JP2674494B2 - Optical receiving circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver circuit, and more particularly to an optical receiver circuit used for a low speed data link of an optical communication system.

[0002]

2. Description of the Related Art Generally, a photo diode is used as a light receiving element in an optical receiving circuit installed in an optical communication system, and a signal converted into an electric signal by the photodiode is subjected to signal processing to obtain a good optical receiving signal. There is something.

FIG. 3 shows the configuration of an optical receiving circuit using such a conventional photodiode. In this figure, the input terminal of the amplifier 101 is connected to the anode electrode of the photodiode 100. This amplifier 101
Then, the electric signal supplied from the photodiode 100 is amplified with a constant amplification factor and output.

The output terminal side of the amplifier 101 is connected to the inverting input terminal of the comparator 102 and the resistor 105 is connected.
Is connected to the non-inverted input terminal of the comparator 102 via. The comparator 102 discriminates the signal input to the inverting input terminal by using the potential of the non-inverting input terminal as a threshold, and obtains an electric signal having two values.

A resistor 106 is connected between the normal input terminal of the comparator 102 and the output terminal of the comparator 102, and a capacitor is connected between the normal input terminal of the comparator 102 and earth ground. 107 is connected. The optical receiving circuit is configured by the above configuration.

FIG. 4 shows input / output signal waveforms of the comparator shown in FIG. In the description of FIG. 4, reference is made to FIG.

In FIG . 3, the output of the amplifier 101 is directly input to the inverting input terminal of the comparator 102. Amplifier 1
In No. 01, the signal / noise (S / N) characteristics are taken into consideration, and since there is a minimum necessary band, the rising a and the falling b of the output waveform shown in FIG. 4 are given a certain slope.

This comparator 102 employs an automatic threshold value setting circuit which is extremely stable against fluctuations in the power supply voltage. The feature of this automatic threshold setting circuit is that the comparator 10
The difference is that the voltage difference between the signal at the inverting input terminal 2 and the output of the comparator at the output terminal is divided by a certain optimum ratio and used as the threshold voltage. Therefore, the comparator 102 can be made to depend only on the input signal and the output signal.

The signal input to the inverting input terminal of the comparator 102 and the signal output to the output terminal of the comparator 102 are:
High-level and low-level voltage values are alternately generated, and the comparator 102 operates according to the level.

In the comparator 102, the threshold voltage of the non-inverting input terminal and the signal voltage of the inverting input terminal cross each other to operate the comparator 102, and a capacitor is placed between the non-inverting input terminal of the comparator 102 and the ground. Since 107 is provided, a sufficient time constant can be obtained at the rising edge a and the falling edge b of the threshold voltage waveform input to the normal input terminal of the comparator 102.

In the input / output characteristic diagram of FIG. 4, V _IN shown by a thick line in B shows an input waveform of the comparator 102, and V _th shown by a thin line A shows a threshold waveform of the comparator 102. C shows the output waveform of the rectangular comparator, and shows that jitter occurs in the x and y times of this C waveform.

As an example of the above-described optical receiving circuit or its main circuit constituent parts, Japanese Patent Laid-Open No. 62-257244 is disclosed.
JP-A-63-248256 and JP-A-62-285537, and optical receiver circuits disclosed in JP-A-57-43300 and 57-132421.
There is a comparator used for the optical receiving circuit described in Japanese Patent Publication No.

The optical receiving circuit described in Japanese Patent Laid-Open No. 62-257244 uses a binary double-current code as a transmission code, and when the start bit is detected, the polarity of the start bit is compared with the average value of the received signal. A first threshold value that is offset by a predetermined value to the same polarity is used, and after the start bit is detected, the first threshold value is changed to a second threshold value that corresponds to the average value of the received signal. By doing so, the error in detecting the start bit is eliminated.

The optical receiver circuit disclosed in Japanese Patent Laid-Open No. 63-248256 receives intermittent data such as burst signals, and detects the state of no signal input to detect the threshold voltage of the comparator. Is set to an initial value so that no error pulse is output due to noise when there is no signal.

In the optical receiver circuit disclosed in Japanese Patent Laid-Open No. 62-285537, since the peak voltage is detected by using the automatic threshold value setting circuit, the time until it is once held becomes relatively short, and Each time it is held, it takes a long time to recover, so the hold time can be kept long.

On the other hand, in the comparator used in the optical receiving circuit disclosed in Japanese Patent Application Laid-Open No. 57-43300, the signal received by the radar device is compared with a predetermined threshold voltage, and the threshold voltage is compared. The signal processing is performed only on the above received signals.

Further, in the comparator used in the optical receiving circuit and the like described in JP-A-57-43300, the rounding waveform of the small signal waveform generated in the transmission system is wave-shaped to obtain the power supply voltage fluctuation characteristic and the temperature. Improve the characteristics.

[0018]

In many of these optical receiving circuits, the circuit is configured to identify a signal by using the input voltage of the inverting input terminal of the comparator as a threshold value.
It takes a long time for the rising and falling portions of the signal waveform of the inverting input terminal of the comparator and the rising and falling portions of the threshold waveform of the non-inverting input terminal of the comparator to cross each other. At this time, there is a risk that jitter occurs at the rising and falling portions that are superimposed on the signal waveform, and when the optical reception level is low, a bit error is generated and the reception sensitivity is degraded.

In particular, in the optical receiving circuit described in Japanese Patent Laid-Open No. 62-257244, the error in the start bit detection can be eliminated, but the noise at the trailing edge cannot be effectively discriminated and the optical signal cannot be detected. If the reception level is low, it may not be detected accurately and bit error may occur.

Further, in the comparator used in the optical receiving circuit disclosed in JP-A-57-43300, power supply voltage fluctuation characteristics and temperature characteristics are obtained by shaping the round waveform of the small signal waveform generated in the transmission system. However, jitter is likely to occur at the fall, which causes a bit error and deteriorates the reception sensitivity.

Therefore, an object of the present invention is to provide an optical receiving circuit which improves the receiving sensitivity by preventing bit error even when the receiving level is low.

[0022]

According to the first aspect of the present invention,
Is (a) an amplifier circuit that amplifies the light receiving output of the light receiving element,
(B) A waveform shaping circuit that shapes the output waveform based on the amplified output of this amplifier circuit, and (c) The waveform shaped by this waveform shaping circuit is input directly to the inverting input terminal to shape the waveform.
The output is input to the non-inverted input terminal through a resistor and then inverted
Divide the voltage difference between the signal at the input terminal and the comparison output at a specified ratio.
The voltage obtained by pressing is applied to the forward input terminal as a threshold value.
Then, the signal input to the inverting input terminal is identified.
A comparison circuit for outputting one of two voltage values as a comparison output , and (d) an output terminal and a normal input terminal of the comparison circuit.
A resistor placed between the child and this forward input terminal and earth
Round consisting of a capacitor placed between and compared
Light an adjustment circuit for adjusting the comparison output outputted from the circuit
Provided in the receiving circuit.

[0023]

[0024]

[0025]

According to the first aspect of the invention, for example, the electric signal supplied from the light receiving element shown in FIG. 1 is amplified by the amplifier circuit to a specific amplification factor. In the waveform shaping circuit, the high frequency output waveform component is bypassed and shaped in response to the amplified output of the amplification circuit. In the comparison circuit, the output whose waveform has been shaped by the waveform shaping circuit is input from its first and second input terminals. The adjustment circuit adjusts the output signal level of the signal waveform-shaped by the waveform shaping circuit from the first and second input terminals of the comparison circuit.

[0026]

[0027]

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. FIG. 1 shows an optical receiving circuit of this embodiment.

In FIG. 1, the input terminal of the amplifier 11 is connected to the anode electrode of the photodiode 10.
In the amplifier 11, the electric signal 50 supplied from the photodiode 10 is amplified with a constant amplification factor and output 51.

A peaking circuit 12 for adjusting the voltage level of the high frequency input voltage is connected to the output terminal side of the amplifier 11. The peaking circuit 12 is an amplifier 11
It is configured by connecting a capacitor 12a and a resistor 12b in parallel to the output of.

The output node 12c of the peaking circuit 12 is connected to the inverting input terminal of the comparator 13 . Further, the non-inverting input terminal of the comparator 13 is connected to the output node 12c of the peaking circuit 12 via the first resistor 14 and the node f. V _IN is the inverting input voltage applied to the inverting input terminal of the comparator 13, and V _th is the comparator 13
This is the normal input voltage applied to the normal input terminal of. The comparator 13 discriminates the signal input to the inverting input terminal by using the potential of the non-inverting input terminal as a threshold, and obtains an electric signal of two values.

A second resistor 15 is connected between the normal input terminal of the comparator 13 and the output terminal of the comparator 13, and the normal input terminal of the comparator 13 and the earth ground 17 are connected together. A capacitor 16 is connected between them. The optical receiving circuit of the present embodiment is configured with the above configuration.

Next, the operation of this optical receiving circuit will be described. FIG. 2 shows input / output signal waveforms of the comparator shown in FIG. In the description of FIG. 2, FIG. 1 will be referred to.

In FIG . 1, the received optical signal is a photodiode.
When the light enters the diode 8, it is photoelectrically converted by the photodiode 8. From the photodiode 8, an electric signal is sent to the amplifier 1
Enter 1 In the peaking circuit 12 , the high frequency component of the output voltage amplified by the amplifier 11 is bypassed to the capacitor 12a via the resistor 12b. Therefore, the output voltage V of the peaking circuit 12 has a shaped waveform with overshoot like the waveform B showing the steep rise and fall shown in FIG. The waveform A represents the threshold voltage V _th of the comparator 13 shown in FIG. When the output of the amplifier 11 is input to the peaking circuit 12 at the inverting input terminal of the comparator 13, the peaking circuit 12 outputs an output with the voltage level of the high frequency voltage shaped.
And the peaking circuit 1
The output of 2 is input to the non-inverted input terminal via the resistor 14.

Further, in this embodiment, the amplifier 11 outputs the signal /
Considering the noise (S / N) characteristics, the output waveform has a rising slope a and a falling slope b with a certain slope because the band is the minimum required band. This comparator 13 employs an automatic threshold value setting circuit which is extremely stable against fluctuations in the power supply voltage. A feature of this automatic threshold setting circuit is that the voltage obtained by dividing the difference voltage between the signal at the inverting input terminal of the comparator 13 and the output of the comparator at the output terminal by a certain optimum ratio is used as the threshold voltage. Therefore, the comparator 13 can be made to depend only on the input signal and the output signal.

As for the signal input to the inverting input terminal of the comparator 13 and the signal output to the output terminal of the comparator 13, high-level and low-level voltage values are alternately generated and the comparator 13
Works according to the level. Also, in the comparator 13,
The threshold voltage of the non-inverting input terminal and the signal voltage of the inverting input terminal cross each other to operate the comparator 13, and a capacitor 16 is provided between the non-inverting input terminal of the comparator 13 and the earth ground 17.
Since the above is provided, a sufficient time constant can be obtained at the rising s and the falling t of the threshold voltage waveform input to the non-inverting input terminal of the comparator 13.

In the optical receiving circuit described above, the peaking circuit 12 is constituted by the resistor 12b and the capacitor 12a so that the high frequency component of the voltage input to the peaking circuit 12 is bypassed. Although the input voltage V _{IN of} 13 is obtained, it goes without saying that the peaking circuit is not limited to this circuit, and any circuit may be used as long as it does not depart from the gist of the present invention.

[0038]

As described above, the invention according to claim 1 is described above.
According to this, even when the reception level is small, it is possible to improve the reception sensitivity by preventing a bit error from occurring. In addition, the signal at the inverting input terminal of the comparison circuit and the comparison output
The voltage obtained by dividing the differential voltage of
As a reverse input terminal
Identify the signal input to the
Since it is output as a comparison output, the comparison result is
It now depends only on the input and output signals of the comparator circuit.
And obtain a circuit that is extremely stable against fluctuations in power supply voltage.
be able to.

[0039]

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of an optical receiving circuit of the present invention.

FIG. 2 is an input / output waveform diagram for explaining the circuit operation of an embodiment of the optical receiving circuit of the present invention.

FIG. 3 is a circuit diagram showing an example of a conventional optical receiving circuit.

FIG. 4 is an input / output waveform diagram for explaining the circuit operation of an example of a conventional optical receiving circuit.

[Explanation of symbols]

10 Amplifier 11, 13 Comparator 12 Peaking Circuit 12a, 16 Capacitor 12b Resistor 14 First Resistor 15 Second Resistor 17 Earth Ground 50 Electric Signal 51 Amplified Output V _IN Inverted Input Voltage V _{th Forward} Input Voltage V _OUT Output Voltage

Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H04L 25/03

Claims (1)

(57) [Claims] 1. An amplifier circuit for amplifying a received light output of a light receiving element, a waveform shaping circuit for shaping an output waveform based on the amplified output of the amplifier circuit, and an inverting input terminal for an output waveform shaped by the waveform shaping circuit. Directly into the waveform-shaped output.
Force is input to the non-inverted input terminal through a resistor, and the inverted input terminal
The voltage difference between the signal of
This voltage is applied to the non-inverted input terminal as a threshold
The signal input to the inverting input terminal is identified by
Between a comparison circuit that outputs one of the voltage values as a comparison output, and between the output terminal of this comparison circuit and the normal input terminal
Placed resistor and this forward input terminal and earth ground
And a capacitor arranged between
And an adjusting circuit for adjusting a comparison output outputted from the optical receiving circuit.