JPH01175439A - Optical receiver - Google Patents

Abstract

PURPOSE:To stabilize the reference level for the binary coding of a comparator regardless of the length of the period of no light signal by digitizing the output signal of an amplifier and storing it in two storage circuits according to the output level of said comparator, and converting their intermediate value into an analog value and thus generating the reference level. CONSTITUTION:When the output signal of a photodetector 1 which is amplified by the amplifier 3 is converted by the comparator 4 into a binary signal, the output signal of the amplifier 3 is digitized by an analog-digital converting circuit 6 and written in a 1st storage circuit 7 when the output of the comparator is at 'H' level or in a 2nd storage circuit 8 when the output of the comparator is at 'L' level, an arithmetic circuit 10 calculates the center value between the digital output values stored in the 1st and 2nd storage circuits 7 and 8, and the output value of the arithmetic circuit 10 is converted into an analog value through a digital-analog converting circuit 11 for analog conversion, so that the analog value is applied as the reference level to the comparator 4. Consequently, the reference level is stable even when the period of no light signal becomes long.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to an optical receiving device for an original data link used in optical communications.

2. Description of the Related Art A conventional optical receiver is shown in FIG. In FIG. 3, a light receiving element 1 detects an optical signal 2, and the signal is applied to a negative phase input (→) and a positive phase input (+) of a comparator 4 via an amplifier 3.
) is compared with the voltage value of "H" level # (!: "L'
It is converted into a level binary signal.

A voltage is applied to the positive phase input (+) of the comparator 4 in the following manner. A series circuit of resistors 6 and 7 is connected between the output of the reference power supply 5 and the output of the amplifier 3, and the midpoint voltage of the resistors 6 and 7 is connected to the comparator via the voltage holding section 8. No voltage is applied to the positive phase input (+) of No.4. The capacitor 12 is used to set a time constant for the holding time of the voltage holding section 8.

FIG. 4(a) shows the negative phase input of comparator 4 (-1 signal waveform S
Fig. 4(b) shows the signal waveform S2 of l and positive phase input (+).
) shows the output waveform of comparator 4. The operation will be explained in detail with reference to FIGS. 3 and 4.

An optical signal 2 inputted to the light receiving element 1 is amplified by an amplifier 3. On the other hand, the output voltage of the reference power supply 5 is set to be approximately the same as the output voltage of the amplifier 3 when the original input is thin, and the resistors 6 and 7 are set to the same resistance value. The midpoint potential of the resistors 6 and 7 changes between the output voltage of the amplifier 3 and the output voltage of the reference power supply 5, and is held by the voltage holding section 8 when the voltage value is at the "H" level. The output waveform of the voltage holding section 8 changes with a time constant determined by the capacitor 12. In the comparator 4, the levels of the waveforms S1 and 82 are compared and converted into a second value signal shown in FIG. 4(b)).

Problems to be Solved by the Invention In such a conventional configuration, there are two cases: when receiving the optical signal 2 continuously and when receiving the optical signal 2 after not receiving the optical signal 2 for a long time. , a difference occurs in the pulse width of the reproduced output signal. Specifically, as in period A in FIG.
When the level is repeated, the output of the voltage holding section 8 indicates approximately the midpoint level of the output of the amplifier 3, so the comparator 4
Output cover m Width M 3 pulse width (“H” level and “L” level
Period A is followed by period B in which there is no optical signal 2, and when period C is reached and optical signal 2 is input, period B changes to period C. In this case, since the output of the heavy pressure holding section 8 rises after the completion of discharge, the output of the comparator 4
The output pulse width of is expanded to T2, and even if the optical signal 2 has the same pulse width, pulse width fluctuation occurs because T1≠T2.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical receiver in which pulse width does not vary in the output of a binary signal even when receiving an optical signal immediately after a no-signal period of the optical signal.

Means for Solving the Problems The optical receiving device of the present invention includes a light receiving element that receives an optical signal, an amplifier that amplifies the output signal of the light receiving element, and an analog-to-digital conversion circuit that converts the output of the amplifier into a digital signal. , a first . a second memory circuit; an arithmetic circuit that calculates the median value between the respective digital output values stored in the second storage circuit; a digital-to-analog conversion circuit that converts the output value of the arithmetic circuit into analog; and an analog conversion circuit for the digital-to-analog conversion circuit; A comparator that binarizes the output signal of the amplifier with the output value as a reference level is provided, and when the output of the comparator is "H"/L/bevel, a digital value is written in the first storage circuit, and the comparator outputs a digital value. The present invention is characterized in that a digital value is written into the second storage circuit when the output is at the "L" level.

Effect: According to this configuration, the output signal of the amplifier is digitally converted to the reference level for binarization by the comparator, and the value is set to the first digit according to the output level of the comparator. It is created by digitally storing it in the second comparison circuit, calculating the intermediate value of both digitally stored values in an arithmetic circuit, and converting it into analog, so that it is stable regardless of the length of the optical signal no-signal period. There is.

EXAMPLE Hereinafter, an example of the present invention will be explained based on FIGS. 1 and 2. Components having the same functions as those in FIG. 3 showing the conventional example will be described with the same reference numerals.

FIG. 1 shows an optical receiver according to the present invention. An optical signal 2 input to the light receiving element 1 is amplified by an amplifier 3. When the signal is amplified by the amplifier 3, the output signal has a slope in its rising and falling edges, as shown in waveform S1 in FIG. 2(a). This signal is converted into a binary signal by the comparator 4 based on the reference level Vref.

The reference level Vref is created as follows.

The output of the amplifier 3 is digitally converted by an A/D conversion circuit 6. The relationship between the reference power supply 5 and the A/D conversion circuit 6 will be explained in detail later. When the output of the comparator 4 is at the "HII" level, the storage control signal S3 of the first storage circuit 7 becomes "H" level, and the digital output value of the A/D conversion circuit 6 becomes the first
is stored in the memory circuit 7 of. When the output of the comparator 4 is at "L" level, the storage control signal S4 of the second storage circuit 8
“H” level is supplied to the A/D via the inverter 9.
The digital output value of the conversion circuit 6 is stored in the second storage circuit 8.

Next, the memory value ■1 of the first memory circuit and the memory value ■2 of the second memory circuit 8 are input to the arithmetic circuit 10, and the midpoint 2-V
The l value [□] is digitally calculated. The output of the arithmetic circuit 10 is applied as a reference level Vref to the negative phase input (→) of the comparator 4 via the L)/A conversion circuit 11.

Note that the reference power supply 5 outputs almost the same voltage as the "L" level of the output of the amplifier 3, and immediately after the power is turned on, the second
The digital output value is given to the output of the memory circuit 8 of the amplifier 3. By kneading, the output of the amplifier 3 becomes "
Even if it indicates the H''' level, the reference level Vref can be applied to the comparator 4, and the binarization of the optical signal can be started immediately.

In this way, the first. Since the reference level Vref is calculated in the arithmetic circuit 10 based on the digital storage value of the second storage circuit 7.8, the reference level Vref is calculated as shown in FIG. 2(a). Even immediately after it ceases to exist over time, its level remains stable, as shown in Figure 2 (
As shown in b), period C can also be converted with the same pulse width TI as period A.

Effects of the Invention As described above, according to the present invention, in addition to converting the output signal of the light receiving element amplified by the amplifier into a binary signal by the comparator,
The output signal of the amplifier is converted into a digital value by an analog-to-digital conversion circuit, and when the output of the comparator is at the "°H°" level, the digital value is written into the first storage circuit, and the output signal of the comparator is written as a digital value. writes a digital value to the second memory circuit when the is at L'' level, and the arithmetic circuit calculates the median value between the respective digital output values stored in the first and second memory circuits, Since the output value of the arithmetic circuit is converted to analog via a digital-to-analog conversion circuit and applied to the comparator as a reference level, even if there is a long period of no signal of the optical signal incident on the photodetector, the comparison The reference level applied to the device is stable, and signal conversion can be performed without pulse width fluctuations.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment of the optical receiving device of the present invention, and FIG.
FIG. 3 is a diagram showing the input and output waveforms of a comparator in the same device, FIG. 3 is a configuration diagram of a conventional optical receiver, and FIG. 4 is a diagram showing input and output waveforms of signals in the conventional comparator. 1... Light receiving element, 2... Optical signal, 3... Amplifier,
4... Comparator, 6... A/D conversion circuit and analog
digital conversion circuit], 7... first storage circuit, 8.
...Second memory circuit, io...Arithmetic circuit, 11...
D/A conversion circuit and digital/analog conversion circuit], V
ref...Reference level.

Claims (1)

[Claims] 1. A light-receiving element that receives an optical signal, an amplifier that amplifies the output signal of the light-receiving element, an analog-to-digital conversion circuit that converts the output of the amplifier to digital, and digital storage of the digital output value of the analog-to-digital conversion circuit. an arithmetic circuit that calculates the median value between each digital output value stored in the first and second memory circuits; and a digital converter that converts the output value of the arithmetic circuit into analog.・Providing an analog conversion circuit and a comparator that binarizes the output signal of the amplifier using the analog output value of the digital-to-analog conversion circuit as a reference level,
An optical device configured to write a digital value into a first storage circuit when the output of the comparator is at the “H” level, and to write a digital value into the second storage circuit when the output of the comparator is at the “L” level. Receiving device.