means for detecting the level of light input to the light receiving element and selectively deriving the outputs of the first and second preamplifiers according to this level. Optical receiver circuit. (2) The first and second preamplifiers are configured to amplify areas of large and small levels, respectively, with a predetermined level as the boundary with respect to the optical input level. An optical receiving circuit according to claim 1.