Method for implementing novel low-distortion digital-modulation direct-drive power amplifier device

Abstract

The present invention relates to the field of plasma generation radio-frequency power supplies, and provides a method for implementing a novel low-distortion digital-modulation direct-drive power amplifier device. In the method, the acquisition of a modulated waveform signal is achieved by using a Δ-Σ oversampling technique, the sampling rate of the modulated waveform signal is further improved by means of an interpolation filter within a PDM pulse distribution unit, and an exciter can generate a multi-phase PDM modulated waveform pulse and a carrier drive pulse, thereby directly driving a power amplifier module to complete carrier generation and waveform modulation. Multi-phase PDM modulation can achieve a better total harmonic distortion (THD) index of a modulated waveform, ensuring that a modulated waveform signal is basically restored without any distortion; however, in order to reduce system complexity and take into account the THD index of the modulated waveform, multi-phase PDM modulation is generally controlled to be within 12 phases. In addition, a modulated waveform signal is divided into multiple equal-amplitude PDM square-wave signals by means of multi-phase PDM modulation and a superposition technique, allowing a power amplifier to operate in a switching state, thereby improving the efficiency of the power amplifier.

Description

A novel method for implementing a low-distortion digital modulation direct-drive power amplifier.

[0001] This application claims priority to Chinese Patent Application No. 202411442074.0, filed on October 16, 2024, entitled "A Method for Implementing a Novel Low-Distortion Digital Modulation Direct Drive Power Amplifier Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to the field of plasma generation radio frequency power supplies, and in particular to a method for implementing a novel low-distortion digital modulation direct drive power amplifier device. Background Technology

[0003] Plasma, a state of matter primarily composed of free electrons and charged particles, is widely present in the universe and is known as the fourth state of matter. It possesses high electrical conductivity and is rich in high-energy electrons, ions, and reactive substances, making it widely applicable in fields such as food processing, metal smelting, environmental remediation, biomedicine, semiconductor etching and thin film deposition, surface cleaning, and aerospace. In practical applications of plasma, the specialized power supply used to generate it is crucial. These typically consist of four types: high-voltage DC power supplies, high-voltage pulse power supplies, high-frequency AC power supplies, and radio frequency (RF) power supplies. RF power supplies are predominantly used in the nuclear technology and semiconductor manufacturing industries. When RF power supplies excite plasma, significant reflection signals are generated during the initial plasma establishment phase due to drastic changes in load impedance. These reflection signals are highly detrimental to the RF power supply. To mitigate this damage, the RF signal is typically modulated using waveforms such as trapezoidal waves or exponential function waves during the initial plasma establishment phase to reduce the accumulation of reflected energy in a short period.

[0004] Currently, there are patents in the industry that disclose how to implement low-distortion power amplifiers. For example, patent number 202110545047.6 discloses a method for implementing a high-power, low-distortion Class D power amplifier based on a high-performance MCU. The main steps are: 1) Selecting and displaying the input signal mode. 2) Preprocessing the input signal to obtain audio data. 3) Transmitting the audio data to the STM32F407 minimum system and outputting PWM to the half-bridge driver module. 4) Each pair of half-bridge driver modules drives a full-bridge power amplification section to achieve power amplification of small signals. 5) Filtering the output of the full-bridge power amplification section. 6) Sampling the current of the output after passing through the low-pass filter and feeding it back to the minimum system. 7) Setting the digital filter according to the output feedback signal to filter the audio data in step 1). 8) Repeating steps 2)-7) to achieve negative feedback control of the output. This invention solves the problem of noise interference at the moment of power-on of Class D power amplifiers at a relatively low cost. It can also compensate for high frequencies through IIR, solving the problem of high filter requirements for Class D power amplifiers at low switching frequencies.

[0005] This invention patent provides a method for implementing a novel low-distortion digital modulation direct drive power amplifier device. This method enables a new technology, a new system, and a new architecture for digital modulation direct drive plasma generation radio frequency power supply. Summary of the Invention

[0006] In view of the problems in a method known to the inventors, the purpose of this invention is to provide a method for implementing a novel low-distortion digital modulation direct drive power amplifier device, which solves the problem described in the background art above: this method can realize a new technology, a new system, and a new architecture for digital modulation direct drive plasma generation radio frequency power supply.

[0007] This invention employs the following technical solution: a method for implementing a novel low-distortion digital modulation direct-drive power amplifier device, comprising: an exciter, which acquires and processes signals of different waveform formats and generates polyphase PDM modulated waveform pulses and carrier drive pulses; and a PDM pulse distribution unit, which further improves the sampling rate of the modulated waveform signal; wherein, this method acquires the modulated waveform signal through Δ-Σ oversampling technology, further improves the sampling rate of the modulated waveform signal through interpolation filters in the PDM pulse distribution unit, and the exciter can generate polyphase PDM modulated waveform pulses and carrier drive pulses, directly driving the power amplifier module to complete carrier generation and waveform modulation.

[0008] The beneficial effects of this invention are as follows: The exciter disclosed in this invention receives modulated waveform signals of various formats (analog signals, digital signals, and text signals) from external sources. The digital signals and text signals are digital modulated waveform signals, with a sampling rate typically of 48kHz. The analog modulated waveform signals undergo analog-to-digital conversion via a modulated waveform AD chip, with a sampling rate typically of 96kHz. Therefore, to facilitate FPGA processing and save FPGA logic resources, a uniform modulated waveform sampling rate of 48kHz is selected. The digital modulated waveform signals are then converted to 48kHz via a modulation waveform rate / format conversion before being sent to the FPGA. The current input modulated waveform format can be selected via a host computer / DIP switch. The number of phases N can be selected via the host computer / DIP switch. The 48kHz modulated waveform signal is then passed through an interpolation filter within the FPGA to increase the sampling rate to 0.048*N kHz. Since the frequency range of radio frequency is 500kHz to 15MHz, a higher number of phases makes it easier to filter out the sampling switching frequency. The interpolated 0.048*N kHz modulated waveform signal is compared with a single-phase triangular wave signal to obtain a PDM pulse signal with a pulse width proportional to the amplitude of the modulated waveform. If 6-phase modulation is selected, then the frequency of the triangular wave signal is 48kHz × 6 = 288kHz.

[0009] As shown in Figures 2 and 3 of this specification, the modulated waveform signals are simultaneously input into different comparators. The phase difference between adjacent N triangular wave signals is 360° / N. After passing through the comparators, multi-phase PDM modulation of the modulated waveform is achieved. The modulated waveform components are in parallel, and the high-frequency noise signal generated by the modulation is a frequency superposition relationship. Therefore, the harmonic frequency is increased, which is more conducive to the miniaturization of the subsequent low-pass filter. Multi-phase PDM modulation can achieve better THD (Total Harmonic Distortion) performance of the modulated waveform, ensuring that the modulated waveform signal is recovered with virtually no distortion. However, to reduce system complexity and maintain the THD performance, multi-phase PDM modulation is generally controlled to within 12 phases. Furthermore, multi-phase PDM modulation and superposition techniques divide the modulated waveform signal into multiple equal-amplitude PDM square wave signals, enabling the power amplifier to operate in a switching state and improving the power amplifier's efficiency.

[0010] Instruction manual illustrations

[0011] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0012] Figure 1 is a system principle block diagram according to one or more embodiments;

[0013] Figure 2 is a block diagram of the PDM principle generated by exciter modulation waveform processing according to one or more embodiments;

[0014] Figure 3 is a block diagram illustrating the principle of multiphase PDM generation according to one or more embodiments;

[0015] Figure 4 is a schematic diagram of a single-phase PDM signal generation principle according to one or more embodiments;

[0016] Figure 5 is a schematic diagram of a three-phase PDM signal generation principle according to one or more embodiments;

[0017] Figure 6 is a schematic diagram of a nine-phase PDM signal generation principle according to one or more embodiments;

[0018] Figure 7 is a block diagram of the PDM modulation principle of a single power amplifier module according to one or more embodiments;

[0019] Figure 8 is a block diagram of a single power amplifier module H-bridge according to one or more embodiments. Detailed Implementation

[0020] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific figures. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of this application can be combined with each other.

[0021] Example 1

[0022] Please refer to Figure 1, which is a system principle block diagram of a novel low-distortion digital modulation direct drive power amplifier device.

[0023] A method for implementing a novel low-distortion digital modulation direct drive power amplifier includes: an exciter, which acquires and processes signals of different waveform formats and generates polyphase PDM modulated waveform pulses and carrier drive pulses.

[0024] The PDM pulse distribution unit further improves the sampling rate of the modulated waveform signal.

[0025] This method acquires the modulated waveform signal through Δ-Σ oversampling technology, further improves the sampling rate of the modulated waveform signal by interpolating the filter through the PDM pulse distribution unit, and the exciter can generate polyphase PDM modulated waveform pulses and carrier drive pulses to directly drive the power amplifier module to complete carrier generation and waveform modulation.

[0026] Please refer to Figure 1. This device includes an exciter, a control unit, a PDM pulse distribution unit, an RF drive distribution unit, a power supply unit, a power amplifier module unit, a matching conversion unit, a power detection unit, a matching box, and a cavity. RS485 is the communication interface.

[0027] Please refer to Figure 1. The exciter mainly performs functions such as acquiring and processing signals of different waveform formats (analog signals, digital signals, and text signals) and generating n multi-phase PDM modulated waveform drive signals, generating RF drive signals, switching internal and external clock references, sampling and acquiring RF voltage and current, and sampling and acquiring power supply data from the power amplifier module. In Figure 1, the synchronization signal is input to the exciter at 1pps and 1kHz frequency. An external reference signal (10MHz) is also input for switching between internal and external clock references. PDM 1, PDM 2...PDM n are the n multi-phase PDM modulated waveform drive signals generated by the exciter.

[0028] Please refer to Figure 1. The PDM pulse distribution unit mainly distributes the n-channel PDM modulated waveform drive signals generated by the exciter, and sends them to the BUCK (buck converter) circuit of the power amplifier module to generate the modulation voltage of the modulated waveform. (N1...) * PDM 1, N1 * PDM 2...N1 * PDM n is assigned to the power amplifier module unit.

[0029] Please refer to Figure 1. The RF drive distribution unit mainly distributes one RF drive signal (RF_Driver) generated by the exciter to the H-bridge circuit of the power amplifier module to generate the carrier voltage. (The N signal is then referred to as N.) * The RF_Driver is fed into the power amplifier module unit.

[0030] Please refer to Figure 1. The matching transformation unit completes impedance change and suppression of specific frequencies through T-type impedance matching and suppression network.

[0031] Please refer to Figure 1. The power supply unit mainly generates the 400V voltage required by the BUCK input of the power amplifier module unit after external power input rectification and filtering, as well as the auxiliary power required by other systems of the whole machine (such as ±15V, +5V, etc.).

[0032] Please refer to Figure 1. The control unit completes the status reading and logic control of all subsystems, as well as external interlocking control and remote control. To ensure system reliability, remote control uses ordinary I / O ports instead of communication-based control, which greatly reduces abnormal shutdowns caused by communication unreliability. The control unit communicates with the computer via Ethernet. Subsystems refer to modules such as the exciter, control unit, PDM pulse distribution unit, RF drive distribution unit, power supply unit, power amplifier module unit, resonant matching conversion unit, power detection unit, and matching box.

[0033] Example 2

[0034] Please refer to Figures 2-8. This embodiment has the same features as Embodiment 1 above, and the similarities will not be elaborated in this embodiment. The specific differences are as follows.

[0035] Referring to Figure 2, the exciter of this invention receives modulated waveform signals in various formats (analog signals, digital signals, and text signals) from external sources. The digital and text signals are digital modulated waveform signals, typically with a sampling rate of 48kHz. The analog modulated waveform signals undergo analog-to-digital conversion via a modulated waveform AD chip, which typically has a sampling rate of 96kHz. To facilitate FPGA processing and conserve FPGA logic resources, a uniform modulation waveform sampling rate of 48kHz is selected. The digital modulated waveform signals are then converted to 48kHz via modulation waveform rate / format conversion before being sent to the FPGA. The current input modulation waveform format can be selected via the host computer / DIP switch. The number of phases N can be selected via the host computer / DIP switch. The 48kHz modulated waveform signal is then passed through an interpolation filter within the FPGA to increase the sampling rate to 0.048*N kHz. Since the RF frequency range is 500kHz to 15MHz, a higher number of phases makes it easier to filter out the sampling switch frequency. The interpolated 0.048*N kHz modulated waveform signal is compared with a single-phase triangular wave signal to obtain a PDM pulse signal with a pulse width proportional to the amplitude of the modulated waveform. If 6-phase modulation is selected here, then the frequency of the triangular wave signal is 48kHz × 6 = 288kHz.

[0036] Referring to Figure 3, the modulated waveform signals of this invention are simultaneously input into different comparators. The phase difference between adjacent N triangular wave signals is 360° / N. After passing through the comparators, multi-phase PDM modulation of the modulated waveform is achieved. The modulated waveform components are in parallel, and the high-frequency noise signal generated by the modulation is a frequency superposition relationship, thus increasing the harmonic frequency, which is more conducive to the miniaturization of the subsequent low-pass filter. Multi-phase PDM modulation can achieve better THD (Total Harmonic Distortion) performance of the modulated waveform, ensuring that the modulated waveform signal is basically restored without distortion. However, in order to reduce the complexity of the system and take into account the THD performance of the modulated waveform, the multi-phase PDM modulation is generally controlled to within 12 phases. In addition, the multi-phase PDM modulation and superposition technology divides the modulated waveform signal into multiple equal-amplitude PDM square wave signals, so that the power amplifier operates in a switching state, improving the efficiency of the power amplifier. N triangular wave signals are represented as sawtooth(wt+0), sawtooth(wt+360*1 / N)...sawtooth(wt+360*n / N), where n=1, 2...N-1, w=48kHz×N.

[0037] Please refer to Figure 4. The present invention generates a PDM pulse signal with a pulse width proportional to the amplitude of the modulated waveform signal by comparing the modulated waveform signal and the triangular wave signal.

[0038] Example 3

[0039] Please refer to Figures 2-8. This embodiment has the same features as Embodiments 1 and 2 above. The similarities will not be elaborated in this embodiment. The specific differences are as follows.

[0040] Please refer to Figure 5. In this invention, three triangular wave signals are 120° apart from each other, which is equivalent to each triangular wave signal being 120° apart. When the amplitude of the modulated waveform is higher than the amplitude of the triangular wave at a certain moment, the number of times is equal to the amplitude of the PDM pulse. Since it is a 3-phase PDM, the maximum PDM amplitude after final synthesis is 3 and the minimum is 0. The higher the PDM amplitude, the larger the modulated waveform signal, and vice versa.

[0041] Please refer to Figure 6. In this invention, nine triangular wave signals are spaced 40° apart from each other, which is equivalent to each triangular wave signal being spaced 40° apart. The number of times the amplitude of the modulated waveform is higher than the amplitude of the triangular wave at a certain moment is the amplitude of the PDM pulse. Because there is a 9-phase PDM, the maximum PDM amplitude after final synthesis is 9 and the minimum is 0. The higher the PDM amplitude, the larger the modulated waveform signal, and vice versa.

[0042] The exciter generates a multiphase PDM modulated waveform pulse signal, and the power amplifier module completes the modulation of the multiphase PDM signal. Here, multiphase generally refers to three-phase, four-phase, six-phase, nine-phase, twelve-phase, or sixteen-phase.

[0043] Example 4

[0044] Please refer to Figures 2-8. This embodiment has the same features as Embodiments 1, 2 and 3 above. The similarities will not be elaborated in this embodiment. The specific differences are as follows.

[0045] Please refer to Figure 7, where N represents the number of phases in a single module. Generally, to reduce the complexity of PDM modulation in a single power amplifier module and to ensure the flexible application of a single module (a single module can stand alone as a system power amplifier), N is usually chosen to be 3 or 4. Once the number of phases in a single module is determined, the number of phases in the overall PDM system will be an integer multiple of 3 or 4. Taking a single module with 4 PDM phases as an example, to obtain better modulation waveform distortion, we can choose 16-phase / 12-phase PDM for the entire system, thus grouping 4 / 3 power amplifier modules together.

[0046] When there is no waveform modulation, the carrier level is modulated by adjusting the fixed duty cycle of the PDM. The higher the duty cycle, the higher the carrier level, and the lower the duty cycle, the lower the carrier level. The waveform modulation formula is shown below.

[0047] S AM (t)=[A0 + A m cosΩt](cosω c t+θ c )=A0[1+m cos Ωt](cosω c t+θ c ) (Formula 1).

[0048] in m represents the modulation depth, S AM (t) represents the modulated carrier level, A0 represents the carrier amplitude, and A m Let cosΩt be the carrier amplitude, and cosω be the modulation signal. c t is the carrier signal, θ c This is the initial phase angle.

[0049] Since the BUCK input is 400V, the carrier level must not exceed 200V to satisfy ±100% modulation. Therefore, the PDM duty cycle must not exceed 50%. The carrier level is equivalent to adding a DC bias to the modulated waveform. The PDM pulse generated by superimposing the carrier level and the modulated waveform level and comparing it with the triangular wave contains the amplitude information of the carrier and the modulated waveform information. The frequency and phase information of the carrier are mainly obtained by the inverter H-bridge circuit after the BUCK circuit in the power amplifier module. The exciter outputs one RF drive signal, which is distributed to each power amplifier module through the RF drive distribution board to complete the control of the H-bridge circuit. The frequency of the H-bridge drive pulse signal is the carrier frequency. If synchronization with other devices is required, the rising edge of the H-bridge drive pulse signal needs to be synchronized with the synchronization signal.

[0050] Please refer to Figure 8. In Figure 8 of this invention, the dead time of the H-bridge and the H-bridge drive pulse signal are generated by the radio frequency drive signal after processing by the circuit, and the dead time is controlled within tens of ns. This meets the requirement of a plasma generation radio frequency power supply frequency range of 500kHz to 15MHz.

[0051] A single power amplifier module can be designed to output 2.5kW, supporting 3-phase / 4-phase PDM modulation. Three / four power amplifier modules support 9-phase / 12-phase / 16-phase PDM modulation. Depending on the required power of the entire unit, the number of modules can be combined to achieve an output power of 2kW to 400kW. If higher power output is required, it can be achieved up to the MW level through parallel connection. High-efficiency and low-distortion RF power supplies can be achieved through multi-phase PDM modulation and switching amplifiers, with power amplifier efficiency >90% and distortion <1%.

[0052] Furthermore, the PDM described in this invention is a modulation method for providing analog signals in the digital domain. In a PDM signal, logic "1" represents a single pulse, and logic "0" represents no pulse. Typically, logic "1" and logic "0" are discontinuous, with logic "1" being relatively evenly distributed throughout each modulation signal period. A single pulse does not represent amplitude; rather, the density of a series of pulses corresponds to the amplitude in an analog signal. A PDM signal composed entirely of "1"s corresponds to a voltage with a positive amplitude; a PDM signal composed entirely of "0"s corresponds to a voltage with a negative amplitude; and alternating "1"s and "0"s correspond to intermediate amplitudes.

[0053] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for implementing a novel low distortion digital modulation direct drive power amplifier device, characterized in that, include: The exciter acquires and processes signals of different waveform formats and generates polyphase PDM modulated waveform pulses and carrier drive pulses. The PDM pulse distribution unit further improves the sampling rate of the modulated waveform signal. This method acquires the modulated waveform signal through Δ-Σ oversampling technology, further improves the sampling rate of the modulated waveform signal by interpolating the filter through the PDM pulse distribution unit, and the exciter can generate polyphase PDM modulated waveform pulses and carrier drive pulses to directly drive the power amplifier module to complete carrier generation and waveform modulation.

2. The implementation method of the novel low distortion digital modulation direct drive power amplifier device according to claim 1, characterized in that: The exciter completes the acquisition and processing of signals of different waveform formats, and generates n multi-phase PDM modulated waveform driving signals, RF driving signals, internal and external clock reference switching, RF voltage and current sampling acquisition, and power amplifier module power supply sampling acquisition.

3. The implementation method of the novel low distortion digital modulation direct drive power amplifier device according to claim 1, characterized in that: The PDM pulse distribution unit distributes the n-channel PDM modulated waveform drive signals generated by the exciter, and the distributed signals are sent to the BUCK circuit of the power amplifier module unit to generate the modulation voltage of the modulated waveform.

4. The implementation method of the novel low distortion digital modulation direct drive power amplifier device according to claim 1, characterized in that: The implementation method of this novel low-distortion digital modulation direct drive power amplifier device also includes an RF drive distribution unit, which completes the distribution of one RF drive signal generated by the exciter and sends it to the H-bridge circuit of the power amplifier module unit to complete the generation of carrier voltage.

5. The implementation method of the novel low distortion digital modulation direct drive power amplifier device according to claim 2, characterized in that: The implementation method of this novel low-distortion digital modulation direct drive power amplifier also includes a matching transformation unit, which completes impedance change and suppression of specific frequencies through T-type impedance matching and suppression network.

6. The implementation method of the novel low distortion digital modulation direct drive power amplifier device according to claim 5, characterized in that: The implementation method of this novel low-distortion digital modulation direct drive power amplifier device also includes a power supply unit, which generates the voltage required for the BUCK input of the power amplifier module unit and the auxiliary power required for other systems of the whole machine after completing the external power input rectification and filtering.

7. The implementation method of the novel low distortion digital modulation direct drive power amplifier device according to claim 1, characterized in that: The implementation method of this novel low-distortion digital modulation direct drive power amplifier also includes a control unit, which performs status reading and logic control of all subsystems of the system, as well as external interlocking control and remote control control.

8. The implementation method of the novel low distortion digital modulation direct drive power amplifier device according to claim 7, characterized in that: The remote control is achieved using a standard I / O port.

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