JPH11136196A - Optical receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an error from occurring even if noise is added to an optical input signal at the time of maximum input by adding offset voltage to threshold voltage of a limiter amplifier and controlling the offset voltage according to the size of a mean value of the optical input signal. SOLUTION: After an optical input signal is inputted to a photodiode 1 and converted into a current signal, it is converted into a voltage signal by a preamplifier 2. An output voltage signal of the preamplifier 2 is inputted to a positive phase input terminal of a limiter amplifier 3 and is amplified into a voltage signal of a desired amplitude level with threshold voltage that is given to a reverse phase input terminal of the amplifier 3 by a direct current voltage source 5 as a decision reference. In such cases, resistance 6 and a capacitor 7 for smoothing detect a mean value of a current of a photodiode 1 which is in proportion to the optical input signal and controls the source 5 by voltage that is applied to both ends of the resistance 6. That is, offset voltage is added to threshold of the amplifier 3 at the time of optical input maximum and the offset voltage is made almost zero at the time of optical input minimum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver used for optical communication using an optical fiber as a transmission line.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing a configuration of a conventional optical receiver. In FIG. 5, 1 is a photodiode of a light receiving element, 2 is a preamplifier, 3 is a limiter amplifier, 4 is a clock extraction / data identification circuit, and 5 is a DC voltage source.

Next, the operation will be described. The optical input signal, which is a binary digital signal, is input to the photodiode 1 and converted into a current signal, and then converted into a voltage signal by the preamplifier 2. The output voltage signal of the preamplifier 2 is input to the positive-phase input terminal of the limiter amplifier 3, and is amplified by the DC voltage source 5 to a voltage signal of a desired amplitude level using the threshold voltage applied to the negative-phase input terminal of the limiter amplifier 3 as a determination reference. Is done. This threshold voltage is set at the center of the input voltage signal amplitude. The output voltage signal of the limiter amplifier 3 is input to a data identification circuit 4, which extracts a clock component from the input signal, identifies data, and outputs a clock signal and a data signal.

[0004]

Since the conventional optical receiver is configured as described above, especially when using the photodiode 1 and the preamplifier 2 with high sensitivity, when the optical input is the maximum input, the optical input signal is reduced. When the noise is superimposed, the noise is emphasized and output as compared with the signal component due to the non-linearity of the input / output characteristics of the preamplifier 2, and exceeds the threshold voltage of the limiter amplifier 3 provided by the DC voltage source 5, thereby generating an error. There was a problem of doing it. Further, since the threshold value of the limiter amplifier 3 is fixed to the center value of the amplitude of the input voltage signal, there is a problem that the threshold voltage is not always optimal for the light receiving sensitivity.

The present invention has been made to solve such a problem, and it is an object of the present invention to provide a high-sensitivity optical receiver which does not generate an error when an optical input signal is deteriorated, for example, when noise is superimposed. The purpose is.

[0006]

In the optical receiver according to the first aspect of the present invention, an offset voltage is added to the threshold voltage of the limiter amplifier 3, and the offset voltage is controlled by the average value of the optical input signal, thereby maximizing the offset voltage. An error is prevented from occurring even when noise is added to the optical input signal at the time of input.

In the optical receiver according to the second invention, the first
By adding a function of temperature compensation for the offset voltage to the optical receiver according to the invention of the present invention, the offset voltage is optimized even if the ambient temperature fluctuates.

In the optical receiver according to the third aspect of the present invention, the offset voltage of the threshold voltage of the limiter amplifier 3 is controlled not by the average value of the optical input signal but by the magnitude of the amplitude value of the optical input signal. Even if the effective value of the signal amplitude fluctuates due to deterioration, no error occurs, and the resistance to noise added to the optical input signal is ensured.

Further, in the optical receiver according to the fourth invention, the third
By adding a function of temperature compensation for the offset voltage to the optical receiver according to the invention of the present invention, the offset voltage is optimized even if the ambient temperature fluctuates.

Further, in the optical receiver according to the fifth aspect of the present invention, the offset voltage of the threshold voltage of the limiter amplifier 3 is controlled by the ratio of the average value of the optical input signal to the output amplitude of the preamplifier 2, thereby controlling the optical input. Even if the effective value of the signal amplitude fluctuates due to signal deterioration, no error occurs,
In addition, the resistance to noise added to the optical input signal is ensured.

Further, in the optical receiver according to the sixth aspect, the fifth aspect is provided.
By adding a function of temperature compensation for the offset voltage to the optical receiver according to the invention of the present invention, the offset voltage is optimized even if the ambient temperature fluctuates.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. FIG. 1 is a block diagram showing Embodiment 1 of the present invention. In FIG.
Is a preamplifier, 3 is a limiter amplifier, 4 is a data identification circuit, 5 is a DC voltage source, 6 is a resistor, 7 is a smoothing capacitor, and 8 is a temperature detector.

Next, the operation will be described. An optical input signal which is a binary digital signal of 0 and 1 is a photodiode 1
And converted into a current signal, and then converted by the preamplifier 2 into a voltage signal. The output voltage signal of the preamplifier 2 is input to the positive-phase input terminal of the limiter amplifier 3, and is amplified by the DC voltage source 5 to a voltage signal of a desired amplitude level using the threshold voltage applied to the negative-phase input terminal of the limiter amplifier 3 as a determination reference. Is done. The output voltage signal of the limiter amplifier 3 is input to a data identification circuit 4, which extracts a clock component from the input signal, identifies data, and outputs a clock signal and a data signal.

FIG. 4 shows the relationship between the output voltage signal level of the preamplifier 2 and the optical input signal level, which are highly sensitive. The output voltage amplitude of the preamplifier 2 is proportional to the optical input signal in the linear region in the figure, but becomes constant even if the optical input signal increases in the saturation region in the figure. Here, it is assumed that noise is superimposed on the 0 level of the digital signal. When the optical input signal level is low, the 0 level and the 1 level are both in the linear region, and a voltage signal proportional to each is output from the preamplifier 2, so that the ratio between the 1 level and the noise level is not different from the optical input signal. However, as the optical input signal level increases, one level of the digital signal enters the saturation region, and as shown in the figure, the noise level in the linear region is emphasized compared to the signal component and output, and the ratio of the one level to the noise level is reduced. Will change. Therefore, if the threshold voltage of the limiter amplifier 3 is set at the center of the output voltage signal amplitude of the preamplifier 2 as in a conventional optical receiver, an error occurs.

Then, the average value of the current of the photodiode 1 proportional to the optical input signal is detected by the resistor 6 connected to the cathode of the photodiode 1 and the capacitor 7 for smoothing. Voltage source 5
Control. That is, at the time of maximum light input, an offset voltage is added to the threshold value of the limiter amplifier 3 by ΔV in FIG. 4 to prevent the occurrence of an error due to noise, and the offset voltage becomes almost zero at the time of minimum light input. However, the offset voltage is not completely set to 0 even when the light input is at a minimum, and is set to a voltage at which the reception sensitivity becomes the best. By doing as described above, it is possible to configure a high-sensitivity optical transceiver without causing an error at the maximum optical input even for an optical input signal having noise.

Further, since the frequency characteristics and the input / output characteristics of the preamplifier 2 vary depending on the temperature, the optimum value of the threshold voltage of the limiter amplifier 3 also varies with the temperature. Therefore, by detecting the ambient temperature with the temperature detector 8 and finely adjusting the output voltage of the DC voltage source 5 with the detected output signal, a more optimal offset voltage can be set.

Embodiment 2 FIG. FIG. 2 is a block diagram showing Embodiment 2 of the present invention, and 9 is a peak detector. In the first embodiment of the present invention, the average value of the current of the photodiode 1 is detected.
When an optical signal having a reduced level ratio, that is, an optical signal having a degraded extinction ratio is input, the preamplifier 2 has the same optical power.
The amplitude of the signal output from the amplifier becomes small, and the offset voltage applied to the threshold voltage of the limiter amplifier 3 becomes excessive. Therefore, in the second embodiment, not the average value of the current of the photodiode 1 but the amplitude value of the AC voltage applied to both ends of the resistor 6 is detected by the peak detector 9, and the DC voltage is output by the DC voltage signal output from the peak detector 9. Voltage source 5
, An optimum threshold voltage is given to the limiter amplifier 3. That is, when the optical input is at its maximum, an offset voltage corresponding to the extinction ratio of the optical input signal is added to the threshold voltage of the limiter amplifier 3, so that the optical receiver can withstand not only the noise of the optical signal but also the deterioration of the extinction ratio of the optical signal. Can be configured. Further, high sensitivity can be obtained by giving an optimum offset voltage even when the light input is minimum.

Also, as in the first embodiment of the present invention, the output voltage of the DC voltage source 5 is finely adjusted by the temperature detector 8 in consideration of the temperature characteristics of the preamplifier 2, so that a more optimal offset voltage can be set. Will be possible.

Embodiment 3 FIG. 3 is a block diagram showing Embodiment 3 of the present invention. In the second embodiment of the present invention, the deterioration of the ratio between the 1 level and the 0 level of the optical signal, that is, the deterioration of the extinction ratio is realized by detecting the peak value of the AC voltage applied to the resistor connected to the photodiode 1. However, in the third embodiment, the threshold voltage of the limiter amplifier 3 is controlled by the ratio between the amplitude of the output voltage signal of the preamplifier 2 and the average value of the current of the photodiode 1. In FIG. 3, the peak detector 9 detects the amplitude value of the output voltage signal of the preamplifier 2. The DC voltage averaged by the resistor 6 and the capacitor 7 connected to the cathode of the photodiode 1 is input to the DC voltage source 5 together with the output DC voltage of the peak detector 9. The DC voltage source 5 compares the two input voltages and gives a threshold voltage to the limiter amplifier 3. When the extinction ratio of the input optical signal is deteriorated, the output voltage amplitude of the preamplifier 2 is reduced and the output voltage of the peak detector is reduced. However, since the average value of the current of the photodiode 1 does not change, the voltage applied across the resistor 6 is also reduced. It does not change. Therefore, when the extinction ratio of the optical input signal is degraded, the ratio between the output of the peak detector 9 and the voltage applied across the resistor 6 is reduced. In other words, when the extinction ratio of the optical input signal is degraded, by controlling the offset voltage of the threshold voltage of the limiter amplifier 3 which is given at the time of the maximum optical input to be small, not only the noise of the optical signal but also the degradation of the extinction ratio of the optical signal An optical receiver that can withstand the above can be configured. Further, high sensitivity can be obtained by giving an optimum offset voltage even when the light input is minimum.

Further, the output voltage of the DC voltage source 5 is finely adjusted by the temperature detector 8 in consideration of the temperature characteristics of the preamplifier 2 as in the first and second embodiments of the invention. An optimal offset voltage can be set.

[0021]

According to the first aspect of the present invention, at the time of maximum optical input, noise is added to the optical input signal by adding an offset voltage controlled by the average value of the optical input signal to the threshold voltage of the limiter amplifier 3. However, no error occurred, and a high-sensitivity optical receiver could be constructed by optimizing the offset.

According to the second aspect, the temperature variation tolerance can be provided by adding a temperature compensation function to the offset voltage applied to the threshold voltage of the limiter amplifier 3 to the first aspect.

According to the third aspect of the present invention, when the optical input is at a maximum,
By adding an offset voltage controlled by the magnitude of the amplitude of the optical input signal to the threshold voltage of the limiter amplifier 3, no error occurs even if the effective value of the signal amplitude changes due to deterioration of the extinction ratio of the optical input signal. In addition, an optical receiver that can withstand noise added to an optical input signal can be configured.

Further, according to the fourth aspect, the temperature variation tolerance can be provided by adding a temperature compensation function to the offset voltage applied to the threshold voltage of the limiter amplifier 3 to the third aspect.

According to the fifth aspect, when the optical input is at the maximum,
By adding an offset voltage controlled by the ratio between the average value of the optical input signal and the output amplitude of the preamplifier 2 to the threshold voltage of the limiter amplifier 3, the effective value of the signal amplitude fluctuates due to deterioration of the extinction ratio of the optical input signal. Thus, an optical receiver which does not generate an error and which can withstand noise added to an optical input signal can be constructed.

Further, according to the sixth aspect, the temperature variation tolerance can be provided by adding a temperature compensation function to the offset voltage applied to the threshold voltage of the limiter amplifier 3 to the fifth aspect.

[Brief description of the drawings]

FIG. 1 is a block diagram showing Embodiment 1 of an optical receiver according to the present invention.

FIG. 2 is a block diagram showing Embodiment 2 of the optical receiver according to the present invention.

FIG. 3 is a block diagram showing Embodiment 3 of an optical receiver according to the present invention.

FIG. 4 is a diagram showing a relationship between a preamplifier output level and an optical input level.

FIG. 5 is a block diagram showing a conventional optical receiver.

[Explanation of symbols]

Reference Signs List 1 photodiode, 2 preamplifier, 3 limiter amplifier, 4 data discrimination reproduction circuit, 5 DC voltage source, 6
Resistance, 7 capacitor, 8 temperature detector, 9 peak detector.

Claims (6)

[Claims] A photodiode for converting an optical input signal into a current signal; a preamplifier connected to an anode of the photodiode for converting a current signal of the photodiode into a voltage signal; and a preamplifier connected to an output terminal of the preamplifier. A limiter amplifier for amplifying the output signal of the preamplifier to a voltage signal of a desired level; a data identification and reproduction circuit for reproducing and outputting a clock / data signal from the output signal of the limiter amplifier; A resistor for generating a voltage corresponding to the current signal of the photodiode, a smoothing capacitor connected in parallel with the resistor, and a DC voltage connected to the cathode of the photodiode and determined by the voltage of the resistor, the limiter amplifier And a DC voltage source for providing as a threshold voltage And an optical receiver. 2. A DC voltage source further comprising a temperature detector for inputting a signal corresponding to an ambient temperature.
An optical receiver as described. 3. A photodiode for converting an optical input signal into a current signal, a preamplifier connected to an anode of the photodiode for converting a current signal of the photodiode into a voltage signal, and a preamplifier connected to an output terminal of the preamplifier. A limiter amplifier for amplifying the output signal of the preamplifier to a voltage signal of a desired level; a data identification and reproduction circuit for reproducing and outputting a clock / data signal from the output signal of the limiter amplifier; A resistor for generating a voltage signal corresponding to a current signal of the photodiode, a peak detector connected to the cathode of the photodiode for outputting a DC voltage signal proportional to a peak value of the voltage signal of the resistor, and the peak detector The DC voltage determined by the output DC voltage signal of the And a DC voltage source for providing a threshold voltage to the optical receiver. 4. A DC voltage source further comprising a temperature detector for inputting a signal corresponding to an ambient temperature.
An optical receiver as described. 5. A photodiode for converting an optical input signal to a current signal, a preamplifier connected to an anode of the photodiode for converting a current signal of the photodiode to a voltage signal, and a preamplifier connected to an output terminal of the preamplifier. A limiter amplifier for amplifying the output signal of the preamplifier to a voltage signal of a desired level; a data identification and reproduction circuit for reproducing and outputting a clock / data signal from the output signal of the limiter amplifier; A resistor for generating a voltage corresponding to the current signal of the photodiode, a smoothing capacitor connected in parallel to the resistor, and a DC voltage signal connected to the output of the preamplifier and proportional to the peak value of the output signal of the preamplifier. A peak detector to be output, an output DC voltage signal of the peak detector and the above-described resistor. An optical receiver for providing a DC voltage controlled by a ratio of a voltage applied to the resistance to the limiter amplifier as a threshold voltage. 6. A DC voltage source further comprising a temperature detector for inputting a signal corresponding to an ambient temperature.
An optical receiver as described.