Acousto-optic modulator driving circuit

Abstract

The invention discloses an acousto-optic modulator driving circuit, which comprises a local oscillation signal generator module, an analog driving modulation amplification module, a digital driving modulation amplification module and a power supply modulation module, and is characterized in that the local oscillation signal generator module is formed by connecting a crystal oscillation circuit, a low-pass filter circuit and a power divider; the analog driving modulation amplification module is formed by connecting a variable gain amplification circuit, a pre-amplification circuit, a power amplification circuit, a matching and low-pass filter circuit and a radio frequency output port; the digital driving modulation amplification module is formed by connecting a keying modulation circuit, a pre-amplification circuit, a power amplification circuit, a matching and low-pass filtering circuit and a radio frequency output port. The local oscillation signal generator module generates high-frequency sinusoidal signals through the crystal oscillation circuit and the low-pass filter circuit, local oscillation signals are provided for the analog driving modulation amplification module and the digital driving modulation amplification module at the same time through the power divider, the average power consumption is reduced, and the area and cost of a circuit board are saved.

Description

Technical Field

[0001] The present invention belongs to the technical field of acousto-optic modulators, and specifically relates to a low-power acousto-optic modulator driving circuit integrating analog and digital modulation, which is mainly used for low power consumption and small volume of the driving circuit to realize miniaturization and high stability performance of the laser. Background Art

[0002] The acousto-optic modulation system is based on the principle of the acousto-optic effect. When the laser beam emitted by the laser is incident on the ultrasonic surface at an oblique Bragg angle, Bragg diffraction will occur. The diffracted light is modulated by the ultrasonic signal into 0th and 1st order diffracted light. The power of the 0th and 1st order diffracted light can be controlled by changing the ultrasonic power in the incident acousto-optic medium. Ultrasonic waves use electroacoustic transducers to convert the RF signal output by the driving source into ultrasonic oscillations. Therefore, a driving source with higher frequency stability is a key component of the acousto-optic modulation system. Its RF signal off-ratio, power consumption and other indicators directly affect the extinction ratio, temperature drift and other performance of the laser as a whole.

[0003] In order to improve the extinction ratio in laser manufacturing, two-way analog drive and digital drive cascade are generally used to form two-way acousto-optic modulation. The analog drive modulates the Gaussian waveform of the light pulse, and the digital drive further improves the extinction ratio. However, the disadvantage is that the two acousto-optic modulators occupy a relatively large volume, and the traditional drive circuit is based on the power amplifier circuit, while the actual drive source output signal is in the form of a narrow time slot pulse. The static power consumption in the off time slot is very high, which makes the overall drive source power consumption of the laser relatively high, and puts forward higher requirements for laser heat dissipation and temperature control. The temperature drift performance of the laser is difficult to guarantee. It is difficult to meet the requirements of laser wind measurement radar for small size and low power consumption of lasers. Summary of the invention

[0004] In view of the above deficiencies in the prior art, the present invention provides a low-power consumption analog and digital drive integrated acousto-optic modulator driving circuit to reduce the overall volume of the analog and digital drive sources and reduce the power consumption level.

[0005] The technical solution adopted by the present invention to solve the technical problem is: an acousto-optic modulator driving circuit, comprising a local oscillator signal generator module formed by connecting a crystal oscillator circuit, a low-pass filter circuit and a power divider, and an analog drive modulation amplifier module and a digital drive modulation amplifier module respectively connected to the power divider, wherein the analog drive modulation amplifier module comprises a variable gain amplifier circuit, a first preamplifier circuit, a first power amplifier circuit, a first matching and low-pass filter circuit and a first radio frequency output port connected in sequence, and the digital drive modulation amplifier module comprises a keying modulation circuit, a second preamplifier circuit, a second power amplifier circuit, a second matching and low-pass filter circuit connected in sequence. The first and second RF output ports are connected to the power supplies of the first preamplifier circuit and the second preamplifier circuit, and the first and second power amplifier circuits are connected to the power supplies of the first power amplifier circuit. The power modulation module is also comprised of a power input interface, a step-down and voltage stabilizing circuit, and a pulse power modulation circuit. The power input interface is respectively connected to the step-down and voltage stabilizing circuit and the second power amplifier circuit, the step-down and voltage stabilizing circuit is simultaneously connected to the second preamplifier circuit and the pulse power modulation circuit, the pulse power modulation circuit is connected to the second power amplifier circuit, the subtractor circuit and the analog input port are sequentially connected in front of the variable gain amplifier circuit, and the pulse steepening circuit and the digital input port are sequentially connected in front of the keying modulation circuit.

[0006] The acousto-optic modulator driving circuit has a local oscillator signal generator module that uses an active crystal oscillator in the form of a CMOS output, and uses an LC-based low-pass filter circuit to shape a square wave into a sine wave, which is then sent to an analog drive modulation amplifier module and a digital drive modulation amplifier module through a power divider.

[0007] The variable gain amplifier circuit of the acousto-optic modulator driving circuit adopts the VCA824 chip. When the analog input control voltage changes from -1 to 1, the amplifier gain can change linearly by 40dB, thereby realizing the amplitude modulation function in a relatively simple manner. In addition, the output power is amplified as a whole by driving the amplifier circuit and the power amplifier circuit, so as to achieve a maximum output power of more than 1W of the RF output interface.

[0008] The described acousto-optic modulator driving circuit, whose digital driving modulation amplifier module adopts single-pole single-throw switch chip ADG901, in the short time slot when the digital input is high level, the switch is turned on, and the local oscillator signal is output to the driving amplifier circuit, in the wide time slot when the digital input is low level, the switch is turned off, and the RF signal has no output. When the switch is turned off, the input-output isolation is 40dB, thus achieving a 40dB turn-off ratio of the digital driving RF output. In addition, the digital input pulse signal passes through the Schmitt trigger, and the signal with slow edge changes is shaped into a rectangular wave with steep edges, and the noise superimposed on the high and low levels of the rectangular pulse can be effectively removed, and the non-gate is still replaced by a high-speed response NAND gate. The acousto-optic modulator driving circuit is characterized in that its pulse power supply modulation circuit adopts gate driver LM5112. When the digital modulation input is in a short time slot of high level, LM5112 outputs high level, the drain of NMOSFET is turned off, 5V power is output to the gate of power amplifier tube through diode, and the power amplifier circuit starts to work. When the digital modulation input is in a wide time slot of low level, LM5112 outputs high level, the drain of NMOSFET is turned on, the gate voltage of power tube is 0, the power amplifier circuit stops working, and the static current is almost zero. By reducing the high static current of the power amplifier circuit in the time slot without output, the average power consumption of the driving source is greatly reduced.

[0009] The low-pass filter circuit of the described acousto-optic modulator driving circuit adopts an LC second-order low-pass filter, and the relationship between the cut-off frequency and the inductance and capacitance value is: .

[0010] In the acousto-optic modulator driving circuit, the amplifier of the first preamplifier circuit adopts the SBF5089Z chip produced by RFMD, and the first power amplifier circuit adopts the N-type enhanced field effect radio frequency power transistor PD85004 chip.

[0011] In the acousto-optic modulator driving circuit, the first matching and low-pass filtering circuit adopts a fourth-order LC low-pass filter.

[0012] The core circuit of the pulse steepening circuit of the described acousto-optic modulator driving circuit is a Schmitt trigger composed of two-level NOT gates, wherein the upper and lower levels V+ and V- of the Schmitt gate are calculated by the following formulas: .

[0013] The beneficial effects of the present invention are: The present invention adopts power pulse modulation technology to close the gate of the power amplifier during non-transmitting time slots, greatly reducing the static current, thereby significantly reducing the average power consumption of the driving source, which can be reduced by more than 50% in theory. The present invention uses a power divider to divide the local oscillator signal source into two, and simultaneously inputs them into analog modulation and digital modulation circuits, and the analog and digital driving sources can share a set of power modulation and power conversion circuits, saving the area and cost of the circuit board.

[0014] The digital drive circuit of the present invention uses a Schmitt trigger to shape the digital modulation input signal, and the rising edge and the falling edge can be reduced to less than 10ns. After passing through the acousto-optic modulator, the rising edge and the falling edge of the optical pulse are within 40ns, realizing the rapid shutdown of the optical signal; at the same time, the Schmitt trigger reduces the possibility of laser light leakage by suppressing the noise of the digital input signal, which is a key indicator of the laser wind measurement radar. In addition, through a high-isolation single-pole single-throw switch, the final optical extinction ratio of the digital drive source after passing through the acousto-optic modulator can reach more than 50dB. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a circuit principle block diagram of an embodiment of the present invention; Figure 2 is a principle block diagram of a subtractor circuit according to an embodiment of the present invention; Figure 3 It is a principle block diagram of a crystal oscillator circuit according to an embodiment of the present invention; Figure 4 is a principle block diagram of a low-pass filter circuit according to an embodiment of the present invention; Figure 5 is a principle block diagram of a variable gain amplifier circuit according to an embodiment of the present invention; Figure 6 is a principle block diagram of a first preamplifier circuit according to an embodiment of the present invention; Figure 7 is a principle block diagram of a first power amplifier circuit according to an embodiment of the present invention; Figure 8 is a principle block diagram of a first matching and low-pass filtering circuit according to an embodiment of the present invention; Fig. 9 is a principle block diagram of a keying modulation circuit according to an embodiment of the present invention; Fig.10 1 is a principle block diagram of a pulse steepening circuit according to an embodiment of the present invention; Fig.11 It is a principle block diagram of a voltage reduction and voltage stabilization circuit according to an embodiment of the present invention; Fig.12 The figure is a principle block diagram of a pulse power modulation circuit according to an embodiment of the present invention.

[0016] The figures are marked as follows: 1—crystal oscillator circuit, 2—low-pass filter circuit, 3—power divider, 4—analog input port, 5—subtractor circuit, 6—variable gain amplifier circuit, 7—first preamplifier circuit, 8—first power amplifier circuit, 9—first matching and low-pass filter circuit, 10—first RF output port, 11—digital input port, 12—pulse steepening circuit, 13—keying modulation circuit, 14—second preamplifier circuit, 15—second power amplifier circuit, 16—second matching and low-pass filter circuit, 17—second RF output port, 18—power input interface, 19—voltage reduction and voltage stabilization circuit, 20—pulse power modulation circuit. DETAILED DESCRIPTION

[0017] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0018] Reference Figure 1 As shown, an acousto-optic modulator driving circuit disclosed in the present invention includes a local oscillator signal generator module, an analog drive modulation amplifier module, a digital drive modulation amplifier module and a power modulation module.

[0019] The local oscillator signal generator module is formed by connecting a crystal oscillator circuit 1, a low-pass filter circuit 2 and a power divider 3, and the power divider 3 is connected to the analog drive modulation amplifier module and the digital drive modulation amplifier module respectively. The local oscillator signal generator module adopts an active crystal oscillator in the form of CMOS output. Since the output square wave carries a large number of high-order harmonic signals, in order to avoid the influence of high-frequency signals on the acousto-optic modulator, an LC-based low-pass filter circuit 2 is used to shape the square wave into a sine wave, and then sent to the analog drive modulation amplifier module and the digital drive modulation amplifier module through the power divider 3. The active crystal oscillator has a low cost, and the analog and digital drive sources share a crystal oscillator source to save PCB area.

[0020] The output of the first preamplifier circuit 7 is connected to the input of the first power amplifier circuit 8, the output of the second preamplifier circuit 14 is connected to the input of the second power amplifier circuit 15, and the power supplies of the first preamplifier circuit 7 and the second preamplifier circuit 14 are connected, and the power supplies of the first power amplifier circuit 8 and the second power amplifier circuit 15 are connected. The front of the variable gain amplifier circuit 6 is connected to the subtractor circuit 5 and the analog input port 4 in sequence, and the front of the keying modulation circuit 13 is connected to the pulse steepening circuit 12 and the digital input port 11 in sequence.

[0021] The present invention firstly uses the power divider 3 to divide the local oscillator signal into two, and outputs it to analog and digital modulation at the same time, which not only saves one time of the local oscillator signal module area, but also ensures the consistency of the frequency of the RF signal output by the analog and digital driving sources. The gate voltage of the power amplifier circuit is controlled to be in the form of pulse input by using the power pulse modulation technology, so that the drain of the power amplifier tube is closed in the off time slot when the RF signal has no output, and the static power consumption is solved to 0. Since the driving source itself is a pulse output mode of narrow time slot, the duty cycle of the off time slot reaches more than 80%, so theoretically the static power consumption of the driving source can be reduced by more than 50%, so that the power consumption of the driving source can be greatly reduced.

[0022] The subtractor circuit 5 is as follows Figure 2 As shown, an operational amplifier chip AD8009 is used. When the input pulse signal is 0 to 1V, the output pulse is adjusted to -1 to 1V, so that the gain of the variable gain amplifier circuit 6 changes linearly with the modulation signal by 40dB. As an embodiment of the present invention, resistors R1=R2=100Ω, R3=R4=400Ω, V1 is a reference signal obtained by dividing the 5V voltage by resistors R25 and R26, R25=9KΩ, R26=1KΩ, and V2 is an analog input pulse modulation signal of 0 to 1V.

[0023] The crystal oscillator circuit 1 uses an active crystal oscillator with a frequency temperature stability within 20ppm. Since the output signal is in the form of a CMOS square wave signal, and the local oscillator signal is generally a sine signal, a low-pass filter circuit 2 is used to filter out high-frequency harmonics to obtain a fundamental signal such as 40MHz, and then a power divider 3 is used to provide a high-frequency local oscillator signal for both the analog drive modulation and the digital drive modulation modules. Figure 3 As shown, the low-pass filter circuit 2 is as follows Figure 4 As shown, using LC second-order low-pass filter, the relationship between the cut-off frequency and the inductance and capacitance value is: .

[0024] As an embodiment of the present invention, the inductor L1 = 150nH, the capacitor C3 = 220pF, the insertion loss at 40MHz is 5dB, and the suppression at 80MHz is greater than 8dBc.

[0025] The analog drive modulation amplification module is formed by sequentially connecting a variable gain amplification circuit 6, a first preamplification circuit 7, a first power amplification circuit 8, a first matching and low-pass filtering circuit 9 and a first RF output port 10. The variable gain amplification circuit 6 realizes a 40dB change in RF output power when the analog modulation voltage changes from -1 to 1, the first preamplification circuit 7 provides a signal gain of 18dB, the first power amplification circuit 8 provides a signal gain of 17dB, and the first matching and low-pass filtering circuit 9 completes the optimal load transmission of power and the filtering of high-order harmonics.

[0026] The variable gain amplifier circuit 6 is as follows Figure 5 As shown, the amplifier uses the VCA824 chip produced by TI. When the gain control voltage changes linearly from -1 to 1V, the circuit gain will change linearly by 40dB. The rated maximum gain is configured by the gain resistor R10 and the feedback resistor R9. The calculation formula is .

[0027] The first preamplifier circuit 7 is as follows Figure 6 As shown, the amplifier uses the SBF5089Z chip produced by RFMD, and the gain in the range of DC to 500MHz is about 20dB. The input and output capacitors C5 / C6 play a role of DC isolation. As an embodiment of the present invention, C5=1uF, C6=1nF, C7=1uF, C8=C9=1uF, L2=6.8nH, L3=6.8uH, the measured 40MHz gain is about 17dB, and the saturation power is about 16dBm.

[0028] The first power amplifier circuit 8 is as follows Figure 7As shown, the N-type enhancement field effect RF power transistor PD85004 chip is used, and the measured gain at 40MHz is 17dB, and the maximum output power is about 2W. The gate voltage is powered by the power pulse modulation signal Vt. In the high-level transmission time slot, the transistor is turned on and the RF signal is output, while in the low-level time slot, the transistor is turned off, no RF signal is output, and the static current is almost zero.

[0029] The first matching and low-pass filtering circuit 9 is as follows Figure 8 As shown, a fourth-order LC low-pass filter is used as an embodiment of the present invention, inductor L6=L7=150nH, capacitor C20=C21=220pF, insertion loss 0.1dB at 40MHz, suppression greater than 29dB at 80MHz. The input uses a PI-type matching network to match the load 50 ohms to the impedance position when the amplifier outputs maximum power.

[0030] The digital drive modulation amplification module is formed by sequentially connecting a keying modulation circuit 13, a second preamplification circuit 14, a second power amplifier circuit 15, a second matching and low-pass filter circuit 16, and a second RF output port 17. The keying modulation circuit 13 realizes the on-off of the signal through the SPST switch, and the 40dB isolation further improves the turn-off ratio of the optical signal. The digital drive modulation amplification module adopts a single-pole single-throw switch chip ADG901. In a short time slot when the digital input is a high level, the switch is turned on, and the local oscillator signal is output to the drive amplifier circuit. In a wide time slot when the digital input is a low level, the switch is turned off, and the RF signal has no output. When the switch is turned off, the input-output isolation is 40dB, so that the digital drive RF output has a turn-off ratio of 40dB. In addition, the digital input pulse signal passes through a Schmitt trigger, and the signal with a slow edge change is shaped into a rectangular wave with a steep edge, and the noise superimposed on the high and low levels of the rectangular pulse can be effectively removed. The non-gate is still replaced by a high-speed response non-and gate.

[0031] The principle of the amplification circuit and the matching circuit is basically the same as that of the analog drive module. Fig. 9 As shown, the single-pole single-throw switch uses the ADG901 chip produced by ADI, with an operating frequency range of 0 to 4.5 GHz and an isolation of 40 dB.

[0032] The pulse steepening circuit 12 is as follows Fig.10 As shown in the figure, the core circuit is a Schmitt trigger composed of two levels of NOT gates. The Schmitt trigger can shape a signal with slow edge changes into a rectangular wave with steep edges, and can effectively remove the noise superimposed on the high and low levels of the rectangular pulse. The calculation formulas for the upper and lower levels V+ and V- of the Schmitt gate are as follows: .

[0033] As an embodiment of the present invention, the NAND gate uses the integrated chip SN74LVCG00W produced by TI. Since IOmax=32mA, the design parameters are VT+=3V, VT-=2V, R1=1kΩ, and R2=5kΩ. It is verified by actual measurement that when the rising and falling edges of the Vin input pulse signal are set to 100ns, the rising and falling edges of the output Vout pulse signal are only within 3ns.

[0034] The power modulation module is composed of a 12V DC power input interface 18, a step-down and voltage stabilizing circuit 19 and a pulse power modulation circuit 20, wherein the 12V power input interface 18 is respectively connected to the step-down and voltage stabilizing circuit 19 and the second power amplifier circuit 15, the step-down and voltage stabilizing circuit 19 is simultaneously connected to the second preamplifier circuit 14 and the pulse power modulation circuit 20, the pulse power modulation circuit 20 is connected to the second power amplifier circuit 15, wherein the step-down and voltage stabilizing circuit 19 steps down the 12V DC power supply to 5V to power the devices in the front stage of the power amplifier circuit to reduce power consumption, and the pulse power modulation circuit 20 modulates the 5V DC power supply into a pulse to supply the gate of the power amplifier circuit, and uses the gate voltage to be 0 when the power amplifier tube is turned off to reduce the static power consumption of the RF signal in the time slot without output, so that the power consumption of the acousto-optic modulator driving source is greatly reduced.

[0035] Buck and voltage stabilizing circuit 19 Fig.11 As shown, the DCDC chip TPS54302 and the LDO voltage regulator chip TPS7A8101 produced by TI are used. The input voltage is 12V, which is first stepped down to 5.5V and then outputted at 5V to reduce the power consumption of the 5V circuit and suppress the influence of power supply noise.

[0036] The pulse power modulation circuit 20 is as follows Fig.12 As shown, the gate driver LM5112 produced by TI is used. The input pulse signal is input to the power pulse modulation circuit while controlling the keying modulation circuit 13, so that the VCC 5V power supply is only output to the gate of the power amplifier tube in the high pulse time slot, and the power amplifier tube is turned on when the gate is high level and stops working when the gate is low level, which can significantly reduce the static power consumption of the power amplifier circuit. Since the duty cycle of the low level of the modulated pulse signal reaches more than 80%, the static power consumption of the driving source also accounts for 80% of the shutdown time slot, so theoretically the power consumption of the driving source can be reduced by more than 50%, so that the power consumption of the laser can be greatly reduced, and the influence of temperature rise on the laser system indicators can be reduced.

[0037] Obviously, the above description is not a limitation of the present invention. Changes in resistance and capacitance values ​​and changes in the selection of key components made by technicians in this technical field without changing the circuit scheme should also fall within the protection scope of the present invention.

Claims

1. An acousto-optic modulator driving circuit, characterized in that: The invention comprises a local oscillator signal generator module formed by connecting a crystal oscillator circuit (1), a low-pass filter circuit (2) and a power divider (3), and an analog drive modulation amplifier module and a digital drive modulation amplifier module respectively connected to the power divider (3), wherein the analog drive modulation amplifier module comprises a variable gain amplifier circuit (6), a first preamplifier circuit (7), a first power amplifier circuit (8), a first matching and low-pass filter circuit (9) and a first radio frequency output port (10) connected in sequence, and the digital drive modulation amplifier module comprises a keying modulation circuit (13), a second preamplifier circuit (14), a second power amplifier circuit (15), a second matching and low-pass filter circuit (16) and a second radio frequency output port (10) connected in sequence. The output port (17) further comprises a power modulation module consisting of a power input interface (18), a step-down and voltage stabilizing circuit (19) and a pulse power modulation circuit (20), wherein the power input interface (18) is respectively connected to the step-down and voltage stabilizing circuit (19) and the second power amplifier circuit (15), the step-down and voltage stabilizing circuit (19) is simultaneously connected to the second preamplifier circuit (14) and the pulse power modulation circuit (20), the pulse power modulation circuit (20) is connected to the second power amplifier circuit (15), the variable gain amplifier circuit (6) is connected in front of the subtractor circuit (5) and the analog input port (4), and the keying modulation circuit (13) is connected in front of the pulse steepening circuit (12) and the digital input port (11).

2. The acousto-optic modulator driving circuit according to claim 1, characterized in that: The local oscillator signal generator module adopts an active crystal oscillator in the form of CMOS output, and adopts an LC-based low-pass filter circuit (2) to shape the square wave into a sine wave, which is then sent to the analog drive modulation amplifier module and the digital drive modulation amplifier module through a power divider (3).

3. The AOM driving circuit according to claim 2, characterized in that: The amplifier of the variable gain amplifier circuit (6) adopts a VCA824 chip.

4. The AOM driving circuit according to claim 2, characterized in that: The digital drive modulation amplification module adopts a single-pole single-throw switch chip ADG901.

5. An AOM driving circuit according to claim 1, 2, 3 or 4, characterized in that: The pulse power supply modulation circuit (20) adopts a gate driver LM5112.

6. An AOM driving circuit according to claim 1, 2, 3 or 4, characterized in that: The low-pass filter circuit (2) adopts an LC second-order low-pass filter, and the relationship between the cut-off frequency and the inductance and capacitance value is: .

7. An acousto-optic modulator driving circuit according to claim 1, 2, 3 or 4, characterized in that: The amplifier of the first preamplifier circuit (7) adopts the SBF5089Z chip produced by RFMD, and the first power amplifier circuit (8) adopts the N-type enhanced field effect radio frequency power transistor PD85004 chip.

8. An acousto-optic modulator driving circuit according to claim 1, 2, 3 or 4, characterized in that: The first matching and low-pass filtering circuit (9) adopts a fourth-order LC low-pass filter.

9. An AOM driving circuit according to claim 1, 2, 3 or 4, characterized in that: The core circuit of the pulse steepening circuit (12) is a Schmitt trigger composed of two levels of NOT gates, wherein the upper and lower levels V+ and V- of the Schmitt gate are calculated by the following formulas: .

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