A laser diode driving circuit and a laser displacement sensor

Abstract

The application discloses a laser diode driving circuit and a laser displacement sensor. The laser diode driving circuit comprises a reference voltage generating unit for generating a constant reference bias voltage; a sampling amplification unit for applying the reference bias voltage to a photodiode to provide a reverse bias, converting a monitoring current generated by the photodiode into a monitoring voltage signal output based on the reference bias voltage; a power setting unit for outputting a setting voltage signal representing target laser power; and a comparison driving unit for comparing the monitoring voltage signal with the setting voltage signal, adjusting a driving current flowing through a light-emitting diode according to a comparison result, so that a laser assembly maintains constant power emission. The application solves the technical problem that a stable reverse bias voltage cannot be provided for a photodiode under the condition of lacking a negative voltage power supply, and realizes high-precision and high-stability laser constant power emission.

Description

Technical Field

[0001] This application relates to the fields of laser control and photoelectric detection technology, specifically to a laser diode driving circuit and a laser displacement sensor. Background Technology

[0002] Laser diodes (LDs) are widely used in high-precision measurement fields, such as laser displacement sensors, due to their excellent directionality and high brightness. In these applications, the stability of the laser emission power directly determines the measurement accuracy. Therefore, it is usually necessary to design an automatic power control (APC) circuit, which uses a photodiode (PD) packaged inside the laser component to monitor the laser power and dynamically adjust the drive current based on the feedback signal.

[0003] Existing high-precision APC driver circuits typically employ a dual power supply (e.g., positive and negative voltage supply) to enable the operational amplifier to linearly amplify and process the weak photocurrent generated by the photodiode. However, the dual power supply design requires an additional negative voltage generation circuit, which not only increases the size and cost of the circuit board but also introduces additional power supply noise interference.

[0004] Another common approach is to use a single power supply. However, the inventors discovered that in a single-supply APC circuit, the monitoring signal generated by the photodiode is typically very weak and close to ground potential (i.e., 0V). Limited by the input common-mode voltage range and output swing of the operational amplifier, signal processing is prone to nonlinear distortion when near ground potential. Therefore, how to easily and stably provide the required reverse bias voltage to the photodiode under single-supply conditions to ensure its linear operating region is also a challenge faced by existing technologies. Summary of the Invention

[0005] The purpose of this application is to provide a laser diode driving circuit and a laser displacement sensor to solve the technical problems of poor signal processing linearity, complex reverse bias design, and high cost and large size of existing APC driving circuits under single power supply.

[0006] In a first aspect, this application provides a laser diode driving circuit for driving a laser component comprising a light-emitting diode and a photodiode, including: A reference voltage generation unit is used to generate a constant reference bias voltage. A sampling amplification unit, whose input terminal is connected to the photodiode and the reference voltage generation unit, is used to apply the reference bias voltage to the photodiode to provide reverse bias, and to convert the monitoring current generated by the photodiode into a monitoring voltage signal output based on the reference bias voltage; The power setting unit is used to output a setting voltage signal that characterizes the target laser power; The comparison driving unit has its input terminals connected to the output terminals of the sampling amplification unit and the power setting unit, respectively, and its output terminal connected to the light-emitting diode. It is used to compare the monitoring voltage signal with the set voltage signal and adjust the driving current flowing through the light-emitting diode according to the comparison result so that the laser component maintains constant power emission.

[0007] Secondly, this application provides a laser displacement sensor, comprising: A laser emitting unit is used to emit laser light towards the object being measured. A photoelectric receiving unit is used to receive laser signals reflected back from the object under test; A signal processing unit, connected to the photoelectric receiving unit, is used to calculate the displacement of the object being measured based on the laser signal. The laser emitting unit includes the laser diode driving circuit as described in the first aspect.

[0008] This application provides a laser diode driving circuit and a laser displacement sensor. The laser diode driving circuit generates a constant reference bias voltage through a reference voltage generation unit, applies the reference bias voltage to the photodiode using a sampling amplification unit, and converts the monitoring current generated by the photodiode into a monitoring voltage signal based on the reference bias voltage. Finally, a comparison driving unit compares the monitoring voltage signal with a set voltage signal to adjust the driving current of the light-emitting diode. Addressing the difficulty in designing reverse bias for photodiodes under single-supply power supply, this application directly applies the reference bias voltage to the photodiode using a sampling amplification unit, solving the technical problem of not being able to provide a stable reverse bias voltage for the photodiode under conditions lacking a negative voltage power supply. This ensures that the photodiode operates in the optimal linear region and simplifies the power supply circuit structure. Addressing the problem that weak signals are easily affected by the nonlinear region near ground potential in single-supply operational amplifiers, this application converts the monitoring current into a monitoring voltage signal based on the reference bias voltage, achieving a rise in signal potential. This solves the technical problem that the monitoring voltage signal is prone to nonlinear distortion or being submerged by noise when approaching zero potential, enabling ordinary single-supply operational amplifiers to achieve high-precision linear signal processing throughout the entire range and reducing device costs. By constructing a closed-loop negative feedback control using a comparative drive unit, the technical problem of unstable laser emission power due to temperature or voltage fluctuations was solved, achieving high-precision and high-stability constant power laser emission. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 A schematic diagram of a laser diode driving circuit provided in an embodiment of this application is shown.

[0011] Figure 2 A schematic diagram of the sampling amplification unit provided in an embodiment of this application is shown.

[0012] Figure 3 Another schematic diagram of the sampling amplification unit provided in the embodiments of this application is shown.

[0013] Figure 4 A schematic diagram of a reference voltage generation unit provided in an embodiment of this application is shown.

[0014] Figure 5 A schematic diagram of the power setting unit provided in an embodiment of this application is shown.

[0015] Figure 6 A schematic diagram of another power setting unit provided in an embodiment of this application is shown.

[0016] Figure 7 A schematic diagram of a comparison driving unit provided in an embodiment of this application is shown.

[0017] Figure 8 Another schematic diagram of the comparison driving unit provided in an embodiment of this application is shown.

[0018] Figure 9 Another schematic diagram of the laser diode driving circuit provided in an embodiment of this application is shown.

[0019] Figure 10 This illustration shows yet another schematic diagram of a laser diode driving circuit provided in an embodiment of this application. Detailed Implementation

[0020] To enable those skilled in the art to better understand the solutions of this application, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0021] In the embodiments of this application, it should be noted that, in this document, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0022] Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0023] It should be noted that in the embodiments of this application, "connection" can be understood as electrical connection. The connection between two electrical components can be a direct or indirect connection between the two electrical components. For example, the connection between A and B can be a direct connection between A and B, or an indirect connection between A and B through one or more other electrical components.

[0024] In the circuit structure provided by the embodiments of this application, the connection nodes do not represent actual existing components, but rather represent the junctions of related couplings in the circuit diagram. In other words, these nodes are equivalent to the junctions of related couplings in the circuit diagram.

[0025] This application provides a laser diode driving circuit for driving a laser component comprising a light-emitting diode (LED) and a photodiode. Optionally, the laser component is typically a light-emitting diode (LD) and a photodiode (PD) integrated in a specific package. In this application embodiment, the laser component is preferably a C-type laser diode, i.e., the cathode of the LED and the cathode of the photodiode are connected to a common terminal, or the anode of the LED and the anode of the photodiode are connected to a common terminal, depending on the polarity design of the driving circuit. Of course, those skilled in the art will understand that by adjusting the power supply polarity and the type of driving transistor, this driving circuit can also be applied to A-type or B-type packaged laser components. Such circuits are widely used in devices with extremely high requirements for laser power stability, such as high-precision laser displacement sensors, laser rangefinders, or industrial laser scanning equipment.

[0026] Figure 1 This application provides a schematic diagram of a laser diode driving circuit according to an embodiment of the present application. Figure 1 As shown, the laser diode driving circuit includes: A reference voltage generation unit is used to generate a constant reference bias voltage. Optionally, the reference voltage generation unit is used to provide a non-zero DC bias level for subsequent signal processing. In a single-supply system, ground potential is often not the optimal signal processing reference, especially for weak signals. The reference bias voltage output by the reference voltage generation unit is a preset fixed voltage that does not fluctuate with load changes, providing a basic potential reference for setting the operating point of the photodiode and linearly amplifying the signal.

[0027] The sampling amplification unit, with its input connected to a photodiode and a reference voltage generation unit, applies a reference bias voltage to the photodiode to provide reverse bias and converts the monitoring current generated by the photodiode into a monitoring voltage signal output based on the reference bias voltage. Optionally, the sampling amplification unit performs level clamping and signal conversion. First, it introduces the reference bias voltage from the reference voltage generation unit to one end of the photodiode, using the potential difference to put the photodiode in a reverse bias state, thereby ensuring the linearity and response speed of the photoelectric conversion. Second, the sampling amplification unit receives the monitoring current generated by the photodiode due to light exposure and converts this monitoring current into a voltage signal. It is worth noting that this conversion is not relative to ground, but relative to the aforementioned reference bias voltage. Therefore, the output monitoring voltage signal is actually the superposition of the reference bias voltage and the photocurrent conversion voltage. This processing method effectively raises the weak monitoring signal above the reference voltage, avoiding distortion that may occur when the signal is close to zero potential.

[0028] A power setting unit is used to output a setting voltage signal characterizing the target laser power. Optionally, the power setting unit provides a control target. The magnitude of the setting voltage signal represents the user's desired optical power emitted by the laser diode. For example, the power setting unit can be an adjustable voltage source circuit, allowing the user to adjust the level of the setting voltage signal according to actual needs (such as different measurement distances or the material of the object being measured), serving as a reference standard for subsequent comparison stages.

[0029] The comparison drive unit has its input terminals connected to the output terminals of the sampling amplification unit and the power setting unit, respectively, and its output terminal connected to a light-emitting diode. It is used to compare the monitoring voltage signal with the set voltage signal and adjust the drive current flowing through the light-emitting diode according to the comparison result so that the laser component maintains constant power emission.

[0030] Optionally, the comparison drive unit receives two input signals: a monitoring voltage signal representing the current actual optical power and a set voltage signal representing the desired optical power. These two signals are compared in real time. If the monitoring voltage signal is lower than the set voltage signal, it indicates that the current laser power is insufficient, and the comparison drive unit automatically increases the drive current output to the light-emitting diode. Conversely, if the monitoring voltage signal is higher than the set voltage signal, it indicates that the current laser power is too high, and the comparison drive unit automatically decreases the drive current. Through this dynamic comparison and adjustment, the laser diode drive circuit eventually reaches a balanced state, ensuring that the monitoring voltage signal always follows the set voltage signal, thereby achieving constant power emission from the laser component.

[0031] The laser diode driving circuit provided in this application addresses the difficulty in designing reverse bias for photodiodes under single-supply power supply. This application utilizes a sampling amplification unit to directly apply a reference bias voltage to the photodiode, solving the technical problem of not being able to provide a stable reverse bias voltage for the photodiode under conditions lacking a negative voltage power supply. This ensures the photodiode operates in its optimal linear region and simplifies the power supply circuit structure. Addressing the issue that weak signals are easily affected by the nonlinear region near ground potential in single-supply operational amplifiers, this application converts the monitoring current into a monitoring voltage signal based on the reference bias voltage, achieving a rise in signal potential. This solves the technical problem that the monitoring voltage signal is prone to nonlinear distortion or being submerged by noise when approaching zero potential, enabling ordinary single-supply operational amplifiers to achieve high-precision linear signal processing across the entire range and reducing device costs. Through closed-loop negative feedback control constructed by the comparison driving unit, the technical problem of unstable laser emission power with temperature or voltage fluctuations is solved, achieving high-precision and high-stability constant-power laser emission.

[0032] In some embodiments, Figure 2 A schematic diagram of the sampling amplification unit provided in an embodiment of this application is shown, as follows: Figure 2 As shown, the sampling amplification unit includes a first operational amplifier and a feedback impedance network.

[0033] In this configuration, the non-inverting input of the first operational amplifier is connected to a reference voltage generation unit, and the inverting input is connected to one end of a photodiode. A feedback impedance network is connected between the inverting input and the output of the first operational amplifier to clamp the voltage at the inverting input to a reference bias voltage, thereby causing the output of the first operational amplifier to output a monitoring voltage signal. Specifically, the monitoring voltage signal is the superposition of the voltage drop across the feedback impedance network and the reference bias voltage. Optionally, this structure constitutes a transimpedance amplifier with DC bias. The clamping is achieved using the virtual short characteristic of the operational amplifier. Since the non-inverting input of the first operational amplifier is connected to a constant reference bias voltage, the operational amplifier automatically adjusts its output under negative feedback, forcing the voltage at the inverting input to be consistent with that at the non-inverting input (i.e., maintained at the reference bias voltage potential). The purpose is twofold: First, to provide reverse bias for the photodiode. Since the other end of the photodiode (usually the cathode) is typically connected to the power supply voltage, while the end connected to the inverting input of the first operational amplifier (usually the anode) is clamped at the reference bias voltage, a stable voltage difference is formed between them (this voltage difference equals the power supply voltage minus the reference bias voltage). This reverse bias effectively reduces the junction capacitance of the photodiode, improving its response speed and linearity. Second, to establish a zero-point reference for the signal. When there is no light (i.e., the monitoring current is 0), there is no voltage drop on the feedback impedance network, and the voltage at the output of the first operational amplifier is equal to the reference bias voltage, not ground potential. This means that subsequent monitoring voltage signals oscillate based on this reference bias voltage, effectively avoiding the nonlinear "dead zone" of a single-supply operational amplifier near ground potential, ensuring the integrity of weak signals.

[0034] Understandably, to further improve circuit robustness and prevent damage to the first operational amplifier from electrostatic discharge or surge voltage, a protection circuit can be configured at the inverting input of the first operational amplifier. Specifically, in practical applications, an input resistor can be connected in series between the photodiode and the inverting input of the first operational amplifier to limit transient current flowing to the operational amplifier. Simultaneously, the inverting input of the first operational amplifier can also be connected to the power supply via a first clamping diode and to ground via a second clamping diode. These two diodes form a bidirectional clamping protection network: when an overvoltage higher than the power supply voltage occurs at the input, the first clamping diode conducts to discharge the voltage to the power supply; when a negative voltage lower than ground potential occurs, the second clamping diode conducts to clamp the voltage to near ground potential. This design effectively prevents physical damage to the input stage of the first operational amplifier caused by electrostatic discharge or abnormal signals.

[0035] In some embodiments, Figure 3Another schematic diagram of the sampling amplification unit provided in an embodiment of this application is shown, as follows: Figure 3 As shown, the feedback impedance network includes a first resistor and a second resistor connected in series, and a feedback capacitor connected in parallel with the first resistor and the second resistor. Optionally, the total impedance value of the feedback impedance network determines the transimpedance gain of the sampling amplifier unit, that is, the amount of output voltage change that can be generated by a unit input monitoring current. The feedback capacitor is used for phase compensation and signal filtering. On the one hand, since the photodiode itself has junction capacitance, when it is superimposed on the input capacitance of the operational amplifier, it is easy to introduce additional poles in the feedback loop, resulting in insufficient phase margin of the circuit and thus causing self-excitation. The addition of the feedback capacitor can introduce a zero point to cancel the influence of the above-mentioned poles and ensure the stability of the operational amplifier. On the other hand, the feedback capacitor, together with the first resistor and the second resistor, constitutes a low-pass filter, which can effectively filter out high-frequency noise or transient spike interference that may be mixed into the monitoring current, thereby outputting a smoother and cleaner monitoring voltage signal.

[0036] It is understood that the specific topology of the feedback impedance network is not limited to the dual-resistor series structure shown in the figure. In practical applications, those skilled in the art can flexibly adjust the network structure according to the target gain, the space constraints of the circuit board layout, or specific accuracy requirements. For example, a single high-precision resistor, or a series or parallel combination of multiple resistors, can be used to construct the feedback resistor section; similarly, the capacitance and number of feedback capacitors can also be adjusted according to the cutoff frequency requirements. As long as the impedance network is connected between the inverting input and output terminals of the operational amplifier, and can realize the current-to-voltage conversion and maintain signal stability, it is within the scope of the concept of this application.

[0037] In some embodiments, Figure 4 A schematic diagram of a reference voltage generation unit provided in an embodiment of this application is shown, as follows: Figure 4 As shown, the reference voltage generation unit includes a first voltage divider resistor and a second voltage divider resistor connected in series between the power supply and ground. The reference bias voltage is formed at the connection node of the first and second voltage divider resistors. Optionally, in this embodiment, a stable artificial reference point (i.e., virtual ground) is constructed in a single-supply system based on the principle of resistor voltage division. The first voltage divider resistor is connected between the power supply and the voltage divider node, and the second voltage divider resistor is connected between the voltage divider node and ground. By selecting high-precision resistor elements, the level value of the reference bias voltage can be accurately set.

[0038] It is understandable that, to further improve the purity and stability of the reference bias voltage, filtering designs are usually incorporated into actual circuits. Specifically, a filter capacitor can be connected in parallel between the connection node of the first and second voltage divider resistors (i.e., the reference voltage output terminal) and ground. This filter capacitor acts as an AC bypass, filtering out high-frequency ripple noise that may exist on the power line, providing a low-impedance AC grounding path, and preventing power fluctuations from directly coupling into the high-sensitivity sampling amplification unit through the reference voltage, thereby ensuring that the final output monitoring voltage signal has a high signal-to-noise ratio. Furthermore, although this embodiment demonstrates a resistor voltage divider, the specific circuit form of the reference voltage generation unit is not limited to the resistor voltage divider structure described in this embodiment. The core of this application is to provide a stable DC level as a bias reference for the system, rather than limiting the specific means of generating this voltage. Therefore, in practical applications, this unit can also be implemented in other forms depending on the different requirements for voltage accuracy, temperature drift coefficient, or cost. As long as a constant voltage that can maintain the reverse bias of the photodiode and enable the sampling circuit to operate normally can be generated, it falls within the protection scope of this application.

[0039] In some embodiments, Figure 5 A schematic diagram of the power setting unit provided in an embodiment of this application is shown, as follows: Figure 5 As shown, the power setting unit includes a power adjustment circuit and a hardware limiting circuit.

[0040] The power adjustment circuit includes a variable resistor element for adjusting the magnitude of the set voltage signal within a preset allowable range. The hardware limiting circuit includes at least one current-limiting resistor connected in series with the variable resistor element to divide the voltage. This current-limiting resistor is used to limit the set voltage signal to a preset safe threshold voltage when the variable resistor element is adjusted to its limit position. Optionally, the power setting unit is used to construct a fail-safe power control mechanism. In laser applications, the level of the set voltage signal directly determines the final emitted laser power. Although power can be limited by software or mechanical limits, both methods carry the risk of failure (such as software crashes or the knob being forcibly turned too far). This embodiment employs a hardware limiting scheme, utilizing the voltage division principle of physical resistors to establish the upper voltage limit. Specifically, the current-limiting resistor is connected in series between the set power supply terminal and the variable resistor element. When the user adjusts the variable resistor to its minimum resistance (i.e., attempting to obtain the maximum power limit position), due to the presence of the current-limiting resistor, the power supply voltage at the set power supply terminal cannot be directly applied to the output terminal, but is instead forcibly divided. This ensures that no matter how the user operates the product, even in the event of a short circuit in the variable resistor, the set voltage signal will never exceed the preset safety threshold voltage. This design is crucial to ensuring that laser products comply with eye safety standards (such as IEC 60825-1 Class 2).

[0041] Understandably, the specific topology of the hardware limiting circuit can be flexibly configured according to actual needs. As one implementation method, Figure 6 A schematic diagram of another power setting unit provided in an embodiment of this application is shown, such as... Figure 6 As shown, the hardware limiting circuit can be configured as a resistor network consisting of a first current-limiting resistor, a second current-limiting resistor, and a lower bias resistor. Specifically, the first and second current-limiting resistors act as pull-up current-limiting elements, connected in series between the set power supply terminal and the high-potential terminal of the variable resistor element (such as a potentiometer), while the lower bias resistor is connected between the low-potential terminal of the variable resistor element and ground. By precisely setting the resistance ratio of the first, second, and lower bias resistors, an upper voltage limit is artificially constructed. With this structure, even when the variable resistor element is adjusted to its minimum resistance (i.e., the extreme position where the maximum voltage is attempted to be output), the output set voltage signal is merely the inherent voltage division value of the fixed resistor network, thus strictly locking the voltage within the preset safety threshold and completely eliminating the risk of excessive laser power from a physical perspective.

[0042] It should be noted that the setting power supply terminal may be different from the power supply used by the aforementioned reference voltage generation unit, sampling amplification unit, and comparison driving unit. In the embodiments of this application, it is preferable to use a setting power supply terminal that is independent of and lower than the power supply used by the aforementioned reference voltage generation unit, sampling amplification unit, and comparison driving unit. The purpose is to better match the level standards of commonly used microcontrollers or logic control circuits by using a low-voltage (e.g., 3.3V) setting power supply terminal.

[0043] In some embodiments, Figure 7 A schematic diagram of the comparison driving unit provided in an embodiment of this application is shown, as follows: Figure 7 As shown, the comparison drive unit includes a second operational amplifier and a drive transistor assembly.

[0044] In this system, the non-inverting input of the second operational amplifier receives the set voltage signal, the inverting input receives the monitored voltage signal, and the output is connected to the control terminal of the driving transistor assembly. The current path of the driving transistor assembly is connected in series in the power supply circuit of the LED. Optionally, the second operational amplifier compares the set value (non-inverting input voltage) with the actual value (inverting input voltage) in real time. When the monitored actual optical power is lower than the set target (i.e., monitored voltage signal < set voltage signal), the voltage at the output of the operational amplifier increases, the conduction degree of the driving transistor assembly increases (i.e., equivalent resistance decreases), thereby increasing the driving current flowing through the LED and increasing the optical power. Conversely, when the actual optical power is higher than the set target, the output voltage of the operational amplifier decreases, the conduction degree of the driving transistor assembly decreases, limiting the driving current and decreasing the optical power. This dynamic adjustment process can automatically offset the effects of power supply fluctuations or device temperature drift, maintaining a constant laser output power.

[0045] In some embodiments, the driving transistor assembly includes a first driving transistor and a second driving transistor connected in a cascaded manner.

[0046] In this design, the base of the first driving transistor is connected to the output of the second operational amplifier, the collector of the first driving transistor is connected to the power supply, and the emitter of the first driving transistor is connected to the base of the second driving transistor through a resistor network. The collector or emitter of the second driving transistor is connected in series in the power supply circuit of the light-emitting diode (LED) to control the current flowing through the LED. Optionally, the cascaded first and second driving transistors aim to resolve the contradiction between the output driving capability of the operational amplifier and the high current requirements of the laser diode. Typically, operational amplifiers have weak output current capabilities (usually only in the milliampere range), making it difficult to directly drive laser diodes requiring tens or even hundreds of milliamperes of current. In this embodiment, the first driving transistor acts as an emitter follower or pre-amplifier stage, utilizing its current amplification characteristics to convert the weak voltage / current signal output by the second operational amplifier into a current signal with strong driving capability. This current signal then drives the second driving transistor to control the high current switching of the main circuit. This design significantly improves the overall current gain of the circuit.

[0047] Understandably, the specific connection method of the second driver transistor in the power supply circuit (i.e., collector output or emitter output) depends on the specific circuit topology design and the package polarity of the laser component. The word "or" is used here to encompass two mainstream driving architectures: First, when using a common-emitter amplifier or high-side switching configuration, the emitter of the second driver transistor (usually PNP type) is connected to the power supply, while its collector is connected in series with the anode of the LED. In this case, the collector acts as the output terminal, providing a large voltage swing and current gain, suitable for scenarios requiring high voltage differential drive. Second, when using a common-collector amplifier or emitter follower configuration, the collector of the second driver transistor (usually NPN type) is directly connected to the power supply, while its emitter is connected in series in the LED's power supply circuit. In this case, the emitter acts as the output terminal, and the circuit has high input impedance and low output impedance characteristics. Although the voltage gain is slightly less than 1, it has excellent current buffering capability and frequency response. Therefore, regardless of whether the designer places the load (light-emitting diode) on the collector side or the emitter side of the transistor, as long as it achieves the function of controlling the circuit current using the transistor, it falls within the protection scope of this application.

[0048] It is understandable that the specific topology of the peripheral configuration circuitry (i.e., the bias section and the coupling section) driving the transistor assembly can be optimized based on the characteristics of the transistor. As one implementation method, Figure 8 Another schematic diagram of the comparison driving unit provided in an embodiment of this application is shown, such as... Figure 8 As shown, the driving transistor assembly employs a two-stage amplification structure to meet the requirements of high-power driving and power supply optimization. Specifically, the first driving transistor is preferably an NPN transistor, and the second driving transistor is preferably a PNP transistor. The specific connection is as follows: the base of the first driving transistor is connected to the output of the second operational amplifier. The collector of the first driving transistor serves as the power input terminal, employing a dual-power supply structure: one path connects to the first power supply terminal via a first power supply resistor, and the other path connects to the second power supply terminal with a higher voltage via a second power supply resistor. Simultaneously, the collector is grounded through a first filter capacitor and a second filter capacitor connected in parallel. The emitter of the first driving transistor serves as the output terminal and is connected to an interstage resistor network. This resistor network includes a first interstage resistor and a second interstage resistor. Specifically, the emitter of the first driving transistor is connected to the base of the second driving transistor after being connected in series with the first and second interstage resistors. Furthermore, to provide a turn-off bias, the emitter of the first driving transistor is also connected to the emitter of the second driving transistor through the first interstage resistor. The collector of the second driver transistor is connected to the anode of the LED to output the drive current. Its base is also connected to ground via a base pull-down resistor to provide a path for base current discharge.

[0049] It should be noted that the first power supply terminal mentioned above is the power supply for the aforementioned reference voltage generation unit and sampling amplification unit, used to ensure the consistency of the reference potential of each unit. For example... Figure 8 The introduction of a second power supply terminal with a higher voltage amplitude, as shown, aims to improve the voltage compliance range of the driver stage. Since high-power laser diodes exhibit a significant forward voltage drop during operation, and the driver transistor itself has a saturation voltage drop when conducting large currents, using only the first power supply terminal may limit the linearity of the maximum drive current under extreme conditions due to sufficient voltage margin. Therefore, introducing a second power supply terminal with a higher voltage through a second power supply resistor can effectively prevent drive clipping or distortion caused by insufficient voltage margin. Of course, this second power supply terminal is merely an engineering optimization method for specific high-voltage drop laser components or high dynamic range requirements, and is not a necessary feature of the technical solution in this application. In practical applications, if the voltage of the first power supply terminal is sufficient to cover the total voltage drop requirement of the load circuit, the second power supply terminal can be omitted, and the driver stage can be powered directly by the first power supply terminal alone.

[0050] In some embodiments, Figure 9 Another schematic diagram of the laser diode driving circuit provided in an embodiment of this application is shown, such as... Figure 9 As shown, the laser diode driving circuit also includes an input control interface connected to the power setting unit. This interface receives pulse width modulation (PWM) signals to control the on / off state of the laser emitted by the LED. The input control interface includes a switching transistor. The base of the switching transistor receives the PWM signal, the emitter is connected to a preset power supply terminal, and the collector is connected to the power input terminal of the power setting unit. The switching transistor is used to turn on or off the power supply from the preset power supply terminal to the power setting unit according to the PWM signal, thereby controlling the on / off state of the laser emitted by the LED by adjusting the set voltage signal. Optionally, the input control interface is designed to use digital signals to perform high-speed modulation on subsequent analog circuits. When the switching transistor is on, the power supply terminal supplies power to the power setting unit, and the circuit generates a normal set voltage signal. The comparison driving unit drives the laser diode to emit light according to this signal. When the switching transistor is off, the power setting unit loses power, and the set voltage signal quickly drops to 0V. At this time, the comparison driving unit detects that the target power is zero and automatically cuts off the driving current of the LED through a negative feedback mechanism. It has significant advantages such as low switching loss, fast response speed, and no impact on the impedance matching of the main drive circuit.

[0051] In one implementation, the switching transistor is preferably configured as a high-side switch, using a PNP transistor (or a P-channel MOSFET). Its emitter is connected to the aforementioned setting power supply terminal, and its collector is connected to one end of the variable resistor element in the power setting unit. A base-limiting current resistor is typically connected in series between the base and the external PWM signal source (used to output the pulse width modulation signal). Simultaneously, the base is also connected to the setting power supply terminal via a pull-up resistor (i.e., the base and emitter are at the same potential). In this configuration, the control logic is active low. When the input pulse width modulation signal is low, the emitter junction of the switching transistor is forward-biased and conducts, current flows through the collector into the variable resistor element, the setting voltage signal is output normally, and the laser is turned on. When the signal is high, the switching transistor is turned off, cutting off the current flowing into the variable resistor element, the setting voltage signal disappears, and the laser is turned off. By adjusting the duty cycle of the PWM signal, linear adjustment of the average laser power can be achieved.

[0052] In some embodiments, Figure 10 This illustration shows yet another schematic diagram of the laser diode driving circuit provided in an embodiment of this application, such as... Figure 10 As shown, the laser diode driving circuit also includes an electrostatic discharge (ESD) protection unit. Specifically, the ESD protection unit includes a first Zener diode and a second Zener diode, both of which are connected in reverse parallel with the light-emitting diode (LED). Optionally, the ESD protection unit is used to prevent damage to the LED due to electrostatic discharge or power surges. Since the LED is the core component for laser emission, its PN junction is extremely fragile and costly. Therefore, this embodiment employs multiple protection strategies to enhance its surge resistance.

[0053] It is understandable that the specific connection relationship between the first and second Zener diodes is as follows: the cathodes of the first and second Zener diodes are both connected to the anode of the LED; the anodes of the first and second Zener diodes are also connected to the cathode of the LED, which is also the common pin of the LED and photodiode in the laser assembly. When encountering high-energy electrostatic discharge (ESD), the two Zener diodes can share the surge current, thereby enabling the ESD protection unit to withstand higher instantaneous power than a single diode, preventing the diode itself from burning out due to overheating. If one of the Zener diodes fails due to long-term operation (e.g., open-circuit failure), the other diode can still continue to provide clamping protection, thus greatly extending the overall lifespan and reliability of the laser drive product.

[0054] This application also provides a laser displacement sensor, comprising: A laser emitting unit is used to emit laser light towards the object being measured. The photoelectric receiving unit is used to receive the laser signal reflected back by the object being measured; The signal processing unit, connected to the photoelectric receiving unit, is used to calculate the displacement of the object being measured based on the laser signal. The laser emitting unit includes a laser diode driving circuit as described in the above embodiments.

[0055] The laser displacement sensor provided in this application addresses the difficulty in designing reverse bias for photodiodes under single-supply power supply. This application utilizes a sampling amplification unit to directly apply a reference bias voltage to the photodiode, solving the technical problem of not being able to provide a stable reverse bias voltage for the photodiode under conditions lacking a negative voltage power supply. This ensures the photodiode operates in its optimal linear region and simplifies the power supply circuit structure. Addressing the issue that weak signals are easily affected by the nonlinear region near ground potential in single-supply operational amplifiers, this application converts the monitoring current into a monitoring voltage signal based on the reference bias voltage, achieving a rise in signal potential. This solves the technical problem that the monitoring voltage signal is prone to nonlinear distortion or noise overload when approaching zero potential, enabling ordinary single-supply operational amplifiers to achieve high-precision linear signal processing across the entire measurement range, reducing device costs. Through closed-loop negative feedback control constructed by the comparison drive unit, the technical problem of unstable laser emission power with temperature or voltage fluctuations is solved, achieving high-precision and high-stability constant-power laser emission.

[0056] The above description, in conjunction with specific embodiments, provides a further detailed explanation of this application and should not be construed as limiting the specific implementation of this application to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of this application, and all such modifications and substitutions should be considered within the scope of protection of this application.

Claims

1. A laser diode driving circuit for driving a laser assembly comprising a light-emitting diode and a photodiode, characterized in that, include: A reference voltage generation unit is used to generate a constant reference bias voltage. A sampling amplification unit, whose input terminal is connected to the photodiode and the reference voltage generation unit, is used to apply the reference bias voltage to the photodiode to provide reverse bias, and to convert the monitoring current generated by the photodiode into a monitoring voltage signal output based on the reference bias voltage; The power setting unit is used to output a setting voltage signal that characterizes the target laser power; The comparison driving unit has its input terminals connected to the output terminals of the sampling amplification unit and the power setting unit, respectively, and its output terminal connected to the light-emitting diode. It is used to compare the monitoring voltage signal with the set voltage signal and adjust the driving current flowing through the light-emitting diode according to the comparison result so that the laser component maintains constant power emission.

2. The laser diode driving circuit according to claim 1, characterized in that, The sampling amplification unit includes a first operational amplifier and a feedback impedance network; The non-inverting input of the first operational amplifier is connected to the reference voltage generation unit, and the inverting input is connected to one end of the photodiode; The feedback impedance network is connected between the inverting input terminal and the output terminal of the first operational amplifier, and is used to clamp the voltage at the inverting input terminal of the first operational amplifier to the reference bias voltage, so that the output terminal of the first operational amplifier outputs the monitoring voltage signal. The monitoring voltage signal is the superposition of the voltage drop across the monitoring current on the feedback impedance network and the reference bias voltage.

3. The laser diode driving circuit according to claim 2, characterized in that, The feedback impedance network includes a first resistor and a second resistor connected in series, and a feedback capacitor connected in parallel with the first resistor and the second resistor.

4. The laser diode driving circuit according to claim 1, characterized in that, The reference voltage generation unit includes a first voltage divider resistor and a second voltage divider resistor connected in series between the power supply and ground, wherein the reference bias voltage is formed at the connection node of the first voltage divider resistor and the second voltage divider resistor.

5. The laser diode driving circuit according to claim 1, characterized in that, The power setting unit includes a power adjustment circuit and a hardware limiting circuit; The power regulation circuit includes a variable resistor element for adjusting the magnitude of the set voltage signal within a preset allowable range; The hardware limiting circuit includes at least one current-limiting resistor connected in series with the variable resistor element to divide the voltage. The at least one current-limiting resistor is used to limit the set voltage signal to within a preset safety threshold voltage when the variable resistor element is adjusted to its limit position.

6. The laser diode driving circuit according to claim 1, characterized in that, The comparison driving unit includes a second operational amplifier and a driving transistor assembly; The non-inverting input of the second operational amplifier is used to receive the set voltage signal, the inverting input is used to receive the monitored voltage signal, and the output is connected to the control terminal of the driving transistor assembly. The current path of the driving transistor assembly is connected in series in the power supply circuit of the light-emitting diode.

7. The laser diode driving circuit according to claim 6, characterized in that, The driving transistor assembly includes a first driving transistor and a second driving transistor connected in a cascaded manner; The base of the first driving transistor is connected to the output terminal of the second operational amplifier, the collector of the first driving transistor is connected to the power supply, the emitter of the first driving transistor is connected to the base of the second driving transistor through a resistor network, and the collector or emitter of the second driving transistor is connected in series in the power supply circuit of the light-emitting diode to control the current flowing through the light-emitting diode.

8. The laser diode driving circuit according to claim 1, characterized in that, It also includes an input control interface, which is connected to the power setting unit and is used to receive pulse width modulation signals to control the on and off of the laser emitted by the light-emitting diode; The input control interface includes a switching transistor. The base of the switching transistor is used to receive the pulse width modulation signal, the emitter is connected to a preset power supply terminal, and the collector is connected to the power input terminal of the power setting unit. The switching transistor is used to turn on or off the power supply from the preset power supply terminal to the power setting unit according to the pulse width modulation signal, so as to control the laser of the light-emitting diode by adjusting the preset voltage signal.

9. The laser diode driving circuit according to claim 1, characterized in that, It also includes an electrostatic discharge (ESD) protection unit, which includes a first Zener diode and a second Zener diode, both of which are connected in reverse parallel with the light-emitting diode.

10. A laser displacement sensor, characterized in that, include: A laser emitting unit is used to emit laser light towards the object being measured. A photoelectric receiving unit is used to receive laser signals reflected back from the object under test; A signal processing unit, connected to the photoelectric receiving unit, is used to calculate the displacement of the object being measured based on the laser signal. The laser emitting unit includes a laser diode driving circuit as described in any one of claims 1 to 9.

Images