An amplitude-adjustable 10ps ultra-fast differential Gaussian pulse generator

Abstract

The present invention relates to an ultra-fast 10ps differential Gaussian pulse generator with adjustable amplitude. The generator comprises a pulse shaping circuit, a high-voltage conversion circuit, a low-voltage conversion circuit, a high-voltage regulation circuit, an avalanche circuit, a first low-voltage regulation circuit, a first step circuit, a second low-voltage regulation circuit, a second step circuit, a differential circuit, a bandpass filter, and an impedance converter. The ultra-fast picosecond differential Gaussian pulse generator disclosed herein utilizes avalanche technology, with the adjustment circuit added to the avalanche circuit to achieve adjustable pulse amplitude.

Description

Technical Field

[0001] The invention belongs to the field of electronic circuits, and in particular relates to an amplitude-adjustable 10ps ultra-fast differential Gaussian pulse generator in this field. Background Art

[0002] Ground Penetrating Radar (GPR) is a fast, efficient, and non-destructive geophysical survey device. It is widely used in highway inspections. The "Highway Roadbed and Pavement Field Testing Specification (JTGE60-2008)" explicitly stipulates that GPR must be used for highway inspections. For non-destructive testing of the thickness of various surface layers on asphalt concrete roads, an air-coupled antenna is used. This suspended antenna, typically mounted on the rear of a vehicle, can detect the delamination of various structural layers in asphalt pavement, detect defects in each layer, and analyze and assess the severity of defects, providing a basis for treatment.

[0003] The transmit pulse format used by ground-coupled antennas in ground-penetrating radars is typically a Gaussian pulse. Compared to ground-coupled antennas, air-coupled horn antennas are larger and have a wider bandwidth. Using a Gaussian pulse results in more low-frequency components oscillating on the antenna, resulting in a more stationary echo signal, significantly impacting the antenna's vertical resolution. The advantage of a differential Gaussian pulse is that it contains no zero-frequency components and has a smaller low-frequency component, effectively avoiding signal oscillation. Therefore, air-coupled horn antennas often use a differential Gaussian pulse format. This format achieves antenna impedance matching and maximizes power transmission. Furthermore, since this antenna is air-coupled, its detection speed is limited by the antenna's operating repetition rate when used on a vehicle. Therefore, a high repetition rate is required to ensure rapid detection.

[0004] Existing picosecond pulse technologies, such as the avalanche transistor series-parallel Marx circuit high-frequency, high-voltage picosecond pulse generator and its application (Application No. 201911319429.6), have high amplitudes but slow rise times, resulting in low main frequency, low pulse repetition frequency, and large size, making them unsuitable for ground-penetrating radar applications. Another example is the avalanche transistor Marx circuit picosecond pulse generator based on microstrip transmission (Application No. 201610776347.4), which has high amplitudes but slow rise times and pulse widths, low pulse repetition frequency, and Gaussian pulse output. The pulse output of the air-coupled antenna transmitting end of a ground-penetrating radar must be a differential Gaussian pulse to better match the antenna and maximize its effectiveness. Therefore, these technologies are far from sufficient for air-coupled antenna applications. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a high-repetition-rate ultra-fast picosecond differential Gaussian pulse generator with adjustable pulse width and amplitude, so that it can not only achieve ultra-fast pulses of tens of picoseconds, but also generate differential Gaussian pulses. At the same time, the pulse width and amplitude of the output pulse can be adjusted to generate differential Gaussian pulses of different amplitudes and pulse widths.

[0006] The present invention adopts the following technical solutions:

[0007] A 10ps ultra-fast differential Gaussian pulse generator with adjustable amplitude is improved in that it includes a pulse shaping circuit, a high-voltage conversion circuit, a low-voltage conversion circuit, a high-voltage regulation circuit, an avalanche circuit, a first low-voltage regulation circuit, a first step circuit, a second low-voltage regulation circuit, a second step circuit, a differential circuit, a band-pass filter and an impedance converter, wherein the pulse shaping circuit receives an input trigger pulse and is electrically connected to the avalanche circuit, and inputs direct current to the high-voltage conversion circuit and the low-voltage conversion circuit respectively; the high-voltage conversion circuit is electrically connected to the avalanche circuit through the high-voltage regulation circuit; the low-voltage conversion circuit is electrically connected to the first step circuit through the first low-voltage regulation circuit; the low-voltage conversion circuit is also electrically connected to the second step circuit through the second low-voltage regulation circuit; the avalanche circuit is electrically connected to the impedance converter via the first step circuit, the second step circuit, the differential circuit and the band-pass filter in sequence; and the impedance converter outputs a pulse signal.

[0008] Furthermore, the high-voltage regulating circuit regulates the avalanche voltage of the avalanche circuit, thereby controlling the output pulse amplitude of the avalanche circuit.

[0009] Furthermore, the first low-voltage regulating circuit can regulate the step current of the first step circuit, so that the step transistor of the first step circuit operates at different operating points, thereby forming an extremely fast rising edge in the range of 50ps-250ps.

[0010] Furthermore, the second low-voltage regulating circuit can regulate the step current of the second step circuit, so that the step pulse output by the first step circuit is quickly cut off, thereby forming a Gaussian pulse that rises quickly and then cuts off quickly.

[0011] Furthermore, the impedance transformer is a multi-section microstrip line.

[0012] Furthermore, the output pulse signal amplitude is adjusted in the range of 5V-120V, and the pulse width is adjusted in the range of 60ps-200ps.

[0013] Furthermore, the pulse generator operates at a repetition frequency of 1500 kHz.

[0014] Furthermore, the signal transmission line of the pulse generator forms a transmission impedance together with the bottom ground. By changing the width of the transmission line, the transmission impedance can be changed so that the impedance of the output pulse end reaches 50 ohms, thereby achieving impedance matching.

[0015] Furthermore, an SMA connector is welded at the output end of the pulse generator, and a high-performance coaxial transmission line is used for matching transmission.

[0016] The beneficial effects of the present invention are:

[0017] The ultra-fast picosecond differential Gaussian pulse generator disclosed in the present invention adopts avalanche technology, and an adjustment circuit is added to the avalanche circuit to achieve the purpose of adjustable pulse amplitude. The working repetition frequency is high, which can reach 1500kHz. This working repetition frequency can basically ensure that the vehicle-mounted detection speed reaches 80km / h, greatly improving the detection speed and detection efficiency. Two step circuits are designed to perform step processing on the leading and trailing edges of the pulse respectively to obtain ultra-fast Gaussian pulses. An adjustment circuit is added to these two step circuits to achieve the purpose of adjustable pulse width. The Gaussian pulse passes through a differential capacitor to achieve the differential function. The capacitor is then combined with the microstrip line to form a bandpass filter. A multi-section impedance transformer is used to achieve transmission impedance transformation and impedance matching transmission. Finally, a 50-ohm impedance circuit is formed by the microstrip line and the ground to achieve impedance matching of the ultra-fast picosecond differential Gaussian pulse, and finally outputs a differential Gaussian pulse with adjustable amplitude and pulse width to the air-coupled antenna. It has high center frequency, wide working frequency band, high working repetition frequency, compact structure, low heat generation, impedance matching with coaxial transmission system, and high radiation power. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a circuit block diagram of the pulse generator disclosed in the present invention;

[0019] Figure 2 It is a connection diagram of the step circuit in the pulse generator disclosed in the present invention;

[0020] Figure 3 It is an equivalent circuit diagram of the high-impedance microstrip line in the pulse generator disclosed in the present invention;

[0021] Figure 4 It is a schematic diagram of a single-section impedance matching device in the pulse generator disclosed in the present invention;

[0022] Figure 5 It is a schematic diagram of an optimized impedance converter in the pulse generator disclosed in the present invention;

[0023] Figure 6 is a calculation diagram of the microstrip line width of the pulse generator disclosed in the present invention;

[0024] Figure 7This is a diagram of the output pulse waveform of the pulse generator disclosed in the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention. At the same time, the specific embodiments described herein are merely examples thereof, and research related to the present invention should be included in the present invention and fall within the scope of protection of the present invention.

[0026] Example 1: This embodiment discloses an amplitude-adjustable 10ps ultra-fast differential Gaussian pulse generator, such as Figure 1 As shown, it includes a pulse shaping circuit, a high-voltage conversion circuit, a low-voltage conversion circuit, a high-voltage regulation circuit, an avalanche circuit, a first low-voltage regulation circuit, a first step circuit, a second low-voltage regulation circuit, a second step circuit, a differential circuit, a band-pass filter and an impedance converter, wherein the pulse shaping circuit receives an input trigger pulse and is electrically connected to the avalanche circuit, and inputs direct current to the high-voltage conversion circuit and the low-voltage conversion circuit respectively, the high-voltage conversion circuit is electrically connected to the avalanche circuit through the high-voltage regulation circuit, the low-voltage conversion circuit is electrically connected to the first step circuit through the first low-voltage regulation circuit, and the low-voltage conversion circuit is also electrically connected to the second step circuit through the second low-voltage regulation circuit, the avalanche circuit is electrically connected to the impedance converter through the first step circuit, the second step circuit, the differential circuit and the band-pass filter in sequence, and the impedance converter outputs a pulse signal.

[0027] Avalanche circuits can be connected in series using Marx cascade technology to obtain output pulses with higher amplitudes, thereby detecting relatively deeper targets.

[0028] The high-voltage regulating circuit regulates the avalanche voltage of the avalanche circuit, thereby controlling the output pulse amplitude of the avalanche circuit.

[0029] The first low-voltage regulating circuit can regulate the step current of the first step circuit, so that the step tube of the first step circuit operates at different operating points, thereby forming an extremely fast rising edge in the range of 50ps-250ps.

[0030] The second low-voltage regulating circuit can regulate the step current of the second step circuit, so that the step pulse output by the first step circuit is quickly cut off, thereby forming a Gaussian pulse that rises quickly and then cuts off quickly.

[0031] The differential circuit differentiates the resulting Gaussian pulse, and different differential capacitors have a significant impact on the final output. The bandpass filter filters the differentiated Gaussian pulse, retaining the desired frequency components and reducing the low-frequency components to ensure that the energy is within the required bandwidth.

[0032] A multi-section microstrip line quarter-wavelength impedance transformer was designed. This impedance transformer achieves transmission line matching and impedance transformation within a very confined space, enabling more efficient transmission of differential Gaussian pulse energy, improving transmission efficiency and maximizing transmitted energy. Furthermore, the multi-section impedance transformer can expand the operating frequency bandwidth of the pulse signal, enriching the transmitted signal energy and achieving detection objectives.

[0033] The pulse generator can be used to detect the thickness of each surface layer of asphalt roads with air-coupled antennas. The output pulse signal amplitude is adjustable in the range of 5V-120V, and the pulse width is adjustable in the range of 60ps-200ps. The pulse output form is a differential Gaussian pulse with good pulse symmetry.

[0034] The pulse generator generates pulses with essentially symmetrical amplitude and timing, effectively preventing signal oscillation and improving vertical resolution. Reasonable circuit parameter design and the selection of optimized transistors (selecting appropriate avalanche transistors and designing a reasonable avalanche circuit) enable the antenna to operate at a repetition frequency of 1500kHz.

[0035] The pulse generator output is unbalanced. The signal transmission line and the underlying ground plane form a transmission impedance. Changing the transmission line width can adjust the transmission impedance, ultimately achieving a 50 ohm impedance at the output pulse end, achieving impedance matching. An SMA connector is soldered to the output end, and a high-performance coaxial transmission line is used for matching transmission. This ensures maximum energy transmission to the antenna, radiating more energy for better detection results.

[0036] The input trigger pulse and input DC power are provided by the main control part of the ground penetrating radar, or by a pulse signal generator and a DC regulated power supply. The required pulse signal is output through an avalanche circuit, a step circuit, a differential circuit, an impedance matcher, etc.

[0037] The DC high-voltage module in this embodiment uses a high-voltage DC power supply module manufactured by Tianjin Hengbo High-Voltage Power Supply. This power supply module generates a fixed 150V high voltage. This high voltage is then passed through a voltage regulation circuit with a potentiometer, and the PBHV8540 is used to follow the output, increasing output capacity and ensuring the normal operation of the avalanche circuit. This high-voltage regulation circuit, when used in conjunction with the PBHV8540, allows the voltage divider adjusted by the potentiometer to stably follow the output, ensuring that the avalanche circuit has the ability to adjust the output amplitude. If the output amplitude is to be further increased, the Marx cascade technology can be used to ensure sufficient power and ensure the normal operation of the cascade circuit.

[0038] The step circuit diagram used in this embodiment is as follows Figure 2As shown in the figure, the first step recovery diode is connected in parallel to the pulse circuit to step the large, slow pulse generated by the avalanche, generating a fast-rising step pulse. The second step recovery diode is connected in series to quickly cut off the fast-rising step pulse, forming a Gaussian pulse with a rapid rise and then a rapid cutoff. The purpose of adding a step adjustment circuit to the circuit is to adjust the step current by adjusting the potentiometer, thereby controlling the amplitude of the output pulse and the time of the rapid rise or fall, thereby achieving adjustable output amplitude and pulse width.

[0039] This embodiment designs a microstrip line with a variable width. The two parallel capacitors of the microstrip line with a narrower width can be ignored. The circuit is equivalent to a series inductor. The inductor and the capacitor form a bandpass filter. The method of combining capacitors and microstrip lines to generate a bandpass filter is used to filter out clutter. The microstrip line equivalent circuit diagram is shown in the figure below. Figure 3 shown.

[0040] This embodiment uses a quarter-wavelength impedance transformer with multiple sections of microstrip lines. The schematic diagram of a single-section impedance transformer is shown in FIG. Figure 4 As shown. Since the frequency band of a single-section impedance converter is relatively narrow, this embodiment uses a multi-section impedance converter and optimizes its connection to reduce the impedance mutation, thereby reducing the reflection caused by the impedance change when the microstrip line width changes. The optimized schematic diagram of the multi-section impedance converter is shown in Figure 5 shown.

[0041] By using impedance converters to match transmission lines and achieve impedance transformation within a very confined space, differential Gaussian pulse energy is transmitted more effectively, further improving transmission efficiency and maximizing transmitted energy. Furthermore, multi-section impedance converters can expand the operating bandwidth of the pulse signal, enriching the transmitted signal energy and achieving detection objectives.

[0042] This embodiment finally uses high-performance and high-quality coaxial cable for output, and its characteristic impedance is 50 ohms. Therefore, the impedance of the microstrip line should be 50 ohms at the final output. The microstrip line width is calculated using the microstrip line calculation software TXLINE. The microstrip line schematic and microstrip line calculation are as follows: Figure 6 As shown in the figure, since the operating center frequency of the designed pulse generator has reached above 2 GHz and the broadband signal can reach 4 GHz, the high-frequency dielectric board Rogers 4350 is selected, which has a dielectric constant of about 3.5.

[0043] The measured output pulse waveform of this embodiment is as follows Figure 7This graph was measured using a DSOX6004A oscilloscope, with its input port set to 50 ohm impedance. When testing with 50 ohm impedance, the input pulse amplitude must be within ±5V to protect the oscilloscope. This example was tested with two 20dB attenuators. The test result shows 1.04V, but the actual value should be 104V. The graph shows a peak-to-peak output pulse of 116ps, with a single pulse rise time of approximately 60ps. The waveform is very symmetrical.

Claims

1. An amplitude-adjustable 10ps ultra-fast differential Gaussian pulse generator, characterized by: It includes a pulse shaping circuit, a high-voltage conversion circuit, a low-voltage conversion circuit, a high-voltage regulation circuit, an avalanche circuit, a first low-voltage regulation circuit, a first step circuit, a second low-voltage regulation circuit, a second step circuit, a differential circuit, a band-pass filter and an impedance converter, wherein the pulse shaping circuit receives an input trigger pulse and is electrically connected to the avalanche circuit, inputs direct current to the high-voltage conversion circuit and the low-voltage conversion circuit respectively, the high-voltage conversion circuit is electrically connected to the avalanche circuit through the high-voltage regulation circuit, the low-voltage conversion circuit is electrically connected to the first step circuit through the first low-voltage regulation circuit, the low-voltage conversion circuit is also electrically connected to the second step circuit through the second low-voltage regulation circuit, the avalanche circuit is electrically connected to the impedance converter in sequence through the first step circuit, the second step circuit, the differential circuit and the band-pass filter, and the impedance converter outputs a pulse signal; The high voltage regulating circuit regulates the avalanche voltage of the avalanche circuit, thereby controlling the output pulse amplitude of the avalanche circuit; The first low-voltage regulating circuit can regulate the step current of the first step circuit so that the step transistor of the first step circuit operates at different operating points, thereby forming an extremely fast rising edge in the range of 50ps-250ps; The second low-voltage regulating circuit can regulate the step current of the second step circuit so that the step pulse output by the first step circuit is quickly cut off, thereby forming a Gaussian pulse that rises quickly and then cuts off quickly; The output pulse signal amplitude is adjustable in the range of 5V-120V, and the pulse width is adjustable in the range of 60ps-200ps; The pulse generator operates at a repetition frequency of 1500kHz.

2. The 10 ps ultra-fast differential Gaussian pulse generator with adjustable amplitude according to claim 1, characterized in that: The impedance transformer is a multi-section microstrip line.

3. The 10 ps ultra-fast differential Gaussian pulse generator with adjustable amplitude according to claim 1, characterized in that: The signal transmission line of the pulse generator forms a transmission impedance together with the bottom ground. By changing the width of the transmission line, the transmission impedance can be changed so that the impedance of the output pulse end reaches 50 ohms, achieving impedance matching.

4. The 10 ps ultra-fast differential Gaussian pulse generator with adjustable amplitude according to claim 1, characterized in that: Solder an SMA connector to the output end of the pulse generator and use a high-performance coaxial transmission line for matching transmission.

Images