WO2017216841A1 - Optical communication module - Google Patents

Abstract

An optical communication module uses a direct modulation laser diode for generating an optical signal from an electrical signal, and comprises a laser diode driver circuit to which an N-value multivalued signal is inputted and which supplies a current to the direct modulation laser diode. The laser diode driver circuit is provided with: a ringing compensation circuit which comprises a means for generating a ringing compensation waveform having constant duration and amplitude after data switching of the N-value multivalued signal, and subtracting the ringing compensation waveform from the N-value multivalued signal; and an output circuit which uses, as an input, a voltage signal outputted by the ringing compensation circuit and supplies, to a laser diode, a modulated current signal obtained by converting the voltage signal to a current signal, and a bias current. Consequently, the optical communication module which converts the optical signal and the electrical signal into each other by pulse amplitude modulation using the direct modulation laser diode and a photodiode makes it possible to support high-speed transmission at low cost and improve communication quality.

Description

Optical communication module

The present invention relates to an optical communication module, and is a communication device that mutually converts an optical signal and an electric signal by pulse amplitude modulation using a direct modulation laser diode and a photodiode, and is compatible with high-speed transmission at low cost. The present invention relates to an optical communication module suitable for improving quality.

In recent years, with an increase in communication speed between data processing apparatuses, the communication speed has changed from 10 Gbps to 25 Gbps, 50 Gbps, and the like. With such an increase in communication speed, for example, application of an optical communication device compatible with an optical fiber cable is progressing as a server device or a router device in a data center. An optical communication device is usually premised on long-distance transmission such as a kilometer order between devices, and it is important to ensure high speed and reliability associated with this transmission distance.

Among such optical communication devices, there are many devices having a relatively large size (for example, on the order of several tens of centimeters or metric order), but communication using electric signals is usually performed inside the devices. Has been done. That is, the optical communication device converts an optical signal input from the outside into an electrical signal, performs a predetermined process while performing short-distance communication (for example, metric order) inside the device using this electrical signal, and then again performs the electrical signal. Is converted into an optical signal and output to the outside. In this short-distance communication, for example, communication using an electrical signal using a copper wire cable or the like is performed. However, as the communication speed increases, the transmission waveform quality of the copper wire cable significantly decreases. For this reason, in addition to inter-device transmission, it has been required to apply optical communication to short-range communication inside such a device. In this case, in the optical communication, all internal signal processing of the router or the like is performed by an electrical signal, and therefore it is necessary to convert the electrical signal into an optical signal by an optical element. For this reason, in the transition from copper cable to optical fiber cable, telecommunications is composed of parts that are relatively inexpensive and highly reliable compared to optical communication. Low power, low cost, and improved reliability are important.

However, as the communication speed increases, the intersymbol interference caused by the insufficient bandwidth of the laser diode LD degrades the optical transmission waveform, making it difficult to achieve a communication speed exceeding 50 Gbps, for example. As a means to improve the intersymbol interference of the optical transmission waveform, it is conceivable to improve the operating band of the laser diode LD. Since the failure rate is higher than that of the device and the cost is increased, the transition from telecommunications to optical communication in short-distance communication is hindered. For this reason, instead of using a laser diode LD capable of higher speed operation, it is possible to compensate for the shortage of the band of the laser diode LD by using waveform equalization by an electric circuit, thereby reducing the cost and high reliability of the photoelectric conversion unit. It is effective in terms of conversion.

Furthermore, it is promising to use pulse amplitude modulation (PAM) instead of conventional binary transmission (NRZ: Non-Return-to-Zero) as a means of improving the communication speed without increasing the symbol rate. For example, in the IEEE 802.3 committee, with regard to the specifications of the optical interface of a 400-Gigabit Ethernet optical transceiver, a modulation scheme of 50 Gbps, 4-level pulse amplitude modulation (PAM4) is available in the categories of transmission distances of 2 km and 10 km. It has been adopted. In this modulation system, a 2-bit signal is transmitted in one stage with four signal amplitudes (level 0 “00”, level 1 “01”, level 2 “10”, level 3 “11”). The frequency band required for the communication speed is 1/2. For this reason, it is possible to improve the communication speed without using a laser diode LD capable of higher speed operation.

For example, Patent Document 1 discloses a technique for compensating for deterioration in transmission quality caused by a shortage of the band of the laser diode LD. Patent Document 1 describes a laser diode driver circuit provided with an asymmetric pre-emphasis circuit for improving the operating band of a laser diode in a high-speed optical transmission circuit. Specifically, a pre-emphasis circuit including a delay circuit and a duty ratio adjustment circuit is shown. As a result, it is possible to compensate for the high-speed driving of the laser diode and the degradation (rise and fall asymmetry) of the optical signal transmission characteristics.

On the other hand, factors that degrade the optical transmission waveform include ringing in the optical transmission waveform due to the influence of the relaxation oscillation frequency of the laser diode LD in addition to the intersymbol interference caused by the insufficient bandwidth of the laser diode LD. Deteriorating transmission characteristics. Ringing refers to a state in which the response becomes oscillating when the signal changes stepwise.

Hereinafter, the relationship between the relaxation oscillation frequency and the ringing in the laser diode LD will be described with reference to FIGS. 19 and 20.
FIG. 19 is a graph showing the relationship between the input frequency and the optical output power in the laser diode LD.
FIG. 20 is a diagram for explaining that ringing occurs at the rise and fall of the step response waveform.
As shown in FIG. 19, the laser diode LD has different optical output powers output in the vicinity of the relaxation oscillation frequencies (fr_L, fr_M, fr_H) depending on the bias current. Here, relaxation oscillation is a phenomenon in which optical output oscillates when a pulsed current is injected into a semiconductor laser, and the frequency at that time is called relaxation oscillation frequency. The value of the relaxation oscillation frequency is determined by the device structure of the laser diode LD, and the response characteristic rapidly decreases above this frequency. Therefore, the upper limit frequency at which the laser diode LD can operate is determined based on this relaxation oscillation frequency. At the communication speed exceeding 50 Gbps, the peak gain positions (fr_L, fr_M, fr_H) generated by the relaxation oscillation frequency are lower than the basic frequency of the communication speed. In the optical output waveform of the laser diode LD, ringing due to overshoot occurs at the rising edge, while ringing due to undershoot occurs at the falling edge, and transmission quality deteriorates.

Furthermore, in N-value PAM transmission, the eye amplitude (the amplitude in the eye waveform, which will be described later) is 1 / N compared to NRZ transmission. It is necessary to increase the amplitude of the modulation current to be supplied. Therefore, the influence of ringing becomes larger than that for NRZ transmission. Further, since the value of the relaxation oscillation frequency increases as the bias current supplied to the laser diode LD increases, for example, when applied to PAM4 transmission, at the time of data transition from level 0 to level 3 at the rise, at the fall Is the ringing amount at the time of data transition from level 3 to level 0.

Thus, in PAM4 transmission, the amount of ringing generated by the laser diode LD differs for each amplitude level. Therefore, when compensation for ringing is attempted using a waveform equalization technique of an electric circuit, etc. On the other hand, it is necessary to change the optimum compensation amount. Furthermore, the rise time and fall time are degraded due to insufficient bandwidth of the laser diode LD, and the transition time is delayed until the steady state of each amplitude level is reached. The transmission quality is deteriorated. Further, as described above, since the relaxation oscillation frequency changes depending on the bias current, the deterioration of the fall time becomes larger than the rise time, and there arises a problem that the response characteristics of the rise and fall become asymmetric. .

JP 2012-43933 A

The laser diode driver circuit LDD described in Patent Document 1 emphasizes rising and falling in advance (pre-emphasis) as means for compensating for transmission quality degradation caused by insufficient bandwidth of the laser diode LD. This will improve the lack of bandwidth.

Hereinafter, the configuration and operation of the laser diode driver circuit LDD described in Patent Document 1 will be briefly described with reference to FIGS. 21 and 22.
FIG. 21 is a configuration diagram of a laser diode driver circuit LDD described in Patent Document 1. The symbols are changed for convenience of explanation.
FIG. 22 is a diagram showing step response waveforms of the rising and falling laser diode driver circuits of Patent Document 1. In FIG.

The configuration of the laser diode driver circuit LDD described in Patent Document 1 includes a laser characteristic compensation circuit LD_EQ and an output circuit Drv as shown in FIG.

The laser characteristic compensation circuit LD_EQ includes a delay circuit DEL, a duty ratio adjustment circuit DUTYAdj, a pre-buffer circuit PrBufm, a pre-buffer circuit PrBufe, and an addition / subtraction circuit ADD.

The input voltage signal of the laser diode driver circuit LDD is branched into the pre-buffer circuit PrBufm and the delay circuit DEL, respectively. The voltage signal branched into the delay circuit DEL is the voltage signal branched into the pre-buffer circuit PrBufm. Is output with a certain delay difference. The voltage signal having this delay difference is subtracted by the addition / subtraction circuit ADD from the other voltage signal having no delay difference, so that a voltage signal having a large rising and falling enhancement amount as shown in FIG. 22 is obtained. Generated. In addition, the duty ratio is adjusted by the duty ratio adjustment circuit DUTYAdj so that the period of the “H” level becomes longer, and it is possible to generate a voltage signal that has a larger amount of fall emphasis (asymmetric pre-emphasis) than the rise. is there. The voltage signal emphasized at the rise and fall is converted into a current signal by the output circuit Drv, and the current signal having the asymmetric pre-emphasis characteristic is driven to drive the laser diode LD, so that the band of the laser diode LD is insufficient. In addition, an optical signal having a uniform rise time and fall time can be output.

However, the following problems occur in the above-described conventional technology. Applying the prior art asymmetric pre-emphasis improves the rise time and fall time, while the influence of the relaxation oscillation frequency of the laser diode LD also emphasizes the effects of overshoot and undershoot after data transition. As a result, the ringing characteristics become larger, and the eye opening (pattern for evaluating the waveform quality of the eye waveform, which will be described later) is reduced. Furthermore, in the prior art, the characteristics of the laser diode LD are compensated with a certain amount of enhancement at the rise and fall, so when applied to PAM transmission, after the data transition of each amplitude level caused by the bias current dependence of the relaxation oscillation frequency. There also arises a problem that variations in the amount of ringing that occurs cannot be compensated.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an optical communication module that mutually converts an optical signal and an electrical signal by pulse amplitude modulation using a direct modulation laser diode and a photodiode. An object of the present invention is to provide an optical communication module that supports high-speed transmission at low cost and improves communication quality.

The configuration of the optical communication module for solving the above-described problem is that an optical signal and an electric signal are expressed by an N-value multilevel signal (N is a positive integer) that is pulse-amplitude modulated so as to transmit N-bit information per symbol. Communication module using a direct-modulation laser diode that mutually converts signals and generates an optical signal from an electrical signal, and inputs an N-value multilevel signal and supplies a current to the direct-modulation laser diode The laser diode driver circuit has means for generating a ringing compensation waveform having a fixed time width and amplitude after data switching of the N-level multilevel signal and subtracting the ringing compensation waveform from the N-level multilevel signal. The voltage signal of the ringing compensation circuit having the ringing compensation circuit output and the voltage signal of the ringing compensation circuit output is converted into a current signal in the laser diode. In which an output circuit for supplying a regulated current signal and the bias current.

This configuration makes it possible to compensate for the band degradation peculiar to the laser diode LD characteristics, the influence of ringing due to relaxation oscillation, and the asymmetry of the rise and fall, and uses a directly modulated laser diode that is advantageous for low cost and downsizing. Thus, highly reliable high-speed communication by pulse amplitude modulation becomes possible.

According to the present invention, in an optical communication module that mutually converts an optical signal and an electrical signal by pulse amplitude modulation using a direct modulation laser diode and a photodiode, the optical communication module that supports high-speed transmission at low cost and improves communication quality. A communication module can be provided.

It is a block diagram which shows schematic structure of the optical communication module OMD. It is a figure which shows the eye waveform of the PAM4 signal of laser diode LD output. It is a block diagram of a laser diode driver circuit LDD, an encoding logic circuit ENC_BK, and a laser diode LD. It is a detailed block diagram of the ringing compensation circuit LD_RING_COMP. It is a timing chart explaining operation | movement of the ringing compensation circuit LD_RING_COMP. It is a figure which shows the improvement of the step response waveform in the rise and fall by the ringing compensation effect. It is a detailed block diagram of the transition time adjustment circuit TRAN_ADJ_CNT of the encoding logic circuit ENC_BK. It is a figure which shows the improvement of the step response waveform of the rise at the time of PAM4 transmission by adjustment of the transition time adjustment circuit TRAN_ADJ_CNT, and a fall. It is a detailed block diagram of the pre-data transition LD compensation circuit PRE_TRAN_LD_EQ of the encoding logic circuit ENC_BK. 6 is a timing chart for explaining the operation of the pre-data transition LD compensation circuit PRE_TRAN_LD_EQ. FIG. 6 is a diagram showing an eye waveform of a PAM4 signal of LD output, comparing the case where the laser diode driver circuit LDD including the encoding logic circuit ENC_BK and the ringing compensation circuit LD_RING_COMP of the first embodiment is not used with the case where it is used. is there. It is a graph which shows the relationship between the input frequency and optical output power in laser diode LD which shows the waveform degradation by a hole burning effect. It is a figure explaining the waveform degradation by the hole burning effect generate | occur | produces in the optical output waveform of laser diode LD. It is a block diagram of the laser diode driver circuit LDD for compensating the hole burning effect. FIG. 14B is a circuit diagram of the laser diode driver circuit LDD shown in FIG. 14A. FIG. 2 is a configuration diagram including a laser diode temperature compensation control circuit LD_TEMP_CNT in the transmission system (electrical → optical conversion) of the optical communication module shown in FIG. 1. 14B is a configuration diagram including a laser diode temperature compensation control circuit LD_TEMP_CNT in the laser diode driver circuit LDD for compensating the hole burning effect of FIG. 14A. FIG. FIG. 2 is a configuration diagram in which a hole burning compensation circuit is incorporated in a transimpedance amplifier circuit TIA in the receiving system (light → electrical conversion) of the optical communication module shown in FIG. 1. FIG. 5 is a configuration diagram in which a receiver laser diode temperature compensation control circuit LD_TEMP_CNT_Rx for performing temperature compensation of a laser diode LD is incorporated in a configuration in which a hole burning compensation circuit is incorporated in a transimpedance amplifier circuit TIA. It is a graph which shows the relationship between the input frequency and optical output power in laser diode LD. It is a figure explaining that ringing occurs at the rise and fall of the step response waveform. 2 is a configuration diagram of a laser diode driver circuit LDD described in Patent Document 1. FIG. It is a figure which shows the step response waveform of the rising and falling laser diode driver circuit of patent document 1. FIG.

Hereinafter, each embodiment according to the present invention will be described with reference to FIGS. 1 to 18.

In the following embodiments, description will be made using quaternary pulse amplitude modulation (PAM4) that transmits information of 2 bits per symbol as an example of pulse amplitude modulation. However, the present invention may be applied to other multi-value numbers such as 8-value and 16-value.

The circuit elements constituting each functional block of the embodiment are not particularly limited, but are formed on a semiconductor substrate such as single crystal silicon by an integrated circuit technology such as a CMOS (complementary MOS transistor) or a bipolar transistor. The In the embodiment, a MOSFET (Metal / Oxide / Semiconductor / Field / Effect / Transistor: MOS transistor) or a bipolar transistor is used, but a non-oxide film is not excluded as a gate insulating film. The connection of the substrate potential of the transistor is not specified in the drawing, but the connection method is not particularly limited as long as the transistor can operate normally.

Embodiment 1
Hereinafter, a first embodiment according to the present invention will be described with reference to FIGS. 1 to 11.

First, a schematic configuration of the optical communication module OMD will be described with reference to FIG.
FIG. 1 is a block diagram showing a schematic configuration of the optical communication module OMD.

The optical communication module of the present embodiment is used for communication between information processing apparatuses such as servers and routers placed in a data center or the like, or between apparatuses. The information processing apparatus is constituted by a housing having a width and a depth of several tens of centimeters and a height of 1 to 2 m, for example. A large number of communication connectors are provided on the surface of the housing, and each is, for example, an Ethernet cable terminal or an optical fiber cable terminal. The boards in the information processing apparatus and the apparatuses are connected via an optical communication path (typically, an optical fiber cable) OF. In such an information processing apparatus, the length of each optical communication line OF may reach several meters, for example. In this case, if a copper wire cable or the like is used instead of the optical communication path OF, there is a possibility that it may not be able to cope with communication of several tens of Gbps level due to transmission loss. Therefore, it is beneficial to use the optical communication module of this embodiment.

As shown in FIG. 1, the optical communication module OMD includes an encoding / decoding logic circuit LOG, an analog front end block AFE, and an optical element block OBK.

The optical element block OBK includes a laser diode LD and a photodiode PD. The laser diode LD is an element that receives an electric signal (current signal) and outputs the electric signal to the transmission optical communication line OFtx. The photodiode PD is an element that converts an optical signal input from the receiving optical communication line OFrx into an electric signal (current signal). Each of the laser diode LD and the photodiode PD is composed of, for example, individual semiconductor chips. Actually, a plurality of laser diodes LD and photodiodes PD are integrated in an array in accordance with the number of communication channels. Exists as.

The analog front end block AFE includes a laser diode driver circuit LDD and a transimpedance amplifier circuit TIA. The laser diode driver circuit LDD is a circuit that drives the laser diode LD. The transimpedance amplifier circuit TIA is a circuit that amplifies the current signal from the photodiode PD and converts it into a voltage signal.
In the example shown in FIG. 1, the analog front end block AFE and the encoding / decoding logic circuit LOG are formed in one semiconductor chip LSI_OP, but the laser diode driver circuit LDD and the transimpedance amplifier circuit TIA are individually provided. It is good also as another chip | tip.

When the communication speed exceeds 50 Gbps, it is difficult to satisfy the loss budget and jitter budget required for transmission in the conventional binary (NRZ) transmission due to the band limit of the electric circuit of the optical element block and the influence of transmission loss. It has become. Therefore, in the present embodiment, in the transmission system, the encoding logic circuit ENC_BK in the LOG converts the NRZ signal into a multi-value signal that has been subjected to pulse amplitude modulation (PAM), and in the reception system, the decoding logic circuit DEC_BK in the LOG. To convert the PAM signal into an NRZ signal.

Here, the eye waveform of the PAM4 signal will be described with reference to FIG.
FIG. 2 is a diagram showing an eye waveform of a PAM4 signal output from the laser diode LD.

The eye waveform (eye pattern) is obtained by sampling a large number of signal waveform transitions and overlaying them and displaying them graphically. If a plurality of waveforms are overlapped at the same position, the waveform is of good quality.

In the PAM4 signal, a 2-bit signal is transmitted between 1 symbol with 4 levels of signal amplitude (level 0 “00”, level 1 “01”, level 2 “10”, level 3 “11”). Ensuring eye opening of eye waveforms (upper eye, middle eye, lower eye) is necessary to improve transmission quality.

The optical communication module OMD is electrically connected to a logical operation processing circuit logic device LSI_LG that performs predetermined protocol processing required in a higher layer of communication outside the optical communication module OMD, and is included in the logical operation processing circuit logic device LSI_LG. An electric voltage signal is transmitted / received to / from a transmission rate conversion circuit SDC (not shown) called SerDes (Serializer / Deserializer) or the like. For example, between the logical operation processing circuit logic device LSI_LG and the optical communication module OMD, 25 Gbps × 2 (2 channels) electrical signals are transmitted and received, and encoded / decoded into a PAM4 signal in the encoding / decoding logic circuit LOG. Communication between the boards via the optical communication lines OFtx and OFrx is performed with a PAM4 optical signal (symbol rate of 25 Gbps) of 50 Gbps × 1 channel. In the example shown in FIG. 2, the burden of electrical transmission is reduced by reducing the transmission speed around the channel between the optical communication module OMD and the logic operation processing circuit logic device LSI_LG. The front end block AFE and the encoding / decoding logic circuit LOG are integrated in the same semiconductor process, but are the analog front end block AFE and the encoding / decoding logic circuit LOG mounted as separate semiconductor chips, respectively? Alternatively, the encoding / decoding logic circuit LOG may be integrated in an LSI_LG outside the OMD.

Next, the detailed configuration and operation of each part of the optical communication module OMD will be described with reference to FIGS.
FIG. 3 is a configuration diagram of the laser diode driver circuit LDD, the encoding logic circuit ENC_BK, and the laser diode LD.

The laser diode driver circuit LDD, the encoding logic circuit ENC_BK, and the laser diode LD in FIG. 1 constitute a transmission system that receives an electrical signal from the logic operation processing circuit logic device LSI_LG and transmits an optical signal to the optical communication line OFtx. To do.

In this embodiment, the relaxation oscillation frequency of the laser diode LD on the transmission side has a value lower than the fundamental frequency of the communication speed within the amplitude range of the modulation current supplied by the laser diode driver circuit LDD. It is assumed that a laser diode LD in which ringing due to overshoot or undershoot occurs in a steady state of each amplitude level of the signal is used. The optical communication module OMD of this embodiment compensates for the influence of this ringing with an electric circuit, thereby enabling high-speed communication exceeding the operating band of the laser diode LD without requiring improvement of the band of the laser diode LD. Therefore, it is possible to reduce the cost and improve the reliability of the optical communication module.

The laser diode driver circuit LDD in this embodiment includes an output circuit Drv and a ringing compensation circuit LD_RING_COMP. The output circuit Drv is a circuit that supplies a constant bias current and a modulation current to the laser diode LD. The ringing compensation circuit LD_RING_COMP is a circuit that compensates for the influence of ringing generated by the laser diode LD.

The ringing compensation circuit LD_RING_COMP reduces the influence of ringing by subtracting a ringing compensation waveform having a fixed time width and amplitude from the main signal at the rising and falling edge timings of each amplitude level of the PAM signal. To do. Here, the time width and amplitude of the ringing compensation waveform are independent of each amplitude level in accordance with the time width and amplitude of the ringing waveform observed in the step response of the laser diode LD with respect to each amplitude level of the PAM signal. Adjusted. With this configuration, the influence of ringing observed at each amplitude level of the PAM signal can be compensated with an optimum value, and the eye opening of all eye waveforms of the PAM signal can be enlarged and jitter can be reduced.

Next, details of the configuration of the encoding logic circuit ENC_BK will be described.

The encoding logic circuit ENC_BK includes a shift register SR, a PAM signal generation logic circuit PAM_GEN_LOG, a digital-analog converter DAC, a transition time adjustment circuit TRAN_ADJ_CNT, and a pre-data transition LD compensation circuit PRE_TRAN_LD_EQ. The shift register SR is a circuit that holds data (data A) of the PAM signal immediately before a plurality of NRZ signals. The PAM signal generation logic circuit PAM_GEN_LOG is, for example, a circuit that encodes an N-channel NRZ signal into an N-value PAM signal. The digital-analog converter DAC is a circuit that converts a digital signal output from the PAM signal generation logic circuit PAM_GEN_LOG into an analog signal. The transition time adjustment circuit TRAN_ADJ_CNT is a circuit that delays the transition start time by a fixed delay amount according to each amplitude level. The pre-data transition LD compensation circuit PRE_TRAN_LD_EQ is a circuit that performs waveform emphasis before rising and falling data transitions.

Here, in the example of FIG. 3, a 1-channel PAM4 signal is generated from a 2-channel NRZ signal. However, the input signal may be a PAM signal, and the operation speed of the circuit and the electrical transmission path To reduce the effect of loss, reduce the bit rate of the input NRZ signal and increase the number of channels to generate a PAM signal (for example, generate a 50 Gbps PAM4 signal from 4 channels x 12.5 Gbps NRZ signal) Also good. Specifically, the transition time adjustment circuit TRAN_ADJ_CNT determines the data transition from the previous data (data A) and the next data (data B) to the rising edge and falling edge, and from data A to data B. The later amplitude level is determined, and the transition start time delay of data B is adjusted so that the phase difference of the trajectory until the steady state of each amplitude level is reached in the data transition from data A to data B is minimized. It has become a thing. With this configuration, it is possible to reduce jitter due to deterioration of the data transition time caused by a lack of bandwidth of the laser diode LD and improve the signal quality of PAM transmission. Further, the pre-data transition LD compensation circuit PRE_TRAN_LD_EQ determines the rising edge and falling edge and the data A to data B from the previous data (data A) and the next data (data B) information. Waveform enhancement is performed by adding a compensation waveform having a fixed time width and amplitude to data A in the data transition from data A to data B. With this configuration, the band of the laser diode LD can be improved without affecting the ringing compensation circuit LD_RING_COMP that performs the compensation process on the data B after the rising and falling edges, thereby compensating for the intersymbol interference. Can do.

Next, the detailed configuration and operation of the ringing compensation circuit LD_RING_COMP will be described with reference to FIGS.
FIG. 4 is a detailed configuration diagram of the ringing compensation circuit LD_RING_COMP.
FIG. 5 is a timing chart for explaining the operation of the ringing compensation circuit LD_RING_COMP.
FIG. 6 is a diagram showing the improvement of the step response waveform at the rise and fall due to the ringing compensation effect.

The ringing compensation circuit LD_RING_COMP includes a buffer circuit Bufm, an overshoot compensation circuit RISE_COMP, and an undershoot compensation circuit FALL_COMP. Buffer circuit Bufm is a circuit for amplifying the primary voltage signal _{V M.} The overshoot compensation circuit RISE_COMP is a circuit that compensates for the influence of ringing due to overshoot at the rise from the voltage signal branched from the main signal. The undershoot compensation circuit FALL_COMP is a circuit that compensates for the influence of ringing due to undershoot at the falling edge.

Each of the overshoot compensation circuit RISE_COMP and the undershoot compensation circuit FALL_COMP includes delay circuits DEL_R and DEL_F, edge detection circuits EdgeDec_R and EdgeDec_F, and compensation amount adjustment amplifiers Bupe_R and Bufe_F. Delay circuit DEL_R, DEL_F is a circuit that provides a constant delay ΔT corresponding to each amplitude level of PAM signals to the branch voltage signal from the mains voltage signal _{V M.} The edge detection circuits EdgeDec_R and EdgeDec_F are circuits that detect a rising edge and a falling edge for each amplitude level of the PAM signal and generate a ringing compensation waveform having a time width of ΔT. The compensation amount adjustment amplifiers Bufe_R and Bufe_F are circuits that adjust the amplitude of the ringing compensation waveform with a constant gain for each amplitude level of the PAM signal.

Next, the operation of the ringing compensation circuit LD_RING_COMP in this configuration example will be described with reference to the timing chart of FIG.

First, with regard to the rise, the input signal _{V M} of the PAM4 signal, three types of delay circuits overshoot compensation circuit RISE_COMP (Del_Lv3R, Del_Lv2R, Del_Lv1R), the fixed delay _{(ΔT R1, ΔT R2, ΔT} R3 ) Having a voltage signal V _M (V _M′R1 , V _M′R2 , V _M′R2 ). Here, ΔT _R1 , ΔT _R2 , and ΔT _R3 are delay times applied when generating voltage waveforms from level 0 to level 3, level 0 to level 2, and level 0 to level 1, respectively, and T _R1 < There is a relationship of ΔT _R2 <ΔT _R3 . That is, the ringing per unit time is most intense when the level is 0 to 3, and when the level is 0 to 2, the level 0 to level 1 corresponds to the second.

Next, three edge detection circuit compares (EdgeDec_Lv1R, EdgeDec_Lv2R, EdgeDec_Lv3R) the V _{M 'and} delayed by the delay circuit and the mains voltage signal _{V M} at, by detecting a rising edge at each amplitude level of the PAM4 signal Then, a compensation waveform having a time width (ΔT _R1 , ΔT _R2 , ΔT _R3 ) corresponding to the delay amount of the delay circuit is generated. Furthermore, three ringing compensation waveforms (V _R1 , V _R2 , V _R3 ) adjusted to optimum amplitude values (−α1R, −α2R, −α3R) are generated using three compensation amount adjusting amplifiers, and buffered adding these ringing compensation waveform subtraction circuit ADD_R at the output of circuit BUFM, it produces an output waveform V _RC which blunted after a data transition of the rise of the amplitude level.

Similarly, with respect to the fall, the undershoot compensation circuit FALL_COMP has a constant time width (ΔT _F0 , ΔT _F1 , ΔT _F2 ) and amplitude (β0F, (3) Generate three ringing compensation waveforms having (β1F, β2F), and add these ringing compensation waveforms at the output of the buffer circuit Bufm by the adder / subtractor circuit ADD_F, thereby changing the output data gently after the falling data transition. Generate _VRC . Again, there is a relationship of T _F1 <ΔT _F2 <ΔT _F3 .

Here, with reference to FIG. 6, the effect of reducing the influence of ringing in this embodiment using step response waveforms at the rise and fall will be described. When the ringing compensation circuit LD_RING_COMP is not applied, a ringing waveform having a different time width and amplitude is generated for each amplitude level of the PAM4 signal at both rising and falling edges due to the influence of relaxation oscillation of the laser diode LD. By using the ringing compensation circuit LD_RING_COMP, the influence of the ringing of the laser diode LD is reduced by smoothly changing the waveform after the rising and falling edges in advance according to the time width and amplitude of these ringing waveforms. Is possible.

As described above, by using the optical communication module and the optical communication device including the laser diode driver circuit LDD shown in FIGS. 3 and 4, the laser diode is insufficient in the required communication band and has a large influence of ringing. Using an LD, it is possible to realize a high-speed and high-quality optical transmission / reception operation by pulse amplitude modulation with a low-cost and highly reliable optical communication module.

Next, a detailed configuration and operation of the transition time adjustment circuit TRAN_ADJ_CNT of the encoding logic circuit ENC_BK will be described with reference to FIGS.
FIG. 7 is a detailed configuration diagram of the transition time adjustment circuit TRAN_ADJ_CNT of the encoding logic circuit ENC_BK.
FIG. 8 is a diagram illustrating improvement in the step response waveform of the rise and fall during PAM4 transmission by adjusting the transition time adjustment circuit TRAN_ADJ_CNT.

In this configuration example, a 1-channel PAM4 signal is generated without increasing the symbol rate from 2-channel NRZ signals (Data 1 and Data 2). For example, in the case of PAM4 transmission with a baud rate of 25 Gbps, a PAM4 signal of 50 Gbps is generated from an NRZ signal of 2 channels × 25 Gbps.

The encoding logic circuit ENC_BK in this embodiment includes a shift register SR, a PAM signal generation logic circuit PAM_GEN_LOG, and a transition time adjustment circuit TRAN_ADJ_CNT.

The shift register SR is a circuit composed of four latch circuits LAT that hold data (Data A) immediately before the two-channel NRZ signal. The PAM signal generation logic circuit PAM_GEN_LOG is a circuit that encodes a 2-channel NRZ signal into a PAM4 signal. The digital-analog converter DAC is a circuit that converts a digital signal into an analog signal. The transition time adjustment circuit TRAN_ADJ_CNT is a circuit that delays the transition start time by a fixed delay amount according to each amplitude level.

The transition time adjustment circuit TRAN_ADJ_CNT includes a phase control logic circuit PH_CNT_LOG and a phase rotation circuit IP. The phase control logic circuit PH_CNT_LOG is a circuit that determines the direction of data transition to each amplitude level of the PAM4 signal from the information of DataA and the next data (DataB), and outputs a phase control signal for controlling the clock phase. is there. The phase rotation circuit IP is a circuit that adjusts the phase of the clock signal CLK in accordance with the phase control signal.

Here, the phase rotation circuit IP can adjust the clock phase with an accuracy of 1 ps or less by dividing the symbol rate into 64 phases, for example, when the baud rate exceeds 25 Gbps. By using the phase-adjusted clock signal, the timing of the clock when generating the PAM signal in the PAM signal generation logic circuit PAM_GEN_LOG is adjusted in accordance with the data transition to each amplitude level of the PAM signal, thereby obtaining a desired It is possible to delay the transition start time by a certain delay amount with respect to the data transition. In this configuration example, the clock signal is assumed to be a full rate. However, if it is difficult to configure the clock distribution system at the full rate due to the performance limit of the circuit and power consumption, the clock signal is The signal may be slowed down to 1/2 or 1/4 and may be configured at half rate or quarter rate.

Next, the operation and effect of the transition time adjustment circuit TRAN_ADJ_CNT in the present configuration example will be described using step response waveforms for each amplitude level at the rise and fall in FIG. As shown by the step response waveform indicated by the dotted line in FIG. 8, when the transition time adjustment circuit TRAN_ADJ_CNT is not applied, the waveform is gently changed in advance by the insufficient bandwidth of the laser diode or by the ringing compensation circuit LD_RING_COMP described in FIG. As a result, the transition time deteriorates, and both the rising and falling trajectories to each data transition (rise: level 0 to level 1, level 2, level 3, falling: level 3 to level 2, level 1 and level 0) increase, jitter of the PAM signal increases, and transmission quality deteriorates.

In the present configuration example, as indicated by the solid line in FIG. 8, first, at the rising edge, from the level 0 to the level 2 on the basis of the orbit (level 0 to level 1) where the slope of the data transition to the steady state is the most gentle. By delaying the transition start time to ΔT_Tran_RLv2 and delaying the transition start time from level 0 to level 3 by ΔT_Tran_RLv3, the variation in each data transition with respect to the trajectory from level 0 to level 1 is minimized, so that the PAM signal Improve jitter characteristics. Note that there is a relationship of ΔT_Tran_RLv2 <ΔT_Tran_RLv3. Similarly, the transition start time from level 3 to level 1 is delayed by ΔT_Tran_FLv1 with reference to the trajectory (level 3 to level 2) where the slope of the data transition to the steady state is the smoothest even at the fall, and from level 3 to level By delaying the transition start time to 0 by ΔT_Tran_FLv0, trajectory variation between data transitions can be minimized, jitter can be reduced, and the transmission quality of the PAM signal can be improved. Note that there is a relationship of ΔT_Tran_FLv1 <ΔT_Tran_FLv0.

As described above, by using the optical communication module and the optical communication device including the encoding logic circuit ENC_BK shown in FIG. It is possible to realize a high-speed and high-quality optical transmission / reception operation by pulse amplitude modulation with an optical communication module having high performance.

Next, a detailed configuration and operation of the pre-data transition LD compensation circuit PRE_TRAN_LD_EQ of the encoding logic circuit ENC_BK will be described with reference to FIGS. 9 and 10.
FIG. 9 is a detailed configuration diagram of the pre-data transition LD compensation circuit PRE_TRAN_LD_EQ of the encoding logic circuit ENC_BK.
FIG. 10 is a timing chart for explaining the operation of the pre-data transition LD compensation circuit PRE_TRAN_LD_EQ.

The pre-data transition LD compensation circuit PRE_TRAN_LD_EQ in this embodiment includes a data transition detection circuit DATA_TRAN_DEC_R, a pre-rise transition compensation waveform generation circuit PRE_TRAN_EQ_R, an addition / subtraction circuit ADD_R_2, a falling data transition detection circuit DATA_TRAN_DEC_F, and a pre-fall transition compensation waveform. A generation circuit PRE_TRAN_EQ_F and an addition / subtraction circuit ADD_F_2 are included. The data transition detection circuit DATA_TRAN_DEC_R is a circuit that detects a rising edge from information of the previous data (Data A) and the next data (Data B) and generates an LD compensation signal at a timing before the rising data transition. The pre-rise transition compensation waveform generation circuit PRE_TRAN_EQ_R is a circuit that adjusts the amplitude of the compensation pulse before the rise transition. The addition / subtraction circuit ADD_R_2 is a circuit that adds the output signal V _{EQ_R} of the pre-rising transition compensation waveform generation circuit to the DAC output V _PRE . On the other hand, the falling data transition detection circuit DATA_TRAN_DEC_F is a circuit that detects a falling edge and generates an LD compensation signal at a timing before the falling data transition. The pre-falling transition compensation waveform generation circuit PRE_TRAN_EQ_F is a circuit that adjusts the amplitude of the compensation pulse before the falling transition. The addition / subtraction circuit ADD_F_2 is a circuit that adds the output signal V _{EQ_F} of the pre-falling transition compensation waveform generation circuit to the DAC output V _PRE .

Next, the operation of the pre-data transition LD compensation circuit PRE_TRAN_LD_EQ in this configuration example will be described with reference to the timing chart of FIG. The pre-rise transition compensation waveform generation circuit PRE_TRAN_EQ_R and the pre-fall transition compensation waveform generation circuit PRE_TRAN_EQ_F are the rise and fall timings from the information of the previous data (DataA) and the next data (DataB), respectively. _{Are detected} , and LD compensation signals V _{EQ_R} and V _{EQ_F} for emphasizing rising and falling at the timing before data transition are generated. The addition / subtraction circuit ADD_R_2 and the addition / subtraction circuit ADD_F_2 can enhance the waveform before the data transition by adding these LD compensation signals to the PAM4 signal generated from the two-channel NRZ signal. Unlike the prior art described in Patent Document 1, the waveform is emphasized before data transition, so that the compensation signal is added after data transition without affecting the compensation operation of the ringing compensation circuit LD_RING_COMP shown in FIG. Further, the falling transition time can be increased, and the influence of ringing of the laser diode LD can be improved, and the band shortage of the laser diode LD can also be improved. Also, by increasing the time width of the LD compensation signal for the fall rather than the rise, the asymmetry of the rise and fall caused by the bias current dependence of the frequency characteristics of the laser diode LD is compensated, and an equal optical transmission signal is obtained. Can be output. In this configuration example, an LD compensation signal having a constant amplitude and a time width is added before the rising and falling data transitions regardless of the amplitude level of the PAM signal. When more precise LD compensation is required, the data transition detection circuit DATA_TRAN_DEC is parallelized so that it can detect the data transition of each amplitude level, and the frequency of the target laser diode for the data transition of each amplitude level The amplitude and time width of the LD compensation signal may be changed according to the characteristics.

As described above, by using the optical communication module and the optical communication device including the encoding logic circuit ENC_BK illustrated in FIG. 9, the laser diode LD in which the band is insufficient with respect to the necessary communication band and ringing occurs is used. It is possible to realize a high-speed and high-quality optical transmission / reception operation by pulse amplitude modulation with a low-cost and highly reliable optical communication module.

Next, the effect of improving the communication quality when the laser diode driver circuit LDD including the encoding logic circuit ENC_BK and the ringing compensation circuit LD_RING_COMP of the present embodiment is used will be described with reference to FIG.
FIG. 11 shows the eye waveform of the PAM4 signal of the LD output in comparison with the case where the laser diode driver circuit LDD including the encoding logic circuit ENC_BK and the ringing compensation circuit LD_RING_COMP of the first embodiment is not used. FIG.
As shown in FIG. 11A, when the laser diode driver circuit LDD including the encoding logic circuit ENC_BK and the ringing compensation circuit LD_RING_COMP of the first embodiment is not used, the intersymbol interference due to the insufficient band of the laser diode LD. Due to the influence of ringing, the eye amplitude and the eye width become smaller at each amplitude level. On the other hand, when the laser diode driver circuit LDD including the encoding logic circuit ENC_BK and the ringing compensation circuit LD_RING_COMP of the first embodiment is used as shown in FIG. As the operating band is improved, the variation between data transitions is reduced, and the eye amplitude and eye width can be increased at all amplitude levels (upper eye, middle eye, and lower eye).

As described above, by using the optical communication module and the optical communication device including the laser diode driver circuit LDD and the encoding logic circuit ENC_BK of the first embodiment, the laser diode having a large influence of ringing due to insufficient bandwidth of the laser diode. Even with this, it is possible to realize a high-speed optical transmission / reception operation by low-cost and high-quality pulse amplitude modulation.

[Embodiment 2]
A second embodiment according to the present invention will be described below with reference to FIGS. 12 to 14B.

First, the hole burning effect will be described with reference to FIGS.
FIG. 12 is a graph showing the relationship between the input frequency and the optical output power in the laser diode LD showing the waveform deterioration due to the hole burning effect.
FIG. 13 is a diagram for explaining that waveform degradation due to the hole burning effect occurs in the optical output waveform of the laser diode LD.

In high-speed, high-light-power direct-modulation laser diodes LD, transmission quality may deteriorate due to the hole burning effect in addition to the ringing waveform due to insufficient bandwidth and relaxation oscillation of the laser diode LD due to device performance limitations.

The hole burning effect is a phenomenon in which the gain of the optical output power deteriorates and falls like a hole at a low frequency f_HB as shown by the frequency characteristics of the laser diode LD in FIG. The value of the frequency f_HB is, for example, about several GHz in the case of a laser diode LD whose -3 dB band is about 20 GHz. As shown by the step response waveforms of the rising and falling edges in FIG. 13, the degradation of the optical output power at f_HB due to the hole burning effect reaches the steady state for each amplitude level of the PAM signal, and the light at the rising edge The output waveform is gradually raised, and the optical output waveform is gradually lowered at the fall. As a result, the influence of intersymbol interference becomes large and the transmission quality is deteriorated. Here, the degradation of the optical output power due to the hole burning effect does not depend on the magnitude of the bias current supplied to the laser diode LD, and is almost constant.

Next, a laser diode driver circuit LDD for compensating for the hole burning effect will be described with reference to FIGS. 14A and 14B.
FIG. 14A is a configuration diagram of a laser diode driver circuit LDD for compensating for the hole burning effect.
FIG. 14B is a circuit diagram of the laser diode driver circuit LDD shown in FIG. 14A.

The laser diode driver circuit LDD includes a transmitter hole burning compensation circuit LD_HB_COM_Tx and an output circuit Drv. The transmitter hole burning compensation circuit LD_HB_COM_Tx is a circuit that compensates for the deterioration of the optical output power in the low band due to the hole burning effect of the laser diode LD. The output circuit Drv is a circuit that supplies a modulation current and a bias current to the laser diode LD.

The transmission unit hole burning effect compensation circuit LD_HB_COM_Tx includes a hole burning compensation filter HB_FIL, a compensation amount adjustment amplifier G_AMP, and an addition / subtraction circuit ADD. The hole burning compensation filter HB_FIL is a circuit that generates a hole burning compensation signal for compensating for deterioration in optical output power due to the hole burning effect from a signal obtained by branching the input signal of the laser diode driver circuit LDD. The compensation amount adjustment amplifier G_AMP is a circuit that adjusts the amplitude of the hole burning compensation signal from the output of the hole burning compensation filter HB_FIL. The addition / subtraction circuit ADD is a circuit that adds the output of the compensation amount adjustment amplifier G_AMP to the input signal of the laser diode driver circuit LDD.

Here, the band of the hole burning compensation filter HB_FIL is characterized by being adjusted according to the band f_HB in which the optical output power is degraded due to the hole burning effect of the laser diode LD to be driven. That is, by making the transfer characteristic of the hole burning compensation filter opposite to the deterioration of the optical output power due to the hole burning effect, the frequency characteristic at the laser diode output is flattened. This configuration compensates for the degradation of the low-frequency optical output power caused by the hole burning effect with the hole burning compensation signal generated by the electric circuit, so that even if a laser diode LD having a large influence of the hole burning effect is used, high quality is achieved. Can be transmitted. Further, the hole burning compensation circuit in this configuration example can obtain the same effect not only on the PAM signal but also on the NRZ signal.
The laser diode driver circuit LDD for compensating for the hole burning effect shown in FIG. 14A can be realized by a circuit as shown in FIG. 14B, for example.
In the configuration example shown in FIG. 14B, the hole burning compensation filter HB_FIL includes a high-pass filter composed of a capacitive element and a resistance element, and an emitter follower circuit for adding a hole burning compensation signal to the output of the output circuit Drv at high speed. Consists of. Here, the resistance element used in the high-pass filter is adjusted so that the band of the filter coincides with the band f_HB of deterioration due to the hole burning effect of the laser diode LD to be driven. Here, in the present embodiment, the first-order high-pass filter is used. However, when a steeper compensation signal is required due to the effect of the hole burning effect, the order of the high-pass filter is increased or the filter configuration is increased. May be changed. In addition, since the bipolar transistor is used in this configuration example, the current addition speed is increased by the emitter follower circuit. However, in the CMOS circuit, the source follower circuit or the circuit that can drive the output of the hole burning compensation filter HB_FIL. Any circuit configuration can be used.

As described above, by using the optical communication module and the optical communication device including the laser diode driver circuit LDD for compensating the hole burning effect shown in FIG. 14A, the optical output power in the low band due to the hole burning effect of the laser diode LD. It is possible to compensate for the degradation of the transmission and to perform the transmission / reception operation with high speed and high transmission quality.

[Embodiment 3]
Hereinafter, a third embodiment according to the present invention will be described with reference to FIG.
FIG. 15 is a configuration diagram including a radar diode temperature compensation control circuit LD_TEMP_CNT in the transmission system (electrical-to-optical conversion) of the optical communication module shown in FIG.

The radar diode temperature compensation control circuit LD_TEMP_CNT includes an LD temperature monitor TEMP_SENS, an analog / digital converter ADC, and a register REG. The LD temperature monitor TEMP_SENS is a circuit that monitors the temperature of the laser diode LD. The analog-digital converter ADC is a circuit that converts an analog signal into a digital signal. The register REG is a circuit that holds values in a plurality of tables against temperature fluctuations of the laser diode LD.

Since the relaxation oscillation frequency and −3 dB frequency of the laser diode LD vary depending on the temperature, the ringing waveform generated by the overshoot and undershoot of the laser diode LD also varies depending on the temperature. As a means for compensating for the temperature fluctuation of the laser diode LD, it is conceivable to use a Peltier element to keep the temperature of the laser diode LD constant. However, temperature compensation by the Peltier element increases power consumption and downsizing also in size. It becomes difficult. Therefore, in this configuration example, the temperature of the laser diode LD is monitored by the laser diode LD temperature monitor TEMP_SENS, and each LD compensation function (shown in FIG. 1) prepared in advance as a table corresponding to the monitored temperature ( By rewriting the contents of the register REG to optimum setting values of the ringing compensation circuit LD_RING_COMP, the transition time adjustment circuit TRAN_ADJ_CNT, and the pre-data transition LD compensation circuit PRE_TRAN_LD_EQ, it becomes possible to compensate for the temperature change of the laser diode LD. Here, as a specific method of the LD temperature monitor TEMP_SENS, by monitoring the temperature of the laser diode LD from the change in the optical output power of the laser diode LD using the photodiode PD as a monitor, or by using a thermistor or the like. Realize.

As described above, by using the optical communication module and the optical communication device including the transmission system including the laser diode temperature compensation control circuit LD_TEMP_CNT shown in FIG. It is possible to perform transmission and reception operations with high speed and high transmission quality.

[Embodiment 4]
Hereinafter, a fourth embodiment according to the present invention will be described with reference to FIG.
FIG. 16 is a block diagram of the laser diode driver circuit LDD for compensating for the hole burning effect of FIG. 14A, including a laser diode temperature compensation control circuit LD_TEMP_CNT.

In the present embodiment, as shown in FIG. 16, the laser diode temperature compensation control circuit LD_TEMP_CNT is mounted on the transmitter hole burning effect compensation circuit LD_HB_COM_Tx shown in FIG. 14A, and the hole burning compensation filter HB_FIL and the compensation amount are mounted. By rewriting the contents of the register REG so that the adjustment amplifier G_AMP has an optimum value, it is possible to compensate for the temperature variation of the laser diode LD. In addition, the loop band of the laser diode temperature compensation control circuit LD_TEMP_CNT is only required to compensate for optical signal deterioration (temperature drift) associated with the temperature change of the laser diode LD. Therefore, high-speed operation exceeding 25 Gbps is not required, and at most It only needs to operate in a band of about MHz.

As described above, by using the optical communication module and the optical communication device including the transmission system including the laser diode temperature compensation control circuit LD_TEMP_CNT shown in FIG. It is possible to perform transmission and reception operations with high speed and high transmission quality.

[Embodiment 5]
Hereinafter, the fifth embodiment of the present invention will be described with reference to FIG.
FIG. 17 is a configuration diagram in which a hole burning compensation circuit is incorporated in the transimpedance amplifier circuit TIA in the receiving system (light-to-electrical conversion) of the optical communication module shown in FIG.

The transimpedance amplifier circuit TIA in this embodiment includes a preamplifier PRAMP, a receiver hole burning compensation circuit LD_HB_COM_Rx, a limit amplifier LA, and a clock / data recovery CDR (Clock Data Recovery). The preamplifier PRAMP is a circuit that converts a current signal from the photodiode PD into a voltage signal. The receiver hole burning compensation circuit LD_HB_COM_Rx is a circuit that compensates for the hole burning effect of the laser diode LD on the receiver side. The limit amplifier LA is a circuit that limits the output amplitude to a constant regardless of the input light power of the photodiode PD. The clock / data recovery CDR is a circuit that is provided at the output of the LA and separates the clock and data.

Here, it is assumed that the receiver hole burning compensation circuit LD_HB_COM_Rx is mounted before the voltage signal is limited, that is, within an amplitude range in which linear operation is ensured.

The receiving part hole burning effect compensation circuit LD_HB_COM_Rx is composed of a hole burning compensation filter HB_FIL, a compensation amount adjustment amplifier G_AMP, and an addition / subtraction circuit ADD. The hole burning compensation filter HB_FIL is a circuit that generates a hole burning compensation signal for compensating for deterioration in optical output power due to the hole burning effect from a signal obtained by branching the input signal of the preamplifier PRAMP. The compensation amount adjustment amplifier G_AMP is a circuit that adjusts the amplitude of the hole burning compensation signal from the output of the hole burning compensation filter HB_FIL. The addition / subtraction circuit ADD is a circuit that adds the output of G_AMP to the input signal of PRAMP.

Here, the band of the hole burning compensation filter HB_FIL is adjusted according to the band f_HB in which the optical output power is degraded due to the ruburning effect of the laser diode LD on the transmission side. With this configuration, the output voltage of PRAMP is as low as several tens of mV compared to the output circuit Drv on the transmission side. Therefore, unlike the transmission part hole burning compensation circuit LD_HB_COM_Tx shown in FIG. By mounting the burning compensation circuit, it is possible to compensate for the hole burning effect of the laser diode LD with low power. Further, the hole burning compensation circuit in this configuration example can obtain the same effect not only on the PAM signal but also on the NRZ signal.

[Embodiment 6]
The sixth embodiment of the present invention will be described below with reference to FIG.
FIG. 18 is a configuration diagram in which a receiver laser diode temperature compensation control circuit LD_TEMP_CNT_Rx for implementing temperature compensation of the laser diode LD is incorporated in a configuration in which a hole burning compensation circuit is incorporated in the transimpedance amplifier circuit TIA.

Here, the receiver laser diode temperature compensation control circuit LD_TEMP_CNT_Rx specifically observes an eye waveform such as the output of the limit amplifier LA with the eye monitor EYM, and the voltage component of the eye waveform and the eye opening degree in the time axis direction are determined. For example, the value of the resistance element for changing the constant of the hole burning compensation filter HB_FIL or the gain of the compensation amount adjustment amplifier G_AMP is adjusted so as to be maximized. In addition, the receiver laser diode temperature compensation control circuit LD_TEMP_CNT_Rx is provided with, for example, an LMS algorithm logic circuit LMS_ALG to calculate an error voltage and an error phase between an optimum voltage signal assumed to be an output of a CDR and the like and a reference signal indicating a clock phase. Even if a configuration is adopted in which each parameter of the hole burning compensation filter HB_FIL and the compensation amount adjusting amplifier G_AMP is optimized so that the error is minimized by an optimization algorithm such as Sign-Sign LMS (Least Mean Square). Good. By adopting such a configuration, it is possible to compensate the temperature of the laser diode LD without providing a functional block for performing temperature compensation of the laser diode LD such as a Peltier element or a photodiode PD as a monitor on the transmission side. A low-cost and small-sized optical communication module can be realized. The loop band of the temperature compensation control circuit LD_TEMP_CNT_Rx only needs to compensate for the optical signal deterioration (temperature drift) associated with the temperature change of the laser diode LD. Therefore, high-speed operation exceeding 25 Gbps is not required, and at most about several MHz. It suffices to operate in the band.

LSI_LG: logical operation processing circuit logic device OBK ... optical element block LD ... laser diode PD ... photodiode LDD ... laser diode driver circuit TIA ... transimpedance amplifier circuit AFE ... analog front end block OMD ... optical communication module LOG ... encoding / decoding logic Circuits OFtx, OFrx ... Optical communication line LSI_OP ... Semiconductor chip PAM ... Pulse amplitude modulation NRZ ... Binary transmission SR ... Shift register PAM_GEN_LOG ... PAM signal generation logic circuit DAC ... Digital analog converter TRAN_ADJ_CNT ... Transition time adjustment circuit PRE_TRAN_LD_EQ ... LD before data transition Compensation circuit CLK ... Clock signal ENC_BK ... Encoding logic circuit DEC_BK ... Decoding logic circuit LD_RING_COMP ... Ging compensation circuit Drv ... Output circuit ADD, ADD_R, ADD_F, ADD_R_2, ADD_F_2 ... Addition / subtraction circuit DEL_R, DEL_F ... Delay circuit EDeg_LOG_R ... Rising edge detection circuit EDeg_LOG_L ... Falling edge detection circuit Buffer_R, Bufe_SE ... Compensation amount adjustment amplifier MPR Compensation circuit FALL_COMP: Undershoot compensation circuit LD_RING_COMP: Ringing compensation circuit Bufm ... Buffer circuit LAT ... Latch circuit IP ... Phase rotation circuit PH_CNT_LOG ... Phase control logic circuit DATA_TRAN_DEC_R ... Rising data transition detection circuit DATA_TRAN_DEC_F ... Falling data transition detection circuit PRE_TRAN_EQ_ Before transition Compensation waveform generation circuit PRA_TRAN_EQ_F ... Compensation waveform generation circuit before falling transition LD_HB_COM_Tx ... Transmitter hole burning effect compensation circuit HB_FIL ... Hole burning compensation filter TERM ... Termination circuit DUM_LD ... LD dummy circuit LD_TEMP_CNT ... Laser diode temperature compensation control circuit G_AMP ... Compensation amount Adjustment amplifier LD_HB_COM_Rx: Receiver hole burning effect compensation circuit PRAMP ... Preamplifier LA ... Limit amplifier CDR ... Clock / data recovery LD_TEMP_CNT_Rx ... Receiver laser diode temperature compensation control circuit EYM ... Eye monitor LMS_ALG ... LMS algorithm logic circuit OPT_COM ... Optical characteristic compensation control TEMP_SENS ... LD temperature monitor ADC ... Analog / digital converter REG ... Registers PrBufm, PrBufe ... Pre-buffer circuit DUTYAdj ... Duty ratio adjustment circuit DEL ... Delay circuit LD_EQ ... Laser characteristic compensation circuit

Claims (16)

1. An optical signal and an electrical signal are mutually converted by an N (N is a positive integer) -value multilevel signal that is pulse-amplitude modulated to transmit N bits of information per symbol, and an optical signal is generated from the electrical signal. An optical communication module using a modulation type laser diode,
   A laser diode driver circuit that inputs the N-value multilevel signal and supplies current to the direct modulation laser diode;
   The laser diode driver circuit is:
   A ringing compensation circuit that generates a ringing compensation waveform having a constant time width and amplitude after data switching of the N-value multilevel signal, and subtracts the ringing compensation waveform from the N-value multilevel signal;
   An optical communication module comprising: a modulation current signal obtained by converting a voltage signal into a current signal and an output circuit for supplying a bias current to the direct modulation laser diode by using a voltage signal output from the ringing compensation circuit.
2. The relaxation oscillation frequency of the direct modulation laser diode is lower than the fundamental frequency when supplying current from the laser diode driver circuit,
   The time width and amplitude of the ringing compensation signal generated by the ringing compensation match the time width and amplitude value of the ringing waveform caused by overshoot and undershoot that occur after data switching of the direct modulation laser diode. The optical communication module according to claim 1, wherein the optical communication module is adjusted.
3. The time width and amplitude of the ringing compensation waveform generated by the ringing compensation circuit are:
   A ringing waveform generated after data switching to each amplitude level at the rise of the N-value multilevel signal;
   3. The optical communication module according to claim 2, wherein the optical communication module is independently adjusted in accordance with a ringing waveform generated after data switching to each amplitude level when the N-value multilevel signal falls.
4. An encoding logic circuit for inputting the N-value multilevel signal to the laser diode driver circuit;
   The encoding logic circuit includes:
   A shift register circuit for holding previous symbol multi-value data and next symbol multi-value data of the N-value multi-value signal;
   An amplitude multilevel signal generation logic circuit for generating the N-level multilevel signal from the next symbol multilevel data;
   A digital-analog conversion circuit that converts a digital signal that is an output of the amplitude multi-value signal generation logic circuit into an analog signal;
   The previous symbol multi-value data and the next symbol multi-value data are input to the timing of the clock signal supplied to the width multi-value signal generation logic circuit when the next symbol multi-value data is generated. The optical communication module according to claim 1, further comprising a transition time adjustment circuit that gives a constant phase difference according to an amplitude level after the data switching of the next symbol multilevel data.
5. The delay amount of the transition start time in the data switching of the next symbol multilevel data adjusted by the transition time adjustment circuit is:
   Based on the trajectory where the slope of the data transition from the previous symbol multi-value data to the next symbol multi-value data at the time of data switching is the most gentle,
   5. The optical communication module according to claim 4, wherein rise and fall are adjusted so that variation in trajectory between data transitions until reaching each amplitude level of the N-value multilevel signal is minimized. .
6. The encoding logic circuit includes a laser diode compensation circuit before the data transition,
   The laser diode compensation circuit before data transition is
   Using the previous symbol multilevel data and the next symbol multilevel data as inputs, rising emphasis having reverse characteristics with respect to a rising edge having a constant time width and amplitude at the timing before the data transition of the rising edge of the N-level multilevel signal Generate waveforms,
   In the timing before the data transition of the falling edge of the N-value multilevel signal, a falling emphasis waveform having a reverse characteristic with respect to the falling edge having a constant time width and amplitude is generated,
   5. The optical communication module according to claim 4, wherein the rising emphasis waveform and the falling emphasis waveform are added at an output of the digital-analog conversion circuit.
7. The ringing compensation circuit includes:
   A buffer circuit for amplifying an input signal of the laser diode driver circuit;
   An overshoot compensation circuit that compensates for a ringing waveform generated at the rising edge using a voltage signal branched from the input signal as input,
   An undershoot compensation circuit that compensates for a ringing waveform generated at the falling edge using a voltage signal branched from an input signal of the laser diode driver circuit as an input;
   The overshoot compensation circuit and the undershoot compensation circuit each provide N−1 delays that give a constant delay amount corresponding to each amplitude level of the N-level multilevel signal to the voltage signal branched from the input signal. Circuit,
   The rising and falling edges are detected for each amplitude level of the N-level multilevel signal, and the ringing compensation waveform having the delay time width is detected at the timing after the data transition. An edge detection circuit that generates a reverse characteristic;
   A compensation amount adjusting amplifier that adjusts the amplitude of the ringing compensation waveform with a constant gain for each amplitude level of the N-value multilevel signal;
   An addition / subtraction circuit for adding the output signal of the compensation amount adjusting amplifier at the output of the buffer circuit;
   The optical communication module according to claim 1, wherein an output of the addition / subtraction circuit is input to the output circuit.
8. The time width and amplitude of the ringing compensation waveform generated by the edge detection circuit are such that the difference between the response waveform at the output of the direct modulation laser diode and the steady state for each amplitude level of the N-level multilevel signal is minimized. So that
   8. The optical communication module according to claim 7, wherein a delay amount of the delay circuit and a gain of the compensation amount adjusting amplifier are adjusted.
9. The transition time adjustment circuit includes:
   Direction of data transition from the previous symbol multilevel data and the next symbol multilevel data to the next symbol multilevel data and the N-level multilevel with the previous symbol multilevel data and the next symbol multilevel data as input. A phase control logic circuit that determines the amplitude level of the signal and outputs a phase control signal for adjusting the clock phase;
   A phase rotation circuit that adjusts the phase of the clock signal supplied to the amplitude multilevel signal generation logic circuit in response to the phase control signal;
   The rising and falling waveforms are adjusted by the phase adjustment of the clock signal so that the variation in trajectory between data transitions until the amplitude level of the N-level multilevel signal is reached is minimized. The optical communication module according to claim 4.
10. The laser diode compensation circuit before data transition is
    Using the preceding symbol multilevel data and the next symbol multilevel data as inputs, detecting a rising edge of the next symbol multilevel data from the previous symbol multilevel data and the next symbol multilevel data, and before the rising data transition A rising data transition detection circuit that generates a rising emphasis signal at a timing with a reverse characteristic with respect to the rising edge, and
    A pre-rise-up compensation waveform generation circuit that adjusts the amplitude of the rise-up signal,
    An addition / subtraction circuit for adding the rising emphasis signal of the output of the pre-rise compensation waveform generation circuit with the output of the digital-analog conversion circuit;
    A falling edge of the next symbol multi-value data is detected from the previous symbol multi-value data and the next symbol multi-value data, and the falling emphasis signal has a reverse characteristic with respect to the fall at the timing before the falling data transition. A falling data transition detection circuit to be generated;
    A pre-fall compensation waveform generation circuit that adjusts the amplitude of the fall emphasis signal; and an addition / subtraction circuit that adds the fall emphasis signal output from the pre-fall compensation waveform generation circuit at the output of the digital-analog conversion circuit. The optical communication module according to claim 6.
11. The time width and amplitude of the rising emphasis signal and the time width and amplitude of the falling emphasis signal are:
    11. The light according to claim 10, wherein each of the amplitude level, rising edge, and falling edge of the N-value multilevel signal is adjusted independently corresponding to the frequency characteristic of the direct modulation laser diode. Communication module.
12. An optical communication module using a direct modulation laser diode that mutually converts an optical signal and an electrical signal and generates an optical signal from the electrical signal,
    A laser diode driver circuit for supplying current to the direct modulation laser diode;
    The laser diode driver circuit is:
    A hole burning compensation circuit;
    An output circuit,
    The hole burning compensation circuit is:
    Using a voltage signal branched from the input signal of the laser diode driver circuit as an input, hole burning having a reverse transfer characteristic with respect to the degradation of the light output in the low band caused by the hole burning effect of the direct modulation laser diode A hole-burning compensation filter comprising a compensation filter or a high-pass filter having the same band as that in which the degradation of the optical output occurs.
    A compensation amount adjusting amplifier that adjusts the amplitude of the output signal of the hole burning compensation filter and generates a hole burning compensation signal;
    An addition / subtraction circuit for adding the output signal of the compensation amount adjustment amplifier at the input of the laser diode driver circuit,
    The output circuit supplies a modulated current signal obtained by converting a voltage signal into a current signal and a bias current to the direct modulation laser diode by using the voltage signal output from the hole burning compensation circuit as an input.
13. The laser diode driver circuit has a laser diode temperature compensation control circuit,
    The laser diode temperature compensation control circuit is:
    A laser diode temperature monitor for monitoring the temperature of the direct modulation laser diode;
    A digital-analog conversion circuit for converting the output signal digital signal of the laser diode temperature monitor;
    The ringing compensation circuit, the transition time adjustment circuit, and a storage circuit that holds a set value of the pre-data transition laser diode compensation circuit,
    The laser diode temperature compensation control circuit is:
    Transmission quality due to deterioration of ringing waveform and transition time caused by temperature change of direct modulation laser diode by rewriting the set value of the storage circuit to the optimum value prepared in advance according to temperature change of the direct modulation laser diode The optical communication module according to claim 6, wherein the deterioration is compensated.
14. The laser diode driver circuit has a laser diode temperature compensation control circuit,
    The laser diode temperature compensation control circuit is:
    A laser diode temperature monitor for monitoring the temperature of the direct modulation laser diode;
    A digital-analog conversion circuit for converting the output signal digital signal of the laser diode temperature monitor;
    A storage circuit for holding a set value of the hole burning compensation circuit;
    Transmission quality due to deterioration of ringing waveform and transition time caused by temperature change of direct modulation laser diode by rewriting the set value of the storage circuit to the optimum value prepared in advance according to temperature change of the direct modulation laser diode The optical communication module according to claim 12, wherein the optical communication module is compensated for deterioration.
15. An optical communication module using a direct modulation laser diode that mutually converts an optical signal and an electrical signal and generates an optical signal from the electrical signal, and a photodiode that generates an electrical signal from the optical signal,
    It has a transimpedance amplifier circuit that amplifies the current signal from the photodiode and converts it into a voltage signal,
    The transimpedance amplifier circuit is:
    A preamplifier that converts the single-phase current signal, which is the photodiode output, into a single-phase voltage signal as input and amplifies it;
    A hole burning compensation circuit that receives the voltage signal that is the preamplifier output, and
    An optical communication module, wherein the hole burning compensation circuit compensates for a deterioration in optical output power in a low band due to a hole burning effect of the direct modulation laser diode.
16. Furthermore, it has a laser diode temperature compensation control circuit,
    The laser diode temperature compensation control circuit is:
    Optimum that maximizes the eye opening by detecting the eye opening degree of the hole burning compensation circuit output in accordance with the change in the characteristics of the optical waveform input to the photodiode due to the temperature change of the direct modulation laser diode. 16. The optical communication module according to claim 15, wherein an error signal between the value and the detection result is generated, and a set value of the hole burning compensation circuit is automatically adjusted so that the error signal becomes small.

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