Laser driver open circuit detection circuit

Abstract

The invention discloses a laser drive open circuit detection circuit, comprising a laser drive circuit, a laser LD, a resistor R T , resistor Rs, third constant current source I T and comparator COMPARATOR, resistor R T With the third constant current source I T After the series connection, the two ends are connected between the positive end of the resistor Rterm and the ground, and the resistor R T One end is connected to the positive end of the resistor Rterm, and the other end is connected to the third constant current source I T One end of the resistor Rs is connected to the negative end of the resistor Rterm, and the other end is connected to the other input end of the comparator COMPARATOR. T The voltage at the other end of the resistor Rs is the voltage Vref1, and the voltage at the other end of the resistor Rs is the voltage Vout1. By comparing the voltage Vref1 and the voltage Vout1, it is determined whether the laser driving circuit and the laser LD are open. It has the following advantages: it is easy to realize the laser driving open circuit detection, does not need to be powered off or use external detection tools, and does not affect the normal operation of the laser driving circuit and the laser.

Description

Technical Field

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

[0002] In the production process of laser driver modules (especially in the process of packaging and bonding the laser LD and the driver chip) or in the use stage of the laser driver module (due to external factors or other factors), the bonding wire between the driver chip and the laser LD may be disconnected, which causes the driving current to be unable to flow into the laser LD normally, and the laser LD does not emit light. Although the problem of open circuit between the driver chip and the laser LD 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 the open circuit between the laser LD and the driver chip package.

[0003] like Figure 1 The present invention is a schematic diagram of an existing laser LD driver open circuit detection scheme. A resistor RFAULT is connected in series between the output end of the driver circuit and the laser LD. 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 LD), the voltage is amplified by the DI FF_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 LD.

[0004] Disadvantages of existing technical solutions:

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

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

[0007] 3. Connecting a resistor in series with the output end of the laser LD 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 driving open circuit detection circuit, which overcomes 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 circuit comprises a laser drive circuit and a laser LD. The laser drive circuit comprises a main circuit and two branches branched from the main circuit and connected in parallel. One common end of the two branches is connected to the main circuit, and the other common end is grounded. A first constant current source Ibiasp and a resistor Rterm are connected in series to the main circuit, one branch is connected in series to a second constant current source Imod, and the other branch is connected in series to the laser LD. The laser LD is driven to work by the first constant current source Ibiasp and the second constant current source Imod.

[0012] Also includes the resistor R T , resistor Rs third constant current source I T and a comparator COMPARATOR, assuming that one end of the resistor Rterm connected to the first constant current source Ibiasp is the positive end, and the other end of the resistor Rterm is the negative end. T With the third constant current source I T After the series connection, the two ends are connected between the positive end of the resistor Rterm and the ground respectively, and the resistor R T One end is connected to the positive end of the resistor Rterm, and the other end is connected to the third constant current source I T One end of the resistor Rs is connected to the negative end of the resistor Rterm, and the other end is connected to the other input end of the comparator COMPARATOR. T The voltage at the other end of the resistor Rs is the voltage Vref1, and the voltage at the other end of the resistor Rs is the voltage Vout1. The voltage Vref1 is compared with the voltage Vout1 by the comparator COMPARATOR to determine whether there is an open circuit between the laser driving circuit and the laser LD.

[0013] Where, the resistance value of the resistor Rterm is R term , the resistor R T The resistance value is R term *N, N is greater than or equal to 1; suppose the output current of the second constant current source Imod is The third constant current source I T The output value is I θ Less than I th , I th The threshold current for turning on the laser LD.

[0014] In one embodiment: a capacitor C is also included S , the capacitor C S The capacitor C forms a filter circuit with the resistor Rs. S One end of is connected to the other end of resistor Rs, and the other end is grounded.

[0015] In one embodiment, the resistance value of the resistor Rs is much greater than the resistance value of the resistor Rterm.

[0016] In one embodiment, the comparator COMPARATOR is a hysteresis comparator.

[0017] The laser driving open circuit detection circuit comprises a laser driving circuit and a laser LD. The laser 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 VINP and a second input end VINN. One end of the first triode is connected to a load Z L The first transistor is connected to the output end of the first constant current source Ibiasp, the other end of the first transistor is connected to the input end of the second constant current source Imod, one end of the second transistor is connected to the output end of the first constant current source Ibiasp through a resistor Rterm, the other end of the second transistor is connected to the input end of the second constant current source Imod, the output end of the second constant current source Imod is grounded, the laser LD is connected to one end of the second transistor connected to the resistor Rterm, and the other end is grounded;

[0018] Also includes the resistor R T , resistor Rs third constant current source I T and a comparator COMPARATOR, assuming that one end of the resistor Rterm connected to the first constant current source Ibiasp is the positive end, and the other end of the resistor Rterm is the negative end. T With the third constant current source I T After the series connection, the two ends are connected between the positive end of the resistor Rterm and the ground respectively, and the resistor R T One end is connected to the positive end of the resistor Rterm, and the other end is connected to the third constant current source I T One end of the resistor Rs is connected to the negative end of the resistor Rterm, and the other end is connected to the other input end of the comparator COMPARATOR. T The voltage at the other end of the resistor Rs is the voltage Vref1, and the voltage at the other end of the resistor Rs is the voltage Vout1. The voltage Vref1 is compared with the voltage Vout1 by the comparator COMPARATOR to determine whether there is an open circuit between the laser driving circuit and the laser LD.

[0019] Where, the resistance value of the resistor Rterm is R term , the resistor R T The resistance value is R term *N, N is greater than or equal to 1; let the output current of the second constant current source Imod be I mod , the third constant current source I T The output value is I θ Less than I th , I th The threshold current for turning on the laser LD.

[0020] In one embodiment: a capacitor C is also included S , the capacitor C S The capacitor C forms a filter circuit with the resistor Rs. S One end of is connected to the other end of resistor Rs, and the other end is grounded.

[0021] In one embodiment: the resistor Rs and the capacitor C S The configured time constant is greater than the input time duration of the input voltage of the first input terminal or the input voltage of the second input terminal.

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

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

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

[0025] 1. This detection circuit will not affect the working performance of the original driving circuit and laser LD.

[0026] 2. 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, so as to determine whether the connection between the drive circuit and the laser LD is normal.

[0027] 3. The circuit of this technical solution is applicable to any external input signal frequency and amplitude, that is, it can determine whether the connection between the laser LD and the laser driving circuit is normal for any input signal frequency and amplitude.

[0028] 4. The laser drive open circuit detection circuit designed by this technical solution has a simple structure and is easy to implement, without the need to cut off power or use external detection tools. 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 It is a schematic diagram of an existing laser LD driver open circuit detection solution.

[0031] Figure 2 This is a schematic diagram of the laser driving circuit described in Example 1.

[0032] Figure 3This is a schematic diagram of the laser drive open circuit detection circuit described in Example 1.

[0033] Figure 4 This is a schematic diagram of the laser drive open circuit detection circuit described in Example 2. DETAILED DESCRIPTION

[0034] Example 1, please refer to Figure 2 and Figure 3 :

[0035] Laser drive open circuit detection circuit, including laser drive circuit, laser LD, please refer to Figure 2 The laser driving circuit includes a first transistor and a second transistor that can form a differential circuit. The control ends of the first transistor and the second transistor are respectively connected to the first input end and the second input end. One end of the first transistor is connected to the load Z L The first transistor is connected to the output end of the first constant current source Ibiasp, the other end of the first transistor is connected to the input end of the second constant current source Imod, one end of the second transistor is connected to the output end of the first constant current source Ibiasp through a resistor Rterm, the other end of the second transistor is connected to the input end of the second constant current source Imod, the output end of the second constant current source Imod is grounded, the laser LD is connected to one end of the second transistor connected to the resistor Rterm, and the other end is grounded; Figure 2 shown.

[0036] When the laser LD is connected to the laser driving circuit normally, the laser driving circuit and the laser LD can work normally by properly configuring the output current Ibiasp of the first constant current source Ibiasp and the second constant current source Imod. The average current flowing through the resistor Rterm is defined as I term The resistance of the resistor Rterm is R term From the figure, we can see that the average current I flowing into the laser LD is out It is equal to the difference between the average current flowing through the resistor Rterm and the average current flowing into the second transistor Q2, that is,

[0037] I out =I term -I C2 (1)

[0038] In the equilibrium state (VINP = VINN), That is, the average current flowing through the second transistor Q2 is The output current of the second constant current source Imod is I mod ; When the laser LD is working normally

[0039] When the laser LD is disconnected from the laser driving circuit, the average current flowing through the resistor Rterm is equal to the average current flowing into the second transistor Q2.

[0040] We can compare the average value of the current Iterm with The size can be used to determine whether the laser LD and the laser driving circuit are connected normally.

[0041] When the laser LD is connected to the laser driving circuit normally, So there is the following derivation:

[0042]

[0043]

[0044]

[0045] because so

[0046] Among them, V P is the voltage of node P in the figure, and I θ <I th , where I th is the laser LD turn-on threshold voltage, N is greater than or equal to 1. When the laser LD is working normally, I θ <I out , so there is

[0047]

[0048] make R T =N*R term

[0049]

[0050] Therefore, when the laser LD is connected to the laser driving circuit normally,

[0051]

[0052] When the laser LD is disconnected from the laser driving circuit, I out =0,

[0053]

[0054] This discrimination method actually uses the voltage V OUT1 and V ref1 The voltage drop relative to node P does not require accurate calculation of V OUT1 and Vref1 Voltage value. OUT1 and V ref1 The voltage value accuracy requirement is not high, so the complexity of circuit design is greatly reduced.

[0055] The laser drive open circuit detection circuit is designed based on inequalities (2) and (3), as follows: Figure 3 The laser driver open circuit detection circuit also includes a resistor R T , resistor Rs third constant current source I T and a comparator COMPARATOR, assuming that one end of the resistor Rterm connected to the first constant current source Ibiasp is the positive end, and the other end of the resistor Rterm is the negative end. T With the third constant current source I T After the series connection, the two ends are connected between the positive end of the resistor Rterm and the ground respectively, and the resistor R T One end is connected to the positive end of the resistor Rterm, and the other end is connected to the third constant current source I T One end of the resistor Rs is connected to the negative end of the resistor Rterm, and the other end is connected to the other input end of the comparator COMPARATOR. T The voltage at the other end of the resistor Rs is the voltage Vref1, and the voltage at the other end of the resistor Rs is the voltage Vout1. The voltage Vref1 is compared with the voltage Vout1 by the comparator COMPARATOR to determine whether there is an open circuit between the laser driving circuit and the laser LD.

[0056] Among them, the resistor R T The resistance value is R term * N, N is greater than or equal to 1; the third constant current source I T The output value is I θ Less than I th , I th The threshold current for turning on the laser LD.

[0057] Also includes capacitor C S , the capacitor C S The capacitor C forms a filter circuit with the resistor Rs. S One end of the resistor Rs is connected to the other end of the resistor Rs, and the other end is grounded. S The configured time constant is greater than the input time duration of the input voltage of the first input terminal or the input voltage of the second input terminal.

[0058] The resistance value of the resistor Rs is much greater than the resistance value of the resistor Rterm. The open circuit detection circuit designed in this way has no effect on the performance of the laser driving circuit and the laser LD, and under the condition of reasonable configuration of each current source of the laser driving circuit, for a differential signal pair (first input terminal VINP, second input terminal VINN) of any input rate and amplitude, the voltage values ​​of the voltage Vout1 and the voltage Vref1 have only very small ripples, and the output state of the comparator COMPARATOR is only related to the connection state of the laser LD and the laser driving circuit, and has nothing to do with the input signal.

[0059] In this embodiment, the comparator COMPARATOR is a hysteresis comparator. When the laser LD is normally connected to the laser driving circuit, V OUT1 <V ref1 , the comparator COMPARATOR outputs a low level; when the laser LD is disconnected from the laser drive circuit, V OUT1 >V ref1 , the comparator circuit outputs a high level. The output state of the comparator can be used to determine whether the laser LD and the drive circuit are connected normally.

[0060] Example 2, please refer to Figure 4 :

[0061] The laser drive open circuit detection circuit comprises a laser drive circuit and a laser LD. The laser drive circuit comprises a main circuit and two branches branched from the main circuit and connected in parallel. One common end of the two branches is connected to the main circuit, and the other common end is grounded. A first constant current source Ibiasp and a resistor Rterm are connected in series on the main circuit, one branch is connected in series with a second constant current source Imod, and the other branch is connected in series with the laser LD. The laser LD is driven to work by the first constant current source Ibiasp and the second constant current source Imod.

[0062] According to the same detection principle as that of the first embodiment, an open circuit detection circuit is designed for the laser driving circuit of the second embodiment. The open circuit detection circuit also includes a resistor R T , resistor Rs third constant current source I T and a comparator COMPARATOR, assuming that one end of the resistor Rterm connected to the first constant current source Ibiasp is the positive end, and the other end of the resistor Rterm is the negative end. T With the third constant current source I T After the series connection, the two ends are connected between the positive end of the resistor Rterm and the ground respectively, and the resistor R T One end is connected to the positive end of the resistor Rterm, and the other end is connected to the third constant current source I TOne end of the resistor Rs is connected to the negative end of the resistor Rterm, and the other end is connected to the other input end of the comparator COMPARATOR. T The voltage at the other end of the resistor Rs is the voltage Vref1, and the voltage at the other end of the resistor Rs is the voltage Vout1. The voltage Vref1 is compared with the voltage Vout1 by the comparator COMPARATOR to determine whether there is an open circuit between the laser driving circuit and the laser LD.

[0063] Among them, the resistance value of the resistor Rterm is R term , the resistor R T The resistance value is R term *N, N is greater than or equal to 1; suppose the current of one branch is The third constant current source I T The output value is I θ Less than I th , I th The threshold current for turning on the laser LD.

[0064] Also includes capacitor C S , the capacitor C S The capacitor C forms a filter circuit with the resistor Rs. S One end of is connected to the other end of resistor Rs, and the other end is grounded.

[0065] The resistance of the resistor Rs is much greater than the resistance of the resistor Rterm, so that the open circuit detection circuit has no effect on the performance of the laser driving circuit and the laser LD, and the output state of the comparator COMPARATOR is only related to the connection state of the laser LD and the laser driving circuit, and has nothing to do with the input signal.

[0066] The comparator COMPARATOR is a hysteresis comparator. When the laser LD is connected to the laser driving circuit normally, V OUT1 <V ref1 , the comparator COMPARATOR outputs a low level; when the laser LD is disconnected from the laser drive circuit, V OUT1 >V ref1 , the comparator circuit outputs a high level. The output state of the comparator can be used to determine whether the laser LD and the drive circuit are connected normally.

[0067] 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 drive open circuit detection circuit, comprising a laser drive circuit and a laser LD, wherein the laser drive circuit comprises a main circuit and two branches branched from the main circuit and connected in parallel, wherein one common end of the two branches is connected to the main circuit, and the other common end is grounded, wherein a first constant current source Ibiasp and a resistor Rterm are connected in series to the main circuit, one branch is connected in series to a second constant current source Imod, and the other branch is connected in series to the laser LD, and the laser LD is driven to work by the first constant current source Ibiasp and the second constant current source Imod; Features: Also includes the resistor R T , resistor Rs, third constant current source I T and a comparator COMPARATOR, assuming that one end of the resistor Rterm connected to the first constant current source Ibiasp is the positive end, and the other end of the resistor Rterm is the negative end. T With the third constant current source I T After the series connection, the two ends are connected between the positive end of the resistor Rterm and the ground respectively, and the resistor R T One end is connected to the positive end of the resistor Rterm, and the other end is connected to the third constant current source I T One end of the resistor Rs is connected to the negative end of the resistor Rterm, and the other end is connected to the other input end of the comparator COMPARATOR. T The voltage at the other end of the resistor Rs is the voltage Vref1, and the voltage at the other end of the resistor Rs is the voltage Vout1. The voltage Vref1 is compared with the voltage Vout1 by the comparator COMPARATOR to determine whether there is an open circuit between the laser driving circuit and the laser LD. Among them, the resistance value of the resistor Rterm is R term , the resistor R T The resistance value is R term *N, N is greater than or equal to 1; assuming that the current of the second constant current source Imod is The third constant current source I T The output value is I θ Less than I th , I th The threshold current for turning on the laser LD.

2. The laser driving open circuit detection circuit according to claim 1, characterized in that: Also includes capacitor C S , the capacitor C S The capacitor C forms a filter circuit with the resistor Rs. S One end of is connected to the other end of resistor Rs, and the other end is grounded.

3. The laser drive open circuit detection circuit according to claim 1 or 2, characterized in that: The resistance value of the resistor Rs is much greater than the resistance value of the resistor Rterm.

4. The laser driving open circuit detection circuit according to claim 1, characterized in that: The comparator COMPARATOR is a hysteresis comparator.

5. A laser drive open circuit detection circuit, comprising a laser drive circuit and a laser LD, wherein the laser drive circuit comprises a first transistor and a second transistor capable of forming a differential circuit, wherein the control ends of the first transistor and the second transistor are respectively connected to a first input end VINP and a second input end VINN, and one end of the first transistor is connected to a load Z L The first transistor is connected to the output end of the first constant current source Ibiasp, the other end of the first transistor is connected to the input end of the second constant current source Imod, one end of the second transistor is connected to the output end of the first constant current source Ibiasp through a resistor Rterm, the other end of the second transistor is connected to the input end of the second constant current source Imod, the output end of the second constant current source Imod is grounded, the laser LD is connected to one end of the second transistor connected to the resistor Rterm, and the other end is grounded; Features: Also includes the resistor R T , resistor Rs third constant current source I T and a comparator COMPARATOR, assuming that one end of the resistor Rterm connected to the first constant current source Ibiasp is the positive end, and the other end of the resistor Rterm is the negative end. T With the third constant current source I T After the series connection, the two ends are connected between the positive end of the resistor Rterm and the ground respectively, and the resistor R T One end is connected to the positive end of the resistor Rterm, and the other end is connected to the third constant current source I T One end of the resistor Rs is connected to the negative end of the resistor Rterm, and the other end is connected to the other input end of the comparator COMPARATOR. T The voltage at the other end of the resistor Rs is the voltage Vref1, and the voltage at the other end of the resistor Rs is the voltage Vout1. The voltage Vref1 is compared with the voltage Vout1 by the comparator COMPARATOR to determine whether there is an open circuit between the laser driving circuit and the laser LD. Among them, the resistance value of the resistor Rterm is R term , the resistor R T The resistance value is R term *N, N is greater than or equal to 1; let the output current of the second constant current source Imod be I mod , the third constant current source I T The output value is I θ Less than I th , I th The threshold current for turning on the laser LD.

6. The laser driving open circuit detection circuit according to claim 5, characterized in that: Also includes capacitor C S , the capacitor C S The capacitor C forms a filter circuit with the resistor Rs. S One end of is connected to the other end of resistor Rs, and the other end is grounded.

7. The laser driving open circuit detection circuit according to claim 6, characterized in that: The resistor Rs and capacitor C S The configured time constant is greater than the input time duration of the input voltage of the first input terminal or the input voltage of the second input terminal.

8. The laser driving open circuit detection circuit according to claim 5 or 6, characterized in that: The resistance value of the resistor Rs is much greater than the resistance value of the resistor Rterm.

9. The laser driving open circuit detection circuit according to claim 5, characterized in that: The comparator COMPARATOR is a hysteresis comparator.

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