JPH02200041A - Light receiving circuit - Google Patents

Abstract

PURPOSE:To secure a satisfactory range of identification against the fluctuation of the mark rate of an input signal by applying the output signal of a surface acoustic wave SAW filter to a peak value detecting circuit to obtain the output voltage corresponding to the mark rate and applying the output voyage to an identification reproduction circuit. CONSTITUTION:The received optical signal is converted into an electric signal by a photodetecting element 1 and then amplified by a main amplifier circuit 4, etc. The electric signal received from the circuit 4 is inputted to an identification circuit 5 via a capacitor 13 as well as to a SAW filter 6. The output of the filter 6 is distributed via a distribution circuit 7 to be set at a prescribed amplitude via an amplitude limiting circuit 8 and inputted to the circuit 5. At the same time, a peak value detecting circuit 10 produces the DC voltage in response to the set amplitude. The DC voltage undergoes the level conversion via a DC-DC converter 11 and is applied to an amplified current signal. Thus, it is possible to apply an identification level corresponding to the input mark rate to the circuit 5 against an input signal having a fluctuating mark rate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical receiving circuit, and particularly to a detection method for detecting the mark rate of an optical signal.

[Conventional technology]

Generally, the one shown in FIG. 6 is known as an optical receiving circuit for an optical communication device.

Referring to FIG. 5, the optical signal received by the light receiving element 21 is converted into an electrical signal here, and the preamplifier circuit 22. The signal is amplified by a variable gain amplifier circuit 23 and a main amplifier circuit 24. This amplified current signal is then transmitted to the identification reproducing circuit 25. Differential circuit 3
1 and the control circuit 32. As shown in the diagram with the handle 9, amplification and distribution into two parts is performed by AC coupling.

The control circuit 62 controls the gain of the variable gain amplifier circuit 23 based on this amplified current signal to set the light reception level to a predetermined value.

The differential output from the differentiating circuit 31 is given to a surface acoustic wave filter (sAW filter) 26 via a capacitor 64, where a clock is extracted.

Then, a timing amplification circuit 27 and an amplitude limiting circuit 28
The signal is amplified to a required amplitude to generate an identification clock, which is provided to the identification reproducing circuit 25 by the two-way distribution circuit 29. The identification and reproduction circuit 25 performs identification and reproduction of the amplified current signal using the identification clock.

By the way, when the transmission path code is an RZ multiplied signal.

However, in the case of a signal whose mark rate varies, its DC level varies depending on the mark rate. the result.

When such a signal is applied to the identification reproducing circuit 25 via AC coupling, the identification reproducing circuit 2
5, a code error occurs.

For this reason, the conventional optical receiving circuit is equipped with a DC regeneration circuit 30 using a diode or a transistor in front of the identification regeneration circuit 25, as shown in FIG. A predetermined discrimination level adjustment voltage is applied from the outside, and then the discrimination is performed by the discrimination reproducing circuit 25.

[Problem that the invention seeks to solve]

In the above-mentioned conventional optical receiving circuit, when an input signal is accompanied by mark rate fluctuation, the DC regeneration circuit clamps the baseline side of the input signal.

Further, a predetermined identification level is applied externally by an identification level adjustment voltage VTR. For this reason, if the operation of the DC regeneration circuit is insufficient, there will be no operating margin in the identification range.Especially for high-speed digital signals with transmission speeds of Gigabits per second (Gb/s) or higher, as shown in Figure 4. As shown in the figure, because the clamping operation of the DC regeneration circuit becomes incomplete, one of the input signals
” is mistaken for “0” (curve a in Figure 4).

The range of the point where "0" is mistaken for "1" (curve b in Figure 4) changes with the mark rate, and when a constant external voltage is applied, the effective operable range is the 40th diagonal line. Limited to the range shown.

As described above, the conventional optical receiving circuit has a problem in that it is not possible to ensure a sufficient identification range against fluctuations in the mark rate of the input signal.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical communication circuit that can sufficiently secure a discrimination range against mark rate fluctuations of input signals.

[Means to solve the problem]

According to the present invention, there is provided a light receiving element that converts an optical signal into an electrical signal, a preamplifier circuit that amplifies the electrical signal, and an output signal of the preamplifier circuit that changes the gain according to the level of the optical signal. a variable gain amplifier circuit that amplifies the output signal of the variable gain amplifier circuit to a predetermined amplitude, a main amplifier circuit that further amplifies the output signal of the variable gain amplifier circuit and sends out an amplified electrical signal, and an identification and regeneration circuit that identifies and reproduces this amplified electrical signal; a SAW filter that extracts a clock component from the amplified electrical signal and outputs the clock component signal; an amplitude limiting circuit that amplifies the clock component signal to a predetermined amplitude; and an amplitude limiting circuit that amplifies the clock component signal to a predetermined amplitude; It has a peak value detection circuit that converts it into a DC voltage, and a DC voltage-DC voltage conversion circuit that converts the level of the output DC voltage of the peak value detection circuit and applies it as an identification voltage to the amplified electric signal input to the identification circuit. , an optical receiving circuit is obtained in which the R-specific regeneration circuit identifies and regenerates the amplified electric signal to which the identification voltage is applied based on the clock component signal.

〔Example〕

Next, the present invention will be explained with reference to examples.

Referring to FIG. 1, an optical signal received from a transmission line (not shown) is converted into an electrical signal by a light receiving element 1, and a preamplifier circuit 2. The signal is amplified by the variable gain amplifier circuit 6 and the main amplifier circuit 4. On this occasion.

The control circuit 12 controls the variable gain amplifier circuit 3 based on the output of the main amplifier circuit 4. As a result, the main amplifier circuit 4 outputs an electrical signal with a constant amplitude. An electrical signal from the main amplifier circuit 4 (hereinafter referred to as an amplified electrical signal) is input to the identification circuit 5 via the capacitor 16 and is also input to the SAW filter 6. Then, the clock component is extracted by the SAW filter 6, and a sine wave whose output amplitude differs according to the change in mark rate is obtained as the output of the SAW filter.

The output of the SAW filter 6 (hereinafter referred to as filter output) is sent to the distribution circuit 7 by an amplitude limiting circuit 8 and a peak value detection circuit 10.
distributed to. The filter output is set to a predetermined amplitude by an amplitude limiting circuit 8 and is inputted to an identification reproducing circuit 5 via a nine-part distribution circuit 9.

On the other hand, the peak value detection circuit 10 generates a DC voltage according to the amplitude of the filter output. This DC voltage is level-converted by a DC-DC converter 11, and this output voltage (VDC) is applied to an amplified current signal via a resistor 14.

As a result, as shown in FIG. 2, for an input signal whose mark rate varies, a discrimination level corresponding to the input mark rate is given to the discrimination reproducing circuit 5.

〔Effect of the invention〕

As explained above, in the present invention, the output signal of the SAW filter is given to the peak value detection circuit to obtain the output voltage according to the mark rate. Since this output voltage is applied to the discrimination/reproduction circuit, a discrimination level corresponding to the variation in the mark rate can be obtained, and there is an effect that deterioration of the effective discrimination range due to the variation in the mark rate of the input signal can be reduced.

[Brief explanation of the drawing]

FIG. 1 shows an example of an optical receiving circuit according to the present invention.
2 is a diagram showing the change in the distinguishable range and output voltage (Voc) with respect to the mark rate in the optical receiving circuit shown in FIG. 1. FIG. 6 is a block diagram showing the conventional optical receiving circuit. The figure is a diagram showing the distinguishable range and effective distinguishable range with respect to the mark rate in the optical receiving circuit shown in FIG. 3. DESCRIPTION OF SYMBOLS 1... Light receiving element, 2... Preamplifier circuit, 3... Variable gain amplifier circuit, 4... Main amplifier circuit, 5... Identification regeneration circuit, 6... SAW filter, 7, 9...Distribution circuit. 8... Amplitude limiting circuit, 10... Peak value detection circuit. 11...DC-DC converter, 12... Control circuit.

Claims (1)

[Claims] 1. A light receiving element that converts an optical signal into an electrical signal, a variable gain amplifier that amplifies the electrical signal to a predetermined amplitude level and outputs an amplified electrical signal, and receives the amplified electrical signal and extracts a clock component. a clock component extracting means for transmitting a clock signal using a clock signal, an identification voltage generating means for receiving the clock signal, generating a DC voltage corresponding to the amplitude of the clock signal, and applying the generated DC voltage to the amplified electric signal as an identification voltage; 1. An optical receiving circuit comprising identification and reproducing means for identifying and reproducing an amplified electric signal given based on the clock signal.