JPH05152863A - Optical receiver - Google Patents

Abstract

PURPOSE:To provide the optical receiver in which an identification level is automatically made proper in response to a level of an input signal resulting in not incurring pulse width fluctuation. CONSTITUTION:A peak detection circuit consists of an operational amplifier 27 having two noninverting input circuits. An attenuator 23 attenuates an output voltage of a reception amplifier 22 by a half, an auxiliary voltage circuit 26 generates an auxiliary voltage higher than a level of the reception amplifier 22 at the time of non-light by a guard voltage Vg and an output voltage of the attenuator 23 and an output voltage of the auxiliary voltage circuit 26 are inputted to the peak detection circuit. Since a maximum value of both the outputs is latched by the peak detection circuit, an amplitude median level of the output voltage of the reception amplifier 22 or the auxiliary voltage which is higher is fed to a comparator 32 as an identification voltage thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver for converting a digital optical signal into a digital electric signal.

[0002]

2. Description of the Related Art Generally, in a receiving amplifier that receives a digital optical signal, the output waveform is considerably distorted from the original pulse waveform. Therefore, in the optical receiver, as shown in FIG. 4A, the received voltage 2 is discriminated as “high” or “low” by using the predetermined voltage 1 as an identification voltage, and FIG.
Pulse 3 is reproduced.

In the pulse reproduction, the identification voltage V _th is preferably set at the center level of the amplitude V _p of the output voltage of the receiving amplifier so that the pulse width does not change.
However, since the amplitude V _p of the output voltage of the receiving amplifier differs depending on the length of the optical fiber and the like, the pulse regenerator automatically sets the identification voltage V _th at the center level of the amplitude V _p. A level adjusting circuit (hereinafter abbreviated as ATC) is provided.

A pulse regenerator equipped with such an ATC works well when the signal is sufficiently large, but when there is no light input, the no-light level of the output voltage of the receiving amplifier is the identification voltage V _th.
And a malfunction occurs. Therefore, the identification voltage V _th must be higher than the no-light level by the guard voltage V _g so that the no-light level can be determined as the no-light level.

Therefore, in the conventional ATC, the amplitude V_pWhen
Guard voltage V_gTwice the voltage of 2V_gIntermediate level with
Voltage is generated, and this is used as the identification voltage V of the pulse regenerator._thage
Was there. That is, V_th= (V_p+ 2V_g) / 2
I was there. According to this formula, V_pWhen = 0, V_th= V_gso
Yes, V_pIs 2V_gWhen it is sufficiently larger than V_th= V _p
/ 2.

[0006]

However, in such an ATC, when the central level of the received amplitude and the guard voltage V _g are close to each other, a voltage significantly higher than the central level of the received amplitude is generated. That is, as shown in FIG. 5, although the identification voltage V _th is originally required to change with respect to the amplitude V _p as shown by the solid line 11, the characteristic as shown by the chain line 12 is exhibited. Become.

For example, when V _p / 2 = V _g = 100 mV, the ATC outputs 200 mV, and the error from 11 is 10
0 mV, the error rate reaches 100%. Therefore, the optical input signal is weak and the central level of the received amplitude is the guard voltage V _g.
When it is slightly higher, the reproduction pulse width becomes much narrower than the original signal pulse width. In other words, there is a drawback that weak light cannot be received correctly.

An object of the present invention is to provide an optical receiver capable of reproducing a pulse faithful to an optical input signal even when the optical signal is weak.

[0009]

The optical receiver of the present invention comprises:
The output voltage of the attenuator that attenuates the output voltage of the receiving amplifier that amplifies the output of the light receiving element by half, or the output voltage of the receiving amplifier itself is input to the first non-inverting input circuit of the operational amplifier, and when the minimum light is input, The output voltage of the auxiliary voltage circuit that generates a voltage higher than the output voltage of the receiving amplifier by a predetermined amount is input to the second non-inverting input circuit of the operational amplifier,
By inputting the output voltage of the operational amplifier to the inverting input circuit, the operational amplifier determines the peak value of the output voltage of the receiving amplifier or the output voltage of the attenuator and the output voltage of the auxiliary voltage circuit, whichever is higher. A peak detection circuit that detects and outputs the signal is formed, and the output voltage of the operational amplifier or the output voltage of the operational amplifier is attenuated in half by the attenuator, and the output voltage of the receiving amplifier is shaped by the comparator as the identification voltage. It is configured.

[0010]

According to the structure of the present invention, the higher peak value of the central level of the output voltage of the attenuator, that is, the output voltage of the receiving amplifier and the output voltage of the auxiliary voltage circuit, that is, the guard voltage, is detected by the operational amplifier. The output voltage of the operational amplifier is output and the output voltage of the receiving amplifier is shaped by the comparator using the output voltage of the operational amplifier as a discrimination voltage, or the output voltage of the receiving amplifier and the output voltage of the auxiliary voltage circuit, that is, a voltage twice the guard voltage, is output. The peak value of the higher one is detected by the operational amplifier and output, and the output voltage of the attenuator that attenuates the output voltage of this operational amplifier by half is used as the identification voltage to shape the waveform of the output voltage of the reception amplifier by the comparator.

As a result, when there is no light, the guard voltage is output as the discrimination voltage, and no malfunction occurs. Further, when the optical input is weak, the center level of the output voltage of the receiving amplifier is output as the discrimination voltage, and pulse reproduction with a small pulse width variation can be performed.

[0012]

[First Embodiment] A first embodiment of the present invention will be described below with reference to FIGS. 1 to 3. In addition,
In this embodiment, for simplicity, the no-light level of the receiving amplifier is set to 0 V and V _g = 100 mV.

In FIG. 1, reference numeral 22 is a receiving amplifier for amplifying the output of a photodiode 21 which is a light receiving element, and 23 is an attenuator in which a resistance 24 having a resistance value R1 and a resistance 25 having a resistance value R2 are connected in series. Is. By equalizing the resistors R1 and R2 of the resistors 24 and 25, the output voltage of the receiving amplifier 22 is attenuated by half. Reference numeral 26 is an auxiliary voltage circuit that generates an auxiliary voltage W _g higher than the output voltage of the receiving amplifier 22 by the guard voltage V _g when no light is input.

Reference numeral 27 is an operational amplifier having a first non-inverting input circuit 28, a second non-inverting input circuit 29, and an inverting input circuit 30. Each of the input circuits 28 to 30 is an NPN
It is composed of transistors. The output voltage of the attenuator 23 is input to the first non-inverting input circuit 28, and the output voltage W _g (= of the auxiliary voltage circuit 26 is input to the second non-inverting input circuit 29.
V _g ), and the operational amplifier 27 is connected to the inverting input circuit 30.
The output voltage of is fed back. Also, this operational amplifier 27
Connects a capacitor 31 to a part of the output.

With the above configuration, the operational amplifier 27
Constitutes a peak detection circuit that detects and outputs the peak value of the higher one of the output voltage of the attenuator 23 and the output voltage of the auxiliary voltage circuit 26. 32 is an operational amplifier 27
Is a comparator for discriminating the output voltage of the reception amplifier 22 into "high" and "low" by using the output voltage of the above as the identification voltage V _th .

The operation of the optical receiver configured as described above will be described below. Without the capacitor 31, in the operational amplifier 27, the sum of the collector current I _c1 of the transistor forming the first non-inverting input circuit 28 and the collector current I _c2 of the transistor forming the second non-inverting input circuit 29 is inverted. It works so as to be equal to the collector current I _{c3 of the} transistor that constitutes the input circuit 30.

Therefore, the base voltage of the transistor forming the first non-inverting input circuit 28 is V _b1 , the base voltage of the transistor forming the second non-inverting input circuit 29 is V _g , and the inverting input circuit 30 is _Assuming that the base voltage of the constituent transistors is V _b3 , each base voltage V _b1 , V
The relationship of Formula 1 is established between _g and V _b3 .

[0018]

[Number 1] _{exp (V b1 / β) +} exp (V g / β) = exp (V b3 / β) where a beta = kT / q, is 26mV at room temperature. That is, when the base voltage V _{b1 of the} transistor forming the first non-inverting input circuit 28 changes in accordance with the received signal, the operational amplifier 27 outputs the base voltage V _b satisfying Formula 1.
_b3 will be output.

Since the capacitor 31 holds the peak value of the base voltage _Vb3 , the operational amplifier 27 functions as a peak detection circuit for the base voltage _Vb3 . Now, V _b1 = V _p / 2
As a result, when the relation between the base voltage V _b3 and the amplitude V _p of the output voltage of the reception amplifier 22 is calculated, the solid line 41 in FIG. 2 is obtained. The broken line 42 indicates the ideal curve.

First, the output voltage of the receiving amplifier 22 is 2 V _g.
The case when the size is sufficiently larger will be described. At this time, since the base voltage V _b1 is sufficiently higher than the guard voltage V _g , the second
The transistor forming the non-inverting input circuit 29 is turned off. In Formula 1, the second term on the left side can be ignored, so V _b3 =
It becomes V _b1 . That is, the central level of the output signal of the reception amplifier 22 is output from the operational amplifier 27.

Next, the output voltage of the receiving amplifier 22 is 2V.
_gWhen it is sufficiently smaller, the base voltage V_b1Is the guard voltage
V_gConfigured the first non-inverting input circuit because it is much smaller
The transistor that turns on turns off. In Equation 1, the first term on the left side
Can be ignored, so V_b3= V _gBecomes I.e. gar
Voltage V_gIs output from the operational amplifier 27. Next,
Output voltage of receiving amplifier 22 is 2V_gWhen is equal to
Explain. Base voltage V shown by solid line 41_b3And ideal
The error from the curve 42 is maximum at this time. V_b1= V_g
Than number 1

[0022]

[Number 2] 2exp (V _g / β) = a exp (V _b3 / β). From _Expression 2, V _b3 = V _g +18 mV. That is, the base voltage V _b3 is slightly higher than the guard voltage V _g , but the difference is only 18 mV, which is 100 in the conventional example.
Very small compared to mV.

The base voltage V _b3 thus extracted
Is applied to the comparator 32 as the identification voltage V _th . As described above, according to this embodiment, the maximum error is only 18
At mV, the discrimination voltage V _th can be generated with an error rate of 18%. As a result, even if the optical signal is weak, it is possible to perform pulse reproduction faithful to the optical input signal. In addition, since the guard voltage V _g is output as the identification voltage V _th when there is no light, no malfunction occurs.

Although the non-light level of the receiving amplifier 22 is set to 0V in this embodiment, it is not necessarily 0V, so that the non-light level of the receiving amplifier 22 is generated as shown in FIG. The reference voltage device 51 may be provided. [Second Embodiment] Hereinafter, a second embodiment of the present invention will be described with reference to FIG.
Will be described with reference to. In this embodiment also, for simplicity, the level of the receiving amplifier when there is no light is set to 0 V and V _g = 1.
It is set to 00 mV.

In FIG. 6, the transistor forming the second non-inverting input circuit 63 and the transistor forming the inverting input circuit 64 of the operational amplifier 61 are twice as large as the transistors forming the first non-inverting input circuit 62. It is composed of area. The basic operation of the operational amplifier 61 is similar to that shown in FIG. It is not necessary to double both.

The differences will be described below. The operation of the optical receiver configured as above will be described below. In this optical receiver, the relationship of Expression 3 holds for the same reason as Expression 1.

[0027]

In [number 3] _{exp (V b1 / β) +} 2exp (V g / β) = 2exp (V b3 / β) number 3, and the V _b1 = V _g,

[0028]

## EQU4 ## 3exp (V _g / β) = 2exp (V _b3 / β). From number 4,

[0029]

## _EQU5 ## V _b3 = V _g +10 mV. That is, the difference between the base voltage V _b3 and the guard voltage V _g is only 10 mV, that is, the error rate is 10%.
When the base voltage V _b1 is sufficiently smaller than the guard voltage V _g , the transistor 62 forming the first non-inverting input circuit 62 is turned off, and the first term on the left side can be ignored in Formula 3, so that V _b3 = V _g . Become. That is, the guard voltage V _g is output from the operational amplifier 61.

Further, when the base voltage V _b1 is sufficiently higher than the guard voltage V _g , the transistor 63 forming the second non-inverting input circuit 63 is turned off, and in the equation 3, the second side on the left side is used.
Since the term can be ignored, V _b3 = V _b1 −18 mV. That is, the identification voltage V _th is 18 mV lower than the center level of the output voltage of the reception amplifier 22. In this case, V _b1 = 200
If it is mV, the error rate is only 9%, which means that the maximum error rate is improved from that of FIG.

As described above, according to this embodiment, the amplitude center level of the output voltage of the reception amplifier 22 and the guard voltage V are set.
_{When g} is equal, the discrimination voltage V _th can be generated with an error of only 10 mV. As a result, even if the optical signal is weak, it is possible to perform pulse reproduction faithful to the optical input signal. In addition, since the guard voltage V _g is output as the identification voltage V _th when there is no light, no malfunction occurs.

[Third Embodiment] A third embodiment of the present invention will be described below with reference to FIG. In this embodiment as well, for simplicity, the no-light level of the receiving amplifier is set to 0V.
And V _g = 100 mV. In FIG. 7, 7
Reference numeral 1 denotes an auxiliary voltage circuit that generates an auxiliary voltage that is twice the guard voltage V _g , that is, 2 V _g higher than the output voltage of the reception amplifier 22 when there is no light input. The output voltage of the receiving amplifier 22 is directly input to the first non-inverting input circuit 28 of the operational amplifier 27 having the same configuration as the conventional example, and the second
The output voltage of the auxiliary voltage circuit 71 is input to the non-inverting input circuit 29.

The attenuator 23 is provided between the receiving amplifier 22 and the operational amplifier 27 in the embodiment of FIG. 1, but in this embodiment, the output voltage of the operational amplifier 27 is input and the input voltage is input. Half of the voltage is applied to the comparator 32 as the identification voltage V _th . Other configurations are the same as those in FIG.
The operation of the optical receiver configured as above will be described below.

In this optical receiver, the equation (6) is used for the same reason as the equation (1).
The relationship is established.

[0035]

Where exp (V _b1 / β) + exp (2V _g / β) = exp (V _b3 / β) Here, when the maximum error occurs, that is, the output voltage of the reception amplifier 22 is the output of the auxiliary voltage circuit 71. The case when the voltage is equal to the voltage will be described. From V _b1 = 2V _g , Equation 6 is

[0036]

## EQU7 ## 2exp (2V _g / β) = exp (V _b3 / β). From number 7,

[0037]

## EQU8 ## Although V _b3 = 2V _g +18 mV is obtained, the identification voltage V _th is half the base voltage V _b3 , and thus V _th = V _g +9 mV. That is, the difference between the identification voltage V _th and the guard voltage V _g is only 9 mV.

As described above, according to this embodiment, the discrimination voltage V _th can be generated with a maximum error of only 9 mV and an error rate of 9%. Similar to the configuration of the operational amplifier 27 shown in FIG. 6, the transistors constituting the second non-inverting input circuit 29 and the transistors constituting the inverting input circuit 30 are the transistors constituting the first non-inverting input circuit 28. If the area is twice as large as
Becomes V _b3 = 2V _g +10 mV.

Since the identification voltage V _th is half the base voltage V _b3 , V _th = V _g +5 mV. That is, when the amplitude center level of the output voltage of the reception amplifier 22 and the guard voltage V _g are equal, the discrimination voltage V _th can be generated with an error of only 5 mV, and the effects of the above-described embodiment can be obtained.

[0040]

According to the optical receiver of the present invention, the peak detecting circuit is configured by using the operational amplifier having the first and second non-inverting input circuits and the inverting input circuit, and the center of the output voltage of the receiving amplifier is formed. The higher peak of the value and the guard voltage is detected and generated as the discrimination voltage, and this discrimination voltage is compared with the output voltage of the receiving amplifier, so that the discrimination voltage automatically changes according to the level of the input signal. It is possible to perform pulse reproduction that is optimized for the pulse width without causing fluctuations in the pulse width. In addition, the pulse reproduction can be performed faithfully to the optical input signal without malfunctioning when there is no light and even when the optical input is weak. Therefore, it is possible to always perform stable information reproduction even when incorporated in a long-distance optical communication system.

[Brief description of drawings]

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

FIG. 2 is a characteristic diagram showing a discrimination voltage characteristic of the optical receiver of FIG.

FIG. 3 is a block diagram showing a configuration of a modified example of the optical receiver.

FIG. 4 is a waveform diagram illustrating a pulse reproduction method in a conventional example.

FIG. 5 is an amplitude-discrimination voltage characteristic diagram for explaining an amplitude and a discrimination voltage in a conventional example.

FIG. 6 is a block diagram showing a configuration of an optical receiver according to a second exemplary embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration of an optical receiver according to a third exemplary embodiment of the present invention.

[Explanation of symbols]

 21 Photodiode 22 Receiving Amplifier 23 Attenuator 26 Auxiliary Voltage Circuit 27 Operational Amplifier 28 First Non-Inverting Input Circuit 29 Second Non-Inverting Input Circuit 30 Inverting Input Circuit 32 Comparator

Claims (4)

[Claims] 1. A receiving amplifier that amplifies the output of a light receiving element, an attenuator that attenuates the output voltage of the receiving amplifier by half, and a voltage that is higher by a predetermined amount than the output voltage of the receiving amplifier at the time of minimum light input. To feed back its own output voltage, a first non-inverting input circuit that receives the output voltage of the attenuator, and a second non-inverting input circuit that receives the output voltage of the auxiliary voltage circuit. An operational amplifier having an inverting input circuit, which constitutes a peak detection circuit for detecting and outputting a peak value of a higher one of the output voltage of the attenuator and the output voltage of the auxiliary voltage circuit; An optical receiver comprising: a comparator for shaping the output voltage of the receiving amplifier by using the output voltage of the amplifier as a discrimination voltage. 2. The optical receiver according to claim 1, wherein the first non-inverting input circuit comprises a transistor having an area half that of a transistor forming at least one of the second non-inverting input circuit and the inverting input circuit. 3. A receiving amplifier for amplifying the output of the light receiving element, an auxiliary voltage circuit for generating a voltage higher than the output voltage of the receiving amplifier at the time of minimum light input by a predetermined amount, and an input voltage for the output voltage of the receiving amplifier. A first non-inverting input circuit for inputting and a second input for the output voltage of the auxiliary voltage circuit
Of the output voltage of the receiving amplifier and the output voltage of the auxiliary voltage circuit, whichever has a higher peak value is detected and output. An operational amplifier that constitutes a peak detection circuit, an attenuator that attenuates the output voltage of the operational amplifier by half, and a comparator that shapes the output voltage of the receiving amplifier by using the output voltage of the attenuator as an identification voltage. Optical receiver. 4. The optical receiver according to claim 3, wherein the first non-inverting input circuit comprises a transistor having an area half that of a transistor forming at least one of the second non-inverting input circuit and the inverting input circuit.