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EP-4742528-A1 - HIGH-FREQUENCY SIGNAL GENERATING DEVICE

EP4742528A1EP 4742528 A1EP4742528 A1EP 4742528A1EP-4742528-A1

Abstract

A radio-frequency signal generator according to the present invention includes: (A) a clock signal generation unit that generates a clock signal using harmonic components that are generated by a nonlinear amplifier; (B) a DDS (direct digital synthesizer) that uses the clock signal as a system clock for performing internal processing and generates a frequency signal having a frequency that is set in frequency setting data; and (C) a higher frequency unit that is composed of an inactive frequency multiplier that does not use active elements and that increases the frequency of the frequency signal generated by the DDS. The clock signal is generated by using the harmonic components that are generated by the nonlinear amplifier, an increase in speed is handled by shortening a delay time in a variable function of the frequency, and a high C/N ratio is handled by suppressing a spurious emission and a phase noise.

Inventors

  • TEI, UNBOU

Assignees

  • Kyosan Electric Mfg. Co., Ltd.

Dates

Publication Date
20260513
Application Date
20240401

Claims (6)

  1. A radio-frequency signal generator, comprising: a clock signal generation unit configured to generate a clock signal using harmonic components generated by an amplifier having nonlinearity; a direct digital synthesizer (DDS) configured to generate a frequency signal with a frequency set in frequency setting data, using the clock signal as a system clock for performing internal processing; and a higher frequency unit consisting of an inactive frequency multiplier with no active elements and configured to increase the frequency of the frequency signal generated by the DDS.
  2. The radio-frequency signal generator according to claim 1, wherein the clock signal generation unit comprises: a reference signal oscillator configured to generate a periodic signal at a specified frequency as a reference signal; a nonlinear amplifier configured to generate harmonic components for a fundamental wave of the reference signal; a narrowband harmonic filter configured to pass only the harmonic components; and a radio-frequency amplifier configured to amplify the harmonic components passed through the narrowband harmonic filter, and the clock signal generation unit is configured to generate an output signal in the radio-frequency amplifier as a clock signal.
  3. The radio-frequency signal generator according to claim 1, wherein the higher frequency unit comprises: a differential output unit configured to generate a differential signal of the frequency signal in the DDS; an inactive frequency multiplier configured to multiply a frequency of the differential signal; and a target frequency band filter configured to pass a target frequency component from a multiplication signal thus multiplied, and the higher frequency unit is configured to use the frequency component passed through the target frequency band filter as an output signal.
  4. The radio-frequency signal generator according to claim 1, wherein the clock signal generation unit comprises: a reference signal oscillator configured to generate a frequency signal at a specified frequency as a reference signal; a nonlinear amplifier configured to generate harmonic components for a fundamental wave of the reference signal; a narrowband harmonic filter configured to pass only the harmonic components; and a radio-frequency amplifier configured to amplify the harmonic components passed through the narrowband harmonic filter, and the clock signal generation unit is configured to generate an output signal in the radio-frequency amplifier as a clock signal, and wherein the higher frequency unit comprises: a differential output unit configured to generate a differential signal of the frequency signal in the DDS; an inactive frequency multiplier configured to multiply a frequency of the differential signal; and a target frequency band filter configured to passe a target frequency component from a multiplication signal thus multiplied, and the higher frequency unit is configured to output the frequency component passed through the target frequency band filter as an output signal.
  5. The radio-frequency signal generator according to claim 2 or 4, wherein the nonlinear amplifier is a buffer amplifier or a class-C amplifier.
  6. The radio-frequency signal generator according to claim 3 or 4, wherein the differential output unit is a differential amplifier or a harmonic transformer, and the inactive frequency multiplier is a rectifier type multiplier consisting of Schottky diodes or rectifier diodes.

Description

[TECHNICAL FIELD] The present invention relates to a radio-frequency signal generator in which an output frequency is variable. [BACKGROUND ART] Linear amplifier-type radio-frequency power supplies, which are used in semiconductor manufacturing equipment, liquid crystal panel manufacturing equipment and others, supply radio-frequency signals (RF signals) in VHF to UHF bands (100 MHz to 1 GHz). The radio-frequency power supplies have a radio-frequency signal generator to generate radio-frequency signals (RF signals) with variable frequency. As radio-frequency signal generators for generating a radio-frequency signal (RF signal) with variable frequency, there are known frequency synthesizers employing a direct digital synthesizer (DDS) (see Patent Literatures 1 and 2). These frequency synthesizers include a frequency mixer and a phase-locked loop (PLL) circuit that increase the frequency of DDS signals as peripheral devices of the DDS. Figure 4A shows a configuration example of a radio-frequency signal generator having a frequency mixer. A radio-frequency signal generator 100 includes a reference signal oscillator 101 that generates a periodic signal at a specific frequency, a DDS 102 that generates a signal at a frequency specified by frequency setting data using the output from the reference signal oscillator 101 as a clock signal, a local oscillator 103 that outputs a local oscillation wave, a mixer 104 that mixes the output signal from the DDS 102 with the local oscillation wave, a multiplier 105 that multiplies a mixed signal produced by the mixer 104, and a frequency divider 106 that divides a signal output from the multiplier 105. A frequency division ratio of the frequency divider 106 is varied on the basis of the frequency setting data to thereby vary an output frequency. Figure 4B shows a configuration example of a radio-frequency signal generator having a PLL circuit. A radio-frequency signal generator 110 includes a clock signal source 111 that outputs a clock signal, a DDS 112 that generates a signal at the frequency specified by frequency setting data based on the clock signal, a PLL circuit 113 that outputs an oscillation signal at a set frequency on the basis of the frequency of the DDS signal, and a control unit 114 that outputs the frequency setting data. The PLL circuit 113 includes a phase comparator 113a, a loop filter 113b, a voltage control oscillator (VOC) 113c, and a frequency divider 113d. [PRIOR ART DOCUMENT] [PATENT LITERATURE] [Patent Literature 1] Japanese Patent Laid-Open Publication No. 2000-124740[Patent Literature 2] Japanese Patent Laid-Open Publication No. 2022-113497 [SUMMARY OF THE INVENTION] [PROBLEMS TO BE SOLVED BY THE INVENTION] The radio-frequency signal generators, which is known as a frequency synthesizer, using the conventional DDS for generating a frequency signal with variable frequency have problems, such as a delay time occurring in the PLL circuit and decrease in a carrier-to-noise ratio (C/N ratio) caused by a spurious emission and phase noise generation occurring in the peripheral devices of the DDS and the PLL circuit. When the frequency is variable, response characteristics of the frequency mixer or the voltage control oscillator (VOC) of the PLL circuit cause a delay in an output signal, and a lock-up time taken to lock a PLL output to a predetermined frequency in a PLL loop becomes approximately 1 ms to several ms. Figure 5 shows an example of a delay time in a radio-frequency signal generator having a PLL circuit. When a frequency is changed from f1 to f2, a writing process of frequency data of a PLL to a DDS is carried out. As an example of such a case, it takes 1.72 ms to write, and the time taken for the frequency to stabilize due to repetitive processing in the PLL loop is 38.67 ms when the frequency is changed from 450 MHz to 460 MHz, and is 34.67 ms when the frequency is changed from 460 MHz to 450 MHz. Furthermore, due to the circuit elements, such as the frequency mixer and the voltage control oscillator (VOC) of the PLL circuit, the spurious emission and the phase noise cause the decrease in the carrier-to-noise ratio (C/N ratio) of the frequency signal generated by the radio-frequency signal generator. Figure 6 is a schematic diagram that illustrates the spurious emission and the phase noise. In a case where a modulation signal for modulating the phase of a carrier signal is a periodic signal, a harmonic spurious emission occurs at a frequency that is integer multiple of a fundamental wave. The phase noise occurs in a double sideband of the carrier signal and is expressed as the carrier-to-noise ratio (C/N ratio). In the field of radio-frequency signal generator, if it is required to generate an output signal with fast and variable frequency and having a high C/N ratio, conventional radio-frequency signal generators have a problem of difficulty in achieving fast frequency and high C/N ratio due to the delay in the lock-up time, the spurious e