Laser current driving circuit and system

Abstract

The utility model relates to the technical field of optical communication, in particular to a laser current driving circuit and a laser current driving system, which output voltage to a normal phase input end of an operational amplifier through a voltage source, and simultaneously, current flowing through a laser generates voltage drop on a sampling unit. The voltage drop is input to the negative input end of the operational amplifier as a voltage sampling value; the current flowing through the sampling unit is equal to the output voltage of the voltage source divided by the resistance value of the sampling unit. When the current flowing through the laser changes, the current is multiplied by the resistance value of the sampling unit to obtain the output voltage signal of the voltage source, and the magnitude of the current flowing through the laser can be adjusted by resetting the output voltage signal of the voltage source so as to meet the working requirement of the laser; the utility model has the advantages of simple circuit structure, less devices and low heat dissipation requirement, can effectively save the board arrangement space, and can effectively enlarge the range of the current flowing through the laser only by replacing the power tube.

Description

TECHNICAL FIELD

[0001] The utility model relates to optical communication technical field, in particular to a kind of laser current driving circuit and system. BACKGROUND

[0002] Optical device or optical chip usually needs to apply different current to reach the required working condition, such as multi-channel laser, which needs multiple independent current sources. The bias current required by the laser is getting larger and larger, and the output current of the existing current source chip cannot meet the requirements. In order to have greater optical power output of the laser, the common practice is to use multiple current source chips in parallel output method to increase the output current, so as to meet the needs of the laser. But once the number of channels of the laser becomes larger, more current source chips are needed, which will bring challenges to the board and heat dissipation.

[0003] Therefore, it is urgent to overcome the defects of the prior art in the technical field. SUMMARY

[0004] The technical problem to be solved by the utility model is how to solve the problem that the existing current source chip cannot meet the bias current required by the laser.

[0005] The utility model adopts the following technical solutions:

[0006] In a first aspect, a laser current driving circuit is provided, comprising: a voltage source, an operational amplifier, a power tube and a sampling unit.

[0007] The output end of the voltage source is connected with the positive input end of the operational amplifier, the output end of the operational amplifier is connected with the control end of the power tube, one end of the power tube is used to connect with the negative electrode of the laser, and the positive electrode of the laser is connected with the power supply voltage.

[0008] The other end of the power tube is connected with the inverting input end of the operational amplifier and one end of the sampling unit respectively, and the other end of the sampling unit is grounded.

[0009] Preferably, when the power tube is a MOS tube, the output end of the operational amplifier is connected with the gate of the MOS tube, the source of the MOS tube is connected with the inverting input end of the operational amplifier and one end of the sampling unit respectively, and the drain of the MOS tube is used to connect with the negative electrode of the laser.

[0010] Preferably, the sampling unit is a sampling resistor, one end of the sampling resistor is connected with the other end of the power tube, and the other end of the sampling resistor is grounded.

[0011] Preferably, when the maximum operating current of the laser is less than or equal to 300mA, the resistance of the sampling resistor is less than or equal to 4.3Ω.

[0012] Preferably, the voltage source comprises a Voltage to Digital Analog Converter (VDAC) unit, and an output terminal of the VDAC unit is connected with the positive input terminal of the operational amplifier.

[0013] Preferably, the output voltage of the VDAC unit ranges from 1.1V to 2.5V.

[0014] Preferably, the model of the VDAC unit is DAC80508 or LM5815.

[0015] Preferably, the model of the operational amplifier is LM841 or AD8615.

[0016] Preferably, the supply voltage ranges from 3.3V to 5V.

[0017] In the second aspect, a laser current driving system is provided, which comprises the laser current driving circuit as described in the first aspect and a laser, one end of a power tube in the laser current driving circuit is connected with a negative electrode of the laser, and a positive electrode of the laser is connected with a supply voltage.

[0018] Compared with the prior art, the utility model has the advantages of:

[0019] The utility model discloses a voltage source output voltage to the positive input terminal of operational amplifier, and because of the " virtual short " characteristic of operational amplifier, the voltage of the positive input terminal of operational amplifier is substantially equal to the voltage of the negative input terminal. Therefore, the voltage drop generated on the sampling unit is equal to the voltage of the positive input terminal, and then the current flowing through the sampling unit is equal to the output voltage of the voltage source divided by the resistance value of the sampling unit. Based on this circuit structure, it can be known that the current flowing through the sampling unit is equal to the bias current of the laser. In actual use, when the bias current flowing through the laser needs to be changed, the output voltage signal of the voltage source can be obtained by multiplying the resistance value of the sampling unit and the bias current, and the size of the current flowing through the laser can be adjusted by reconfiguring the output voltage signal of the voltage source to meet the working requirements of the laser.

[0020] In addition, during the circuit design stage, only a suitable power tube needs to be selected, and the output current range can be expanded to meet the bias current requirements of different lasers, avoiding the scheme of adopting multiple current source chips in parallel. The utility model circuit structure is simple, can effectively save the board space, and has few devices and low heat dissipation requirements. BRIEF DESCRIPTION OF DRAWINGS

[0021] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of a laser current driving circuit provided in an embodiment of the present invention;

[0023] Figure 2 This is a schematic diagram of a laser current driving circuit provided in an embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram of the structure of a laser current driving system provided in an embodiment of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit the present utility model.

[0026] Unless the context otherwise requires, throughout the specification and claims, the term "comprising" is interpreted as openly inclusive, meaning "including, but not limited to." In the description of the specification, terms such as "one embodiment," "some embodiments," "exemplary embodiment," "example," "specific example," or "some examples" are intended to indicate that a particular feature, structure, material, or characteristic associated with that embodiment or example is included in at least one embodiment or example of this disclosure. The illustrative representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics mentioned may be included in any suitable manner in any one or more embodiments or examples; that is, although they may be incorporated into embodiments or examples using the above terms for reasons such as order and position, it does not limit them to be incorporated in combination by a single embodiment or example.

[0027] In the description of this utility model, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this disclosure, unless otherwise stated, "a plurality of" means two or more. Furthermore, for example, the description may use the prefix "A" or "B" to describe the same type of nouns as two independent entities. In this case, the features defined with "A" and "B" are used only to distinguish between similar entities and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0028] In describing some embodiments, the terms "coupled," "coupled," and "connected," and their derivative expressions, may be used. For example, the term "connected" may be used in describing some embodiments to indicate that two or more components have direct physical or electrical contact with each other. Similarly, the term "coupled" may be used in describing some embodiments to indicate that two or more components have direct physical or electrical contact. However, the terms "connected" or "coupled" may also refer to two or more components that do not have direct contact with each other but still cooperate or interact with each other, such as "optical coupling" or "wireless connection." The embodiments disclosed herein are not necessarily limited to the scope of this invention.

[0029] Furthermore, the technical features involved in the various embodiments of this utility model described below can be combined with each other as long as they do not conflict with each other.

[0030] Example 1:

[0031] To address the problems of existing technologies, this embodiment proposes a laser current driving circuit, such as... Figure 1 As shown, it includes: a voltage source, an operational amplifier (shown as U1 in the figure), a power transistor (shown as Q1 in the figure), and a sampling unit; the output terminal of the voltage source is connected to the non-inverting input terminal of the operational amplifier, the output terminal of the operational amplifier is connected to the control terminal of the power transistor, one end of the power transistor is used to connect to the negative terminal of a laser (shown as LD in the figure), and the positive terminal of the laser is connected to the power supply voltage (i.e., VCC); the other end of the power transistor is connected to the inverting input terminal of the operational amplifier and one end of the sampling unit, and the other end of the sampling unit is grounded.

[0032] The voltage source is used to send a voltage signal to the operational amplifier. The voltage source is typically generated by a power supply circuit or output by a microcontroller or other device via digital-to-analog conversion.

[0033] In one embodiment, such asFigure 2 As shown, the voltage source comprises a VDAC unit, and an output terminal of the VDAC unit is connected to a positive input terminal of the operational amplifier. The output voltage of the VDAC unit ranges from 1.1V to 2.5V. The model of the VDAC unit is DAC80508 or LM5815. If high-precision current adjustment is required, a 16-bit VDAC unit such as DAC80508 (16-bit) can be selected. If the precision requirement for the current is general, a 12-bit VDAC unit such as LM5815 (12-bit) can be selected.

[0034] The operational amplifier is configured to receive a voltage signal from the voltage source and amplify the voltage signal. In one embodiment, the model of the operational amplifier is LM841 or AD8615.

[0035] The power tube is configured to provide sufficient current to drive the laser. A control terminal of the power tube is connected to an output terminal of the operational amplifier, and the working state (i.e., the conduction degree) of the power tube is controlled by the output signal of the operational amplifier. One end of the power tube is connected to the negative electrode of the laser, and the other end of the power tube is connected to an inverting input terminal of the operational amplifier and the sampling unit, respectively. The selection of the power tube needs to consider the current flowing through the power tube and the voltage drop. According to the most extreme consideration, if the current flowing through the power tube is 300mA and the voltage drop of the power tube is 1.5V, the dissipation power of the power tube is 0.45W, and a power tube with a dissipation power of 1W or more can be selected, and at the same time, heat dissipation measures are taken.

[0036] In one embodiment, as shown in FIG. 2, the output terminal of the operational amplifier is connected to the gate of the power tube, the source of the power tube is connected to the inverting input terminal of the operational amplifier and one end of the sampling unit, respectively, and the drain of the power tube is configured to be connected to the negative electrode of the laser. Figure 2 In one embodiment, as shown in FIG. 2, the output terminal of the operational amplifier is connected to the gate of the power tube, the source of the power tube is connected to the inverting input terminal of the operational amplifier and one end of the sampling unit, respectively, and the drain of the power tube is configured to be connected to the negative electrode of the laser.

[0037] Figure 2 ​As shown, the sampling unit is a sampling resistor (as shown by R1 in the figure), one end of the sampling resistor is connected to the other end of the power tube, and the other end of the sampling resistor is grounded. When the maximum working current of the laser is less than or equal to 300 mA, the resistance of the sampling resistor is less than or equal to 4.3Ω. Among them, the value of the sampling resistor needs to be selected according to the maximum working current of the laser. For a general laser, its maximum working current generally does not exceed 300mA, the power supply voltage is 3.3V (in an embodiment, the power supply voltage ranges from 3.3V to 5V), the forward working voltage of the laser is 2V, and the voltage falling on the sampling resistor is not more than 1.3V, so the value of the sampling resistor is not more than 4.3Ω. The value of the sampling resistor needs to be reasonably selected by taking into account the feedback voltage and the power consumption of itself, and more specifically, it will not be described in detail in this embodiment.

[0038] In one embodiment, referring to Figure 2 , the working principle of the entire driving circuit is as follows:

[0039] The voltage source outputs a voltage signal VI to the non-inverting input end IN+ of the operational amplifier. According to the virtual short characteristic of the operational amplifier, the voltage of the inverting input end IN- of the operational amplifier will tend to VI. Therefore, the calculation method of the current Ild flowing through the sampling unit can be Ild=VI / R1, where R1 is the resistance of the sampling unit. By changing the amplitude of VI, the size of the current Ild can be adjusted to meet the working requirements of the laser.

[0040] Specifically, according to Ohm's law I=U / R, in the case where the resistance of the sampling resistor is fixed, the current Ild flowing through the sampling resistor (i.e., the current flowing through the power tube, which is equivalent to the size of the current source used to drive the laser) is proportional to the voltage across the sampling resistor. Among them, when the amplitude of the voltage signal output by the VDAC unit is increased (i.e., VI is increased), according to Ild=VI / R1, since R1 is constant, VI is increased, so Ild is increased, thereby increasing the current flowing through the power tube, i.e., the current source is increased. Conversely, when the amplitude of the voltage signal output by the VDAC unit is reduced (i.e., VI is reduced), the current Ild flowing through the sampling resistor will be reduced, thereby reducing the current flowing through the power tube, and the current source is also reduced.

[0041] At the same time, by replacing the power tube with different parameters, the range of the output current can be expanded to meet the requirements of different lasers. It is worth noting that all the contents related to the control method in this embodiment are based on the working principle of the corresponding device and belong to the prior art, which will not be described in detail in this embodiment.

[0042] Among them, the expansion of the output range of the current source by replacing the power tube specifically includes:

[0043] In the original circuit, the output current of the current source is limited by the parameters of the power tube itself. If the maximum allowable current of the currently used power tube is small, the maximum current that the current source can output will be limited by this. When a power tube with a larger maximum allowable current is replaced, since the new power tube can withstand and conduct a larger current, without changing the basic working principle of other parts of the circuit such as the sampling resistor and the operational amplifier, the circuit can output a larger current. For example, assuming that the maximum allowable current of the power tube in the original circuit is 100 mA, by replacing it with a suitable high-power tube, its maximum allowable current can be expanded to 500 mA or even higher, thus conveniently expanding the output range of the current source. Moreover, such expansion usually only requires a simple replacement of the power tube, without the need for large-scale changes to the structure of the entire circuit such as the feedback loop, so the output range of the current source can be conveniently expanded by replacing the power tube.

[0044] In summary, in the embodiment, the voltage source outputs a voltage to the non-inverting input terminal of the operational amplifier. Due to the "virtual short" characteristic of the operational amplifier, the voltage at the non-inverting input terminal of the operational amplifier is substantially equal to the voltage at the inverting input terminal. Therefore, the voltage drop generated on the sampling unit is equal to the voltage at the non-inverting input terminal, and the current flowing through the sampling unit is equal to the output voltage of the voltage source divided by the resistance value of the sampling unit. Based on this circuit structure, it can be known that the current flowing through the sampling unit is equal to the bias current of the laser. In actual use, when the bias current flowing through the laser needs to be changed, the output voltage signal of the voltage source can be obtained by multiplying the resistance value of the sampling unit by the bias current, and the size of the current flowing through the laser can be adjusted by reconfiguring the output voltage signal of the voltage source to meet the working requirements of the laser.

[0045] In addition, during the circuit design stage, only a suitable power tube needs to be selected to expand the output current range to meet the bias current requirements of different lasers, avoiding the use of a parallel connection scheme of multiple current source chips. The circuit structure of the utility model is simple, can effectively save the board space, has few devices, and has low heat dissipation requirements.

[0046] Embodiment 2

[0047] In order to further illustrate the laser current driving circuit proposed in embodiment 1, in this embodiment, a laser current driving system will be proposed. In one embodiment, as shown in Figure 3 FIG. 1, it includes the laser current driving circuit as described in embodiment 1 and a laser, one end of the power tube in the laser current driving circuit is connected to the negative electrode of the laser, and the positive electrode of the laser is connected to the power supply voltage.

[0048] In summary, the embodiment outputs the voltage of the voltage source to the positive input terminal of the operational amplifier, and due to the "virtual short" characteristic of the operational amplifier, the voltage of the positive input terminal of the operational amplifier is substantially equal to the voltage of the negative input terminal. Therefore, the voltage drop generated on the sampling unit is equal to the voltage of the positive input terminal, and then the current flowing through the sampling unit is equal to the output voltage of the voltage source divided by the resistance value of the sampling unit. Based on the circuit structure, it can be known that the current flowing through the sampling unit is equal to the bias current of the laser. In actual use, when the bias current flowing through the laser needs to be changed, the output voltage signal of the voltage source can be obtained by multiplying the resistance value of the sampling unit by the bias current, and the size of the current flowing through the laser can be adjusted by reconfiguring the output voltage signal of the voltage source to meet the working requirements of the laser.

[0049] In addition, during the circuit design stage, only a suitable power tube needs to be selected, and the output current range can be expanded to meet the bias current requirements of different lasers, avoiding the parallel connection scheme of multiple current source chips.

[0050] The specific structure of the laser current driving circuit is described in Embodiment 1, and will not be repeated in this embodiment.

[0051] The above only describes the preferred embodiments of the utility model, and does not limit the utility model, and any modification, equivalent replacement and improvement within the spirit and principle of the utility model should be included in the protection scope of the utility model.

Claims

1. A laser current drive circuit, characterized by, The application relates to a laser current driving circuit. The output end of the voltage source is connected with the positive input end of the operational amplifier, the output end of the operational amplifier is connected with the control end of the power tube, one end of the power tube is used for being connected with the negative electrode of a laser, and the positive electrode of the laser is connected with a power supply voltage. The other end of the power tube is connected with the inverting input end of the operational amplifier and one end of the sampling unit respectively, and the other end of the sampling unit is grounded. When the power tube is a MOS tube, the output end of the operational amplifier is connected with the gate of the MOS tube, the source of the MOS tube is connected with the inverting input end of the operational amplifier and one end of the sampling unit respectively, and the drain of the MOS tube is used for being connected with the negative electrode of the laser.

2. The laser current driver circuit of claim 1, wherein, The sampling unit is a sampling resistor, one end of the sampling resistor is connected with the other end of the power tube, and the other end of the sampling resistor is grounded.

3. The laser current driver circuit of claim 1, wherein, When the maximum working current of the laser is less than or equal to 300 mA, the resistance of the sampling resistor is less than or equal to 4.3 omega.

4. The laser current driver circuit of claim 3, wherein, The voltage source comprises a VDAC unit, and the output end of the VDAC unit is connected with the positive input end of the operational amplifier.

5. The laser current driver circuit of claim 1, wherein, The output voltage of the VDAC unit ranges from 1.1 V to 2.5 V.

6. The laser current driver circuit of claim 5, wherein, The model of the VDAC unit is DAC80508 or LM5815.

7. The laser current driver circuit of claim 5, wherein, The model of the operational amplifier is LM841 or AD8615.

8. The laser current driver circuit of claim 1, wherein, The power supply voltage ranges from 3.3 V to 5 V.

9. The laser current driving circuit of claim 1, wherein, The application further relates to a laser comprising the laser current driving circuit and the laser, and one end of the power tube in the laser current driving circuit is connected with the negative electrode of the laser, and the positive electrode of the laser is connected with the power supply voltage.

10. A laser current drive system, characterized by, ​

Images