Laser driver, chip and laser driving method

Abstract

The present application discloses a laser driver, a chip, and a laser driving method to provide a relatively mature top modulation function integration solution, and the top modulation circuit is compatible with both amplitude modulation top modulation and frequency modulation top modulation functions; at the same time, it overcomes the problems of top modulation distortion and difficult control of top modulation parameters in the prior art. The present application provides a laser driver, which is used to connect to a laser and drive the laser to output a required optical signal, and the laser driver includes: a top modulation module, which is used to obtain a top modulation signal and generate a top modulation current according to the top modulation signal, and the top modulation module is also used to connect to the laser and output the top modulation current to the laser; a business module, which is used to obtain a business signal and generate a business current according to the business signal, and the business module is also used to connect to the laser and output the business current to the laser; the top modulation current and the business current jointly drive the laser, so that the laser emits an optical signal according to the top modulation signal and the business signal.

Description

Technical Field

[0001] The present application relates to the field of optical signal transmission, and in particular to a laser driver, a chip, and a laser driving method. Background Art

[0002] In the optical communication network of LAN (local area network)-WDM (Wavelength Division Multiplexing) architecture, such as the wireless 5G fronthaul (AAU (Active Antenna Unit) connected to DU (Distribute Unit) networking architecture, WDM PON (Passive Optical Network) field, the pilot tone modulation technology (PT) is often required to achieve wavelength pairing of near-end and far-end optical modules and related OAM management (Operation Administration and Maintenance).

[0003] Each channel usually transmits two types of information, one is the service signal and the other is the top modulation signal. The service signal transmits high-speed service data, and the top modulation signal is used for monitoring and management data. The basic principle of the top modulation technology is to load the low-speed top modulation signal into the high-speed service signal at the transmitting end, and parse the top modulation signal through filtering and sampling at the receiving end, so as to transmit monitoring and operation management information such as wavelength adjustment and temperature monitoring.

[0004] The top modulation technology is generally divided into two types: frequency modulation and amplitude modulation. Different system manufacturers choose different top modulation methods according to the usage scenarios and usage habits. Correspondingly, module manufacturers will also design corresponding optical modules according to the needs of system manufacturers, and install corresponding top modulation circuits at the board level to match frequency modulation or amplitude modulation. At the same time, there are often incompatibility between the solutions of different system manufacturers, and the layout space of module manufacturers is tight and the layout design is complicated. In addition, there are not many solutions in the industry that integrate the top modulation function inside the optical transceiver chip.

[0005] In the prior art, the modulated signal output after top modulation usually has a large distortion problem, and there is also the problem that the top modulation power and top modulation depth are difficult to accurately control. Modulation depth refers to: the peak amplitude deviation value that must be limited in the case of double-sideband amplitude modulation. It is usually the ratio of the difference between the maximum amplitude and the minimum amplitude of the modulated wave to the sum of the maximum amplitude and the minimum amplitude of the carrier, expressed as a percentage. Summary of the invention

[0006] In view of this, the present application provides a laser driver, a chip and a laser driving method to provide a more mature top modulation function integration solution, and the top modulation circuit is compatible with both amplitude modulation top modulation and frequency modulation top modulation functions, and can also overcome the top modulation distortion problem in the prior art and the disadvantage that the top modulation parameters are difficult to control.

[0007] The present application provides a laser driver, which is used to be connected to a laser and drive the laser to output a required optical signal, and the laser driver includes: a top modulation module, which is used to obtain a top modulation signal and generate a top modulation current according to the top modulation signal, and the top modulation module is also used to be connected to the laser and output the top modulation current to the laser; a service module, which is used to obtain a service signal and generate a service current according to the service signal, and the service module is also used to be connected to the laser and output the service current to the laser; the top modulation current and the service current jointly drive the laser, so that the laser emits an optical signal according to the top modulation signal and the service signal.

[0008] Optionally, the top adjustment module includes a first operational amplifier, a top adjustment digital-to-analog conversion unit, a first N-type transistor and a top adjustment resistor, and: the first operational amplifier includes a non-inverting input terminal and an inverting input terminal, wherein the non-inverting input terminal is used to obtain the top adjustment signal, and the output terminal of the first operational amplifier is connected to the gate of the first N-type transistor; the top adjustment digital-to-analog conversion unit is connected to the non-inverting input terminal of the first operational amplifier through a first resistor, and is used to provide a first voltage to the non-inverting input terminal of the first operational amplifier; the drain of the first N-type transistor is used to be connected to the laser, and the source is grounded through the top adjustment resistor, and the non-grounded end of the top adjustment resistor is also connected to the inverting input terminal of the first operational amplifier.

[0009] Optionally, a register is further included, connected to the top-adjusting digital-to-analog conversion unit and the top-adjusting resistor, and is used to control the magnitude of the first voltage output by the top-adjusting digital-to-analog conversion unit, and is used to control the resistance value of the top-adjusting resistor.

[0010] Optionally, the AM top modulation signal includes a digital signal, and the FM top modulation signal includes an analog signal.

[0011] Optionally, the digital signal includes a digital signal based on Manchester encoding, and the analog signal includes one of a sine analog signal and a cosine analog signal.

[0012] Optionally, a bias module is also included, wherein the bias module is used to be connected to the laser and output a bias current to the laser.

[0013] Optionally, the bias module includes a bias current source, one end of which is used to be connected to the laser, and the other end of which is grounded, and is used to output a bias current to the laser.

[0014] Optionally, the bias module includes a bias digital-to-analog conversion unit, a subtractor, a voltage divider unit, a second operational amplifier, a second N-type transistor and a bias resistor, wherein: the bias digital-to-analog conversion unit is used to provide a bias voltage; the subtractor includes a first input terminal and a second input terminal, and the first input terminal is connected to the bias digital-to-analog conversion unit, and the second input terminal is connected to the output terminal of the top adjustment digital-to-analog conversion unit through the voltage divider unit; the second operational amplifier includes a non-inverting input terminal and an inverting input terminal, and the non-inverting input terminal is connected to the output terminal of the subtractor, and the output terminal of the second operational amplifier is connected to the gate of the second N-type transistor; the drain of the second N-type transistor is connected to the drain of the first N-type transistor, the source of the second N-type transistor is grounded through the bias resistor, and the non-grounded end of the bias resistor is also connected to the inverting input terminal of the second operational amplifier.

[0015] Optionally, the voltage divider unit includes a second resistor and a third resistor, wherein a first end of the third resistor is connected to an output end of the top adjustment digital-to-analog conversion unit, a second end of the third resistor is connected to a first end of the second resistor, a second end of the second resistor is grounded, and a first end of the second resistor is also connected to a second input end of the subtractor, and: a resistance value of the second resistor is equal to a resistance value of the bias resistor, and a resistance value of the third resistor is equal to a difference between the top adjustment resistor and the bias resistor.

[0016] Optionally, the business module includes: a switch, used to switch the on / off state according to the business signal, turned on when the business signal is at a high level, and turned off when the business signal is at a low level, and one end of the switch is used to connect to the laser; a business current source, one end of which is grounded and the other end is connected to the other end of the switch, for providing business current.

[0017] The present application also provides a chip, including the laser driver. The chip is also integrated with a laser, and the laser is connected to the laser driver and emits a required optical signal following the driving current of the laser driver.

[0018] The present application also provides a laser driving method, comprising the following steps: providing a top modulation signal, wherein the top modulation signal includes one of a frequency modulation top modulation signal and an amplitude modulation top modulation signal; obtaining a top modulation current according to the top modulation signal; obtaining a service current according to a service signal; and outputting the top modulation current and the service current to the laser to drive the laser.

[0019] Optionally, when obtaining the top-adjusting current according to the top-adjusting signal, the following steps are included: providing a first operational amplifier, the first operational amplifier including a non-inverting input terminal and an inverting input terminal, and the output terminal of the operational amplifier is connected to the gate of a first N-type triode, the source of the first N-type triode is grounded through a top-adjusting resistor, the drain is connected to the laser, and the inverting input terminal is connected to the non-grounded terminal of the top-adjusting resistor; providing a first voltage;

[0020] The first voltage and the top adjustment signal are coupled to a non-inverting input terminal of the operational amplifier.

[0021] Optionally, the magnitude of the first voltage is adjusted, and / or the magnitude of the top trimming resistor is adjusted, thereby adjusting the magnitude of the top trimming current.

[0022] Optionally, when obtaining the business current according to the business signal, the following steps are included: providing a business current source, one end of the business current source is grounded, and the other end is connected to the laser through a switch; when the business signal is present, the business current source and the laser are turned on, and the business current source provides the laser with business current.

[0023] Optionally, the method further includes the following steps: providing a bias current to the laser; and adjusting the magnitude of the bias current so that the sum of the top adjustment current and the bias current is constant.

[0024] The laser driver, chip and laser driving method in the present application directly convert the top modulation signal into a top modulation current, which is directly superimposed on the business current and applied to the laser, thereby not affecting the working point of the modulation signal, reducing the probability of outputting a distorted modulation signal, and having a simpler implementation method and less interference, effectively avoiding crosstalk between signals and interference with the working point, and improving the accuracy and stability of the signal.

[0025] Furthermore, the laser driver, chip and laser driving method in the present application can realize frequency modulation and amplitude modulation in the chip, and the corresponding circuit of the laser driver is integrated inside the chip, which saves the board space of the optical module equipped with the laser and improves the design flexibility of the optical module.

[0026] Furthermore, the top adjustment mode of the top adjustment module integrated in the chip can be freely selected, and the top adjustment power and top adjustment depth can be adjusted, which will be very meaningful for the module design freedom of the module manufacturer and the technical use flexibility of the system manufacturer. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 Schematic diagram of the structure of the laser driver in one embodiment of the present application.

[0029] Figure 2 Schematic diagram of the structure of the laser driver in one embodiment of the present application.

[0030] Figure 3 Schematic diagram of the structure of the bias module in one embodiment of the present application.

[0031] Figure 4 Schematic diagram of the process flow of the laser driving method in one embodiment of the present application. DETAILED DESCRIPTION

[0032] Research has found that the reason why the above problems exist in the prior art is that in the prior art, the low-speed top modulation signal is first pre-loaded into the driving power supply voltage, and then the power supply voltage is coupled to the modulation signal. The power supply voltage will affect the working point of the modulation signal, and the modulation signal will be affected by interference. The coupled modulation signal will be distorted.

[0033] In addition, since the modulation signal is loaded with a top modulation signal, there is a nonlinear problem when converting the modulation signal into a modulation current that drives the laser. At this time, whether using a MOSFET (Metal-Oxide-SemiconductorField-Effect Transistor) or a BJT (Bipolar Junction Transistor) NPN high-speed amplifier tube, the process of converting voltage to current is nonlinear, which not only further aggravates the distortion of the signal, but also makes it difficult to accurately control parameters such as the top modulation power and top modulation depth.

[0034] The laser driver, the chip and the laser LD driving method are further described below in conjunction with the accompanying drawings and embodiments.

[0035] See also Figure 1 , is a schematic diagram of the structure of the laser driver described in one embodiment of the present application.

[0036] The present application provides a laser driver, which is used to connect to a laser LD and drive the laser LD to output a desired optical signal, and the laser driver includes: a top modulation module 100, which is used to obtain a top modulation signal and generate a top modulation current Ipt according to the top modulation signal, and the top modulation module 100 is used to connect to the laser LD and output the top modulation current Ipt to the laser LD. The top modulation signal includes one of a frequency modulation top modulation signal and an amplitude modulation top modulation signal. The laser driver also includes a service module 103, which is used to obtain a service signal and generate a service current according to the service signal, and the service module 103 is also used to connect to the laser LD and output the service current to the laser LD.

[0037] In this embodiment, the top modulation signal is directly converted into a top modulation current Ipt, and the top modulation current Ipt is directly superimposed on the service current to jointly drive the laser LD, so that the laser LD emits an optical signal according to the top modulation signal and the service signal.

[0038] In this embodiment, there is no coupling relationship between the low-speed top-modulated signal and the high-speed business signal before they are converted into the corresponding top-modulated current Ipt and modulation current of the laser LD. It is no longer necessary to load the top-modulated signal to the power supply voltage first, and therefore it is no longer necessary to couple the power supply voltage loaded with the top-modulated signal to the modulation signal. Therefore, it will not affect the working point of the modulation signal, thereby causing the output of a distorted modulation signal. The implementation is simpler and the interference is smaller, which effectively avoids crosstalk between signals and interference with the working point, and improves the accuracy and stability of the signal.

[0039] The laser LD can be either a directly modulated laser (DML) or an electro-absorption modulated laser (EML).

[0040] When driving the laser LD, the service current and a bias current are required, and the bias current can be provided by a bias module. Figure 1 , Figure 2 The bias module includes a bias current source Ibias, and the bias current source Ibias outputs a bias current to the laser LD, so that the laser LD works in a normal working state.

[0041] Since the laser driver directly converts the top modulation signal into current, the laser driver can realize the corresponding top modulation function regardless of whether the top modulation signal is a frequency modulation top modulation signal or an amplitude modulation top modulation signal. The top modulation signal includes one of a frequency modulation top modulation signal and an amplitude modulation top modulation signal.

[0042] The FM signal corresponds to a small-amplitude, low-frequency periodic signal, such as a sine signal or a cosine signal in an analog signal. The AM signal only needs to be a small-amplitude, low-frequency signal, and periodicity is no longer required. Therefore, the AM signal may include a digital signal, and the digital signal includes a digital signal based on Manchester coding. Manchester coding includes the clock and data in the signal stream, and transmits the clock synchronization signal to the other party while transmitting the code information. Each code element of Manchester coding is modulated into two levels, so the data transmission rate is only 1 / 2 of the modulation rate.

[0043] It should be noted that the small amplitude referred to here means that the amplitude of the top modulation signal is 1% or 1 / 1000 of the amplitude of the service signal. Those skilled in the art can set the amplitude of the AM top modulation signal and the FM top modulation signal as needed.

[0044] The top adjustment module 100 includes a first operational amplifier 101, a top adjustment digital-to-analog conversion unit PT_DAC, a first N-type transistor MN1, and a top adjustment resistor R1. The first operational amplifier 101 includes a non-inverting input terminal and an inverting input terminal, and the non-inverting input terminal is used to obtain the top adjustment signal. The top adjustment digital-to-analog conversion unit PT_DAC is connected to the non-inverting input terminal of the first operational amplifier 101 through a first resistor R0, and is used to provide a first voltage to the non-inverting input terminal of the first operational amplifier 101. The gate of the first N-type transistor MN1 is connected to the output terminal of the first operational amplifier 101, the drain is used to be connected to the laser LD, and the source is grounded through the top adjustment resistor R1. The non-grounded end of the top adjustment resistor R1 is also connected to the inverting input terminal of the first operational amplifier 101.

[0045] In this embodiment, the first operational amplifier 101 is an electronic integrated circuit containing a multi-stage amplifier circuit, wherein the input stage is a differential amplifier circuit having a high input resistance and the ability to suppress zero drift; the intermediate stage mainly performs voltage amplification and has a high voltage amplification factor, and is generally composed of a common emitter amplifier circuit; the output stage is connected to the load, and has the characteristics of strong load capacity and low output resistance, and the output signal of the first operational amplifier 101 is proportional to the signal voltage difference between the two input terminals.

[0046] In other embodiments, the structure of the first operational amplifier 101 may also be set as required, and the actual implementation is diverse.

[0047] The top-trimmed digital-to-analog conversion unit PT_DAC is connected to the non-inverting input terminal of the first operational amplifier 101 through a first resistor R0 , and the top-trimmed signal is pulled up to a first voltage output by the top-trimmed digital-to-analog conversion unit PT_DAC through the first resistor R0 .

[0048] When the top adjustment signal and the first voltage are given to the non-inverting input terminal of the first operational amplifier 101, due to the large voltage difference between the non-inverting input terminal and the inverting input terminal, the first N-type transistor MN1 is turned on, the source and drain of the first N-type transistor MN1 are connected, one end of the laser LD is connected to a voltage VCC, and the other end is grounded through the source and drain of the first N-type transistor MN1.

[0049] The first operational amplifier 101 constructs feedback between the inverting input terminal and the output terminal through the first N-type transistor MN1, and the output voltage of the first operational amplifier 101 is affected by the input voltage of the non-inverting input terminal in the initial state, so the input signal of the inverting input terminal of the first operational amplifier 101 follows the change of the signal input at the non-inverting input terminal. Figure 1 , Figure 2 ,exist Figure 1 , 2 In the illustrated embodiment, the voltage input to the inverting input terminal is equal to the voltage input to the positive input terminal, both of which are top trimming voltages. The top trimming voltage and the first voltage output by the top trimming digital-to-analog conversion unit PT_DAC are related to the amplitude of the top trimming signal.

[0050] Since the first operational amplifier 101 follows the input top modulation signal well, the top modulation current Ipt converted from the top modulation signal does not have a nonlinear problem.

[0051] The top trim module 100 further includes a register connected to the top trim digital-to-analog conversion unit PT_DAC and the top trim resistor R1 for controlling the magnitude of the first voltage output by the top trim digital-to-analog conversion unit PT_DAC and for controlling the resistance value of the top trim resistor R1.

[0052] In one embodiment, the register includes a top trimming digital-to-analog conversion unit PT_DAC register, connected to the top trimming digital-to-analog conversion unit PT_DAC, and used to control the output voltage of the top trimming digital-to-analog conversion unit PT_DAC. The register also includes a top trimming resistor R1 register, connected to the top trimming resistor R1, and used to control the resistance value of the top trimming resistor R1.

[0053] Since the size of the top trimming current Ipt is related to the top trimming voltage and the resistance value of the top trimming resistor R1, and is the result of dividing the top trimming voltage by the top trimming resistor R1, and the top trimming voltage is related to the coupling mode and the first voltage output by the top trimming digital-to-analog conversion unit PT_DAC, the size of the top trimming current Ipt can be adjusted by adjusting the first voltage of the top trimming digital-to-analog conversion unit PT_DAC and the resistance value of the top trimming resistor R1 through the register, thereby adjusting the top trimming power.

[0054] In one embodiment, the top trimming signal may be loaded to the non-inverting input terminal of the first operational amplifier 101 by AC coupling. AC coupling is to remove the DC component in the top trimming signal by coupling with a DC blocking capacitor. At this time, the top trimming depth of the top trimming process is related to the output voltage of the top trimming digital-to-analog conversion unit PT_DAC, the resistance value of the top trimming resistor R1, and the swing amplitude of the top trimming signal.

[0055] In other embodiments, the top trimming signal may be loaded to the non-inverting input terminal of the first operational amplifier 101 by DC coupling. At this time, the top trimming depth of the top trimming process is determined by the output voltage of the top trimming digital-to-analog conversion unit PT_DAC and the resistance value of the top trimming resistor R1.

[0056] As can be seen from the above, the top trimming depth of this top trimming process can be adjusted by the first voltage outputted by the top trimming digital-to-analog conversion unit PT_DAC, the resistance value of the top trimming resistor R1 and the swing amplitude of the top trimming signal, and can also be adjusted by the first voltage outputted by the top trimming digital-to-analog conversion unit PT_DAC and the resistance value of the top trimming resistor R1.

[0057] Therefore, when the first voltage outputted by the top trimming digital-to-analog conversion unit PT_DAC and the resistance value of the top trimming resistor R1 are adjustable, the top trimming depth is also adjustable.

[0058] Furthermore, since a common mode point needs to be provided during AC coupling, when the top-adjusting signal is input to the non-inverting input terminal of the first operational amplifier 101 by means of AC coupling, the output voltage of the top-adjusting digital-to-analog conversion unit PT_DAC can provide a common mode voltage for the top-adjusting signal, thereby providing a common mode point. When the top-adjusting signal is input to the non-inverting input terminal of the first operational amplifier 101 by means of DC coupling, the output voltage of the top-adjusting digital-to-analog conversion unit PT_DAC can provide a maximum voltage for the top-adjusting signal, and the maximum voltage refers to the voltage indicated by the high level.

[0059] See also Figure 3, is a schematic diagram of the structure of the bias module 102 in one embodiment.

[0060] In this embodiment, the laser driver further includes a bias module 102 , and the bias module 102 is used to be connected to the laser LD and output a bias current to the laser LD.

[0061] exist Figure 1 , Figure 2 In the illustrated embodiment, the bias module 102 includes a bias current source Ibias, one end of which is connected to the laser LD, and the other end of which is grounded, for outputting a bias current to the laser LD.

[0062] exist Figure 3 In the illustrated embodiment, the bias module 102 includes a bias digital-to-analog conversion unit BIAS_DAC, a subtractor 301, a second operational amplifier 302, a second N-type transistor MN2, and a bias resistor Rbias. The bias digital-to-analog conversion unit BIAS_DAC is used to provide a bias voltage. One end of the subtractor 301 is connected to the bias digital-to-analog conversion unit BIAS_DAC, and one end is connected to the top adjustment module 100 through a voltage divider. The voltage divider includes a second resistor R2 and a third resistor R3, and the resistance of the second resistor R2 is equal to the bias resistor Rbias, and the resistance of the third resistor R3 is equal to the difference between the top adjustment resistor R1 and the bias resistor Rbias.

[0063] The non-inverting input terminal of the second operational amplifier 302 is connected to the output terminal of the subtractor 301. The gate of the second N-type transistor MN2 is connected to the output terminal of the second operational amplifier 302, the drain is connected to the service module 103 and the bias module 102, the source is grounded through the bias resistor Rbias, and the non-grounded end of the bias resistor Rbias is also connected to the inverting input terminal of the second operational amplifier 302.

[0064] The subtractor 301 is a basic integrated operational amplifier circuit, which is generally implemented by an operational circuit consisting of an integrated operational amplifier and an external feedback network. The signal outputted from the output end of the subtractor 301 is the difference between the bias voltage and the output voltage of the top adjustment digital-to-analog conversion unit PT_DAC.

[0065] exist Figure 3 In the illustrated embodiment, the voltage divider is connected to the output terminal of the top-adjusting digital-to-analog converter PT_DAC, and is used to divide the output voltage of the top-adjusting digital-to-analog converter PT_DAC and output the voltage division result to an input terminal of the subtractor 301 .

[0066] The voltage divider unit includes a second resistor R2 and a third resistor R3, wherein a first end of the third resistor R3 is connected to an output end of the top adjustment digital-to-analog conversion unit PT_DAC, and a second end is connected to a first end of the second resistor R2, a second end of the second resistor R2 is grounded, a first end of the second resistor R2 is also connected to a second input end of the subtractor 301, and a resistance value of the second resistor R2 is equal to a resistance value of the bias resistor Rbias, and a resistance value of the third resistor R3 is equal to a difference between the top adjustment resistor R1 and the bias resistor Rbias.

[0067] The bias module 102 also includes a second operational amplifier 302, the non-inverting input terminal of the second operational amplifier 302 is connected to the output terminal of the subtractor 301, and the inverting input terminal of the second operational amplifier 302 is connected to the output terminal of the second operational amplifier 302, so the inverting input terminal of the second operational amplifier 302 follows the positive input terminal of the second operational amplifier 302.

[0068] The voltage obtained at one input end of the subtractor 301 is Vpt*R2 / R1. When the output voltage Vpt of the top adjustment digital-to-analog conversion unit PT_DAC is DC-coupled to the subtractor 301, the voltage obtained at the input end of the subtractor 301 is Vpt*R2 / R1, and the output voltage of the subtractor 301 is Vbias-Vpt*R2 / R1. The bias current Ibias is (Vbias-Vpt*R2 / R1) / R2, and the top adjustment current Ipt=Vpt / R1.

[0069] When the output voltage Vbias of the top adjustment digital-to-analog conversion unit PT_DAC is AC-coupled to the subtractor 301, the voltage obtained by the input end of the subtractor 301 is Vpt*R2 / 2*R1, and the output voltage of the subtractor 301 is Vbias-Vpt*R2 / 2*R1. The bias current Ibias is (Vbias-Vpt*R2 / 2*R1) / R2. The top adjustment current Ipt=Vpt / 2*R1.

[0070] At this time, no matter it is DC coupling or AC coupling, the sum of the bias current Ibias and the top adjustment current Ipt is Vbias / R2, which is a constant value.

[0071] Therefore, in this embodiment, due to the bias module 102, automatic power adjustment can be achieved. The bias digital-to-analog conversion unit BIAS_DAC automatically adjusts the bias current according to the top-modulated current Ipt to compensate for the change in output optical power caused by the change in the top-modulated current Ipt, thereby offsetting the optical power generated by the top-modulated current Ipt, and making corresponding compensation for the change in average optical power caused by the top-modulated signal, thereby ensuring the stability of the average optical power output by the laser LD to which the laser driver is connected.

[0072] Therefore, as long as the top adjustment function is enabled, the laser driver can realize automatic power control and keep the sum of the bias current and the top adjustment current Ipt constant, so that when the top adjustment is enabled and the top adjustment parameters are adjusted, the output average optical power is not affected. A corresponding compensation mechanism is provided for the phenomenon of average optical power change caused by the top adjustment signal, namely, automatic power control compensation, to ensure the stability of the output average optical power.

[0073] In some other embodiments, a current mirror structure may be used to implement automatic power control. The purpose of automatic power control is to keep the top-adjusting current Ipt and the bias current constant. Therefore, the top-adjusting current Ipt may be passed through a current mirror so that the bias current shunts this part of the current, thereby achieving the purpose of constant current.

[0074] The service module 103 includes: a switch K1, one end of which is connected to the laser, and is used to switch on and off according to the service signal, the switch K1 is turned on when the service signal is at a high level, and is turned off when the service signal is at a low level; a service current source Imod, one end of which is grounded and the other end is connected to the second end of the switch K1, and is used to provide service current to the laser LD when the switch K1 is turned on.

[0075] The service module 103 provides the service current only when the service signal is at a high level. The service current, the bias current and the top adjustment current Ipt drive the laser LD together, so that the laser LD outputs the required optical signal.

[0076] In this embodiment, by converting the top modulation signal to the top modulation current Ipt, and loading the top modulation current Ipt to the bias current, the problem of modulation signal distortion caused by using the top modulation signal to modulate the power supply signal when acquiring the modulation signal is avoided, and the nonlinear problem when the modulation signal is converted into the modulation current caused by the modulation signal distortion is also avoided. In addition, due to the existence of the register, the value of the first voltage output by the top modulation digital-to-analog conversion unit PT_DAC and the resistance value of the top modulation resistor R1 can be adjusted. Therefore, the top modulation power and top modulation depth of the laser driver are adjusted through the corresponding register, which improves the output accuracy of the top modulation signal and the flexibility of the top modulation operation. In addition, the present invention also makes an automatic power control circuit of the laser LD under the condition of enabling the top modulation function to ensure the stability of the operation of the laser LD.

[0077] In addition, in this embodiment, since the corresponding top adjustment function circuit is integrated, the top adjustment mode can be freely selected, and the top adjustment power and top adjustment depth are adjustable, it will be very meaningful for the module design freedom of the module manufacturer and the technical use flexibility of the system manufacturer.

[0078] In an embodiment of the present application, a chip is also provided, and the chip includes the laser driver.

[0079] Since the chip has the laser driver in the above embodiment, it can realize frequency modulation and top modulation, and can also realize amplitude modulation and top modulation. In addition, the corresponding circuit of the laser driver is integrated inside the chip, which saves the board space of the optical module equipped with the laser LD and improves the design flexibility of the optical module.

[0080] Furthermore, the top adjustment mode of the top adjustment module 100 integrated in the chip can be freely selected, and the top adjustment power and top adjustment depth can be adjusted, which will be very meaningful for the module design freedom of the module manufacturer and the technical use flexibility of the system manufacturer.

[0081] In an embodiment of the present application, a laser LD driving method is also provided.

[0082] The driving method comprises the following steps: providing a top modulation signal, wherein the top modulation signal comprises one of a frequency modulation top modulation signal and an amplitude modulation top modulation signal; obtaining a top modulation current according to the top modulation signal; obtaining a service current according to a service signal; and outputting the top modulation current and the service current to the laser to drive the laser.

[0083] See also Figure 4 , is a schematic flow chart of the steps of the laser LD driving method described in one embodiment of the present application.

[0084] In this embodiment, the laser LD driving method comprises the following steps:

[0085] Step S101: providing a top modulation signal, wherein the top modulation signal includes one of a frequency modulation top modulation signal and an amplitude modulation top modulation signal.

[0086] The FM top modulation signal corresponds to a periodic signal with a small amplitude and a low frequency, such as a sine signal or a cosine signal in an analog signal. The AM top modulation signal only needs to be a low frequency signal with a small amplitude, and no periodicity is required. Therefore, the AM top modulation signal may include a digital signal, and the digital signal includes a digital signal based on Manchester encoding.

[0087] It should be noted that the small amplitude referred to here means that the amplitude of the top modulation signal is 1% or 1 / 1000 of the amplitude of the service signal. Those skilled in the art can set the amplitude of the AM top modulation signal and the FM top modulation signal as needed.

[0088] Step S102: obtaining a top adjustment current Ipt according to the top adjustment signal.

[0089] When the top trimming current Ipt is obtained according to the top trimming signal, the following steps are included: providing a first operational amplifier 101, the first operational amplifier 101 includes a non-inverting input terminal and an inverting input terminal, and the output terminal of the operational amplifier is connected to the gate of a first N-type triode, the source of the first N-type triode MN1 is grounded through a top trimming resistor R1, the drain is connected to the laser LD, and the inverting input terminal is connected to the non-grounded end of the top trimming resistor R1; providing a first voltage; coupling the first voltage and the top trimming signal to the non-inverting input terminal of the operational amplifier.

[0090] Specifically, in this embodiment, the first voltage is given by the top trimming digital-to-analog conversion unit PT_DAC. Since the size of the top trimming current Ipt is related to the size of the top trimming voltage and the resistance value of the top trimming resistor R1, and is the result of dividing the top trimming voltage by the top trimming resistor R1, the size of the top trimming voltage is related to the first voltage output by the top trimming digital-to-analog conversion unit PT_DAC and the coupling mode. Therefore, the size of the top trimming current Ipt can be adjusted by adjusting the first voltage output by the top trimming digital-to-analog conversion unit PT_DAC and the resistance value of the top trimming resistor R1, thereby adjusting the top trimming power.

[0091] The coupling mode includes direct current coupling and alternating current coupling. When the top trimming signal is loaded to the non-inverting input terminal of the first operational amplifier 101 by adopting the alternating current coupling mode, the top trimming depth of the top trimming process is related to the output voltage of the top trimming digital-to-analog conversion unit PT_DAC, the resistance value of the top trimming resistor R1, and the swing amplitude of the top trimming signal.

[0092] When the top trimming signal is loaded to the non-inverting input terminal of the first operational amplifier 101 by DC coupling, the top trimming depth of the top trimming process is determined by the output voltage of the top trimming digital-to-analog conversion unit PT_DAC and the resistance value of the top trimming resistor R1.

[0093] As can be seen from the above, the top trimming depth of this top trimming process can be adjusted by the first voltage outputted by the top trimming digital-to-analog conversion unit PT_DAC, the resistance value of the top trimming resistor R1 and the swing amplitude of the top trimming signal, and can also be adjusted by the first voltage outputted by the top trimming digital-to-analog conversion unit PT_DAC and the resistance value of the top trimming resistor R1.

[0094] Therefore, when the first voltage outputted by the top trimming digital-to-analog conversion unit PT_DAC and the resistance value of the top trimming resistor R1 are adjustable, the top trimming depth is also adjustable.

[0095] Step S103: Adjusting the top trim power and top trim depth. Specifically, adjusting the magnitude of the first voltage output by the top trim digital-to-analog conversion unit PT_DAC and / or adjusting the magnitude of the top trim resistor R1, thereby adjusting the magnitude of the top trim current Ipt, thereby adjusting the top trim power and top trim depth.

[0096] In some embodiments, the top trimming digital-to-analog conversion unit PT_DAC and the top trimming resistor R1 are both connected to a register, and the register controls the magnitude of the first voltage output by the top trimming digital-to-analog conversion unit PT_DAC, and controls the magnitude of the top trimming resistor R1. Therefore, by adjusting the first voltage and / or the magnitude of the top trimming resistor R1 through the register, the magnitude of the top trimming current Ipt is adjusted, thereby adjusting the top trimming power and the top trimming depth.

[0097] Step S104: Acquire the service current according to the service signal.

[0098] When obtaining the service current according to the service signal, the following steps are included: providing a service current source Imod, one end of the service current source Imod is grounded, and the other end is connected to the laser LD through a switch K1; when the service signal exists, the first current source and the laser LD are turned on, and the first current source provides the service current for the laser LD.

[0099] The service module 103 provides the service current only when there is a service signal. The service current, the bias current and the top adjustment current Ipt drive the laser LD together, so that the laser LD outputs the required optical signal.

[0100] Step S105: outputting the bias current, the top adjustment current Ipt and the service current to the laser LD.

[0101] In this embodiment, a bias current is provided to the laser. The magnitude of the bias current can be controlled so that the sum of the top adjustment current Ipt and the bias current is constant.

[0102] In some embodiments, the bias module 102 may be used to achieve a constant sum of the top adjustment current Ipt and the bias current.

[0103] The bias module 102 includes a bias digital-to-analog conversion unit BIAS_DAC, a subtractor 301, a second operational amplifier 302, a second N-type transistor MN2, and a bias resistor Rbias. The bias digital-to-analog conversion unit BIAS_DAC is used to provide a bias voltage. One end of the subtractor 301 is connected to the bias digital-to-analog conversion unit BIAS_DAC, and one end is connected to the top adjustment module 100 through a voltage divider. The voltage divider includes a second resistor R2 and a third resistor R3, and the resistance of the second resistor R2 is equal to the bias resistor Rbias, and the resistance of the third resistor R3 is equal to the difference between the top adjustment resistor R1 and the bias resistor Rbias.

[0104] The non-inverting input terminal of the second operational amplifier 302 is connected to the output terminal of the subtractor 301. The gate of the second N-type transistor MN2 is connected to the output terminal of the second operational amplifier 302, the drain is connected to the service module 103 and the bias module 102, the source is grounded through the bias resistor Rbias, and the non-grounded end of the bias resistor Rbias is also connected to the inverting input terminal of the second operational amplifier 302.

[0105] The subtractor 301 is a basic integrated operational amplifier circuit, which is generally implemented by an operational circuit consisting of an integrated operational amplifier and an external feedback network. The signal outputted from the output end of the subtractor 301 is the difference between the bias voltage and the output voltage of the top adjustment digital-to-analog conversion unit PT_DAC.

[0106] exist Figure 3 In the illustrated embodiment, the voltage divider is connected to the output terminal of the top-adjusting digital-to-analog converter PT_DAC, and is used to divide the output voltage of the top-adjusting digital-to-analog converter PT_DAC and output the voltage division result to an input terminal of the subtractor 301 .

[0107] A first end of the third resistor R3 in the voltage divider unit is connected to the output end of the top adjustment digital-to-analog conversion unit PT_DAC, and a second end is connected to a first end of the second resistor R2, a second end of the second resistor R2 is grounded, and a first end of the second resistor R2 is also connected to a second input end of the subtractor 301, and a resistance value of the second resistor R2 is equal to a resistance value of the bias resistor Rbias, and a resistance value of the third resistor R3 is equal to a difference between the top adjustment resistor R1 and the bias resistor Rbias.

[0108] When AC coupling is used for input, the voltage obtained at one input end of the subtractor 301 is Vpt*R2 / R1, and the voltage obtained at the other input end is the bias voltage Vbias. The output voltage of the subtractor 301 is (Vbias-Vpt*R2 / R1). Since the bias module 102 also includes a second operational amplifier 302, the non-inverting input end of the second operational amplifier 302 is connected to the output end of the subtractor 301, and the inverting input end is connected to the output end of the second operational amplifier 302. Therefore, the inverting input end of the second operational amplifier 302 follows the positive input end of the second operational amplifier 302, and the bias current Ibias = (Vbias-Vpt*R2 / R1) / R2. At this time, the sum of the bias current and the top adjustment current Ipt = Vpt / R1 is Vbias / R2, and the sum is a certain value.

[0109] When the input is in a DC coupling mode, when the top-modulated digital-to-analog conversion unit PT_DAC still outputs Vpt, the voltage obtained at one input end of the subtractor 301 is Vpt*R2 / 2*R1.

[0110] At this time, the output voltage of the subtractor 301 is Vbias-Vpt*R2 / 2*R1, so the bias current Ibias is (Vbias-Vpt*R2 / 2*R1) / R2, that is, (Vbias / R2-Vpt / 2*R1). Since the top adjustment current Ipt is Vpt / 2*R1, the sum of the bias current and the top adjustment current is still Vbias / R2, which is a constant value.

[0111] Therefore, in this embodiment, due to the bias module 102, automatic power adjustment can also be achieved. The bias digital-to-analog conversion unit BIAS_DAC will automatically adjust the size of the bias current according to the size of the top-adjusting current Ipt to compensate for the change in the output optical power caused by the change in the top-adjusting current Ipt, thereby offsetting the optical power generated by the top-adjusting current Ipt, and making corresponding compensation for the phenomenon of the average optical power change caused by the top-adjusting signal, thereby ensuring the stability of the average optical power output by the laser LD to which the laser driver is connected.

[0112] Therefore, as long as the top adjustment function is enabled, the laser driver can realize automatic power control and keep the sum of the bias current and the top adjustment current Ipt constant, so that when the top adjustment is enabled and the top adjustment parameters are adjusted, the output average optical power is not affected. A corresponding compensation mechanism is provided for the phenomenon of average optical power change caused by the top adjustment signal, namely, automatic power control compensation, to ensure the stability of the output average optical power.

[0113] In some other embodiments, a current mirror structure may be used to implement automatic power control. The purpose of automatic power control is to keep the top-adjusting current Ipt and the bias current constant. Therefore, the top-adjusting current Ipt may be passed through a current mirror so that the bias current shunts this part of the current, thereby achieving the purpose of constant current.

[0114] In this embodiment, by loading the top adjustment signal into the bias current, the problem of modulation signal distortion caused by using the top adjustment signal to modulate the power supply signal when acquiring the modulation signal is avoided, and the problem of nonlinearity when the modulation signal is converted into the modulation current caused by the modulation signal distortion is also avoided. In addition, since the value of the first voltage can be adjusted, and the resistance value of the top adjustment resistor R1 can be adjusted, the top adjustment power and top adjustment depth of the laser driver can also be adjusted, thereby improving the output accuracy of the top adjustment signal and the flexibility of the top adjustment operation. In addition, the present invention also performs automatic power control of the laser LD under the condition that the top adjustment function is enabled, which can ensure the stability of the operation of the laser LD.

[0115] In addition, in this embodiment, since the corresponding top adjustment function circuit is integrated, the top adjustment mode can be freely selected, and the top adjustment power and top adjustment depth are adjustable, it will be very meaningful for the module design freedom of the module manufacturer and the technical use flexibility of the system manufacturer.

[0116] The above descriptions are merely embodiments of the present application and are not intended to limit the patent scope of the present application. Any equivalent structural or equivalent process transformations made using the contents of the specification and drawings of the present application, such as the mutual combination of technical features between the embodiments, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A laser driver, characterized in that: include: A top adjustment module, used for acquiring a top adjustment signal and generating a top adjustment current according to the top adjustment signal, wherein the top adjustment module is also used for connecting to a laser and outputting the top adjustment current to the laser; A service module, used for acquiring a service signal and generating a service current according to the service signal, wherein the service module is further used for connecting to the laser and outputting the service current to the laser; The top modulation current and the service current jointly drive the laser, so that the laser emits an optical signal according to the top modulation signal and the service signal; The top adjustment module includes a first operational amplifier, a top adjustment digital-to-analog conversion unit, a first N-type transistor and a top adjustment resistor, and: the first operational amplifier includes a non-inverting input terminal and an inverting input terminal, wherein the non-inverting input terminal is used to obtain the top adjustment signal, and the output terminal of the first operational amplifier is connected to the gate of the first N-type transistor; the top adjustment digital-to-analog conversion unit is connected to the non-inverting input terminal of the first operational amplifier through a first resistor, and is used to provide a first voltage to the non-inverting input terminal of the first operational amplifier; the drain of the first N-type transistor is used to be connected to the laser, and the source is grounded through the top adjustment resistor, and the non-grounded end of the top adjustment resistor is also connected to the inverting input terminal of the first operational amplifier; A bias module, the bias module is used to be connected to the laser and output a bias current to the laser; The bias module comprises a bias current source, one end of which is used to be connected to the laser, and the other end of which is grounded, and is used to output a bias current to the laser; The bias module includes a bias digital-to-analog conversion unit, a subtractor, a voltage divider, a second operational amplifier, a second N-type transistor and a bias resistor, wherein: the bias digital-to-analog conversion unit is used to provide a bias voltage; the subtractor includes a first input terminal and a second input terminal, and the first input terminal is connected to the bias digital-to-analog conversion unit, and the second input terminal is connected to the output terminal of the top adjustment digital-to-analog conversion unit through the voltage divider unit; the second operational amplifier includes a non-inverting input terminal and an inverting input terminal, and the non-inverting input terminal is connected to the output terminal of the subtractor, and the output terminal of the second operational amplifier is connected to the gate of the second N-type transistor; the drain of the second N-type transistor is connected to the drain of the first N-type transistor, the source of the second N-type transistor is grounded through the bias resistor, and the non-grounded end of the bias resistor is also connected to the inverting input terminal of the second operational amplifier.

2. The laser driver according to claim 1, characterized in that: It also includes a register connected to the top-adjusting digital-to-analog conversion unit and the top-adjusting resistor, used to control the magnitude of the first voltage output by the top-adjusting digital-to-analog conversion unit, and used to control the resistance value of the top-adjusting resistor.

3. The laser driver according to claim 1, characterized in that: The top modulation signal includes an amplitude modulation top modulation signal and an frequency modulation top modulation signal, and the amplitude modulation top modulation signal includes a digital signal, and the frequency modulation top modulation signal includes an analog signal.

4. The laser driver according to claim 3, characterized in that: The digital signal includes a Manchester-coded digital signal, and the analog signal includes one of a sine analog signal and a cosine analog signal.

5. The laser driver according to claim 4, characterized in that: The voltage divider unit includes a second resistor and a third resistor, wherein a first end of the third resistor is connected to an output end of the top adjustment digital-to-analog conversion unit, a second end of the third resistor is connected to a first end of the second resistor, a second end of the second resistor is grounded, and a first end of the second resistor is also connected to a second input end of the subtractor, and: The resistance value of the second resistor is equal to the resistance value of the bias resistor, and the resistance value of the third resistor is equal to the difference between the top adjustment resistor and the bias resistor.

6. The laser driver according to claim 1, characterized in that: The business module includes: A switch, used for switching the on / off state according to the service signal, being turned on when the service signal is at a high level, and being turned off when the service signal is at a low level, and one end of the switch is used for connecting to the laser; A service current source has one end grounded and one end connected to the other end of the switch, and is used for providing service current.

7. A chip, characterized in that: The chip comprises a laser driver as claimed in any one of claims 1 to 6, wherein the chip further integrates a laser, the laser is connected to the laser driver and emits a required optical signal following a driving current of the laser driver.

8. A laser driving method, used to drive the laser driver according to any one of claims 1 to 6, characterized in that: The laser driving method comprises the following steps: Providing a top modulation signal, wherein the top modulation signal includes one of a frequency modulation top modulation signal and an amplitude modulation top modulation signal; Acquire a top adjustment current according to the top adjustment signal; Acquire business current according to business signal; The top-modulation current and the service current are output to the laser to drive the laser.

9. The laser driving method according to claim 8, characterized in that: When obtaining the top adjustment current according to the top adjustment signal, the following steps are included: A first operational amplifier is provided, wherein the first operational amplifier comprises a non-inverting input terminal and an inverting input terminal, and the output terminal of the operational amplifier is connected to the gate of a first N-type triode, the source of the first N-type triode is grounded through a top-adjusting resistor, the drain is connected to the laser, and the inverting input terminal is connected to the non-grounded end of the top-adjusting resistor; providing a first voltage; The first voltage and the top adjustment signal are coupled to a non-inverting input terminal of the operational amplifier.

10. The laser driving method according to claim 9, characterized in that: The magnitude of the first voltage is adjusted, and / or the magnitude of the top adjustment resistor is adjusted, thereby adjusting the magnitude of the top adjustment current.

11. The laser driving method according to claim 8, characterized in that: When obtaining the service current according to the service signal, the following steps are included: Providing a service current source, wherein one end of the service current source is grounded, and the other end is connected to the laser through a switch; When the service signal is present, the service current source and the laser are turned on, and the service current source provides the laser with service current.

12. The laser driving method according to claim 8, characterized in that: The following steps are also included: providing a bias current to the laser; The magnitude of the bias current is adjusted so that the sum of the top adjustment current and the bias current is constant.

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