Oscillator loop phase noise suppression structure and method

Abstract

The invention discloses an oscillator loop phase noise suppression structure and method, and relates to the technical field of microwave signal sources. The input end of the first coupler is connected with the output end of the amplifier with low 1 / f phase noise, and a straight-through port is connected with the LO end of a double-balanced mixer; the amplifier input end of the oscillator is connected with the coupling output end of the first coupler; one end of the voltage-controlled phase shifter is connected with the amplifier of the oscillator, and the other end is connected with the input end of the second coupler; the power port of the second coupler is connected with the RF end of the double-balanced mixer; the IF end of the double-balanced mixer is connected to the working voltage port of the VCP of the voltage-controlled phase shifter after passing through the integrator PI; by combining an amplifier with low 1 / f phase noise with a high gain amplifier, it is possible to have very high gain and ultra-low phase noise.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave signal sources, and in particular to an oscillator loop phase noise suppression structure and method. Background Art

[0002] The basic principle of an oscillator is to generate a periodic output signal through a positive feedback loop and an appropriate feedback network, as well as resonance conditions and gain compensation. Under this principle, signal generation in various frequency bands can be achieved. In order to achieve the generation of high-frequency signals, dielectric oscillators have been developed. Its circuit contains a dielectric (such as a crystal, capacitor or inductor) and is usually activated to generate an oscillation signal of a specific frequency. This type of oscillator is widely used in wireless communications, radio frequency electronics, radar, television and many other electronic devices.

[0003] Phase noise is a common form of noise, especially in frequency-related circuits such as frequency synthesizers and clock generators. For example, in frequency synthesizers, phase noise can affect the stability and accuracy of the signal. It is usually described in the form of Phase Noise Power Spectral Density, with units of dBc / Hz, which represents the ratio of phase noise power to carrier power within a unit frequency range. Phase noise power spectral density usually increases with the increase of carrier frequency, so different degrees of compensation or suppression are required in different frequency ranges. The cause of oscillator phase noise can be due to noise sources inside the oscillator, such as thermal noise and 1 / f noise of transistors, or due to external environmental influences, such as temperature changes, power supply fluctuations, etc. To reduce oscillator phase noise, a series of technical measures are usually required, such as optimizing circuit design, reducing temperature sensitivity, using high-quality crystal oscillators, etc.

[0004] At present, METobar et al. have proposed a method based on interference method to reduce the phase noise of power amplifier, such as Figure 1 As shown, using HC as an interferometer, the two coherent and destructive signals are mixed with a phase difference of 90° to complete amplitude noise detection and phase noise detection. The former is fed back to VCA to suppress the amplitude noise coupled into the phase detection end, and the latter is fed back to VCP to suppress the phase noise of the amplifier.

[0005] However, if the current method uses active feedback to reduce the phase noise of the amplifier, it will make the system more complicated to a certain extent, and it is difficult to adjust and has requirements for input power. First of all, in terms of system complexity, the use of active noise feedback will definitely make the entire system more complicated. Although the interference method has a high phase detection efficiency, it uses many additional devices; in terms of adjustment, the interference method must not only ensure the coherence condition, but also ensure that the phase noise and amplitude noise are orthogonal in the demodulation link, otherwise the two will couple with each other and the feedback result will be poor; the last aspect is the power requirement. The interference method requires an interference arm as the reference end of the mixer. The port has high power requirements, resulting in a large electronic noise contributed by the mixer, resulting in poor feedback results. Summary of the invention

[0006] In view of the shortcomings of the prior art that it is difficult to suppress the oscillator phase noise, resulting in poor feedback results, the present invention proposes an oscillator loop phase noise suppression structure and method, which suppresses and maintains the amplifier 1 / f phase noise by reasonably allocating power and introducing a phase noise feedback loop, thereby solving the problems existing in the prior art.

[0007] A microwave oscillator loop amplifier phase noise suppression structure, comprising:

[0008] An amplifier with low 1 / f phase noise, whose input terminal is used to receive a power signal;

[0009] A first coupler, whose input end is connected to the output end of the amplifier with low 1 / f phase noise; a through port of the first coupler is connected to the LO end of the double-balanced mixer, and whose output end is connected to the input end of the amplifier of the oscillator;

[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 an input end connected to the output end of the voltage-controlled phase shifter, and the output end of the second coupler is used for outputting a power signal; and the coupling port of the second coupler is connected to the RF end of the double-balanced mixer.

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

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

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

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

[0016] The present invention also provides a method for suppressing phase noise of an oscillator loop, comprising the following steps:

[0017] Use an amplifier with low 1 / f phase noise to amplify the input power signal;

[0018] The amplified power signal is input into 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 into 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 into an RF port of a double-balanced mixer;

[0020] By adjusting the phase of the voltage-controlled phase shifter, the phases of the LO end and the RF end of the double-balanced mixer after the input power signal are 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 of the oscillator;

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

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

[0023]

[0024] Among them, n Mixer is the noise floor of the double-balanced mixer; γ P.D is the sensitivity coefficient of the double-balanced mixer as a phase detector; represents the phase noise of the amplifier from the oscillator; when When the detected voltage signal δV Dec Amplifier phase noise that reflects the detected oscillator

[0025] Furthermore, it also includes connecting a voltage-controlled phase shifter to the front end of the amplifier of the oscillator, adjusting the phase of the voltage-controlled phase shifter so that the phases of the LO end and the RF end of the double-balanced mixer are orthogonal, detecting a voltage signal through the IF port of the double-balanced mixer, and the voltage signal is proportional to the residual phase noise of the amplifier of the oscillator; the voltage signal is fed back to the bias voltage of the voltage-controlled phase shifter after passing through a proportional integrator, thereby compensating for the 1 / f noise of the low-frequency band of the amplifier of the oscillator.

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

[0027] The present invention uses two amplifiers, a low-gain and low-1 / f phase noise amplifier is used to increase the feed-in power; the high-gain amplifier assumes the main amplification function; a double-balanced mixer is used as a phase detector in the feedback loop to suppress the phase noise of the oscillator amplifier, and due to the effect of phase feedback servo, the two amplifiers can be combined to have a very high gain and ultra-low phase noise; due to the introduction of the front-end low phase noise amplifier, it can be suitable for lower feed-in power, and while meeting the low 1 / f phase noise, it can also have a very high gain. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic diagram of an existing amplifier noise reduction structure based on interference method;

[0029] Figure 2 1 is a flow chart of a method for suppressing phase noise of a microwave oscillator loop amplifier in an embodiment of the present invention;

[0030] Figure 3 It is a structural schematic diagram of moving the VCP to the front end of the amplifier in an embodiment of the present invention;

[0031] Figure 4 This is a structural diagram of a direct mixing phase detection method applied to an amplifier noise reduction in an embodiment of the present invention;

[0032] Figure 5 Amplifier noise reduction test results in the embodiment of the present invention

[0033] Figure 6 The figure is a test result of the amplifier noise reduction method in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0035] The present invention proposes an oscillator loop phase noise suppression structure, such as Figure 2As shown, a structure of a combination of a low 1 / f phase noise and low gain amplifier and a high gain amplifier is adopted, and a phase-detection feedback loop is externally constructed to perform a 1 / f phase noise compensation scheme, which specifically includes an amplifier with low 1 / f phase noise, whose input end is used to receive a power signal; a first coupler, whose input end is connected to the output end of the amplifier with low 1 / f phase noise; a through port of the first coupler is connected to the LO end of a double-balanced mixer, and whose output end is connected to the input end of an amplifier of an oscillator; a voltage-controlled phase shifter, whose input end is connected to the output end of the amplifier of the oscillator; a second coupler, whose input end is connected to the output end of the voltage-controlled phase shifter, and the output end of the second coupler is used to output a power signal; and a coupling port of the second coupler is connected to the RF end of the double-balanced mixer.

[0036] Based on the same inventive concept, the present 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 unidirectional power transmission.

[0038] S2. Use a 1 / 10 coupler to couple 1 / 10 of the power to the main amplifier, connect it to the VCP phase shifter and then connect it to another 1 / 10 coupler to use the main power for output. If necessary, connect an isolator at the input / output end of the amplifier.

[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. At this time, the detected voltage signal is proportional to the residual phase noise of the main amplifier.

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

[0042] The above scheme ( Figure 2 ) is at the back end. Due to its own insertion loss, the output power will be reduced. However, the input power of the main amplifier of this scheme is higher, and the corresponding thermal noise will be lower. Similarly, VCP can also be moved to the front end of the main amplifier. The adjustment method is the same, such as Figure 3 As shown, the benefit of such regulation is that the overall output power can be increased.

[0043] In the feedback loop, a double-balanced mixer is used as a phase detector, VCP is used as a phase noise feedback actuator, a low 1 / f phase noise amplifier LPNA with a gain of G15 (Gain = 15dB) is used as a pre-amplifier with lower 1 / f phase noise, and G45 (Gain = 45dB) is used as the main amplifier with higher gain. Figure 4 The IN-OUT in the circuit 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 by the two measurement arms after mixing, filtering and amplification can be expressed as:

[0045]

[0046] when When the detected voltage signal δV Dec Can reflect the detected amplifier phase noise

[0047] The purpose of using a low phase noise amplifier at the front end of the present invention is to increase the input power, and the gain reaches 15dB. Assuming that the input power is only -10dBm, it can reach 5dBm after being increased, and the increased power is given to the LO reference end of the mixer (phase detector). However, in the 5dBm main path, the present invention uses a 10dB coupler to couple a small amount of power of about -5dBm to the main amplifier for amplification. Since the gain of the main amplifier reaches 45dB, and it is generally saturated at 16dBm. At this time, the output 16dBm link end is connected in series with a voltage-controlled phase shifter, and a 10dB coupler is used to couple 6dBm to the RF end of the mixer. The phase of the voltage-controlled phase shifter (VCP) is adjusted so that the phases of the LO end and the RF end are orthogonal, so that the DC voltage output by the IF port of the mixer reflects the voltage change introduced by the phase noise of the main amplifier. The voltage noise is fed back to the voltage-controlled phase shifter through a proportional integrator, 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 test, the present invention uses the RF signal source E8257D to generate a 10.8GHz point frequency signal (this signal is not a specified value), and couples out 7dBm power as a reference signal for subsequent measurement of the amplifier phase noise after noise reduction. The generated 10.8GHz signal passes through a fixed attenuator to reduce the power to -20dBm and gives it to Figure 5 The input side of the structure, Figure 5In the corresponding blue box, after the phase noise feedback is turned on, the output signal reaches 10dBm. A 10dB coupler is used to couple the 0dB power out and mix it with the 7dBm reference signal to measure the phase noise. The test results are as follows Figure 6 As shown, even under the condition of weak power (-20dBm) feeding, the phase noise measured by the present invention is still lower than -110dBc / Hz@1Hz. Combining G15 and G45 can achieve an effective gain of 36dB, and the phase noise is -110dBc / Hz@1Hz.

[0049] The present invention uses a mixer as a phase detector and suppresses the phase noise of the low-noise amplifier of the X-band oscillator. In the two-port network of the amplifier, an additional reference arm is constructed to measure the additional phase noise of the amplifier; the mixer is directly used as a phase detector instead of using a hybrid coupler as an interference phase detector. A method of combining a low-gain, low-1 / f phase noise amplifier and a high-gain amplifier: In the scheme of the present invention, two amplifiers are used, and the low-gain, low-1 / f phase noise amplifier is used to increase the feed power; the high-gain amplifier assumes the main amplification function; due to the effect of phase feedback servo, the two amplifiers can be combined to have a very high gain and ultra-low phase noise; due to the introduction of the front-end low phase noise amplifier, it can be suitable for lower feed power. While meeting the low 1 / f phase noise, it can also have a very high gain.

[0050] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An oscillator loop phase noise suppression structure, characterized in that: include: An amplifier with low 1 / f phase noise, whose input terminal is used to receive a power signal; A first coupler, whose input end is connected to the output end of the amplifier with low 1 / f phase noise; a through port of the first coupler is connected to the LO end of the double-balanced mixer, and whose output end is connected to the input end of the amplifier of the oscillator; a voltage-controlled phase shifter, the input of which is connected to the output of the amplifier of the oscillator; The second coupler has an input end connected to the output end of the voltage-controlled phase shifter, and the output end of the second coupler is used for outputting a power signal; and the coupling port of the second coupler is connected to the RF end of the double-balanced mixer.

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

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

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

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

6. A method for suppressing phase noise of an oscillator loop, characterized in that: The following steps are involved: Use an amplifier with low 1 / f phase noise to amplify the input power signal; The amplified power signal is input into 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 into the amplifier of the oscillator for amplification; The amplified power signal is coupled using a second coupler, and the coupled power signal is input into an RF port of a double-balanced mixer; By adjusting the phase of the voltage-controlled phase shifter, the phases of the LO end and the RF end of the double-balanced mixer after the input power signal are 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 of the oscillator; The voltage signal is fed back to the bias voltage of the voltage-controlled phase shifter after passing through a proportional integrator, thereby compensating the low-frequency 1 / f noise of the oscillator's amplifier.

7. The method for suppressing phase noise of an oscillator loop according to claim 6, characterized in that: The detected voltage signal is expressed as: Among them, n Mixer is the noise floor of the double-balanced mixer; γ P.D is the sensitivity coefficient of the double-balanced mixer as a phase detector; represents the phase noise of the amplifier from the oscillator; when When the detected voltage signal δV Dec Amplifier phase noise that reflects the detected oscillator 8. The method for suppressing phase noise of an oscillator loop according to claim 6, characterized in that: The invention also includes connecting a voltage-controlled phase shifter to the front end of the amplifier of the oscillator, adjusting the phase of the voltage-controlled phase shifter so that the phases of the LO end and the RF end of the double-balanced mixer are orthogonal, detecting a voltage signal through the IF port of the double-balanced mixer, and the voltage signal is proportional to the residual phase noise of the amplifier of the oscillator; the voltage signal is fed back to the bias voltage of the voltage-controlled phase shifter after passing through a proportional integrator, so as to compensate for the 1 / f noise of the low-frequency band of the amplifier of the oscillator.

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