A low phase noise sapphire oscillator

Abstract

The present application discloses a low-phase-noise sapphire oscillator, which includes a main loop, a phase-locked loop, and a frequency discrimination loop. In the main loop, the oscillation output by the sapphire resonator passes through a low-noise amplifier, a band-pass filter, and a first voltage-controlled phase shifter, and then a part of it is output through the first branch of the first coupler, and the other part is sent to the input end of the sapphire resonator as a loop-back signal through the second branch of the first coupler. In the frequency discrimination loop, the loop-back signal generates a second sampling signal through the third coupler, and after passing through the second voltage-controlled phase shifter, it is mixed with the reflection signal at the input end of the sapphire resonator to generate a first voltage-controlled signal to control the first voltage-controlled phase shifter. In the phase-locked loop, the loop-back signal generates a first sampling signal through the second coupler, and after frequency division, it is mixed with the oscillation output by the crystal oscillator to generate a second voltage-controlled signal to control the second voltage-controlled phase shifter. The present application solves the problem of poor near-end phase noise performance of the existing sapphire oscillator.

Description

Technical Field

[0001] This application relates to the field of microwave technology, and particularly to a sapphire oscillator with ultra-low phase noise. Background Art

[0002] As a commonly used frequency source in weapon systems, the phase noise of an oscillator is a very critical technical index, directly affecting the performance of modern electronic systems. In modern receivers, large dynamic range, high selectivity, wideband frequency agility, etc. are all limited by phase noise. Especially in a complex electromagnetic environment, the phase noise of the local oscillator signal directly affects the extraction of weak and useful signals during the mixing process; in modern communication systems, phase noise not only affects the bit error rate and carrier frequency tracking accuracy, but also affects the measurement of in-channel and out-of-channel performance of communication receivers.

[0003] The sapphire resonator has ultra-low dielectric loss and a resonant frequency range in the high-frequency band, and has received more and more attention in recent years. It is commonly used in the research and production of X-band low-phase-noise dielectric oscillators. Since no frequency doubling or other operations are required, the far-end phase noise performance of the oscillator is excellent. However, the resonant frequency of the sapphire resonator is greatly affected by temperature changes, which results in poor near-end phase noise performance of the sapphire oscillator. It is very necessary to study a sapphire oscillator with low noise, miniaturization, and high frequency stability. In addition to possible theoretical analysis, there have been mainly two solutions to this situation in the past: one method is to improve the temperature control accuracy of the constant-temperature device of the sapphire resonator, which increases the complexity and development difficulty of the system equipment, and thus increases the cost; the other method is to lock the output signal to a 100 MHz crystal oscillator through frequency division. This method will deteriorate the far-end phase noise performance of the oscillator to a certain extent based on the noise floor of the frequency division device itself. Summary of the Invention

[0004] This application proposes a low-phase-noise sapphire oscillator to solve the problem of poor near-end phase noise performance of existing sapphire oscillators.

[0005] An embodiment of this application provides a low-phase-noise sapphire oscillator, including a main loop, a phase-locked loop, and a frequency discrimination loop.

[0006] In the main loop, the oscillation output by the sapphire resonator passes through a low-noise amplifier, a band-pass filter, and a first voltage-controlled phase shifter. One part is output through the first branch of the first coupler, and the other part is sent as a loop-back signal to the input end of the sapphire resonator through the second branch of the first coupler.

[0007] In the frequency discrimination loop, the loop-back signal generates a second sampling signal through the third coupler, and after passing through the second voltage-controlled phase shifter, it is mixed with the reflection signal at the input end of the sapphire resonator to generate a first voltage-controlled signal to control the first voltage-controlled phase shifter.

[0008] In the phase-locked loop, the loopback signal generates a first sampling signal through a second coupler, and after frequency division, it is mixed with the oscillation output by the crystal oscillator to generate a second voltage-controlled signal, which controls the second voltage-controlled phase shifter.

[0009] Preferably, the first voltage-controlled signal is subjected to loop filter amplification processing before being input into the first voltage-controlled phase shifter; the second voltage-controlled signal is subjected to loop filter amplification processing before being input into the second voltage-controlled phase shifter.

[0010] Preferably, the frequency division is performed by DDS from 13 to 100 MHz; the crystal oscillator frequency is 100 MHz.

[0011] Further preferably, the relative bandwidth of the band-pass filter 5 is less than 0.5%.

[0012] The above at least one technical solution adopted in the embodiments of the present application can achieve the following beneficial effects:

[0013] The significance of the present invention lies in providing an implementation method of a room-temperature X-band ultra-low phase-noise sapphire oscillator, which reduces the phase noise of the output signal by using a frequency discrimination circuit, improves the stability of the output signal power by using a phase-locked loop, takes into account the characteristics of low phase noise and high stability, and improves the product system of the sapphire oscillator. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawings described herein are used to provide a further understanding of the present application, and constitute a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application, and do not constitute an improper limitation of the present application. In the drawings:

[0015] Figure 1 It is a principle block diagram of an ultra-low limit high sapphire oscillator. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] In order to make the objectives, technical solutions, and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in conjunction with the specific embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0017] The following will describe in detail the technical solutions provided by the embodiments of the present application in conjunction with the drawings.

[0018] Figure 1 It is a principle block diagram of an ultra-low limit high sapphire oscillator.

[0019] An embodiment of the present application provides a low-phase-noise sapphire oscillator, which includes a main loop, a phase-locked loop, and a frequency discrimination loop. In the main loop, the oscillation output by the sapphire resonator 3 passes through a low-noise amplifier 4, a band-pass filter 5, and a first voltage-controlled phase shifter 6. A part of the oscillation is output through the first branch of the first coupler 7, and the other part is sent to the input end of the sapphire resonator as a loop-back signal through the second branch of the first coupler.

[0020] Generally, a high-Q sapphire resonator and a band-pass filter with a relative bandwidth less than 0.5% are selected as the frequency-selective devices of the oscillation main loop. Multiple X-band amplifiers with low additional phase noise are cascaded (4 in the figure) as the loop gain to construct the oscillation main loop of the sapphire oscillator, and the signal is output through the first branch of the first coupler.

[0021] In the frequency discrimination loop, the loop-back signal passes through the third coupler 1 to generate a second sampling signal. After passing through the first voltage-controlled phase shifter 9, it is mixed with the reflection signal at the input end of the sapphire resonator to generate a first voltage-controlled signal to control the first voltage-controlled phase shifter.

[0022] For example, the reflection signal of the resonator is extracted through the circulator 2. At the same time, the oscillation signal is extracted by the third coupler 1 in the main loop. After the two are input into the mixer 11, an error level is generated through loop filtering and amplification 12. By locking the first voltage-controlled phase shifter 6 in the main loop, the comparison result is fed back to the main loop to form a complete frequency discrimination circuit. The function of this part is to reduce the far-end phase noise of the output signal by using the high-Q characteristic of the sapphire resonator. When a circulator is used at the input end of the sapphire resonator, the reflection signal at the input end of the sapphire resonator is input through the second port of the circulator 2 and led out through the third port. The loop-back signal is input through the first port of the circulator 2 and output through the second port to the input end of the sapphire resonator. Further, the reflection signal at the input end of the sapphire resonator is amplified by a low-noise amplifier 10 before mixing.

[0023] In the phase-locked loop, the loop-back signal passes through the second coupler 8 to generate a first sampling signal. After frequency division, it is mixed with the oscillation output by the crystal oscillator 14 to generate a second voltage-controlled signal to control the second voltage-controlled phase shifter.

[0024] For example, a signal is extracted from the main loop through the second coupler 8, divided by the DDS 13 to 100 MHz, and then input into the mixer 15 together with the output signal of the 100 MHz crystal oscillator 14. An error level is generated through loop filtering and amplification 16. By locking the second voltage-controlled phase shifter 9 in the frequency discrimination circuit, a complete phase-locked loop is formed. The function of this part is to reduce the near-end phase noise of the output signal by using the high stability of the quartz crystal.

[0025] Based on the basic oscillation circuit, the present invention combines a frequency discriminator circuit with a phase-locked loop. While reducing the near-end phase noise of the oscillator, it ensures that the original far-end phase noise does not deteriorate. By reasonably selecting the parameters of the loop filter amplifier, the finally output signal takes into account the characteristics of low phase noise and high stability, and can achieve a phase noise of -130 dBc / Hz @ 1 kHz and -150 dBc / Hz @ 10 kHz for the X-band output signal.

[0026] It should also be noted that the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such process, method, commodity or device. Without more limitations, the element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, method, commodity or device including the said element.

[0027] The above are only the embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the scope of the claims of the present application.

Claims

1. A low phase noise sapphire oscillator, characterized in that, It includes a main loop, a phase-locked loop, and a frequency discriminator loop; In the main loop, the oscillation output by the sapphire resonator passes through a low-noise amplifier, a band-pass filter, and a first voltage-controlled phase shifter, and then a part of it is output through the first branch of the first coupler, and the other part is sent as a feedback signal to the input end of the sapphire resonator through the second branch of the first coupler; In the frequency discriminator loop, the feedback signal generates a second sampling signal through the third coupler, and after passing through the second voltage-controlled phase shifter, it is mixed with the reflection signal at the input end of the sapphire resonator to generate a first voltage-controlled signal to control the first voltage-controlled phase shifter; In the phase-locked loop, the feedback signal generates a first sampling signal through the second coupler, and after frequency division, it is mixed with the oscillation output by the crystal oscillator to generate a second voltage-controlled signal to control the second voltage-controlled phase shifter.

2. The low-phase-noise sapphire oscillator according to claim 1, wherein The first voltage-controlled signal is subjected to loop filtering and amplification processing before being input into the first voltage-controlled phase shifter.

3. The low-phase-noise sapphire oscillator according to claim 1, wherein The second voltage-controlled signal is subjected to loop filtering and amplification processing before being input into the second voltage-controlled phase shifter.

4. The low-phase-noise sapphire oscillator according to claim 1, wherein The frequency division is performed to 100 MHz using DDS technology.

5. The low-phase-noise sapphire oscillator according to claim 1, wherein The reflection signal at the input end of the sapphire resonator is input through the second port of the circulator and led out through the third port; The feedback signal is input through the first port of the circulator and output through the second port to the input end of the sapphire resonator.

6. The low-phase-noise sapphire oscillator according to claim 1, wherein The reflection signal at the input end of the sapphire resonator is amplified by a low-noise amplifier before mixing.

7. The low-phase-noise sapphire oscillator according to claim 1, wherein The relative bandwidth of the band-pass filter is less than 0.5%.

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