Laser driver open circuit detection method and detection circuit

Abstract

The invention discloses a laser drive open circuit detection method and detection circuit. The drive circuit includes a first triode and a second triode that can form a differential circuit. The control ends of the first triode and the second triode are respectively connected to a first input end and a second input end. One end of the first triode and the second triode are respectively connected to a first constant current source after connecting to a load ZL and a resistor Rterm, and the other end is respectively connected to a second constant current source after connecting to a resistor R1 and a resistor R2. The output end of the second constant current source is grounded, and the laser is connected between one end of the second triode and the ground. When the input voltage of the first input end is equal to the input voltage of the second input end and Iterm>Imod / 2, it indicates that the connection between the laser and the drive circuit is normal; on the contrary, when Iterm≤Imod / 2, it indicates that the laser and the drive circuit are in an open circuit state. It has the following advantages: it does not affect the normal operation of the drive circuit, the judgment process is real-time and automatic, no human intervention is required, the detection circuit structure is simple, easy to implement, and the power consumption is low.

Description

Technical Field

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

[0002] In the production process of laser driver modules (especially in the process of packaging and bonding the laser and driver chip) or in the use stage of laser driver modules (due to external factors or other factors), the bonding wire between the driver chip and the laser may be disconnected, which will cause the driving current to fail to flow into the laser normally and the laser will not emit light. Although the problem of open circuit 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 circuit, it is necessary to design a detection circuit inside the driver chip that can automatically detect open circuit between the laser and driver chip packaging.

[0003] like Figure 1 This is a schematic diagram of an existing laser driver open circuit detection solution. A resistor RFAULT is connected in series between the output end of the driver 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.

[0004] Disadvantages of existing technical solutions:

[0005] 1. Connecting a resistor in series with the laser at the output end will reduce the modulation current of the laser.

[0006] 2. Connecting a resistor in series with the output end of the laser will consume a certain voltage margin and generate unnecessary energy consumption.

[0007] 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.).

[0008] 4. The presence of parasitic capacitance at the input of the DIFF_AMP amplifier will also affect the bandwidth of the drive circuit, thereby affecting the rise and fall time of the drive current. Summary of the invention

[0009] The present invention provides a laser drive open circuit detection method and a detection circuit, which overcome the deficiencies of the prior art described in the background technology.

[0010] The technical solution adopted by the present invention to solve its technical problem is:

[0011] A laser drive open circuit detection method, comprising a drive circuit, the drive circuit comprising a first triode and a second triode capable of forming a differential circuit, the control ends of the first triode and the second triode being respectively connected to a first input end and a second input end, one end of the first triode being connected to an output end of a first constant current source after being connected to a load ZL, the other end of the first triode being connected to an input end of a second constant current source after being connected to a resistor R1, one end of the second triode being connected to an output end of the first constant current source after being connected to a resistor Rterm, the other end of the second triode being connected to an input end of the second constant current source after being connected to a resistor R2 The output end of the second constant current source is grounded and is connected in parallel between one end of the second transistor and the ground when the laser is not open-circuited; assuming that the output current of the second constant current source is Imod, and the average current flowing through the resistor Rterm is Iterm, when the input voltage of the first input terminal VINP is equal to the input voltage of the second input terminal VINN and Iterm>Imod / 2, it indicates that the connection between the laser and the drive circuit is normal; when the input voltage of the first input terminal VINP is equal to the input voltage of the second input terminal VINN and Iterm≤Imod / 2, it indicates that the laser and the drive circuit are in an open-circuit state.

[0012] In one embodiment: according to Ohm's law and mathematical relationship derivation, the comparison between Iterm and Imod / 2 is converted into a comparison between voltage values, thereby determining whether the laser and the driving circuit are normally connected.

[0013] A laser driver open circuit detection circuit, comprising:

[0014] A driving circuit, the driving circuit comprises a first triode and a second triode capable of forming a differential circuit, the control ends of the first triode and the second triode are respectively connected to a first input end and a second input end, one end of the first triode is connected to an output end of a first constant current source after being connected to a load ZL, the other end of the first triode is connected to an input end of a second constant current source after being connected to a resistor R1, one end of the second triode is connected to an output end of the first constant current source after being connected to a resistor Rterm, the other end of the second triode is connected to an input end of a second constant current source after being connected to a resistor R2, the output end of the second constant current source is grounded, and is connected in parallel between one end of the second triode and the output end of the second constant current source when the laser is not open-circuited; assuming that the output current of the second constant current source is Imod, and the current flowing through the resistor Rterm is Iterm;

[0015] The monitoring voltage acquisition circuit is used to acquire the voltage across the resistor Rterm when the current Iterm flows through the resistor Rterm, and the voltage across the resistor Rterm is set as the monitoring voltage;

[0016] A reference voltage acquisition circuit is used to acquire an equivalent voltage of the voltage across the resistor Rterm when the current Imod / 2 flows through the resistor Rterm, and the equivalent voltage is set as a reference voltage;

[0017] The comparator is used to compare the monitoring voltage with a reference voltage.

[0018] In one embodiment: the monitoring voltage acquisition circuit can amplify the monitoring voltage by A times, and the reference voltage acquisition circuit can amplify the reference voltage by A times. The monitoring voltage and the reference voltage after A times amplification are sent to the comparator for size comparison, and A is greater than or equal to 1.

[0019] In one embodiment: the monitoring voltage acquisition circuit includes a resistor Rdet1, a resistor Rdet2 and an operational amplifier, one end of the resistor Rdet1 is connected to one end of the resistor Rterm and the other end is connected to an input end of the operational amplifier, one end of the resistor Rdet2 is connected to the other end of the resistor Rterm and the other end is connected to the other input end of the operational amplifier, and the output end of the operational amplifier is connected to an input end of the comparator.

[0020] In one embodiment: the monitoring voltage acquisition circuit further includes a capacitor C1 and a capacitor C2, one end of the capacitor C1 is connected to an input end of the operational amplifier and the other end is grounded, and one end of the capacitor C2 is connected to the other input end of the operational amplifier and the other end is grounded.

[0021] In one embodiment: the time constant formed by the resistor Rdet1 and the capacitor C1 is greater than a preset time, and the time constant formed by the resistor Rdet2 and the capacitor C2 is greater than a preset time, and the preset time is the input time of the input voltage of the first input terminal VINP or the input voltage of the second input terminal.

[0022] In one embodiment, the resistance value of the resistor Rdet1 is much greater than the resistance value of the resistor Rterm, and the resistance value of the resistor Rdet2 is much greater than the resistance value of the resistor Rterm.

[0023] In one embodiment: the reference voltage acquisition circuit includes a third constant current source and a resistor Rref, one end of the resistor Rref is connected to the output end of the third constant current source and the other end is grounded, and one end of the resistor Rref is connected to the other input end of the comparator.

[0024] In one embodiment: the output current of the third constant current source is set to Imod / 2N, the resistance value of the resistor Rref is set to N*A times the resistance Rterm, and N is greater than or equal to 1.

[0025] In one embodiment, the comparator is a hysteresis comparator.

[0026] Compared with the background technology, this technical solution has the following advantages:

[0027] 1. The monitoring voltage acquisition circuit and reference voltage acquisition circuit designed in this technical solution will not affect the working performance of the original driving circuit and the laser.

[0028] 2. This technical solution uses the difference in current value flowing through the resistor Rterm when the drive circuit and the laser are open circuit and normally connected to determine whether the connection between the drive circuit and the laser is normal. This method does not affect the normal working state of the drive circuit.

[0029] 3. This technical solution cleverly applies the relationship between current and voltage drop (Ohm's law), mathematical formula derivation and reasonable circuit design to convert the comparison of current size into the comparison of voltage size, thereby determining whether the connection between the drive circuit and the laser is normal.

[0030] 4. The formula derivation in the circuit design process of this technical solution and the designed circuit all use the average current value flowing through the resistor Rterm and the transistor Q2, but the designed circuit is applicable to any input signal frequency and amplitude, that is, the laser drive open circuit detection method and detection circuit can determine whether the connection between the laser and the drive circuit is normal for any input signal frequency and amplitude.

[0031] 5. The laser drive open circuit detection circuit designed by this technical solution has a simple structure and is easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0033] Figure 1 It is a structural schematic diagram of an existing laser drive open circuit detection circuit described in the background technology.

[0034] Figure 2 This is the laser driving circuit diagram.

[0035] Figure 3 This is a block diagram of a laser driver open circuit detection circuit described in this embodiment.

[0036] Figure 4 This is a specific circuit diagram of a laser driver open circuit detection circuit described in this embodiment. DETAILED DESCRIPTION

[0037] like Figure 2The figure shows a laser driving circuit. The driving circuit includes a first switch Q1 tube and a second triode Q2 that can form a differential circuit, the control ends of the first triode Q1 and the second triode Q2 are respectively connected to the first input end and the second input end of the differential circuit, one end of the first triode is connected to the output end of the first constant current source Is1 after being connected to the load ZL, the other end of the first triode Q1 is connected to the input end of the second constant current source Is2 after being connected to the resistor R1, one end of the second triode Q1 is connected to the output end of the first constant current source Is1 after being connected to the resistor Rterm, the other end of the second triode Q2 is connected to the input end of the second constant current source Is2 after being connected to the resistor R2, the output end of the second constant current source Is2 is grounded, and when the laser is normally connected, the anode of the laser is connected to one end of the second triode Q2, and the cathode is grounded.

[0038] Assume that the output current of the second constant current source Is2 is Imod, the current flowing through the resistor Rterm is Iterm, the input voltage of the first input terminal VINP, and the input voltage of the second input terminal VINP. When the laser is connected to the driving circuit normally, after reasonably configuring the output current Ibiasp of the first constant current source Is1 and the output current Imod of the second constant current source Is2, the driving circuit and the laser can work normally. It can be seen from the figure that under normal working conditions, the average current flowing through the first transistor and the second transistor is Imod / 2, and the current Iout flowing into the laser is equal to the current Iterm flowing through the resistor Rterm and the current I flowing into the transistor Q2. C2 The difference is

[0039] Iout=Iterm-I C2

[0040] In the equilibrium state (VINP = VINN), I C2 =Imod / 2; therefore, under normal working conditions, Iterm>I C2 , that is, Iterm>Imod / 2.

[0041] When the laser is disconnected from the driving circuit, the current Iterm flowing through the resistor Rterm and the current Iterm flowing into the transistor Q2 are C2 Equal, in equilibrium, Iterm = Imod / 2.

[0042] Therefore, whether the laser and the driving circuit are connected normally can be determined by comparing the current Iterm and Imod / 2 in the equilibrium state.

[0043]

[0044] In order to make it easier to compare the currents, both ends of the inequality group in equation (1) are multiplied by a resistor Rterm and a coefficient A, and the resulting inequality group (2) between the two voltage quantities is obtained.

[0045]

[0046] According to Ohm's law, the comparison between Iterm and Imod / 2 can be converted into a comparison between voltage values, thereby determining whether the laser is normally connected to the drive circuit.

[0047] A laser driver open circuit detection circuit, such as Figure 3 and Figure 4 As shown, according to formula (2), the design includes:

[0048] A driving circuit, the driving circuit comprises a first transistor Q1 and a second transistor Q2 capable of forming a differential circuit, the control ends of the first transistor Q1 and the second transistor Q2 are respectively connected to the first input end and the second input end of the differential circuit, one end of the first transistor Q1 is connected to the output end of the first constant current source Is1 after being connected to a load ZL, the other end of the first transistor Q1 is connected to the input end of the second constant current source Is2 after being connected to a resistor R1, one end of the second transistor Q2 is connected to the output end of the first constant current source Is1 after being connected to a resistor Rterm, the other end of the second transistor Q2 is connected to the input end of the second constant current source Is2 after being connected to a resistor R2, the output end of the second constant current source Is2 is grounded, and is connected in parallel between one end of the second transistor Q2 and the ground when the laser is not open; assuming that the output current of the second constant current source Is2 is Imod, and the current flowing through the resistor Rterm is Iterm;

[0049] The monitoring voltage acquisition circuit is used to acquire the voltage across the resistor Rterm when the current Iterm flows through the resistor Rterm, and the voltage across the resistor Rterm is set as the monitoring voltage;

[0050] A reference voltage acquisition circuit is used to acquire an equivalent voltage of the voltage across the equal-valued resistor Rterm when the current Imod / 2 flows through the equal-valued resistor Rterm, and the equivalent voltage is set as a reference voltage;

[0051] The comparator COMPARATOR is used to compare the monitoring voltage with a reference voltage.

[0052] The monitoring voltage acquisition circuit can amplify the monitoring voltage by A times, and the reference voltage acquisition circuit can amplify the reference voltage by A times. The monitoring voltage and the reference voltage after A times amplification are sent to the comparator COMPARATOR for size comparison, and A is greater than or equal to 1.

[0053] The monitoring voltage acquisition circuit includes a resistor Rdet1, a resistor Rdet2, a capacitor C1, a capacitor C2 and an operational amplifier DIFF_AMP, one end of the resistor Rdet1 is connected to one end of the resistor Rterm and the other end is connected to the first input end of the operational amplifier DIFF_AMP, one end of the resistor Rdet2 is connected to the other end of the resistor Rterm and the other end is connected to the second input end of the operational amplifier DIFF_AMP, one end of the capacitor C1 is connected to the first input end of the amplifier DIFF_AMP, the other end of the capacitor C1 is grounded, one end of the capacitor C2 is connected to the second input end of the amplifier DIFF_AMP, the other end of the capacitor C2 is grounded, and the monitoring voltage is amplified A times by the operational amplifier DIFF_AMP.

[0054] Since the resistance values ​​of resistors Rdet1 and Rdet2 are much larger than the resistance value of resistor Rterm, the time constant formed by resistor Rdet1 and capacitor C1 as well as resistor Rdet2 and capacitor C2 is larger than the input duration of the input end of the driving circuit. Therefore, when the driving circuit and the laser are working normally, the monitoring voltage acquisition circuit will not affect the performance of the driving circuit.

[0055] The reference voltage acquisition circuit includes a third constant current source Is3 and a resistor Rref, one end of the resistor Rref is connected to the output end of the third constant current source Is3 and the other end is grounded, and one end of the resistor Rref is connected to the other input end of the comparator COMPARATOR. The output current of the third constant current source Is3 is set to Imod / 2N, that is, the output current of the third constant current source Is3 changes according to the change of the output current of the second constant current source Is2, and the reference voltage is a real-time value that changes with the tracking current Imod, which can make the comparison result of the monitoring voltage and the reference voltage more accurately reflect the connection between the laser and the driving circuit. The resistance value of the resistor Rref is set to N*A times of the resistor Rterm, and N is greater than or equal to 1. By reducing the output current of the third constant current source Is3 to Imod / 2N, the power consumption of the reference voltage acquisition circuit can be reduced.

[0056] The first input terminal of the comparator COMPARATOR is connected to the output terminal of the operational amplifier DIFF_AMP, and the second input terminal is connected to the output terminal of the reference voltage acquisition circuit.

[0057] The comparator COMPARATOR adopts a hysteresis comparator, which can overcome the jitter interference of the comparator input signal near the threshold value.

[0058] like Figure 3As shown, the operational amplifier DIFF_AMP collects the DC voltage across the resistor Rterm and amplifies it by A times to obtain a voltage value VT=Iterm*Rterm*A. After the Imod current is reduced to Imod / 2N, it flows through a resistor with a resistance value of Rterm*N*A to obtain a reference voltage value VMOD=(Imod / 2N)*Rterm*N*A. The in-phase input terminal of the comparator COMPARATOR is connected to VMOD, and the inverting input terminal is connected to VT. By using the comparator COMPARATOR to compare the voltages of VT and VMOD, it can be determined whether the connection between the laser and the drive circuit is normally connected or in an open circuit state. When the comparator COMPARATOR outputs a high level, it means that the laser and the drive circuit are in a disconnected state; when the comparator COMPARATOR outputs a low level, it means that the laser and the drive circuit are normally connected.

[0059] The detection method and detection circuit described in this case do not affect the working performance of the driving circuit itself, the circuit structure is simple, easy to implement, and the detection result is accurate.

[0060] 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 method, characterized in that: A drive circuit is provided, the drive circuit includes a first triode and a second triode capable of forming a differential circuit, the control ends of the first triode and the second triode are respectively connected to a first input end and a second input end, one end of the first triode is connected to an output end of a first constant current source after being connected to a load ZL, the other end of the first triode is connected to an input end of a second constant current source after being connected to a resistor R1, one end of the second triode is connected to the output end of the first constant current source after being connected to a resistor Rterm, the other end of the second triode is connected to an input end of the second constant current source after being connected to a resistor R2, and the second constant The output end of the current source is grounded, and is connected in parallel between one end of the second transistor and the ground when the laser is not open-circuited; assuming that the output current of the second constant current source is Imod, and the current flowing through the resistor Rterm is Iterm, when the input voltage of the first input terminal VINP is equal to the input voltage of the second input terminal VINN and Iterm>Imod / 2, it indicates that the connection between the laser and the driving circuit is normal; when the input voltage of the first input terminal VINP is equal to the input voltage of the second input terminal VINN and Iterm≤Imod / 2, it indicates that the laser and the driving circuit are in an open-circuit state.

2. A laser driver open circuit detection method according to claim 1, characterized in that: According to Ohm's law, the comparison between the current Iterm and the current Imod / 2 is converted into a comparison between voltage values, and the obtained voltage value is used to determine whether the laser is normally connected to the driving circuit.

3. A laser driver open circuit detection circuit, characterized in that: include: A driving circuit, the driving circuit comprises a first triode and a second triode capable of forming a differential circuit, the control ends of the first triode and the second triode are respectively connected to a first input end and a second input end, one end of the first triode is connected to an output end of a first constant current source after being connected to a load ZL, the other end of the first triode is connected to an input end of a second constant current source after being connected to a resistor R1, one end of the second triode is connected to an output end of the first constant current source after being connected to a resistor Rterm, the other end of the second triode is connected to an input end of a second constant current source after being connected to a resistor R2, the output end of the second constant current source is grounded, and is connected in parallel between one end of the second triode and the output end of the second constant current source when the laser is not open-circuited; assuming that the output current of the second constant current source is Imod, and the current flowing through the resistor Rterm is Iterm; The monitoring voltage acquisition circuit is used to obtain the voltage difference across the resistor Rterm when the current Iterm flows through the resistor Rterm, and the voltage across the resistor Rterm is set as the monitoring voltage; A reference voltage acquisition circuit is used to acquire an equivalent voltage of the voltage across the resistor Rterm when the current Imod / 2 flows through the resistor Rterm, and the equivalent voltage is set as a reference voltage; The comparator is used to compare the monitoring voltage with a reference voltage.

4. The laser driver open circuit detection circuit according to claim 3, characterized in that: The monitoring voltage acquisition circuit can amplify the monitoring voltage by A times, and the reference voltage acquisition circuit can amplify the reference voltage by A times. The monitoring voltage and the reference voltage after A times amplification are sent to the comparator for size comparison, and A is greater than or equal to 1.

5. The laser driver open circuit detection circuit according to claim 4, characterized in that: The monitoring voltage acquisition circuit includes a resistor Rdet1, a resistor Rdet2 and an operational amplifier, one end of the resistor Rdet1 is connected to one end of the resistor Rterm and the other end is connected to an input end of the operational amplifier, one end of the resistor Rdet2 is connected to the other end of the resistor Rterm and the other end is connected to the other input end of the operational amplifier, and the output end of the operational amplifier is connected to an input end of the comparator.

6. The laser driver open circuit detection circuit according to claim 5, characterized in that: The monitoring voltage acquisition circuit also includes a capacitor C1 and a capacitor C2. One end of the capacitor C1 is connected to an input end of the operational amplifier and the other end is grounded. One end of the capacitor C2 is connected to the other input end of the operational amplifier and the other end is grounded.

7. The laser driver open circuit detection circuit according to claim 6, characterized in that: The time constant formed by the resistor Rdet1 and the capacitor C1 is greater than a preset time, and the time constant formed by the resistor Rdet2 and the capacitor C2 is greater than a preset time, which is the input time of the input voltage of the first input terminal VINP or the input voltage of the second input terminal VINN.

8. The laser driver open circuit detection circuit according to claim 6, characterized in that: The resistance value of the resistor Rdet1 is much greater than the resistance value of the resistor Rterm, and the resistance value of the resistor Rdet2 is much greater than the resistance value of the resistor Rterm.

9. The laser driver open circuit detection circuit according to claim 4, characterized in that: The reference voltage acquisition circuit includes a third constant current source and a resistor Rref, one end of the resistor Rref is connected to the output end of the third constant current source and the other end is grounded, and one end of the resistor Rref is connected to the other input end of the comparator.

10. The laser driver open circuit detection circuit according to claim 9, characterized in that: The output current of the third constant current source is set to Imod / 2N, and the resistance value of the resistor Rref is set to N*A times of the resistor Rterm, where N is greater than or equal to 1.

11. A laser driver open circuit detection circuit according to any one of claims 3 to 10, characterized in that: This comparator is a hysteresis comparator.

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