JPH01226255A - Optical receiver circuit - Google Patents

Abstract

PURPOSE:To maintain the duty ratio of an output signal at 50% without adjusting a bias level, etc., and to prevent the waveform distortion of the output signal by coupling and feedback-controlling the positive phase output and the negative phase input, and the negative output and the positive input of a discrimination circuit provided with the input and the output of a positive phase and a negative phase. CONSTITUTION:The title circuit is constituted of a photodiode 11 to convert an input optical signal into an electric signal, a preamplifier 12 to amplify an input signal outputted by the photodiode 11, a low-pass filter which removes a high frequency component from the output signal of the preamplifier 12 and consists of a coil L and a capacitor C, and the discrimination circuit 14. Here, the positive phase output and the negative phase input, and the negative phase output and the positive phase input of the discrimination circuit 14 are connected respectively through a resistors R1 and R2, and are controlled by negative feedback. Here, the resistors R1 and R2 determine feedback quantity from the output of the discrimination circuit 14 as combined resistance, and simultaneously, their middle points are connected respectively to the capacitors C1 whose one ends are grounded, and in addition, a positive phase side and a negative phase side are coupled through the capacitor C2.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a circuit configuration of an optical receiver. More specifically, the present invention relates to a new configuration of an optical receiver circuit in which the output duty ratio is maintained at 50% without adjustment, and can be advantageously utilized in the field of optical communications. be.

BACKGROUND OF THE INVENTION FIG. 5 is a circuit diagram schematically showing the general configuration of a conventional optical receiver circuit.

As shown in FIG. 5, this circuit includes a photodiode 1 that converts an input optical signal into an electrical signal, a preamplifier 2 that amplifies the output signal of the photodiode 1 prior to reproduction processing, and a coil and a capacitor C. It is mainly composed of a low-pass filter 3 configured by the following, and a discriminator 4 that reproduces a received signal from the electrical signal that has passed through the low-pass filter 3.

In this circuit, an optical signal input to a photodiode 1 is converted into a current signal, then amplified by a preamplifier 2, further filtered out by a low-pass filter 3 to remove noise components, and then input to a discriminator 4 for waveform reproduction. be done. Note that the discriminator 4 is provided with a pair of inputs and an output, each having a positive phase and a negative phase, and outputs mutually complementary output signals RD.
, RD.

Problems to be Solved by the Invention By the way, in the conventional optical receiver circuit as described above,
Its output level is exclusively determined by the bias level of the discriminator 4. Therefore, in such a circuit, when the optical receiver is shipped or when the optical receiver circuit is installed according to each application, it is necessary to adjust the bias level while monitoring the output of each optical receiver circuit. had to be done individually.

If this adjustment is not performed, if the adjustment is incomplete, or if the installation conditions change even after further adjustment, the duty ratio of the output signal will not be 50%, resulting in waveform distortion in the output signal. occurs. Therefore, adjustment work is essential for conventional optical receiver circuits.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a novel optical receiver circuit that solves the above problems of the prior art and can maintain an appropriate duty ratio without adjustment.

Means for Solving the Problems According to the present invention, in an optical receiver circuit provided with a discriminator as an output buffer, the discriminator has inputs of normal phase and reverse phase and outputs of normal phase and reverse phase. a first feedback circuit that combines a positive phase output and a negative phase input; and a second feedback circuit that combines a negative phase output and a positive phase input of the discriminator; An optical receiver circuit is provided that is configured such that a duty ratio is maintained at 50%.

Further, according to a preferred aspect of the present invention, each of the first and second feedback circuits includes a pair of resistors connected in series between the output and the input of the discriminator; A grounded capacitor having one end connected between each of the resistors may be provided, and further, each pair of resistors inserted in the first and second feedback circuits may be connected to each other via a capacitor. Advantageously, they are coupled together.

Operation The optical receiver circuit according to the present invention has a main W feature that it is provided with a feedback control circuit that combines a positive phase output and a negative phase input, and a negative phase output and a positive phase input, respectively.

That is, in the optical receiver circuit according to the present invention, as will be specifically described later, when the duty ratio of the output signal changes, the threshold level is automatically changed to maintain the duty ratio at 50%. dripping Therefore, the optical receiver circuit according to the present invention operates under optimum conditions and without waveform distortion without any adjustment at the time of shipment or during grounding/use.

The present invention will be described in more detail below with reference to the drawings, but what is disclosed below is only one embodiment of the present invention and does not limit the technical scope of the present invention in any way.

Embodiment FIG. 1 is a circuit diagram showing an example of the configuration of an optical receiver circuit constructed according to the present invention.

As shown in FIG. 1, this circuit also includes a photodiode 11 that converts an input optical signal into an electrical signal, a preamplifier 12 that amplifies the input signal output from the photodiode 11, and a high-frequency component from the output signal of the preamplifier 12. It mainly consists of a low-pass filter 13 consisting of a coil and a capacitor C, and a discriminator 14.

Furthermore, the circuit shown in FIG.
The positive phase output and negative phase input, as well as the negative phase output and positive phase input, are connected via resistors R1 and R2, respectively, to provide negative feedback. Here, the resistors R1 and R2 determine the amount of feedback from the output of the discriminator 14 as a combined resistance, and -i is connected to the grounded capacitor C1 at the midpoint of the resistors R1 and R2, and the positive The phase side and the negative phase side are coupled via a capacitor C2.

FIGS. 2(a) and 2(b) are signal waveform diagrams illustrating the operation of the circuit as described above.

In this circuit, for some reason the output signal does not change as shown in Figure 2 (
When waveform distortion as shown in a) occurs, the average value of the signal, as shown by the dotted line in the figure, rises above the original threshold level of this signal, shown by the dashed line in the figure. In the circuit shown in Figure 1, the positive phase output is connected to the negative phase input, that is, negative feedback is applied, so the input threshold level will increase as a result. Become. In this way, the signal waveform output from this circuit is as shown in Figure 2 (
As shown in b), a normal signal waveform with a duty ratio of 50% is obtained.

Further, FIGS. 3(a) and 3(b) are also diagrams for explaining the operation of the circuit shown in FIG. 1.

In other words, in the circuit shown in Fig. 1, if waveform distortion as shown in Fig. 3(a) occurs, the average level of the output signal decreases as shown in Fig. 3(a), and the The threshold value of the negative phase input connected to the phase output decreases,
As shown in FIG. 3(b), the duty ratio is 50%.

FIG. 4 is a diagram illustrating a method for checking the operation of the circuit as described above. In FIG. 4, the same components as in FIG. 1 are given the same reference numbers as in FIG. 1.

That is, in the circuit shown in FIG.
While inputting an optical signal with a duty ratio of 50%, when inputting the signal extracted from the positive phase output of the discriminator 14 to the oscilloscope 22 via the 50Ω coaxial cable 21 and observing the waveform, this circuit always Duty - 50%
It is certain that the signal is being output.

Effects of the Invention As detailed above, in the optical receiver circuit according to the present invention, the normal phase output and the negative phase input, and the negative phase output and the positive phase input of the discriminator equipped with the positive phase and negative phase inputs and outputs. By combining and performing feedback control, the duty ratio of the output signal can be maintained at 50% without adjusting the bias level, etc., and waveform distortion of the output signal can be prevented.

Therefore, there is no need to perform adjustment work when shipping the product or installing it in a predetermined system, improving productivity and making handling easier.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of an optical receiver circuit constructed according to the present invention, and FIGS. 2(a) and (b) show that waveform distortion occurs in the output signal in the circuit shown in FIG. FIGS. 3(a) and 3(b) illustrate the operation of the circuit when other waveform distortion occurs in the output signal in the circuit shown in FIG. FIG. 4 is a diagram illustrating a method for checking the operation of the circuit shown in FIG. 1, and FIG. 5 is a circuit diagram illustrating the configuration of a conventional optical receiver circuit. be. [Main reference numbers] 111...Photodiode, 2.12...Preamplifier, 3.13...Low pass filter, 4.14...Discriminator, 21...Coaxial cable, 22. ...Oscilloscope patent applicant Sumitomo Electric Industries, Ltd.

Claims (3)

[Claims] (1) In an optical receiver circuit equipped with a discriminator as an output buffer, which has positive-phase and negative-phase inputs and positive-phase and negative-phase outputs, the positive-phase output and negative-phase input of the discriminator are combined. and a second feedback circuit that combines a negative phase output and a positive phase input of the discriminator so that the output duty ratio of the optical receiver is maintained at 50%. An optical receiver circuit comprising: (2) Each of the first and second feedback circuits includes a pair of resistors connected in series between the output and the input of the discriminator, and one end connected between the pair of resistors. 2. An optical receiver circuit as claimed in claim 1, characterized in that it comprises a respective connected ground capacitor. (3) According to the first or second claim, wherein a pair of resistors inserted in each of the first and second feedback circuits are coupled to each other via a capacitor. The optical receiver circuit described.