Laser drive circuit and laser system

Abstract

The invention provides a laser driving circuit and a laser system, and belongs to the technical field of laser modulation. According to the laser driving circuit, a signal input end is connected with a first operational amplifier and a second operational amplifier; the output end of the first operational amplifier is connected with the first high-pass filter and the first low-pass filter, and the second input end of the first operational amplifier is connected with the first high-pass filter and the second low-pass filter; the output end of the second operational amplifier is connected with the second high-pass filter and the third low-pass filter, and the second end of the second operational amplifier is connected with the third low-pass filter and the third high-pass filter; the weight control circuit is connected with the first low-pass filter and the second high-pass filter; the current control circuit is connected with the weight control circuit and the sampling circuit; and the sampling circuit is connected with the second low-pass filter and the third high-pass filter. According to the scheme, the laser driving circuit with low direct-current error, large bandwidth and low noise can be realized, meanwhile, self-oscillation cannot be generated, and the gain is flat.

Description

Technical Field

[0001] The present invention relates to the field of laser modulation, and in particular to a laser driving circuit and a laser system comprising the laser driving circuit. Background Art

[0002] Related laser driver circuits utilize a single operational amplifier. The performance of a single operational amplifier affects the performance of the laser driver circuit. High-speed, low-noise operational amplifiers often have limited input characteristics. Using a high-speed, low-noise operational amplifier in a laser driver circuit can generate input offset voltage and current, degrading the laser driver circuit's DC characteristics. High-precision operational amplifiers offer good DC characteristics, but poor noise and bandwidth characteristics. This generates high current noise, which in turn degrades the laser linewidth. Furthermore, an excessively narrow bandwidth can affect laser modulation. Summary of the Invention

[0003] In view of this, the present invention provides a laser driving circuit and a laser system including the laser driving circuit to solve the technical problems of poor DC characteristics, poor noise characteristics and narrow bandwidth of related laser driving circuits.

[0004] In a first aspect, the present application provides a laser driving circuit based on parallel operational amplifiers, the laser driving circuit comprising: a signal input end, a first operational amplifier, a second operational amplifier, a first high-pass filter, a second high-pass filter, a third high-pass filter, a first low-pass filter, a second low-pass filter, a third low-pass filter, a weight control circuit, a current control circuit and a sampling circuit; wherein the signal input end is connected to the first operational amplifier and the second operational amplifier; the output end of the first operational amplifier is connected to the first high-pass filter and the first low-pass filter, and the negative feedback input end of the first operational amplifier is connected to the first high-pass filter and the second low-pass filter; the output end of the second operational amplifier is connected to the second high-pass filter and the third low-pass filter, and the negative feedback input end of the second operational amplifier is connected to the third low-pass filter and the third high-pass filter; the weight control circuit is connected to the first low-pass filter and the second high-pass filter; the current control circuit is connected to the weight control circuit and the sampling circuit; and the sampling circuit is connected to the second low-pass filter and the third high-pass filter.

[0005] Optionally, the signal input end is configured to obtain a laser modulation signal from the outside world and output the laser modulation signal to the first operational amplifier and the second operational amplifier respectively; the first low-pass filter is configured to output the first DC component output by the first operational amplifier to the weight control circuit; the first high-pass filter is configured to output the first AC component output by the first operational amplifier to the negative feedback end of the first operational amplifier; the second high-pass filter is configured to output the second AC component output by the second operational amplifier to the weight control circuit; the third low-pass filter is configured to output the second DC component output by the second operational amplifier to the negative feedback end of the second operational amplifier; the second low-pass filter is configured to output the DC component corresponding to the DC component of the sampling circuit to the negative feedback end of the first operational amplifier; the third high-pass filter is configured to output the AC component of the sampling circuit to the negative feedback end of the second operational amplifier.

[0006] Optionally, the first low-pass filter includes a first inductor and a fourth capacitor, and the weight control circuit includes a fifth resistor and a sixth resistor; the first end of the first inductor is connected to the output end of the first operational amplifier, and the second end of the first inductor is connected to the first end of the fifth resistor and the first end of the fourth capacitor; the second end of the fifth resistor is connected to the first end of the sixth resistor, and the second end of the fourth capacitor is connected to the ground; the first high-pass filter includes a first capacitor and a first resistor, the first end of the first resistor is connected to the negative feedback end of the first operational amplifier, the second end of the first resistor is connected to the first end of the first capacitor, and the second end of the first capacitor is connected to the output end of the first operational amplifier.

[0007] Optionally, the second high-pass filter includes a second capacitor, a first end of the second capacitor is connected to the output end of the second operational amplifier, and a second end of the second capacitor is connected to the second end of the sixth resistor; the third low-pass filter includes a second inductor and a second resistor, a first end of the second inductor is connected to the output end of the second operational amplifier, a second end of the second inductor is connected to the second end of the second resistor, and a first end of the second resistor is connected to the negative feedback end of the second operational amplifier.

[0008] Optionally, the current control circuit includes a field effect transistor, the gate of the field effect transistor is connected to the first end of the sixth resistor; the sampling circuit includes a seventh resistor, the first end of the seventh resistor is connected to the drain of the field effect transistor, and the second end of the seventh resistor is connected to the ground.

[0009] Optionally, the second low-pass filter includes a third inductor and a third resistor, the first end of the third inductor is connected to the first end of the seventh resistor, the second end of the third inductor is connected to the first end of the third resistor, and the second end of the third resistor is connected to the negative feedback end of the first operational amplifier.

[0010] Optionally, the third high-pass filter includes a third capacitor and a fourth resistor, the first end of the third capacitor is connected to the first end of the seventh resistor, the second end of the third capacitor is connected to the first end of the fourth resistor, and the second end of the fourth resistor is connected to the negative feedback end of the second operational amplifier.

[0011] Optionally, the bandwidth of the first operational amplifier is lower than the bandwidth of the second operational amplifier; and the output noise of the first operational amplifier is higher than the output noise of the second operational amplifier.

[0012] In a second aspect, a laser system is provided. The laser system includes: a modulation signal source, the laser driving circuit according to the first aspect, and a laser, wherein the modulation signal source is configured to provide a modulation signal to the laser driving circuit, and the laser is connected to the source of the field-effect transistor.

[0013] The solution of the present application can realize a laser driving circuit with low DC error, large bandwidth and low noise, while not generating self-oscillation and having flat gain. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 shows a schematic structural diagram of the laser driving circuit of the present application; and

[0015] Figure 2 A detailed structural diagram of the laser driving circuit of the present application is shown. DETAILED DESCRIPTION

[0016] Below, the specific embodiments of the present application will be described in detail with reference to the accompanying drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. In the following exemplary embodiments, the embodiments described are not all embodiments of the present application. Instead, they are merely examples of devices and methods consistent with certain aspects of the present application as detailed in the appended claims. The embodiments and features in the embodiments of the present application may be combined with each other unless there is a conflict.

[0017] A single operational amplifier is used in related laser drive circuits. The performance of a single operational amplifier affects the performance of the laser drive circuit. If a high-speed, low-noise operational amplifier (such as the ADA4897) is used, the input characteristics of high-speed, low-noise operational amplifiers are generally poor, so the DC characteristics will be degraded due to the influence of input offset voltage and input offset current. If a high-precision operational amplifier (such as the AD8551) is used, the noise and bandwidth characteristics of high-precision operational amplifiers are generally poor, so the current noise generated will be relatively large, which will cause the laser linewidth to degrade. In addition, the low bandwidth of a high-precision operational amplifier will also affect the modulation of the laser, making it unsuitable for laser modulation.

[0018] Based on the above problems, the present application provides a laser driver circuit for a laser. The laser can be used in a frequency-modulated continuous wave (FMCW) laser radar or other lasers. The solution of the present application adopts a high-precision operational amplifier and a high-speed / low-noise operational amplifier in parallel. By adjusting the parallel weight of the two through a weight control circuit, a wider bandwidth can be obtained than the bandwidth of a high-speed / low-noise operational amplifier alone. At the same time, a noise level substantially the same as that of a high-speed / low-noise operational amplifier and a DC error substantially the same as that of a high-precision operational amplifier are obtained, which can significantly improve the performance of the laser driver circuit.

[0019] Figure 1 FIG1 shows a schematic diagram of the structure of the laser driving circuit of the present application. Figure 1 The laser driving circuit 10 includes: a signal input terminal 11, a first operational amplifier 12, a second operational amplifier 13, a first high-pass filter 122, a second high-pass filter 131, a third high-pass filter 133, a first low-pass filter 121, a second low-pass filter 123, a third low-pass filter 132, a weight control circuit 14, a current control circuit 15 and a sampling circuit 16.

[0020] The signal input terminal 11 is connected to the first operational amplifier 12 and the second operational amplifier 13, and is configured to receive a laser modulation signal from the outside and output the laser modulation signal to the first operational amplifier 12 and the second operational amplifier 13, respectively. The outside can be the front end of a laser radar or other equipment that can provide a laser modulation signal. For example, the signal input terminal 11 can receive a laser modulation signal from an external laser modulator. The laser modulation signal can be a voltage signal, such as a modulation signal of a frequency modulated continuous wave (FMCW) laser radar. The frequency of the frequency modulation signal can be a signal in the range of 200Hz-100KHz. When used in an FMCW laser radar, the modulation signal can be a triangle wave signal or a sawtooth wave signal. The signal input terminal 11 can provide the laser modulation signal to the first operational amplifier 12 and the second operational amplifier 13, respectively.

[0021] The output of the first operational amplifier 12 is connected to the first high-pass filter 122 and the first low-pass filter 121, and the negative feedback input of the first operational amplifier 12 is connected to the first high-pass filter 122 and the second low-pass filter 123. The output of the second operational amplifier 13 is connected to the second high-pass filter 131 and the third low-pass filter 132, and the negative feedback input of the second operational amplifier 13 is connected to the third low-pass filter 132 and the third high-pass filter 133.

[0022] The first operational amplifier 12 can output a first DC component DC1 and a first AC component AC1. The second operational amplifier 13 can output a second DC component DC2 and a second AC component AC2. The first high-pass filter 122, the second high-pass filter 131, and the third high-pass filter 133 of the present application are configured to allow the first AC component AC1 and the second AC component AC2 to pass through, while isolating the first DC component DC1 and the second DC component DC2. The first low-pass filter 121, the second low-pass filter 123, and the third low-pass filter 132 of the present application are configured to allow the first DC component DC1 and the second DC component DC2 to pass through, while isolating the first AC component AC1 and the second AC component AC2.

[0023] The weight control circuit 14 is connected to the first low-pass filter 121 and the second high-pass filter 131 ; the current control circuit 15 is connected to the weight control circuit 14 and the sampling circuit 16 ; the sampling circuit 16 is connected to the second low-pass filter 123 and the third high-pass filter 133 .

[0024] Specifically, the first low-pass filter 121 is configured to output the first DC component DC1 output by the first operational amplifier 12 to the weight control circuit 14; the first high-pass filter 122 is configured to output the first AC component AC1 output by the first operational amplifier 12 to the negative feedback terminal of the first operational amplifier 12. The second high-pass filter 131 is configured to output the second AC component AC2 output by the second operational amplifier 13 to the weight control circuit 14; the third low-pass filter 132 is configured to output the second DC component DC2 output by the second operational amplifier 13 to the negative feedback terminal of the second operational amplifier 13; the second low-pass filter 123 is configured to output the DC component DC3 corresponding to the DC component of the sampling circuit 16 to the negative feedback terminal of the first operational amplifier 12; and the third high-pass filter 133 is configured to output the AC component AC3 of the sampling circuit 16 to the negative feedback terminal of the second operational amplifier 13.

[0025] Specifically, the first operational amplifier 12 can be a high-precision operational amplifier, and the second operational amplifier 13 can be a low-noise operational amplifier. High-precision operational amplifiers are characterized by high noise, narrow bandwidth, good input characteristics, good temperature drift performance, good DC characteristics, and poor AC characteristics. Low-noise operational amplifiers are characterized by low noise, wide bandwidth, poor input characteristics, poor temperature drift performance, good AC characteristics, and poor DC characteristics.

[0026] exist Figure 1 In the illustrated embodiment, the first operational amplifier 12 (a high-precision operational amplifier) has two feedback loops: a high-frequency feedback loop and a low-frequency feedback loop. The high-frequency AC component in the signal output by the first operational amplifier 12 is fed back to the negative feedback input of the first operational amplifier 12 by the first high-pass filter 122, which passes high-frequency signals and isolates low-frequency signals. The high-frequency AC component does not contribute to the laser drive current. The low-pass filter passes low-frequency signals, and the output signal of the first operational amplifier 12 passes sequentially through the first low-pass filter 121, the weight control circuit 14, the current control circuit 15, and the sampling circuit 16. The DC signal from the sampling circuit 16 is then input to the negative feedback input of the first operational amplifier 12 via the second low-pass filter 123, providing feedback of the low-frequency component output by the first operational amplifier 12. The low-frequency DC component participates in controlling the current control circuit 15 to generate the drive current for the load (laser).

[0027] The second operational amplifier 13 (low-noise operational amplifier) also has two feedback loops: a high-frequency feedback loop and a low-frequency feedback loop. The third low-pass filter 132 passes low-frequency signals, feeding back the low-frequency DC component output by the second operational amplifier 13 to its negative feedback input. This low-frequency DC component does not contribute to the laser's drive current. The high-pass filter, which passes high-frequency signals and isolates low-frequency signals, feeds back the high-frequency AC component in the output signal of the second operational amplifier 13 to its negative feedback input via the second high-pass filter 131, the weighted control circuit 14, the current control circuit 15, the sampling circuit 16, and the third high-pass filter 133. This provides feedback on the high-frequency component output by the second operational amplifier 13. The high-frequency AC component participates in controlling the current control circuit 15 to generate the drive current for the load (laser). The first high-pass filter 122 minimizes the impact of the high-precision operational amplifier on noise. The third low-pass filter 132 can feed back the DC output signal of the low-noise operational amplifier to the negative feedback input terminal of the second operational amplifier 13 as much as possible, so as to maintain the best AC output characteristics, the most stable gain, and the largest possible bandwidth.

[0028] In the embodiment of the present application, since the high-precision operational amplifier has good DC characteristics and poor AC characteristics, and the low-noise operational amplifier has good AC characteristics and poor DC characteristics, the solution of the present application provides a weight control circuit 14. The weight control circuit 14 is configured to enable the DC component output by the high-precision operational amplifier to participate in driving the laser (load), and to enable the AC component output by the low-noise operational amplifier to participate in driving the laser, thereby achieving the effect of large bandwidth\low noise\high precision.

[0029] Theoretically, optimal performance can be achieved by weight control circuit 14 weighting the high-precision operational amplifier to 100% at 0 Hz and the low-noise operational amplifier to 100% at all other frequencies. This fully utilizes the excellent input characteristics of the high-precision operational amplifier and the excellent output characteristics of the low-noise operational amplifier. In practical applications, by configuring weight control circuit 14, a wide-bandwidth, low-noise, and high-precision laser driver circuit can be obtained.

[0030] Figure 2 This is a detailed structural diagram of the laser driving circuit provided by this application. Figure 2 , Figure 2The signal input terminal 11 receives a modulation signal for modulating the laser from the outside world (e.g., a front-end circuit or a modulation signal generation circuit). The modulation signal can be a triangular wave signal in the range of 200 Hz to 100 kHz. The modulation signal generation circuit can be a modulation signal generation circuit composed of a field programmable gate array (FPGA), a digital-to-analog converter (DAC), an operational amplifier, etc. The specific structure of the modulation signal generation circuit is known to those skilled in the art and is not described in detail in this application.

[0031] The first low-pass filter 121 includes a first inductor L1 and a fourth capacitor C4, and the weight control circuit 14 includes a fifth resistor R5 and a sixth resistor R6; the first end of the first inductor L1 is connected to the output end OUT1 of the first operational amplifier, and the second end of the first inductor L1 is connected to the first end of the fifth resistor R5 and the first end of the fourth capacitor C4; the second end of the fifth resistor R5 is connected to the first end of the sixth resistor R6.

[0032] The first high-pass filter 122 includes a first capacitor C1 and a first resistor R1, a first end of the first resistor R1 is connected to the negative feedback terminal IN1- of the first operational amplifier, a second end of the first resistor R1 is connected to the first end of the first capacitor C1, and a second end of the first capacitor C1 is connected to the output terminal OUT1 of the first operational amplifier.

[0033] The second high-pass filter 131 includes a second capacitor C4 , a first end of the second capacitor C4 is connected to the output end OUT2 of the second operational amplifier 13 , and a second end of the second capacitor C4 is connected to the second end of the sixth resistor R6 .

[0034] The third low-pass filter 132 includes a second inductor L2 and a second resistor R2, a first end of the second inductor L2 is connected to the output terminal OUT2 of the second operational amplifier 13, a second end of the second inductor L2 is connected to the second end of the second resistor R2, and a first end of the second resistor R2 is connected to the negative feedback terminal IN2- of the second operational amplifier 13.

[0035] Current control circuit 15 includes a field-effect transistor (FET) M1, whose gate G is connected to the first end of a sixth resistor (R6). FET M1 operates in a saturation region under the control of the voltage at gate G, thereby controlling the current flowing through the load and sampling circuit and ensuring that the voltage across the sampling resistor is equal to the modulation signal voltage source.

[0036] The sampling circuit 16 includes a seventh resistor R7 , a first end of the seventh resistor R7 is connected to the drain D of the field effect transistor M1 , and a second end of the seventh resistor R7 is connected to the ground.

[0037] The second low-pass filter 123 includes a third inductor L3 and a third resistor R3, a first end of the third inductor L3 is connected to the first end of the seventh resistor R7, a second end of the third inductor L3 is connected to the first end of the third resistor R3, and a second end of the third resistor R3 is connected to the negative feedback terminal IN1- of the first operational amplifier 12.

[0038] The third high-pass filter 133 includes a third capacitor C3 and a fourth resistor R4, the first end of the third capacitor C3 is connected to the first end of the seventh resistor R7, the second end of the third capacitor C3 is connected to the first end of the fourth resistor R4, and the second end of the fourth resistor R4 is connected to the negative feedback terminal IN2- of the second operational amplifier 13.

[0039] Optionally, Figure 2 A second power supply VCC2 is also shown in the figure. The second power supply VCC2 is used to provide an operating voltage to the first operational amplifier 12 and the second operational amplifier 13.

[0040] During the development of this application, the inventors discovered that the parameter values of the various components of the laser driver circuit of this application need to ensure that, while the first and second operational amplifiers can function normally, the first operational amplifier 12's effect on the driver circuit 10 is concentrated in the DC and as low-frequency range as possible, and the second operational amplifier 13's effect on the driver circuit 10 is concentrated in the low-frequency to high-frequency range as possible. At the same time, the bandwidth should be as large as possible, the gain curve should be smooth, and self-oscillation, gain bulges, and gain dips should be avoided. An example of the parameter values of the various components of the laser driver circuit of this application is provided below.

[0041] Table 1

[0042]

[0043] It should be noted that in order to minimize noise, the value of R6 should be selected as small as possible and the value of R5 should be as large as possible. However, when R6 is too small, self-oscillation may occur. Therefore, in order to take into account both noise and stability, the preferred ratio of R5 to R6 is 100:1.

[0044] By using the technical solution of the present application, the bandwidth of the laser driving circuit of the present application is slightly larger than the bandwidth of the second operational amplifier 13, the DC error is basically consistent with the DC error of the first operational amplifier 12, and the total noise and noise density are basically consistent with those using the second operational amplifier alone.

[0045] In one example, the inventors used an AD8551 operational amplifier as first operational amplifier 12 and an ADA4896 operational amplifier as second operational amplifier 13. Simulations demonstrated that the laser driver circuit of this application can minimize the DC error of first operational amplifier 12 and achieve a wider bandwidth than second operational amplifier 13, while maintaining minimal noise. Specific results are shown in the table below.

[0046] Table 2

[0047]

[0048] It is understood that in the laser driver circuit provided in this application, the first operational amplifier 12 and the second operational amplifier 13 are not limited to the AD8551 and AD4896. Other precision operational amplifiers and low-noise operational amplifiers can also be used. The laser driver circuit of this application can also achieve the above technical effects. To avoid repetition, this application does not describe them in detail here.

[0049] In some embodiments, the present application also provides a laser system 1. Figure 1 and Figure 2 The laser system includes: a modulation signal source 30, a laser driving circuit 10 of the present application; and a laser 20 (load R8, see Figure 2 ), wherein the modulation signal source 30 provides the laser to the laser driving circuit 10 and the laser 20 is connected to the source S of the field effect transistor M1.

[0050] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present invention.

Claims

1. A laser driving circuit based on parallel operational amplifiers, characterized in that: The laser driving circuit comprises: A signal input terminal, a first operational amplifier, a second operational amplifier, a first high-pass filter, a second high-pass filter, a third high-pass filter, a first low-pass filter, a second low-pass filter, a third low-pass filter, a weight control circuit, a current control circuit, and a sampling circuit; in, The signal input terminal is connected to the first operational amplifier and the second operational amplifier; The output terminal of the first operational amplifier is connected to the first high-pass filter and the first low-pass filter, and the negative feedback input terminal of the first operational amplifier is connected to the first high-pass filter and the second low-pass filter; The output terminal of the second operational amplifier is connected to the second high-pass filter and the third low-pass filter, and the negative feedback input terminal of the second operational amplifier is connected to the third low-pass filter and the third high-pass filter; The weight control circuit is connected to the first low-pass filter and the second high-pass filter; The current control circuit is connected to the weight control circuit and the sampling circuit; The sampling circuit is connected to the second low-pass filter and the third high-pass filter.

2. The laser driving circuit according to claim 1, wherein: The signal input terminal is configured to receive a laser modulation signal from the outside and output the laser modulation signal to the first operational amplifier and the second operational amplifier respectively; The first low-pass filter is configured to output a first DC component output by the first operational amplifier to the weight control circuit; The first high-pass filter is configured to output the first AC component output by the first operational amplifier to the negative feedback terminal of the first operational amplifier; The second high-pass filter is configured to output a second AC component output by the second operational amplifier to the weight control circuit; The third low-pass filter is configured to output the second DC component output by the second operational amplifier to the negative feedback terminal of the second operational amplifier; The second low-pass filter is configured to output a DC component corresponding to the DC component of the sampling circuit to a negative feedback terminal of the first operational amplifier; The third high-pass filter is configured to output the AC component of the sampling circuit to the negative feedback terminal of the second operational amplifier.

3. The laser driving circuit according to claim 1 or 2, characterized in that: The first low-pass filter includes a first inductor and a fourth capacitor, and the weight control circuit includes a fifth resistor and a sixth resistor; The first end of the first inductor is connected to the output end of the first operational amplifier, the second end of the first inductor is connected to the first end of the fifth resistor and the first end of the fourth capacitor; the second end of the fifth resistor is connected to the first end of the sixth resistor, and the second end of the fourth capacitor is connected to ground; The first high-pass filter includes a first capacitor and a first resistor, the first end of the first resistor is connected to the negative feedback end of the first operational amplifier, the second end of the first resistor is connected to the first end of the first capacitor, and the second end of the first capacitor is connected to the output end of the first operational amplifier.

4. The laser driving circuit according to claim 3, wherein: The second high-pass filter includes a second capacitor, a first end of the second capacitor is connected to the output end of the second operational amplifier, and a second end of the second capacitor is connected to the second end of the sixth resistor; The third low-pass filter includes a second inductor and a second resistor, the first end of the second inductor is connected to the output end of the second operational amplifier, the second end of the second inductor is connected to the second end of the second resistor, and the first end of the second resistor is connected to the negative feedback end of the second operational amplifier.

5. The laser driving circuit according to claim 3, wherein: The current control circuit includes a field effect transistor, and the gate of the field effect transistor is connected to the first end of the sixth resistor; The sampling circuit includes a seventh resistor, a first end of the seventh resistor is connected to the drain of the field effect transistor, and a second end of the seventh resistor is connected to the ground.

6. The laser driving circuit according to claim 5, characterized in that: The second low-pass filter includes a third inductor and a third resistor, the first end of the third inductor is connected to the first end of the seventh resistor, the second end of the third inductor is connected to the first end of the third resistor, and the second end of the third resistor is connected to the negative feedback terminal of the first operational amplifier.

7. The laser driving circuit according to claim 5, characterized in that: The third high-pass filter includes a third capacitor and a fourth resistor, the first end of the third capacitor is connected to the first end of the seventh resistor, the second end of the third capacitor is connected to the first end of the fourth resistor, and the second end of the fourth resistor is connected to the negative feedback end of the second operational amplifier.

8. The laser driving circuit according to claim 1, wherein: The bandwidth of the first operational amplifier is lower than the bandwidth of the second operational amplifier; and the output noise of the first operational amplifier is higher than the output noise of the second operational amplifier.

9. A laser system comprising: a modulation signal source, a laser driving circuit according to any one of claims 1 to 8, and a laser, The modulation signal source is configured to provide a laser modulation signal to the laser driving circuit, and the laser is connected to the laser driving circuit.

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