KR101988920B1 - Optical receiving apparatus having improved burst mode clock and data recovery performance for multilevel optical signal and method thereof - Google Patents

Abstract

The present invention relates to a multilevel optical reception device with an increased burst mode clock and data recovery performance, which enables an optical line terminal (OLT) optical reception device to quickly recover a clock of a multilevel optical signal received in a burst mode, increase reception performance, and fit a processing clock of media access control (MAC) to a communication speed, and a method thereof. According to the present invention, when receiving an uplink multilevel optical signal transmitting data of a plurality of bits as a multilevel optical signal at a time, a preamble of an uplink burst signal frame formed with a pattern for clock recovery and a pattern for adjusting a reception unit is received, such that clock synchronization is quickly performed and the performance of the reception unit is optimized to a corresponding burst signal based on the synched clock through a preset reception unit adjustment pattern, thereby providing an effect of increasing data recovery performance without using a precise device while remarkably increasing a clock recovery speed in a burst mode. According to the present invention, the multilevel optical reception device comprises a photodiode, a burst mode transimpedance amplifier, a limiting amplifier, a burst clock recovery unit, and a clock multiplication unit.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a multi-level optical receiving apparatus and method for improving burst mode clock and data recovery performance,

The present invention relates to a multilevel optical receiving apparatus and method for enhancing a burst mode clock and data restoration performance, and more particularly, to an optical line terminal (OLT) optical receiving apparatus that quickly restores a clock of a multilevel optical signal received in a burst mode And more particularly, to a multilevel optical receiving apparatus and method for enhancing a burst mode clock and data restoration performance that can improve reception performance and match a processing speed of a MAC (Media Access Control) to a communication speed.

The passive optical network (PON) technology is configured to configure a high-speed subscriber network and can process simultaneous access of a plurality of subscribers through a time division scheme or a wavelength division scheme. Among these methods, a cost-effective time-sharing method is mainly used, and EPON (Ethernet PON) or 10G-EPON (10Gigabit EPON) according to IEEE (Institute of Electrical and Electronics Engineers) 802.3av / ah, International Telecommunication Union -Telecommunication Standardization Sector Gigabit PON, XGPON (10Gigabit PON) according to G.984 / 7 and NGPON2 (Next Generation PON) according to G.989 are representative.

In the configuration of such a PON, a single optical line terminal (OLT) installed in the telephone company and an ONT (Optical Network Terminal) or an ONU (Optical Network Unit) of a plurality of subscribers are connected to a remote node, (Point-to-Multipoint) network structure through an optical splitter (using an optical splitter).

FIG. 1 shows a configuration of a general PON. As shown in the figure, an OLT 1 having an optical transceiver 1a for converting an electric signal into an optical signal is connected to a plurality of subscriber ONTs 2 Each ONT 2 is also provided with an optical transceiver 2a. With this configuration, it is possible to provide a high-speed communication service for a plurality of subscriber ONTs 2.

2 is a conceptual diagram for explaining a downlink signal transmission method and an uplink signal transmission method of a PON. 2A is a conceptual diagram for explaining a downlink signal transmission method of a passive optical network. As shown in the figure, when the OLT 1 continuously transmits downstream frame data to be transmitted to the ONT 2, a plurality of ONTs 2_1 and 2_2 are Frame data for itself among the downlink frame data is selectively received. Accordingly, this downstream signal can be continuously transmitted without signal collision only by continuously transmitting a signal modulated by the OLT 1 with its own clock. Also, since all of the downstream signals including the continuous data use the clock of the OLT 1, the ONTs 2 need to recover and synchronize the clock for the downstream signals only once.

However, in the case of an upstream signal in which the ONT 2 transmits upstream frame data to the OLT 1, if a plurality of ONTs 2_1 and 2_2 arbitrarily transmit upstream signals, The ONTs 2_1 and 2_2 transmit the control information about the transmission time point and the data amount of the upstream signal to the individual ONTs 2 through the downstream signal, Generates an uplink burst signal of various sizes based on the corresponding control information and transmits the burst signal without collision.

2B is a conceptual diagram for explaining an uplink signal transmission method of a passive optical network. As shown in FIG. 2B, the ONTs 2_1 and 2_2 generate uplink signals of predetermined amounts of data at different time points and transmit them to the OLT 1 , And each uplink signal is divided into a guard interval (a) to prevent collision.

As shown in the figure, the upstream signal is a burst signal in which the signal is continuously divided. Since each signal uses its own clock of the ONTs 2_1 and 2_2, the clocks of the upstream burst signals are synchronized with each other or with the OLT clock And there is a deviation from the clock of the OLT 1 receiving it.

That is, in the illustrated case, since the individual start timings t1, t2 and t3 of the upstream burst signal are different from the clock of the OLT 1, the OLT 1 restores the clock for each of the upstream burst signals, It must be restored.

In particular, since the upstream burst signals transmitted from the ONTs 2 at different positions are received by the photodiodes inside the optical transceiver of the OLT or the OLT repeater, respectively, with different sizes and signal strengths, the currents generated by the photodiodes are converted into voltages In addition to the amplification of the amplifying transimpedance amplifier (TIA), the 10 Gbps or 25 Gbps high-speed signal is very short, so that the discharge or charging of the internal capacitance of the circuit is not completed. Therefore, the parasitic capacitance value remains in the circuit for a considerable time, and the burst mode clock and data recovery process using the output of the trans-impedance amplifier including a large number of noise signals due to the residual current are considerably difficult and time-consuming.

Therefore, in the case of a commercial product, the guard time between the upstream burst signals is set longer, and the burst mode clock and data restoration are repeatedly inserted (for example, by repeating a 64-bit preamble several tens to several hundred times) To provide sufficient training opportunities for the user, thereby reducing bandwidth.

On the other hand, as the introduction of the fifth generation mobile communication, the spread of high quality services, and the spread of the Internet of Things (IoT) equipment, the bandwidth required for the optical communication used for the subscriber network and the metro network is also increasing steeply.

In this way, the optical communication system that requires a steep increase in the required bandwidth is used. However, the NRZ (NonReturn to Zero) modulation method is used, in which the intensity of the optical signal is divided into two levels of '1' or '0'. However, when NRZ communication is used for 25Gbps, 50Gbps, and 100Gbps ultra-wideband communication, it is difficult to develop due to bit switching time of the femtosecond level. Due to this background, various studies to apply a modulation scheme (for example, PAM (Pulse Amplitude Modulation) 4 or PAM 8) using a multilevel optical signal capable of transmitting a plurality of data through one signal transmission It is progressing.

When such a multi-level optical signal is used, the situation in which the OLT synchronizes the clock for the upstream burst signal every time and restores the data may be extremely deteriorated.

That is, even in the case of the current NRZ burst signal, a bit switching time of a femtosecond level is used for ultra-wideband communication of a level of 25 Gbps or more. This is achieved by synchronizing clocks using at least four different levels of received signals, It is not easy to restore the data. In particular, due to the characteristics of the burst signal, it takes a long time to amplify the clock signal through the multi-level signal after appropriately amplifying it, since the signal size and intensity are different for each ONT and the delay between data is different. It is not easy to restore it, so a precise transmission / reception device is required and restoration quality is also limited.

Further, in the case of the configuration of the current burst mode clock data restoration unit, since the restored data is a method of directly providing a serial signal to the OLT MAC (Media Access Control), for example, at least two bits of data (PAM4 The OLT MAC requires at least twice the clock (25Gbps-> 50Ghz clock) in order to serialize and process it, which makes implementation difficult.

Accordingly, the asymmetric communication scheme using the existing NRZ scheme is not compatible with the policy of the service provider, while the downlink signal uses multi-level and the uplink signal uses the existing NRZ scheme. In recent years, there has been an increasing demand for applying the same speed up and down according to user data uptake, and different modulation schemes are applied to realize uplink and downlink asymmetry.

As a result, there is an increasing need for a new optical receiver that can utilize multilevel optical signals, not only downlinks but also uplink signals. In order to transmit and receive optical signals, it is necessary to increase the reception quality without using expensive, There is an urgent need for an alternative method.

Korean Patent No. 10-1541975 [Title of the invention: Optical communication receiver and chip used therein] Korean Patent No. 10-1078052 [Apparatus and method for restoring received data in a passive optical communication network]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems and it is an object of the present invention to provide a method and apparatus for receiving an upstream multilevel optical signal for transmitting data of a plurality of bits to a multilevel optical signal at a time, By performing a fast clock synchronization by receiving the preamble of the configured uplink burst signal frame and by optimizing the receiving section performance for different burst signals for each ONT through a predefined pattern for adjusting the reception section based on the synchronized clock, And a multilevel optical receiving apparatus and method that improves the burst mode clock and data restoration performance without using the multilevel optical receiving apparatus.

Another object of the present invention is to improve a clock synchronization speed in receiving an upstream burst signal received differently each time in an actual installation environment, to separately perform data restoration, and then to process a plurality of bits of data corresponding to a multi level in parallel And to provide a multilevel optical receiving apparatus and method capable of improving the burst mode clock and data restoration performance by reducing the development burden by maintaining the MAC interface and operation speed at a data transmission rate level.

It is another object of the present invention to provide a method and apparatus for receiving a different test pattern for a discrimination criterion of a multi-level signal of an upstream burst mode signal received each time as a pattern for adjusting a receiving section of a preamble, A burst mode clock and data restoration performance for improving the reception performance by optimizing the individual avalanche photodiodes showing different characteristics according to the received optical power by estimating a reference voltage set for classifying each classification Level light receiving apparatus and method.

The multilevel optical receiving apparatus having improved burst mode clock and data recovery performance according to an embodiment of the present invention receives a multilevel upstream burst signal frame having a preamble including a predetermined clock recovery pattern and restores the clock and data A multilevel optical receiving apparatus for processing through a MAC (Media Access Control), comprising: a photodiode for receiving a multilevel optical signal; a burst mode transimpedance amplifier for converting the current of the photodiode into a voltage; A limiting amplifier for selectively amplifying a plurality of bits corresponding to the division in parallel according to a set reference voltage and providing the plurality of bits in parallel to the MAC, A clock composed of binary patterns consecutively slowed to less than half of the transmission speed It comprises a distance from the pattern burst clock to restore the clock recovery unit, a clock unit for draining the recovered clock from the clock recovery unit bursts in increments in accordance with the transmission rate.

For example, when the multilevel optical signal is PAM (Pulse Amplitude Modulation) -N, the clock recovery pattern repeats the signal corresponding to the minimum data among the N types of signals a plurality of times and repeats the signal corresponding to the maximum data a plurality of times And the transmission rate may be temporarily lowered by constructing the signal set several times.

Here, the limiting amplifier is then separated signal corresponding to the data of the received frame by using the recovered clock signals according to the transmission speed through the clock drain to one of the N type with a reference voltage set the clock for parallel signal from the Log ₂ N bits To the MAC every time.

For example, the preamble of the upstream burst signal frame further includes a receiving section adjustment pattern promised after the clock recovery pattern, and the receiving voltage according to the receiving section adjusting pattern included in the received preamble of the receiving voltage of the transimpedance amplifier And a control unit for estimating a reference voltage set capable of classifying each pattern and applying the same to the limiting amplifier.

Here, the controller may divide the reception voltage corresponding to the different data based on the data of the predetermined receiving section adjustment pattern, and divide the received voltage of the transimpedance amplifier based on the distribution range of the reception voltages stored for each data, The reference voltage can be estimated between the reception voltage range of each data.

In addition, the controller may perform a reference voltage set estimation each time an uplink burst signal frame is received, or receive scheduling information of an uplink burst signal from the MAC, and transmit the uplink burst signal frame received from the terminal, The reference voltage set estimation may be omitted and a previously estimated reference voltage set for the terminal may be used.

The multilevel optical receiving method of improving the burst mode clock and data recovery performance according to another embodiment of the present invention receives a multilevel uplink burst signal frame having a preamble including a promised clock recovery pattern and restores the clock and data Level optical signal received through a photodiode to a voltage through a transimpedance amplifier, a step of converting a reception voltage of the transimpedance amplifier through a limiting amplifier to a set reference voltage And a clock recovery pattern composed of a binary pattern in which a minimum value and a maximum value of a multi-level signal among the signals classified and amplified by the burst clock restoring unit are successively reduced to less than half of the transmission speed, Clock, and through the clock divider Increasing the desired clock by a factor corresponding to the transmission rate, amplifying the received voltage according to the set reference voltage using the clock recovered according to the transmission rate, and outputting a plurality of bits corresponding to the division in parallel To the MAC.

For example, in the case where the multi-level optical signal is PAM-N, the clock recovery pattern repeats the signal corresponding to the minimum data among the N kinds of signals a plurality of times, and sets the signal set for repeating the signal corresponding to the maximum data a plurality of times And temporarily lowering the transmission speed.

Here, the limiting amplifier is a parallel signal of the clock to evacuate through the reference voltage set, a signal corresponding to the data of the received frame by using the recovered clock signals according to the transmission speed through the then separated by one of the N types Log ₂ N bits And providing the MAC to each clock.

For example, the preamble of the upstream burst signal frame further includes a receiving section adjustment pattern promised after the clock recovery pattern, and the control section controls the receiving voltage according to the pattern for adjusting the receiving section included in the preamble among the receiving voltages of the transimpedance amplifier, Estimating a set of reference voltages capable of classifying each pattern, and applying the same to the limiting amplifier.

The multilevel optical receiving apparatus and method for improving the burst mode clock and data restoration performance according to the embodiment of the present invention may be configured such that in receiving an upward multilevel optical signal for transmitting a plurality of bits of data to a multilevel optical signal at a time, A preamble of an uplink burst signal frame in which a pattern for restoration and a pattern for adjusting a reception unit are sequentially formed is received to perform a fast clock synchronization and a reception unit performance is preliminarily determined according to a synchronized clock, It is possible to increase the clock recovery speed in the burst mode dramatically and optimize the other burst signals, thereby improving the data recovery performance without using the precision device.

The multilevel optical receiving apparatus and method for improving the burst mode clock and data restoration performance according to the embodiment of the present invention improves the clock synchronization speed in receiving an upstream burst signal that is received differently each time in actual installation environment, Bit data corresponding to the multi-level is processed in parallel so that the interface and the operation speed of the MAC are maintained at the data transfer rate level, thereby reducing development burden.

A multi-level optical receiving apparatus and method for enhancing burst mode clock and data restoration performance according to an exemplary embodiment of the present invention includes a step of adjusting a test pattern predicted for a discrimination criterion of a multilevel signal of an upstream burst mode signal, Pattern of the received optical signal is classified according to the test pattern and the reference voltage set for classifying each classification is estimated so that the optimization according to the actual use environment of the individual avalanche photodiode showing different characteristics according to the received optical power So that the reception performance can be improved.

1 is a configuration example of a general passive optical network.
2 is a conceptual diagram for explaining a downlink and uplink signal transmission method of a passive optical network;
3 is a conceptual diagram for explaining an upstream signal restoration method of a passive optical network.
4 is a configuration diagram for transmitting and receiving signals in up and down directions of a passive optical network;
FIG. 5 is a conceptual signal graph for explaining a reception state of an upstream signal received in the OLT; FIG.
FIG. 6 is a diagram for comparing laser diode output resolution according to the NRZ modulation method and the PAM 4 modulation method; FIG.
7 is a configuration diagram showing a configuration of a multi-level optical signal transmission / reception system according to an embodiment of the present invention.
8 is a configuration diagram showing a configuration of a PAM4 optical signal transmitting / receiving apparatus according to an embodiment of the present invention.
9 illustrates an example of a preamble structure of an uplink burst signal frame according to an embodiment of the present invention.
10 is an exemplary conceptual diagram for explaining a test pattern, a corresponding multi-level signal, and a reference voltage set estimation method of a multi-level optical receiving apparatus that receives the multi-level signal.
11 is a flowchart for explaining an operation procedure of the present invention.
12 is a conceptual diagram showing the configuration of an SFP device;
Figure 13 is a block diagram of a standard 20-pin equipment connection interface for an SFP device.
14 is a modified 20 pin equipment connection interface configuration diagram of an SFP device;

It is noted that the technical terms used in the present invention are used only to describe specific embodiments and are not intended to limit the present invention. In addition, the technical terms used in the present invention should be construed in a sense generally understood by a person having ordinary skill in the art to which the present invention belongs, unless otherwise defined in the present invention, and an overly comprehensive It should not be construed as meaning or overly reduced. In addition, when a technical term used in the present invention is an erroneous technical term that does not accurately express the concept of the present invention, it should be understood that technical terms that can be understood by a person skilled in the art can be properly understood. In addition, the general terms used in the present invention should be interpreted according to a predefined or context, and should not be construed as being excessively reduced.

Furthermore, the singular expressions used in the present invention include plural expressions unless the context clearly dictates otherwise. The term "comprising" or "comprising" or the like in the present invention should not be construed as necessarily including the various elements or steps described in the invention, Or may include additional components or steps.

In addition, terms including ordinals such as first, second, etc. used in the present invention can be used to describe elements, but the elements should not be limited by terms. Terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein like reference numerals refer to like or similar elements throughout the several views, and redundant description thereof will be omitted.

In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. It is to be noted that the accompanying drawings are only for the purpose of facilitating understanding of the present invention, and should not be construed as limiting the scope of the present invention with reference to the accompanying drawings.

Particularly, although a transmitter applied to a passive optical network (PON) apparatus is described as an example of the present invention, the optical receiver according to an embodiment of the present invention can be used not only for a PON, And thus the technology category is not limited to the receiving device of the transmitter for the PON and covers various optical receiving devices for optical communication.

First, an environment of a passive optical network to which the present invention is applied will be described with reference to FIG. 3 to FIG.

FIG. 3 is a conceptual diagram for explaining an uplink signal restoration method of a passive optical network. As shown in FIG. 3, an optical line terminal (OLT) 1 having an optical transceiver 1a for converting an electric signal and an optical signal, And is connected to a plurality of subscriber ONTs (Optical Network Terminals) 2 through a node RN through an optical transceiver 2a. Since the downlink signal and the uplink signal between them are 1: N communication using a single optical line, different types of signal management and synchronization are required. Due to this characteristic, the uplink signal avoids signal collision between the N ONTs 2 Consideration is needed.

Therefore, the uplink signals are sequentially transmitted according to the schedule allocated to each ONT 2, and the guard time is applied to avoid a signal collision between the signals of the ONTs 2.

Since the upstream signal is transmitted as a burst signal and the internal clock used by the OLT 1 and the internal clock of each ONT 2 are different from each other and the delay time is also different by the transmission line, A burst mode clock and data recovery (BCDR) unit 1b is used to recover an arbitrary ONT clock applied to a received upstream burst signal and confirm received frame data.

Since the BCDR unit 1b must recover the uplink data using the different clock every time, it takes a predetermined time to recover the clock. Usually, the BCDR unit 1b uses preambles (usually 32 bits or 64 bits preamble, ) Is used as the training information to perform clock recovery. Therefore, the control unit 1c, for example, an application specific integrated circuit (ASIC) or an FPGA (Field Programmable Gate Array), which takes charge of control and signal processing only after the operation of the BCDR unit 1b for clock recovery, Lt; / RTI >

The performance of the BCDR unit 1b is improved as the noise of the received upstream signal is decreased. In practice, it is necessary to repeatedly transmit a relatively large number of preambles to guarantee the clock recovery provided from the 1: N remote ONT, The guard time for preventing the signals from overlapping must be set sufficiently, so that the bandwidth of the uplink signal can not be significantly reduced compared to the downlink signal.

As shown in FIG. 4, the OLT-side optical transceiver 10 includes a laser diode driver 14 and a laser diode 15 for internally converting a downstream signal into an optical signal, as shown in FIG. A burst mode transimpedance amplifier (TIA) 12 for converting an output current of the photodiode 11 into a voltage and amplifying the output current, a photodiode 11 for converting an upstream signal into a current signal from an optical signal, And a Limiting Amplifier (LA) 13 that amplifies the amplified signal so as to output as much as a desired swing.

In the case of the upward burst signal, the signal amplified by the limiting amplifier 13 of the optical transceiver 10 is transmitted to the BCDR unit 20. The BCDR unit 20 uses the repeated preamble information from the received signal to transmit the clock Restores the data according to the clock, and provides the restored data to the OLT MAC (Media Access Control) processing unit 30 corresponding to the control unit.

The upstream signal received by the photodiode 11 of the optical transceiver 10 is received from several ONTs as shown in the conceptual graph of FIG. And has a different scale of the segmented burst signal form. The signal illustrated in FIG. 6 is used to explain the concept, and the signal portion corresponding to the actual frame is largely shortened to be exaggerated or reduced. In addition, the bit value shown at the top shows the actual transmitted bit value of the received signal for reference.

As shown in the figure, optical signals received from a plurality of ONTs have different sizes (scales, ratios), are disconnected from each other, and each signal has a shape including noise before and after.

The reason why noise is included before and after each signal is that the laser turn-on time (LD Turn On time) of the ONT optical transceiver that converts the electrical signal of the upstream burst frame data into the optical signal and the photo of the OLT optical transceiver 10 A diode turn-off time (LD Turn-off time) of the ONT optical transceiver and an OLT optical transceiver (10) due to a PDT turn-on time for converting the optical signal into an electrical signal, (PD Turn Off Time) of the photodiode 11 of the first embodiment.

Since the signals having different sizes and including back and forth noise are received in a disconnected state, the burst TIA 12 must variably amplify such a signal, and the amplified signal is amplified by the swing width The BCDR 20 divides the signal into 1's and 0's to find an appointed preamble, restores the clock, and then restores the bit information of the data using the corresponding clock.

As the transmission speed increases to 25 Gbps, 50 Gbps, and 100 Gbps as the communication speed increases, it is becoming increasingly difficult to quickly receive the upward burst signal and restore the clock and data.

Due to the demand for such a communication speed increase, a modulation scheme (for example, PAM (Pulse Amplitude Modulation) 4 or PAM 8) using a multilevel optical signal capable of transmitting a plurality of data through one signal transmission is applied However, even in the case of such a multi-level optical signal, clock recovery and data restoration are required for the upstream burst signal due to the characteristics of the PON. For the NRZ-type conventional burst signal composed of 0 and 1, It is difficult to restore the clock of the upward burst signal based on the multilevel optical signal. Therefore, the clock recovery time is long, and the reception performance due to the failure of the recovery is deteriorated. none.

FIG. 6 is a diagram for comparing laser diode output resolution according to the NRZ modulation method and the PAM 4 modulation method. In general, the transmitter of the optical transceiver includes a digital-to-analog converter (DAC) A monitoring diode (MPD) for monitoring the output of the laser diode is constructed, which includes a laser diode driver (LDD) and a laser diode (LD) for driving the diode.

Since the laser diode constituting the transmitter of the optical transceiver is for remote digital optical communication, even if there is environmental change or deterioration of its own, it is necessary to be able to distinguish the signal. For example, in the case of using NRZ modulation with input 0 and 1, The output of 0 and the output of 1 provided from the diode can be clearly distinguished from each other. The ratio of the light intensity of the first level to the light intensity of the zero level is referred to as an extinction ratio. For example, if the extinction ratio is 3 dB, it means that the difference between the light intensity at the 0 level and the light intensity at the 1 level is doubled.

The larger the extinction ratio is, the smaller the BER (Bit Error Rate) of the transmitted data becomes, and this is almost completely inversely proportional. Therefore, in order to maintain the extinction ratio when operating the laser diode, the control current is varied by feedback through the monitoring photodiode And maintains the extinction ratio for the use period.

However, such a monitoring photodiode is used for feedback, and since there is a characteristic and a deviation in such a photodiode, it is difficult to use it as a purpose for grasping the characteristics of the laser diode.

3A and 3B illustrate characteristic curves of the laser diode. As shown in the graph, the threshold current (the current at the time when the output starts changing) and the saturation current (the current at the time when the output does not increase) (I0 to I1) having high linearity are selected as the usable period.

The laser diode shown in FIG. 3A is an exemplary high-quality laser diode in which a substantial region of the control region has a linear characteristic, and the output difference (difference between P0 and P1) of the use region is significant. That is, since the extinction ratio is high, it is possible to provide high reliability in the NRZ modulation type communication.

3B, when the control region is divided into a plurality of levels, the output difference between the outputs P0 to P3 according to the control currents I0 to I3 is greatly reduced, Which means that the optical receiver must have a fairly high resolution to clearly distinguish them from each other. That is, in case of providing 2-level optical output, the extinction ratio will be determined by the output ratio of P0 and P3. However, when the level is divided into 4 levels, the extinction ratio is reduced to 1/3.

On the other hand, the illustrated case is an example of a high-quality laser diode in which a considerable region of the control region has a linear characteristic. Even in this case, since the transmitted light amount is transmitted through the light ray transmission differently, If the quality is inevitably lowered and the quality of the laser diode used is not good, this problem will become even more serious.

In addition, in the case of a photodiode receiving such a signal, there is also a variation in the reception performance due to the individual characteristics thereof. Particularly, as in the case of the upstream burst signal, The reception error may occur due to the linearity of the reception band, and in the case of the multi-level optical signal, such a problem becomes larger.

Particularly, for the long distance communication, the optical receiving unit uses an avalanche photodiode rather than a general photodiode, which increases the efficiency and sensitivity by forming a secondary carrier for an incident photon by placing a region of light leakage, Due to the changing efficiency and high-speed operation, optical receiving devices of Gbps or more will mostly use the avalanche photodiodes. Due to the operation characteristics of such avalanche photodiode, the reception characteristic greatly changes according to the optical power range of the received signal. Therefore, when receiving the multilevel optical signal, the resolution of the received signal may be lowered due to nonlinearity of the photocurrent depending on the amount of received light .

In addition to the high-speed transmission rate, the receiver that receives the multi-level optical signal bursts from different terminals and restores the clock every time has a slower speed of clock recovery when configured in the conventional manner as shown in FIG. 4, The restoration performance is low and the restored data is a plurality of bits. Therefore, when the serial data is transmitted to the MAC, the operation clock of the MAC must be twice as high as that of the restored clock.

Therefore, the present invention attempts to solve these problems through the configuration shown in Figs. 7 to 10.

7 and 8 are views illustrating a configuration of a multilevel optical signal transmission / reception system according to an exemplary embodiment of the present invention. As shown in FIG. 7, a multilevel optical transmission apparatus 200 and a corresponding optical transmission apparatus 100 . The illustrated multi-level optical receiving apparatus 200 corresponds to an OLT-side optical receiving apparatus for receiving an upstream burst signal.

Basically, PAM 4 is described as an example, but a higher resolution PAM 8 modulation scheme may be used, or a higher resolution may be applied depending on the technology.

The ONT optical transmission apparatus 100 includes a test pattern storage unit 140 for storing a predetermined test pattern and a control unit 130 for controlling the test pattern stored in the test pattern storage unit 140 110 to the laser diode 120. In the case of the test pattern, instead of the preamble of the data frame to be actually transmitted, instead of the preamble of a general frame provided through a conventional MAC (not shown) The control unit 130 may replace the test pattern or may be applied when the test pattern is reflected in the MAC (not shown) before forming the uplink burst signal frame.

9 is a diagram illustrating a part of a preamble structure of an uplink burst signal frame according to an embodiment of the present invention.

In the case of a multilevel (PAM 4 in the illustrated example), the conventional simple NRZ preamble is composed of 0 and 1. However, since 2 bits of data are modulated into one optical signal, the preamble is simply 00 11 00 11. It can be composed of repetitions of.

However, in the case of the present invention, the clock recovery pattern and the reception unit adjustment pattern as shown in the preamble of the frame for the uplink burst signal are included.

As shown in the figure, in the case of the clock recovery pattern, it is not a merely repetition of the lowest value (output corresponding to 00) and the maximum value (output corresponding to 11) of the transmission signal but a high-speed signal and a burst signal must be received at various distances The clock recovery pattern is formed of a binary pattern in which the minimum value and the maximum value of the multilevel signal are successively plural and are slowed to less than half of the transmission rate in order to increase the clock recovery speed.

In the case of PAM 4 as shown in the illustrated example, by configuring a clock restoration pattern by repetition of 00 00 11 11, the perceived transmission rate can be reduced to half. If the repetition of 00 00 00 11 11 11 is configured, The speed can be reduced to 1/3. However, since the required preamble length becomes longer as the bit rate is lowered, it is desirable to determine the clock recovery rate level verified by NRZ.

In order to recover the data from the burst signal having different sizes and starting points each time even if the clock recovery performance for the burst signal is improved by lowering the speed at such a low speed, the characteristics of the laser diode and the characteristics of the avalanche photodiode The level of the reception quality for the multi-level optical signal may be lowered. Therefore, it is necessary to include a test pattern (a reception unit adjustment pattern shown in the figure) for improving the reception performance for every burst signal (or at least once for each upstream frame for each ONT terminal) . Such a reception unit adjustment pattern may be a pattern formed by the data that the optical transmitter 100 and the optical receiver 200 promise.

The optical receiving apparatus 200 for receiving the upstream burst signal having the new preamble according to the present invention includes an avalanche photodiode 210 for receiving a multilevel optical signal, A burst mode transimpedance amplifier 220 for converting a current into a voltage, a differential amplifier 220 for amplifying the received voltage of the transimpedance amplifier 220 in accordance with a set reference voltage, outputting a plurality of bits corresponding to the division in parallel, A limit amplifier 230 for providing a binary signal and a maximum value of a multilevel signal among the signals amplified by the limiting amplifier 230 to the access control circuit 280, A burst clock recovery unit 240 for recovering a clock through a clock recovery pattern configured by a burst clock recovery unit 240, And a MAC 280 for receiving and processing a plurality of bits of the counterpart signal supplied from the limiting amplifier 230 per clock by using the clock recovered by the clock divider 250, .

If the multi-level optical signal is PAM (Pulse Amplitude Modulation) -N, the clock restoration pattern repeats the signal corresponding to the minimum data among the N types of signals a plurality of times and outputs the signal corresponding to the maximum data a plurality of times The burst clock recovery unit 240 detects a clock corresponding to a temporarily lowered transmission rate through the clock recovery pattern, and outputs the clock to the clock divider 250 through the clock divider 250 And restores the detected clock to a clock corresponding to the actual transmission rate. Limiting amplifier 230 and then to one of the N type with a reference voltage set, a signal corresponding to the data of the received frame by using the recovered clock signals according to the transmission rate via a clock drain portion (250) Description Log ₂ N bits To the MAC for each clock.

In the illustrated example, when receiving the PAM 4 burst signal of the 25 Gbps transmission rate, the actual burst clock recovery unit 240 uses the repetition of 00 00 11 11 as the pattern for restoring the clock, The recovery speed can be significantly increased as compared with the case of restoring the clock of 25 Gbps. The recovered temporary clock 12.5 GHz may be amplified twice by the clock divider 250 and then used for data recovery.

Meanwhile, in the optical receiver 200 for receiving a multilevel optical signal as shown in the figure, it is preferable that the limiting amplifier 230 and the MAC 280 are capable of parallel data transmission. 230) is configured to provide 2-bit parallel data for PAM 4 and 3-bit parallel data for PAM 8 to the MAC per clock. If the data of one clock separated by the limiting amplifier 230 is transmitted to the MAC 280 in series, a separate clock is required for the PAM 4 twice the clock corresponding to the transmission rate and three times for the PAM 8, If the interface between the limiting amplifier 230 and the MAC 280 is configured to operate at high speed, development becomes difficult.

The preamble of the received upstream burst signal frame further includes a pattern for adjustment of the reception part after the clock restoration pattern. As shown in the figure, the reception part adjustment pattern included in the received preamble of the reception voltage of the transimpedance amplifier 220 And a reference voltage set capable of distinguishing each pattern is estimated and applied to the limiting amplifier 230. The reference voltage set is divided into a plurality of patterns by referring to the test pattern storage unit 270, And a control unit 260.

That is, the control unit 260 divides the reception voltage of the transimpedance amplifier 220 into different reception voltages corresponding to different data on the basis of the data of the predetermined reception unit adjustment pattern, The reference voltage capable of distinguishing each data is estimated between the reception voltage range of each data.

This will be explained in more detail.

The avalanche photodiode outputs a photocurrent according to the characteristic of the multilevel optical signal. Since the photocurrent differs for each avalanche photodiode and is hard to predict for each intensity of the received optical signal, The characteristics of the currently configured avalanche photodiode corresponding to the level optical signal must be confirmed. In particular, in the case of a burst signal received through an OLT side avalanche photodiode comprising 1: N, the ONT terminals have different received optical signal intensities and should be classified into multi levels.

Accordingly, the control unit 260 divides the received voltage from the transimpedance amplifier 220, which converts the photocurrent of the avalanche photodiode 210 into a voltage, in accordance with the pattern for adjusting the receiving unit stored in the test pattern storage unit 270, If the received optical signal corresponds to the data '01' on the test pattern, the multi-level optical signal corresponding to the data '00' on the test pattern is classified according to the data '00' 00 ',' 01 ',' 10 ', and' 11 ', which represent each pattern, by dividing the received voltage into data corresponding to data' 01 '.

10 is an exemplary conceptual diagram for explaining a receiving section adjusting pattern corresponding to a test pattern and a corresponding multi-level signal and a reference voltage set estimating method of the multi-level optical receiving apparatus receiving the multi-level signal. The received voltage is classified according to the pattern for adjusting the receiver section (the received voltage for the same data is collected and connected by a line).

This means an actual reception range of the received voltage of each pattern of the currently received multi-level burst signal based on the characteristics of the avalanche photodiode configured in the current multi-level optical receiving apparatus 200. In other words, .

10B, the reference voltages LV2 to LV4 that can distinguish each pattern data based on the distribution range of the reception voltages stored for each pattern data can be estimated between the reception voltage distribution ranges for the respective data. For example, It is possible to estimate a reference voltage in the middle of a corresponding area after detecting an area having no reception voltage between reception voltage distribution areas for each pattern data. Further, it is possible to estimate the additional reference voltages LV1 and LV5 by referring to the distribution range of the reception voltages.

The reference voltage sets LV1 to LV5 are used as a criterion for determining which pattern data the received voltage obtained by converting and amplifying the photocurrent of the avalanche photodiode with respect to the currently received multilevel burst signal is amplified by the transimpedance amplifier, Accordingly, the reception voltage can be divided into one of '00', '01', '10' and '11'. If necessary, it may be regarded as noise if it is LV1 or less or LV5 or more.

The limiting amplifier 230 operates with the reference voltage set (LV1 to LV5 in the embodiment) estimated by the control unit 260 through the above process. The limiting amplifier 260 outputs the voltage belonging to the specific range as the target voltage When the reception voltage of the transimpedance amplifier 220 is between LV1 and LV2, the reference voltage set is amplified. When the received voltage is between LV1 and LV2, And amplifies and outputs the amplified data to an output voltage indicating '10' if it is between LV3 and LV4 and amplifies and outputs the amplified data to an output voltage that indicates data '11' if it is between LV4 and LV5 . In addition, the parallel data generating unit generates parallel data through the parallel signal generating unit, and provides the data to the MAC 280 in parallel. If the reception voltage of the transimpedance amplifier 220 is equal to or lower than LV1 or equal to or higher than LV5, the limiting amplifier 230 may be regarded as noise and may not operate.

The control unit 260 performs a reference voltage set estimation each time an uplink burst signal frame is received or receives schedule information of an uplink burst signal from the MAC 280 (a burst signal reception schedule for each ONT terminal) The reference voltage set estimation may be omitted in the case of the uplink burst signal frame received from the terminal that estimates the reference voltage set in the terminal and the reference voltage set previously estimated for the terminal may be used. Of course, such reference voltage set-up can be performed periodically or as needed.

As an example, in the case of the upward burst signal, a silent window section in which no other upstream ONT sends an upstream signal exists in two frame lengths so that a new ONT can register in the OLT. The BS transmits an uplink burst signal for registration to the OLT. In this way, the MAC of the OLT can confirm the new ONT through the silent window. The control unit 260 uses the reception unit adjustment pattern included in the preamble of the upstream burst frame for registration of the new ONT, Estimation can be performed, and then reference voltage set estimation can be omitted for the corresponding ONT. In this case, the length of the preamble can be reduced by omitting the portion for estimating the reference voltage set in the preamble of the upstream burst signal from the ONT.

8, the MAC 280 may have a parallel input / output configuration corresponding to the data size to be transmitted at one time through the multilevel. In the case of PAM4, the 2-bit parallel data may be input to the limiting amplifier 230, And transmits and receives the 2-bit signal to / from an external device or the like that uses actual data after processing it. Further, when a signal for transmission is also received as a 2-bit signal and then processed and transmitted to the other party (ONT), the 2-bit data is supplied to the laser diode driver 290 and modulated into PAM 4, ). ≪ / RTI >

In this case, the optical receiving apparatus 200 uses an internal clock equal to the actual communication speed, and at least a speed less than half of the communication speed can be used in the clock recovery process. In this case, when a multilevel signal transmitted / received to / from a plurality of data is used through a single clock, a clock higher than the communication speed is required for serial / parallel conversion. The internal clocks of the optical receiving apparatus 200, It is possible to improve the convenience of development by using the following clocks.

FIG. 11 is a flow chart illustrating the operation of the present invention, and illustrates an example of a process of receiving a multi-level burst signal frame modulated with PAM 4.

As shown in the figure, a multilevel upstream burst signal frame having a preamble including a clock recovery pattern composed of binary patterns consecutively having a lowest value and a maximum value of a multi-level signal successively twice and being slowed by half of a transmission rate is received through a photodiode And amplifies it through a transimpedance amplifier. Then, the burst clock recovery unit performs synchronization using a clock recovery pattern. After restoring the slower temporary clock, it is amplified twice by the clock divider to restore the actual clock.

After the clock recovery process, the controller estimates a reference voltage set that can distinguish each pattern by classifying the reception voltage according to the reception unit adjustment pattern through the promised test pattern (reception unit adjustment pattern) included in the preamble, This is applied to the limiting amplifier.

When the reception of the preamble is completed in the reception frame and the reception of the actual data is started, the limiting amplifier restores the reception data by using the recovered clock and using the set reference voltage corresponding to the burst signal frame, And provides the data to the MAC in parallel.

Through this process, even if a burst signal having a Gbps speed or more, which is different in the length and the magnitude of the received signal, is received by the multilevel optical signal, it is possible to perform a fast clock synchronization and the data restoration The performance can be improved.

SFP (Small Form Factor Pluggable), SFP + (10Gbps), and SFP28 (25Gbps) devices are used as interfaces for attaching network devices to fiber-based transmission systems such as optical channels or Gigabit Ethernet according to recent various network configuration methods. . That is, a configuration in which an SFP for a fiber-based transmission is connected to an Ethernet switch device and a fiber is connected to the SFP to provide a high-speed channel such as a Gigabit Ethernet or a PON (passive optical network) is generally used. However, SFPs for optical communication that support multi-level are not yet available. In the case of the existing SFP, it is prescribed to use one serial communication for each of the transmission and reception data channels for communication with the equipment. Thus, In order to transmit / receive optical signals, a plurality of data received at one clock must be converted into a serial signal again. For this purpose, the clock of the limiting amplifier or the MAC must be a multiple of the transmission speed.

12, the SFP device 60 includes a device connection interface 61 inserted into a standard SFP port formed in the device and connected to the device when viewed from the external coupling portion, And a line connection interface 62 for connection with an optical line according to a communication scheme.

The equipment connection interface 61 is comprised of a standard 20-pin interface and is provided in the form of a pin exposed substrate, and the line connection interface 62 includes a lighted line transceiver configuration according to the communication method supported by the SFP device.

Here, the equipment connection interface 61 is inserted into a standard SPF port included in the equipment, receives power from the equipment, exchanges information with the equipment, and transmits / receives data to / from the MAC processing unit of the PON communication system Lt; / RTI >

13 is a block diagram of a standard 20-pin equipment connection interface of the SFP device. As shown in FIG. 13, pins 18 and 19 (RD- and RD +) among the illustrated pins are used for receiving data from the equipment Pins 12 and 13 (TD +, TD-) are pins for providing the received data between the SFP devices to the device. Pins 4 and 5 (MOD_DEF (2), MOD_DEF It corresponds to I2C communication pin (SDA_Data, SCL_Clk correspondence) for information exchange between devices. Here, the communication using the I2C communication pins confirms and updates the setting between the internal control unit and the connected equipment in the SFP device, requests the SFP device to send information to the connected equipment, accesses the internal register of the SFP device control unit, And the like.

FIG. 14 is a view showing a modified 20-pin equipment connection interface of the SFP device according to an embodiment of the present invention. As shown in FIG. 14, the conventional 10 pin, 11 pin and 14 pin (VeeR) (VeeT) is used for additional parallel data transmission / reception.

As described above with reference to FIG. 8, in the embodiment of the present invention, when 2 bits of data are transmitted / received on one clock when the PAM 4 scheme is applied, the MAC can process 2-bit parallel data . In order to apply the optical transceiver configured as described above to the SFP, it is necessary to be able to transmit and receive 2-bit data to and from the connected equipment. Therefore, additional data receiving terminals RD2 + and RD2- Credit terminals (TD2 +, TD2-) can be allocated.

In the illustrated example, the arrangement of the pins 10 to 20 is changed, and the transmission / reception terminal sets are separated from each other by using the power supply or the ground. The additional data receiving terminals RD2 + and RD2- and the data transmitting terminals TD2 + and TD2- are sequentially connected to the non-overlapping terminals VeeT, VccT and VccR by using the overlapping pins, Respectively. Of course, such pin arrangement may vary as needed.

As described above, the configuration of the embodiment of the present invention can be configured as an ONT receiving apparatus and can also be implemented in the form of an SFP.

As a result, it is possible to improve the multi-level clock restoration performance and optimize the multi-level reception performance between the devices at the transmitter level through the relatively simple configuration, thereby improving the communication quality at a low cost.

Meanwhile, the control unit of the above-mentioned optical transmitting apparatus or optical receiving apparatus may be composed of an electronic circuit including a combination of active and passive elements having a control function, and may be constituted by a chip including a microcontroller or equivalent control means And the concrete implementation method thereof may encompass various known methods.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or essential characteristics thereof. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

100: Multilevel optical transmitter 110:
120: laser diode 130:
140: Test pattern storage unit 200: Multilevel optical receiver
210: avalanche photodiode 220: transimpedance amplifier
230: Limiting amplifier 240: Burst clock recovery unit
250: clock divider 260:
270: Test pattern storage unit 280: MAC
290: laser diode driver 295: laser diode

Claims (10)

1. A multilevel optical receiving apparatus for receiving a multilevel upstream burst signal frame having a preamble including a predetermined clock recovery pattern, restoring a clock and data, and processing the data through a MAC (Media Access Control)
A photodiode for receiving a multilevel optical signal;
A burst mode transimpedance amplifier for converting the current of the photodiode into a voltage;
Amplifying the received voltage of the transimpedance amplifier in accordance with a set reference voltage, outputting a plurality of bits corresponding to the division in parallel, and providing the same to the MAC;
A burst clock recovery unit for recovering a clock through a clock recovery pattern composed of a binary pattern in which a minimum value and a maximum value of a multi-level signal among the amplified signals amplified by the limiting amplifier are successively plural and are slowed to less than half of a transmission rate;
And a clock divider for multiplying a clock recovered by the burst clock recovery unit to a multiple according to a transmission rate.
The method of claim 1, wherein when the multilevel optical signal is PAM (Pulse Amplitude Modulation) -N, the clock recovery pattern repeats a signal corresponding to minimum data among N kinds of signals a plurality of times, Wherein a plurality of signal sets to be repeated a plurality of times are constructed several times to temporarily lower a transmission speed, thereby enhancing the burst mode clock and data restoration performance.
The method according to claim 2, wherein the limiting amplifier is a clock to evacuate through the reference voltage set, a signal corresponding to the data of the received frame by using the recovered clock signals according to the transmission speed through the then separated by one of the N types Log ₂ N bits And a parallel signal is provided to the MAC for each clock. The multilevel optical receiving apparatus with improved burst mode clock and data recovery performance.
2. The apparatus of claim 1, wherein the preamble of the uplink burst signal frame further comprises a pattern for adjusting a receiver portion after the clock recovery pattern,
And a controller for classifying a received voltage according to a pattern for adjusting a receiver included in a received preamble among the received voltages of the transimpedance amplifier according to each pattern to estimate a reference voltage set capable of distinguishing each pattern and applying the reference voltage set to the limiting amplifier Wherein the burst mode clock and the data recovery performance are improved.
The control unit stores the received voltage of the transimpedance amplifier by dividing the received voltage corresponding to the different data based on the data of the predetermined pattern for adjusting the receiving unit, And estimating a reference voltage that can be discriminated between a reception voltage distribution range for each data, respectively.
The method of claim 4, wherein the controller performs a reference voltage set estimation each time an uplink burst signal frame is received, receives scheduling information of an uplink burst signal from the MAC, Wherein the reference voltage set estimation is omitted for the burst signal frame and the reference voltage set previously estimated for the corresponding terminal is used.
A multilevel optical reception method for receiving a multilevel upstream burst signal frame having a preamble including a promised clock recovery pattern, restoring a clock and data, and processing through a MAC,
Converting the current of the multilevel optical signal received through the photodiode to a voltage through the transimpedance amplifier;
Dividing and amplifying the reception voltage of the transimpedance amplifier according to a set reference voltage through a limiting amplifier;
The burst clock restoring unit restores a clock through a clock recovery pattern composed of a binary pattern in which a minimum value and a maximum value of a multi-level signal among the signals classified and amplified in the limiting amplifier are continuously a plurality of consecutive and slower than half of a transmission rate, Increasing the clock recovered through the divider to a multiple of the clock rate according to the transmission rate;
Wherein the limiting amplifier amplifies the reception voltage according to the set reference voltage using the recovered clock according to the transmission rate, and outputs the plurality of bits corresponding to the division in parallel to the MAC to provide the burst mode clock And a multilevel optical receiving method with improved data recovery performance.
8. The method of claim 7, wherein when the multilevel optical signal is PAM-N, the clock recovery pattern is a pattern for repeating a signal corresponding to minimum data among N kinds of signals a plurality of times, And the transmission speed is temporarily lowered by constructing the set at a plurality of times, thereby improving the burst mode clock and data restoration performance.
The method according to claim 8, wherein the limiting amplifier is the clock drainage unit after separated by one of N type with a reference voltage set, a signal corresponding to the data of the received frame by using the recovered clock signals according to the transfer rate Log ₂ N bits And providing a parallel signal of the clock signal to the MAC for each clock.
8. The method of claim 7, wherein the preamble of the uplink burst signal frame further comprises a receiver adjustment pattern promised after the clock recovery pattern,
The control unit classifies the received voltage according to the pattern for adjusting the receiving unit included in the preamble among the receiving voltages of the transimpedance amplifier according to each pattern to estimate a reference voltage set capable of distinguishing each pattern and applying the reference voltage set to the limiting amplifier Wherein the burst mode clock and the data restoration performance are improved.

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