JP2008060521A - Optical transmitter circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmitter circuit which is capable of driving a light emitting element at a desired high speed. <P>SOLUTION: A first peaking current generating section 1 generates a first peaking current P1 having a steeple shape, which is positive at the rising edge and negative at the falling edge, in synchronism with the transitions of a digital signal S. A second peaking current generating section 3 generates a second peaking current P2 having a steeple shape, which is negative at the rising edge and positive at the falling edge, in synchronism with the transitions of the digital signal S. A first light emitting element driving section 2 produces a first driving current D1 obtained by combining a signal amplitude current according to the amplitude of the digital signal S and the first peaking current P1. A second light emitting element driving section 4 produces a second driving current D2 obtained by combining the signal amplitude current according to the amplitude of the digital signal S and the second peaking current P2. Then, the first and second light emitting element driving sections 2 and 4 drive a light emitting element 5 by using a driving current D3 obtained by subtracting the first driving current D1 from the second driving current D2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical transmission circuit including a circuit for driving a light emitting element at high speed used in the field of optical communication.

  As a drive circuit for operating a light-emitting element (such as an LED) having a relatively low response speed at a high speed, a drive circuit using a peaking technique is generally known. This peaking technique is a technique in which an instantaneous current (hereinafter referred to as peaking current) is applied to the light emitting element to force the light emitting element to respond at high speed. FIG. 20 shows a configuration example of a general conventional light emitting element driving circuit using the peaking technique. FIG. 21 is a waveform diagram for explaining the operation of the conventional light emitting element driving circuit shown in FIG.

  The conventional light emitting element driving circuit shown in FIG. 20 includes a light emitting element 101, a peaking current generator 102, and a light emitting element driver 103. A digital signal S (waveform (a) in FIG. 21) is input to the light emitting element driving unit 103. The peaking current generator 102 generates a peak-shaped peaking current P (waveform (b) in FIG. 21) when the digital signal S rises and falls. The light-emitting element driving unit 103 receives the digital signal S and the peaking current P, and combines the amplitude current corresponding to the amplitude of the digital signal S with the peaking current P (the waveform (c in FIG. 21)). )) Is output. The light emitting element 101 receives the driving current D and outputs an optical signal having a waveform that substantially matches the digital signal S (waveform (d) in FIG. 21). In this way, high-speed response of the light emitting element 101 is realized.

  However, the high-speed response that can be realized with the above-described conventional light emitting element driving circuit is at most about several Mbps. However, since a very large peaking current P is required to realize a high-speed response of several hundred Mbps or more, clipping occurs at the time of falling in the light-emitting element driving unit 103, and the light-emitting element 101 is operated at high speed. There is a problem that can not be. As a method for solving this problem, a method can be considered in which the direct current of the light emitting element driving unit 103 is increased so that clipping does not occur at the time of falling. However, there are problems such as an increase in power consumption and deterioration of the extinction ratio, which is the high / low level ratio of the digital signal. In the worst case, the light emitting element 101 may be broken outside the guaranteed operating range.

  Therefore, a technique for solving such a problem is proposed in Patent Document 1 and the like. FIG. 22 shows a configuration example of a conventional light emitting element driving circuit disclosed in Patent Document 1. FIG. 23 is a waveform diagram for explaining the operation of the conventional light emitting element driving circuit shown in FIG.

The conventional light emitting element drive circuit shown in FIG. 22 has a configuration in which a discharge circuit 104 for extracting a part of the drive current D flowing into the light emitting element 101 is further added to the conventional light emitting element drive circuit shown in FIG. The peaking current generator 102 generates a large peaking current P (waveform (b) in FIG. 23), and the light emitting element driver 103 receives the digital signal S (waveform (a) in FIG. 23) and the peaking current. Then, a drive current D (waveform (c) in FIG. 23) having a waveform obtained by combining the amplitude current of the digital signal S and the peaking current P, that is, a waveform in which the clipping amount at the time of falling is minimized is output. The light emitting element 101 inputs the remaining current D ′ (waveform (d) in FIG. 23) obtained by extracting the current from the drive current D by the discharge circuit 104, and outputs an optical signal (waveform (e) in FIG. 23). Output. With this configuration, the direct current flowing through the light emitting element 101 can be reduced to improve the extinction ratio, and the light emitting element 101 can be operated with a current amount within the guaranteed operating range.
JP 2002-64433 A (FIG. 1)

However, in the conventional light emitting element driving circuit shown in FIG. 22 described above, the driving current D of the light emitting element 101 must be increased by the amount of current drawn by the discharge circuit 104, and the power consumption of the circuit increases.
Further, it is necessary to increase the drive current D so that clipping does not occur. However, since a very large current must be passed, the circuit scale becomes too large to be practical.

  Furthermore, as clipping generation locations, there are clipping generated in the transistors constituting the light emitting element driving unit 103 and clipping generated in the light emitting element 101. However, the conventional light emitting element driving circuit can improve the clipping generated in the light emitting element 101, but cannot improve the clipping generated in the transistor. Therefore, as shown in the waveform (e) of FIG. 23, there is a problem that the light output waveform at the time of falling of the light emitting element 101 becomes distorted and deteriorates.

  Therefore, an object of the present invention is to provide an optical transmission circuit that has a good extinction ratio, low power consumption, and can operate a light emitting element at high speed without causing a rounding of an optical output waveform. is there.

  The present invention is directed to an optical transmission circuit that drives a light emitting element in accordance with an input digital signal. In order to achieve the above object, the optical transmission circuit of the present invention includes first and second peaking current generation units and first and second light emitting element driving units. The first peaking current generator generates a first peaking current synchronized with the rising edge of the digital signal. The second peaking current generator generates a second peaking current synchronized with the falling edge of the digital signal. The first light emitting element driving unit generates a first driving current obtained by combining the signal amplitude current corresponding to the amplitude of the digital signal and the first peaking current. The second light emitting element driving unit generates a second driving current obtained by combining the signal amplitude current corresponding to the amplitude of the digital signal and the second peaking current. Then, the first and second light emitting element driving units drive the light emitting element using a current obtained by subtracting the first driving current from the second driving current.

  Preferably, the first light emitting element driving unit adjusts the signal amplitude current so that the driving current does not have a peaking current synchronized with the falling edge of the digital signal, and the second light emitting element driving unit However, the signal amplitude current is adjusted so as not to have a peaking current synchronized with the rising edge of the digital signal.

  Note that a direct current supply unit that supplies a direct current to the light emitting element may be further included, or a third light emitting element driving unit that directly supplies an amplitude current corresponding to the amplitude of the digital signal to the light emitting element. Good. In the case of this configuration, the first light emitting element driving unit may output only the peaking current synchronized with the rising edge to the light emitting element, and the second light emitting element driving unit may output the peaking current synchronized with the falling edge. May be output to the light emitting element. In this case, the second peaking current generator and the second light emitting element driver may be omitted, and only the rising edge of the digital signal may be compensated.

  Typically, each of the first and second peaking current generators includes a first resistor and a second resistor connected in series, and a capacitor connected in parallel to the first resistor. The first light emitting element driving unit includes an NPN transistor, and the second light emitting element driving unit includes a PNP transistor. Further, the light transmission circuit may include a light emitting element, and the light emitting element is preferably an LED.

  In order to achieve the above object, another optical transmission circuit of the present invention includes a peaking current generator, a light emitting element driver, a signal analyzer, and a clipping generator. The peaking current generator generates a peaking current synchronized with the rising and falling edges of the digital signal. The light emitting element driving unit generates a driving current by combining a signal amplitude current corresponding to the amplitude of the digital signal and a peaking current, and drives the light emitting element using the driving current. The signal analysis unit analyzes the digital signal and sets a control signal based on at least one of the pulse width and the amplitude amount of the digital signal. The clipping generation unit clips the peaking current of the drive current according to the control signal set by the signal analysis unit.

  Preferably, the clipping generation unit sets a ratio of the clipping current amount to the peaking current amount to a predetermined value or less. Further, it is desirable that the clipping generator controls the bias current of the drive current generated by the light emitting element driver.

  Typically, the signal analysis unit includes a pulse width detection unit that detects a pulse width of a digital signal, and a pulse width control unit that sets a control signal according to the detected pulse width. Alternatively, the signal analysis unit includes an amplitude amount detection unit that detects the amplitude amount of the digital signal and an amplitude amount control unit that sets a control signal according to the detected amplitude amount.

  Alternatively, the signal analysis unit adds the pulse width detection unit, the pulse width control unit, the amplitude amount detection unit, and the amplitude amount control unit, and the signal output from the pulse width control unit and the signal output from the amplitude amount control unit. And a processing unit that sets the processed signal as a control signal. In this configuration, a light receiving element that receives an optical signal transmitted from a communication partner device, an amplification unit that amplifies the signal received by the light receiving element, and an amplitude amount of the signal amplified by the amplification unit are detected. A signal detector that controls the amplitude of the digital signal input to the pulse width detector based on the detection result of the signal detector, and the amplitude controller Instead, the peaking current generator may control the amount of peaking current to be generated based on the detection result of the signal detector.

  Specifically, the peaking current generating unit includes a first resistor and a second resistor connected in series, and a capacitor connected in parallel to the first resistor. In particular, when controlling the amount of peaking current to be generated based on the detection result of the signal detector, the peaking current generator is connected in parallel to the first resistor and the second resistor connected in series, and the first resistor. It is preferable to have a configuration in which a plurality of blocks each including a plurality of blocks are provided and any one of the plurality of blocks is selectively switched based on the detection result of the signal detection unit.

The predetermined value a2 / a1, which is the ratio of the clipping current amount a2 to the peaking current amount a1, is preferably determined by the relational expression (6) described in the following best mode. In particular, the clipping generator preferably sets the predetermined value a2 / a1 under the condition of 0 <a2 / a1 ≦ 0.8 when the light emitting element is driven at a transmission speed of about 500 Mbps.
Further, the light transmitting circuit may include a light emitting element, and the light emitting element is preferably an LED.

According to the present invention, the peaking current at the rise time and the fall time are separately applied to eliminate the rounding of the optical signal waveform output from the light emitting element, so that both the rising speed and the falling speed are emitted at a desired speed. The element can be driven. Further, since it is not necessary to increase the direct current so that the peaking current at the falling time is not clipped, the effects of low power consumption and improved extinction ratio can be obtained.
Further, according to the present invention, by setting the ratio of the clipping current to the instantaneous drive current to be equal to or less than a predetermined value, it is possible to realize a high-speed response of the light emitting element and reduce power consumption.

FIG. 1 is a functional block diagram showing a schematic configuration of an optical transmission circuit common to the first to fourth embodiments of the present invention. In FIG. 1, the optical transmission circuit includes a first peaking current generator 1, a first light emitting element driver 2, a second peaking current generator 3, a second light emitting element driver 4, It is comprised with the light emitting element 5. FIG. For the light emitting element 5, a light emitting diode (LED), a laser diode (LD), a super luminescent diode (SLD), a surface emitting laser (VCSEL), or the like is applicable. In the following embodiments, a configuration in which the light emitting element 5 is included in the optical transmission circuit will be described. However, only the light emitting element 5 may have a different configuration.
The operation of the optical transmission circuit having this configuration will be described in detail with reference to the waveform diagram of FIG.

  A digital signal S (waveform (a) in FIG. 2) is input to the first light emitting element driving unit 2 and the second light emitting element driving unit 4, respectively. The first peaking current generator 1 is synchronized with the change of the digital signal S, and generates a peaking current P1 having a steeple shape that is positive when rising and negative when falling (waveform (b) in FIG. 2). The second peaking current generator 3 is synchronized with the change of the digital signal S, and generates a negative spire-shaped peaking current P2 (waveform (c) in FIG. 2) that is negative when rising and positive when falling.

  The first light emitting element driving unit 2 receives the digital signal S and the peaking current P1, and generates a driving current D1 (waveform (d) in FIG. 2) obtained by adding the peaking current P1 to the amplitude current of the digital signal S. . At this time, the first light emitting element driving unit 2 adjusts the direct current to generate the driving current D1 that eliminates the peaking current at the falling portion.

  Also, the second light emitting element driving unit 4 receives the digital signal S and the peaking current P2, and adds the peaking current P2 to the amplitude current of the inverted digital signal S (the waveform (e in FIG. 2)). )). At this time, the second light emitting element driving unit 4 adjusts the direct current to generate the driving current D2 that eliminates the peaking current in the rising portion.

  The light emitting element 5 has a driving current D3 (FIG. 2) obtained by subtracting the driving current D1 generated by the first light emitting element driving unit 2 from the driving current D2 generated by the second light emitting element driving unit 4 by the subtractor. Waveform (f)) is output. The drive current D3 has a falling peaking current and a rising peaking current, and the amplitude current is 0 level or more. Then, by inputting this drive current D3 to the light emitting element 5, it is possible to obtain an optical signal (waveform (g) in FIG. 2) whose amplitude waveform is not deteriorated. In this way, since the rising and falling peaking currents are generated by separate circuits, it becomes easy to avoid the influence of clipping, and the light emitting element 5 can be made to respond at high speed.

Hereinafter, the detailed configuration of the optical transmission circuit of the present invention will be described in order.
[First Embodiment]
FIG. 3 is a diagram illustrating a detailed configuration of the optical transmission circuit according to the first embodiment of the present invention. In the optical transmission circuit according to the first embodiment, each functional block shown in FIG. 1 is configured as follows.

  The first light emitting element driving unit 2 includes a transistor Q2, resistors R3 and R4, and a capacitor C2. An NPN bipolar transistor, an N channel field effect transistor, or the like is used as the transistor Q2. The base of the transistor Q2 is connected to the power supply VCC through a resistor R3, grounded through a resistor R4, and receives a digital signal S through a capacitor C2. The collector of the transistor Q2 is connected to the light emitting element 5. The resistor R3, the resistor R4, and the capacitor C2 are used for adjusting the direct current of the first light emitting element driving unit 2.

  The second light emitting element driving unit 4 includes a transistor Q1, resistors R1 and R2, and a capacitor C1. As the transistor Q1, a PNP bipolar transistor, a P-channel field effect transistor, or the like is used. The base of the transistor Q1 is connected to the power supply VCC through the resistor R1, is grounded through the resistor R2, and receives the digital signal S through the capacitor C1. The collector of the transistor Q1 is connected to the light emitting element 5. The resistor R1, the resistor R2, and the capacitor C1 are used to adjust the direct current of the second light emitting element driving unit 4.

  The first peaking current generator 1 includes resistors R7 and R8 and a capacitor C4. The resistor R7 and the resistor R8 are connected in series and are inserted between the emitter of the transistor Q2 of the first light emitting element driving unit 2 and the ground. The capacitor C4 is connected in parallel with the resistor R7.

  The second peaking current generator 3 includes resistors R5 and R6 and a capacitor C3. The resistor R5 and the resistor R6 are connected in series, and are inserted between the power supply VCC and the emitter of the transistor Q1 of the second light emitting element driving unit 4. The capacitor C3 is connected in parallel with the resistor R5.

  When the digital signal S changes from the high level to the low level, the base voltage of the transistor Q2 decreases, and accordingly, the emitter voltage of the transistor Q2 matches the ground level, so that the first light emitting element driving unit 2 is cut off. Then, the second light emitting element driving unit 4 becomes conductive. Thereby, the driving current D2 obtained by synthesizing the peaking current at the time of falling output from the second light emitting element driving unit 4 and the amplitude current adjusted by the resistors R1 and R2 of the second light emitting element driving unit 4 is obtained. The light is supplied from the emitter of the transistor Q1 to the light emitting element 5.

  Further, when the digital signal S changes from the low level to the high level, the base voltage of the transistor Q2 rises, so that the first light emitting element driving unit 2 is turned on, and the second light emitting element driving unit 4 is connected to the light emitting element 5. Only the bias current (= driving current D2) becomes conductive. As a result, the driving current D1 obtained by synthesizing the peaking current at the time of output outputted from the first light emitting element driving unit 2 and the amplitude current adjusted by the resistors R3 and R4 of the first light emitting element driving unit 2 becomes a transistor. It flows from the collector of Q2 toward the emitter. Accordingly, since the driving current D1 in the direction opposite to this direction flows in the light emitting element 5, the peaking current and the amplitude current at the time of falling are supplied to the light emitting element 5.

  As described above, according to the optical transmission circuit according to the first embodiment of the present invention, the peaking current at the rise time and the fall time are separately given, and the round of the optical signal waveform output from the light emitting element 5 is reduced. lose. Thereby, the light emitting element 5 can be driven at a desired speed for both the rising speed and the falling speed.

[Second Embodiment]
FIG. 4 is a diagram illustrating a detailed configuration of the optical transmission circuit according to the second embodiment of the present invention. The optical transmission circuit according to the second embodiment differs from the optical transmission circuit according to the first embodiment in the configuration of the second light emitting element driving unit 4.

  The second light emitting element driving unit 4 includes a transistor Q1, resistors R1 and R2, and capacitors C1 and C5. The resistor R1, the resistor R2, and the capacitor C1 are used to adjust the direct current of the second light emitting element driving unit 4. The capacitor C5 is inserted between the collector of the transistor Q1 and the light emitting element 5. With this configuration, when the digital signal S is input, the drive current D2 output from the second light emitting element drive unit 4 is an alternating current in which the direct current component is cut out of the current shown in the waveform (e) of FIG. Only the current of the component, that is, the peaking current at the fall time. The drive current D2 having only the AC component and the drive current D1 output from the first light emitting element driving unit 2 are supplied to the light emitting element 5.

  As described above, according to the optical transmission circuit according to the second embodiment of the present invention, since the direct current component is cut from the output of the second light emitting element driving unit 4, the amount of peaking current necessary for the amplitude current is obtained. A larger peaking current amount can be obtained, and the light emitting element 5 can be driven at a higher speed.

[Third Embodiment]
FIG. 5 is a diagram illustrating a detailed configuration of an optical transmission circuit according to the third embodiment of the present invention. The optical transmission circuit according to the third embodiment is different from the optical transmission circuit according to the first embodiment in the configuration of the first light emitting element driving unit 2.

  The first light emitting element driving unit 2 includes a transistor Q2, resistors R3, R4, and R9, and capacitors C2 and C6. The collector of the transistor Q2 is connected to the power supply VCC through the resistor R9 and is connected to the light emitting element 5 through the capacitor C6. With this configuration, when the digital signal S is input, the driving current D1 output from the first light emitting element driving unit 2 is an alternating current in which the direct current component is cut from the current shown in the waveform (d) of FIG. Only the current of the component, that is, the peaking current at the time of rising. The drive current D 1 having only the AC component and the drive current D 2 output from the second light emitting element driving unit 4 are supplied to the light emitting element 5.

  As described above, according to the optical transmission circuit according to the third embodiment of the present invention, the amount of peaking current required for the amplitude current is cut in order to cut the DC component from the output of the first light emitting element driving unit 2. A larger peaking current amount can be obtained, and the light emitting element 5 can be driven at a higher speed.

[Fourth Embodiment]
FIG. 6 is a diagram illustrating a detailed configuration of an optical transmission circuit according to the fourth embodiment of the present invention. The optical transmission circuit according to the fourth embodiment differs from the optical transmission circuit according to the first embodiment in the configurations of the first light emitting element driving unit 2 and the second light emitting element driving unit 4.

The first light emitting element driving unit 2 includes the same transistor Q2, resistors R3, R4, and R9, and capacitors C2 and C6 as in the third embodiment.
The second light emitting element driving unit 4 includes the transistor Q3, the resistor R10, in addition to the circuit block A including the transistor Q1, resistors R1 and R2, and capacitors C1 and C5, as in the second embodiment. And a circuit block B composed of R11 and a capacitor C7. As the transistor Q3, a PNP bipolar transistor, a P-channel field effect transistor, or the like is used.

  As described in the third embodiment, only the peaking current at the time of rising is output from the first light emitting element driving unit 2. On the other hand, as described in the second embodiment, only the peaking current at the time of falling is output from the circuit block A of the second light emitting element driving unit 4, and the circuit block B (= third light emitting element driving unit). ) Outputs an amplitude current obtained by adjusting the DC current of the digital signal S.

  As described above, according to the optical transmission circuit of the fourth embodiment of the present invention, the peaking current that compensates for the rise and fall and the amplitude current are supplied to the light emitting element 5, so that the rise speed and The light emitting element 5 can be easily driven at a desired speed due to the falling speed.

  As shown in FIG. 7, the circuit described in the first to fourth embodiments may further include a direct current supply unit 6 to adjust the amount of direct current supplied to the light emitting element 5. In FIG. 7, a current mirror circuit is used as an example of the DC current supply unit 6, but a configuration capable of supplying other DC current may be used.

[Fifth Embodiment]
As described above, in order to drive the light emitting element 5, it is ideal to use the drive current D3 shown by the waveform (f) in FIG. However, it has been confirmed by the present inventors that the present invention can withstand actual use even if the falling peaking current is reduced to some extent.
In the fifth to ninth embodiments, an optical transmission circuit in which the power consumption is reduced by reducing the falling peaking current will be described.

  First, how much the peaking current of the fall can be reduced will be described. It should be noted that the relational expression described below is for explaining the configuration of the peaking current generator 3 as an example, and it goes without saying that the relational expression changes as the circuit configuration changes.

In the drive current waveform of FIG. 8, the absolute value IPH of the peak current at the rise and the absolute value IPL of the peak current at the fall are the high level current IH and the low level current IL of the digital signal S, and the second peaking. When the resistors R5 and R6 of the current generator 3 are used, they can be expressed by the following equations (1) and (2). B1 is a constant.
IPH = B1 × (R5 / R6) × (IH−IL) + IH (1)
IPL = −B1 × (R5 / R6) × (IH−IL) + IL (2)

Therefore, the peaking current amount a1 shown in FIG. 8 can be expressed by the following equation (3).
a1 = IPH-IH = IL-IPL
= B1 × (R5 / R6) × (IH-IL) (3)

Next, consider the operation at the time of clipping shown in FIG. When the bias current Ib supplied to the base of the transistor Q1 is reduced, the peak current IPL at the time of falling becomes 0 level or less. However, in reality, clipping occurs in the light emitting element 5 and the peak current (= IPL ′) becomes 0 level. Accordingly, it is considered that the peak current IPL at the fall when clipping occurs corresponds to the peak current at the fall when the clipping does not occur below 0 level. Therefore, the clipping current amount a2 can be expressed using the absolute value IPL of the peak current at the time of falling, as in the following equation (4).
a2 = −IPL (4)

  For example, when conditions for driving the light-emitting element 5 with a transmission rate of 500 Mbps and a pulse current amplitude (= IH-IL) of 14.4 mAApp are set, it is necessary under the condition that clipping does not occur (a2 / a1 = 0). The bias current Ib is experimentally 139.5 mA and B1 × (R5 / R6) = 9.15. The peak currents at the time of rising and falling are IPH = 278.4 mA and IPL = 0 mA, respectively, according to the above equations (1) and (2). When the bias current Ib is gradually reduced from the condition that the clipping does not occur, clipping occurs and the output waveform of the light emitting element 5 becomes distorted. At this time, as a result of evaluating a2 / a1 at which the fall time tf is 1 ns (corresponding to a transmission speed of 500 Mbps), it was about 0.8. Under the condition of a2 / a1 = 0.8, the bias current Ib is 36.6 mA, so that the power consumption can be reduced by about 75% compared to the case where no clipping occurs. Other values are IPH = 175.5 mA, IPL ′ = 0 mA (IPL = −102.9 mA), a1 = 131.7 mA, and a2 = 102.9 mA.

Also, FIG. 9 shows a fall when the ratio a2 / a1, which is the ratio between the peaking current amount a1 and the clipping current amount a2, is changed using the amplitude amount (= IH−IL) of the pulse current and the bias current Ib as parameters. The experimental result of time tf is shown. Note that the response speed is slowed down as the fall time tf increases. Thus, in the case of a transmission rate of 500 Mbps with a fall time tf of 1 ns, a high-speed response of 500 Mbps can be realized by setting a2 / a1 to the condition of the following equation (5).

FIG. 9 is expressed by the following relational expression (6). The time tf is such that when a2 / a1 is small, the pulse fall time (first term) determined by the peak current is dominant, and when a2 / a1 is large, the clipping current output from the light emitting element driving unit 4 The fall time (second term) determined by is dominant. In addition, A1, A2, N1, and N2 of Formula (6) are constants. The time constant τ1 of the first term is determined by the transient response of the peak current set by the resistors R5 and R6 and the capacitor C3 of the second peaking current generator 3, and the time constant τ2 of the second term is 2 is determined by the transient response of the transistor Q1 and the light emitting element 5 of the light emitting element driving unit 4. Thereby, a2 / a1 according to the transmission rate can be set.

Next, an optical transmission circuit according to a fifth embodiment of the present invention will be described.
FIG. 10 is a diagram showing a configuration of an optical transmission circuit according to the fifth embodiment of the present invention. In FIG. 10, the optical transmission circuit according to the fifth embodiment includes a peaking current generation unit 3, a light emitting element 5, a light emitting element driving unit 7, a clipping generation unit 8, and a signal analysis unit 9. The signal analysis unit 9 includes a pulse width detection unit 10 and a pulse width control unit 11. The peaking current generator 3 and the light emitting element 5 have the same configurations as those described in the first to fourth embodiments. Hereinafter, an optical transmission circuit according to the fifth embodiment will be described focusing on the light emitting element driving unit 7, the clipping generation unit 8, the pulse width detection unit 10, and the pulse width control unit 11 having different configurations.

  The light emitting element driving unit 7 includes a transistor Q1, a resistor R16, and capacitors C1 and C8. As the transistor Q1, a PNP bipolar transistor, a P-channel field effect transistor, or the like is used. The base of the transistor Q1 is grounded through a resistor R16 and a capacitor C8 connected in series, and the digital signal S is input through the capacitor C1. The collector of the transistor Q1 is connected to the light emitting element 5. A DC voltage output from the clipping generator 8 is applied to a connection point between the resistor R16 and the capacitor C8.

  The pulse width detection unit 10 outputs the input digital signal S to the light emitting element driving unit 7, detects the pulse width of the digital signal S, and outputs the detection result to the pulse width control unit 11 as a detection pulse width. . For example, as shown in FIG. 11, the pulse width control unit 11 includes a comparison unit 11 a, compares a predetermined reference pulse width with a detected pulse width, and outputs a control signal based on the comparison result to the clipping generation unit 8. To do. An example of the pulse width detection unit 10 includes a configuration that detects the falling or rising of a pulse, but other configurations may be used. In addition, the comparison unit 11a is used as an example of the pulse width control unit 11, but a configuration in which a memory unit storing various control signals is provided and any one control signal is read from the memory unit according to the detected pulse width. However, it can be implemented.

  The clipping generator 8 includes resistors R17 to R19, a variable resistor R20, and a transistor Q6. As the transistor Q6, a PNP bipolar transistor, a P-channel field effect transistor, or the like is used. The variable resistor R20, the resistor R19, and the resistor R18 are connected in series and are inserted between the power supply VCC and GND. A connection point between the resistor R18 and the resistor R19 is connected to the base of the transistor Q6. The emitter of the transistor Q6 is connected to the power supply VCC via the resistor R17, and the DC voltage appearing at the emitter is output to the connection point between the resistor R16 and the capacitor C8 of the light emitting element driver 7. The collector of the transistor Q6 is grounded. The resistance value of the variable resistor R20 changes according to the control signal output from the pulse width control unit 11. By controlling the change in the resistance value, the amount of clipping at which the ratio of the amount of clipping current to the amount of peaking current falls below a predetermined value is adjusted.

  For example, when the detection pulse width is longer than the reference pulse width (transmission speed is slow), the bias current Ib of the clipping generator 8 is reduced, and the detection pulse width is shorter than the reference pulse width (transmission speed is fast). In this case, control is performed so that the bias current Ib of the clipping generator 8 is increased. As a result, a drive current in which the clipping current amount a <b> 2 is adjusted to a value corresponding to the transmission speed of the digital signal S can be supplied to the light emitting element 5.

  As described above, according to the optical transmission circuit of the fifth embodiment of the present invention, the amount of clipping at which the ratio of the amount of clipping current to the amount of peaking current is equal to or less than a predetermined value according to the transmission speed of the digital signal S. It can be adjusted automatically to achieve the minimum amount of clipping required for the transmission rate. Thereby, the high-speed response of the light emitting element 5 is realizable, reducing power consumption.

[Sixth Embodiment]
FIG. 12 is a diagram showing a configuration of an optical transmission circuit according to the sixth embodiment of the present invention. In FIG. 12, the optical transmission circuit according to the sixth embodiment includes a peaking current generator 3, a light emitting element 5, a light emitting element driver 7, a clipping generator 8, and a signal analyzer 9. The signal analysis unit 9 includes an amplitude amount detection unit 12 and an amplitude amount control unit 13. In the sixth embodiment, the amplitude amount detection unit 12 and the amplitude amount control unit 13 are different from the configuration of the fifth embodiment. Hereinafter, the optical transmission circuit according to the sixth embodiment will be described focusing on this different configuration.

  The amplitude amount detection unit 12 outputs the input digital signal S to the light emitting element driving unit 7, detects the amplitude amount of the digital signal S, and outputs the detection result to the amplitude amount control unit 13 as a detected amplitude amount. . For example, as shown in FIG. 13, the amplitude amount control unit 13 includes a comparison unit 13a, compares a predetermined reference amplitude amount with a detected amplitude amount, and outputs a control signal based on the comparison result to the clipping generation unit 8. To do. Instead of the comparison unit 13a, a configuration in which a memory unit that stores various control signals is provided and any one of the control signals is read from the memory unit according to the detected amplitude amount can be implemented. The clipping generation unit 8 changes the resistance value of the variable resistor R20 shown in FIG. 10 according to the control signal output from the amplitude amount control unit 13, so that the ratio of the clipping current amount to the peaking current amount becomes a predetermined value or less. Adjust the amount.

  For example, when the detected amplitude amount is larger than the reference amplitude amount, the peak current generated in the peaking current generating unit 3 becomes large. Therefore, the bias current Ib of the clipping generating unit 8 is increased, and the detected amplitude amount becomes the reference amplitude amount. If it is smaller, the bias current Ib of the clipping generator 8 is controlled to be small. As a result, the drive current in which the clipping current amount a <b> 2 is adjusted to a value corresponding to the amplitude amount of the digital signal S can be supplied to the light emitting element 5.

  As described above, according to the optical transmission circuit of the sixth embodiment of the present invention, the clipping amount in which the ratio of the clipping current amount to the peaking current amount is equal to or less than the predetermined value according to the amplitude amount of the digital signal S. It is possible to automatically adjust the amount of clipping to the minimum necessary for the amplitude. Thereby, the high-speed response of the light emitting element 5 is realizable, reducing power consumption.

[Seventh Embodiment]
FIG. 14 is a diagram showing a configuration of an optical transmission circuit according to the seventh embodiment of the present invention. In FIG. 14, the optical transmission circuit according to the seventh embodiment includes a peaking current generation unit 3, a light emitting element 5, a light emitting element drive unit 7, a clipping generation unit 8, and a signal analysis unit 9. The signal analysis unit 9 includes a pulse width detection unit 10, a pulse width control unit 11, an amplitude amount detection unit 12, an amplitude amount control unit 13, and a processing unit 14. The seventh embodiment is a combination of the fifth embodiment and the sixth embodiment, and the configuration of the processing unit 14 is different. Hereinafter, the optical transmission circuit according to the seventh embodiment will be described focusing on this different configuration.

  The processing unit 14 adds the control signal output from the pulse width control unit 11 and the control signal output from the amplitude amount control unit 13, and outputs the addition result to the clipping generation unit 8 as a final control signal. To do. Thereby, the control signal according to both the transmission speed and amplitude amount of the digital signal S can be output.

  As described above, according to the optical transmission circuit of the seventh embodiment of the present invention, the ratio of the clipping current amount to the peaking current amount is equal to or less than a predetermined value according to both the transmission speed and the amplitude amount of the digital signal S. Thus, the clipping amount can be automatically adjusted to the minimum necessary clipping amount for the transmission speed and amplitude amount. Thereby, the high-speed response of the light emitting element 5 is realizable, reducing power consumption.

  Note that the order of the process for detecting the transmission speed of the digital signal S and the process for detecting the amplitude of the digital signal S may be reversed. In the processing unit 14, the method example of outputting the result of adding the control signal of the pulse control unit 11 and the control signal of the amplitude amount control unit 13 as a final control signal has been described. It is also possible to implement a configuration in which a memory unit storing signals is provided and any one final control signal is read from the memory unit in accordance with each control signal.

[Eighth Embodiment]
FIG. 15 is a diagram showing a configuration of an optical transmission circuit according to the eighth embodiment of the present invention. In FIG. 15, the optical transmission circuit according to the eighth embodiment includes a peaking current generation unit 3, a light emitting element 5, a light emitting element driving unit 7, a clipping generation unit 8, and a signal analysis unit 9. The signal analysis unit 9 includes a pulse width detection unit 10, a pulse width control unit 11, an amplitude amount detection unit 12, an amplitude amount control unit 13, a processing unit 14, a light receiving element 15, an amplification unit 16, a signal detection unit 17, and an input signal. The control unit 18 is configured. In the eighth embodiment, the light receiving element 15, the amplification unit 16, the signal detection unit 17, and the input signal control unit 18 are different from the configuration of the seventh embodiment. Hereinafter, the optical transmission circuit according to the eighth embodiment will be described focusing on this different configuration.

  The light receiving element 15 receives an optical signal emitted from a communication partner device (not shown), and outputs an electric signal corresponding to the optical signal to the amplifying unit 16. Note that an antenna may be provided instead of the light receiving element 15, and a wireless signal may be received from a communication partner device. The amplifying unit 16 amplifies the electric signal output from the light receiving element 15 with a predetermined gain. The signal detection unit 17 detects the amplitude amount of the electric signal amplified by the amplification unit 16 and outputs the detection result to the input signal control unit 18 as a detection signal.

  For example, as shown in FIG. 16, the input signal control unit 18 includes a comparison unit 18a and a variable gain amplifier 18b. The comparison unit 18a compares a predetermined reference signal with the detection signal, and outputs a control signal based on the comparison result to the variable gain amplifier 18b as a gain control signal. The variable gain amplifier 18b controls the amplitude amount of the digital signal S according to the gain control signal. It should be noted that other than the variable gain amplifier 18b may be used as long as the amplitude of the digital signal S can be controlled. The digital signal S whose amplitude is controlled is input to the pulse width detection unit 10.

  For example, when the transmission distance is long and the optical signal received by the light receiving element 15 is small, the signal detection unit 17 detects an amplitude amount smaller than a reference amplitude amount in the input signal control unit 18. The signal control unit 18 performs control to increase the amplitude amount of the digital signal S. Based on this result, control is performed to increase the bias current Ib of the clipping generator 8. On the other hand, when the transmission distance is short and the optical signal received by the light receiving element 15 is large, the opposite control is performed.

  As described above, according to the optical transmission circuit according to the eighth embodiment of the present invention, according to both the transmission speed and the amplitude amount of the digital signal S based on the transmission distance with the communication partner apparatus, It is possible to automatically adjust the clipping amount at which the ratio of the clipping current amount to the peaking current amount is equal to or less than a predetermined value so as to obtain the minimum clipping amount necessary for the transmission speed and the amplitude amount. Thereby, the high-speed response of the light emitting element 5 is realizable, reducing power consumption.

[Ninth Embodiment]
FIG. 17 is a diagram showing a configuration of an optical transmission circuit according to the ninth embodiment of the present invention. 17, the optical transmission circuit according to the ninth embodiment includes a peaking current generator 19, a light emitting element 5, a light emitting element driver 7, a clipping generator 8, and a signal analyzer 9. The signal analysis unit 9 includes a pulse width detection unit 10, a pulse width control unit 11, an amplitude amount detection unit 12, an amplitude amount control unit 13, a processing unit 14, a light receiving element 15, an amplification unit 16, and a signal detection unit 17. The In the ninth embodiment, the peaking current generator 19 is different from the configuration of the eighth embodiment. Hereinafter, the optical transmission circuit according to the ninth embodiment will be described focusing on this different configuration.

  The signal detection unit 17 detects the amplitude amount of the electrical signal amplified by the amplification unit 16 and outputs the detection result to the peaking current generation unit 19 as a detection signal. For example, as shown in FIG. 18, the peaking current generation unit 19 includes a plurality of waveform peaking units 19a having different values and a selection unit 19b. The selection unit 19b selectively switches any one of a plurality of waveform peaking units 19a having different values according to the detection signal.

  As described above, according to the optical transmission circuit according to the ninth embodiment of the present invention, according to both the transmission speed and the amplitude amount of the digital signal S based on the transmission distance with the communication partner device, It is possible to automatically adjust the clipping amount at which the ratio of the clipping current amount to the peaking current amount is equal to or less than a predetermined value so as to obtain the minimum clipping amount necessary for the transmission speed and the amplitude amount. Thereby, the high-speed response of the light emitting element 5 is realizable, reducing power consumption.

  Note that the detailed circuits using the resistors, capacitors, and transistors shown in the first to ninth embodiments are examples, and other configurations may be used as long as they have the same functions. Absent. For example, as shown in FIG. 19, the clipping generator 8 may use a plurality of resistors and changeover switches having different values instead of the variable resistor R20. If the input digital signal S is fixed, the resistance value of the variable resistor R20 may be fixed without detecting the pulse width or amplitude amount of the digital signal S.

  In the first to fourth embodiments, the emitter of the transistor Q2 of the first light emitting element driving unit 2 is grounded via the first peaking current generating unit 1, and the second light emitting element driving unit 4 The configuration in which the emitter of the transistor Q1 is connected to the power supply VCC via the second peaking current generator 3 has been described. However, in addition to this connection, the emitter of the transistor Q2 may be connected to the power supply VCC and the emitter of the transistor Q1 may be grounded. Further, although the power supply VCC has been described as the upper limit voltage and the ground level as the lower limit voltage, a negative power supply may be used as the lower limit voltage.

  In the first to fourth embodiments, the example in which the peaking current is generated by the first and second peaking current generators to compensate for both the rising speed and the falling speed has been described. However, the present invention exhibits an effect over the conventional configuration only by the configuration in which the falling speed is compensated for by the first peaking current generator.

  The optical transmission circuit of the present invention can be used for a circuit for driving a light emitting element used in the field of optical communications, and is particularly useful when it is desired to transmit an optical signal at high speed while reducing power consumption.

1 is a functional block diagram showing a schematic configuration of an optical transmission circuit common to first to fourth embodiments of the present invention. Waveform diagram for explaining the operation of the optical transmission circuit shown in FIG. 1 is a detailed configuration diagram of an optical transmission circuit according to a first embodiment of the present invention. Detailed configuration diagram of an optical transmission circuit according to a second embodiment of the present invention Detailed configuration diagram of an optical transmission circuit according to a third embodiment of the present invention Detailed configuration diagram of an optical transmission circuit according to a fourth embodiment of the present invention Detailed configuration diagram of an optical transmission circuit according to another embodiment of the present invention Waveform diagrams for explaining the operation of the optical transmission circuits according to the fifth to ninth embodiments of the present invention The figure which shows the relationship between the clipping current and fall time of the optical transmission circuit which concerns on the 5th-9th embodiment of this invention. Detailed block diagram of an optical transmission circuit according to a fifth embodiment of the present invention Detailed circuit example of the pulse width controller 11 Detailed configuration diagram of an optical transmission circuit according to a sixth embodiment of the present invention Detailed circuit example of the amplitude control unit 13 Detailed block diagram of an optical transmission circuit according to a seventh embodiment of the present invention Detailed configuration diagram of an optical transmission circuit according to an eighth embodiment of the present invention Detailed circuit example of the input signal control unit 18 Detailed block diagram of an optical transmission circuit according to the ninth embodiment of the present invention Detailed circuit example of the peaking current generator 19 Another detailed circuit example of the clipping generator 8 Functional block diagram showing a schematic configuration of a conventional light emitting element driving circuit FIG. 20 is a waveform diagram for explaining the operation of the light-emitting element driving circuit shown in FIG. Functional block diagram showing a schematic configuration of another conventional light emitting element driving circuit FIG. 22 is a waveform diagram for explaining the operation of the light-emitting element driving circuit shown in FIG.

Explanation of symbols

1, 3, 19, 102 Peaking current generator 2, 4, 7, 193 Light-emitting element driving unit 5, 101 Light-emitting element (LED)
6 DC current supply unit 8 Clipping generation unit 9 Signal analysis unit 10 Pulse width detection unit 11 Pulse width control unit 11a, 13a, 18a Comparison unit 12 Amplitude amount detection unit 13 Amplitude amount control unit 14 Processing unit 15 Light receiving element 16 Amplification unit 17 Signal detection unit 18 Input signal control unit 18b Variable gain amplifier 19a Waveform peaking unit 19b Selection unit 104 Discharge circuit C1-C8 Capacitances Q1-Q6 Transistors R1-R20 Resistance

Claims (31)

An optical transmission circuit for driving a light emitting element according to an input digital signal,
A direct current supply unit for supplying a direct current to the light emitting element;
A peaking current generator for generating a peaking current synchronized with the rising edge of the digital signal;
A light emitting element driving unit that generates a driving current by combining the signal amplitude current corresponding to the amplitude of the digital signal and the peaking current, and drives the light emitting element using a current obtained by subtracting the driving current from the DC current; An optical transmission circuit comprising:   2. The optical transmission according to claim 1, wherein the light emitting element driving unit adjusts the signal amplitude current so that the driving current does not have a peaking current synchronized with a falling edge of the digital signal. circuit.   The optical transmission circuit according to claim 1, wherein the light emitting element driving unit outputs only a peaking current synchronized with the rising to the light emitting element.   2. The optical transmission circuit according to claim 1, wherein the peaking current generation unit includes a first resistor and a second resistor connected in series, and a capacitor connected in parallel to the first resistor.   The optical transmission circuit according to claim 1, wherein the light emitting element driving unit includes an NPN transistor.   The optical transmission circuit according to claim 1, wherein the light emitting element is included in the configuration.   The optical transmission circuit according to claim 6, wherein the light emitting element is an LED. An optical transmission circuit for driving a light emitting element according to an input digital signal,
A first peaking current generator for generating a first peaking current synchronized with the rising edge of the digital signal;
A second peaking current generator for generating a second peaking current synchronized with the falling edge of the digital signal;
A first light emitting element driving unit that generates a first driving current obtained by combining a signal amplitude current corresponding to the amplitude of the digital signal and the first peaking current;
A second light emitting element driving unit that generates a second driving current obtained by combining a signal amplitude current corresponding to the amplitude of the digital signal and the second peaking current;
The optical transmission circuit, wherein the first and second light emitting element driving units drive the light emitting element using a current obtained by subtracting the first driving current from the second driving current. The first light emitting element driving unit adjusts the signal amplitude current so that the driving current does not have a peaking current synchronized with a falling edge of the digital signal,
The said 2nd light emitting element drive part adjusts the said signal amplitude current so that the said drive current may not have the peaking current synchronizing with the rising of the said digital signal, The said signal amplitude current is characterized by the above-mentioned. Optical transmission circuit.   The optical transmission circuit according to claim 8, further comprising a direct current supply unit configured to supply a direct current to the light emitting element.   The optical transmission circuit according to claim 10, wherein the first light emitting element driving unit outputs only a peaking current synchronized with the rising to the light emitting element.   The optical transmission circuit according to claim 10, wherein the second light emitting element driving unit outputs only a peaking current synchronized with the falling to the light emitting element.   The optical transmission circuit according to claim 8, further comprising a third light emitting element driving unit that directly supplies an amplitude current corresponding to the amplitude of the digital signal to the light emitting element.   The first and second peaking current generators each include a first resistor and a second resistor connected in series, and a capacitor connected in parallel to the first resistor, respectively. 9. The optical transmission circuit according to 8. The first light emitting element driving unit includes an NPN transistor,
9. The optical transmission circuit according to claim 8, wherein the second light emitting element driving unit includes a PNP transistor.   The optical transmission circuit according to claim 8, wherein the light emitting element is included in the configuration.   The optical transmission circuit according to claim 16, wherein the light emitting element is an LED. An optical transmission circuit for driving a light emitting element according to an input digital signal,
A peaking current generator for generating a peaking current synchronized with the rise and fall of the digital signal;
A light emitting element driving unit that generates a driving current obtained by combining the signal amplitude current corresponding to the amplitude of the digital signal and the peaking current, and drives the light emitting element using the driving current;
A signal analysis unit that analyzes the digital signal and sets a control signal based on at least one of a pulse width and an amplitude amount of the digital signal;
An optical transmission circuit comprising: a clipping generation unit configured to clip the peaking current of the drive current according to a control signal set by the signal analysis unit.   The optical transmission circuit according to claim 18, wherein the clipping generation unit sets a ratio of the clipping current amount to the peaking current amount to a predetermined value or less.   The optical transmission circuit according to claim 18, wherein the clipping generator controls a bias current of the drive current generated by the light emitting element driver. The signal analysis unit
A pulse width detector for detecting a pulse width of the digital signal;
The optical transmission circuit according to claim 18, further comprising: a pulse width control unit that sets a control signal according to the detected pulse width. The signal analysis unit
An amplitude amount detection unit for detecting the amplitude amount of the digital signal;
The optical transmission circuit according to claim 18, further comprising: an amplitude amount control unit that sets a control signal according to the detected amplitude amount. The signal analysis unit
A pulse width detector for detecting a pulse width of the digital signal;
A pulse width control unit that outputs a signal corresponding to the detected pulse width;
An amplitude amount detection unit for detecting the amplitude amount of the digital signal;
An amplitude amount control unit that outputs a signal according to the detected amplitude amount;
The optical transmission circuit according to claim 18, further comprising: a processing unit that sets a signal obtained by adding the signal output from the pulse width control unit and the signal output from the amplitude amount control unit as a control signal. The signal analysis unit
A light receiving element for receiving an optical signal transmitted from a communication partner device;
An amplifier for amplifying a signal received by the light receiving element;
A signal detection unit for detecting an amplitude amount of the signal amplified by the amplification unit;
The optical transmission circuit according to claim 23, further comprising: an amplitude amount control unit that controls an amplitude amount of the digital signal input to the pulse width detection unit based on a detection result of the signal detection unit. The signal analysis unit
A light receiving element for receiving an optical signal transmitted from a communication partner device;
An amplifier for amplifying a signal received by the light receiving element;
A signal detection unit that detects an amplitude amount of the signal amplified by the amplification unit;
The optical transmission circuit according to claim 23, wherein the peaking current generation unit controls the amount of peaking current to be generated based on a detection result of the signal detection unit.   The optical transmission circuit according to claim 18, wherein the peaking current generator includes a first resistor and a second resistor connected in series, and a capacitor connected in parallel to the first resistor.   The peaking current generating unit includes a plurality of blocks including a first resistor and a second resistor connected in series, and a capacitor connected in parallel to the first resistor, based on a detection result of the signal detection unit. The optical transmission circuit according to claim 25, wherein any one of the plurality of blocks is selectively switched. The predetermined value a2 / a1, which is a ratio of the clipping current amount a2 to the peaking current amount a1, includes a time constant τ1 determined by the peaking current generation unit, and a pulse fall time determined by the peaking current; Constants A1, A2, N1, N2, and a fall time tf including a time constant τ2 determined by the light emitting element driving unit and the light emitting element and based on a pulse fall time determined by the clipping current. The optical transmission circuit according to claim 18, wherein the optical transmission circuit is determined by the following relational expression using:

  The clipping generation unit may set the predetermined value a2 / a1 under the condition of 0 <a2 / a1 ≦ 0.8 when driving the light emitting element at a transmission speed of about 500 Mbps. The optical transmission circuit described.   The optical transmission circuit according to claim 18, wherein the light emitting element is included in the configuration.   The optical transmission circuit according to claim 18, wherein the light emitting element is an LED.

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