JPS5856537A - Reception circuit - Google Patents

Abstract

PURPOSE:To obtain an automatic gain controlling system with good stability, by providing a narrow band pass filter to a level detection circuit means connected to an output of an input circuit. CONSTITUTION:An optical signal coded in the coding system which makes a timing component constant, is received at a photodetector 10, amplified at an amplifier 11, and the output signal passes through an equalizer 13 and is inputted to a discrimination circuit 14, where a timing signal from an amplifier 17 is being received and outputs a discriminated data signal serially. The timing component in an output signal of an input circuit 12 passes through a narrow band pass filter 16 and the timing component level is generated from the amplifier 17, and a signal in which this level depends on whether the level is higher or lower than the preset level of a level detector 18, is applied to an automatic gain controlling circuit 19. The amplifier 11 is controlled with a control signal from the circuit 19 according to the fluctuation of the level of the received optical signal to keep the output level constant. Since the filter 16 is provided for to separate noise components from the timing component, the automatic gain control can attain a good stability.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a receiving circuit that performs automatic gain control while monitoring the timing component of a coded signal that keeps the timing component constant.

The automatic gain control format for dealing with input signal level fluctuations in conventional optical receiving circuits is as shown in Figure 1.
A beak detection circuit (2) is provided at the output side of the equalizer (2), and an automatic gain control circuit (3) that responds to the output signal supplies an automatic gain control signal to the light receiving element (4) and the amplifier (ω). As is clear from its configuration, this automatic first gain control circuit can operate regardless of the encoding format of the input signal. , the influence of the mixed key tone components appears strongly,
The disadvantages are that the stability of the automatic balance control is poor and the circuit configuration is complicated.

In Figure 1, (6) is a timing recovery circuit, (7)
is an identification circuit.

The present invention was created by focusing on the encoding format in which the input signal is encoded, and its purpose is to utilize the constancy of the timing component of the input signal to improve the stability of automatic gain control. The object of the present invention is to provide a receiving circuit which has a simple circuit configuration.

Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 2 shows an embodiment circuit of the present invention, in which the photodetector, 0
are amplifiers, and these constitute the input circuit axis. This input circuit a3 has a gain control input. The light-receiving element aQ has an encoding format that makes the timing component constant, for example, IB.
It is encoded and transmitted by IT, and nine optical signals are emitted. The output signal of the light receiving element aIJ is supplied to the identification circuit a4 via an amplifier Dl and an equalization amount αj. This identification circuit α4 is configured to receive a timing signal to be described later and generate a data signal from an output signal corresponding to the equalization amount.

A level detection circuit means is connected to the output of the input circuit. This circuit means includes a narrow band pass filter connected to the output of the amplifier (1), a limit amplifier -η connected to the output of the filter (a), and a nine detection circuit (9) connected to the level detection output of the amplifier. Consists of. In addition to the above-mentioned outputs, the IJ Mitsu amplifier has a timing signal supplied to the identification circuit a◆, and a clock signal (CLK) for generating and synchronizing bipolar output. Further, the input of the detection circuit α may be connected to the output of the filter aQ to constitute the level detection circuit means O.

The output of the level detection circuit means (2) is the automatic gain control circuit 6.
1 and the output of the circuit is connected to the gain control input of input circuit 0.

Next, the operation of the circuit of the present invention having the above configuration will be explained.

Encoding methods that keep timing components constant, such as IBI
The optical signal encoded using the T encoding method is transmitted to the light receiving element (if)
The light is received by the amplification device υ and amplified by the amplification device υ. The output signal of the amplifier I is passed through an equalization ring, and then received and identified by the identification circuit α4 by the timing signal from the limit amplifier Q7), and outputs a data signal in series.

When the level of the optical signal fluctuates while receiving such a data signal, an automatic gain control signal is supplied from automatic gain control circuit 0 to the input circuit axis to keep the output level of the input circuit υ constant. Operate.

The control input signal to this automatic gain control circuit a1 is obtained by passing the timing component of the output signal of the input circuit through a narrow band pass filter A, and generating the level of the timing component from the limit amplifier 6. A signal is generated and supplied from the level detector shaft, depending on whether the signal is higher or lower than the set level preset in the level detector α.

Such an automatic gain control system is provided with a narrow band pass filter aQ at its level detection port to separate the noise component from the timing component, so the stability of the automatic gain control is improved. This effect can be obtained by simplifying the circuit configuration compared to conventional circuits.

Although the above embodiment describes the case where an optical signal is received, it is clear from the gist that the present invention is not limited to this, and it is clear that the present invention is not limited to this. This can also be applied to reception.

As is clear from the above description, the following effects can be obtained according to the present invention.

■ Good stability of automatic gain control.

■ The circuit configuration becomes simpler.

[Brief explanation of the drawing]

FIG. 1 is a conventional circuit diagram, and FIG. 2 is a circuit diagram of the present invention. In the figure, a3 is an input circuit, a is a level detection circuit means, a
1 is an automatic gain control circuit. Patent applicant Fujitsu Limited

Claims (2)

[Claims] (1) An input circuit receives a signal encoded using an encoding method that makes the timing component constant, monitors the timing signal component of the signal using level detection circuit means connected to the output of the input circuit, and outputs the monitor output. A receiver circuit configured to supply an automatic gain control signal to the input circuit in response to a signal. (2) The receiving circuit according to claim 1, wherein the level detection circuit means includes a narrow band pass filter.