Constant current source circuit, laser driver circuit, and optical module

Abstract

The utility model discloses a constant current source circuit, laser driver circuit and optical module, this constant current source circuit includes operational amplifier, transistor and feedback branch, the first input of operational amplifier is connected with first signal transmission branch, the second input of operational amplifier is connected with the output of feedback branch, the output of operational amplifier is connected with the control end of transistor through second signal transmission branch, the transistor is connected in series on load power supply circuit, current sampling resistance also has in series on load power supply circuit, the input of feedback branch is connected between current sampling resistance and transistor. The utility model adopts MCU self DA output end, utilizes operational amplifier to add peripheral resistance and capacitor to build the output adjustable constant current source circuit, and the stability and driving of different current laser are well solved and so on.

Description

Technical Field

[0001] This utility model belongs to the field of optical communication technology, specifically relating to a constant current source circuit, a laser driver circuit, and an optical module. Background Technology

[0002] In silicon photonics modules, the silicon photonics chip requires a stable and continuously emitting laser. This laser is excited by current injection, and different lasers have different input current requirements. While conventional driver circuits offer good stability for single lasers, additional circuitry is needed for lasers with different current requirements, increasing cost and instability. Utility Model Content

[0003] The purpose of this invention is to overcome the defects of the prior art and provide a constant current source circuit, a laser driver circuit, and an optical module.

[0004] In a first aspect, this utility model provides a constant current source circuit, including an operational amplifier, a transistor, and a feedback branch. The first input terminal of the operational amplifier is connected to a first signal transmission branch, the second input terminal of the operational amplifier is connected to the output terminal of the feedback branch, the output terminal of the operational amplifier is connected to the control terminal of the transistor via the second signal transmission branch, the transistor is connected in series in the load power supply circuit, a current sampling device is also connected in series in the load power supply circuit, and the input terminal of the feedback branch is connected to the current sampling device.

[0005] In some embodiments, the second input terminal of the operational amplifier is grounded via a second resistor.

[0006] In some embodiments, the constant current source circuit of this utility model further includes a negative feedback capacitor, one end of which is connected to the second input terminal of the operational amplifier, and the other end of which is connected to the output terminal of the operational amplifier.

[0007] In some embodiments, the first signal transmission branch includes a first resistor, one end of which is connected to the input terminal of the constant current source circuit, and the other end of which is connected to the first input terminal of the operational amplifier.

[0008] or / and,

[0009] The feedback branch includes a third resistor, one end of which is connected to the second input terminal of the operational amplifier, and the other end of which is connected to the current sampling device.

[0010] or / and,

[0011] The second signal transmission branch includes a fourth resistor, one end of which is connected to the output terminal of the operational amplifier, and the other end of which is connected to the control terminal of the transistor.

[0012] or / and,

[0013] One end of the load power supply circuit is connected to the positive terminal of the power supply, and the other end of the load power supply circuit is connected to the negative terminal of the power supply.

[0014] or / and,

[0015] The current sampling device includes a sampling resistor, one end of which is connected to the second terminal of the transistor and the input terminal of the feedback branch, and the other end of which is connected to the negative terminal of the power supply.

[0016] or / and,

[0017] The load power supply circuit is provided with an independent first load connection terminal and a second load connection terminal. The first load connection terminal is connected to the positive terminal of the power supply, and the second load connection terminal is connected to the first terminal of the transistor.

[0018] In some embodiments, the constant current source circuit of the present invention further includes a voltage follower, the input terminal of which is connected to the input terminal of the constant current source circuit, and the output terminal of which is connected to the first input terminal of the operational amplifier via a first signal transmission branch.

[0019] In some embodiments, a filter circuit is provided between the input terminal of the constant current source circuit and the input terminal of the voltage follower. The input terminal of the filter circuit is connected to the input terminal of the constant current source circuit, and the output terminal of the filter circuit is connected to the input terminal of the voltage follower.

[0020] In some embodiments, the filter circuit is an RC filter circuit, including a fifth resistor and a filter capacitor. One end of the fifth resistor is connected to the input terminal of the constant current source circuit, and the other end of the fifth resistor is connected to one end of the filter capacitor and the input terminal of the voltage follower, respectively. The other end of the filter capacitor is grounded.

[0021] In some embodiments, the first input terminal of the operational amplifier is the non-inverting input terminal, and the second input terminal of the operational amplifier is the inverting input terminal.

[0022] In some embodiments, the transistor is a MOS transistor.

[0023] In a second aspect, this disclosure also provides a laser driving circuit, comprising: a constant current source circuit as described in the first aspect, wherein the laser is connected in series in the load power supply circuit.

[0024] Thirdly, this disclosure also provides an optical module, including: a processor and a laser driving circuit as described in the second aspect, the processor having a DA output terminal, one of the DA output terminals of the processor being connected to the input terminal of a constant current source circuit.

[0025] This invention has at least the following beneficial effects: The input terminal Uin of the constant current source circuit can receive the DAC value output by the MCU, controlling the output current of the constant current source. Depending on the different laser chips, different DAC values ​​are output and converted into different currents for the laser, thus meeting the different input current requirements of different lasers and increasing its applicability. Furthermore, when the load changes, Iout will also increase or decrease accordingly, maintaining a stable output current and thereby stabilizing the laser's output.

[0026] This invention utilizes the built-in DA output terminal of the MCU in the optical module to drive a constant current source circuit built with an operational amplifier, external resistors, and capacitors, effectively solving the problems of stability and driving of lasers with different currents. Attached Figure Description

[0027] 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.

[0028] Figure 1 This is a circuit diagram of a constant current source circuit disclosed in one embodiment of the present invention;

[0029] Figure 2 The circuit diagram of a constant current source circuit disclosed in another embodiment of this utility model is shown below.

[0030] Figure 3 This is a block diagram of a DAC logic disclosed in one embodiment of the present invention. Detailed Implementation

[0031] To enable those skilled in the art to better understand the technical solutions of this utility model, exemplary embodiments of this utility model are described below with reference to the accompanying drawings, including various details of the embodiments of this utility model to aid understanding. These should be considered merely exemplary. Therefore, those skilled in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this utility model. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0032] Where there is no conflict, the various embodiments of this utility model and the features thereof can be combined with each other.

[0033] As used herein, the term “and / or” includes any and all combinations of one or more related enumerated entries.

[0034] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, the singular forms “a” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that when the terms “comprising” and / or “made of” are used in this specification, the presence of the stated feature, integral, step, operation, element, and / or component is specified, but the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof is not excluded. Terms such as “connected” or “linked” are not limited to physical or mechanical connections but can include electrical connections, whether direct or indirect.

[0035] Unless otherwise specified, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art. It will also be understood that terms such as those defined in commonly used dictionaries should be interpreted as having the meaning consistent with their meaning in the context of the relevant art and the present invention, and will not be interpreted as having an idealized or overly formal meaning, unless expressly so defined herein.

[0036] Figure 1 This is a schematic diagram of a constant current source circuit provided in an embodiment of this disclosure. Figure 1 As shown, the constant current source circuit includes: an operational amplifier U1, a transistor Q1, and a feedback branch. The first input terminal of the operational amplifier U1 is connected to the first signal transmission branch, the second input terminal of the operational amplifier U1 is connected to the output terminal of the feedback branch, the output terminal of the operational amplifier U1 is connected to the control terminal of the transistor Q1 via the second signal transmission branch, the transistor Q1 is connected in series in the load power supply circuit, a current sampling device is also connected in series in the load power supply circuit, and the input terminal of the feedback branch is connected to the current sampling device.

[0037] In some embodiments, the second input terminal of the operational amplifier is grounded via a second resistor R2.

[0038] A first signal transmission branch has a first connection terminal and a second connection terminal, configured to transmit a signal from the first connection terminal to the second connection terminal. A second signal transmission branch has a third connection terminal and a fourth connection terminal, configured to transmit a signal from the third connection terminal to the fourth connection terminal.

[0039] In some embodiments, the first signal transmission branch includes a first resistor R1, one end of which is connected to the input terminal of the constant current source circuit, and the other end of which is connected to the first input terminal of the operational amplifier U1.

[0040] In some embodiments, the feedback branch includes a third resistor Rf, one end of which is connected to the second input terminal of the operational amplifier U1, and the other end of which is connected to a current sampling device.

[0041] In some embodiments, one end of the load power supply circuit is connected to the positive terminal of the power supply, and the other end of the load power supply circuit is connected to the negative terminal of the power supply.

[0042] In some embodiments, the negative terminal of the power supply is reference ground potential. That is, the second terminal of transistor Q1 is grounded via the sampling branch. The positive terminal of the power supply is VCC.

[0043] In some embodiments, the second signal transmission branch includes a fourth resistor Ro, one end of which is connected to the output of operational amplifier U1, and the other end of which is connected to the control terminal of transistor Q1. The fourth resistor Ro can limit excessive drive current and also eliminate the oscillation signal of the transistor.

[0044] In some embodiments, the current sampling device includes a sampling resistor Rs, one end of which is connected to the second terminal of transistor Q1, and the other end of which is connected to the negative terminal of the power supply. The sampling resistor Rs is primarily used for current sampling.

[0045] In some embodiments, the load power supply circuit is provided with an independent first load connection terminal and a second load connection terminal. The first load connection terminal is connected to the positive terminal of the power supply, and the second load connection terminal is connected to the first terminal of the transistor.

[0046] In some embodiments, the constant current source circuit further includes a negative feedback capacitor C1. One end of the negative feedback capacitor C1 is connected to the second input terminal of the operational amplifier U1, and the other end of the negative feedback capacitor C1 is connected to the output terminal of the operational amplifier U1. C1 is a negative feedback capacitor, which has the functions of isolating DC and filtering. Through frequency-selective feedback, it can improve the stability of the circuit. C1 can also be used as a phase compensation element to cancel parasitic phase differences in the loop, avoid high-frequency self-excited oscillation, and ensure stable circuit operation.

[0047] In some embodiments, the first input terminal of the operational amplifier U1 is the non-inverting input terminal, and the second input terminal of the operational amplifier U1 is the inverting input terminal.

[0048] In some embodiments, the transistor Q1 is a MOS transistor.

[0049] In some embodiments, transistor Q1 is an NMOS transistor, and the conduction condition is Vgs > Von. Q1 is an NMOS transistor, mainly used to increase the driving capability, and a model with low on-resistance should be selected.

[0050] Figure 2Here is a circuit diagram of a constant current source circuit disclosed in another embodiment of this utility model, as shown below. Figure 2 As shown, the constant current source circuit also includes a voltage follower. The input terminal of the voltage follower is connected to the input terminal of the constant current source circuit, and the output terminal of the voltage follower is connected to the first input terminal of the operational amplifier U1 via the first signal transmission branch.

[0051] In some embodiments, a filter circuit is provided between the input terminal of the constant current source circuit and the input terminal of the voltage follower. The input terminal of the filter circuit is connected to the input terminal of the constant current source circuit, and the output terminal of the filter circuit is connected to the input terminal of the voltage follower.

[0052] In some embodiments, the voltage follower includes an operational amplifier U2, with its inverting input connected to its output and its non-inverting input serving as the input. The output of the operational amplifier U2 is also the output of the voltage follower. As a voltage follower, the operational amplifier U2 ensures that the signal is less prone to distortion and enhances driving capability, while the preceding RC filter circuit removes noise from the circuit.

[0053] In some embodiments, the filter circuit is an RC filter circuit, including a fifth resistor R and a filter capacitor C. One end of the fifth resistor R is connected to the input terminal of the constant current source circuit, and the other end of the fifth resistor R is connected to one end of the filter capacitor C and the input terminal of the voltage follower, respectively. The other end of the filter capacitor C is grounded.

[0054] Description of the principle of constant current source implementation:

[0055] This constant current source is a voltage-controlled current source, ensuring that the output current does not change with the load. Assuming that the operational amplifiers are all ideal operational amplifiers, the analysis is performed using "virtual short" and "virtual open" after introducing negative feedback.

[0056] According to the virtual open circuit, the current through the ± input terminals of the U1 operational amplifier is 0, i.e., I1=0. Therefore, Ur1=R1*I1=0; Up=Uin-Ur1=Uin; According to the virtual short circuit, Up=Un=Ui, I2=(Un-0) / R2=Uin / R2;

[0057] If = (Uout - Un / Rf); and according to the relation I2 = In + If, where In = 0, we have I2 = If; input-output relation: Uo = (1 + Rf / R1) * Uin.

[0058] The value of Vin is mainly related to the DAC bit depth of the MCU, the reference voltage, and the decimal value of the input digital quantity. The formula is: Vin=Vref*(da / 2^n). When N=12 and Vref=2.5V, Io=2.5*VDAC / (4096*R1), that is, 0-4096 is the conditional range of this constant current source.

[0059] From the above formula, we can derive the formula for the output current of the constant current source: Iout=Uout / Rs, and Uout=Un, therefore Iout=Uin / Rs.

[0060] When the load current Iout increases, the voltage Uout across the sampling resistor increases, causing the inverting input Un of operational amplifier U1 to increase. The difference between Up and Un decreases, and then the output voltage Uo of operational amplifier U1 decreases, which in turn increases the equivalent resistance of transistor Q1, resulting in a decrease in Io.

[0061] Based on the same inventive concept, this disclosure also provides a laser driving circuit, including: a constant current source circuit as described in any of the above embodiments, wherein the load is a laser chip. A first load connection terminal is connected to one end of the laser chip, and a second load connection terminal is connected to the other end of the laser chip.

[0062] Based on the same inventive concept, this disclosure also provides an optical module, including: a processor and a laser driving circuit as described in any of the above embodiments, wherein the processor has a DA output terminal, and a DA output terminal of the processor is connected to the input terminal of a constant current source circuit.

[0063] In some embodiments, the processor is an MCU.

[0064] Depend on Figure 3 As can be seen, the DAC is directly controlled by the DORx register, but data cannot be written directly to the DORx register. Instead, it is indirectly passed to the DORx register through DHRx to achieve output control of the DAC.

[0065] Through the aforementioned constant current source circuit, the MCU can output a DAC value to the input terminal Uin of the constant current source circuit via a pin, thereby controlling the output current of the constant current source. Depending on the laser chip, different DAC values ​​are output and converted into current to supply the laser, increasing the applicability. Furthermore, when the load changes, Iout will increase or decrease accordingly, maintaining a stable output current and thus ensuring stable laser output.

[0066] Most high-speed optical module MCU solutions have built-in DAC output pins. This invention utilizes the MCU's built-in DA output terminal and employs an operational amplifier with external resistors and capacitors to construct an adjustable constant current source circuit. This effectively solves the stability and driving problems of lasers with different currents.

[0067] The constant current source circuit of this invention is applied inside an optical module and belongs to the field of optical communication. Specifically, it relates to a high-precision constant current source circuit for driving laser diodes (LDs) in optical modules, especially for the noise and temperature stability requirements of constant current sources in high-speed optical modules (such as 100G / 400G).

[0068] Example embodiments have been disclosed herein, and while specific terminology has been used, it is for illustrative purposes only and should be construed as such, and is not intended to be limiting. In some instances, it will be apparent to those skilled in the art that features, characteristics, and / or elements described in conjunction with particular embodiments may be used alone, or in combination with features, characteristics, and / or elements described in conjunction with other embodiments, unless otherwise expressly indicated. Therefore, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of the invention as set forth in the appended claims.

Claims

1. A constant current source circuit, characterized in that: It includes an operational amplifier, a transistor, and a feedback branch. The first input terminal of the operational amplifier is connected to a first signal transmission branch, the second input terminal of the operational amplifier is connected to the output terminal of the feedback branch, the output terminal of the operational amplifier is connected to the control terminal of the transistor via the second signal transmission branch, the transistor is connected in series in the load power supply circuit, a current sampling device is also connected in series in the load power supply circuit, and the input terminal of the feedback branch is connected to the current sampling device.

2. The constant current source circuit as described in claim 1, characterized in that: The second input terminal of the operational amplifier is grounded via the second resistor.

3. The constant current source circuit as described in claim 1, characterized in that: It also includes a negative feedback capacitor, one end of which is connected to the second input terminal of the operational amplifier, and the other end of which is connected to the output terminal of the operational amplifier.

4. The constant current source circuit as described in claim 1, 2, or 3, characterized in that: The first signal transmission branch includes a first resistor, one end of which is connected to the input terminal of the constant current source circuit, and the other end of which is connected to the first input terminal of the operational amplifier. or / and, The feedback branch includes a third resistor, one end of which is connected to the second input terminal of the operational amplifier, and the other end of which is connected to the current sampling device. or / and, The second signal transmission branch includes a fourth resistor, one end of which is connected to the output terminal of the operational amplifier, and the other end of which is connected to the control terminal of the transistor. or / and, One end of the load power supply circuit is connected to the positive terminal of the power supply, and the other end of the load power supply circuit is connected to the negative terminal of the power supply. or / and, The current sampling device includes a sampling resistor, one end of which is connected to the second terminal of the transistor and the input terminal of the feedback branch, and the other end of which is connected to the negative terminal of the power supply. or / and, The load power supply circuit is provided with an independent first load connection terminal and a second load connection terminal. The first load connection terminal is connected to the positive terminal of the power supply, and the second load connection terminal is connected to the first terminal of the transistor.

5. The constant current source circuit as described in claim 1, 2, or 3, characterized in that: It also includes a voltage follower, the input of which is connected to the input of the constant current source circuit, and the output of which is connected to the first input of the operational amplifier via the first signal transmission branch.

6. The constant current source circuit as described in claim 5, characterized in that: A filter circuit is provided between the input terminal of the constant current source circuit and the input terminal of the voltage follower. The input terminal of the filter circuit is connected to the input terminal of the constant current source circuit, and the output terminal of the filter circuit is connected to the input terminal of the voltage follower.

7. The constant current source circuit as described in claim 6, characterized in that: The filter circuit is an RC filter circuit, including a fifth resistor and a filter capacitor. One end of the fifth resistor is connected to the input terminal of the constant current source circuit, and the other end of the fifth resistor is connected to one end of the filter capacitor and the input terminal of the voltage follower. The other end of the filter capacitor is grounded.

8. The constant current source circuit as described in claim 1, 2, or 3, characterized in that: The first input terminal of the operational amplifier is the non-inverting input, and the second input terminal of the operational amplifier is the inverting input; or / and, The transistor is a MOS transistor.

9. A laser driving circuit, characterized in that: include: In any of the constant current source circuits described in claims 1 to 8, the laser is connected in series in the load power supply circuit.

10. An optical module, characterized in that, include: The processor and the laser driving circuit as described in claim 9, wherein the processor has a DA output terminal, and one DA output terminal of the processor is connected to the input terminal of the constant current source circuit.

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