Low phase noise oscillator using negative feedback

Abstract

An oscillator includes a resonator and a first loop. The first loop includes an amplifier and a first coupler. The first loop is electrically coupled to the resonator. The oscillator is configured to produce negative feedback of the amplifier with respect to a shorted terminal or an open terminal of a cavity that models the oscillator at a frequency offset from a carrier frequency in a cavity mode. The oscillator has a bidirectional pass through the loss of the cavity at the frequency offset from the carrier frequency that is less than 4.00 dB.

Description

Background Technology

[0001] Leeson's law is used to design radio frequency (RF) oscillators with low phase noise. Leeson's law describes the output phase noise spectrum as an equation. Expressed in single-sideband form, Leeson's law is as follows:

[0002] L(f) = 10log 10 [(FKT / 2P sav )*(1+f o / (2Q L *Δf) 2 dBc / Hz

[0003] in:

[0004] L(f) = Single-sideband phase noise (dBc / Hz)

[0005] F = Noise figure of the active device in the oscillator (dB)

[0006] K = Boltzmann constant = 1.38 × 10⁻⁶ -23 Joules / degree-K

[0007] T = Temperature of the active device, usually assumed to be 17°C (290°K).

[0008] KT = -174dBm / Hz

[0009] P sav = The power that an active device can obtain from a source, typically a resonator (dBm)

[0010] f o =The output frequency of the oscillator, also known as the carrier frequency

[0011] Q L =Resonator load Q

[0012] Δf = the offset (Hz) from the carrier frequency used to measure phase noise.

[0013] Leeson's rule can be used to describe the output phase noise spectrum of many RF oscillators, whether the RF oscillator is modeled as a negative resistance oscillator, a loop feedback oscillator, or some other electrical model. The phase noise spectrum of the oscillator, denoted by L(f), is determined by providing positive amplitude feedback with a 0° phase shift between the amplifier's output and input. Positive amplitude feedback is provided at the desired output frequency of the oscillator by passing the signal through a resonator.

[0014] The equations in Leeson's rule can be simplified slightly. That is, it is assumed that there will be no feedback at high offset frequencies (also referred to as "high offset" in this paper) that deviate significantly from the output frequency, and the phase noise level will be considered together with the noise figure determined by the amplifier's input impedance as the amplifier's phase noise level. The phase noise floor of an amplifier without feedback is well-known and given by the following equation:

[0015] L(f) = 10log 10 [(FKT / 2P sav (dBc / Hz)

[0016] Figure 1A A simplified schematic diagram of a known oscillator with phase noise generated according to Leeson's law is shown. Figure 1A In the oscillator 100, a primary feedback loop 101 is included, which has a resistor 111, an inductor 112, and a capacitor 113 connected in series, a coupler 120, an amplifier 150, and an isolator 119. The signal propagation direction in the primary feedback loop 101 is counterclockwise. The series resistor-inductor-capacitor (R–L–C) configuration represents a resonator with high-impedance cutoff resonance. Ideally, the resonant frequency is the carrier frequency, but in reality, due to the characteristics of other circuit elements in the oscillator, the resonant frequency may differ slightly from the carrier frequency. The term "off-resonance" refers to a frequency with a phase shift greater than or less than 0° if the resonant frequency of the resonator is the frequency at which the phase shift is 0° and the resonator's losses are minimal. An example of such a resonator could be a quartz crystal resonator with zero output case capacitance. At the carrier frequency, when the phase shift is 0°, the gain around the loop is greater than that of element 1. Although the off-resonant impedance of a parallel RLC resonator is very low, the following description applies equally to parallel R-L-C resonators grounded in parallel, replacing series resonators. Coupler 120 transfers some power as output power from the oscillator loop to the load 189. Isolator 119 is added only to illustrate that Leeson's law assumes the output impedance of amplifier 150 will not affect the phase noise of amplifier 150 in any way, thus the phase noise of amplifier 150 will not be affected by the output impedance.

[0017] One drawback of previous solutions that designed low-noise oscillators so that their output phase noise was described by Leeson's law was that they did not provide, or even attempt to provide, any negative feedback at high offset frequencies to reduce the noise floor, compared to independent amplifiers. This is likely due to the assumption that the output impedance does not affect the phase noise of the amplifier. This results in a higher oscillator phase floor and higher phase noise at high offset frequencies compared to the ways they had found to provide negative feedback in these regions. Therefore, previous solutions that incorporated feedback into the oscillator could improve the phase noise near the resonant frequency, but generally worsened the phase floor and phase noise at high offset frequencies.

[0018] As a separate but related consideration to the above, one type of model used for oscillators is the so-called cavity model. The cavity model is an idealized model in which the signal from the oscillator is idealized to propagate between two highly reflective surfaces within a cavity, where, at the resonant frequency, the round-trip gain is greater than 0 dB and the phase shift is 0°. Figure 1B A simplified schematic diagram of a known cavity model is shown, in which the signal propagates in a cavity mode. In the implementation described later, in Figure 1B In the cavity model 199, the two surfaces 199a and 199b of the cavity can be represented by resistors with very high resistance values ​​(such as 50 megohms) or very low impedance values ​​(such as 50 milliohms). Effectively, such high or low resistance values ​​can be considered as reflective surfaces that reflect incident signals with very low loss in cavity models such as the known cavity model 199. Attached Figure Description

[0019] The exemplary embodiments can be best understood from the following detailed description when read in conjunction with the accompanying drawings. It should be emphasized that the various features are not necessarily drawn to scale. In fact, dimensions may be arbitrarily increased or decreased for clarity of discussion. Where applicable and feasible, the same reference numerals denote the same elements.

[0020] Figure 1A A simplified schematic diagram of a known oscillator with phase noise generated according to Leeson's law is shown.

[0021] Figure 1B A simplified schematic diagram of a known cavity model is shown, in which the signal propagates in a cavity mode.

[0022] Figure 2A An oscillator model near the resonant center is shown according to a representative implementation for a low phase noise oscillator using negative feedback.

[0023] Figure 2BAn oscillator model for a low phase noise oscillator using negative feedback at a high offset frequency is shown according to a representative embodiment.

[0024] Figure 3 A simplified oscillator circuit for a low phase noise oscillator using negative feedback is shown according to a representative embodiment.

[0025] Figure 4A Another simplified oscillator circuit is shown, according to a representative embodiment, for a low phase noise oscillator using negative feedback at a high offset frequency where the cavity model is effective.

[0026] Figure 4B The following is illustrated for use according to a representative implementation. Figure 4A Another view of a simplified oscillator circuit for a low-phase-noise oscillator with negative feedback.

[0027] Figure 4C The following is illustrated for use according to a representative implementation. Figure 4A and 4B Another view of a simplified oscillator circuit for a low-phase-noise oscillator with negative feedback.

[0028] Figure 5A An oscillator circuit implementation for a low phase noise oscillator using negative feedback, according to a representative embodiment, is shown.

[0029] Figure 5B The following is illustrated for use according to a representative implementation. Figure 5A Another view of the oscillator circuit implementation of a low phase noise oscillator with negative feedback.

[0030] Figure 5C The following is illustrated based on a representative implementation scheme. Figure 5A and Figure 5B A modeled cavity view of the oscillator circuit implementation in the diagram.

[0031] Figure 5D The following is illustrated for use according to a representative implementation. Figure 5A The implementation of a modified oscillator circuit for a low-phase-noise oscillator with negative feedback.

[0032] Figure 5E The following is illustrated based on a representative implementation scheme. Figure 5A and Figure 5B The test implementation of the oscillator circuit implementation in the example.

[0033] Figure 6A An oscillator circuit implementation for a low phase noise oscillator using negative feedback, according to a representative embodiment, is shown.

[0034] Figure 6B The following is illustrated for use according to a representative implementation. Figure 6A Another view of the oscillator circuit implementation of a low phase noise oscillator with negative feedback.

[0035] Figure 6C Another oscillator circuit implementation for a low phase noise oscillator using negative feedback, according to a representative embodiment, is shown.

[0036] Figure 6D The following is illustrated based on a representative implementation scheme. Figure 6A and Figure 6B A modeled cavity view of the oscillator circuit implementation in the diagram.

[0037] Figure 6E The following is illustrated based on a representative implementation scheme. Figure 6A and Figure 6B The test implementation of the oscillator circuit implementation in the example.

[0038] Figure 7A The combined amplitude versus frequency curves for a low phase noise oscillator using negative feedback, according to a representative implementation, are shown.

[0039] Figure 7B The following is illustrated for use in generating according to a representative implementation scheme. Figure 7A The implementation of an oscillator circuit for a low phase noise oscillator with negative feedback based on the comprehensive curve in the figure. Detailed Implementation

[0040] The present invention includes the following embodiments:

[0041] 1. An oscillator comprising:

[0042] Resonator; and

[0043] A first loop includes an amplifier and a first coupler, and is electrically coupled to the resonator, wherein the oscillator is configured to generate negative feedback of the amplifier relative to a short-circuit terminal or an open-circuit terminal of the cavity in cavity mode, the cavity simulating the oscillator at a frequency deviating from the carrier frequency, and wherein the oscillator experiences bidirectional losses of less than 4.00 dB through the cavity at the frequency deviating from the carrier frequency.

[0044] 2. The oscillator according to Clause 1, further comprising:

[0045] A second loop, which at least partially overlaps with the first loop and includes at least one circuit component between the input and output of the resonator, wherein the second loop provides a feedback signal to the amplifier with an amplitude greater than -4.00 dB relative to the original signal provided to the amplifier at a frequency deviating from the carrier frequency.

[0046] 3. The oscillator according to Clause 1, further comprising:

[0047] The second loop is located between the input and the output of the resonator and includes the amplifier, the first coupler, the first circulator, the phase shifter, the attenuator, and the second circulator.

[0048] The frequency that deviates from the carrier frequency is a high offset frequency;

[0049] The first circulator controls the direction of the signal flow from the output of the first coupler to the resonator, wherein at frequencies deviating from the carrier frequency, the signal flow is reflected back to the first circulator, which then transmits the signal flow to the phase shifter, the attenuator, and the second circulator.

[0050] The second circulator controls the direction of the signal flow from the phase shifter and the attenuator to the resonator, wherein at frequencies deviating from the carrier frequency, the signal flow is reflected back to the first circulator and routed as input to the amplifier.

[0051] The second loop provides a negative feedback signal with an amplitude greater than -4.00 dB relative to the original signal provided to the amplifier at a frequency deviating from the carrier frequency.

[0052] 4. The oscillator according to Clause 3, wherein the attenuator comprises a second coupler and a resistor between the second coupler and ground.

[0053] 5. The oscillator according to Clause 1, further comprising:

[0054] The second loop includes the amplifier, the first coupler, the second coupler, and the third coupler.

[0055] The frequency that deviates from the carrier frequency is a high offset frequency;

[0056] The second coupler couples the signal stream reflected from the resonator to an attenuator, and then to a phase shifter, wherein the signal stream is input to the third coupler and output from the third coupler toward the resonator, and wherein at frequencies deviating from the carrier frequency, the signal stream is reflected toward the amplifier via the third coupler.

[0057] The second loop provides a negative feedback signal with an amplitude greater than -4.00 dB relative to the original signal input to the amplifier at a frequency deviating from the carrier frequency.

[0058] 6. The oscillator according to Clause 1, wherein for the round trip of the first loop, the first loop phase shifts between -30 degrees and +30 degrees.

[0059] 7. The oscillator according to Clause 1, wherein the second loop implements the cavity mode with negative feedback for the oscillator.

[0060] 8. The oscillator according to Clause 1, wherein the negative feedback is based on the output of the amplifier, which has passed through the main path of the first coupler and reflected from the resonator, and has passed through the coupling path of the third coupler, the phase shifter, the attenuator, the coupling path of the second coupler and toward the resonator, and is reflected at a high offset frequency as feedback to the amplifier through the main path of the second coupler.

[0061] The output of the amplifier is fed back to the amplifier via a combination of reflections from the resonator in the first loop.

[0062] 9. The oscillator according to Clause 8, wherein the second loop includes the second coupler, and the output of the second coupler has a fractional amplitude of the output of the first coupler and is fed back to the amplifier.

[0063] 10. The oscillator according to Clause 1, wherein the cavity mode is generated by the resonator by reflecting the output of the amplifier from the resonator.

[0064] 11. The oscillator according to Clause 1, wherein the oscillator generates the cavity mode at the frequency deviating from the carrier frequency by reflecting the output of the amplifier from the resonator at the frequency deviating from the carrier frequency.

[0065] 12. The oscillator according to Clause 1, wherein the frequency deviating from the carrier frequency is greater than + / - 5 kHz.

[0066] 13. An oscillator comprising:

[0067] Resonator;

[0068] The first loop includes an amplifier and a first coupler, and is electrically coupled to the resonator; and

[0069] The second loop generates negative feedback for the amplifier.

[0070] The oscillator is configured to generate negative feedback of the amplifier relative to a short-circuit terminal or an open-circuit terminal of the cavity in cavity mode, the cavity simulating the oscillator at a frequency deviating from the carrier frequency, and wherein the oscillator has a bidirectional loss of less than 4.00 dB through the cavity at the frequency deviating from the carrier frequency.

[0071] 14. The oscillator according to Clause 13, wherein the second loop provides a feedback signal to the amplifier with an amplitude greater than -4.00 dB relative to the original signal provided to the amplifier at a frequency deviating from the carrier frequency.

[0072] 15. The oscillator according to Clause 13, wherein the second loop comprises the amplifier, the first coupler, the first circulator, the phase shifter, the attenuator, and the second circulator.

[0073] The signal stream reflected from the resonator is guided by the first circulator to the phase shifter, the attenuator, and the second circulator.

[0074] The signal from the phase shifter and the attenuator is guided by the second circulator to the resonator, which reflects the signal flow back to the second circulator, and then back to the amplifier.

[0075] The second loop provides a feedback signal with an amplitude greater than -4.00 dB relative to the original signal provided to the amplifier at a frequency deviating from the carrier frequency.

[0076] 16. The oscillator according to Clause 13, further comprising:

[0077] The second loop includes the amplifier, the first coupler, the second coupler, the phase shifter, the attenuator, and the third coupler.

[0078] The second coupler couples the signal reflected from the resonator to the phase shifter, the attenuator, the third coupler, and then to the resonator, which feeds the signal back to the third coupler at a frequency deviating from the carrier frequency, and provides the amplifier with a signal from the third coupler with a signal amplitude greater than -4.00 dB relative to the original signal provided to the amplifier at the frequency deviating from the carrier frequency as negative feedback.

[0079] 17. The oscillator according to Clause 13, wherein the second loop implements a cavity mode for negative feedback of the oscillator.

[0080] 18. The oscillator according to Clause 13, wherein the negative feedback is based on coupling the output of the amplifier through the first coupler to generate the output of the first coupler, the output of the first coupler being reflected from the resonator and coupled with the fractional amplitude of the reflection of the resonator being fed back to the amplifier.

[0081] The output of the amplifier is fed back to the amplifier through a second loop.

[0082] The second loop includes a second coupler, and

[0083] The output of the second coupler has a fractional amplitude of the output of the first coupler and is fed back to the amplifier.

[0084] 19. The oscillator according to Clause 13, wherein the oscillator generates the cavity mode at the frequency deviating from the carrier frequency by reflecting the output of the amplifier from the resonator at the frequency deviating from the carrier frequency.

[0085] 20. The oscillator according to Clause 13, further comprising:

[0086] An attenuator that changes its attenuation over time to stabilize the second loop.

[0087] In the following detailed description, representative embodiments with specific details disclosed are set forth for purposes of explanation rather than limitation, in order to provide a thorough understanding of embodiments implemented according to this teaching. Descriptions of known systems, apparatuses, materials, methods of operation, and methods of manufacture may be omitted to avoid obscuring the description of representative embodiments. However, such systems, apparatuses, materials, and methods known to those skilled in the art are within the scope of this teaching and can be used according to representative embodiments. It should be understood that the terminology used herein is for describing particular embodiments only and is not intended to be limiting. The defined terms are not only the technical and scientific meanings commonly understood and accepted in the technical field of this teaching.

[0088] It should be understood that although the terms first, second, third, etc., may be used herein to describe various elements or components, these elements or components should not be limited by these terms. These terms are used only to distinguish one element or component from another. Therefore, the first element or component discussed below may be referred to as the second element or component without departing from the teaching of this disclosure.

[0089] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the specification and appended claims, the singular forms “a,” “an,” and “the” include both singular and plural forms, unless the context clearly specifies otherwise. Furthermore, when used herein, the terms “comprising” and / or “including” and / or similar terms explicitly state the presence of the stated features, elements, and / or components, but do not exclude the presence or addition of one or more other features, elements, components, and / or groups thereof. As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0090] Unless otherwise stated, when an element or component is referred to as being “connected to,” “coupled to,” or “adjacent to” another element or component, it should be understood that the element or component may be directly connected to or coupled to the other element or component, or that there may be intermediate elements or components present. That is, these and similar terms include situations where one or more intermediate elements or components may be used to connect two elements or components. However, when an element or component is described as being “directly connected” to another element or component, this only includes situations where the two elements or components are connected to each other without any medium or intermediate elements or components.

[0091] In view of the foregoing, this disclosure is intended to demonstrate one or more advantages specifically pointed out below through its various aspects, embodiments, and / or specific features or sub-components. Exemplary embodiments with specific details disclosed are set forth for purposes of explanation and not limitation in order to provide a thorough understanding of embodiments implemented according to this teaching. However, other embodiments that deviate from the specific details disclosed herein, consistent with this disclosure, remain within the scope of the appended claims. Furthermore, descriptions of well-known devices and methods may be omitted so as not to obscure the description of exemplary embodiments. Such methods and devices are within the scope of this disclosure.

[0092] As described below, the oscillator circuit is configured to generate negative feedback at a high offset frequency, significantly deviating from the resonant center frequency. This negative feedback cancels out the input signal component of the signal input to the amplifier at the high offset frequency, effectively reducing phase noise and phase floor noise at the high offset frequency. The oscillator circuit can utilize a resonator to generate negative feedback, provided that the resonator has a different reflection rate for the incident signal at the resonant center frequency compared to the high offset frequency. As used herein, the term "high offset frequency" refers to those frequencies where reflection in cavity mode will be nearly lossless. For example, for a high-quality quartz resonator used at 100MHz, a frequency offset by + / -5kHz from the resonant center has a reflection loss of less than 0.1dB in the cavity mode, and this can be considered nearly lossless. Therefore, the high offset frequency of a high-quality quartz resonator used in a 100MHz oscillator can be considered to represent a distance greater than +5kHz or less than -5kHz from the resonant center, or typically approximately 6*(fo / 2Q). L In this expression, fo is the output frequency of the oscillator, and Q... L The load Q of the resonator varies based on fo and the distribution of the resonator's response amplitude at different frequencies. For a high-quality quartz resonator used in a 100MHz oscillator, at offset frequencies greater than + / - 5kHz from the resonant center, the reflection loss is nearly lossless, and when used to cancel the input signal component of the input signal to the amplifier at high offset frequencies, the negative feedback will lead to an improvement in phase noise and noise floor. The bidirectional loss of the oscillator circuit through the cavity at the high offset frequencies from the carrier frequency will be less than 4.00dB. Furthermore, the reflection at the resonant center frequency is much smaller than the reflection at high offset frequencies. The stronger reflection at high offset frequencies compared to the resonant center frequency can be used and utilized to obtain a higher negative feedback signal at high offset frequencies. The negative feedback signal is used to reduce the signal power at high offset frequencies relative to the resonant center by canceling the signal power of the amplifier input at high offset frequencies, thus improving the phase noise at high offset frequencies. Figure 2A An oscillator model near the resonant center is shown according to a representative implementation for a low phase noise oscillator using negative feedback.

[0093] exist Figure 2A In the model 200A, the oscillator includes a primary feedback loop 201 with a resistor 211, an inductor 212, and a capacitor 213 connected in series, a coupler 220, and an amplifier 250. The signal propagation direction in the primary feedback loop 201 is counterclockwise. The coupler 220 transfers some power from the primary feedback loop 201 as output power to the load 289.

[0094] By way of explanation, coupler 220 ideally couples power between some, but not all, combinations of two of the three marked points, each corresponding to a different port. Therefore, coupler 220 is a directional coupler of a directional nature, and this is also true for directional couplers in the other embodiments described herein. For example, coupler 220 couples power incident on port 1 such that a portion of the incident power leaves port 2 with relatively low loss and 0° phase shift, and a small portion of the incident power leaves port 3 with relatively higher loss than when leaving port 2. The path from port 1 to port 2 of coupler 220 and other couplers may be referred to herein as the main path, while the path from port 1 to port 3 of coupler 220 and other couplers may be referred to herein as the coupling path. The paths from port 2 to port 1 and from port 3 to port 1 may be referred to by the same names or labels as the corresponding paths from port 1 to port 2 and from port 1 to port 3. Coupler 220 is also a reciprocating device, such that it couples power incident on port 2 away from port 1, and couples power incident on port 3 away from port 1. However, coupler 220 does not couple power incident on port 3 away from port 2, or couples power input on port 2 away from port 3. In other words, coupler 220 couples the signal incident on port 1 by distributing the signal between ports 2 and 3. On the other hand, the signals incident on ports 2 and 3 actually pass entirely through port 1. The actual coupler is very close to an ideal coupler, but there will still be a small amount of leakage in the power incident on port 2 and leaving port 3, and in the power incident on port 3 and leaving port 2. Figure 2A In this context, if coupler 220 couples the power of signal B to signal C, which is 6.00 dB lower than the original signal B, then signal D in the primary feedback loop 201 will be approximately 1.6 dB lower than the level of signal B, and a coupler with this performance will be described as having 6.00 dB coupling or a 6.00 dB coupler. 6.00 dB loss and 1.6 dB loss are example performance characteristics for a 100 MHz carrier signal. In the following text, references to the coupler in the embodiments described herein can be references to couplers having the characteristics described for coupler 220.

[0095] exist Figure 2A In this configuration, amplifier 250 amplifies the signal by 10dB with a 0° phase shift in a counter-clockwise direction. Amplifier 250 also amplifies the signal by -10dB with a 180° phase shift in a clockwise direction. Coupler 220 couples power from port 1 of the primary feedback loop with a 0° phase shift to port 2. (The last sentence appears to be incomplete and possibly refers to a different configuration.) Figure 2A In the process, signal A is input to amplifier 250, signal B is output from amplifier 250, and signal C is power coupled out by coupler 220.

[0096] Figure 2B An oscillator model for a low phase noise oscillator using negative feedback at a high offset frequency is shown according to a representative embodiment.

[0097] exist Figure 2B In the model 200B, the oscillator includes a first resistor 291, an amplifier 250, a coupler 220, a second resistor 292, and a load 289. Figure 2B In this paper, oscillator model 200B has aspects of a cavity model between a first resistor 291 and a second resistor 292. Typically, when describing a cavity mode for electronic circuits or mechanical systems, terminals are described as short-circuited or open-circuited. An open-circuited terminal will produce a reflection with a 0° phase shift and an amplitude identical to the incident wave. A short-circuited terminal will produce a reflection with a 180° phase shift and an amplitude identical to the incident wave. The open-circuited cavity terminals described herein are for resistors with large impedances (such as 50 megohms), as 50 megohms is large enough to withstand an open circuit. An example of an electronic cavity with open-circuited terminals is a semiconductor cavity-mode laser. The short-circuited cavity terminals described herein are for resistors with small impedances (such as 50 milliohms), as 50 milliohms is small enough to withstand a short circuit. An example of an electronic cavity with short-circuited terminals is a waveguide resonator in TE10 mode, where the short-circuited end of the resonator closes the cavity at both ends along the direction of the propagating wave and blocks its reflection. Because the terminals on the cavity are essentially infinite or have zero impedance for the modeling described in this paper, there will be no loss at the terminals.

[0098] Furthermore, in the model with couplers described in this paper, the coupler is considered lossless in terms of loss, and therefore there is no loss except for coupling a portion of the signal away from one of the ports. As a result, the loss in the model may be limited to the loss caused by the attenuator. Because the wave in the cavity mode will travel back and forth through the attenuator twice, the loss in the cavity is only twice the attenuator value. In addition, the phase of the cavity model will remain unchanged during the round trip through the cavity, because for an open circuit, reflection will produce a 0° phase shift, and for a short circuit, reflection will produce a 180° phase shift, after which the phase shift is equivalent to a 0° phase shift. Therefore, the 0° phase shift during the round trip will be converted to a series RLC resonator or a parallel RLC resonator, and a 2.00dB attenuation in the oscillator circuit will result in a 4.00dB round trip loss or a -4.00dB gain. It is certain that when the oscillator circuit consistent with oscillator model 200B is started, the maximum signal at the high offset frequency will be used for the first cycle of the oscillator circuit. Then, for each subsequent cycle, the feedback effect described in this paper at high offset frequencies will result in a lower signal at high offset frequencies. The signal may continue to decrease for each cycle until it reaches equilibrium in the oscillator circuit.

[0099] exist Figure 2B In this configuration, amplifier 250 amplifies the signal by 10 dB with a 0° phase shift in the forward direction. Amplifier 250 amplifies the signal by -10 dB with a 180° phase shift in the reverse direction. Coupler 220 couples the power incident on port 1 of the primary feedback loop with a 0° phase shift to exit port 2. As shown, signal A is input to amplifier 250, signal B is output from amplifier 250, and signal C is the power coupled out by coupler 220. Signal D is the power from signal B, which is not coupled out by coupler 220 and remains on the pass-through path to exit port 2. Signal D is reflected by second resistor 292 as signal E, and then signal E travels in the opposite direction through coupler 220 and amplifier 250. Signal E is then reflected by first resistor 291 as signal F. Figure 2B In the oscillator model, the first resistor 291 and the second resistor 292 have high resistances such as 50 megohms and are used as reflective surfaces of the cavity within the cavity.

[0100] As described in this paper, in oscillator model 200B, negative feedback is generated at high offset frequencies that deviate significantly from the resonant center frequency. This negative feedback is used to cancel the input signal component of the signal input to amplifier 250 at the high offset frequency, thereby effectively reducing phase noise and phase floor noise at the high offset frequency. For the above reasons, the gain of the low phase noise oscillator with negative feedback can be expressed based on the location where the signal round trip in cavity mode produces a -4.00 dB gain or a 4.00 dB loss. At high offset frequencies, the gain is related to the reflection described for cavity mode in terms of the short-circuited or open-circuited terminals of the cavity. In terms of frequency, the high offset frequency of a high-quality quartz resonator used in a 100 MHz oscillator can be considered as those frequencies that deviate from the carrier frequency by more than + / - 5 kHz, or typically approximately 6*(fo / 2Q). L The amplitude distribution includes the maximum amplitude at the center frequency and the lower amplitudes at frequencies below and above the center frequency. Additionally, the aforementioned -4.00dB gain or 4.00dB loss can be expressed by the expression Q. L It can be expressed as fo / (Δf(P-3dB)). In this expression, P is the maximum amplitude at the center frequency, P-3dB is 3.00dB lower than P at two frequencies deviating from the center frequency, and Δf is the absolute frequency difference between the two frequencies deviating from the center frequency.

[0101] Provided the feedback signal in the resonant cavity mode is reasonably large enough to produce the required amplitude reduction, the gain at high offset frequencies is expressed as the round trip of the signal in the resonant cavity, and should be -4.00 dB or higher, corresponding to -2.00 dB or higher gain of the attenuator in cavity mode. In other words, for frequencies greater than 6fo / 2Q... L If the round-trip loss in cavity mode is less than 4.00 dB, there will be sufficient signal for negative feedback to be available close to fo / 2Q. L Significant phase noise improvement is achieved with offsets greater than 6fo / 2Q. L If the round-trip loss through the cavity mode is less than 4.00 dB at the offset, this indicates that the offset is close to fo / 2Q. L At this point, one or more off-resonant reflections can be used to achieve significant phase noise improvement. Above 6fo / 2Q... L When the offset is small, one or more reflections can be considered to be essentially lossless.

[0102] For the implementation described later, the less than 4.00 dB loss bidirectionally through the equivalent cavity at high offset frequencies corresponds to two reflections by the resonator supplying the input signal to the oscillator. Reflections occur in the signal path to feed back to the amplifier. For the high offset frequency component, each reflection results in a loss of less than 2.00 dB, and in the representative implementation described later, both such reflections still retain a substantial negative feedback signal for the amplifier, which in turn allows the amplifier to cancel the input signal at high offset frequencies, thus reducing the noise floor at high offset frequencies. A loss of less than 2.00 dB can be observed in simulations and / or tests of actual circuits, and in some implementations, the actual loss of the feedback signal can be even smaller. (Described later...) Figure 5A In the implementation of / 5B, the equivalent reflection is composed of signal E and signal F, as well as Figure 5A Signals I2 and J are shown in the diagram, causing signal K to be fed back to amplifier 550. Figure 6A In the implementation scheme of / 6B / 6C, the equivalent reflection is composed of signal E and signal F, as well as Figure 6B Signals I2 and J1 are shown in the diagram, which cause signal J2 to be fed back to amplifier 650. Figure 5A The signal K and Figure 6B The feedback of signal J2 is used by amplifiers 550 and 650 to cancel the negative feedback signals of the input signals of these amplifiers at high offset frequencies, which results in a reduction of the phase noise floor at these frequencies in the output signals from these amplifiers.

[0103] Figure 3 A simplified oscillator circuit for a low phase noise oscillator using negative feedback is shown according to a representative embodiment.

[0104] exist Figure 3 In the simplified oscillator circuit 300, a primary feedback loop 301 with a resistor 311, an inductor 312, and a capacitor 313 connected in series, a coupler 320, and an amplifier 350 are included. The signal propagation direction in the primary feedback loop 301 is counterclockwise. The coupler 320 transfers some power from the primary feedback loop 301 as output power to the load 389.

[0105] exist Figure 3 In the circuit, amplifier 350 amplifies the signal by 10dB with a 0° phase shift in the main counterclockwise direction. Amplifier 350 amplifies the signal by -10dB with a 180° phase shift in the clockwise direction. Coupler 320 couples the power out of the primary feedback loop. For example... Figure 3 In the simplified oscillator circuit 300, signal A is input to amplifier 350, signal B is output from amplifier 350, signal C is power coupled out by coupler 320, and signal D remains in the primary feedback loop 301 after the power coupling output of signal C. The conversion from signal B to signal D in coupler 320 enters ports 1 and 2 with a 0° phase shift. In the simplified oscillator circuit 300, negative feedback is generated at a high offset frequency that deviates significantly from the resonant center frequency. This negative feedback is used to cancel the input signal component of the signal input to amplifier 350 at the high offset frequency, thereby effectively reducing phase noise and phase floor noise at the high offset frequency.

[0106] Figure 4A Another simplified oscillator circuit is shown, according to a representative embodiment, for a low phase noise oscillator using negative feedback at a high offset frequency where the cavity model is effective.

[0107] exist Figure 4A In the simplified oscillator circuit 400, there are a first coupler 420, a second coupler 421, a phase shifter 431, a first test port 441 and a second test port 442, a first amplifier 450, a second amplifier 451, a first resistor 491 and a second resistor 492.

[0108] exist Figure 4AIn the simplified oscillator circuit 400, the first resistor 491 and the second resistor 492 have high resistances, such as 50 megohms, and serve as the reflecting surface of the cavity in the cavity model. The phase shifter 431 produces a 90° phase shift and has an impedance of 50 ohms. The first coupler 420 has a 60dB coupling value, 0dB loss, 140dB directivity, and 50-ohm impedance. The second coupler 421 has a 60dB coupling value, 0dB loss, 140dB directivity, and 50-ohm impedance. The first amplifier 450 has a 10dB positive gain and a 90° negative phase shift, as well as a -10dB reverse gain and a 270° negative phase shift. The second amplifier 451 has a 120dB forward gain and a 0° phase shift. The gain of the second amplifier 451 and the coupling values ​​of the first coupler 420 and the second coupler 421 are much higher than those used in actual circuits and are used to better represent performance in the model under ideal conditions. The first test port 441 has a 50-ohm impedance, while the second test port 442 has a 50-ohm impedance.

[0109] For the oscillator circuit described in this paper, compared to Leeson's law oscillators, even at the resonant center, cavity feedback reduces the amplitude of the output signal in cavity mode. The oscillator circuit described in this paper will, for example, be derived from... Figure 4A The amplitude of the power coupled by the first coupler 420 in the oscillator decreases more at high offset frequencies than at the resonant center frequency. This is an important aspect of how high offset phase noise and phase floor noise can be improved. In fact, the round-trip gain of the signal in cavity mode in single-cycle form is lowest at the resonant center frequency before feedback can occur at resonance, and increases at high offset frequencies because the resonator acts like an ideal open circuit of a series RLC resonator, or an ideal short circuit of an ideal parallel RLC resonator. Therefore, at high offset frequencies, when working with larger signals, this higher-level signal can be used to provide higher negative feedback relative to the resonant center, thus preferentially reducing the signal at high offset frequencies. Because the signal gain in cavity mode only asymptotically approaches a certain final value, a single-cycle round-trip gain of -4.00 dB or higher in cavity mode at high offset frequencies is a relatively simple indicator of the benefit of using the low phase noise oscillator with the negative feedback described herein. In other words, a single-cycle round-trip gain of -4.00 dB or less is one aspect of the frequency response obtained at high offset frequencies, but not the only, or even the most important, aspect of the improvement described herein.

[0110] Figure 4B and 4C The diagram illustrates the relationship between the representative implementation scheme and... Figure 4A Additional view of the same simplified oscillator circuit for a low phase noise oscillator using negative feedback. Figure 4A , 4BThe signal flow from the first test port 441 is shown together with 4C. Figure 4A In this circuit, the signal flow begins with signal A, which is input through the first test port 441. Signal A passes through the second amplifier 451 and is output from the second amplifier 451 as signal B. Signal B passes through the first coupler 420, and signal C is emitted from the first coupler 420. Signal C passes through the first amplifier 450, and signal D is emitted from the first amplifier 450 to the second coupler 421.

[0111] Then as Figure 4B As shown, signal E is emitted from the second coupler 421 to the second test port 442. Signal F is also emitted from the second coupler 421, but towards the second resistor 492. Signal F is reflected from the second resistor 492 as signal G. Then as... Figure 4C As shown, signal G passes through the second coupler 421 and the first amplifier 450, and signal H is emitted from the first amplifier 450. Signal H passes through the first coupler 420. As a result, signal I is emitted from the first coupler 420 toward the first test port 441 where the signal dissipates, and signal J is emitted from the first coupler 420 toward the phase shifter 431. Signal K is emitted from the phase shifter 431 and reflected from the first resistor 491 as signal L. Signal L then passes through the phase shifter 431. Additional components of the original signal A (e.g., signal M (not shown), signal N (not shown)) are emitted from the phase shifter 431, pass through the first coupler 420, and provide negative feedback to the original signal input to the amplifier 450, which is Figure 4A Signal C in the middle.

[0112] exist Figure 4A , 4B In 4C, the first resistor 491 and the second resistor 492 strongly reflect the incident signal at high offset frequencies. Due to the high 60dB coupling between ports 1 and 3 of the second coupler 421, there is relatively low loss between the outputs of the first amplifier 450 and the second resistor 492, resulting in low insertion loss in the through path between ports 1 and 2 of the second coupler 421. The first resistor 491, the second resistor 492, and the phase shifter 431 are used to provide negative feedback to the first amplifier 450. Therefore, Figure 4A , 4B Figures 4C and 4C partially illustrate a modeled cavity view for high offset signal components.

[0113] Although not detailed herein, the use of a low-phase-noise oscillator with negative feedback can effectively reduce the amplitude level of the phase noise floor. In the simplified oscillator circuit 400, negative feedback is generated at a high offset frequency, which deviates significantly from the resonant center frequency. This negative feedback is used to cancel the input signal component of the signal input to the first amplifier 450 at the high offset frequency, thereby effectively reducing phase noise and phase noise floor at the high offset frequency. As oscillator performance improves, the noise floor (dBm / Hz) decreases in terms of power and in terms of noise power relative to the carrier (dBc / Hz). However, if described in terms of dynamic range, the signal-to-noise ratio (SNR) in dB increases. Therefore, a signal with a carrier power of +10 dBm and a noise floor of -160 dBm / Hz has a noise floor power relative to a carrier of -170 dBc / Hz, and the SNR measured in a 1 Hz bandwidth is 170 dB. If oscillator performance is improved by further reducing the phase noise floor by 10dB, the phase noise floor is now -170dBm / Hz, the noise power relative to the carrier is -180dBc / Hz, and the signal power relative to noise (measured over a 1Hz bandwidth) is 180dB. Below Figure 7A The curves illustrate examples of how to reduce the noise floor, but these curves will vary depending on the details of the oscillator circuit implementation consistent with the description herein.

[0114] Figure 5A An oscillator circuit implementation for a low phase noise oscillator using negative feedback, according to a representative embodiment, is shown.

[0115] exist Figure 5A In this circuit, oscillator circuit 500A includes resonator 510, primary loop 501, and second loop 502. Resonator 510 includes resistor 511, inductor 512, and capacitor 513. Resistor 511, inductor 512, and capacitor 513 are connected in parallel within resonator 510. Primary loop 501 is the first loop and includes first circulator 561, second circulator 562, first coupler 520, resonator 510, and first amplifier 550. For the round trip of primary loop 500A, primary loop 500A can be phase-shifted between -30° and +30°.

[0116] In the embodiments described herein, the second loop is a feedback loop and includes at least one circuit component. Specifically, in Figure 5AIn one embodiment, the second loop 502 further includes a first circulator 561, a second circulator 562, a first coupler 520, and a first amplifier 550, as well as an attenuator 570 and a phase shifter 531. The sum of the phase shifts through the attenuator 570 and the phase shifter 531 can be, for example, 180°. The first coupler 520 transmits some of the power output from the first amplifier 550 as output power to the load 589.

[0117] Resonator 510 is physically located in primary loop 501, but functionally it is part of both primary loop 501 and second loop 502, as it is crucial for the correct operation of feedback in second loop 502. Resonator 510 exhibits higher reflection for signals at frequencies significantly deviating from the resonant center (carrier frequency) compared to, for example, signals at the resonant center. Using appropriate circuitry, such as in oscillator circuit 500A, a greater amount of negative feedback can be provided at these frequencies significantly deviating from the resonant center. This reduces the amplitude of the high-offset signal component relative to the carrier frequency signal component, thereby improving phase noise. That is, in oscillator circuit 500A, negative feedback is generated at high-offset frequencies significantly deviating from the resonant center frequency, allowing the negative feedback to cancel the input signal component of the signal input to first amplifier 550 at the high-offset frequency, thus effectively reducing phase noise and phase floor noise at high-offset frequencies.

[0118] In other words, primary loop 501 and second loop 502 overlap, and even though phase shifter 531 and attenuator 570 are not in the first loop, they contribute to the characteristics of the feedback to first amplifier 550. Similarly, reflections from resonator 510 contribute to the characteristics of second loop 502, making resonator 510 functionally still part of second loop 502. Therefore, the components added in second loop 502 work together with the components in primary loop 501, which includes resonator 510. Resonator 510 strongly reflects the incident signal component at high offset frequencies, and the reflected signal output from first amplifier 550 is reflected from resonator 510 and circulated into second loop 502 by second circulator 562.

[0119] By explanation, the first circulator 561 and the second circulator 562 along Figure 5AThe counter-clockwise direction changes the direction of the signal flow. Each of the first circulator 561 and the second circulator 562 may have three ports, such that a signal entering either the first circulator 561 or the second circulator 562 at one port will exit the first circulator 561 or the second circulator 562 in a counter-clockwise direction via the next port. As an example, a signal entering the first circulator 561 from the left will exit from the right towards the first amplifier 550, while a signal entering the first circulator 561 from the right will exit from the top towards the attenuator 570.

[0120] For example, resistor 511 has a resistance of 25 ohms, capacitor 513 has a capacitance of 8 μF (microfarads), and inductor 512 has an inductance of 0.316629 pH (pichenries). The first circulator 561 has a one-turn loss of 0.5 dB, and the second circulator 562 has a one-turn loss of 0.5 dB. The first amplifier 550 has a primary gain of 12.00 dB and a phase shift of 0° in the forward direction (S21), an amplitude gain of zero and a phase shift of 0° for its input reflection coefficient (S11), an amplitude gain of zero and a phase shift of 180° for its output reflection coefficient (S22), and an amplitude gain of zero and a phase shift of 0° for its reverse emission coefficient (S12). The first coupler 520 couples power from port 1 to port 2 of the first coupler 520 with a loss of 1.6 dB, and from port 1 to port 3 of the first coupler 520 with a loss of 6.00 dB, from which the signal enters the load 589. The first coupler 520 has a 50-ohm impedance. The second circulator 562 couples the power output from port 2 of the second circulator 562 in a counterclockwise direction to the input of the resonator 510. The reflection from the resonator 510 travels towards the second circulator 562 and is routed toward the phase shifter 531. The phase shifter 531 produces a 90° phase shift and has a 50-ohm impedance. The first circulator 561 couples the power output counterclockwise from the second loop 502 back to the primary loop 501, where the signal circulates clockwise until it reaches the resonator 510. The signal is reflected from resonator 510 and loops counterclockwise back to first circulator 561 in primary loop 501. The signal travels counterclockwise in first circulator 561 and is routed to the input of first amplifier 550, where it provides negative feedback.

[0121] Attenuator 570 can have time-dependent attenuation. For example, attenuator 570 can allow negative feedback to gradually increase so that a second loop 502 with a first circulator 561 and a second circulator 562 can use high feedback without causing oscillation. This can improve the stability of the negative feedback by gradually decreasing the attenuation from an initially large amount. An example of attenuator 570 is a coupler as described herein, but the attenuators described herein are not limited to couplers. For example, an attenuator consistent with the teachings herein could be a resistive attenuator. As long as the circulator circuit provides maximum negative feedback, a circuit such as an oscillator circuit 500A with a first circulator 561 and a second circulator 562 significantly improves phase noise. However, on the first cycle of feedback, the feedback signal back to the input of the first amplifier 550 may be relatively large because there is no feedback for the first cycle, and this may cause ringing in the oscillator circuit 500A. Any such ringing can be avoided by time-dependent attenuation, such that attenuator 570 is initially set high enough to stabilize the oscillator circuit 500A in the presence of feedback, and the output power used for noise is reduced. By reducing the noise output power, a higher level of feedback can be allowed without causing instability, which in turn results in a lower noise output power. As this process continues, the attenuation can eventually be set to 0dB to obtain maximum feedback and maximum noise reduction. This can be implemented in a simple and direct manner using a PIN diode attenuator that allows continuously variable attenuation without increasing noise. Therefore, the attenuator 570 in Figure 5 can have an attenuation that varies over time. An attenuator 570 with a time-varying attenuation at setup can be used to stabilize the second loop 502.

[0122] Figure 5B Including with Figure 5A The same oscillator circuit is 500A. Figure 5A and 5BThe signal flow starting from the input of the first amplifier 550 is illustrated. The input of the first amplifier 550 is the first signal A, and the output of the amplifier is the second signal B. The power coupled from the primary loop 501 by the first coupler 520 is the third signal C, and the power passed through the first coupler 520 in the first loop 501 and the second loop 502 is the fourth signal D. Signal D then enters the second circulator 562, and this power is routed as signal E to the resonator 510. At a high offset frequency, signal E is strongly reflected from the resonator 510 as signal F, which travels back to the second circulator 562 and is routed to the second loop 502, where signal F becomes signal G. Signal G travels toward the phase shifter 531 and leaves the phase shifter 531 and attenuator 570 as signal H, enters the first circulator 561, and turns back to the resonator 510 as signal I1. Signal I1 flows clockwise into primary loop 501, where it travels as signal I2 to resonator 510, and at a high offset frequency, it is strongly reflected by resonator 510 as signal J. Signal J returns to first circulator 561 and is emitted as signal K as input to first amplifier 550, thereby providing feedback to first amplifier 550.

[0123] In addition, Figure 5A and 5B Every variation of the signal generated by the first signal A is not shown. For example, even if the eleventh input enters the first amplifier 550 as signal K, it will result in an additional output, which in turn will result in two more signals being output from the first coupler 520. Therefore, the input A of an amplifier such as the first amplifier 550 can result in many other signal components not specified in the accompanying drawings. That is, Figure 5A and 5B The signal flow shown only illustrates the first cycle of signals with different characteristics present in the oscillator circuit 500A. For example, the first signal A and the eleventh signal k are both inputs to the first amplifier 550, and this reflects one aspect of the feedback characteristics of the oscillator circuit 500A, provided that the eleventh signal k is generated by the first signal A. Additionally, signals may change each time they pass through any element in the primary loop 501 or the second loop 502, or are reflected by any element. For example, signals at frequencies significantly deviating from the carrier signal's high offset frequency can be reflected by the resonator 510, and such signals may lose some power due to reflection.

[0124] exist Figure 5A and 5BIn one implementation, the output of the first amplifier 550 is fed back to the first amplifier 550 via a combination of reflections from the resonator 510 in the primary loop 501. For example, signal E is reflected from the resonator 510 at one point as signal F, and signal I2 is reflected from the resonator 510 at another point as signal J. The reflection of the high offset component of the output of the first amplifier 550 may be due to the second looper 562, as long as the second loop 502 exists. Figure 5B This allows the signal G to be fed into the second loop 502 as feedback to the first amplifier 550, for example. Therefore, the feedback is due to... Figure 5A and Figure 5B The feedback is caused by the second loop 502 in this embodiment, but in this and other embodiments, the feedback may be caused by a combination of reflections from a resonator such as resonator 510.

[0125] Figure 5C The following is illustrated based on a representative implementation scheme. Figure 5A and Figure 5B A modeled cavity view of the oscillator circuit implementation in the diagram. Figure 5C middle, Figure 5A and 5B The cavity-mode performance of the oscillator circuit implementation effectively leads to a short circuit at the high offset frequency of the resonator. The resonator 510 is used as a short circuit modeled by the first resistor 591 and the second resistor 592 with low values ​​(such as 50 milliohms), so it is easier to know why the loss reflection in the first resistor 591 and the second resistor 592 is low, which will lead to a strong negative feedback signal entering the input of the first amplifier 550.

[0126] exist Figure 5C In this circuit, for signals at high offset frequencies, the second loop 502 receives input from the second circulator 562, which is reflected from the second resistor 592 having a 50 milliohm impedance. Due to the high coupling value of 60 dB between ports 1 and 3 of the first coupler 520, there is relatively low loss between the outputs of the first amplifier 550 and the second circulator 562, resulting in low loss in the through path from port 1 to port 2. The second circulator 562 and the first circulator 561, along with the phase shifter 531 and the attenuator 570, are used to provide negative feedback to the first amplifier 550. Therefore, Figure 5C The modeled cavity view is effectively equivalent to Figure 5A and 5B The high offset signal component, and Figure 5C The oscillator circuit in the middle is therefore related to Figure 5A and 5B The same circuit is labeled as oscillator circuit 500A.

[0127] Figure 5DAn implementation of a modified oscillator circuit for a low-phase-noise oscillator using negative feedback, according to a representative embodiment, is shown. Figure 5D In the implementation plan, from Figure 5A and 5B The attenuator 570 is designated as coupler 571. Coupler 571 couples the power from the second loop 502 to produce a 10 dB loss. Coupler 571 has a 50 ohm impedance. Coupler 571 also introduces a 90° phase shift in the second loop 502.

[0128] Figure 5E The following is illustrated based on a representative implementation scheme. Figure 5A and Figure 5B The test implementation of the oscillator circuit implementation in the example.

[0129] exist Figure 5E In one embodiment, the oscillator circuit 500C includes a first test port 541 for inputting a signal to the oscillator circuit implementation, and a second test port 542 for outputting a signal from the oscillator circuit implementation. The input signal from the first test port 541 is input to a second amplifier 551, and the output from the second amplifier 551 is primarily coupled to a first circulator 561 via a second coupler 521. The second test port 542 replaces, for example,... Figure 5C The load 589 in the attached figure receives power from the first power amplifier 550 and is coupled out through the first coupler 520.

[0130] exist Figure 5E In one embodiment, the first resistor 591 may have a 50 milliohm impedance and the second resistor 592 may have a 50 milliohm impedance. The first test port 541 couples power to an oscillator circuit 500C immediately following the first resistor 591, the oscillator circuit serving as a 50 milliohm terminal.

[0131] Figure 6A An oscillator circuit implementation for a low phase noise oscillator using negative feedback, according to a representative embodiment, is shown.

[0132] exist Figure 6AIn this circuit, oscillator circuit 600A includes a resonator 610, a primary loop 601, and a secondary loop 602. Resonator 610 includes a resistor 611, an inductor 612, and a capacitor 613. Resistor 611, inductor 612, and capacitor 613 are connected in parallel within resonator 610. Primary loop 601 is the first loop and includes a first coupler 620, a second coupler 621, a third coupler 622, resonator 610, and a first amplifier 650. Secondary loop 602 further includes the first coupler 620, the second coupler 621, the third coupler 622, the first amplifier 650, a phase shifter 631, and an attenuator 670. First coupler 620 transmits some power from the first amplifier 650 as output power to load 689. For the round trip of primary loop 601, phase shifting of primary loop 601 can occur between -30° and +30°.

[0133] For example, resistor 611 has a resistance of 25 ohms, capacitor 613 has a capacitance of 8 μF (microfarads), and inductor 612 has an inductance of 0.316629 pH (pichenries). The first coupler 620 has a loss of 6.00 dB from port 1 to port 3, the second coupler 621 has a loss of 6.00 dB from port 1 to port 3, and the third coupler 622 has a loss of 6.00 dB from port 1 to port 3. The output of the second coupler 621 has a fractional amplitude of the output of the first coupler 620, and as... Figure 6A As shown in the implementation scheme, the output of the second coupler 621 may also have a fractional amplitude of the output of the third coupler 622.

[0134] The impedance of the first coupler 620 is 50 ohms, the impedance of the second coupler 621 is 50 ohms, and the impedance of the third coupler 622 is 50 ohms. The first amplifier 650 has a primary gain of 16.00 dB and a 0° phase shift in the forward direction (S21), zero amplitude gain and 0° phase shift for its input reflection coefficient (S11), zero amplitude gain and 180° phase shift for its output reflection coefficient (S22), and zero amplitude gain and 0° phase shift for its inverse coefficient (S12). The first coupler 620 couples power from a signal incident on port 1 of the first coupler 620 to a signal leaving port 3 of the first coupler 620 with a loss of 6.00 dB, where the signal becomes signal C and is transmitted to the load 689. The phase shifter 631 produces a 0° phase shift and has an impedance of 50 ohms.

[0135] Resonator 610 is physically located in the primary loop 601, but functionally it is part of both the primary loop 601 and the secondary loop 602, as it is crucial for the correct operation of the feedback in the secondary loop 602. Resonator 610 exhibits higher reflection for signals at frequencies significantly deviating from the resonant center (carrier frequency) compared to, for example, signals relative to the resonant center. Using appropriate circuitry, such as that in oscillator circuit 600A, a greater amount of negative feedback can be provided at these frequencies significantly deviating from the resonant center. This reduces the amplitude of the high-offset signal components relative to the carrier frequency signal components, thereby improving phase noise.

[0136] In other words, the primary loop 601 and the secondary loop 602 overlap, and even though the phase shifter 631 and attenuator 670 are not in the primary loop 601, they still contribute to the characteristics of the feedback to the first amplifier 650. Similarly, the reflection from the resonator 610 contributes to the characteristics of the secondary loop 602, making the resonator 610 functionally still part of the secondary loop 602. Therefore, the components added in the secondary loop 602 work together with the components in the primary loop 601, which includes the resonator 610. The resonator 610 strongly reflects the incident signal component at high offset frequencies, and the reflected signal output from the first amplifier 650 is partially coupled from port 1 of the third coupler 622 to port 3 of the third coupler 622 and enters the secondary loop 602.

[0137] As shown, where each of the second coupler 621 and the third coupler 622 has a 90° phase shift, the sum of the phase shifts between attenuator 670 and phase shifter 631 can be nominally 0°. Attenuator 670 can have time-dependent attenuation, but the final attenuation is lower than the initial attenuation, attenuating to anywhere and including 0 dB. Of course, for different embodiments, the value of oscillator circuit 600A can be varied, such as to optimize performance according to the high offset frequency response sought for oscillator circuit 600A. Similar to attenuator 570 described with respect to the previous embodiment, attenuator 670 can allow the negative feedback to increase gradually so that the secondary loop 602 with the second coupler 621 and the third coupler 622 can use high feedback without causing oscillation. This can improve the stability of the negative feedback by gradually decreasing the attenuation from an initial larger amount. That is, as long as the coupler circuit provides the maximum negative feedback, such as having

[0138] The circuitry of the oscillator circuit 600A with the second coupler 621 and the third coupler 622 significantly improves the phase noise. However, in the first cycle of feedback, the feedback signal returning to the input of the first amplifier 650 may be relatively large because there is no feedback for the first cycle, and this may cause ringing in the oscillator circuit 600A. Any such ringing can be avoided by time-dependent attenuation, such that the attenuator 770 is initially set high enough for the oscillator circuit 600A to stabilize under feedback, and the output power for noise is reduced. By reducing the noise output power, a higher level of feedback can be allowed without causing instability, and this in turn results in lower noise output power. As this process continues, the attenuation can eventually be set to 0dB to obtain maximum feedback and maximum noise reduction. Therefore, the attenuator 670 in Figure 5 can have a time-varying attenuation and can be, for example, a PIN diode attenuator. In the oscillator circuit 600A, negative feedback is generated at a high offset frequency that deviates significantly from the resonant center frequency. This negative feedback is used to cancel the input signal component of the signal input to the first amplifier 550 at the high offset frequency, thereby effectively reducing the phase noise and phase floor noise at the high offset frequency.

[0139] Figure 6B Including with Figure 6A The same oscillator circuit is 600A. Figure 6A and 6BThe signal flow starting from the input of the first amplifier 650 is illustrated. The input of the first amplifier 650 is the first signal A, and the output of the first amplifier 650 is the second signal B. The power coupled from the output of the first amplifier 650 away from the primary loop 601 and the secondary loop 602 through the first coupler 620 is the third signal C, and the power coupled through the first coupler 620 in the primary loop 601 and the secondary loop 602 is the fourth signal D. Signal D is output from port 2 of the first coupler 620 with a loss of 1.6 dB, where it reaches the resonator 610 as signal E through the third coupler 622. Signal E at a high offset frequency is strongly reflected from the resonator 610 and becomes signal F, which is reflected back towards the third coupler 622. Signal F is coupled from the primary loop 601 with a loss of 6.00 dB to the secondary loop 602, where it becomes signal G and reaches the phase shifter 631. After signal G travels through phase shifter 631 and attenuator 670, it becomes signal H and travels to port 3 of second coupler 621. Signal H leaves port 1 of second coupler 621 as signal I1 and reaches signal I2 resonator 610 in a clockwise direction on primary loop 601. At a high offset frequency, signal I2 is strongly reflected from resonator 610 and becomes signal J1, which returns counterclockwise on primary loop 601 to the input of first amplifier 650, where it is fed back as signal J2 to the input of first amplifier 650.

[0140] Figure 6A and 6B The signal flow shown represents only a portion of the signals with different characteristics present in the oscillator circuit 600A. For example, both the first signal A and the tenth signal J2 are inputs to the first amplifier 650, and this reflects one aspect of the feedback characteristics of the oscillator circuit 600A, provided that the tenth signal J2 is generated by the first signal A. Furthermore, signals may change each time they pass through any element in the primary loop 601 or the secondary loop 602, or are reflected by any element. For example, signals at frequencies significantly deviating from the carrier signal's high offset frequency may be reflected by the resonator 610, and such signals may lose some power due to reflection.

[0141] Figure 6C Another oscillator circuit implementation for a low phase noise oscillator using negative feedback, according to a representative embodiment, is shown.

[0142] exist Figure 6CIn this circuit, oscillator circuit 600B includes a resonator 610, a primary loop 601, and a secondary loop 602. Resonator 610 includes a resistor 611, an inductor 612, and a capacitor 613. Resistor 611, inductor 612, and capacitor 613 are connected in parallel within resonator 610. Primary loop 601 includes a first coupler 620, a second coupler 621, a third coupler 622, and a first amplifier 650. Secondary loop 602 further includes the first coupler 620, the second coupler 621, the third coupler 622, the first amplifier 650, a phase shifter 631, and an attenuator 670. First coupler 620 transmits some power output from the first amplifier 650 as output power to load 689.

[0143] and Figure 6A and Figure 6B Compared to the implementation plan, Figure 6C The third coupler 622 in the oscillator circuit 600B couples the power incident on port 1 to the secondary loop 602 through port 2, and couples the power incident on port 1 to the primary loop 601 through port 3. Figure 6C The oscillator circuit 600B provides a scenario where the first amplifier 650 has excessive gain and power to obtain a greater amount of reflected power into the feedback loop. For example, any high-offset frequency portion of the signal incident from port 1 of the third coupler 622 to the resonator 610 will be reflected back from the resonator 610 to the third coupler 622. In the oscillator circuit 600B, the power coupled from port 1 to port 2 of the third coupler 622 will be fed to the secondary loop 602, while... Figure 6A and Figure 6B In the oscillator circuit 600A, the power coupled from port 1 to port 2 of the third coupler 622 is fed back to the primary loop 601. The power fed to the secondary loop 602 can be a larger portion of the power incident on port 1 of the third coupler 622. Figure 6D The following is illustrated based on a representative implementation scheme. Figure 6A and Figure 6B A modeled cavity view of the oscillator circuit implementation in the diagram.

[0144] exist Figure 6D middle, Figure 6A and 6B The cavity-mode performance of the oscillator circuit implementation effectively leads to a short circuit at high offset frequencies. The resonator 610 is used as a short circuit modeled by the first resistor 691 and the second resistor 692 with low values ​​(such as 50 milliohms), so it is easier to know why the loss reflection in the first resistor 691 and the second resistor 692 is low, which will lead to a strong negative feedback signal entering the input of the first amplifier 650.

[0145] exist Figure 6D In this circuit, for signals at high offset frequencies, secondary loop 602 receives input from third coupler 622, the signal being reflected from second resistor 692 with a 50 milliohm impedance. Due to the coupling between ports 1 and 3 of first coupler 620, there is relatively low loss between the outputs of first amplifier 650 and third coupler 622. Third coupler 622 and second coupler 621, along with phase shifter 631 and attenuator 670, are used to provide negative feedback to first amplifier 650. Therefore, Figure 6D The modeled cavity view is effectively equivalent to Figure 6A and 6B The high offset signal component, and Figure 6D The oscillator circuit in the middle is therefore related to Figure 6A and 6D The same circuit is labeled as oscillator circuit 600A.

[0146] Figure 6E The following is illustrated based on a representative implementation scheme. Figure 6A and Figure 6B The test implementation of the oscillator circuit implementation in the example.

[0147] exist Figure 6E In one embodiment, a first test port 641 is used to input a signal to an oscillator circuit implementation of an oscillator circuit 600C, and a second test port 642 is used to output a signal from the oscillator circuit implementation of an oscillator circuit 600C. The input signal from the first test port 641 is input to a second amplifier 651, and the output from the second amplifier 651 is primarily coupled to the first amplifier 650 via a second coupler 621. The second test port 642 replaces... Figure 6A and 6B The load 689 in the middle receives power output from the first power amplifier 650 and coupled out through the first coupler 620.

[0148] exist Figure 6E In one embodiment, the first resistor 691 may have a 50 milliohm impedance and the second resistor 692 may have a 50 milliohm impedance. The first test port 641 couples power to an oscillator circuit 500D immediately following the first resistor 691, the oscillator circuit serving as a 50 milliohm terminal.

[0149] Figure 7A It shows that according to such Figure 7B The figure shows a composite amplitude versus frequency curve for an open-circuit model of a low-phase-noise oscillator using negative feedback, representing a typical implementation.

[0150] exist Figure 7AIn the diagram, the Y-axis represents the losses of the open-loop model of the oscillator circuit, and the X-axis represents the frequency of the signal reflected in the losses. As shown, the minimum loss to reach 100 MHz is -4.00 dB compared to similar oscillators (such as oscillators without negative feedback designed according to Leeson's law). This -4.00 dB loss is merely an illustration of the losses below the resonant center for a specific resonator configuration and is independent of the -4.00 dB round-trip loss of the cavity mode discussed earlier. Therefore, if 100 MHz is the carrier signal for the oscillator circuit shown in Figure 7, the high offset frequency from the carrier signal indicates a loss significantly greater than the loss present in the carrier signal.

[0151] Figure 7B The following is illustrated for use in generating according to a representative implementation scheme. Figure 7A The implementation of an oscillator circuit for a low phase noise oscillator with negative feedback based on the comprehensive curve in the figure.

[0152] exist Figure 7B In this configuration, the oscillator circuit 700 is a test implementation having a first test port 741 for input and a second test port 742 for output. The only loop shown is loop 702, which is the second loop in a similar configuration. Loop 702 includes a first circulator 761, a first amplifier 750, a first coupler 720, a second circulator 762, a phase shifter 731, and an attenuator 770. Resonator circuits are located on the leftmost and rightmost sides. The first resonator circuit includes a resistor 717, an inductor 718, and a capacitor 719, and is located between the second coupler 721 and a resistor 795. The second resonator circuit includes a resistor 711, an inductor 712, and a capacitor 713, and is located between the second circulator 762 and a resistor 796.

[0153] The input signal from the first test port 741 passes essentially through the second amplifier 751 and is coupled from port 3 to port 1 by the second coupler 721 for circulation by the first circulator 761. The first circulator 761 provides the signal from the second coupler 721 as input to the first amplifier 750. The first coupler 720 couples the output of the first amplifier 750 from port 1 to port 3, and then as output to the second test port 742.

[0154] exist Figure 7B In the diagram, resistor 795 has a 50-ohm impedance, and resistor 796 has a 50-ohm impedance. The 50-ohm terminal grounding shown for resistors 795 and 796 indicates the typical 50-ohm input and output impedance of the amplifier.

[0155] As described above, negative feedback is generated at a high offset frequency, which deviates significantly from the resonant center frequency of the oscillator circuit. This negative feedback is used to cancel the input signal component of the signal input to the amplifier at the high offset frequency, thereby effectively reducing phase noise and phase noise floor at the high offset frequency. Therefore, the oscillator circuit can utilize a resonator that reflects the incident signal at the resonant center frequency differently compared to the high offset frequency. The reflection at the resonant center frequency is much smaller than the reflection at the high offset frequency. The stronger reflection at the high offset frequency compared to the resonant center frequency can be used and utilized to obtain a stronger negative feedback signal at the high offset frequency. The negative feedback signal is used to reduce the signal power at the high offset frequency, thus improving the phase noise at the high offset frequency. Therefore, compared to a standalone amplifier, a low-phase-noise oscillator using negative feedback can significantly reduce high-offset phase noise and noise floor. This improvement (reduction) in phase noise is reflected even when using the same resonator as used in known oscillators, and even when using an amplifier with similar power dissipation to other oscillators. The low-phase-noise oscillator using negative feedback described in this paper is a novel type of oscillator, particularly at high offset frequencies. This novel oscillator uses negative feedback in cavity mode to provide low phase noise. As described, the high offset frequency can be greater than fo / 2Q. L The offset frequency is, however, a more convenient way to describe high offset frequencies than the necessary method. As mentioned in the introduction, Leeson-class oscillators do not provide feedback to the amplifier at any offset in cavity mode, and in loop feedback mode, their feedback is greater than fo / 2Q. L The offset begins to decrease rapidly so that the offset is greater than 6fo / 2Q. L The time difference is essentially negligible. Frequency offset is higher than 6fo / 2Q. L This will result in essentially lossless reflection, such that if the round-trip loss through the cavity mode for these offsets is less than 4.00 dB, this will allow for a significant improvement in fo / 2Q. L Negative feedback of phase noise with offsets of 100% and above.

[0156] Furthermore, this paper describes several exemplary circuit topologies using negative feedback in cavity mode, but these are not necessarily the same as the characteristic improvements described herein, such as for 100MHz oscillators or more generally ~6fo / 2Q. LThe high-quality quartz resonator used in the oscillator is the only circuit topology that reduces phase noise at offsets above + / - 5 kHz. A circuit consistent with the description herein will provide an oscillator circuit with a round-trip relative amplitude of -4.00 dB or greater (such as -3.00 dB, -2.00 dB, etc.) at these offsets in cavity mode. To reiterate the timing above, when an oscillator circuit such as oscillator circuit 500A or oscillator circuit 600A starts up, the maximum signal at the high offset frequency will be used for the first cycle of the oscillator circuit. Then, for cycles after the first cycle, the feedback effect at the high offset frequency described herein will result in a lower signal at the high offset frequency.

[0157] Although a low-phase-noise oscillator using negative feedback has been described with reference to several exemplary embodiments, it should be understood that the language used is descriptive and illustrative, not restrictive. As stated and modified herein, changes may be made within the scope of the appended claims without departing from the scope and spirit of the low-phase-noise oscillator using negative feedback. Although a low-phase-noise oscillator using negative feedback has been described with reference to specific devices, materials, and embodiments, the use of a low-phase-noise oscillator using negative feedback is not intended to be limited to the disclosed details, but rather extended to all functionally equivalent structures, methods, and uses, for example, within the scope of the appended claims.

[0158] For example, Figures 5A to 5C The embodiments described herein are exemplary circuits for 6A to 6B, but other circuits for low-phase-noise oscillators using negative feedback can produce similar or even improved results in some respects. The circuits described herein include couplers and circulators as circuit elements, but other circuit elements can be used to perform similar functions. Similarly, in Figures 5A to 5C and Figures 6A to 6B In the embodiments described herein, resonators 510 and 610 are merely illustrative examples, and other types of resonators can be used with oscillator circuits for low-phase-noise oscillators using negative feedback. Circuits equivalent to those shown in the embodiments herein fall within the scope of this disclosure. For example, from Figure 5A The signal K and Figure 6B The negative feedback of signal J2 in the figures is caused by a specific arrangement of specific components in order to cancel out the high offset frequency component of the input signal to the amplifier in these figures. However, other arrangements of other circuit elements can be used to achieve similar characteristic improvements using negative feedback, and will still fall within the scope of the low phase noise oscillators using negative feedback described herein.

[0159] As mentioned above, the improvement in phase noise achieved by a low-phase-noise oscillator using negative feedback will vary depending on whether the oscillator circuit uses a circulator or a coupler, the setting of attenuation and phase shift in the feedback path, and other factors. However, it is possible to achieve, for example... Figure 7A The improvements shown can include an increase of 4.00 dB of loss at the resonant center frequency and an increase of 11.00 dB or more of loss at high offset frequencies. Therefore, even with a 4.00 dB increase in gain to compensate for the excessive loss at the resonant center frequency, an improvement of 7.00 dB or more in phase noise at high offset frequencies is still possible. As a result, a low-phase-noise oscillator using negative feedback will reduce the gain at the resonant frequency and slightly reduce the phase noise near the resonant frequency, but will also significantly reduce the gain, phase noise floor, and phase noise at high offset frequencies far from the resonant frequency.

[0160] The illustrations of the embodiments described herein are intended to provide a general understanding of the structure of various embodiments. These illustrations are not intended as a complete description of all elements and features of the disclosure described herein. Many other embodiments will be apparent to those skilled in the art upon review of the disclosure. Other embodiments can be utilized and derived from this disclosure, allowing structural and logical substitutions and changes to be made without departing from the scope of this disclosure. Furthermore, these illustrations are merely representative and may not be drawn to scale. Some scales in the illustrations may be exaggerated, while others may be minimized. Therefore, this disclosure and the accompanying drawings are to be considered illustrative rather than restrictive.

[0161] One or more embodiments of this disclosure may be referred to individually and / or collectively by the term "invention" herein, for convenience only and not intended to voluntarily limit the scope of this application to any particular invention or inventive concept. Furthermore, although specific embodiments are shown and described herein, it should be understood that any subsequent arrangements designed to achieve the same or similar purpose may replace the specific embodiments shown. This disclosure is intended to cover any and all subsequent modifications or variations of the various embodiments. Combinations of the above embodiments, as well as other embodiments not specifically described herein, will be apparent to those skilled in the art upon review of the description.

[0162] The abstract of the disclosure is provided to comply with 37 C. FR § 1.72(B), and it is understood at the time of filing that it will not be used to interpret or limit the scope or meaning of the claims. Furthermore, in the foregoing detailed description of the invention, various features may have been combined together or described in a single embodiment for the purpose of simplification. This disclosure should not be construed as reflecting an intention that the claimed embodiments require more features than those expressly stated in each claim. Rather, as reflected in the following claims, the subject matter of the invention may address fewer than all features of any of the disclosed embodiments. Therefore, the following claims are incorporated into the detailed description of the invention, each claim independently defining a separately claimed subject matter.

[0163] The foregoing description of the disclosed embodiments is intended to enable those skilled in the art to practice the concepts described in this disclosure. Therefore, the subject matter of the foregoing disclosure should be considered illustrative rather than restrictive, and the appended claims are intended to cover all such modifications, improvements, and other embodiments falling within the true spirit and scope of this disclosure. Accordingly, to the fullest extent permitted by law, the scope of this disclosure shall be determined by the broadest permissible interpretation of the appended claims and their equivalents, without being bound or limited by the foregoing detailed description.

Claims

1. An oscillator comprising: Resonator; and A first loop includes an amplifier and a first coupler, and is electrically coupled to the resonator, wherein the oscillator is configured to generate negative feedback of the amplifier relative to a short-circuit terminal or an open-circuit terminal of the cavity in cavity mode, the cavity simulating the oscillator at a frequency deviating from the carrier frequency, and wherein the oscillator experiences bidirectional losses of less than 4.00 dB through the cavity at the frequency deviating from the carrier frequency.

2. The oscillator according to claim 1, further comprising: A second loop, which at least partially overlaps with the first loop and includes at least one circuit component between the input and output of the resonator, wherein the second loop provides a feedback signal to the amplifier with an amplitude greater than -4.00 dB relative to the original signal provided to the amplifier at a frequency deviating from the carrier frequency.

3. The oscillator according to claim 1, further comprising: The second loop is located between the input and the output of the resonator and includes the amplifier, the first coupler, the first circulator, the phase shifter, the attenuator, and the second circulator. and The frequency that deviates from the carrier frequency is a high offset frequency, wherein the high offset frequency is approximately 6*(fo / 2Q). L ), where fo is the output frequency of the oscillator, and Q L The load Q of the resonator is defined as follows: the first circulator controls the direction of the signal flow from the output of the first coupler to the resonator; at frequencies deviating from the carrier frequency, the signal flow is reflected back to the first circulator, which then transmits the signal flow to the phase shifter, the attenuator, and the second circulator. The second looper controls the direction of the signal flow from the phase shifter and the attenuator to the resonator, wherein at frequencies deviating from the carrier frequency, the signal flow is reflected back to the first looper and routed as input to the amplifier, and the second loop provides a negative feedback signal with an amplitude greater than -4.00 dB relative to the original signal provided to the amplifier at frequencies deviating from the carrier frequency.

4. The oscillator of claim 3, wherein the attenuator comprises a second coupler and a resistor between the second coupler and ground.

5. The oscillator according to claim 1, further comprising: The second loop includes the amplifier, the first coupler, the second coupler, and the third coupler. Wherein: the frequency deviating from the carrier frequency is the high offset frequency, wherein the high offset frequency is approximately 6*(fo / 2Q). L ), where fo is the output frequency of the oscillator, and Q L The load Q of the resonator; the second coupler couples the signal flow reflected from the resonator to an attenuator, and then to a phase shifter, wherein the signal flow is input to the third coupler and output from the third coupler toward the resonator, wherein at frequencies deviating from the carrier frequency, the signal flow is reflected toward the amplifier via the third coupler; and The second loop provides a negative feedback signal with an amplitude greater than -4.00 dB relative to the original signal input to the amplifier at a frequency deviating from the carrier frequency.

6. The oscillator of claim 1, wherein for the round trip of the first loop, the first loop is phase-shifted between -30 degrees and +30 degrees.

7. The oscillator of claim 1, wherein the second loop implements the cavity mode with negative feedback for the oscillator.

8. The oscillator of claim 1, wherein the negative feedback is based on the output of the amplifier, which has passed through the main path of the first coupler and reflected from the resonator, and has passed through the coupling path of the third coupler, the phase shifter, the attenuator, the coupling path of the second coupler and toward the resonator, and is reflected at a high offset frequency as feedback to the amplifier through the main path of the second coupler, wherein the high offset frequency is approximately 6*(fo / 2Q). L ), where fo is the output frequency of the oscillator, and Q L It is the load Q of the resonator. The output of the amplifier is fed back to the amplifier via a combination of reflections from the resonator in the first loop.

9. The oscillator of claim 8, wherein the second loop includes the second coupler, and the output of the second coupler has a fractional amplitude of the output of the first coupler and is fed back to the amplifier.

10. The oscillator of claim 1, wherein the cavity mode is generated by the resonator by reflecting the output of the amplifier from the resonator.

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