A structure and method for suppressing phase noise of an oscillator loop

Abstract

This invention discloses an oscillator loop phase noise suppression structure and method, relating to the field of microwave signal source technology. It includes: a low 1 / f phase noise amplifier; a first coupler input connected to the output of the low 1 / f phase noise amplifier, with a through port connected to the LO terminal of a double-balanced mixer; an oscillator amplifier input connected to the coupled output of the first coupler; a voltage-controlled phase shifter connected at one end to the oscillator amplifier and at the other end to the input of a second coupler; a power port of the second coupler connected to the RF terminal of the double-balanced mixer; and an IF terminal of the double-balanced mixer connected to the VCP operating voltage port of the voltage-controlled phase shifter after passing through an integrator (PI). By combining the low 1 / f phase noise amplifier with a high-gain amplifier, high gain and ultra-low phase noise can be achieved.

Description

Technical Field

[0001] This invention relates to the field of microwave signal source technology, and more specifically to an oscillator loop phase noise suppression structure and method. Background Technology

[0002] The basic principle of an oscillator is to generate a periodic output signal through a positive feedback loop and appropriate feedback network, as well as resonance conditions and gain compensation. This principle allows for the generation of signals in various frequency bands. To generate high-frequency signals, dielectric oscillators have been developed. Their circuitry contains a dielectric material (such as a crystal, capacitor, or inductor), which is typically activated to produce an oscillation signal at a specific frequency. This type of oscillator is widely used in wireless communication, radio frequency electronics, radar, television, and many other electronic devices.

[0003] Phase noise is a common form of noise, especially in frequency-dependent circuits such as frequency synthesizers and clock generators. For example, in frequency synthesizers, phase noise affects signal stability and accuracy. It is usually described as phase noise power spectral density (dBc / Hz), representing the ratio of phase noise power to carrier power per unit frequency range. Phase noise power spectral density typically increases with increasing carrier frequency, therefore different levels of compensation or suppression are required in different frequency ranges. Oscillator phase noise can be caused by internal noise sources within the oscillator, such as transistor thermal noise and 1 / f noise, or by external environmental influences, such as temperature variations and power supply fluctuations. Reducing oscillator phase noise typically requires a series of techniques, such as optimizing circuit design, reducing temperature sensitivity, and using high-quality crystal oscillators.

[0004] Currently, METobar et al. have proposed a method based on interferometry for reducing phase noise in power amplifiers, such as... Figure 1 As shown, by using HC as an interferometer, the two coherent and destructive signals are mixed with a 90° phase difference, which can complete the amplitude noise detection and phase noise detection. The former is fed back to VCA to suppress the amplitude noise coupled into the phase detector, and the latter is fed back to VCP to suppress the phase noise of the amplifier.

[0005] However, current methods for reducing amplifier phase noise using active feedback can complicate the system, increase adjustment difficulty, and impose power requirements. Firstly, regarding system complexity, active noise feedback inevitably increases overall system complexity. While interferometry offers high phase detection efficiency, it requires numerous additional components. Secondly, in terms of adjustment, interferometry must ensure not only coherence but also orthogonality between phase and amplitude noise during demodulation; otherwise, they couple, resulting in poor feedback. Finally, there are power requirements. Interferometry necessitates an interferometer arm as a mixer reference, which demands high power, leading to significant electronic noise contribution from the mixer and consequently poor feedback results. Summary of the Invention

[0006] To address the shortcomings of existing technologies that struggle to suppress oscillator phase noise, resulting in poor feedback performance, this invention proposes an oscillator loop phase noise suppression structure and method. By rationally allocating power and introducing a phase noise feedback loop, the 1 / f phase noise of the sustain amplifier is suppressed, thereby solving the problems existing in the prior art.

[0007] A phase noise suppression structure for a microwave oscillator loop amplifier includes:

[0008] A low 1 / f phase noise amplifier whose input is used to receive power signals;

[0009] A first coupler has its input connected to the output of the low 1 / f phase noise amplifier; the first coupler's through port is connected to the LO terminal of a double-balanced mixer, and its output is connected to the input of the oscillator's amplifier.

[0010] A voltage-controlled phase shifter, the input of which is connected to the output of the amplifier of the oscillator;

[0011] The second coupler has its input terminal connected to the output terminal of the voltage-controlled phase shifter, and its output terminal is used for power signal output; the coupling port of the second coupler is connected to the RF terminal of the double-balanced mixer.

[0012] Furthermore, the input and output terminals of the low 1 / f phase noise amplifier are respectively connected to a first isolator.

[0013] Furthermore, the input and output terminals of the amplifier of the oscillator are respectively connected to a second isolator.

[0014] Furthermore, the gain of the low 1 / f phase noise amplifier is 15 dB.

[0015] Furthermore, the gain of the amplifier in the oscillator is 45dB.

[0016] This invention also proposes a method for suppressing oscillator loop phase noise, comprising the following steps:

[0017] The input power signal is amplified using an amplifier with low 1 / f phase noise;

[0018] The amplified power signal is input to the LO port of the double-balanced mixer; at the same time, the power signal is coupled using the first coupler, and the coupled power signal is input to the amplifier of the oscillator for amplification;

[0019] The amplified power signal is coupled using a second coupler, and the coupled power signal is input to the RF port of the double-balanced mixer.

[0020] By adjusting the phase of the voltage-controlled phase shifter, the phases of the LO and RF terminals of the double-balanced mixer after the input power signal are made orthogonal, and a voltage signal is detected through the IF port of the double-balanced mixer; wherein, the voltage signal is proportional to the residual phase noise of the amplifier in the oscillator;

[0021] The voltage signal is fed back to the bias voltage of the voltage-controlled phase shifter after passing through a proportional-integral converter, thereby compensating for the low-frequency 1 / f noise of the oscillator amplifier.

[0022] Furthermore, the voltage signal detected through the IF port of the double-balanced mixer is proportional to the residual phase noise of the second amplifier, and the detected voltage signal is expressed as follows:

[0023]

[0024] Where, n Mixer It is the noise floor of a double-balanced mixer; γ P.D. It is the sensitivity coefficient of the double-balanced mixer as a phase detector; This represents the phase noise of the amplifier from the oscillator; when At that time, the detected voltage signal δV Dec Amplifier phase noise that can be reflected in the detected oscillator

[0025] Furthermore, it also includes connecting a voltage-controlled phase shifter to the front end of the oscillator's amplifier. By adjusting the phase of the voltage-controlled phase shifter, the phases of the LO and RF terminals of the double-balanced mixer are made orthogonal. A voltage signal is detected through the IF port of the double-balanced mixer. This voltage signal is proportional to the residual phase noise of the oscillator's amplifier. After passing this voltage signal through a proportional-integral converter, it is fed back to the bias voltage of the voltage-controlled phase shifter to compensate for the 1 / f noise in the low-frequency band of the oscillator's amplifier.

[0026] This invention provides an oscillator loop phase noise suppression structure and method, which has the following beneficial effects:

[0027] This invention utilizes two amplifiers: a low-gain, low-1 / f phase noise amplifier to increase the input power; and a high-gain amplifier to perform the main amplification function. A double-balanced mixer is used in the feedback loop as a phase detector to suppress the phase noise of the oscillator amplifier. Due to the phase feedback servo effect, the two amplifiers combined can achieve very high gain and ultra-low phase noise. The introduction of the low-phase noise amplifier at the front end allows for lower input power while maintaining very high gain and low 1 / f phase noise. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of an existing amplifier noise reduction structure based on interferometry.

[0029] Figure 2 This is a schematic flowchart of a method for suppressing phase noise in a microwave oscillator loop amplifier according to an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of the structure in an embodiment of the present invention where the VCP is moved to the front end of the amplifier;

[0031] Figure 4 This is a diagram illustrating the direct mixing phase detection method applied to amplifier noise reduction in this embodiment of the invention.

[0032] Figure 5 This is a structural diagram of the amplifier noise reduction test results in an embodiment of the present invention.

[0033] Figure 6 These are the test results of the amplifier noise reduction method in this embodiment of the invention. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0035] This invention proposes an oscillator loop phase noise suppression structure, such as... Figure 2As shown, a structure combining a low 1 / f phase noise, low-gain amplifier and a high-gain amplifier is employed, with an external phase detection feedback loop for 1 / f phase noise compensation. Specifically, the scheme includes a low 1 / f phase noise amplifier whose input is used to receive the power signal; a first coupler whose input is connected to the output of the low 1 / f phase noise amplifier; a through-port of the first coupler connected to the LO terminal of a double-balanced mixer, whose output is connected to the input of the oscillator amplifier; a voltage-controlled phase shifter whose input is connected to the output of the oscillator amplifier; a second coupler whose input is connected to the output of the voltage-controlled phase shifter, and whose output is used for power signal output; and a coupling port of the second coupler connected to the RF terminal of the double-balanced mixer.

[0036] Based on the same inventive concept, this invention also proposes a method for suppressing oscillator loop phase noise, comprising the following steps:

[0037] S1. Use a low 1 / f phase noise amplifier LPNA as the first stage amplifier and place it at the front end to increase the input power. If necessary, use an isolator to ensure the unidirectionality of power transmission.

[0038] S2. Use a 1 / 10 coupler to couple 1 / 10 of the power to the main amplifier. After phase shifting via VCP, connect another 1 / 10 coupler to use the main power for the output. If necessary, connect isolators at the amplifier input / output terminals.

[0039] S3. Connect the through port of the first 1 / 10 coupler to the LO port of the double-balanced mixer (X-band), and connect the 1 / 10 power port of the second 1 / 10 coupler to the RF port of the double-balanced mixer.

[0040] S4. Adjust the bias voltage of VCP to perform phase pulling, so that the output voltage of the IF port of the double balanced mixer is zero. At this time, the LO and RF ports are in a quadrature state, and the detected voltage signal is proportional to the residual phase noise of the main amplifier.

[0041] S5. Input the voltage obtained in S4 into a low-pass filter or a proportional-integral converter, and then add it to the bias voltage of VCP to achieve compensation for 1 / f noise in the low-frequency band of the second amplifier.

[0042] The above-mentioned scheme ( Figure 2 In this design, the VCP is located at the rear end. Due to its insertion loss, this will reduce the output power, but the main amplifier's feed power will be higher, resulting in lower thermal noise. Similarly, the VCP can be moved to the front end of the main amplifier, and the adjustment method is the same, such as... Figure 3 As shown, the advantage of this adjustment is that it can improve the overall output power.

[0043] In the feedback loop, a double-balanced mixer is used as a phase detector, VCP is used as a phase noise feedback actuator, and a low 1 / f phase noise amplifier LPNA with a gain of G15 (Gain = 15dB) is used as a preamplifier with low 1 / f phase noise. G45 (Gain = 45dB) is used as the main amplifier with high gain. Figure 4 The IN-OUT in the diagram is equivalent to an amplifier with low 1 / f phase noise and high gain.

[0044] When using a mixer as a phase detector to detect the phase noise of an amplifier, a very low noise floor can be obtained due to the common-mode effect. The voltage signal output from the two measuring arms after mixing, filtering, and amplification can be expressed as:

[0045]

[0046] when At that time, the detected voltage signal δV Dec It can reflect the detected amplifier phase noise

[0047] The purpose of using a low-phase-noise amplifier at the very beginning of this invention is to increase the input power, achieving a gain of 15dB. Assuming the input power is only -10dBm, this can be boosted to 5dBm, and the boosted power is supplied to the LO reference terminal of the mixer (phase detector). However, in the 5dBm main path, this invention uses a 10dB coupler to couple out a small amount of power, approximately -5dBm, to the main amplifier for amplification. Since the main amplifier's gain reaches 45dB and typically saturates at 16dBm, a voltage-controlled phase shifter (VCP) is connected in series with the 16dBm output link terminal, and then the 10dB coupler couples out 6dBm to the RF terminal of the mixer. The phase of the VCP is adjusted so that the LO and RF terminals are orthogonal, so that the DC voltage output from the mixer's IF port reflects the voltage change introduced by the main amplifier's phase noise. The voltage noise is fed back to the voltage-controlled phase shifter via a proportional-integral converter, so that the phase noise introduced by the amplifier can be compensated in real time using VCP.

[0048] like Figure 5 As described above, during the testing process, this invention uses an E8257D RF signal source to generate a 10.8GHz spot frequency signal (this signal is not a specified value), and couples out 7dBm of power as a reference signal for subsequent measurement of the amplifier's phase noise after noise reduction. The generated 10.8GHz signal is passed through a fixed attenuator to reduce the power to -20dBm before being supplied to... Figure 5 The input end of the structure, Figure 5In the corresponding blue box, after enabling phase noise feedback, the output signal reaches 10dBm. A 10dB coupler is used to couple the 0dB power out and mix it with a 7dBm reference signal to measure phase noise. The test results are as follows: Figure 6 As shown, even with a low power (-20dBm) feed, the phase noise measured using this invention is still below -110dBc / Hz@1Hz. Combining G15 and G45 can achieve an effective gain of 36dB, and the phase noise is below -110dBc / Hz@1Hz.

[0049] This invention utilizes a mixer as a phase detector and performs phase noise suppression on the low-noise amplifier of an X-band oscillator. An additional reference arm is constructed in the amplifier's two-port network to measure additional phase noise. The mixer is used directly as the phase detector instead of a hybrid coupler as an interferometric phase detector. The method employs a combination of a low-gain, low-1 / f phase-noise amplifier and a high-gain amplifier: In this invention, the low-gain, low-1 / f phase-noise amplifier is used to increase the input power; the high-gain amplifier performs the main amplification function. Due to the phase feedback servo effect, the combination of the two amplifiers achieves very high gain and ultra-low phase noise. The introduction of the low-phase-noise amplifier at the front end allows for lower input power. This achieves both low 1 / f phase noise and very high gain.

[0050] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for suppressing phase noise in an oscillator loop, applied to an oscillator loop phase noise suppression structure, characterized in that, The oscillator loop phase noise suppression structure includes: A low 1 / f phase noise amplifier whose input is used to receive power signals; A first coupler has its input connected to the output of the low 1 / f phase noise amplifier; the first coupler's through port is connected to the LO terminal of a double-balanced mixer, and its output is connected to the input of the oscillator's amplifier. A voltage-controlled phase shifter, the input of which is connected to the output of the amplifier of the oscillator; The second coupler has its input terminal connected to the output terminal of the voltage-controlled phase shifter, and its output terminal is used for power signal output; the coupling port of the second coupler is connected to the RF terminal of the double-balanced mixer. The oscillator loop phase noise suppression method includes the following steps: The input power signal is amplified using an amplifier with low 1 / f phase noise; The amplified power signal is input to the LO port of the double-balanced mixer; at the same time, the power signal is coupled using the first coupler, and the coupled power signal is input to the amplifier of the oscillator for amplification; The amplified power signal is coupled using a second coupler, and the coupled power signal is input to the RF port of the double-balanced mixer. By adjusting the phase of the voltage-controlled phase shifter, the phases of the LO and RF terminals of the double-balanced mixer after the input power signal are made orthogonal, and a voltage signal is detected through the IF port of the double-balanced mixer; wherein, the voltage signal is proportional to the residual phase noise of the amplifier in the oscillator; The voltage signal is fed back to the bias voltage of the voltage-controlled phase shifter after passing through a proportional-integral converter, thereby compensating for the low-frequency 1 / f noise of the oscillator amplifier.

2. The oscillator loop phase noise suppression method according to claim 1, characterized in that, The input and output terminals of the low 1 / f phase noise amplifier are respectively connected to a first isolator.

3. The oscillator loop phase noise suppression method according to claim 1, characterized in that, The input and output terminals of the amplifier of the oscillator are respectively connected to a second isolator.

4. The oscillator loop phase noise suppression method according to claim 1, characterized in that, The gain of the low 1 / f phase noise amplifier is 15 dB.

5. The oscillator loop phase noise suppression method according to claim 1, characterized in that, The gain of the amplifier for the oscillator is 45 dB.

6. The oscillator loop phase noise suppression method according to claim 1, characterized in that, The detected voltage signal is represented as: in, This is the noise floor of a double-balanced mixer; It is the sensitivity coefficient of the double-balanced mixer as a phase detector; This represents the phase noise of the amplifier from the oscillator; when At that time, the detected voltage signal Amplifier phase noise that can be reflected in the detected oscillator .

7. The oscillator loop phase noise suppression method according to claim 1, characterized in that, It also includes connecting a voltage-controlled phase shifter to the front end of the oscillator's amplifier, adjusting the phase of the voltage-controlled phase shifter to make the phases of the LO and RF terminals of the double-balanced mixer orthogonal, detecting a voltage signal through the IF port of the double-balanced mixer, which is proportional to the residual phase noise of the oscillator's amplifier; feeding this voltage signal back to the bias voltage of the voltage-controlled phase shifter after passing it through a proportional-integral converter, thereby compensating for the 1 / f noise in the low-frequency band of the oscillator's amplifier.

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