A laser driver open circuit detection circuit

Abstract

The invention discloses a laser drive open circuit detection circuit, which is provided with a drive circuit, including a laser drive circuit, a laser, and a first monitoring circuit, wherein the output end of the laser drive circuit is connected to the anode end of the laser, and the first monitoring circuit is connected to the output end of the laser drive circuit to obtain a monitoring voltage VOUT1; a reference voltage generating circuit, including a drive mirror circuit, a laser equivalent circuit, and a second monitoring circuit, wherein the second monitoring circuit is connected to the output end of the drive mirror circuit to obtain a reference voltage VOUT_REF; a comparator, wherein the monitoring voltage VOUT1 and the reference voltage VOUT_REF are connected to the input end of the comparator, and whether the connection between the drive circuit and the laser is normal is judged from the output result of the comparator. The detection circuit does not affect the normal working state of the drive circuit, the judgment process is real-time and automatic and does not require human intervention, and does not require power-off operation or external detection tools, and the detection circuit has a simple structure, is easy to implement, and has low power consumption.

Description

Technical Field

[0001] The invention relates to a circuit detection circuit, in particular to a laser drive open circuit detection circuit. Background Art

[0002] In the production process of the laser driver module (especially in the packaging and bonding process of the laser and the driver chip) or in the use stage of the laser driver module (due to external factors or other factors), the wires between the driver chip and the laser may be disconnected, which will cause the driving current to be unable to flow into the laser normally and the laser to be unable to emit light normally. Although the problem of open wires between the driver chip and the laser can be detected by powering off the driver module and using a third-party detection tool, this method is obviously more time-consuming and resource-intensive. In order to reduce the detection time and cost of open wires, it is necessary to design a detection circuit inside the driver chip that can automatically detect in real time whether the packaging wires between the laser and the driver chip are open. Figure 1 This is a schematic diagram of an existing open circuit detection scheme. A resistor RFAULT is connected in series between the output end of the drive circuit and the laser. By detecting the voltage drop on the resistor RFAULT (actually detecting the current flowing through the resistor RFAULT, that is, the current flowing into the laser), it is amplified by the DIFF_AMP amplifier circuit and compared with a threshold voltage VTH, thereby determining whether there is an open circuit between the driver chip and the laser.

[0003] The disadvantages of existing open circuit detection technology solutions are:

[0004] 1. Connecting a resistor in series with the laser at the output end will reduce the amplitude of the laser's modulation current.

[0005] 2. Connecting a resistor in series with the laser at the output end will consume a certain voltage margin, reduce the maximum value of the bias current that the laser can operate, and generate unnecessary energy consumption.

[0006] 3. Connecting a resistor in series with the output end and the laser will affect the performance of the driving current (rise and fall time, amplitude, etc.).

[0007] 4. The presence of parasitic capacitance at the input of the amplifier DIFF_AMP will also affect the bandwidth of the drive circuit, thereby affecting the rise and fall time of the drive current. Summary of the invention

[0008] The present invention provides a laser driving open circuit detection circuit, which overcomes the shortcomings of the prior art described in the background technology.

[0009] The technical solution adopted by the present invention to solve its technical problem is:

[0010] A laser driver open circuit detection circuit, comprising:

[0011] A driving circuit, the driving circuit includes a laser driving circuit, a laser and a first monitoring circuit, wherein the output end of the laser driving circuit is connected to the anode end of the laser and is used to drive the laser to work, the cathode of the laser is grounded, and the first monitoring circuit is connected to the output end of the laser driving circuit and is used to obtain a DC voltage at the output end of the laser driving circuit, which is set as a monitoring voltage VOUT1;

[0012] A reference voltage generating circuit, the reference voltage generating circuit comprising a driving mirror circuit, a laser equivalent circuit and a second monitoring circuit, the circuit structure of the driving mirror circuit is the same as the circuit structure of the laser driving circuit, the output end of the driving mirror circuit is connected to the laser equivalent circuit, the second monitoring circuit is connected in parallel to the output end of the driving mirror circuit, and is used to obtain an output DC voltage of the output end of the driving mirror circuit, which is set as a reference voltage VOUT_REF;

[0013] Comparator, connect the monitoring voltage VOUT1 and the reference voltage VOUT_REF to the input terminal of the comparator, and after the comparator compares the monitoring voltage VOUT1 with the reference voltage VOUT_REF, output the comparison result;

[0014] When the laser driving circuit is normally connected to the laser, the reference voltage VOUT_REF is greater than or equal to the monitoring voltage VOUT1, so that the comparator outputs result 1; when the laser is open, the reference voltage VOUT_REF is less than the monitoring voltage VOUT1, and the comparator outputs result 2 which is the inverse of result 1. The difference in the comparator output results can be used to determine whether the laser and the driving circuit are normally connected.

[0015] In one embodiment, the first monitoring circuit and the second monitoring circuit have the same circuit structure, including a resistor and a capacitor connected in series. The first monitoring circuit includes a resistor R connected in series. s1 And capacitor C1, resistor R s1 One end of the second monitoring circuit is connected to the output end of the driving circuit, and the other end is connected to one end of the capacitor C1, and the other end of the capacitor C1 is grounded; the second monitoring circuit includes a series resistor R s2 And capacitor C2, resistor R s2 One end is connected to the output end of the driving mirror circuit, the other end is connected to one end of the capacitor C2, and the other end of the capacitor C2 is grounded; the monitoring voltage VOUT1 and the reference voltage VOUT_REF are respectively the voltages at the series connection point between the resistor and the capacitor in the first monitoring circuit and the second monitoring circuit.

[0016] In one embodiment, the resistor R S1 The time constant formed by the capacitor C1 is greater than the preset time length, and the resistor R S2The time constant formed by the capacitor C2 is greater than a preset time length, and the preset time length is the input time length of the input voltage of the first input terminal VINP or the input voltage of the second input terminal VINN.

[0017] In one embodiment: the laser equivalent circuit includes a constant voltage circuit V equivalent to the laser pre-bias voltage FB And the resistance R equivalent to the working internal resistance of the laser DUM , the constant voltage circuit V FB and resistor R DUM Series connection, resistor R DUM The other end is grounded.

[0018] In one embodiment: the constant voltage circuit V FB The voltage across the resistor R is set to be greater than the pre-bias voltage of the laser. DUM The resistance value is set to be greater than the working internal resistance of the laser, so that the reference voltage VOUT_REF is greater than the monitoring voltage VOUT1, so that the laser is normally connected to the driving circuit and the comparator outputs a result of one when working normally.

[0019] In one embodiment: the constant voltage circuit V FB It comprises a plurality of NPN transistors connected in series, wherein the emitter of one of the adjacent series-connected NPN transistors is connected to the collector of another NPN transistor, and the base and collector of each NPN transistor are short-circuited.

[0020] In one embodiment: the laser driving circuit includes a P-channel MOS transistor MP0, a P-channel MOS transistor MP1, a triode Q1, a triode Q2, a resistor R1, a resistor R2, a load ZL, and a load Zterm. The gates of the P-channel MOS transistor MP0 and the P-channel MOS transistor MP1 are short-circuited, the drain and the gate of the P-channel MOS transistor MP0 are short-circuited, a first current source is connected in series between the P-channel MOS transistor MP0 and the ground, and the source of the P-channel MOS transistor MP0 and the source of the P-channel MOS transistor MP1 are both connected to a voltage source VDD. The collector of the transistor Q1 is connected to one end of the load ZL and the emitter is connected to one end of the resistor R1, the collector of the transistor Q2 is connected to one end of the load Zterm and the emitter is connected to one end of the resistor R2, the other ends of the load ZL and the load Zterm are both connected to the drain of the P-channel MOS tube MP1, the other ends of the resistor R1 and the resistor R2 are both connected to one end of the second current source, the other end of the second current source is grounded, and the bases of the transistor Q1 and the transistor Q2 are respectively connected to one end and the other end of the laser drive differential input signal source.

[0021] In one embodiment, the driving mirror circuit includes a P-channel MOS transistor MP0, a P-channel MOS transistor MP2, a transistor Q3, a transistor Q4, a resistor R3, a resistor R4, a load Z L1 、Load ZT , capacitor C3, the gate of the P-channel MOS tube MP2 is connected to the gate of the P-channel MOS tube MP0 of the laser driving circuit, and the source of the P-channel MOS tube MP2 is connected to the voltage source VDD; the collector of the transistor Q3 is connected to the load Z L1 The collector of transistor Q4 is connected to the load Z. T The emitter is connected to one end of the resistor R4, and the load Z L1 and load Z T The other end of each of the transistors Q3 and Q4 is connected to the drain of the P-channel MOS tube MP2, the other ends of the resistors R3 and R4 are connected to one end of a third current source, the other end of the third current source is grounded, the bases of the transistors Q3 and Q4 are connected to one end of a capacitor C3, the other end of the capacitor C3 is grounded.

[0022] In one embodiment, there are a plurality of P-channel MOS transistors MP1 connected in parallel, and a plurality of P-channel MOS transistors MP2 connected in parallel, the number of the P-channel MOS transistors MP1 is N times the number of the P-channel MOS transistors MP2, so that the ratio of the sum of the drain currents of the P-channel MOS transistors MP2 to the sum of the drain currents of the P-channel MOS transistors MP1 is 1 / N, N is greater than or equal to 2, the current value of the third current source is 1 / N of the current value of the second current source, and the resistor R DUM The resistance value is N times the working internal resistance of the laser.

[0023] In one embodiment, the comparator is a hysteresis comparator.

[0024] Compared with the background technology, this technical solution has the following advantages:

[0025] 1. This technical solution designs a reference voltage generating circuit with the same structure as the driving circuit and an output DC voltage value equivalent to the DC value of the output voltage when the driving circuit is working normally, without affecting the normal working state of the driving circuit. The generated reference voltage is used to simulate the DC value of the output voltage of the driving circuit when the laser and the driving circuit are working normally. By comparing the magnitude relationship between the DC voltage at the output end of the laser driving circuit and the reference voltage, it can be determined whether the package bonding wire between the laser and the driving circuit is open.

[0026] 2. The drive mirror circuit designed in this technical solution is connected to the laser drive circuit and can track the output DC voltage of the laser drive circuit in real time, so that the open circuit judgment process is carried out automatically in real time without human intervention, and there is no need to cut off power or use external detection tools for detection.

[0027] 3. The comparator designed in this technical solution is a hysteresis comparator, which can avoid the erroneous flipping of the comparator output caused by the monitoring voltage VOUT1 value swinging near the reference voltage VREF_OUT value, thereby avoiding misjudgment.

[0028] 4. In the present technical solution, when the laser is not open-circuited and is working normally, the reference voltage VOUT_REF is set to be greater than or equal to the monitoring voltage VOUT1, and the comparator outputs result 1; that is, the reference voltage VOUT_REF can be set to be slightly larger than the monitoring voltage VOUT1 when the laser driving circuit is working normally, and the reference voltage VOUT_REF generated by the reference voltage generating circuit only needs to be greater than or equal to the monitoring voltage VOUT1 during normal operation. The reference voltage VOUT_REF value does not need to be very precise, which reduces the complexity of the reference voltage generating circuit and makes the circuit easier to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0030] Figure 1 This is a schematic diagram of the structure of the existing laser drive open circuit detection circuit described in the background technology.

[0031] Figure 2 4 is a structural block diagram of the laser driver open circuit detection circuit described in this embodiment.

[0032] Figure 3 Schematic diagram of the structure of the laser driver open circuit detection circuit described in this embodiment.

[0033] Figure 4 Schematic diagram of the driving circuit described in this embodiment.

[0034] Figure 5 FIG. 4 is a circuit diagram of a reference voltage generation circuit according to the present embodiment.

[0035] Figure 6 Schematic diagram of the comparator structure described in this embodiment. DETAILED DESCRIPTION

[0036] Please refer to Figures 2 to 6 , a laser driving open circuit detection circuit includes a driving circuit 10, a reference voltage generating circuit 20 and a comparator 30.

[0037] The driving circuit 10 includes a laser driving circuit 11, a laser 12 and a first monitoring circuit 13. The output end of the laser driving circuit 11 is connected to the anode end of the laser and is used to drive the laser 12 to work. The cathode end of the laser 12 is grounded. The first monitoring circuit 13 is connected to the output end of the laser driving circuit 11 and is used to obtain the output DC voltage of the output end of the laser driving circuit 11, which is set as a monitoring voltage VOUT1.

[0038] The reference voltage generating circuit 20 includes a driving mirror circuit 21, a laser equivalent circuit 22 and a second monitoring circuit 23. The circuit structure of the driving mirror circuit 21 is the same as that of the laser driving circuit 11. The output DC voltage of the driving mirror circuit 21 is equal to or slightly higher than the DC value of the output voltage of the laser driving circuit 11 (when normally connected to the laser). The output end of the driving mirror circuit 21 is connected to the laser equivalent circuit 22. The second monitoring circuit 23 is connected in parallel to the output end of the driving mirror circuit 21 and is used to obtain the output voltage of the output end of the driving mirror circuit 21, which is set as the reference voltage VOUT_REF.

[0039] Comparator 30, connects the monitoring voltage VOUT1 and the reference voltage VOUT_REF to the input terminal of the comparator, and outputs the comparison result after the comparator compares the monitoring voltage VOUT1 and the reference voltage VOUT_REF;

[0040] When the laser driving circuit 11 is normally connected to the laser 12 and operates normally, the reference voltage VOUT_REF is greater than or equal to the monitoring voltage VOUT1, so that the comparator outputs result one; when the laser 12 is open, the reference voltage VOUT_REF is less than the monitoring voltage VOUT1, and the comparator 30 outputs result two which is the inverse of result one. The difference in the output results of the comparator 30 can be used to determine whether the laser and the driving circuit are normally connected.

[0041] Please refer to Figure 3 The first monitoring circuit 13 and the second monitoring circuit 23 have the same circuit structure. The first monitoring circuit 13 includes a resistor R connected in series. S1 and capacitor C1, resistor R S1 One end is connected to the output end of the laser driving circuit 11, and the other end is connected to the capacitor C1. The other end of the capacitor C1 is grounded. The second monitoring circuit 23 includes a resistor R S2 and capacitor C2, resistor R S2 One end is connected to the output end of the driving mirror circuit 21, and the other end is connected to the capacitor C2. The other end of the capacitor C2 is grounded. The resistor R S1 and capacitor C1 and resistor R S2 The time constant formed by the capacitor C2 is greater than the input voltage of the first input terminal VINP or the input voltage of the second input terminal VINN. The monitoring voltage VOUT1 is the resistor R S1 The voltage at the connection point of the capacitor C1 and the reference voltage VOUT_REF is the voltage of the resistor R in the second monitoring circuit 23. S2 The voltage at the connection point with capacitor C2.

[0042] The laser equivalent circuit 22 is used to simulate the equivalent circuit model of the laser 12, including a constant voltage circuit V equivalent to the laser pre-bias voltage. FB And the resistance R equivalent to the working internal resistance of the laser DUM , the constant voltage circuit V FB and resistor R DUM Series connection, resistor R DUM The other end is grounded.

[0043] For details, please refer to Figure 4 The laser driving circuit 11 includes a P-channel MOS transistor MP0, a P-channel MOS transistor MP1, a triode Q1, a triode Q2, a resistor R1, a resistor R2, a load ZL, and a load Zterm. The gate of the P-channel MOS transistor MP0 is short-circuited with the gate of the P-channel MOS transistor MP1, the drain of the P-channel MOS transistor MP0 is short-circuited with the gate, and a first current source I is connected in series between the drain of the P-channel MOS transistor MP0 and the ground. S1 , the source of the P-channel MOS transistor MP0 and the source of the P-channel MOS transistor MP1 are both connected to the voltage source VDD; the collector of the transistor Q1 is connected to one end of the load ZL and the emitter is connected to one end of the resistor R1, the collector of the transistor Q2 is connected to one end of the load Zterm and the emitter is connected to one end of the resistor R2, the other ends of the load ZL and the load Zterm are both connected to the drain of the P-channel MOS transistor MP1, and the other ends of the resistor R1 and the resistor R2 are both connected to the second current source I S2 One end of the second current source I S2 The other end of the transistor Q1 is grounded, and the bases of the transistor Q2 are connected to one end and the other end of the differential input signal source as a first input terminal VINP and a second input terminal VINN, respectively.

[0044] For details, please refer to Figure 5 The driving mirror circuit 21 includes a P-channel MOS tube MP2, a transistor Q3, a transistor Q4, a resistor R3, a resistor R4, a load Z L1 、Load Z T , capacitor C3, the gate of the P-channel MOS tube MP2 is connected to the gate of the P-channel MOS tube MP0 of the laser driving circuit, and the source of the P-channel MOS tube MP2 is connected to the voltage source VDD; the collector of the transistor Q3 is connected to the load Z L1 The collector of transistor Q4 is connected to the load Z. T The emitter is connected to one end of the resistor R4, and the load Z L1 and load Z T The other ends of the resistors R3 and R4 are connected to the drain of the P-channel MOS tube MP2, and the other ends of the resistors R3 and R4 are connected to the third current source I S3One end of the third current source I S3 The other end of is grounded, the bases of the transistors Q3 and Q4 are both connected to one end of the capacitor C3, and the other end of the capacitor C3 is grounded.

[0045] In this embodiment, the working principle of the laser drive open circuit detection circuit is analyzed by taking the laser 12 type of VCSEL (Vertical-Cavity Surface-Emitting Laser, VCSEL for short) as an example.

[0046] When the VCSEL laser is connected to the laser driving circuit normally, the P-channel MOS tube MP1 works in the saturation region, and the current mirror relationship between the P-channel MOS tube MP1 and the P-channel MOS tube MP0 remains normal. VOUT1 = (Ibiasp-Imod)*R VCSEL +V FB , where R VCSEL Represents the equivalent resistance of the VCSEL laser, V FB represents the laser pre-bias, Ibiasp is the current flowing from the P-channel MOS tube MP1 to point P1, and Imod is the current flowing into the second current source I S2 From the expression of VOUT1, it can be seen that the monitoring voltage VOUT1 and the reference voltage VOUT_REF have nothing to do with the input signal rate and signal amplitude of the laser driving circuit, and the comparator output result has nothing to do with the input signal rate and signal amplitude of the laser driving circuit, that is, the laser open circuit detection circuit is suitable for laser driving circuits with any input signal rate and amplitude.

[0047] In the design process of the reference voltage generation circuit, in order to save current and power consumption, the current value flowing from the P-channel MOS tube MP2 to the P2 point can be designed to be Ibiasp / N, and the third current source I S3 The tail current of the differential pair is designed to be Imod / N, and the resistor R DUM The value is designed to be N*R VCSEL , N can be a relatively large integer (for example, N = 100). This generates a reference voltage VOUT_REF≈VOUT1=(Ibiasp / N-Imod / N)*N*R which is equivalent to the value of the monitoring voltage VOUT1. VCSEL +V FB In actual VCSEL laser devices, R VCSEL and V FB can be obtained by actually measuring the laser. Typically, R VCSEL =50Ω,V FB=1.5V. And the reference voltage VOUT_REF remains unchanged regardless of whether the laser is normally connected to the driver chip or in an open circuit condition. The N-fold current ratio relationship can be set as follows: suppose that a plurality of P-channel MOS tubes MP1 and a plurality of P-channel MOS tubes MP2 are connected in parallel, and the number of the P-channel MOS tubes MP1 is N times the number of the P-channel MOS tubes MP2, so that the ratio of the sum of the drain currents of the P-channel MOS tubes MP2 to the sum of the drain currents of the P-channel MOS tubes MP1 is 1 / N, and the third current source I S3 The current value of the second current source I S2 1 / N of the current value, assuming that the resistance R DUM The resistance value is N times the working internal resistance of the laser.

[0048] Typically, V FB =1.5V, and the conduction voltage between the base and emitter of the NPN transistor is V be ≈0.75V, V FB The design can be Figure 3 The two NPN transistors or diodes connected in series or several MOS tubes are used to realize the above. Specifically, when the constant voltage circuit V of the equivalent laser pre-bias is FB When two NPN transistors are connected in series, the emitter of one of the adjacent series-connected NPN transistors is connected to the collector of the other NPN transistor, and the base and collector of each NPN transistor are short-circuited.

[0049] In actual design, the reference voltage VOUT_REF is designed to be higher than the monitoring voltage VOUT1 (i.e. (Ibiasp-Imod)*R VCSEL +V FB ) value is slightly higher, for example, about 100mV. In this way, when the VCSEL laser is connected to the laser driving circuit normally, the monitoring voltage VOUT1 is less than the reference voltage VOUT_REF, and the comparator outputs a low level. FB The voltage across the resistor R is set to be greater than the pre-bias voltage of the laser. DUM The resistance value is set to be greater than N*R VCSEL , so that when the VCSEL laser is normally connected to the laser driving circuit, the reference voltage VOUT_REF is greater than the monitoring voltage VOUT1, so that the comparator outputs a low level.

[0050] Under the design conditions described above, when the connection between the VCSEL laser and the driving circuit is in an open circuit state, the drain current flowing through the P-channel MOS tube MP1 no longer follows the mirror relationship with the drain current of the P-channel MOS tube MP0, and the drain current flowing through the P-channel MOS tube MP1 is equal to the drain current flowing through the second current source I S2The current Imod flows through the drain current of the P-channel MOS tube MP1, and the P-channel MOS tube MP1 enters the linear working area. The voltage difference between the source and drain of the P-channel MOS tube MP1 decreases, the voltage at point P1 increases, the monitoring voltage VOUT1 increases, and the monitoring voltage VOUT1 is greater than the reference voltage VOUT_REF, and the comparator outputs a high level.

[0051] Through the above description of the driving circuit, the reference voltage generating circuit and the comparator, it can be known that by checking the output state of the comparator, it is possible to determine whether the VCSEL laser is connected to the laser driving circuit normally. The reference voltage VOUT_REF output by the reference voltage generating circuit does not need to be very precise, which can reduce the complexity of the reference voltage generating circuit design and make the reference voltage generating circuit easy to implement. At the same time, the monitoring voltage value VOUT1 has nothing to do with the rate and signal amplitude of the input signal of the laser driving circuit. The comparator uses a hysteresis comparator to avoid the erroneous flipping of the comparator output caused by the swing of the monitoring voltage VOUT1 value near the reference voltage VREF_OUT value, thereby avoiding misjudgment.

[0052] By comparing the DC voltage at the output end of the laser driving circuit 11 (i.e., the monitoring voltage VOUT1) with the corresponding reference voltage (i.e., the reference voltage VOUT_REF) through the comparator 30, it can be determined whether the laser 12 is normally connected to the laser driving circuit 11. When the output voltage of the comparator 30 is a low level, it means that the laser 12 is normally connected to the laser driving circuit 11; when the output voltage of the comparator 30 is a high level, it means that the laser 12 is disconnected from the laser driving circuit 11. VOUT_REF≈VOUT1=(Ibiasp / N-Imod / N)*N*R VCSEL +V FB It can be seen that the value of the reference voltage VOUT_REF described in this case can change with the current value of the P-channel MOS tube MP1 in the laser driving circuit 11 and the second current source in the laser driving circuit 11, that is, the reference voltage VOUT_REF value can track the output DC voltage of the driving circuit in real time, and realize real-time judgment of whether the laser and the driving circuit are open, without the need for human intervention, power off or external detection tools.

[0053] The laser type involved in the present invention is not limited to VCSEL laser devices, but is also applicable to other lasers that adopt direct current coupling drive forms such as DFB (Distributed Feedback Laser), and the anode of the laser is connected to the output end of the driving circuit, and the cathode of the laser is grounded.

[0054] The above description is only a preferred embodiment of the present invention, and therefore cannot be used to limit the scope of the present invention. That is, equivalent changes and modifications made according to the patent scope of the present invention and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A laser driver open circuit detection circuit, characterized in that: include: A driving circuit, the driving circuit includes a laser driving circuit, a laser and a first monitoring circuit, the output end of the laser driving circuit is connected to the anode end of the laser and is used to drive the laser to work, the cathode of the laser is grounded, the first monitoring circuit is connected to the output end of the laser driving circuit, and is used to obtain the output DC voltage of the output end of the laser driving circuit, which is set as a monitoring voltage VOUT1; a reference voltage generating circuit, the reference voltage generating circuit includes a driving mirror circuit, a laser equivalent circuit and a second monitoring circuit, the circuit structure of the driving mirror circuit is the same as the circuit structure of the laser driving circuit, the output end of the driving mirror circuit is connected to the laser equivalent circuit, the second monitoring circuit is connected to the output end of the driving mirror circuit, and is used to obtain the output DC voltage of the driving mirror circuit. The output voltage of the output end of the dynamic mirror circuit is set as the reference voltage VOUT_REF; the comparator connects the monitoring voltage VOUT1 and the reference voltage VOUT_REF to the input end of the comparator, and the comparator compares the monitoring voltage VOUT1 with the reference voltage VOUT_REF and outputs the comparison result; when the laser driving circuit is normally connected to the laser, the reference voltage VOUT_REF is greater than or equal to the monitoring voltage VOUT1, and the comparator outputs result one; when the laser is open-circuited, the reference voltage VOUT_REF is less than the monitoring voltage VOUT1, and the comparator outputs result two which is the inverse of result one, and whether the laser is normally connected to the laser driving circuit is determined by the difference in the comparator output results.

2. The laser driver open circuit detection circuit according to claim 1, characterized in that: The first monitoring circuit and the second monitoring circuit have the same circuit structure, including a resistor and a capacitor connected in series. The first monitoring circuit includes a resistor R connected in series. s1 And capacitor C1, resistor R s1 One end of the second monitoring circuit is connected to the output end of the driving circuit, and the other end is connected to one end of the capacitor C1, and the other end of the capacitor C1 is grounded; the second monitoring circuit includes a series resistor R s2 And capacitor C2, resistor R s2 One end is connected to the output end of the driving mirror circuit, the other end is connected to one end of the capacitor C2, and the other end of the capacitor C2 is grounded; the monitoring voltage VOUT1 and the reference voltage VOUT_REF are respectively the voltages at the series connection point between the resistor and the capacitor in the first monitoring circuit and the second monitoring circuit.

3. The laser driver open circuit detection circuit according to claim 1, characterized in that: The laser equivalent circuit includes a constant voltage circuit V equivalent to the laser front bias voltage. FB and the resistance R equivalent to the working internal resistance of the laser DUM , the constant voltage circuit V FB and resistor R DUM Series connection, resistor R DUM One end is grounded.

4. The laser driver open circuit detection circuit according to claim 3, characterized in that: The constant voltage circuit V FB The voltage at both ends is set to be greater than the front bias voltage of the laser, so that the reference voltage VOUT_REF is greater than the monitoring voltage VOUT1, so that the comparator outputs a result of one when the laser is normally connected to the driving circuit.

5. The laser driver open circuit detection circuit according to claim 3, characterized in that: The resistor R DUM The resistance value is set to be greater than the working internal resistance of the laser, so that the reference voltage VOUT_REF is greater than the monitoring voltage VOUT1, and the comparator outputs a comparison result of one.

6. The laser driver open circuit detection circuit according to claim 3, characterized in that: The constant voltage circuit V FB It comprises a plurality of NPN transistors connected in series, wherein the emitter of one of the adjacent series-connected NPN transistors is connected to the collector of another NPN transistor, and the base and collector of each NPN transistor are short-circuited.

7. A laser driver open circuit detection circuit according to any one of claims 1 to 6, characterized in that: The laser driving circuit includes a P-channel MOS transistor MP0, a P-channel MOS transistor MP1, a triode Q1, a triode Q2, a resistor R1, a resistor R2, a load ZL, and a load Zterm. The gate of the P-channel MOS transistor MP0 and the gate of the P-channel MOS transistor MP1 are short-circuited, the drain of the P-channel MOS transistor MP0 and the gate are short-circuited, a first current source is connected in series between the P-channel MOS transistor MP0 and the ground, and the source of the P-channel MOS transistor MP0 and the source of the P-channel MOS transistor MP1 are both connected to a voltage source V DD; the collector of the transistor Q1 is connected to one end of the load ZL and the emitter is connected to one end of the resistor R1, the collector of the transistor Q2 is connected to one end of the load Zterm and the emitter is connected to one end of the resistor R2, the other ends of the load ZL and the load Zterm are both connected to the drain of the P-channel MOS tube MP1, the other ends of the resistor R1 and the resistor R2 are both connected to one end of the second current source, the other end of the second current source is grounded, and the bases of the transistor Q1 and the transistor Q2 are connected to the laser drive input differential signal source.

8. The laser driver open circuit detection circuit according to claim 7, characterized in that: The driving mirror circuit includes a P-channel MOS tube MP0, a P-channel MOS tube MP2, a transistor Q3, a transistor Q4, a resistor R3, a resistor R4, a load Z L1 、Load Z T , capacitor C3, the gate of the P-channel MOS tube MP2 is connected to the gate of the P-channel MOS tube MP0 of the laser driving circuit, and the source of the P-channel MOS tube MP2 is connected to the voltage source VDD; the collector of the transistor Q3 is connected to the load Z L1 The collector of transistor Q4 is connected to the load Z. T The emitter is connected to one end of the resistor R4, and the load Z L1 and load Z T The other end of each of the transistors Q3 and Q4 is connected to the drain of the P-channel MOS tube MP2, the other ends of the resistors R3 and R4 are connected to one end of a third current source, the other end of the third current source is grounded, the bases of the transistors Q3 and Q4 are connected to one end of a capacitor C3, the other end of the capacitor C3 is grounded.

9. The laser driver open circuit detection circuit according to claim 8, characterized in that: A plurality of P-channel MOS transistors MP1 connected in parallel and a plurality of P-channel MOS transistors MP2 connected in parallel are provided, the number of the P-channel MOS transistors MP1 is N times the number of the P-channel MOS transistors MP2, so that the ratio of the sum of the drain currents of the P-channel MOS transistors MP2 to the sum of the drain currents of the P-channel MOS transistors MP1 is 1 / N, N is greater than or equal to 2, the current value of the third current source is 1 / N of the current value of the second current source, and the resistor R DUM The resistance value is N times the working internal resistance of the laser.

10. A laser driver open circuit detection circuit according to any one of claims 1 to 6, characterized in that: This comparator is a hysteresis comparator.

11. The laser driver open circuit detection circuit according to claim 2, characterized in that: The resistor R S1 The time constant formed by the capacitor C1 is greater than the preset time length, and the resistor R S2 The time constant formed by the capacitor C2 is greater than a preset time length, and the preset time length is the input time length of the input voltage of the first input terminal VINP or the input voltage of the second input terminal VINN.

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