JPH0818429A - Optical receiver - Google Patents

Abstract

PURPOSE:To handle a current/voltage converter, a voltage amplifier and an identification device as respectively independent circuit constitution and to perform circuit design for satisfying characteristics required for respective circuits relating to an optical receiver for receiving optical pulse signals and converting them into electric pulse signals. CONSTITUTION:The current/voltage converter 2 is set independent of a voltage amplification differential amplifier 3 for performing offset adjustment. Then, a reference value output circuit 6 divides a peak value detected in a peak value detection circuit 5 by a prescribed ratio, adds the output of an offset adjustment circuit 4 to an obtained voltage and supplies it to the inversion input terminal of the voltage amplification differential amplifier 3. Thus, the voltage amplification differential amplifier 3 performs the differential amplification of the voltage by comparing an output voltage from the current/voltage converter 2 with a voltage value supplied from the reference value output circuit 6 as a threshold value, simultaneously performs the offset adjustment and transmits the output to the identification device 7.

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 receiving an optical pulse signal and converting it into an electric pulse signal, and more particularly, to an optical receiver from a plurality of subscriber side devices ONU (Optical Network Unit).
Center-side device OSU (Opt that receives the optical pulse signal sent by the DMA (Time Division Multiple Access) method
ical subscriber unit).

As a basic technology for supporting a future communication infrastructure, great expectations are placed on the technical development of an optical subscriber transmission system. The demand for service that uses communication is gradually changing from the telephone main body to the demand for diversity and high speed, and in order to respond to these demands in a timely manner, the optical network of the subscriber network, which is ahead of the actualization of needs, is being sought. Is desired. The present invention provides one of the devices for opticalizing such a subscriber network.

[0003]

2. Description of the Related Art A conventional optical subscriber transmission system is shown in FIG.
As shown in FIG. 3, the center side device OSU 101 and the plurality of subscriber side devices ONUs 102 to 104 are connected to the star coupler 105.
Are connected by a single optical fiber 106. Then, the center-side device OSU101 converts the electric pulse signal into an optical pulse signal by optical intensity modulation to convert the optical fiber 1
06, and the optical pulse signal is output to the star coupler 105.
And is sent to the subscriber side devices ONUs 102 to 104. The subscriber-side devices ONUs 102 to 104 demodulate the optical pulse signals into electric pulse signals. Also, transmission in the opposite direction is similarly performed. Center side device OSU101
And the subscriber-side devices ONUs 102 to 104 perform bidirectional multiplex transmission, and a single optical fiber 106 is used to perform multiplexing in the time domain in TCM (Time Compression Multipl).
exing) has been adopted.

That is, as shown in FIG. 13, in the TCM, a downstream optical signal is sent from the center side device OSU 101 to the subscriber side devices ONU 102 to 104 in the first half of one frame, and from the subscriber side devices ONU 102 to 104 in the latter half. An upstream optical signal is sent to the center-side device OSU101. In the downstream optical signal, all signals to each subscriber side device ONU are time-division multiplexed and transmitted, and each subscriber side device ONU10
2 to 104 take out only the signals (# 1 to #n) destined for themselves by the addressing information written in the overhead (OH) at the head position of the downstream optical signal. The center-side device OSU 101 is a subscriber-side device ONU 102-104.
Transmission delay time up to, and based on the transmission delay time and the length of each upstream burst signal from the subscriber side devices ONU102-104, each subscriber side device ONU102-104 has overhead. The transmission timing designation information for designating the timing at which each upstream burst signal should be transmitted is noted. Therefore, in the upstream optical signal, each of the subscriber side devices ONUs 102 to 104
Transmits a burst signal (# 1 to #n) from its own station in accordance with this transmission timing designation information. The transmission timing designation information is set so that a guard time is sandwiched between the burst signals so that the burst signals from the subscriber-side devices ONUs 102 to 104 do not overlap.

As an optical receiver for use in the above transmission system, there has conventionally been a device as shown in FIG. 14, for example. That is, the output of the light receiving element 110 is connected to the non-inverted input terminal (+) of the differential input / output transimpedance type amplifier 111, and the peak detector 112 is connected to the non-inverted output terminal of this amplifier 111. Detector 112
Is fed back to the inverting input terminal (-) of the amplifier 111. The peak detector 112 detects the peak value of the non-inverted output of the amplifier 111, and inputs the voltage value that is half the peak value as a threshold value to the inverting input terminal of the amplifier 111. Therefore, the amplifier 111 compares the pulsed signal from the light receiving element 110 input to the non-inverting input terminal with a threshold value and converts the pulsed voltage signal into a pulsed voltage signal.

With this differential input / output transimpedance amplifier 111 alone, when the center-side device OSU 101 and the subscriber-side devices ONUs 102 to 104 are far apart from each other or the number of branches in the star coupler 105 is large, for example. Since the reception level is very small, the discriminator 116 lacks the amplitude for discriminating between "0" and "1" of the signal. Therefore, the voltage amplifier 113 is connected to the subsequent stage of the amplifier 111. Furthermore, the transimpedance type amplifier 1
11, the offset voltage generated in 11, the extinction ratio deterioration of the transmitted optical signal, the reflected light generated in the star coupler 105, the light receiving element
Since the discriminator 116 may cause a discrimination error when no optical signal is input due to a current offset or the like due to the dark current of 10, the offset adjustment circuits 114 and 115 are used as the differential input / output transimpedance amplifier 111. Is connected to the non-inverted input terminal and the inverted input terminal to cancel the cause of the identification error when no optical signal is input.

[0007]

However, in this receiver, the transimpedance type amplifier 11 for differential input / output is used.
Since the current / voltage conversion circuit is configured by 1, the obtained non-feedback gain is reduced to ½ or less, and the offset adjustment circuits 114 and 115 are connected to the input terminal of the amplifier 111, which is parasitic. The capacitance is added to the amplifier 111, and the band of the output signal of the amplifier 111 deteriorates. Further, noise generated from the offset adjustment circuits 114 and 115 is also superposed on the signal current, so that the S / N of the amplifier 111 is deteriorated and the minimum reception level is deteriorated. Further, the offset adjustment of the offset adjustment circuits 114 and 115 is performed after the initial setting by the amplifier 1 due to a change in power supply voltage, a change in temperature, and the like.
11 is a so-called feed-forward control according to the characteristics of the offset adjustment circuits 114 and 115 with respect to the fluctuation of the offset voltage, and an appropriate correction cannot be performed with respect to the fluctuation of the offset voltage. In addition, this optical receiver is installed on the center side device O
In order to apply to the SU101, the subscriber unit ONU1
Since the respective reception levels when the respective upstream burst signals from 02 to 104 are received are different, the peak detector 112 responds at high speed and holds the peak value by the previous burst signal within a short time between the upstream burst signals. If you cannot achieve this, you must complete the discharge of the capacitor
It is conceivable that the signal pulse width of the output of the receiver fluctuates and synchronous reproduction becomes impossible in the circuit connected to the next stage. There is a problem in that it is difficult to perform optimal design because there is a restriction on the setting of circuit constants that solves such a problem.

The present invention solves such a problem,
An object of the present invention is to provide an optical receiver in which a current / voltage converter, a voltage amplifier, and a discriminator can be treated as independent circuit configurations, and a circuit can be designed to satisfy the characteristics required for each circuit. .

[0009]

In the present invention, in order to achieve the above object, as shown in FIG. 1, a light receiving element 1 and a current / voltage conversion for converting a current from the light receiving element 1 into a voltage and outputting the voltage. Amplifier 2, a voltage amplification differential amplifier 3 having a non-inversion output terminal and an inversion output terminal in which the output of the current / voltage converter 2 is connected to its own non-inversion input terminal (+), and a voltage amplification differential amplifier 3 The peak value of the output amplitude of the offset adjustment circuit 4 and the output amplitude of the current / voltage converter 2 are calculated by averaging the respective outputs of the non-inverting output terminal and the inverting output terminal of the A peak value detection circuit 5 for detecting,
A reference for dividing the peak value detected by the peak value detection circuit 5 by a predetermined ratio, adding the output of the offset adjustment circuit 4 to the obtained voltage, and supplying the voltage to the inverting input terminal (-) of the voltage amplification differential amplifier 3. An optical receiver is provided, which has a value output circuit 6 and a discriminator 7 that outputs an electric pulse signal based on the output of the voltage amplification differential amplifier 3.

[0010]

In the configuration as described above, the current / voltage converter 2 is set independently of the voltage amplification differential amplifier 3 for offset adjustment. The offset adjustment circuit 4, the peak value detection circuit 5, and the reference value output circuit 6 are connected to the voltage amplification differential amplifier 3, and the offset adjustment circuit 4
The outputs of the non-inverted output terminal and the inverted output terminal of the voltage amplification differential amplifier 3 are averaged, the difference is calculated, and the difference is averaged and output to the reference value output circuit 6. On the other hand, the peak value detection circuit 5 detects the peak value of the output amplitude of the current / voltage converter 2 and outputs it to the reference value output circuit 6. The reference value output circuit 6 divides the peak value detected by the peak value detection circuit 5 by a predetermined ratio and adds the output of the offset adjustment circuit 4 to the obtained voltage to invert the input terminal of the voltage amplification differential amplifier 3. Supply to (-). Therefore, the voltage amplification differential amplifier 3 compares the output voltage from the current / voltage converter 2 with the voltage value supplied from the reference value output circuit 6 as a threshold value, performs differential amplification of the voltage, and also performs offset adjustment. At the same time, the output is sent to the discriminator 7.

As described above, since the current / voltage converter 2, the voltage amplification differential amplifier 3, and the discriminator 7 have independent circuit configurations, each circuit should be optimized independently of other circuits. Is possible.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram showing the configuration of the first embodiment of the optical receiver of the present invention. This optical receiver is a device O on the center side.
It is provided in the SU.

In the figure, the output of the light receiving element 10 is input to the current / voltage conversion circuit 11. The current / voltage conversion circuit 11 has
It is composed of an input / output parallel feedback circuit including a grounded-emitter amplifier and an emitter-follower amplifier, and a polarity inverting circuit.
The output terminal of the current / voltage conversion circuit 11 is connected to the non-inverting input terminal (+) of the differential amplifier 12 for voltage amplification, and also passes through the peak detector 13, the voltage divider 14, and the adder 15 in order. Connected to the inverting input terminal (−) of the differential amplifier 12. The peak detector 13 is the current / voltage conversion circuit 1
The peak value of the output amplitude of 1 is detected, and the voltage divider 14 divides the peak value into 1/2.

On the other hand, the low-pass filter (LPF1) 1 is provided at the normal output terminal and the inverting output terminal of the differential amplifier 12.
6, differential amplifier 17, low-pass filter (LPF2) 1
8 are connected in order, and the output of the low pass filter 18 is input to the adder 15. The low-pass filter 16, the differential amplifier 17, and the low-pass filter 18 are the differential amplifier 1
2 is a feedback circuit for canceling the offset voltage of 2, the deterioration of the extinction ratio of the transmitted light signal, the reflected light generated by the star coupler, the current offset due to the dark current of the light receiving element 10, and the like. The force and the inverted output are averaged by the low-pass filter 16. Next, the differential amplifier 17 takes the difference between the average values and amplifies the difference by a predetermined amount. Then, the low-pass filter 18 determines the response speed of the feedback circuit, removes unnecessary high-frequency components included in the difference, and outputs the DC voltage to the adder 15. This DC voltage becomes 0 when the output of the differential amplifier 12 has no offset.

The adder 15 adds the voltage that is half the peak value and the offset adjustment DC voltage, and outputs the result as a reference voltage (threshold value) to the inverting input terminal of the differential amplifier 12. The differential amplifier 12 compares the voltage input from the current / voltage conversion circuit 11 with a reference voltage, and outputs high-level and low-level signals from the normal output terminal to the normal input terminal (+ ). The reference voltage VREF is supplied to the inverting input terminal (−) of the discriminator 19, and the discriminator 19 compares the input high-level and low-level signals with the reference voltage VREF to “0”, “1”. The electric pulse signal of “” is output.

FIG. 3 and FIG. 4 are diagrams showing a concrete circuit configuration of the first embodiment. The current / voltage conversion circuit 11 has
The input / output parallel feedback circuit is a grounded-emitter transistor Q.
1 and an emitter follower transistor Q3, and a feedback resistor RF that connects the emitter of the transistor Q3 and the base of the transistor Q1. Also, the polarity reversing circuit is constituted by the transistor Q4 and the transistor Q5.

The peak detector 13 comprises an emitter follower transistor Q10, a diode D10 and a capacitor C10.
The output of the current / voltage conversion circuit 11 is rectified by the diode D10 and the capacitor C10 is charged.
Therefore, the peak value of the output amplitude of the current / voltage conversion circuit 11 is held in the capacitor C10. A transistor Q80 is connected in parallel to the capacitor C10,
When a reset pulse described later is input to the base of the transistor Q80, the electric charge held in the capacitor C10 is discharged, and the holding of the peak value is canceled. This will be described later in detail.

The voltage divider 14 and the adder 15 include two emitter follower transistors Q20 and Q21, and two resistors R22 connected in series connected to their respective emitters.
And R23. The peak value detected by the peak detector 13 is input to the base of the emitter follower transistor Q20, and the emitter follower transistor Q21
The output of the low-pass filter 18 is input to the base of the. The two resistors R22 and R23 have the same resistance value,
Mutual connection points are connected to the inverting input terminal of the differential amplifier 12.

Between the output terminal of the current / voltage conversion circuit 11 and the non-inverted input terminal of the differential amplifier 12, the same level amplification as that by the peak detector 13 and the voltage divider 14 is performed. Emitter follower transistor Q11,
Diode D11, emitter follower transistor Q2
2 and resistors R11, R24, R25 are inserted. The characteristic values of these inserted parts are the same as the characteristic values of the corresponding transistor Q10, diode D10, transistor Q20, and resistors R10, R20, and R22, respectively.

The low pass filter 16 includes resistors R30 and R
31 and a capacitor C30, and the low-pass filter 18 includes a resistor R32 and a capacitor C31. The low-pass filter 16 may have the circuit configuration of the low-pass filter LPF3 shown in FIG.

The reference voltage VREF of the discriminator 19 is generated by the constant current source 19a and the resistor R40, and its value is
It is set to a voltage value higher than the noise voltage when no optical signal is input. It should be noted that instead of setting the reference voltage in the differential amplifier 12 as in the conventional case, the discriminator 1 in the subsequent stage of the differential amplifier 12
Since it is set to 9, it becomes very easy to set the reference voltage.

FIG. 5 shows the differential amplifier 12 and the discriminator 19.
It is a circuit diagram which shows the inside. That is, the differential amplifier 12
Is composed of transistors Q30, Q31 and Q32, and the discriminator 19 is composed of transistors Q35, Q36 and Q37. Further, the constant current source 19a includes a transistor Q3
3, Q34 and a current mirror type circuit. Note that the illustration of the signal lines from the differential amplifier 12 to the low-pass filter 16 is omitted in the figure.

Next, the reset pulse will be described. FIG. 6 is a graph for explaining the peak value in the conventional device. That is, when the center side device OSU receives the upstream signal shown in FIG. 13, the amplitude of the burst signal # 2 is considerably smaller than the amplitude of the burst signal # 1 as shown in the figure, or as shown in FIG. When the burst signal # 1 contains a series of low-level codes, the following problems occur.

First, when there is a continuous low level code in the burst signal # 1, if the rectification time constant of the peak detection circuit is small, immediately after the continuous low level code (t1).
, The peak value is greatly reduced, and as a result, pulse width variation is caused. Also, burst signal #
When the amplitude of 2 is much smaller than the amplitude of the burst signal # 1, if the rectification time constant of the peak detection circuit is large, the burst value # 2 cannot be reproduced because the peak value does not decrease sufficiently during the guard time. A problem occurs.
It is difficult to set the rectification time constant of the peak detection circuit so that both of these problems do not occur.

Therefore, in the present invention, as shown in FIG.
The rectification time constant of the peak detector 13 is set to a large value so that no trouble occurs even when there is a continuous low level code in the burst signal, and the peak detector is reset by a reset pulse during the guard time. The electric charge of the capacitor C10 which holds the peak value in 13 is discharged.

With respect to this reset pulse, the center side device OSU previously designates the timing to be transmitted by each subscriber side device ONU by the transmission timing designation information, so that the center side device OSU has each burst signal. I know the ending timing of. Therefore, the center side device OSU generates a reset pulse during the guard time.

FIG. 8 is a block diagram showing the structure of the reset pulse generating circuit. That is, each subscriber side device ONU
The memories 21 to 23 are provided corresponding to
The timing for generating the reset pulse is stored in the memory 3. And each of these stored timings,
In the comparator 24, the count value sent from the internal operation counter 25 is compared, and when they match, the comparator 24 causes the pulse generator 26 to generate a reset pulse.

FIG. 9 is a circuit diagram showing a peak detector of a type different from the peak detector 13 shown in FIG. That is, the operational amplifier 30 is incorporated in the voltage follower feedback in order to improve the non-linearity of the diode D10 and compensate for the voltage drop. Peak detector 13 of FIG.
May have such a circuit configuration. In FIG. 9, the same parts as those shown in FIG. 3 are designated by the same reference numerals.

Next, a second embodiment of the optical receiver of the present invention will be described. FIG. 11 is a block diagram showing the configuration of the second embodiment. In the figure, the same components as those of the first embodiment, which are the same as those of the first embodiment, are designated by the same reference numerals, and the description thereof will be omitted. The light receiving element 10 and the current / voltage conversion circuit 11 are not shown.

The output of the transistor Q5 (FIG. 3) is input to the non-inverting input terminal (+) of the operational amplifier 30. The operational amplifier 30 is the one shown in FIG. In the second embodiment,
A transistor Q22 and resistors R24 and R25 are connected to the non-inverting input terminal of the differential amplifier 12 for voltage amplification.
These are provided so as to have the same level amplification as the level amplification by the voltage divider 14, and have the same characteristic values as the corresponding transistor Q20 and resistors R20 and R22, respectively.

Further, the normal output and the inverted output of the differential amplifier 12 are input to the normal input terminal and the inverted input terminal of the differential amplifier 35 constituting the discriminator 19, respectively. Since both outputs of the differential amplifier 12 are at the same level when no optical signal is input, in this case, the output of the differential amplifier 35 becomes a "0" signal or a "1" signal due to noise. It flutters. In order to prevent this, a differential amplifier 36 is provided between the output terminal of the peak detector 13 (+ terminal side of the capacitor C10) and the differential amplifier 35, and the differential amplifier 36 detects no optical signal input. And the differential amplifier 35
Is forcibly made to be a "0" signal.

As described above, in the second embodiment, the discriminator (differential amplifier 35) is provided with the reference voltage VREF as in the first embodiment.
The configuration does not have to be provided. Although any of the above-described embodiments has been described as an optical receiver provided in the center-side device OSU, any of the embodiments can be applied to the subscriber-side device ONU, except for the input of the reset pulse.

In any of the above embodiments, the voltage divider 1
Although the resistors R22 and R23 of No. 4 have the same resistance value, and therefore the peak value is halved by the voltage divider 14, the resistance values of the resistors R22 and R23 are set to different ratios and the peak value is set. May be divided by another division ratio.

[0034]

As described above, according to the present invention, current /
The voltage converter is set independently of the voltage amplification differential amplifier that performs offset adjustment, and the voltage amplification differential amplifier compares the output voltage from the current / voltage converter with the voltage value based on the peak value as the threshold value. And differential amplification of the voltage,
Offset adjustment is also performed at the same time, and the output is sent to the discriminator. As described above, the current / voltage converter, the voltage amplification differential amplifier, and the discriminator have independent circuit configurations, so that it is possible to design a circuit that satisfies the characteristics required for each circuit. That is, S / N can be improved for the current / voltage converter, stability of high-speed negative feedback can be achieved, and negative feedback for offset compensation can be achieved for the voltage amplification differential amplifier. The stability can be achieved, and the threshold can be easily set for the discriminator.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a block diagram showing a configuration of a first embodiment of an optical receiver of the present invention.

FIG. 3 is a diagram showing a specific circuit configuration of the first embodiment.

FIG. 4 is a diagram showing a specific circuit configuration of the first embodiment.

FIG. 5 is a circuit diagram showing the inside of a differential amplifier and a discriminator.

FIG. 6 is a graph illustrating a peak value in a conventional device.

FIG. 7 is a graph illustrating a peak value according to the present invention.

FIG. 8 is a block diagram showing a configuration of a reset pulse generation circuit.

FIG. 9 is a circuit diagram showing a peak detector.

FIG. 10 is a circuit diagram of a low pass filter.

FIG. 11 is a block diagram showing a configuration of a second embodiment.

FIG. 12 is a diagram showing an optical subscriber transmission system.

FIG. 13 is a TCM frame configuration diagram.

FIG. 14 is a block diagram of a conventional optical receiver.

[Explanation of symbols]

 1 Light receiving element 2 Current / voltage converter 3 Voltage amplification differential amplifier 4 Offset adjustment circuit 5 Peak value detection circuit 6 Reference value output circuit 7 Discriminator

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H04B 10/14 10/04 10/06

Claims (7)

[Claims] 1. An optical receiver for receiving an optical pulse signal and converting it into an electric pulse signal, a light receiving element, a current / voltage converter for converting a current from the light receiving element into a voltage and outputting the voltage, and the current. / A voltage amplification differential amplifier having a non-inverting output terminal and an inverting output terminal, in which the output of the voltage converter is connected to its own non-inverting input terminal, and a non-inverting output terminal and an inverting output terminal of the voltage amplifying differential amplifier. An offset adjustment circuit that averages each output and then takes the difference, and outputs the averaged difference, a peak value detection circuit that detects the peak value of the amplitude of the output of the current / voltage converter, and the peak A reference value output circuit that divides the peak value detected by the value detection circuit by a predetermined ratio, adds the output of the offset adjustment circuit to the obtained voltage, and supplies the result to the inverting input terminal of the voltage amplification differential amplifier, A discriminator that outputs an electric pulse signal based on the output of the voltage amplification differential amplifier, and an optical receiver. 2. The discriminator is composed of a differential amplifier, the output of the voltage amplification differential amplifier is connected to its non-inverting input terminal, and a predetermined voltage as a threshold value is connected to its inverting input terminal. The optical receiver according to claim 1, which is characterized in that. 3. The discriminator is composed of a differential amplifier, and a non-inverting input terminal and an inverting input terminal of the discriminator are respectively connected to a non-inverting output terminal and an inverting output terminal of the voltage amplification differential amplifier. 2. A circuit for forcing the output of the differential amplifier of the discriminator to a low level when the optical pulse signal from the transmitter is not input to the differential amplifier of the discriminator. Optical receiver described. 4. The optical receiver according to claim 1, wherein the current / voltage converter includes an input / output parallel feedback circuit including a grounded-emitter amplifier and an emitter-follower amplifier, and a polarity inverting circuit. 5. The optical receiver according to claim 1, wherein the peak value detection circuit includes a voltage follower circuit including an operational amplifier and a diode that constitutes a feedback circuit of the operational amplifier. 6. The reference value output circuit includes two emitter follower amplifiers, each of which receives a peak value detected by the peak value detection circuit and an output of the offset adjustment circuit into each base, and the two emitter follower amplifiers. 2. The two resistors having the same resistance value, which are connected to each emitter, are connected in series, and have their connection points connected to the inverting input terminal of the voltage amplification differential amplifier. Optical receiver. 7. The reset signal generating means for generating a reset signal at each end of each optical pulse signal based on the overhead information is further provided, and the peak value detection circuit is provided for each input of the optical pulse signal from each transmitter. A rectifier circuit including a capacitor for detecting and holding a peak value and a parallel connection to the capacitor, each reset signal from the reset signal generating means is input to the base, and the capacitor is discharged when each reset signal is input. The optical receiver according to claim 1, further comprising: