KR102687522B1 - Transmission clock generation apparatus and method for passive optical network terminal based on recovery clock - Google Patents

Abstract

The present invention relates to a transmission clock generation device and method of a passive optical communication terminal based on a recovery clock that enable an optical network terminal (ONT) receiving a downlink signal from an optical line terminal (OLT) of a passive optical network (PON) to use a local clock in which a jitter is removed as a clock for transmitting an uplink signal of the ONT based on a clock recovered from the downlink signal, wherein an inexpensive VCTCXO is applied as an ONT clock, an ONT local clock is controlled to have the same speed as that of a recovery clock based on a jitter-comprising recovery clock recovered from the downlink signal received from the OLT, and the ONT local clock generated through the same enables to transmit the uplink signal to the clock from which jitter has been removed while being the same as the OLT by using as an uplink signal transmission clock, thereby having an effect of improving communication quality and reducing a BCDR processing load by facilitating a burst mode clock data recovery (BCDR) of the OLT.

Description

Transmission clock generation apparatus and method for passive optical network terminal based on recovery clock}

The present invention relates to an apparatus and method for generating a transmission clock for a passive optical communication terminal based on a restored clock, and in particular, to an optical network terminal (ONT) that receives a downstream signal from an optical line terminal (OLT) of a passive optical network (PON). The present invention relates to an apparatus and method for generating a transmission clock for a passive optical communication terminal based on a restored clock, which allows the local clock from which jitter has been removed based on the restored clock to be used as a clock for upstream signal transmission of the ONT.

Passive optical network (PON) technology is intended to construct a high-speed subscriber network and is configured to handle simultaneous access of multiple subscribers through time division or wavelength division. Among these methods, the cost-effective time sharing method is mainly used, such as EPON (Ethernet PON) according to IEEE (Institute of Electrical and Electronics Engineers) 802.3av/ah, 10G-EPON (10Gigabit EPON), and ITUT (International Telecommunication Union). -Telecommunication Standardization Sector) Representative examples include GPON (Gigabit PON) according to G.984/7, XGPON (10Gigabit PON), and NGPON2 (Next Generation PON) according to G.989.

PON is a one-to-many (Point) connection between one OLT (Optical Line Terminal) and multiple subscribers' ONT (Optical Network Terminal) or ONU (Optical Network Unit) through a remote node (using an optical splitter), which is a manual optical branch device. to Multipoint) network structure.

Due to the nature of this one-to-many network structure, the transmission methods for downstream signals, where the OLT transmits signals to the ONT, and upstream signals, where multiple ONTs transmit signals to the OLT, are different. In the case of downstream signals, signals for multiple ONTs are provided continuously and each ONT selects and uses its own signal among the received signals. However, in the case of uplink signals, multiple ONTs use their own signals to prevent collisions between signals transmitted to the OLT. It uses a burst transmission method that transmits its signal to the OLT only during the transmission period allocated to it.

ONT is physically separated from OLT, and since ONT has multiple terminals and is installed at customers, it is a product focused on mass production. Therefore, in order to reduce costs, a relatively inexpensive oscillator is used to generate a local clock (ONT clock), so there is a deviation from the clock of the downstream signal transmitted by the OLT. Therefore, in order to check the data from the signal received from the OLT, the ONT restores the clock of the OLT based on the corresponding signal and checks the data included in the received signal based on the restored clock (OLT clock). At this time, since the downstream signal is provided continuously, the ONT only needs to restore the OLT's clock once.

However, in the case of an upward burst signal, the signals of multiple ONTs with different optical distances and various deviations of the local clocks used are segmented and transmitted to the OLT, so the OLT must use the ONT transmitting the upward signal to receive the signal for each ONT. Whenever there is a change, the clock of the ONT is restored from the signal transmitted by the ONT during a certain section of the upstream signal transmitted by the relevant ONT, that is, the pre-amplifier section, and then data is restored from the received signal based on this. Therefore, OLT requires relatively high optical power reception to restore the burst signal within a short time each time, the circuit configuration for clock data restoration is complex, and the reference oscillator precision required for clock restoration also requires a very high level. .

Due to the characteristics of this PON environment, the ONT attempts to improve burst mode clock data recovery (BCDR) performance by using the same clock as the OLT clock by using the restored clock restored from the downstream signal received from the OLT as a clock for transmitting the upstream signal. There have been attempts to do this, but jitter occurs in the photoelectric conversion stage of the optical receiving device configured on the ONT, and additional jitter occurs in the process of restoring the clock based on the signal containing jitter. Due to this accumulated jitter, there is difficulty in improving the ONT transmission clock when the restored clock itself is used as a clock for upstream signal transmission.

In other words, although there is some deviation from the OLT's perspective, it is necessary to restore the jitter-containing unstable clock (clock restored from the ONT) using the BCDR structure, which is designed to quickly restore the jitter-free ONT local clock. This happens. In this case, BCDR performance may decrease compared to when using a local clock based on a low-quality oscillator provided by the ONT.

In a situation where various multimedia transmission and reception and large-capacity data generation and registration are becoming common, improvement of BCDR performance and reception sensitivity due to rapid increase in upstream data transmission volume are very important technical factors affecting PON performance. However, as the supply of ONT is also rapidly increasing due to the vast demand for optical communication, there are environmental constraints that prevent the application of high-quality oscillators for the price competitiveness of ONT. Therefore, it is possible to improve the BCDR performance of OLT while using a relatively low-quality oscillator. Research is currently underway to provide an upstream signal with a stable clock.

Korean Patent No. 10-1725335 [Title of invention: Clock and data recovery circuit] Korean Patent No. 10-1988920 [Title of invention: Multi-level photoreduction device and method with improved burst mode clock and data recovery performance]

The purpose of the present invention to solve the above problems is to apply an inexpensive VCTCXO (Voltage-Control Temperature-Compensated is controlled to have the same speed as the restoration clock, and the ONT local clock generated through this is used as a clock for transmitting the upstream signal, thereby transmitting the upstream signal with the same clock as the OLT but with jitter removed to restore the OLT's burst mode clock data. To provide an apparatus and method for generating a transmission clock of a passive optical communication terminal based on a restored clock that facilitates (BCDR).

Another object of the present invention is to control the ONT local clock to be equal to the counter value of the restored clock by comparing the restored clock recovered from the downstream signal received from the OLT and the local clock of the ONT based on the counter value measured during a preset period. The present invention provides an apparatus and method for generating a transmission clock for a passive optical communication terminal based on a restored clock that uses simple hardware to make the ONT local clock, which is relatively prone to errors, similar to the OLT clock. In other words, the purpose is to improve clock jitter performance by combining an inexpensive oscillator with simple, easy-to-implement hardware.

Another object of the present invention is to provide an apparatus and method for generating a transmission clock for a passive optical communication terminal based on a restored clock, which can improve the BCDR performance of the OLT by controlling the local clock of the ONT to within ±1 clock error based on the restored clock. It is provided.

Another object of the present invention is to use two relatively inexpensive ONT local clocks, check the deviation between them in advance, synchronize them, and then use one of the ONT local clocks as a tracking clock to set the restored clock and count value as a reference. The remaining ONT local clocks are controlled to within ±1 clock error, and the remaining ONT local clocks are controlled at half the control amount that controls the tracking clock, and the clock is used as a clock for upward signal transmission to maintain an error of less than 1 clock during the counting period. To provide an apparatus and method for generating a transmission clock of a passive optical communication terminal based on a restored clock.

Another object of the present invention is to use the ONT local clock for upstream signal transmission by synchronizing the ONT local clock with the precise OLT clock included in the downstream signal provided by the OLT, as well as precise time synchronization or clock synchronization in the upper communication layer. To provide an apparatus and method for generating a transmission clock for a passive optical communication terminal based on a restored clock that can be used for the purpose of.

The transmission clock generating device of a passive optical communication terminal based on a restored clock according to an embodiment of the present invention is a transmission clock generating device configured in a passive optical communication terminal that receives a downstream signal from an OLT (Optical Line Terminal) and transmits an upstream signal to the OLT. , a clock data recovery unit that receives electrical signals according to the received optical signal and restores the clock and data, a local clock generator that outputs a local clock but can control the speed of the output clock with voltage, and a clock data recovery unit. The restored restored clock and the local clock output from the local clock generator are counted for each preset period, the counting deviation of the local clock is checked based on the restored clock, and then a control voltage is provided to the local clock generator to reduce the counting deviation. It includes a transmission clock generator and a MAC (Media Access Control) processor that uses the clock of the local clock generator, corrected under the control of the transmission clock generator, as a clock for upstream signal transmission.

As an example, the transmission clock generator may set the counting period so that the deviation between the respective counting values of the restored clock and the local clock does not exceed 1.

As an example, the transmission clock generator may use the number of clocks corresponding to the unit frame section of passive optical communication as a counting period.

As an example, the transmission clock generator counts the restored clock recovered from the clock data recovery unit and the local clock output from the local clock generator, and when the restored clock counting value is equal to the number of clocks according to the preset period, the corresponding restored clock A counter unit that provides the deviation of the local clock counting value as a clock deviation value based on the counting value and resets the counting values, and provides a control voltage calculated based on the clock deviation value provided by the counter unit to the local clock generator. It may include a clock control unit that provides

The transmission clock generator of a passive optical communication terminal based on a restored clock according to another embodiment of the present invention is a transmission clock generator configured in a passive optical communication terminal that receives a downward signal from the OLT and transmits an upward signal to the OLT. It has the same configuration as the local clock generator, a clock data recovery unit that receives electrical signals and restores the clock and data, a local clock generator that outputs a local clock but can control the speed of the output clock with voltage, A tracking local clock generator that operates separately from the local clock generator and outputs a tracking local clock, compensates for the operation deviation of the local clock generator and the tracking local clock generator, synchronizes their clock speeds, and restores them in the clock data recovery unit. Counting the restored clock and the tracking local clock generated by the tracking local clock generator for each preset cycle, checking the counting deviation of the tracking local clock based on the restored clock, and then controlling the tracking local clock generator to reduce the counting deviation, A transmission clock generator that controls the local clock generator with a control amount less than the deviation reduction control amount of the tracking local clock generator, and a MAC that uses the clock of the local clock generator corrected under the control of the transmit clock generator as a clock for upstream signal transmission. Includes a processing unit.

As an example, the transmission clock generator includes a synchronization unit that generates local clock deviation compensation information to synchronize the local clock and the tracking local clock based on the clock deviation information of the local clock generator and the tracking local clock generator, and a clock data recovery unit. A counter unit that provides as a clock deviation value the counting value deviation for each preset period for the restored restored clock and the tracking local clock output by the tracking local clock generator, and a first circuit calculated so that the clock deviation value provided by the counter unit is reduced. A control voltage is provided to the tracking local clock generator, and a second control voltage is used to control the control amount to half of the control amount to reduce the clock deviation of the tracking local clock generator based on the first control voltage and the local clock deviation correction information of the synchronization unit. It includes a clock control unit that provides a local clock generator.

As an example, the counter unit may set the counting period so that the deviation between the values counted for the restored clock and the tracking local clock does not exceed 1.

As an example, the counter unit uses the number of clocks corresponding to the unit frame section of passive optical communication as a counting cycle, counts the restored clock and the tracking local clock respectively, and the counting value of the restored clock corresponds to the number of clocks required for unit frame transmission. Each time it becomes a value, the deviation of the tracking local clock counting value can be counted based on this, provided as a clock deviation value, and the counting values can be reset.

A transmission clock generation method of a passive optical communication terminal based on a restored clock according to another embodiment of the present invention is a method of generating a transmission clock of a transmission clock generator configured in a passive optical communication terminal that receives a downward signal from the OLT and transmits an upward signal to the OLT. As a step, a clock data recovery unit restores the clock and data from an electrical signal according to the received optical signal, a local clock generator capable of controlling the speed of the output clock with a voltage outputs a local clock, and a transmission clock generator. The local clock generator counts the restored clock restored by the clock data restoration unit and the local clock generated by the local clock generator at preset intervals, checks the counting deviation of the local clock based on the restored clock, and reduces the counting deviation. It includes providing a control voltage to the MAC processing unit and using the clock of the local clock generator corrected under the control of the transmission clock generator as a clock for upstream signal transmission.

A transmission clock generation method of a passive optical communication terminal based on a restored clock according to another embodiment of the present invention is a method of generating a transmission clock of a transmission clock generator configured in a passive optical communication terminal that receives a downward signal from the OLT and transmits an upward signal to the OLT. As a step, a clock data recovery unit restores the clock and data from an electrical signal according to the received optical signal, a local clock generator capable of controlling the speed of the output clock with a voltage outputs a local clock, and a local clock generator A tracking local clock generator that has the same configuration as and operates separately from the local clock generator outputs a tracking local clock, and a transmit clock generator compensates for the operation deviation of the local clock generator and the tracking local clock generator to generate their clocks. The speed is synchronized, the recovery clock restored by the clock data recovery unit and the tracking local clock generated by the tracking local clock generator are counted for each preset period, the counting deviation of the tracking local clock is checked based on the restoration clock, and the corresponding counting deviation is calculated. Controlling the tracking local clock generator to reduce and controlling the local clock generator with a control amount less than the deviation reduction control amount of the tracking local clock generator, and the local clock generator corrected by the MAC processing unit according to the control of the transmission clock generator. It includes using a clock as a clock for upward signal transmission.

An apparatus and method for generating a transmission clock for a passive optical communication terminal based on a restored clock according to an embodiment of the present invention applies an inexpensive VCTCXO as an ONT clock, and generates an ONT local clock based on a restored clock including jitter recovered from the downstream signal received from the OLT. It is controlled to have the same speed as the restoration clock, and the ONT local clock generated through this is used as a clock for transmitting the upstream signal, thereby restoring the OLT's burst mode clock data by transmitting the upstream signal with the same clock as the OLT but with jitter removed. This has the effect of improving communication quality and reducing BCDR processing load by making (BCDR) easier.

In addition, an embodiment of the present invention compares the restored clock recovered from the downstream signal received from the OLT and the local clock of the ONT based on the counter value measured during a preset period to make the ONT local clock equal to the counter value of the restored clock. By controlling the ONT local clock, which is relatively prone to error, to be similar to the OLT clock through simple hardware, the BCDR performance of the OLT is improved, and the quality of the ONT's local clock is also improved by keeping the ONT's local clock the same as the OLT. There is an effect.

In addition, the embodiment of the present invention uses two local clocks of the ONT, checks the deviation between them in advance and synchronizes them, then uses one of the corresponding ONT local clocks as a tracking clock to calculate ± Controlled to within 1 clock error, and controlling the remaining ONT local clocks to half the control amount that controls the tracking clock, and using that clock as a clock for upward signal transmission, communication is maintained with an error of less than 1 clock during the counting period. It has the effect of improving quality. In other words, an error of less than 1 clock can have the effect of significantly improving the BCDR performance of the OLT by actually controlling the level of deviation between the OLT clock and the ONT clock to the phase error level.

Furthermore, the embodiment of the present invention synchronizes the ONT local clock with the precise OLT clock, so even if there is no separate time information transmission and synchronization configuration, the ONT local clock is used for time synchronization or clock synchronization required by upper layer communication protocols such as Ethernet communication using PON. It can be used as a reference clock, can be used to provide accurate time information during network failure recovery, and can be used to support encrypted communication using synchronized time information.

Figure 1 is a diagram showing the configuration of a typical passive optical network.
Figure 2 is a conceptual diagram illustrating the downlink and uplink signal transmission methods of a passive optical network.
Figure 3 is an example diagram showing the configuration of an OLT for restoring an upstream burst signal.
Figure 4 is an example diagram showing the configuration of an ONT for downstream signal restoration.
Figure 5 is a configuration diagram showing the configuration of an ONT including a transmission clock generator for a passive optical communication terminal based on a recovered clock according to an embodiment of the present invention.
Figure 6 is a conceptual diagram illustrating the operation method of a transmission clock generation device according to an embodiment of the present invention.
Figure 7 is an exemplary diagram showing the control process of the transmission clock generation device according to an embodiment of the present invention.
Figure 8 is a configuration diagram showing the configuration of an ONT including a transmission clock generator for a passive optical communication terminal based on a recovered clock according to another embodiment of the present invention.
Figure 9 is an exemplary diagram showing a control process of a transmission clock generation device according to another embodiment of the present invention.

It should be noted that the technical terms used in the present invention are only used to describe specific embodiments and are not intended to limit the present invention. In addition, the technical terms used in the present invention, unless specifically defined in a different sense in the present invention, should be interpreted as meanings generally understood by those skilled in the art in the technical field to which the present invention pertains, and should not be overly comprehensive. It should not be interpreted as meaningless or in an excessively reduced sense. Additionally, if the technical terms used in the present invention are incorrect technical terms that do not accurately express the idea of the present invention, they should be replaced with technical terms that can be correctly understood by those skilled in the art. In addition, general terms used in the present invention should be interpreted according to the definition in the dictionary or according to the context, and should not be interpreted in an excessively reduced sense.

Additionally, as used in the present invention, singular expressions include plural expressions unless the context clearly dictates otherwise. In the present invention, terms such as “consists of” or “comprises” should not be construed as necessarily including all of the various components or steps described in the invention, and some of the components or steps may not be included. It should be interpreted that it may or may further include additional components or steps.

Additionally, terms including ordinal numbers, such as first, second, etc., used in the present invention may be used to describe components, but the components should not be limited by the terms. Terms are used only to distinguish one component from another. For example, a first component may be referred to as a second component, and similarly, the second component may be referred to as a first component without departing from the scope of the present invention.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the attached drawings. However, identical or similar components will be assigned the same reference numbers regardless of the reference numerals, and duplicate descriptions thereof will be omitted.

Additionally, when describing the present invention, if it is determined that a detailed description of related known technologies may obscure the gist of the present invention, the detailed description will be omitted. In addition, it should be noted that the attached drawings are only intended to facilitate easy understanding of the spirit of the present invention, and should not be construed as limiting the spirit of the present invention by the attached drawings.

In particular, as an embodiment of the present invention, an optical receiving device of OLT (Optical Line Terminal) among passive optical network (PON) equipment is described. However, among various optical communication equipment, it is necessary to receive an upward burst signal and perform burst mode clock and data recovery. It can be widely applied to optical receiving devices in equipment that Meanwhile, ONT (Optical Network Terminal) is substantially the same as ONU (Optical Network Unit).

Figure 1 shows the configuration of a typical passive optical network (PON). Looking at the configuration of this PON, it basically consists of one Optical Line Terminal (OLT) installed in a telephone office and an Optical Network Terminal (ONT) or ONU (ONU) of multiple subscribers. The Optical Network Unit has a point to multipoint network structure through a manual optical branch device, the Remote Node (using an optical splitter).

As shown, the OLT (1) equipped with an optical transmitting and receiving unit (1a) that converts electrical signals and optical signals to each other is connected to a plurality of subscriber ONTs (2) through a remote node (RN), and each ONT (2) An optical transmitting/receiving unit 2a is also configured in each case. Through this configuration, high-speed communication services can be provided to a plurality of subscriber ONTs (2).

Figure 2 is a conceptual diagram for explaining a PON downstream signal transmission method and an upstream signal transmission method. FIG. 2A is a conceptual diagram to explain a downlink signal transmission method in a passive optical network. As shown, when the OLT (1) sequentially sends downlink frame data to the ONT (2), the plurality of ONTs (2_1, 2_2) It selects and receives frame data about itself from the downstream frame data. Therefore, continuous data transmission without signal collision is possible simply by continuously transmitting the signal modulated by the OLT (1) with its own clock. In addition, since all downstream signals consisting of continuous data use the clock of OLT (1), each ONT (2) only needs to restore and synchronize the clock for these downstream signals once. In other words, the ONT receiver that receives such a downstream signal can maintain higher sensitivity than the OLT receiver, which will be explained later.

Figure 2b is a conceptual diagram for explaining the uplink signal transmission method of a passive optical network. As shown, in the case of an uplink signal in which the ONT (2) transmits uplink frame data to the OLT (1), there is a possibility that the signals may collide if multiple ONTs (2_1, 2_2) randomly transmit uplink signals. When the OLT (1), which knows the information (number, distance, etc.) about (2), transmits control information about the transmission time and data amount of the upstream signal to each ONT (2) through a downstream signal, each ONT (2_1) , 2_2) generates upward burst signals of various sizes based on the corresponding control information and transmits them without collision.

OLT(1) must restore the clock for each burst signal transmitted by each ONT to restore the data contained in the signal. Therefore, the clock must be synchronized within the preamble transmission period included in each burst signal, so the clock must be restored from the received burst signal. Not only does it consume a lot of resources to restore, but there is a limit to the clock restoration time, so you have to endure a decrease in reception sensitivity.

FIG. 3 is an exemplary diagram showing the configuration of an OLT for burst signal recovery, and the upstream signal reception method will be described in more detail with reference to FIG. 2B.

ONT (2_1, 2_2) generates upstream signals with a set amount of data at different times and transmits them to OLT (1). Each upstream signal is divided into a guard section (a) to prevent collisions.

In the case of this upward signal, as shown, it is a burst signal in which the signal is continuously segmented, and since each signal uses its own clock of individual ONT (2_1, 2_2), the clocks of the upward burst signal are not synchronized with each other or with the OLT clock. Therefore, there is a deviation from the clock of OLT (1) receiving it.

That is, in the case shown, t1, t2, and t3, which are the individual start points of the upward burst signal, have a deviation from the clock of OLT(1), so OLT(1) restores the clock each time for each upward burst signal and transmits data accordingly. It must be restored.

In particular, the upward burst signals transmitted from the ONT (2) at different positions are disconnected with different sizes and signal strengths and are received by the OLT (1). The received optical signals pass through a condenser lens (not shown) and are transmitted to the optical transceiver. It is received through the photodiode (PD) in (1a). The photodiode (PD) generates a small current according to the optical signal, and the transimpedance amplifier (TIA) converts the small current according to the optical signal into a voltage and amplifies it. In the operation of this TIA, the amplification rate varies each time by considering signal attenuation depending on the distance of the ONT. Meanwhile, in the case of high-speed signals of tens of Gbps or more that are being applied recently, the discharging or charging of the capacitance inside the circuit is not completely achieved within each signal cycle, so the parasitic capacitance remains inside the circuit for a considerable period of time, causing an increase in the output of the transimpedance amplifier (TIA). A significant amount of noise signals are included.

The output of the transimpedance amplifier (TIA) is converted into digital signals of 0 and 1 according to the reference value of the limit amplifier (LA). The clock of this received digital signal corresponds to the internal clock of the ONT and has a phase difference from the OLT clock. Therefore, in order to obtain data normally, the phase of the received digital signal is restored by adjusting the OLT clock by considering the phase difference between the OLT and ONT clocks. Should be.

Therefore, the digital signal provided through the limit amplifier (LA) is synchronized with the OLT clock through the burst mode clock data recovery (BCDR) (1b), due to the noise described above and the different clock phases for each ONT. The restoration process is quite difficult, and the time delay is bound to be significant. Therefore, for BCDR, the ONT increases the reliability of clock recovery by repeatedly providing meaningless preamble (32-bit or 64-bit) signals. However, the communication bandwidth is reduced by the repeated preamble, and reception loss occurs during the BCDR process. It increases.

The restored serial data provided by the BCDR (1b) is received by the OLT's MAC processing unit (1c), converted to parallel data, and then used. When communication quality is low, retransmission is frequently required due to errors in the received data, etc. To reduce , data must contain more information for error correction, which reduces communication quality.

Ultimately, in a situation where upward burst signals are explosively increasing due to the rapid expansion of 5G or IoT, this burst mode clock data recovery process is a major cause of received signal loss, so to extend the communication distance of PON, the reception sensitivity must be improved. If you want to increase it, you need to reduce the burden on clock synchronization of the upstream burst signal.

Figure 4 is an exemplary diagram showing the configuration of an ONT.

As shown, the ONT 2, similar to the OLT 1, includes an optical transceiver 2a, a clock data recovery unit 2b, and a MAC processing unit 2c of the ONT.

The optical signal received by the ONT (2) is received by the photo diode (PD) of the optical transceiver (2a) through a condenser lens (not shown), amplified through a transimpedance amplifier (TIA), and a limit amplifier (LA). It is converted into a digital signal of 0 and 1. The clock of this received digital signal corresponds to the clock of the OLT and is different in phase and speed from the local clock (ONT_clk) of the ONT.

Accordingly, the clock data recovery (CDR) 2b restores the OLT clock from the digital signal provided through the limit amplifier (LA). In the case of the downstream signal, since it is a continuous signal, clock recovery is not only easy but also accurate, so the restored clock is almost identical to the actual OLT clock.

However, the upstream signal transmitted by the MAC processing unit 2c of the ONT to the OLT 1 through the optical transmitting and receiving unit 2a is modulated using the local clock (ONT_clk) configured internally by the ONT 2, so the OLT ( There is a deviation from the clock of 1), and from the perspective of OLT (1), the clock deviation (deviation in both phase and speed) is different for each ONT (2) included in the upward burst signal, increasing the difficulty of BCDR. do.

In the case of OLT(1), an expensive and precise oscillator is configured to generate the clock, but in the case of ONT(2), due to unit cost issues, a relatively inexpensive Temperature-Compensated XO (TCXO) is used or a Voltage-Control Temperature-Compensated XO (VCTCXO) is used. ) is used. In the case of TCXO, it compensates for changes due to temperature that affect clock speed deviation, and is configured to maintain a stable clock speed by controlling the operating voltage according to temperature based on an internal temperature sensor and a pre-prepared lookup table. The VCTCXO is what makes the internal voltage control of the TCXO possible externally, and they are inexpensive at the level of 0.1~0.2$ and 0.2~0.3$, respectively, and can provide somewhat stable clocks.

However, compared to the clock used in OLT, there is a significant deviation in the VCTCXO used in ONT, and the BCDR difficulty of OLT increases due to the clock deviation accumulated for each ONT during high-speed data transmission.

Meanwhile, as seen earlier, the restored clock restored from the CDR of ONT(2) is the same as the OLT clock, so when all ONTs(2) modulate and transmit an upward signal with the restored OLT clock(A), OLT(1) (2) By receiving an upward burst signal with no significant speed deviation, the load due to BCDR is reduced and synchronization quality is improved. As a result, the preamplifier length can be reduced, which can improve communication quality.

However, in the case of the clock (A) restored from the actual downstream signal due to the jitter generated in the reception process of the optical transceiver (2a) and the jitter generated in the CDR (2b) process, the clock speed is equal to the OLT (1) clock. However, due to noise caused by jitter, a situation occurs in which the clock rising and falling timing becomes irregular, that is, a situation in which small phase changes occur frequently.

In other words, considering a clock restoration environment in which the clock is restored by comparing and locking the received random clock while adjusting the generated clock, if the overall clock speed is slightly different, but the phase of the clock is stable (ONT local clock is used as an upward signal) If the clock speed is the same as OLT, but the phase change of the clock is severe (when a restored clock containing jitter is used as a clock for the upstream signal), clock restoration becomes much more difficult.

Therefore, it is difficult to directly use the restored clock restored by the CDR 2b of the ONT 2 for upstream signal transmission.

In the present invention, instead of directly using a restored clock that contains jitter and is difficult to use as an upstream signal, the local clock provided by the VCTCXO configured in the ONT is controlled based on the restored clock to transmit a stable upstream signal at the same level as the OLT clock. By generating a clock, the BCDR performance of OLT is improved, and through this, communication quality can be improved.

Figure 5 is a configuration diagram showing the configuration of an ONT including a transmission clock generator of a recovered clock-based passive optical communication terminal 100 according to an embodiment of the present invention.

As shown, the passive optical communication terminal 100 includes an optical transmitting and receiving unit 110 including an optical receiving unit 111 that receives a downward signal from the OLT and an optical transmitting unit 112 that transmits an upstream signal to the OLT, and an optical receiving unit. It uses a clock data recovery (CDR) 120 that restores the clock and data from the digital signal provided by (111), and a VCTCXO that outputs a local clock but can control the speed of the output clock with a voltage. The local clock generator 150 converts the restored data into parallel data, converts the data to be transmitted into serial data, and then uses the clock of the local clock generator 150 as an upward signal transmission clock to convert serial data. It includes a MAC processing unit 130 that provides modulation to the optical transmitter 112.

As discussed above, the optical receiver 111 includes a photo diode (PD) that converts the received optical signal into an electrical signal, a transimpedance amplifier (ITA) that converts the electrically converted signal into a voltage and amplifies it, and an amplified It includes a limit amplifier (LA) that divides the voltage into 0 and 1.

The optical transmitter 110 includes a laser diode driver (LDD) that drives a laser diode according to a signal provided from the MAC processing unit 130, and a laser diode (LD) that outputs an optical signal according to the driving of the laser diode driver (LDD). Includes.

Of course, the optical transceiver 110 may include a plurality of optical systems for receiving and outputting optical signals, but these are omitted in the illustrated example.

The embodiment of the present invention utilizes the fact that although the restored clock restored through the clock data recovery unit 120 includes jitter, its clock speed is the same as the OLT clock. In particular, a counter is utilized to generate an accurate upstream signal clock based on the recovery clock even with a simple hardware configuration and low load.

As shown, in the embodiment of the present invention, the transmission clock generator 140 is configured to control the local clock generator 150 so that its output clock is as similar as possible to the restored clock.

The transmission clock generator 140 counts the restored clock restored by the clock data restoration unit 120 and the local clock output from the local clock generator 150 for each preset period, and calculates the counting deviation of the local clock based on the restored clock. After checking, a control voltage is provided to the local clock generator 150 to reduce the corresponding counting deviation.

The MAC (Media Access Control) processor 130 uses the clock of the local clock generator 150, which is corrected under the control of the transmission clock generator 140, as a clock for uplink signal transmission.

The transmission clock generator 140 preferably sets the counting period so that the deviation between the respective counting values of the restored clock and the local clock does not exceed 1, and more preferably sets the number of clocks corresponding to the unit frame section of passive optical communication. It can be used as a counting cycle.

For example, in the case of 10Gbps PON, the number of clocks generated during 125㎲, the length of one frame, can be used as the standard period. In the case of 10Gbps PON, it actually operates at a transmission speed of 9.95328Gbps and transmits 155,520 bytes of signals during 125㎲, so when converted to bits, the number of clocks generated during 125㎲ is 1,244,160.

Therefore, while at least 1,244,160 clocks are transmitted, the occurrence of ±1 clock error is continuously monitored, and if ±1 clock error occurs, a control voltage to reduce the error is generated and sent to the local clock generator 150. Provides control voltage.

In the case of a typical VCTCXO, an error of several tens per second may occur, and since 8000 frames are transmitted per second at a clock speed of 10Gbps, the counting error when transmitting one frame does not exceed ±1, and typically ranges from tens to hundreds. After counting and comparing frames, it reaches a level where ±1 error can be confirmed.

Ultimately, in the case of the present invention, it is possible to provide a clock for upstream signal transmission that is almost identical to the OLT clock at a level that controls the occurrence of one clock error for tens to hundreds of frames through the local clock 150 composed of a VCTCXO.

The transmission clock generator 140 counts the restored clock restored by the clock data restorer 120 and the local clock output by the local clock generator 150, and the restored clock counting value is set at a preset period (for example, 10 Gbps). In communication, when the number of clocks (e.g., 1,244,160 in 10Gbps communication) is equal to 125㎲, that is, the period in which the counting number of the restored clock is 1,244,160, the deviation of the local clock counting value based on the corresponding restored clock counting value is the clock deviation value. It includes a counter unit 141 that provides and resets counting values, and a clock control unit 142 that provides a control voltage calculated based on the clock deviation value provided by the counter unit 141 to the local clock generator 150. can do.

Figure 6 is a conceptual diagram for explaining the operation method of the transmission clock generation devices 120, 130, 140, and 150 according to an embodiment of the present invention. As shown, there is no deviation from the restored clock (a) depending on the situation. An example of the counting results of the local clocks (b, c, d) that are not generated or generated and the situational counter unit 141 and the control signal generation of the clock control unit 142 at this time is shown.

In the case of the restored clock (CDR_clk), it contains noise whose phase changes due to jitter, but since the speed of the restored clock matches the speed of the OLT, when counting this in the counter unit 141, 1 frame (125) based on 10Gbps speed The number of clocks in ㎲ is 1,244,160.

Therefore, by counting only the number of clocks, ignoring the phase of the corresponding restored clock, if the counting value reaches 1,244,160, it becomes the period of one frame. At this time, the counting value of the local clock (ONT_clk) of the ONT counted during the same counting start and end period as the restored clock maintains the same 1,244,160 with no deviation from the restored clock for a considerable period of time.

Basically, in the case of the local clock (ONT_clk), the clock is generated based on VCTCXO, so the temperature deviation is compensated to provide a relatively accurate clock. However, as the usage time increases, when compared to the accurate clock, a small error accumulates, resulting in different ONTs. Clock deviation occurs.

The clock of the ONT (100) based on 10Gbps outputs a clock of 19.44MHz, and this is used to generate the ONT clock of 9.95328GHz. However, if the usage time is long, an error of several to tens of Hz may occur, and this is multiplied. The deviation of the ONT clock increases.

Therefore, in the present invention, according to the characteristics of the VCTCXO, a cycle in which a clock error of one or less is likely to occur is set, and the deviation between the counting values of the restored clock and the local clock during the cycle is checked to determine that ±1 clock error is the counting difference. That is, when the clock deviation value is confirmed, the VCTCXO of the local clock generator 150 is immediately controlled to correct the clock error, so that even if the usage period is accumulated, the local clock is restored to the clock within ±1 clock error during one cycle. You can synchronize.

As shown in the example, when the speed of the local clock slows down as shown in FIG. 6c at a speed of 10 Gbps and the counting value for one frame is 1,255,159, that is, a clock deviation value of -1 is confirmed, the clock control unit 142 is a local clock generator. For example, by providing a control voltage of +0.1V (increasing the current control voltage by 0.1V) to 150, the clock speed of the local clock generator 150 can be increased to reduce the corresponding deviation.

If the control speeds up the local clock as shown in FIG. 6D and the counting value for one frame is 1,255,161, that is, a clock deviation value of +1 is confirmed, the clock control unit 142 operates the local clock generator 150. For example, by providing a control voltage of -0.1V (lowering the current control voltage by 0.1V), the clock speed of the local clock generator 150 can be reduced to reduce the corresponding deviation.

In this way, if the local clock according to the ONT local clock generator 150 is controlled to be the same as the OLT clock for each preset period, and the local clock is used as a clock for uplink signal modulation, the BCDR performance of the OLT that received it is greatly improved. It can be improved. In other words, the BCDR of the OLT has the same clock speed as the OLT clock being compared, and the ONT signal with a clock deviation of less than 1 per frame only needs to be synchronized by checking the phase difference according to the distance, so the load and recovery time for the BCDR are reduced. and the quality of the restored clock can be improved, resulting in improved communication quality.

Figure 7 is an exemplary diagram showing the control process of the transmission clock generation device according to an embodiment of the present invention. The left side shows the counting value of the local clock for one cycle, and the right side shows the control voltage deviation of the local clock generator 150 of the clock control unit when the counting value differs by 1 from the reference, and the curve shows the ONT local clock ( ONT_clk) showed a change.

The dotted line shows the measurement section, but in reality, it does not change drastically from cycle to cycle and maintains the same counting value as the restoration clock for a considerable period, and the example shown shows an extreme case by exaggerating this.

Even in such extreme cases, the ONT local clock maintains a clock deviation of ±1 level per frame cycle.

Of course, if deviations in the clock counting value frequently occur due to the control of the clock control unit 142, the control amount can be reduced. This is controlled in a way to suppress the occurrence of deviations as much as possible through various known control methods (controlling the trend of occurrence of deviations). By reflecting the variable control with a more detailed control voltage, the clock of the local clock generator 150 can be maintained similar to the clock of the OLT.

Nevertheless, in the case of the present invention described above with reference to FIG. 5, as errors accumulate, the ONT local clock inevitably has an error of ±1 clock compared to the restored clock.

8 and 9, the present invention further provides another embodiment of a transmission clock generation device for a passive optical communication terminal based on a restored clock that does not generate an error of ±1 clock.

Figure 8 is a configuration diagram showing the configuration of an ONT 100' including a recovery clock-based passive optical communication terminal transmission clock generation device according to another embodiment of the present invention.

As shown, the basic components of the configuration diagram previously seen in FIG. 5, which are the optical transceiver 110, clock data recovery unit 120, and MAC processing unit 130, are all used as is.

However, the tracking local clock generator 160 is applied in addition to the existing local clock generator 150', and the transmission clock generator 140' operates based on the corresponding tracking local clock generator 160. change

The tracking local clock generator 160 has the same configuration as the local clock generator 150' and operates separately from the local clock generator 150' to output a tracking local clock.

Such VCTCXO-based local clock generators (150', 160) are relatively inexpensive, costing about $0.2~0.3, so adding one more unit will make a small difference in the total ONT (100') unit price.

In the illustrated embodiment, the tracking local clock generator 160 is controlled based on an error of ±1 clock compared to the restored clock, but the local clock generator 160, which is actually used as a clock for the transmission signal, is controlled by the tracking local clock. By controlling the generator 160 with a smaller control amount (for example, half) than the control amount that controls the local clock generator 160, the output clock of the local clock generator 160 can be maintained with an error of less than ±1 from the restored clock.

To this end, the transmission clock generator 140' compensates for the operating deviation of the local clock generator 150' and the tracking local clock generator 160 to synchronize their clock speeds, and the clock data recovery unit 120 The recovered clock and the tracking local clock generated by the tracking local clock generator 160 are counted for each preset period (e.g., one frame length/number of clocks), and the counting deviation of the tracking local clock is checked based on the restored clock. Then, the tracking local clock generator 160 is controlled to reduce the corresponding counting deviation, and the local clock generator 150' is controlled with a control amount less than the deviation reduction control amount of the tracking local clock generator 160.

Looking at this further, the transmission clock generator 140' generates a local clock for synchronizing the local clock and the tracking local clock based on the clock deviation information of the local clock generator 150' and the tracking local clock generator 160. The cycle (restored clock and tracking local clock) for the synchronization unit 143 that generates deviation compensation information, the restored clock restored by the clock data recovery unit 120, and the tracking local clock output by the tracking local clock generator 160 A counter unit 141' that provides the counting value deviation for each period (for example, the time of one frame or the number of clocks during that time) as a clock deviation value in which the deviation of each counted value does not exceed 1, and the counter unit ( The first control voltage calculated to reduce the clock deviation value provided by 141') is provided to the tracking local clock generator 160, and based on the first control voltage and the local clock deviation correction information of the synchronization unit 143. It includes a clock control unit 142' that provides the local clock generator 150' with a second control voltage to control the local clock generator 150' to half the control amount to reduce the clock deviation of the tracking local clock generator 160.

In the above embodiment, the clock control unit 142' is configured to control the tracking local clock generator 160 and the local clock generator 150' at the same time, but the tracking local clock generator 160 and the local clock generator The control for synchronization between the units 150' (control according to local clock deviation compensation information) may be performed by the synchronization unit 143 separately from the control for synchronization of the restored clock and the tracking local clock of the clock control unit 142'. there is.

Meanwhile, the counter unit 141' can use the number of clocks corresponding to the unit frame section of passive optical communication (for example, 1,244,160 in the case of 10G PON) as a counting cycle, and counts the restored clock and the tracking local clock respectively, Whenever the counting value of the restored clock becomes a value corresponding to the number of clocks required for unit frame transmission, the deviation of the tracking local clock counting value is calculated based on this and provided as a clock deviation value (one of -1, 0, or 1). Counting values can be reset.

The MAC (Media Access Control) processor 130 uses the clock of the local clock generator 150', which has been corrected under the control of the transmission clock generator 140', as a clock for upstream signal transmission, as shown in FIG. 5. An upstream signal modulated with a clock closer to the OLT clock than the example configuration can be transmitted, and the OLT's BCDR load and performance can be further improved.

Figure 9 is an exemplary diagram showing the control process of the transmission clock generating device 140' according to another embodiment of the present invention shown in Figure 8.

As shown, on the left is the counting value of the tracking local clock (fONT_clk) for one cycle, and on the right is the tracking local clock generator 160 of the clock control unit 142' when the counting value differs by 1 from the reference. It shows the control voltage deviation, and the solid curve shows the change in the tracking local clock (fONT_clk).

The vertical dotted line shows the measurement section, but in reality, it does not change drastically from cycle to cycle and maintains the same counting value as the restored clock for a considerable period, and the example shown shows an extreme case by exaggerating this.

Even in such extreme cases, the tracking local clock maintains a clock deviation of ±1 level per frame period.

Meanwhile, the clock control unit 142' provides the tracking local clock generator 160 with a first control voltage calculated to reduce the clock deviation value, and accordingly, the tracking local clock has an error of ±1 or less as shown in the solid line. It follows the restoration clock in the range. Rather than using this tracking local clock (fONT_clk) as an actual upstream signal clock, the local clock generator 150' synchronized with the tracking local clock generator 160 is used to control the amount less than the control amount of the tracking local clock generator 160. By controlling the local clock generator 150' by generating a second control voltage for controlling the size of the control amount (half the level in the illustrated embodiment), a local clock (ONT_clk) such as the dotted line curve can be generated. there is. Since the local clock is controlled with a control amount that is about half of the control amount that controls the tracking local clock generator 160 to follow the restored clock, the deviation between the local clock and the restored clock can be maintained within an error range of less than ±1. .

In the illustrated example, since the speed of the tracking local clock generator 160 is controlled at ±0.1V, the local clock generator 150' is controlled at ±0.05V to reflect the error occurrence state of the tracking local clock, thereby providing better recovery. It is possible to generate a clock for upward signal modulation that matches the clock.

In this way, by using a simple counter in composition, it is possible to easily identify and compensate for the deviation of the local clock in which the deviation from the restored clock is accumulated, and by limiting this compensation cycle to the level of one clock, the speed is similar to that of the restored clock. Since a clock for an upstream signal with a stable phase can be generated, communication quality can be improved by improving the BCDR performance of OLT. In addition, another relatively inexpensive local clock generator is configured for tracking and is used to perform control to reduce the deviation from the restored clock. However, the local clock generator that will actually be used as the clock for the upstream signal is larger than the local clock generator for tracking. By controlling with a small amount of control, the clock deviation can be less than 1 clock, providing a more stable clock for uplink signals, thereby further improving communication quality. In other words, an error of less than 1 clock can have the effect of significantly improving BCDR performance because it actually controls the OLT clock and ONT clock deviation level to the phase error level.

Furthermore, some or all of the clock data recovery unit 120 and the transmission clock generation units 140 and 140' shown in FIGS. 5 and 8 may be configured inside the MAC processing unit 130.

Meanwhile, since the local clock (ONT_clk) provided by the ONT local clock generator 150' is synchronized with the OLT clock (recovery clock) included in the downstream signal within one clock error, even if only the local clock (ONT_clk) is used, Signal processing or data processing synchronized with the clock of the OLT is possible, and the MAC processing unit 130 uses the local clock (ONT_clk) as a clock for upstream signal transmission, in addition to improving the BCDR performance of the OLT, the local clock (ONT_clk) ONT_clk) can be used in situations that require time and clock synchronization between various long-distance communication devices.

For example, when an OLT failure occurs and the working OLT is replaced with a standby OLT to provide redundancy (generally Type B protection in PON), upper layer communication that transmits Ethernet frames using PON is continued until the PON network is stabilized. Data communication is interrupted, and in this case, the time synchronization process for maintaining the Ethernet communication session is also interrupted and the local ONT clock is used. Since the normal local ONT clock has a deviation from the OLT clock, time synchronization for Ethernet communication is interrupted. During this period, it was often difficult to apply to an environment requiring a high-precision clock due to the deviation of the local ONT clock. However, as in the present invention, when the local ONT clock is quickly synchronized with the clock of the OLT included in the downstream signal, the working OLT can Even in a situation where the standby OLT is switched to the standby OLT and transmits a downstream signal to reconfigure the PON network, continuous synchronization with the OLT clock is achieved, so the MAC processing unit 130 performs a separate time synchronization procedure or time synchronization required for upper layer communication. By simply using the local ONT clock without transmitting or receiving data, a high-precision clock can be maintained stably during the failure recovery period. In particular, this continuous high-quality clock provision has the advantage of being applicable even to situations that are sensitive to the clock environment, such as 6G.

In addition, even when using lightweight IoT encrypted communication that utilizes the unique distance characteristics of a specific remote terminal according to the communication time difference with the remote terminal, the MAC processing unit 130 does not need to configure time information exchange in the upper layer for separate time synchronization. The local ONT clock synchronized with the OLT clock can be used to measure precise communication time differences, making it possible to use lightweight encrypted communication in a simplified manner.

In addition, even in situations where it is necessary to check accurate time information or ground zero (every second), the MAC processing unit 130 can simply utilize the local ONT clock without separate synchronization configuration.

In the end, by controlling the inexpensive local ONT clock generator through rapid clock count comparison based on the clock counter, the local ONT clock generator provides a jitter-free OLT clock, which not only improves the quality of the communication network but also enables it to be used for various upper layer communications. It has the effect of providing additional functions as well.

Anyone skilled in the art to which the present invention pertains can make modifications and changes to the above-described content without departing from the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention, but are for illustrative purposes, 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 interpreted in accordance with the claims below, and all technical ideas within the equivalent scope should be construed as being included in the scope of rights of the present invention.

Furthermore, the transmission clock generation device of the passive optical communication terminal may be implemented with hardware components, software components, and/or a combination of hardware components and software components.

Additionally, components described in the embodiments include, for example, a processor, a controller, an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable gate array (FPGA), and a programmable logic unit (PLU). It may be implemented using one or more general-purpose or special-purpose computers, such as a logic unit, microprocessor, or any other device capable of executing and responding to instructions.

Software may include a computer program, code, instructions, or a combination of one or more of these, and may independently or collectively instruct the delay detection device to operate as desired. can do.

The various devices and components described herein may be implemented by optical elements, sensing elements, hardware circuits (e.g., semiconductor-based logic circuits), firmware, software, or a combination thereof. For example, it can be implemented using transistors, logic gates, and electronic circuits in the form of various electrical structures, and lenses and filters in the form of optical structures.

100: ONT 110: Optical transmitting and receiving unit
111: Father Gwangsu 112: Father Gwangsong
120: clock data recovery unit 130: MAC processing unit
140, 140': Transmission clock generation unit 141, 141': Counter unit
142, 142': clock control unit 143: synchronization unit
150, 150': local clock generator 160: tracking local clock generator

Claims (10)

A transmission clock generator configured in a passive optical communication terminal that receives a downstream signal from the OLT and transmits an upstream signal to the OLT,
a clock data recovery unit that receives an electrical signal according to the received optical signal and restores clock and data;
a local clock generator that outputs a local clock and can control the speed of the output clock with a voltage;
a tracking local clock generator that has the same configuration as the local clock generator and operates separately from the local clock generator to output a tracking local clock;
The clock speeds of the local clock generator and the tracking local clock generator are compensated for to synchronize their clock speeds, and the restored clock restored by the clock data recovery unit and the tracking local clock generated by the tracking local clock generator are preliminarily combined. After counting for each set period and checking the counting deviation of the tracking local clock based on the restored clock, the tracking local clock generator is controlled to reduce the counting deviation, and the local clock generator is controlled with a control amount less than the deviation reduction control amount of the tracking local clock generator. a transmission clock generator that controls the clock generator;
A transmission clock generator for a passive optical communication terminal based on a restored clock, including a MAC processing unit that uses the clock of the local clock generator corrected under the control of the transmission clock generator as a clock for uplink signal transmission.
The method according to claim 1, wherein the transmission clock generator includes a synchronization unit that generates local clock deviation compensation information for synchronizing the local clock and the tracking local clock based on clock deviation information of the local clock generator and the tracking local clock generator. ;
a counter unit that provides the preset counting value deviation for each period with respect to the restored clock restored by the clock data recovery unit and the tracking local clock output by the tracking local clock generator as a clock deviation value;
A first control voltage calculated to reduce the clock deviation value provided by the counter unit is provided to the tracking local clock generator, and the tracking local clock is generated based on the first control voltage and the local clock deviation correction information of the synchronization unit. A transmission clock generator for a passive optical communication terminal based on a restored clock, comprising a clock control unit that provides the local clock generator with a second control voltage to control the local clock generator to half the control amount controlled to reduce the clock deviation of the generator.
The apparatus of claim 2, wherein the counter unit sets a counting period so that a deviation between the values counted for the restored clock and the tracking local clock does not exceed 1.
The method according to claim 2, wherein the counter unit uses the number of clocks corresponding to the unit frame section of passive optical communication as a counting cycle, counts the restored clock and the tracking local clock respectively, and the counting value of the restored clock is required for unit frame transmission. A transmission clock generator for a passive optical communication terminal based on a restored clock, which counts the deviation of the tracking local clock counting value based on this whenever it becomes a value corresponding to the clock number, provides it as a clock deviation value, and resets the counting values. .
A transmission clock generation method of a transmission clock generator configured in a passive optical communication terminal that receives a downward signal from the OLT and transmits an upward signal to the OLT, comprising:
A clock data recovery unit recovering clock and data from an electrical signal according to a received optical signal;
A local clock generator capable of controlling the speed of the output clock with a voltage outputs a local clock;
outputting a tracking local clock by a tracking local clock generator that has the same configuration as the local clock generator and operates separately from the local clock generator;
The transmission clock generator compensates for the operation deviation of the local clock generator and the tracking local clock generator to synchronize their clock speeds, and the restored clock restored by the clock data recovery unit and the tracking signal generated by the tracking local clock generator After counting the local clock at a preset period and checking the counting deviation of the tracking local clock based on the restored clock, the tracking local clock generator is controlled to reduce the counting deviation, and the tracking local clock generator is controlled to be less than the deviation reduction control amount of the tracking local clock generator. controlling the local clock generator with a control amount;
A method of generating a transmission clock for a passive optical communication terminal based on a restored clock, comprising the step of a MAC processing unit using the clock of the local clock generator corrected under the control of the transmission clock generator as a clock for uplink signal transmission. delete delete delete delete delete

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