阅读说明：本技术 一种基于多谐振器的低噪声晶体振荡器及其实现方法 (Low-noise crystal oscillator based on multiple resonators and implementation method thereof ) 是由 田培洪 于 2020-07-23 设计创作，主要内容包括：本发明公开了一种基于多谐振器的低噪声晶体振荡器,主要解决现有晶体振荡器在降低振荡器输出信号的本底相位噪声,产品调试难度加大,不利于批量生产的问题。该晶体振荡器包括与外部稳压供电电源相连的滤波电路,集电极与供电电路相连的晶体管放大器,与晶体管放大器的基极相连的主振选频回路、反馈电容,与反馈电容相连的晶体选频反馈电路,与主振电路且和反馈电容相连的LC并联谐振网络,以及与晶体管放大器相连的晶体滤波电路。本发明能有效提高电路选频特性和电路有载Q值,降低振荡信号近载频段的相位噪声,同时在主振射极输出设置一个高Q晶体选频反馈电路,充分利用晶体谐振器的窄带选频特性,改善远载频段的信号相位噪声指标。(The invention discloses a multi-resonator-based low-noise crystal oscillator, which mainly solves the problems that the existing crystal oscillator reduces the background phase noise of an output signal of the oscillator, increases the product debugging difficulty and is not beneficial to batch production. The crystal oscillator comprises a filter circuit connected with an external voltage-stabilizing power supply, a transistor amplifier with a collector connected with the power supply circuit, a main oscillation frequency-selecting loop connected with a base of the transistor amplifier, a feedback capacitor, a crystal frequency-selecting feedback circuit connected with the feedback capacitor, an LC parallel resonance network connected with the main oscillation circuit and the feedback capacitor, and a crystal filter circuit connected with the transistor amplifier. The invention can effectively improve the frequency selection characteristic and the loaded Q value of the circuit, reduce the phase noise of the oscillation signal in the near-load frequency band, and meanwhile, a high-Q crystal frequency selection feedback circuit is arranged at the output of the main oscillator emitter, thereby fully utilizing the narrow-band frequency selection characteristic of the crystal resonator and improving the signal phase noise index in the far-load frequency band.)

1. A method for realizing a low-noise crystal oscillator based on a multi-resonator is characterized by comprising the following steps:

(S1) a capacitance three-point type oscillation circuit is constructed by using a transistor circuit, a main oscillation frequency selection circuit and an LC parallel resonance network, wherein the transistor circuit provides negative resistance for the oscillation circuit and meets the amplitude condition required by oscillation;

(S2) adjusting the inductance and capacitance values in the main oscillation frequency-selecting circuit in the oscillation circuit to meet the phase condition necessary for oscillation of the capacitance three-point oscillation circuit, thereby generating a main oscillation frequency signal;

(S3) the inductance and capacitance values in the main oscillation frequency-selecting circuit in the oscillation circuit are continuously adjusted to meet the amplitude balance condition and the phase balance condition which are necessary for the oscillation of the capacitance three-point oscillation circuit, and a stable oscillation signal is generated.

2. The method of claim 1, wherein a frequency-selective feedback circuit is connected to the negative resistance circuit of the transistor in step (S1) to suppress the B-mode oscillation, increase the Q-factor of the circuit, and improve the signal-to-noise ratio of the circuit.

3. A low-noise crystal oscillator based on multi-resonator is characterized by comprising a filter circuit (1) connected with an external voltage-stabilizing power supply, a transistor amplifier Q300 with a collector connected with the filter circuit (1), a main oscillation frequency-selecting circuit (2) connected with the base of the transistor amplifier Q300, a feedback capacitor C301, a crystal frequency-selecting feedback circuit (3) with an input end connected with the other end of the feedback capacitor C301, an LC parallel resonant network (4) with one end connected with the main oscillation frequency-selecting circuit (2) and the other end connected with the feedback capacitor C301, and a crystal filter circuit (5) with an input end connected with an emitter of the transistor amplifier Q300 and an output end as an oscillation signal output end; the crystal frequency-selecting feedback circuit (3) is provided with two output ends, one of the output ends is connected with the common end of the main vibration frequency-selecting circuit (2) and the LC parallel resonance network (4) and is grounded, and the other output end is connected with the input end of the crystal filter circuit (5).

4. A multi-resonator-based low noise crystal oscillator according to claim 3, further comprising three bias resistors: the circuit comprises a first bias resistor R301 connected between the collector and the base of the transistor amplifier, a second bias circuit R300 connected in parallel with two ends of the main oscillation frequency selection circuit, and a third bias resistor R302 with one end connected with the emitter of the transistor amplifier and the other end grounded.

5. A multi-resonator-based low-noise crystal oscillator according to claim 4, wherein said filter circuit comprises a capacitor C306 having one end connected to the collector of the transistor amplifier and the other end connected to ground, a resistor R303 connected to the collector of the transistor amplifier, and a capacitor C308 having one end connected to the resistor R303 and the other end connected to ground; the common end of the resistor R303 and the capacitor C308 is connected with an external voltage-stabilizing power supply.

6. The multi-resonator-based low-noise crystal oscillator according to claim 5, wherein the master frequency selection circuit comprises a capacitor C300, an inductor L300 and a quartz resonator Y300 which are connected in series in sequence; the free end of the capacitor C300 is connected with the base of the transistor amplifier, and the free end of the quartz resonator Y300 is grounded.

7. The multi-resonator-based low-noise crystal oscillator according to claim 6, wherein the crystal frequency-selecting feedback circuit comprises a quartz resonator Y301, an adjustable capacitor C303, an inductor L302, and a blocking capacitor C304; the input end of the quartz resonator Y301 is connected with the feedback capacitor, the free end of the blocking capacitor C304 is connected with the emitter of the transistor amplifier, and the grounding end of the quartz resonator Y301 is grounded.

8. A multi-resonator-based low-noise crystal oscillator according to claim 7, wherein said crystal filter circuit comprises a capacitor C305, an inductor L303, a tunable capacitor C307, and a quartz resonator Y302; the free end of the capacitor C305 is connected to the emitter of the transistor amplifier, and the free end of the quartz resonator Y302 serves as an oscillation signal output end.

Technical Field

The invention relates to the technical field of quartz crystal oscillators, in particular to a multi-resonator-based low-noise crystal oscillator and an implementation method thereof.

Background

With the continuous development of modern communication and radar technologies, the phase noise of a frequency source becomes one of the key indexes of system performance. The crystal oscillator is used as an excellent signal source to provide reference frequency signals for a plurality of electronic devices such as instruments, communication equipment and radar systems, is a key core device of the instruments, the communication equipment and the radar systems, and the phase noise index of the crystal oscillator is often a main factor limiting the performance of the whole electronic system.

As shown in fig. 1, when the quartz resonator is the harmonic overtone response waveform of the harmonic overtone crystal, and the quartz resonator is the harmonic overtone crystal, the means for reducing the phase noise of the crystal oscillator is to increase the signal-to-noise ratio of the circuit system as much as possible, and generally two ways of exciting the crystal with larger signal power and increasing the effective Q of the circuit are adopted. Under the condition that the circuit background noise is certain, the phase noise of the crystal oscillator can be effectively reduced by increasing the excitation power of the crystal (such as CN201210228232.3), but the change of the frequency of the oscillator along with the time (aging characteristic) is possibly degraded by excessively high excitation; a narrow-band filter (crystal filter) is added at the signal output end of the crystal oscillator to reduce the background phase noise of the output signal of the oscillator, but the additional cost is high, the miniaturization is difficult, the product debugging difficulty is increased, and the mass production is not facilitated.

The existing typical low-noise oscillator adopts a double-rotation SC cut quartz resonator, compared with other cut quartz resonators, the SC cut quartz resonator has the characteristics of stress compensation and thermal transient compensation, and the oscillator manufactured by the SC cut quartz resonator has the advantages of good starting-up characteristic, small aging rate, good short stability index, strong irradiation resistance, excellent acceleration resistance, good high-temperature working characteristic and the like, so that the application is very wide. The SC-cut quartz crystal resonator has relatively complicated vibration modes, i.e., a mode vibration (thickness stretching vibration), a mode vibration (thickness distortion vibration) of the B mode, and a mode vibration (thickness shear vibration) of the C mode (as shown in fig. 2). Wherein, only if the temperature curve of the C-mode vibration frequency is a cubic curve, the temperature curve has a zero temperature coefficient point, and is a vibration mode required by people. The mode A is far away from the mode C and can be ignored during design, but the mode B vibration is close to the mode C, so that the mode B suppression of the conventional LC network brings great trouble to the design, the problem can be thoroughly solved by adopting a high-Q narrow-band crystal resonator, and the product realization efficiency is improved.

Disclosure of Invention

The invention aims to provide a multi-resonator-based low-noise crystal oscillator and an implementation method thereof, and mainly solves the problems that the existing crystal oscillator is higher in additional cost, more difficult to miniaturize, higher in product debugging difficulty and not beneficial to batch production when the background phase noise of an output signal of the oscillator is reduced.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a method for realizing a low-noise crystal oscillator based on a multi-resonator comprises the following steps:

(S1) a capacitance three-point type oscillation circuit is constructed by using a transistor circuit, a main oscillation frequency selection circuit and an LC parallel resonance network, wherein the transistor circuit provides negative resistance for the oscillation circuit and meets the amplitude condition required by oscillation;

(S2) adjusting the inductance and capacitance values in the main oscillation frequency-selecting circuit in the oscillation circuit to meet the phase condition necessary for oscillation of the capacitance three-point oscillation circuit, thereby generating a main oscillation frequency signal;

(S3) the inductance and capacitance values in the main oscillation frequency-selecting circuit in the oscillation circuit are continuously adjusted to meet the amplitude balance condition and the phase balance condition which are necessary for the oscillation of the capacitance three-point oscillation circuit, and a stable oscillation signal is generated.

Further, a crystal frequency-selecting feedback circuit is connected to the negative resistance circuit of the transistor in the step (S1) to suppress the B-mode oscillation, thereby increasing the Q value of the circuit and improving the signal-to-noise ratio of the circuit.

The invention also provides a low-noise crystal oscillator based on the multi-resonator, which comprises a filter circuit connected with an external voltage-stabilizing power supply, a transistor amplifier Q300 with a collector connected with the filter circuit, a main oscillation frequency-selecting circuit connected with the base of the transistor amplifier Q300, a feedback capacitor C301, a crystal frequency-selecting feedback circuit with an input end connected with the other end of the feedback capacitor C301, an LC parallel resonance network with one end connected with the main oscillation frequency-selecting circuit and the other end connected with the feedback capacitor C301, and a crystal filter circuit with an input end connected with the emitter of the transistor amplifier Q300 and an output end as an oscillation signal output end; the crystal frequency-selecting feedback circuit is provided with two output ends, wherein one output end is connected with the common end of the main vibration frequency-selecting circuit and the LC parallel resonance network and is grounded, and the other output end is connected with the input end of the crystal filter circuit.

Further, the oscillator further comprises three bias resistors: the circuit comprises a first bias resistor R301 connected between the collector and the base of the transistor amplifier, a second bias circuit R300 connected in parallel with two ends of the main oscillation frequency selection circuit, and a third bias resistor R302 with one end connected with the emitter of the transistor amplifier and the other end grounded.

Further, the filter circuit comprises a capacitor C306 with one end connected with the collector of the transistor amplifier and the other end grounded, a resistor R303 connected with the collector of the transistor amplifier, and a capacitor C308 with one end connected with the resistor R303 and the other end grounded; the common end of the resistor R303 and the capacitor C308 is connected with an external voltage-stabilizing power supply.

Further, the main vibration frequency selection circuit comprises a capacitor C300, an inductor L300 and a quartz resonator Y300 which are sequentially connected in series; the free end of the capacitor C300 is connected with the base of the transistor amplifier, and the free end of the quartz resonator Y300 is grounded.

Further, the crystal frequency-selecting feedback circuit comprises a quartz resonator Y301, an adjustable capacitor C303, an inductor L302 and a blocking capacitor C304 which are sequentially connected in series; the input end of the quartz resonator Y301 is connected with the feedback capacitor, the free end of the blocking capacitor C304 is connected with the emitter of the transistor amplifier, and the grounding end of the quartz resonator Y301 is grounded.

Further, the crystal filter circuit comprises a capacitor C305, an inductor L303, an adjustable capacitor C307 and a quartz resonator Y302 which are sequentially connected in series; the free end of the capacitor C305 is connected to the emitter of the transistor amplifier, and the free end of the quartz resonator Y302 serves as an oscillation signal output end.

Compared with the prior art, the invention has the following beneficial effects:

the invention provides a very low phase noise crystal oscillating circuit, which is different from an oscillating circuit formed by the existing single crystal resonator, the frequency is not adjusted on a main oscillation resonator, the main oscillation resonator is not excited to oscillate with high power to obtain low noise performance, the frequency selection characteristic and the loaded Q value of the circuit are improved through the high quality factor (Q value) of a frequency selection feedback crystal resonator, the phase noise of a near-load frequency band of an oscillating signal is reduced, meanwhile, a high Q crystal frequency selection feedback circuit is arranged at the output of a main oscillation emitter, and the signal phase noise index of a far-load frequency band is improved by utilizing the narrow-band frequency selection characteristic of the crystal resonator.

Drawings

FIG. 1 is a diagram of the overtone response waveform of a prior art quartz crystal resonator.

FIG. 2 is a schematic diagram of amplitude-frequency response of a vibration mode of a prior art SC-cut quartz resonator.

Fig. 3 is an overall circuit schematic of an embodiment of the present invention.

Fig. 4 is a frequency response curve of a negative resistance after the feedback crystal branch is connected in accordance with an embodiment of the present invention.

Fig. 5 is a frequency response curve of the phase after the feedback crystal branch is accessed according to an embodiment of the present invention.

FIG. 6 is a graph of the measured phase noise of the present invention.

Wherein, the names corresponding to the reference numbers are:

the circuit comprises a 1-filter circuit, a 2-main vibration frequency selection circuit, a 3-crystal frequency selection feedback circuit, a 4-LC parallel resonance network and a 5-crystal filter circuit.

Detailed Description

The present invention will be further described with reference to the following description and examples, which include but are not limited to the following examples.