JP2001211035A - Preamplifier and optical receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To resolve the problem that the output amplitudes of the transforming impedance amplifier decrease and bit errors occur, because of the non-linearity of input-output characteristic of the transforming impedance amplifier which converts the optical current into the voltage signals, when the extinction ratio of input optical signals is deteriorated in the conventional optical receivers. SOLUTION: The output amplitude of the transforming impedance amplifier is prevented from being reduced by regulating the input-output characteristic of the transforming impedance amplifier, according to detected variation of extinction ratio of the input signals by the variation of the relative value of the amplitude and average of the output of the transforming impedance amplifier.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a preamplifier and an optical receiver for optical communication using an optical fiber as a transmission line.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing a configuration of a conventional optical receiver. In FIG. 4, reference numeral 1 denotes a photodiode as a light receiving element, 2 denotes a transimpedance amplifier,
Is the amplifier built into the transimpedance amplifier,
4 is a variable resistor incorporated in the transimpedance amplifier, 5 is a DC voltage detector, and 6 is a discriminator / regenerator.

Next, the operation will be described. The binary digital optical input signal of 0 and 1 is converted into a current signal by the photodiode 1 and input to the transimpedance amplifier 2. This current signal is transmitted to the transimpedance amplifier 2
When a voltage is generated in proportion to the resistance value of the variable resistor 4 built in the device, the voltage is converted into a voltage signal at a current-to-voltage conversion ratio proportional to the resistance value. The identification regenerator 6 extracts a clock from the input voltage signal, and outputs a data signal and a clock signal identified and reproduced by the clock. DC voltage detector 5
Detects the average value of the voltage signal output from the transimpedance amplifier 2 and supplies an output voltage proportional to the average value to the variable resistor 4. Variable resistor 4 according to this voltage output
, That is, the current-voltage conversion magnification is controlled. FIG.
Shows the relationship between the optical input waveform and the output voltage waveform of the transimpedance amplifier 2. It is assumed that the input / output characteristics of the transimpedance amplifier 2 have the characteristics shown by the solid curve g1 in FIG. In FIG. 5A, the horizontal axis is the optical input power input to the photodiode 1, the vertical axis is the voltage output of the transimpedance amplifier 2, and the current-voltage conversion magnification is R1 with a large slope at the optical input Pth0.
To R2 with a small inclination. Pth0 corresponds to a switching point of the resistance value of the variable resistor 4. Thus, the variable resistor 4
, The current-voltage conversion magnification of the transimpedance amplifier 2 is controlled so as to increase the optical receiver to obtain a desired receiving sensitivity in a region where the optical input signal is small. In a large area, the discriminating regenerator 6 is controlled to be small so as not to be saturated by an increase in the input voltage amplitude. Here, as an initial value when the optical input signal is large, the 0 level of the optical input signal is Pi.
Assuming that the 0 and 1 levels are Pi1, the output amplitude at that time is V1 as shown in FIG.

[0004]

Since the conventional optical receiver is configured as described above, for example, in FIG. 5B, for example, the driving condition of a laser diode used as a light source varies depending on temperature or the like. If only the 0 level of the optical input signal changes from Pi0 to Pi2, that is, if the extinction ratio indicating the ratio between the 1 level and the 0 level of the optical signal is degraded, the output voltage of the transimpedance amplifier 2 in FIG. The amplitude decreases from V1 to V2. This is because when the optical input signal is large, one level of the optical signal is in the region of the value R2 where the current-to-voltage conversion magnification of the transimpedance amplifier 2 is small, while level 0 is in the region of the large value R1 of the current-voltage conversion magnification. This is a phenomenon that occurs because the output voltage amplitude of the transimpedance amplifier 2 is reduced, and noise at the 0 level is relatively emphasized to cause deterioration of the SN ratio, which causes a bit error.

The present invention solves such a problem. When the optical input signal is small, the same sensitivity as that of the conventional receiver can be obtained. When the optical input signal is large, the optical input signal can be obtained. It is an object of the present invention to provide an optical receiver in which a bit error does not occur even if the ratio between the 0 level and the 1 level, that is, the extinction ratio is deteriorated.

[0006]

A preamplifier according to a first aspect of the present invention includes a transimpedance amplifier for converting an output current signal of a photodiode into a voltage signal by juxtaposing an operational amplifier and a variable resistor, and a preamplifier of the transimpedance amplifier. A DC voltage detector for detecting a DC component, a peak detector for detecting an amplitude value of an output signal from the transimpedance amplifier, and a comparison result between a detection voltage of the DC voltage detector and a detection voltage of the peak detector And setting means for setting the resistance value of the variable resistor based on the detection voltage of the DC voltage detector.

A preamplifier according to a second aspect of the present invention includes a transimpedance amplifier for juxtaposing an operational amplifier and a variable resistor for converting an output current signal of a photodiode into a voltage signal, and a DC for detecting a DC component of an output signal from the transimpedance amplifier. A voltage detector, an average value detector that detects an average value of a current signal flowing through the photodiode, a peak detector that detects an amplitude value of the current signal flowing through the photodiode, and a detection voltage of the average value detector. Setting means for setting the variable resistor based on a result of comparison between the variable resistance and a detection voltage of the peak detector and a detection voltage of the DC voltage detector.

A preamplifier according to a third aspect of the present invention includes a transimpedance amplifier for converting an output current signal of a photodiode into a voltage signal by juxtaposing an operational amplifier and a variable resistor, and a DC for detecting a DC component of an output signal from the transimpedance amplifier. A voltage detector, a peak detector that detects an amplitude value of an output signal from the transimpedance amplifier, an average detector that detects an average value of a current signal flowing through the photodiode, and detection of the average detector. Based on the comparison result of the voltage and the detection voltage of the peak detector and the detection voltage of the DC voltage detector,
Setting means for setting the variable resistance.

The preamplifier according to the fourth aspect of the present invention has a large value when the current-voltage conversion magnification is smaller than a certain set value for an optical signal input to the photodiode, and switches to a small value when the optical signal is larger than the set value. It has such characteristics.

According to a fifth aspect of the present invention, there is provided an optical receiver, comprising: a preamplifier according to the first aspect of the invention; a photodiode for receiving an optical input signal; and a data signal and a clock signal identified and reproduced from the output signal of the preamplifier. An optical receiver comprising an identification regenerator.

An optical receiver according to a sixth aspect of the present invention is a preamplifier according to the second aspect of the invention, a photodiode for receiving an optical input signal, and discriminating and reproducing a data signal and a clock signal from an output signal of the preamplifier according to the first aspect. An optical receiver comprising an identification regenerator.

An optical receiver according to a seventh aspect of the present invention is a preamplifier according to the third aspect of the invention, a photodiode for receiving an optical input signal, and discriminating and reproducing a data signal and a clock signal from an output signal of the preamplifier according to the first aspect. An optical receiver comprising an identification regenerator.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a block diagram showing a first embodiment of the present invention. In FIG. 1, reference numeral 7 denotes a resistance value setting device for controlling a resistance value of a variable resistor 4 incorporated in a transimpedance amplifier 2; Reference numeral 9 denotes a peak detector for detecting the output voltage amplitude value, and reference numeral 9 denotes a comparator for comparing the output voltage of the peak detector 8 with the output voltage of the DC voltage detector 5 and providing a control signal to the resistance value setting device 7. A preamplifier is composed of 2, 5, 7, 8, and 9. In the drawing, the same reference numerals as those in FIG. 4 indicate the same equivalent products.

Next, the operation will be described. The comparator 9 outputs the output voltage amplitude value (Vp
The control signal is not output when the ratio of the output voltage (eak) to the output voltage average value (Vav) is above a certain threshold value A, and the control signal is output when the ratio becomes below the A value. FIG. 6 shows the relationship between the output amplitude value Vpeak and the output average value Vav of the output voltage of the transimpedance amplifier. When no control signal is given, the resistance value setting unit 7 outputs the output voltage of the DC voltage detector 5 to the variable resistance 4 as it is,
When a control signal is given from the comparator 9, a value smaller than the output voltage of the DC voltage detector 5 is output to the variable resistor 4. The input / output characteristics of the transimpedance amplifier 2 are set to the solid line g1 in FIG. FIG. 7 shows the characteristics of the current-voltage conversion magnification of the transimpedance amplifier 2 and the output voltage of the resistance value setting device 7 with respect to the optical input power. The horizontal axis of FIG. 7 shows the optical input power input to the photodiode 1, and the vertical axis shows the transformer. 7 shows the current-voltage conversion magnification of the impedance amplifier 2 (FIG. 7B) and the output value of the resistance value setting device 7 (FIG. 7A). The solid line g
The optical input power dependency of the current-voltage conversion magnification of the transimpedance amplifier 2 corresponding to 1 is represented by y1, and the optical input power dependency of the output of the resistance value setting unit 7 is represented by x1, and the optical input power corresponding to FIG. When the value is Pth0, the current-voltage conversion magnification is switched from R1 to R2.

If the ratio of the output voltage amplitude value of the transimpedance amplifier 2 to the average output voltage value is equal to or greater than the threshold voltage A value of the comparator 9 when the 0 level and 1 level of the optical input signal are Pi0 and Pi1, respectively. Since the output voltage of the DC voltage detector 5 is applied to the variable resistor 4 as it is, the output amplitude of the transimpedance amplifier 2 becomes V1 as in the conventional receiver. Next, when the extinction ratio of the optical input signal is deteriorated, for example, when only the 0 level fluctuates and becomes Pi2, the output voltage amplitude of the transimpedance amplifier 2 decreases.

At this time, when the threshold voltage A value of the comparator 9 is set so that the ratio between the output voltage amplitude and the output voltage average value becomes equal to or less than the A value, the voltage output from the resistance value setting device 7 becomes DC
This is because the output voltage of the voltage detector 5 becomes lower than that of FIG. 7, and the output characteristic of the resistance value setting device 7 shifts from x1 to x2 and the current-voltage conversion magnification characteristic of the transimpedance amplifier 2 shifts from y1 to y2 in FIG. The switching point of the current-voltage conversion magnification shifts from Pth0 to Pth1 which is larger. That is, the input / output characteristic changes from g1 to g2 in FIG. 5A, and the output voltage amplitude of the transimpedance amplifier 2 becomes V3 as shown in FIG. 5C, and the decrease in the amplitude can be suppressed. By setting the threshold value of the comparator 9 to a desired value in this way, it is possible to compensate for a decrease in the output voltage amplitude of the transimpedance amplifier 2 when the optical input signal is large. In a region where the optical input signal is small, the transimpedance amplifier 2 has a large current-voltage conversion magnification like the conventional optical receiver, so that the receiving sensitivity is equivalent to that of the conventional receiver.

Embodiment 2 FIG. FIG. 2 is a block diagram showing Embodiment 2 of the present invention. Reference numeral 10 denotes a resistor connected to the cathode side of the photodiode, and 11 denotes an average detector. 2, 5, 7, 8, 9, 10, and 11 constitute a preamplifier.

The optical input signal is converted into a current signal by the photodiode 1, and this current signal is observed as a voltage signal at both ends of the resistor 10. Deterioration of the extinction ratio of the optical input signal can also be detected by comparing the amplitude value and the average value of the voltage signal. An amplitude value and an average value of the voltage between both ends of the resistor 10 are detected by a peak detector 8 and an average value detector 11, respectively. The detected amplitude value and average value are input to the comparator 9. The comparator 9 outputs a control signal when the ratio of the amplitude value to the average value becomes equal to or less than a certain threshold value as in the first embodiment. Similarly to the first embodiment, when no control signal is given,
The output voltage of the voltage detector 5 is output to the variable resistor 4 as it is, and a value smaller than the output voltage of the DC voltage detector 5 is output to the variable resistor 4 when there is no control signal. With this configuration, if the threshold value of the comparator 9 is set to a desired value, the switching point of the current-voltage conversion magnification of the transimpedance amplifier 2 is controlled when the extinction ratio of the input optical signal is deteriorated. Thus, it is possible to suppress a decrease in the output voltage amplitude of the transimpedance amplifier 2 as in the first embodiment.

Embodiment 3 FIG. 3 is a block diagram showing Embodiment 3 of the present invention. 2,5,7,8,9,1
A preamplifier is constituted by 0 and 11.

The deterioration of the extinction ratio of the optical input signal can also be detected by taking the ratio of the output voltage amplitude value of the transimpedance amplifier 2 to the average value of the current signal flowing through the photodiode 1. In the third embodiment, the average value of the voltage across the resistor 10 is detected by the average value detector 11, and the output voltage amplitude value of the transimpedance amplifier 2 is detected by the peak detector 8. As in the first embodiment, by comparing the two values and controlling the voltage output from the resistance value setting device 7 to the variable resistor 4 when the ratio of the average value of the amplitude value to a desired threshold value or less is reduced. Further, when the extinction ratio of the optical input signal is deteriorated, the switching point of the current-voltage conversion magnification of the transimpedance amplifier 2 is controlled, so that the decrease in the output voltage amplitude of the transimpedance amplifier 2 can be suppressed.

[0021]

According to the first, fourth and fifth aspects of the present invention, the deterioration of the extinction ratio is detected by comparing the average value and the amplitude value of the output voltage signal of the transimpedance amplifier 2, and the relative amplitude value is detected. When the value decreases, the current-voltage conversion magnification of the transimpedance amplifier 2 is controlled so that the output amplitude of the transimpedance amplifier 2 does not decrease and the S / N ratio is increased. realizable. Further, in the region where the optical input signal is small, the same sensitivity as the conventional receiver can be ensured by making the current-voltage conversion magnification the same as that of the conventional optical receiver.

According to the second, fourth and sixth aspects of the invention, the deterioration of the extinction ratio is detected by comparing the average value of the current signal flowing through the photodiode 1 with the amplitude value, and the relative value of the amplitude value decreases. In this case, by controlling the current-voltage conversion magnification of the transimpedance amplifier 2 and increasing the S / N ratio without decreasing the output amplitude of the transimpedance amplifier 2, bit error free can be realized when the optical input signal is large. Further, in the region where the optical input signal is small, the same sensitivity as the conventional receiver can be ensured by making the current-voltage conversion magnification the same as that of the conventional optical receiver.

According to the third, fourth, and seventh aspects of the invention, the deterioration of the extinction ratio is detected by comparing the average value of the current signal flowing through the photodiode 1 with the amplitude value of the output voltage signal of the transimpedance amplifier 2. When the relative value of the amplitude value decreases, the current-voltage conversion magnification of the transimpedance amplifier 2 is controlled, and the transimpedance amplifier 2
By preventing the output amplitude from decreasing and increasing the SN ratio, bit error free can be realized when the optical input signal is large. Further, in the region where the optical input signal is small, the same sensitivity as the conventional receiver can be ensured by making the current-voltage conversion magnification the same as that of the conventional optical receiver.

[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 block diagram showing a conventional optical receiver.

FIG. 5 is a diagram showing a relationship between an optical input waveform and a transimpedance amplifier output waveform.

FIG. 6 is a diagram showing a relationship between an average value and an amplitude value of a transimpedance amplifier output voltage.

FIG. 7 is a diagram illustrating a relationship between a current-voltage conversion magnification of a transimpedance amplifier and an output of a resistor setting device.

[Explanation of symbols]

Reference Signs List 1 photodiode, 2 transimpedance amplifier, 3 operational amplifier, 4 variable resistor, 5 DC voltage detector, 6 discriminator / reproducer, 7 resistance value setting device, 8 peak detector, 9 comparator, 10 average value detector, 11 resistance .

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 10/06

Claims (7)

[Claims] A transimpedance amplifier for judging an output current signal of a photodiode into a voltage signal by juxtaposing an operational amplifier and a variable resistor; a DC voltage detector for detecting a DC component of an output signal from the transimpedance amplifier; A peak detector for detecting an amplitude value of an output signal from the transimpedance amplifier; a comparison result between a detection voltage of the DC voltage detector and a detection voltage of the peak detector; and a detection voltage of the DC voltage detector. A setting means for setting a resistance value of the variable resistor. 2. A transimpedance amplifier for juxtaposing an operational amplifier and a variable resistor to convert an output current signal of a photodiode into a voltage signal; a DC voltage detector for detecting a DC component of an output signal from the transimpedance amplifier; An average value detector that detects an average value of a current signal flowing through the photodiode, a peak detector that detects an amplitude value of the current signal flowing through the photodiode, a detection voltage of the average value detector, and a value of the peak detector. Setting means for setting the variable resistor based on a comparison result with a detection voltage and a detection voltage of the DC voltage detector. 3. A transimpedance amplifier for juxtaposing an operational amplifier and a variable resistor to convert an output current signal of a photodiode into a voltage signal; a DC voltage detector for detecting a DC component of an output signal from the transimpedance amplifier; A peak detector that detects an amplitude value of an output signal from a transimpedance amplifier, an average value detector that detects an average value of a current signal flowing through the photodiode, a detection voltage of the average value detector, and the peak detector And a setting means for setting the variable resistor based on a result of comparison with the detected voltage and a detection voltage of the DC voltage detector. 4. The current-voltage conversion magnification has a large value when the optical signal input to the photodiode is smaller than a certain set value, and switches to a small value when the optical signal is larger than the set value. The preamplifier according to claim 1. 5. A preamplifier according to claim 1, a photodiode for receiving an optical input signal, and an identification regenerator for recognizing and reproducing a data signal and a clock signal from an output signal of the preamplifier according to claim 1. Characteristic optical receiver. 6. A preamplifier according to claim 2, a photodiode for receiving an optical input signal, and an identification regenerator for recognizing and reproducing a data signal and a clock signal from an output signal of the preamplifier according to claim 1. Characteristic optical receiver. 7. A preamplifier according to claim 3, a photodiode for receiving an optical input signal, and an identification regenerator for recognizing and reproducing a data signal and a clock signal from an output signal of the preamplifier according to claim 1. Characteristic optical receiver.