JP4972696B2 - Optical transmission circuit and optical communication system - Google Patents

Description

  The present invention relates to an optical transmission circuit and an optical communication system including an optical transmission circuit and an optical reception circuit, and particularly to an optical transmission circuit and an optical communication system that perform optical communication exceeding several tens of Gbps using a laser diode. It relates to effective technology.

  For example, Patent Document 1 describes an optical transmission circuit that suppresses fluctuations in the extinction ratio of laser output light due to changes in laser characteristics. Specifically, the optical output from the laser diode is detected by a photodiode, and the laser diode bias current is changed according to the direct current component of the photodiode output, and the difference between the maximum and minimum values of the photodiode output is calculated. A circuit is provided that detects and controls the gain of the variable gain amplifier (laser diode drive circuit) so that the difference is constant. This compensates for temperature fluctuations that occur in the threshold current of the laser diode and temperature fluctuations that occur in the slope of the output optical power with respect to the laser drive current.

JP 2003-298181 A

  In recent years, with an increase in communication speed, the communication speed of an optical communication apparatus has changed from 10 Gbps to 25 Gbps, 40 Gbps, and the like, and improvement in the quality of transmission waveforms has become increasingly important. As a factor that degrades the quality of the transmission waveform, there is a temperature characteristic of a laser diode serving as a transmission element for optical communication. FIG. 16 is an explanatory diagram showing an example of temperature characteristics of optical output power in a laser diode (LD). As shown in FIG. 16, the laser diode (LD) increases as the threshold current (Ith), which is the minimum driving current necessary for performing optical output, becomes higher, and the optical output power (P ) Decreases as the temperature increases.

  Therefore, in order to maintain the same optical output power regardless of the temperature, as shown in FIG. 16, an operation range (Pmin to Pmax) in which the gradient of the optical output power with respect to the LD drive current is linear, and For example, as described in Patent Document 1, temperature fluctuations that occur in the threshold current and temperature fluctuations that occur in the slope of the optical output power may be compensated. However, as a result of studies by the present inventors, it has been found that if the communication speed is further increased, it is difficult to realize sufficient waveform quality even if such compensation is performed.

  FIG. 17 is an explanatory diagram showing an example of temperature characteristics of the relaxation oscillation frequency in the laser diode (LD). The relaxation oscillation is a phenomenon in which the optical output vibrates when a pulsed current is injected into the semiconductor laser, and the frequency at that time is called the relaxation oscillation frequency. The value of the relaxation oscillation frequency is determined by the device structure of the LD, and the response characteristic rapidly decreases above this frequency. Therefore, the upper limit frequency at which the LD can operate is determined based on this relaxation oscillation frequency. FIG. 17 shows the characteristics of the relaxation oscillation frequency with respect to the LD drive current (here, represented by √ (Ib−Ith) using the bias current Ib and the threshold current Ith) and the temperature dependence of the characteristics. . As shown in FIG. 17, in order to maintain a constant relaxation oscillation frequency, it is necessary to increase the bias current Ib as the temperature increases.

  When the bias current is increased in this way, the problem shown in FIG. 18 occurs. FIG. 18 is an explanatory diagram showing an example of temperature characteristics of optical output power in a laser diode (LD) and an optical output waveform (eye pattern) at a high temperature. As shown in FIG. 18, the characteristic of the optical output power with respect to the LD driving current becomes nonlinear (the inclination decreases) as the LD driving current increases, and the nonlinear characteristic appears at a portion where the LD driving current is small as the temperature increases. Therefore, when the bias current Ib of the LD drive current is increased to improve the relaxation oscillation frequency, it becomes necessary to set the operation range (Pmin to Pmax) of the optical output power in the above-described nonlinear region. It gets higher.

  In this case, for example, when the LD drive current is increased / decreased with a uniform width around the bias current Ib (ht) during high temperature operation, the light output waveform (eye pattern) from the LD is an intermediate corresponding to Ib (ht). With reference to the optical output power Pmid, the amplitude HP on the high power side is smaller than the amplitude LP on the low power side by ΔP. As a result, the cross point of the eye pattern deviates from the center position of the amplitude, so that the eye size becomes small and sufficient waveform quality cannot be obtained.

  The present invention has been made in view of the above, and an object of the present invention is to provide an optical transmission circuit and an optical communication system capable of realizing an increase in communication speed. The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in the present application, the outline of a typical embodiment will be briefly described as follows.

  The optical transmission circuit according to the present embodiment includes a laser diode, a bias current source, a driver circuit, a detection circuit block, and first compensation means. The bias current source supplies a bias current to the laser diode, and the driver circuit adds the first drive current to the bias current, thereby causing the laser diode to emit light with high optical output power, and generating the second drive current from the bias current. By subtracting, the laser diode emits light with low optical output power. The detection circuit block includes a temperature detection circuit that detects the temperature of the laser diode, and outputs a first control signal whose value varies based on the detection result of the temperature detection circuit and the magnitude of the bias current described above. The first compensation means sets the difference between the magnitude of the first drive current and the magnitude of the second drive current according to the value of the first control signal.

  Thus, based on the temperature of the laser diode and the magnitude of the bias current, the difference between the driving current on the high optical output power side and the driving current on the low optical output power side of the laser diode can be made different. Even when a region where the output power characteristic is nonlinear is used, the eye pattern of the light output from the laser diode can be kept in good quality. That is, if the bias current is increased, the relaxation signal frequency can be increased. On the other hand, the optical output power characteristic becomes nonlinear and the eye pattern is distorted as the temperature increases. Therefore, by compensating the distortion in the eye pattern with the first compensation means described above, it is possible to realize a higher communication speed as a result.

  Further, the optical transmission circuit according to the present embodiment reduces the amplitude between the high optical output power and the low optical output power of the laser diode, instead of eliminating the distortion of the eye pattern by the first compensation means described above. This eliminates the distortion of the eye pattern. In other words, by reducing the amplitude, the optical output power characteristic can be equivalently regarded as a linear region, so that the distortion of the eye pattern can be eliminated. This method is relatively useful when performing communication at a short distance. In addition to increasing the communication speed, the amplitude is small, so that power consumption can be reduced.

  Of the inventions disclosed in the present application, the effects obtained by the representative embodiments will be briefly described. Thus, the communication speed can be increased.

1 is a block diagram showing an example of a schematic configuration in an optical communication system according to Embodiment 1 of the present invention. FIG. 2 is a conceptual diagram illustrating various compensation contents for keeping the light output power from a laser diode uniform in the transmission circuit block of FIG. 1. The details of the transmission circuit block in the optical communication system of FIG. 1 are shown, and (a) and (b) are block diagrams showing different configuration examples. It is a block diagram which shows the modification of the transmission circuit block of Fig.3 (a). FIG. 4 is a diagram showing a main operation concept of a pre-driver circuit in the transmission circuit block of FIGS. 3 (a) and 3 (b). FIG. 4 is a circuit block diagram showing a detailed configuration example of the transmission circuit block of FIG. FIG. 7 is a waveform diagram showing a main operation example in the transmission circuit block of FIG. 6. It is a figure which shows the operation | movement concept for compensating the nonlinear characteristic of optical output power in the optical transmission circuit by Embodiment 2 of this invention. In the optical transmission circuit by Embodiment 2 of this invention, the detail of the transmission circuit block in the optical communication system of FIG. 1 is shown, (a), (b) is a block diagram which shows a respectively different structural example. . FIG. 10 is a circuit block diagram showing a detailed configuration example of the transmission circuit block in FIG. It is a block diagram which shows the structural example of the principal part in the optical communication system by Embodiment 3 of this invention. FIG. 12 is a circuit block diagram illustrating a configuration example of an eye pattern monitor circuit in the reception circuit block of FIG. 11. It is a conceptual diagram showing an example of the operation | movement content in the optical communication system by Embodiment 4 of this invention. It is a circuit block diagram which shows the structural example of the principal part of the optical communication system at the time of using the communication system of FIG. FIG. 10 is a circuit block diagram showing a configuration example of main parts of an optical communication system according to a fifth embodiment of the present invention. It is explanatory drawing which shows an example of the temperature characteristic of the optical output power in a laser diode. It is explanatory drawing which shows an example of the temperature characteristic of the relaxation oscillation frequency in a laser diode. It is explanatory drawing which shows an example of the temperature characteristic of the optical output power in a laser diode, and the optical output waveform (eye pattern) at the time of high temperature. It is a block diagram which shows the modification of Fig.3 (a) and FIG. FIG. 5 is a circuit diagram illustrating a configuration example of the laser driver circuit in the transmission circuit block of FIG. 4.

  In the following embodiment, when it is necessary for the sake of convenience, the description will be divided into a plurality of sections or embodiments. However, unless otherwise specified, they are not irrelevant, and one is the other. Some or all of the modifications, details, supplementary explanations, and the like exist. Further, in the following embodiments, when referring to the number of elements (including the number, numerical value, quantity, range, etc.), especially when clearly indicated and when clearly limited to a specific number in principle, etc. Except, it is not limited to the specific number, and may be more or less than the specific number.

  Further, in the following embodiments, the constituent elements (including element steps and the like) are not necessarily indispensable unless otherwise specified and apparently essential in principle. Needless to say. Similarly, in the following embodiments, when referring to the shapes, positional relationships, etc. of the components, etc., the shapes are substantially the same unless otherwise specified, or otherwise apparent in principle. And the like are included. The same applies to the above numerical values and ranges.

  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 a known integrated circuit technology such as a CMOS (complementary MOS transistor). . In the embodiment, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) (abbreviated as a MOS transistor) is used as an example of a MISFET (Metal Insulator Semiconductor Field Effect Transistor), but a non-oxide film is not excluded as a gate insulating film. Absent. Although the connection of the substrate potential of the MOS transistor is not particularly specified in the drawing, the connection method is not particularly limited as long as the MOS transistor can operate normally.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.

(Embodiment 1)
FIG. 1 is a block diagram showing an example of a schematic configuration of an optical communication system according to Embodiment 1 of the present invention. An optical communication system SYS shown in FIG. 1 includes, for example, digital signal processing circuits LOG_TX and LOG_RX, a feedforward equalizer circuit FFE, a clock data recovery circuit CDR, a transmission circuit block TX_BK, a reception circuit block RX_BK, and an optical transmission cable. (Optical fiber etc.) It is comprised including OF_TX and OF_RX.

  LOG_TX outputs a desired transmission data signal to TX_BK via FFE. TX_BK generates an optical signal corresponding to the transmission data signal, and transmits this optical signal to RX_BK of another optical communication device (not shown) via OF_TX. The FFE is a circuit that performs so-called waveform equalization (waveform shaping) for compensating inter-symbol interference (ISI) or the like that may occur in, for example, OF_TX. On the other hand, an optical signal generated by TX_BK of another optical communication device (not shown) is transmitted via OF_RX. This optical signal is received by RX_BK, and RX_BK generates a reception signal corresponding to this optical signal and outputs it to the CDR. The CDR reproduces a clock signal and a received data signal from this received signal and outputs them to LOG_RX. LOG_RX receives the clock signal and the received data signal and performs desired processing.

  TX_BK generates a pre-driver circuit PDV that amplifies the output signal of the FFE, a laser driver circuit LDV that generates a driving current according to the output of the PDV, and an optical signal according to the driving current from the LDV, and transmits the optical signal to OF_TX A laser diode LD is provided. On the other hand, RX_BK further includes a photodiode PD that generates a current signal corresponding to the optical signal from OF_RX, a transimpedance amplifier circuit TIA that amplifies and converts the current signal into a voltage signal, and further amplifies the output of TIA. Is provided with a post-amplifier circuit PAMP.

  In such an optical communication system SYS, the communication speed of data performed via the optical transmission cables OF_TX and OF_RX reaches several tens of Gbps (for example, 25 Gbps) or more. In order to cope with this, as described in FIG. 17 and the like, it is necessary to improve the relaxation oscillation frequency of the LD, but it is sufficient to increase the communication speed only by improving the frequency by structural improvement of the LD. There is a possibility that it cannot be performed, and an increase in bias current is required. In this case, as shown in FIG. 18, there is a concern about distortion of the eye pattern particularly at high temperatures. Since the current signal output by the PD of RX_BK is in a very small order, for example, several hundred μA, there is a high possibility that the TIA malfunctions when the eye pattern is distorted. Further, as the speed increases, TX_BK itself tends to generate heat, and there is a greater concern about eye pattern distortion. Therefore, it is beneficial to use various methods described later.

  FIG. 2 is a conceptual diagram illustrating various compensation contents for keeping the optical output power from the laser diode LD uniform in the transmission circuit block TX_BK of FIG. In FIG. 2, it is assumed that a region in which the slope of the optical output power with respect to the LD drive current becomes nonlinear at high temperatures is used as the LD bias current Ib is increased in order to improve the relaxation oscillation frequency of the LD. Yes. Here, a case is considered in which the LD is transitioned between the maximum optical output power Pmax higher by ΔPac and the minimum optical output power Pmin lower by ΔPac than the intermediate optical output power Pmid, regardless of the temperature. That is, it is considered to obtain an optical output power having a constant amplitude regardless of the temperature and whose center position is the cross point of the eye pattern. For this purpose, compensation for the following three is required.

  The first compensation target is the difference (ΔIb) between the LD bias current Ib (lt) at low temperature corresponding to Pmid and the LD bias current Ib (ht) at high temperature corresponding to Pmid. The second compensation target is the difference between the LD driving current (Iac (lt)) at low temperature and the LD driving current (Iac1 (ht)) at high temperature necessary to obtain ΔPac. The third object of compensation is an LD driving current (Iac1 (ht)) required to obtain an optical output power that is lower by ΔPac with respect to Pmid at a high temperature and an LD that is required to obtain an optical output power that is higher by ΔPac. This is the difference from the drive current (Iac2 (ht)).

  FIG. 3 shows details of the transmission circuit block TX_BK in the optical communication system of FIG. 1, and (a) and (b) are block diagrams showing different configuration examples. A transmission circuit block (optical transmission circuit) TX_BK1a shown in FIG. 3A includes a pre-driver circuit PDV1a, a laser driver circuit LDV1a, a laser diode LD1, and a temperature / light detection circuit block PTDET_BK. LDV1a is provided between driver circuit DRV that outputs charging current Iac1 or discharging current Iac2 according to an input voltage signal, and variable current source ISb1 that is provided between the output node of DRV and ground power supply voltage GND and generates bias current Ib. And. LD1 has an anode connected to power supply voltage VCC and a cathode connected to an output node of DRV, and outputs an optical signal using (Ib−Iac1) or (Ib + Iac2) as a drive current. This optical signal is sent to the optical transmission cable OF_TX and also sent to PTDET_BK.

  PTDET_BK includes a light detection sensor and a temperature sensor, and detects the power of the optical signal from LD1 and the temperature of LD1. Based on these detection results, three types of control signals S_CTLb, S_CTLg, and S_CTLo are generated. S_CTLb varies according to the detection result of the light detection sensor, and controls the value of the bias current Ib of the variable current source ISb1 described above. That is, S_CTLb controls the value of Ib so as to keep the power of the optical signal constant, thereby realizing the compensation of the first compensation target (ΔIb) described in FIG.

  The pre-driver circuit PDV1a includes a variable amplifier circuit VAMPp that receives a differential input and outputs a differential output, and a variable offset circuit VOF that adds an offset between the differential pair. The differential output from the PDV 1a becomes the input of the driver circuit DRV described above. Although VOF is provided on the output side of VAMPp here, it can be provided on the input side. Here, the gain of VAMPp is controlled by the control signal S_CTLg described above. S_CTLg varies depending on the detection result of the temperature sensor. That is, S_CTLg reduces the magnitude of the AC current signal Iac via DRV by reducing the gain of VAMPp at low temperatures, and increases the gain of VAMPp at high temperatures by reducing the gain of VAMPp. Increase the size. Thereby, the compensation of the second compensation target (difference between Iac (lt) and Iac1 (ht)) described in FIG. 2 is realized.

  The variable offset circuit VOF is controlled by the control signal S_CTLo described above. S_CTLo varies depending on the detection result of the light detection sensor and the detection result of the temperature sensor. That is, S_CTLo controls the offset voltage of the VOF so that the input amplitude on the high level side, for example, toward the driver circuit DRV becomes larger than the input amplitude on the low level side at a high temperature, and the discharge current (Iac2 via IDR2) ) Is larger than the charging current (Iac1). Thereby, the compensation of the third compensation target (difference between Iac1 (ht) and Iac2 (ht)) described in FIG. 2 is realized.

  The transmission circuit block (optical transmission circuit) TX_BK1b shown in FIG. 3B is different from the transmission circuit block TX_BK1a shown in FIG. 3A in that the predriver circuit PDV1a of TX_BK1a is replaced with the predriver circuit PDV1b, and TX_BK1a The laser driver circuit LDV1a is replaced with the laser driver circuit LDV1b. The PDV 1b has a configuration in which the variable amplifier circuit VAMPp in the PDV 1a is replaced with the amplifier circuit AMPp, and the LDV 1b has a configuration in which the driver circuit DRV in the LDV 1a is replaced with the variable driver circuit VDRV. Here, the control signal S_CTLg from the temperature / light detection circuit block PTDET_BK is input to VDRV instead of VAMPp. That is, the above-described TX_BK1a is configured to change the output amplitude by changing the input amplitude of the driver circuit in the laser driver circuit, but TX_BK1b is configured to change the output amplitude without changing the input amplitude of the driver circuit. ing.

  FIG. 4 is a block diagram showing a modification of the transmission circuit block TX_BK1a of FIG. The transmission circuit block TX_BK1a 'shown in FIG. 4 differs from the transmission circuit block TX_BK1a shown in FIG. 3A in the configurations of the laser driver circuit LDV1a' and the laser diode LD1 '. In the LDV 1 a ′, a variable current source ISb 1 ′ is provided between the output node of the driver circuit DRV and the power supply voltage VCC. The LD 1 ′ has an anode connected to the DRV output node and a cathode connected to the ground power supply voltage GND. In accordance with the difference in polarity, the driver circuit DRV generates a charging current (Iac2) and a discharging current (Iac1) opposite to FIG. 3 (a). The configuration example of FIG. 4 and the configuration example of FIG. 3A are properly used according to the specifications of the laser diode.

  FIG. 5 is a diagram showing a main operation concept of the pre-driver circuit PDV in the transmission circuit block TX_BK of FIGS. 3 (a) and 3 (b). First, as described in FIG. 18, the discharge current (Iac2) applied to the bias current Ib when obtaining high optical output power at a high temperature and the charging current (Iac1) subtracted from Ib when obtaining low optical output power. Since the current value on the Iac2 side is insufficient, the cross point of the eye pattern with the optical output power as the vertical axis shifts from the center to the plus side (high temperature characteristics in FIG. 5). Therefore, the characteristic of FIG. 18 at a high temperature is virtually regarded as a linear characteristic, and an eye pattern in which the cross point is shifted to the minus side by an amount equal to the above-described shift amount on the plus side under this virtual condition ( In order to generate the correction characteristic of FIG. 5, the laser diode is driven. Specifically, the shortage of the current value on the Iac2 side described above is compensated, and the laser diode is driven by adding an offset so that Iac1 <Iac2. Then, the above-described plus shift amount at the time of high temperature and the virtually corrected minus shift amount are offset, and as a result, the cross point of the eye pattern is set at the center. This enlarges the eye and improves the waveform quality.

  FIG. 6 is a circuit block diagram showing a detailed configuration example of the transmission circuit block TX_BK1a in FIG. In FIG. 6, the variable amplifier circuit VAMPp included in the pre-driver circuit PDV1a includes NMOS transistors MNp and MNn as a differential pair, a current source ISd as a tail current source, and resistors Rp and Rn as a differential load. I have. MNp and MNn have sources connected in common, MNp has a gate connected to a positive input node PI, a drain connected to a negative output node NO, and MNn has a gate connected to a negative input node NI and a drain connected to a positive output node. Connected to each PO. ISd is connected between the sources of MNp and MNn and the ground power supply voltage GND. One ends of Rp and Rn are commonly connected to the power supply voltage VCC, the other end of Rp is connected to NO, and the other end of Rn is connected to PO. The variable offset circuit VOF included in the PDV 1a is connected between the negative output node NO and GND, is connected between the variable current source ISn that flows the current In, and the positive output node PO and GND, and flows the current Ip. A variable current source ISp is provided.

  In FIG. 6, a temperature / light detection circuit block PTDET_BK1 includes a photodiode PD1 serving as a light detection sensor, a low-pass filter LPF, an error amplifier circuit EA, a temperature sensor TSEN such as a thermistor, and an offset voltage conversion table TBLo. And a gain control conversion table TBLg. PD1 outputs a current signal corresponding to the optical signal from the laser diode LD1. The LPF converts the current signal into a voltage signal and smoothes it. That is, a voltage corresponding to the average optical output power of the LD 1 is output from the LPF. The EA amplifies a difference between the output voltage from the LPF and a preset reference voltage Vref, and generates a control signal S_CTLb. Vref is a voltage value for setting the intermediate optical output power Pmid in FIG. 2 in advance, and EA is an output voltage of LPF (that is, average optical output power) is Vref (that is, predetermined Pmid) via S_CTLb. The magnitude of the bias current Ib is controlled so as to converge to. Thereby, the compensation of the first compensation object described in FIG. 2 is performed.

  TSEN detects the temperature of LD1. The TBLg receives the detection result of TSEN and outputs a control signal S_CTLg corresponding to the detection result to the variable amplifier circuit VAMPp. VAMPp changes the gain according to S_CTLg, for example, by changing the magnitudes of Rp and Rn, or changing the current value of ISd. TBLg outputs S_CTLg that increases the gain of VAMPp as the temperature of LD1 increases, and thereby compensates the second compensation target described in FIG. TBLo receives the output voltage of LPF (which may be equivalent to reference voltage Vref or bias current Ib) and the detection result of TSEN, and outputs a control signal S_CTLo according to it to variable offset circuit VOF. The VOF increases the offset amount (that is, the difference between the current In and the current Ip) as the output voltage (equivalently Vref or Ib) of the LPF increases in accordance with S_CTLo, and increases the offset amount as the temperature increases. As a result, the third compensation target described in FIG. 2 is compensated.

  Each table (TBLg, TBLo) can be realized by various methods by appropriately combining general-purpose circuits such as a logic operation circuit, a memory circuit, an analog / digital conversion circuit, a digital / analog conversion circuit, and the like. is there. For example, a method of performing conversion by simply holding input data and output data corresponding to each input data in a memory circuit, or defining a conversion formula between input and output in advance, and outputting output data for input data to a logic operation circuit The method of calculating by etc. is mentioned. In some cases, it may be realized by a dedicated analog circuit that receives an analog input, performs weighting according to the size, and generates a weighted analog output.

  FIG. 7 is a waveform diagram showing a main operation example in the transmission circuit block TX_BK1a of FIG. FIG. 7 shows an operation example associated with the variable offset circuit VOF of FIG. As shown in FIG. 7, first, a case is assumed in which a signal having the same voltage amplitude on the high level side and voltage amplitude on the low level side is input to the differential input nodes PI and NI of the variable amplifier circuit VAMPp in FIG. Here, in the VOF of FIG. 6, when the control signal S_CTLo is controlled so that, for example, In becomes larger than Ip by ΔI, the center voltage level of the positive output node PO is higher than the center voltage level of the negative output node NO. Steady waveform transition is performed in a state where it is increased by ΔI × Rp. As a result, as shown in FIG. 7, the differential voltage amplitude on the high level side with respect to PO becomes larger than the differential voltage amplitude on the low level side, and the driver circuit DRV in FIG. The laser diode LD1 is driven using a discharge current (Iac2) larger than the current (Iac1).

  As described above, by using the optical transmission circuit and the optical communication system according to the first embodiment, typically, when the bias current of the laser diode is increased to improve the relaxation oscillation frequency, the temperature further increases. Even when it fluctuates, the waveform quality of good optical output power can be ensured, so that the communication speed can be increased.

(Embodiment 2)
In the first embodiment described above, the nonlinear characteristic of the optical output power at high temperature or the like is compensated by adjusting the offset voltage by the variable offset circuit VOF. However, in the second embodiment, a similar method is used by using a different method. Compensate. FIG. 8 is a diagram illustrating an operation concept for compensating for the nonlinear characteristic of the optical output power in the optical transmission circuit according to the second embodiment of the present invention. As described in FIG. 5, when the nonlinear region is used at a high temperature or the like, the discharge current (Iac2) with respect to the bias current Ib is insufficient as compared with the charging current (Iac1). The cross point of the eye pattern shifted from the center to the plus side (high temperature characteristics in FIG. 8).

  Therefore, the characteristics of the optical output power at a high temperature and the like are virtually regarded as linear characteristics, and under this virtual condition, the above-described eye pattern (high temperature characteristics in FIG. 8) is vertically changed with the central axis in the vertical axis direction as a reference. The laser diode is driven to generate an eye pattern (correction characteristics in FIG. 8) as intended. Specifically, such a virtual eye pattern is generated by processing the waveform shape by waveform equalization. Then, the eye pattern shown in the high temperature characteristic of FIG. 8 and the eye pattern shown in the correction characteristic of FIG. 8 cancel each other, and as a result, the cross point of the eye pattern is set at the center. This enlarges the eye and improves the waveform quality.

  FIG. 9 shows details of the transmission circuit block TX_BK in the optical communication system of FIG. 1 in the optical transmission circuit according to the second embodiment of the present invention. (A) and (b) are different configuration examples. FIG. The transmission circuit block (optical transmission circuit) TX_BK2a shown in FIG. 9A includes a pre-driver circuit PDV2a, a laser driver circuit LDV1a, a laser diode LD1, and a temperature / light detection circuit block PTDET_BK. The TX_BK2a in FIG. 9A has a configuration in which the predriver circuit PDV1a of TX_BK1a is replaced with the predriver circuit PDV2a of TX_BK2a, as compared with the transmission circuit block TX_BK1a of FIG. Accordingly, PTDET_BK is configured to output the control signal S_CTLe toward the PDV 2a, unlike the case of FIG. Since the configuration other than these is the same as that of FIG. 3A, detailed description thereof is omitted.

  The PDV 2a is, for example, a waveform equalization circuit configured by combining a plurality of variable amplifier circuits and a plurality of variable delay circuits. The control signal S_CLLe controls the variable amount of each variable amplifier circuit and variable delay circuit, whereby the PDV 2a generates an output waveform having a predetermined waveform shape. For example, the third compensation object described in FIG. 2 can be compensated by generating a waveform shape corresponding to the correction characteristic of FIG. 8 described above. Further, the PDV 2a changes the overall amplitude of the waveform shape according to S_CTLe. As a result, the second compensation object described in FIG. 2 can be compensated.

  On the other hand, the transmission circuit block (optical transmission circuit) TX_BK2b shown in FIG. 9B includes a pre-driver circuit PDV2b, a laser driver circuit LDV1b, a laser diode LD1, and a temperature / light detection circuit block PTDET_BK. The TX_BK2b in FIG. 9B has a configuration in which the predriver circuit PDV1b of TX_BK1b is replaced with the predriver circuit PDV2b of TX_BK2b, as compared with the transmission circuit block TX_BK1b of FIG. 3B. Accordingly, PTDET_BK is configured to output a control signal S_CTLe to PDV 2b, unlike the case of FIG. 3B. Since the configuration other than these is the same as that of FIG. 3B, detailed description thereof is omitted.

  The PDV 2b is, for example, a waveform equalization circuit configured by combining a plurality of variable amplifier circuits and a plurality of variable delay circuits, similarly to the PDV 2a of FIG. 9A. The control signal S_CTLe controls the variable amount of each variable amplifier circuit and variable delay circuit, whereby the PDV 2b generates an output waveform having a predetermined waveform shape. For example, the third compensation object described in FIG. 2 can be compensated by generating a waveform shape corresponding to the correction characteristic of FIG. 8 described above. However, unlike the case of FIG. 9A, the compensation of the second compensation target is performed by the laser driver circuit LDV1b. Note that the connection relationship between the laser diode LD1 and the laser driver circuits LDV1a and LDV1b in FIGS. 9A and 9B can be changed as appropriate as shown in FIG.

  FIG. 10 is a circuit block diagram showing a detailed configuration example of the transmission circuit block TX_BK2b in FIG. 9B. In FIG. 10, the pre-driver circuit PDV2b includes, for example, three variable amplifier circuits VAMP1 to VAMP3, two variable delay circuits VDLY1 and VDLY2, and an adder circuit ADD. VDLY1 delays the input signal to PDV2b, and VDLY2 delays the output signal of VDLY1. VAMP1 amplifies the input signal to PDV2b, VAMP2 amplifies the output signal of VDLY1, and VAMP3 amplifies the output signal of VDLY2. The ADD adds the output signals of VAMP1 to VAMP3 and outputs them to the laser driver circuit LDV1b.

  In FIG. 10, a temperature / photodetection circuit block PTDET_BK2 includes a photodiode PD1 serving as a photodetection sensor, a low-pass filter LPF, an error amplifier circuit EA, a temperature sensor TSEN such as a thermistor, and a waveform equalization control signal. A conversion table TBLe and a gain control conversion table TBLg are provided. That is, PTDET_BK2 in FIG. 10 has a configuration in which the offset voltage conversion table TBLo in PTDET_BK1 is replaced with TBLe in PTDET_BK2, as compared with the temperature / light detection circuit block PTDET_BK1 in FIG. Since the configuration other than this is the same as PTDET_BK1 in FIG. 6, detailed description thereof is omitted.

  TBLe receives the output voltage of LPF (equivalently Vref or Ib) and the detection result of TSEN, and outputs a control signal S_CTLe corresponding to it to PDV2b. PDV2b receives S_CTLe, individually sets the gains of VAMP1 to VAMP3, and individually sets the delay amounts of VDLY1 and VDLY2, thereby creating an output waveform shape corresponding to the correction characteristics of FIG. In TBLe, the relationship between the output voltage of LPF (equivalently Vref or Ib) and the detection result of TSEN, the gains of VAMP1 to VAMP3, and the delay amounts of VDLY1 and VDLY2 is defined in advance. Similar to the case of FIG. 6, this can be realized by various methods, for example, by appropriately combining general-purpose circuits.

  As described above, by using the optical transmission circuit according to the second embodiment, it is typically possible to increase the communication speed as in the first embodiment. When the offset method shown in FIG. 5 is compared with the waveform equalization method shown in FIG. 8, the offset method shown in FIG. This can be realized with a simple circuit configuration and circuit control. On the other hand, the waveform equalization method of FIG. 8 performs two-dimensional adjustments (vertical axis direction and horizontal axis direction), resulting in a complicated circuit configuration and circuit control. However, the shape of the eye pattern of optical output power is two-dimensional. Therefore, the eye can be further expanded and the communication speed can be further increased.

(Embodiment 3)
In the first and second embodiments described above, the nonlinear characteristic of the optical output power at a high temperature or the like is compensated for in the transmission circuit block. In the third embodiment, this compensation is performed using the reception circuit block. FIG. 11 is a block diagram showing a configuration example of main parts of an optical communication system according to Embodiment 3 of the present invention. FIG. 11 shows a transmission circuit block TX_BK3 that transmits an optical signal, a reception circuit block RX_BK3 that receives this optical signal, and a clock data recovery circuit CDR connected to the subsequent stage. TX_BK3 includes, for example, a laser diode LD1, a laser driver circuit LDV1a, and a predriver circuit PDV1a similar to those in FIG.

  On the other hand, RX_BK3 includes a photodiode PD, a transimpedance amplifier circuit TIA, a post-amplifier circuit PAMP, and a feedback control circuit FBCTL. The PD is provided between the power supply voltage VCC and the input node of the TIA, receives the optical signal from the TX_BK3, and generates a current signal corresponding to the magnitude. The TIA includes an amplifier circuit AMP1 and a voltage conversion feedback resistor Rf provided between the input node and the output node thereof, and converts the current signal transmitted to the input node of the TIA into a voltage signal. The PAMP amplifies the voltage signal from the TIA and outputs it to the clock data recovery circuit CDR.

  The FBCTL includes an eye pattern monitor circuit EYM connected to an input node of the CDR, a bit error rate detection circuit BERDET connected to an output node of the CDR, or both, and a control signal according to the processing result of these circuits. Output S_CTLLog. The pre-driver circuit PDV1a of TX_BK3 controls the offset amount in the variable offset circuit VOF as described in FIG. 3A and the gain in the variable amplifier circuit VAMPp according to this S_CTLlog. That is, the configuration example of FIG. 11 monitors the quality of the received signal, and performs feedback control on TX_BK3 so that the quality of the received signal is further improved, so that the eye pattern in the eye pattern of the optical output power described above can be obtained. In this way, the eye pattern distortion caused by the nonlinear characteristics as described in the first and second embodiments is indirectly eliminated.

  FIG. 12 is a circuit block diagram showing a configuration example of the eye pattern monitor circuit EYM in the reception circuit block RX_BK3 of FIG. The eye pattern monitor circuit EYM shown in FIG. 12 includes a plurality of flip-flop circuits FF0, FF1,... FFn, a clock generation circuit CLKGEN, a determination circuit JDG, and a feedback signal generation circuit FBGEN. CLKGEN generates clock signals φ0, φ1,..., Φn whose phases are sequentially different at regular intervals. FFn latches the input signal EIN with φ0, φ1,..., Φn, respectively. JDG determines the eye width of EIN using the outputs of FF0 to FFn. FBGEN outputs a feedback signal (control signal) S_CTL (S_CTLlog) corresponding to the determination result of JDG.

  In such a configuration, for example, CLKGEN uses a clock signal having a period T (for example, two periods) longer than one period of EIN, and clock signals φ0 to φ0 having phases different in units of (T / (n + 1)). Let φn be generated. Then, if EIN is random data, the output logic level is inverted at any of FF0 to FFn as a boundary, so that JDG can recognize (determine) the EIN eye width based on the position of this boundary. It becomes possible. The FBGEN changes the value of the control signal S_CTL in a direction to increase the eye width of the EIN while sequentially monitoring the eye width determined by the JDG.

  Further, the bit error rate detection circuit BERDET in FIG. 11 is used, for example, at the initial setting of the communication environment (so-called training). For example, the BERDET monitors the reception result (that is, the reproduction data signal via the CDR) for the optical signal that has been known from the transmission circuit block TX_BK3 and has the expected value of the data pattern in advance during the training period. The bit error rate (BER) is detected by comparison with the expected value. Then, the value of the control signal S_CTL is changed in the direction in which the bit error rate decreases. In EYM and BERDET, the direction in which the value of the control signal S_CTL is changed is determined empirically, for example, when the result deteriorates with the previous change direction, the value is changed in the opposite direction.

  As described above, by using the optical communication system according to the third embodiment, typically, the communication speed can be increased with the expansion of the eye pattern. Unlike the first and second embodiments described above, the method of the third embodiment is a method of comprehensively improving the deterioration of the eye pattern caused by various factors. It is possible that the communication speed can be increased as compared with the first and second modes. However, the method according to the third embodiment does not always eliminate the distortion of the eye pattern as described in FIG. 18, and an optimal solution cannot be obtained because complicated control is required. There is also a risk that control will diverge in the process of obtaining the optimal solution. From this point of view, it is desirable to use the method described in the first and second embodiments.

(Embodiment 4)
In the fourth embodiment, a method for realizing an increase in communication speed without performing various compensations as described in the first to third embodiments will be described. FIG. 13 is a conceptual diagram showing an example of the operation contents in the optical communication system according to the fourth embodiment of the present invention. In the first to third embodiments described above, the waveform quality is improved by compensating for the distortion caused by using the non-linear region, and the speed is increased. However, as shown in FIG. 13, although the nonlinear region is used, if the amplitude (or extinction ratio) of the optical output power (drive current of the laser diode LD) is reduced, the linear region can be used substantially.

  In the example of FIG. 13, for example, during a low temperature operation, a current signal (Iac (lt)) is supplied to the laser diode LD centering on the bias current Ib (lt), and during a high temperature operation, Ib (lt) The current signal (Iac (ht)) is supplied centering on a bias current Ib (ht) higher than. Accordingly, the LD generates an optical signal having an amplitude of Pmin (lt) to Pmax (lt) around the average optical output power Pave (lt) during the low temperature operation, and the average optical output power Pave during the high temperature operation. An optical signal having an amplitude of Pmin (ht) to Pmax (ht) around (ht) is generated.

Specifically, for example, at low temperature (25 ° C.), Ib (lt) = 24 mA, Pave (lt) = 7 mW, (Pmax (lt) −Pmin (lt)) = 2 mW, etc., and high temperature (85 ° C.) , Ib (ht) = 53 mA, Pave (ht) = 11.5 mW, (Pmax (ht) −Pmin (ht)) = 2 mW, and the like. As a comparative example, in the case of FIG. 16 described above, for example, Pmax = 10 mW, Pmin = 1 mW, (Pmax−Pmin) = 9 mW, and the like. In this case, the extinction ratio (10 × log ₁₀ (Pmax / Pmin)) is 10 dB.

  Usually, optical fiber networks such as the Internet are premised on long-distance transmission (for example, several hundred km), so a relatively large optical output power amplitude (9 mW, etc.) and extinction ratio (10 dB, etc.) are ensured. There is a need to. However, for example, when performing communication by short-distance transmission (for example, several centimeters to several tens of meters) between devices arranged to some extent, it is not always necessary to ensure a large optical output power amplitude and extinction ratio. . In such a case, the communication using the method as shown in FIG. 13 eliminates the distortion of the eye pattern caused by using the nonlinear region as described in FIG. I can plan. Furthermore, since the amplitude of the optical output power (LD drive current) is small, power consumption can be reduced. In FIG. 13, the average value (Pave (lt), Pave (ht)) of the optical output power is changed between the low temperature operation and the high temperature operation, while the relaxation oscillation frequency is secured. This is to reduce power consumption. Reduction of power consumption leads to reduction of noise and suppression of self-heating, which contributes to further increase in communication speed.

  FIG. 14 is a circuit block diagram showing a configuration example of a main part of the optical communication system when the communication method of FIG. 13 is used. FIG. 14 shows a transmission circuit block TX_BK4 included in one optical communication device DEV1, a reception circuit block RX_BK4 and a clock data recovery circuit CDR included in another optical communication device DEV2, and TX_BK4 passes through the optical transmission cable OF. In this example, RX_BK4 receives the transmitted optical signal. TX_BK4 in DEV1 includes a laser driver circuit LDV1a including a driver circuit DRV and a variable current source ISb1, a laser diode LD1, and a temperature detection circuit block TDET_BK.

  The DRV receives an output from the feed-forward equalizer circuit FFE (see FIG. 1) in the previous stage and generates a charging current (Iac1) or a discharging current (Iac2) corresponding to the output. ISb1 is provided between the output node of DRV and the ground power supply voltage GND, and generates a bias current Ib. LD1 is provided between the output nodes of the power supply voltage VCC and DRV, and is driven by (Ib−Iac1) or (Ib + Iac2). TDET_BK detects the temperature of LD1 and controls the magnitude of Ib in ISb1 based on the result. That is, the bias currents Ib (lt) and Ib (ht) as shown in FIG. 13 are controlled.

  On the other hand, RX_BK4 in DEV2 includes a photodiode PD, a variable current source ISr, a transimpedance amplifier circuit TIA, a DC component detection circuit DCDET, a post-amplifier circuit PAMP, and an error amplifier circuit EA2. The PD is provided between the power supply voltage VCC and the input node of the TIA, receives the optical signal from the optical transmission cable OF, and generates a current signal corresponding to the magnitude. ISr is provided between the input node of TIA and GND. The TIA includes an amplifier circuit AMP1 and a voltage conversion feedback resistor Rf provided between the input node and the output node thereof, and amplifies the current signal transmitted to the input node of the TIA and converts it into a voltage signal. DCDET is, for example, a low-pass filter or the like, and detects the DC component Vdc included in the voltage signal output from the TIA. The PAMP differentially amplifies the voltage signal from the TIA with reference to this Vdc and outputs it to the clock data recovery circuit CDR. For example, the magnitude of the AC component contained in the voltage signal from the TIA is several mmV to several tens mmV, and the PAMP amplifies this signal to several hundred mV.

  The EA 2 amplifies a difference between the direct current component Vdc detected by the DCDET and a predetermined reference voltage Vref1, and controls the magnitude of the output current of the ISr according to the result. That is, as shown in FIG. 13, when the average optical output power (Pave) of the optical signal is increased according to the temperature, Vdc detected by the DCDET also increases. In response, EA2 increases the output current of ISr. To control. When the average optical output power of the optical signal increases, the magnitude of the direct current component included in the current signal generated by the PD also increases. Therefore, by increasing the output current of ISr so as to cancel out the increase of the direct current component, TIA Is supplied with an alternating current component included in the current signal from the PD and a bias current always having a constant value. By stabilizing the TIA bias point in this way, the TIA can perform a stable amplification operation with a predetermined amplification factor over a wide band.

  As described above, by using the optical communication system according to the fourth embodiment, it is typically possible to increase the communication speed. Here, as an example, the DC component detection circuit DCDET, the error amplifier circuit EA2, and the variable current source ISr are used to stabilize the operation of the transimpedance amplifier circuit TIA. However, the present invention is not limited to such a configuration. Any configuration that stabilizes the bias point of TIA can be changed as appropriate. For example, a level shift circuit or the like is inserted between one end of the feedback resistor Rf and the input node of the amplifier circuit AMP1, and the level shift amount of the level shift circuit is controlled instead of controlling the current value of the variable current source ISr. Such a configuration may be adopted.

(Embodiment 5)
In the fifth embodiment, the communication method in FIG. 13 is realized using a configuration different from that in FIG. 14 described in the fourth embodiment. FIG. 15 is a circuit block diagram showing a configuration example of the main part of the optical communication system according to the fifth embodiment of the present invention. The optical communication system shown in FIG. 15 has the same transmission circuit block configuration as the optical communication system shown in FIG. 14, but the reception circuit block configuration is different. That is, here, a transmission circuit block TX_BK4 included in a certain optical communication device DEV1, a reception circuit block RX_BK5 and a clock data recovery circuit CDR included in another optical communication device DEV3 are shown, and TX_BK4 passes through the optical transmission cable OF. In this example, the RX_BK 5 receives the transmitted optical signal.

  RX_BK5 includes a feedback control circuit FBCTL2 in addition to the photodiode PD, variable current source ISr, transimpedance amplifier circuit TIA, and postamplifier circuit PAMP similar to those in the reception circuit block RX_BK4 of FIG. That is, the error amplifier circuit EA in RX_BK4 is replaced with FBCTL2 in RX_BK5. The FBCTL2 includes an eye pattern monitor circuit EYM connected to an input node of the CDR, a bit error rate detection circuit BERDET connected to an output node of the CDR, or both, and a control signal according to a processing result of these circuits. S_CTLr is output. The variable current source ISr controls the amount of bias current supplied to the PD in accordance with this S_CTLr.

  The configuration and operation of FBCTL2 are the same as those of feedback control circuit FBCTL described in FIGS. 11 and 12 of the third embodiment. In other words, the FBCTL2 monitors the quality of the received signal and performs feedback control on the variable current source ISr so that the quality of the received signal is further improved. As a result, the transformer as described in FIG. This is intended to stabilize the bias point of the impedance amplifier circuit TIA.

  As described above, by using the optical communication system according to the fifth embodiment, it is typically possible to increase the communication speed as in the case of the fourth embodiment. However, although not as in the case of the third embodiment, the control may be slightly complicated for the same reason as described above. From this viewpoint, it is preferable to use the method of the fourth embodiment described above.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiments. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

  For example, in FIGS. 3 and 6 of the first embodiment, the configuration example in which the offset is added to the differential amplifier circuit in the pre-driver circuit is shown. However, as shown in FIG. Alternatively, a configuration in which an offset is added to a single-type amplifier circuit is also possible. In the example of FIG. 19, the pre-driver circuit PDV1c includes a single variable amplifier circuit VAMPp 'and an offset adjustment variable current source ISn' connected to the output thereof. For example, when ISn ′ outputs a charging current of ΔI, the charging current for the driver circuit DRV increases by ΔI, and the discharging current decreases by ΔI. This adds an offset voltage.

  In the first and second embodiments described above, for example, a laser driver circuit as shown in FIG. 20 is used, and compensation accompanying use of the nonlinear region is performed by adjusting the output waveform of the pre-driver circuit. FIG. 20 is a circuit diagram showing a configuration example of the laser driver circuit LDV1a ′ in the transmission circuit block TX_BK1a ′ of FIG. The LDV 1a 'illustrated in FIG. 20 includes, for example, NMOS transistors MN1 to MN4, PMOS transistors MP1 and MP2, and a current source ISb. Each of MN1 and MN2 becomes a differential input pair, and ISb is connected to the common source node. A common fixed voltage is applied to the gates of MN3 and MN4, and the sources are connected to the drains of MN1 and MN2, respectively. In MP1 and MP2, a common fixed voltage is applied to the gates, and the drains are connected to the drains of MN3 and MN4, respectively. A laser diode LD1 'is connected between the drains of MP2 and MN4 and GND.

  Here, for example, when the “H” level is applied to the gate of MN1 (“L” level to the gate of MN2), the drive current of the laser diode LD1 increases and the “L” level (gate of MN2 gate) increases to the gate of MN1. When “H” level is applied, the drive current of LD1 decreases. As shown in FIG. 7, when the drive current is increased, the voltage amplitude applied between the gates of MN1 and MN2 is made larger than the voltage amplitude when the drive current is decreased. Compensation can be realized. By using such a so-called CML (Current Mode Logic) type laser driver circuit, the LD 1 ′ can be driven at a high speed, and the speed can be further increased by adding MN 3 and MN 4 serving as gate grounding.

  When the laser driver circuit as shown in FIG. 20 is used, the output waveform of the pre-driver circuit serving as the input may be adjusted. Depending on the circuit configuration of the laser driver circuit, the laser driver circuit itself may be controlled. Compensation associated with the use of the non-linear region can also be performed. For example, when the driver circuit DRV itself in the laser driver circuit LDV includes a variable current source for setting a charging current and a variable current source for setting a discharging current, the two variable current sources are controlled by a control signal. What is necessary is just to control by S_CTLo and to have a difference in each current value.

  The optical transmission circuit and the optical communication system according to the present embodiment can be widely applied to all products that perform optical communication using a laser diode, typified by an optical system using an optical fiber.

SYS Optical communication system LOG Digital signal processing circuit TX_BK Transmission circuit block RX_BK Reception circuit block PDV Pre-driver circuit LDV Laser driver circuit LD Laser diode OF Optical transmission cable FFE Feedforward equalizer circuit CDR Clock data recovery circuit IS Current source DRV driver circuit VAMP Variable Amplifier circuit VOF Variable offset circuit S_CTL Control signal PTDET_BK Temperature / photodetection circuit block AMP Amplifier circuit VDRV Variable driver circuit R Resistance NI, PI Input node NO, PO Output node MN NMOS transistor MP PMOS transistor EA Error amplifier circuit PD Photodiode LPF Low Pass filter TBL conversion table TSEN Temperature sensor VDLY Variable delay Circuit ADD adder circuit PAMP post amplifier circuit FBCTL feedback control circuit EYM eye pattern monitor circuit BERDET bit error rate detecting circuit FF flip-flop circuit CLKGEN clock generation circuit JDG decision circuit FBGEN feedback signal generation circuit TDET_BK temperature detection circuit blocks DCDET DC component detecting circuit

Claims (9)

A laser diode that emits light while transitioning between high optical output power and low optical output power;
A bias current source for supplying a bias current to the laser diode;
Adding the first drive current to the bias current causes the laser diode to emit light at the high optical output power, and subtracting the second drive current from the bias current causes the laser diode to emit light at the low optical output power. A driver circuit;
A detection circuit block that includes a temperature detection circuit that detects the temperature of the laser diode, and that outputs a first control signal whose value varies based on the detection result of the temperature detection circuit and the magnitude of the bias current;
First compensation means for setting a difference between the magnitude of the first drive current and the magnitude of the second drive current according to a value of the first control signal ;
A first pre-driver circuit having an output node connected to an input node of the driver circuit;
The optical transmission circuit according to claim 1, wherein the first compensation means is realized by adding an offset of an amount corresponding to the first control signal to the output signal of the first pre-driver circuit. The optical transmission circuit according to claim 1 ,
The detection circuit block further includes a light detection circuit for detecting an average magnitude of light output power from the laser diode, and according to a difference between a detection value of the light detection circuit and a predetermined set value. Output a second control signal whose value fluctuates;
The optical transmission circuit further comprises second compensation means for setting the magnitude of the bias current from the bias current source in accordance with the value of the second control signal. The optical transmission circuit according to claim 2 , wherein
The detection circuit block outputs a third control signal whose value varies based on the detection result of the temperature detection circuit,
The optical transmission circuit further includes third compensation means for setting a gain of the driver circuit or a gain of the first pre-driver circuit according to a value of the third control signal. The optical transmission circuit according to claim 1,
And a second pre-driver circuit having an output node connected to an input node of the driver circuit,
The first compensation means is realized by configuring the second pre-driver circuit with a waveform equalization circuit and setting various control parameters associated with the waveform equalization according to the first control signal. An optical transmission circuit. The optical transmission circuit according to claim 4 , wherein
The detection circuit block further includes a light detection circuit for detecting an average magnitude of light output power from the laser diode, and according to a difference between a detection value of the light detection circuit and a predetermined set value. Output a second control signal whose value fluctuates;
The optical transmission circuit further comprises second compensation means for setting the magnitude of the bias current from the bias current source in accordance with the value of the second control signal. The optical transmission circuit according to claim 5 , wherein
The detection circuit block outputs a third control signal whose value varies based on the detection result of the temperature detection circuit,
The optical transmission circuit further includes third compensation means for setting a gain of the driver circuit or a gain of the second pre-driver circuit according to a value of the third control signal. A transmission circuit block for transmitting an optical signal;
A receiving circuit block for receiving the optical signal transmitted from the transmitting circuit block;
The transmission circuit block includes:
A laser diode that emits light while transitioning between high optical output power and low optical output power;
A bias current source for supplying a bias current to the laser diode;
Adding the first drive current to the bias current causes the laser diode to emit light at the high optical output power, and subtracting the second drive current from the bias current causes the laser diode to emit light at the low optical output power. A driver circuit;
An output node comprising a pre-driver circuit connected to an input node of the driver circuit;
The receiving circuit block includes:
A photodiode that outputs a current signal according to the optical output power of the laser diode;
An amplifier circuit for amplifying and converting the current signal from the photodiode into a voltage signal;
A detection circuit block disposed downstream of the amplifier circuit, for monitoring the signal quality of the received signal transmitted through the amplifier circuit, and outputting a first control signal whose value varies according to the monitoring result. ,
The transmitting circuit block further have a first compensation means for setting in accordance with the difference between the size of the size and the second driving current of said first drive current to the value of the first control signal,
The optical communication system, wherein the first compensation means is realized by adding an offset of an amount corresponding to the first control signal to the output signal of the pre-driver circuit . The optical communication system according to claim 7 .
The detection circuit block latches the received signal transmitted through the amplifier circuit at a plurality of different clock phases, and determines the eye size in the eye pattern of the received signal based on the latch result. An optical communication system, wherein the value of the first control signal is varied so that the size of the first control signal increases. Including a transmission circuit block for transmitting the first optical signal;
The transmission circuit block includes:
A laser diode that emits light while transitioning between high optical output power and low optical output power;
A bias current source for supplying a bias current to the laser diode;
Adding the first drive current to the bias current causes the laser diode to emit light at the high light output power, and subtracting the second drive current from the bias current causes the laser diode to emit light at the low light output power. A driver circuit;
A temperature detection circuit for detecting the temperature of the laser diode;
The bias current source increases the bias current as the temperature of the laser diode detected by the temperature detection circuit increases.
The magnitudes of the first drive current and the second drive current are set to substantially constant values regardless of the temperature of the laser diode ,
And a receiving circuit block for receiving the second optical signal,
The receiving circuit block includes:
A photodiode that outputs a current signal according to the optical output power of the second optical signal;
A correction current source that outputs a correction current and subtracts the correction current from the current signal output from the photodiode;
A transimpedance amplifier circuit that amplifies a current obtained by subtracting the correction current from the current signal of the photodiode and converts the current into a voltage signal;
A DC component detection circuit that extracts a DC voltage component from the output voltage of the transimpedance amplifier circuit;
An optical communication system, comprising: a correction current control circuit that controls the magnitude of the correction current output from the correction current source so that an output voltage of the DC component detection circuit maintains a constant value .

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