A microwave voltage-controlled oscillator with low phase noise

Abstract

The present application belongs to the technical field of frequency source circuit, and discloses a microwave voltage-controlled oscillator with low phase noise, which comprises a resonance network and a negative resistance network, and further comprises a noise reduction circuit network capable of increasing the isolation degree of the negative resistance network and the resonance network; the oscillation signal input end of the noise reduction circuit network is connected with the oscillation signal output end of the resonance network, and the oscillation signal output end of the noise reduction circuit network is connected with the oscillation signal input end of the negative resistance network; the Q value of the noise reduction circuit network is higher than that of the resonance network. The present application increases the isolation degree of the negative resistance network and the resonance network by inserting the noise reduction circuit network between the traditional negative resistance network and the resonance network, and improves the phase noise of the output signal of the microwave voltage-controlled oscillator. The present application starts from the circuit structure of the microwave voltage-controlled oscillator, and can improve the phase noise of the microwave voltage-controlled oscillator under the condition that the component selection and the process implementation form of the microwave voltage-controlled oscillator are determined.

Description

Technical Field

[0001] This invention belongs to the field of frequency source circuit technology and relates to a voltage-controlled oscillator, specifically a low-phase-noise microwave voltage-controlled oscillator. Background Technology

[0002] As the core component of a microwave signal generator, the phase noise of the microwave voltage-controlled oscillator is a key factor restricting the performance of the microwave signal generator.

[0003] like Figure 1 As shown, from the perspective of negative resistance oscillation in a microwave voltage-controlled oscillator (VCO), the VCO mainly consists of two parts: a resonant network with frequency selection function, composed of a first varactor diode and LC elements; and a negative resistance network with energy compensation function, composed of transistors or other types of transistors and RLC elements. After the microwave VCO is powered on, the resonant network selects the signal that meets the phase condition; the negative resistance network provides the energy required for the oscillation of that frequency signal. Using a microwave VCO, a signal of a specific frequency is generated, and the most important indicator for measuring the quality of this signal is phase noise. From the start-up and stabilization process of the microwave VCO, it can be seen that two important factors affecting its phase noise are the Q value of the resonant circuit and the noise of the negative resistance circuit.

[0004] Therefore, traditional methods for improving phase noise usually start from two aspects: 1. Try to increase the Q value of the resonant network, for example, by using high-Q components such as coaxial dielectric resonators or FBAR resonators to act as the resonant network; 2. Select active devices with low noise figure and low 1 / f noise to act as oscillators, for example, by using bipolar transistors.

[0005] However, both of the aforementioned methods for improving phase noise achieve their purpose by changing the selection of components or the manufacturing process. In the actual design process of a microwave voltage-controlled oscillator, once the component selection and the manufacturing process of the microwave voltage-controlled oscillator are determined, both the Q value of the resonant network and the noise level of the oscillator tube will be fixed.

[0006] How to further reduce the phase noise of microwave voltage-controlled oscillators (VCOs) when the selection of components and the manufacturing process of microwave VCOs are already determined is a technical problem that urgently needs to be solved. Summary of the Invention

[0007] The purpose of this invention is to improve the phase noise of a microwave voltage-controlled oscillator (VCO) based on the circuit structure of the VCO, given the selection of components and the determined manufacturing process of the VCO, thereby providing a low-phase-noise microwave VCO.

[0008] To achieve the above objectives, the technical solution adopted by this invention is as follows:

[0009] A low-phase-noise microwave voltage-controlled oscillator includes a resonant network and a negative resistance network, and further includes a noise reduction circuit network that can increase the isolation between the negative resistance network and the resonant network.

[0010] The oscillation signal input terminal of the noise reduction circuit network is connected to the oscillation signal output terminal of the resonant network, and the oscillation signal output terminal of the noise reduction circuit network is connected to the oscillation signal input terminal of the negative resistance network.

[0011] The Q value of the noise reduction circuit network is higher than that of the resonant network;

[0012] Furthermore, the equivalent impedance of the noise reduction circuit network satisfies the following condition.

[0013] 1 / (2*π*f0*C 等效 Formula ① < 10;

[0014] Where f0 is the oscillation frequency of the resonant network, and C 等效 This is the equivalent capacitance of the noise reduction circuit network.

[0015] As a limitation, the noise reduction circuit network consists of a first capacitor and a second capacitor connected in series;

[0016] The oscillation signal output terminal of the resonant network is connected to one end of the first capacitor, the other end of the first capacitor is connected to one end of the second capacitor, and the other end of the second capacitor is connected to the oscillation signal input terminal of the negative resistance network.

[0017] As a second limitation: the negative resistance network includes a first oscillating transistor, a first resistor to a fourth resistor, a first inductor to a third inductor, and a third capacitor to a seventh capacitor;

[0018] The base of the first oscillating transistor is connected to one end of the sixth capacitor and one end of the second inductor, respectively; the other end of the sixth capacitor serves as the oscillation signal input terminal of the impedance network, and is connected to the oscillation signal output terminal of the noise reduction circuit network, the emitter of the first oscillating transistor, and one end of the third inductor, respectively; the other end of the third inductor is grounded through a parallel circuit composed of the seventh capacitor and the fourth resistor.

[0019] The other end of the second inductor is connected to one end of the second resistor, one end of the third capacitor, and one end of the third resistor, respectively. The other end of the second resistor is grounded, the other end of the third capacitor is grounded, and the other end of the third resistor is connected to one end of the first resistor, one end of the fourth capacitor, and one end of the first inductor, respectively. The other end of the first resistor is connected to the power supply terminal, the other end of the fourth capacitor is grounded, the other end of the first inductor is connected to the collector of the first oscillating transistor, and one end of the fifth capacitor is connected to the power supply terminal. The other end of the fifth capacitor serves as the oscillation signal output terminal of the negative resistance network.

[0020] As a further limitation: the resonant network includes a first varactor diode, a fourth inductor, a fifth inductor, an eighth capacitor, and a ninth capacitor;

[0021] The cathode of the first varactor diode is connected to the power-adjustable terminal on one side and grounded through the ninth capacitor on the other side. The anode of the first varactor diode is connected to one end of the eighth capacitor and one end of the fourth inductor through the fifth inductor, respectively. The other end of the fourth inductor is grounded.

[0022] The other end of the eighth capacitor serves as the oscillation signal output terminal of the resonant network and is connected to the oscillation signal input terminal of the noise reduction circuit network.

[0023] As a third limitation: the negative resistance network includes a second oscillating transistor, eleventh to fourteenth resistors, eleventh to thirteenth inductors, and eleventh to fourteenth capacitors;

[0024] The base of the second oscillating transistor is connected to one end of the twelfth inductor; the other end of the twelfth inductor is connected to one end of the twelfth resistor, one end of the eleventh capacitor, and one end of the thirteenth resistor, respectively; the other end of the twelfth resistor is grounded; the other end of the eleventh capacitor is grounded; the other end of the thirteenth resistor is connected to one end of the eleventh resistor, one end of the eleventh inductor, and one end of the twelfth capacitor, respectively; the other end of the eleventh resistor is connected to the power supply terminal; the other end of the twelfth capacitor is grounded; the other end of the eleventh inductor is connected to the collector of the second oscillating transistor and one end of the thirteenth capacitor, respectively; the other end of the thirteenth capacitor serves as the oscillation signal output terminal of the negative resistance network.

[0025] The emitter of the second oscillating transistor is connected to one end of the thirteenth inductor. The common terminal of the two is connected to the oscillation signal input terminal of the negative resistance network and the oscillation signal output terminal of the noise reduction circuit network. The other end of the thirteenth inductor is grounded through a parallel circuit composed of the fourteenth capacitor and the fourteenth resistor.

[0026] As a further limitation of the third definition: the resonant network includes a second varactor diode, a fourteenth inductor, a fifteenth capacitor, and a sixteenth capacitor;

[0027] The cathode of the second varactor diode is connected to the power-adjustable terminal on one side and to the fifteenth and sixteenth capacitors in sequence on the other side, and then connected to the oscillation signal input terminal of the noise reduction circuit network; the anode of the second varactor diode is grounded; the common terminal of the fifteenth and sixteenth capacitors is grounded through the fourteenth inductor.

[0028] As a fourth limitation: the negative resistance network includes the third oscillating transistor, the twenty-first to twenty-fourth resistors, the twenty-first to twenty-third inductors, and the twenty-first to twenty-fourth capacitors;

[0029] The base of the third oscillating transistor is connected to one end of the twenty-second inductor, and their common terminal serves as the oscillation signal input terminal of the negative resistance network and is connected to the oscillation signal output terminal of the noise reduction circuit network. The other end of the twenty-second inductor is connected to one end of the twenty-second resistor, one end of the twenty-first capacitor, and one end of the twenty-third resistor, respectively. The other end of the twenty-second resistor is grounded. The other end of the twenty-first capacitor is grounded. The other end of the twenty-third resistor is connected to one end of the twenty-first resistor, one end of the twenty-first inductor, and one end of the twenty-second capacitor, respectively. The other end of the twenty-first resistor is connected to the power supply terminal. The other end of the twenty-second capacitor is grounded. The other end of the twenty-first inductor is connected to the collector of the third oscillating transistor and one end of the twenty-third capacitor, respectively. The other end of the twenty-third capacitor serves as the oscillation signal output terminal of the negative resistance network.

[0030] The emitter of the third oscillating transistor is connected to ground in sequence through the 23rd inductor and the 24th resistor, and also grounded through the 24th capacitor.

[0031] As a further limitation of the fourth limitation: the resonant network includes a third varactor diode, a twenty-fourth inductor, a twenty-fifth capacitor, and a twenty-sixth capacitor;

[0032] The cathode of the third varactor diode is connected to the power-adjustable terminal on one side and to the 25th and 26th capacitors in sequence on the other side, and then connected to the oscillation signal input terminal of the noise reduction circuit network; the anode of the third varactor diode is grounded; the common terminal of the 25th and 26th capacitors is grounded through the 24th inductor.

[0033] The present invention, by adopting the above-described technical solution, achieves the following technical advancements compared to existing technologies:

[0034] (1) The present invention increases the isolation between the negative resistance network and the resonant network by inserting a noise reduction circuit network between the traditional negative resistance network and the resonant network, thereby improving the phase noise of the output signal of the microwave voltage-controlled oscillator;

[0035] (2) Starting from the circuit structure of microwave voltage-controlled oscillator, this invention can improve the phase noise of microwave voltage-controlled oscillator under the condition that the selection of components and the implementation form of microwave voltage-controlled oscillator are determined;

[0036] (3) The noise reduction circuit network added in this invention has the following characteristics: it can increase the isolation between the negative resistance network and the resonant network; the noise reduction circuit network does not affect the start-up conditions of the microwave voltage-controlled oscillator; and it has a high Q value.

[0037] (4) The noise reduction circuit network provided by the present invention is used to modify the S-band voltage-controlled oscillator. After modification, compared with the original, the phase noise is reduced by 6dB to 13dB in the range of f01kHz to 1MHz.

[0038] (5) The noise reduction circuit network provided by the present invention is used to modify the C-band voltage-controlled oscillator. After modification, compared with before modification, the phase noise is reduced by 6dB in the range of f01kHz to 1MHz.

[0039] (6) The noise reduction circuit network provided by the present invention is used to modify the X-band voltage-controlled oscillator. After modification, compared with the original, the phase noise is reduced by 5dB in the range of f01kHz to 1MHz.

[0040] This invention belongs to the field of frequency source circuit technology and can improve the phase noise of microwave voltage-controlled oscillators when the selection of components and the implementation of microwave voltage-controlled oscillators are determined. Attached Figure Description

[0041] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0042] In the attached diagram:

[0043] Figure 1 This is a block diagram of a microwave voltage-controlled oscillator circuit, a prior art technology of this invention.

[0044] Figure 2 This is a circuit block diagram of Embodiment 1 of the present invention;

[0045] Figure 3 This is a circuit diagram of the noise reduction circuit network in Embodiment 1 of the present invention;

[0046] Figure 4 This is a schematic diagram of the S-band voltage-controlled oscillator circuit in Embodiment 1 of the present invention;

[0047] Figure 5 This is a schematic diagram of the low-phase-noise S-band voltage-controlled oscillator circuit in Embodiment 1 of the present invention;

[0048] Figure 6 This is a phase noise test diagram of the S-band voltage-controlled oscillator in Embodiment 1 of the present invention;

[0049] Figure 7 This is a phase noise test diagram of the low phase noise S-band voltage-controlled oscillator in Embodiment 1 of the present invention;

[0050] Figure 8 This is a schematic diagram of the C-band voltage-controlled oscillator circuit in Embodiment 2 of the present invention;

[0051] Figure 9 This is a schematic diagram of the low-phase-noise C-band voltage-controlled oscillator circuit in Embodiment 2 of the present invention;

[0052] Figure 10 This is a phase noise test diagram of the C-band voltage-controlled oscillator in Embodiment 2 of the present invention;

[0053] Figure 11 This is a phase noise test diagram of the low phase noise C-band voltage-controlled oscillator in Embodiment 2 of the present invention;

[0054] Figure 12 This is a schematic diagram of the X-band voltage-controlled oscillator circuit in Embodiment 3 of the present invention;

[0055] Figure 13 This is a schematic diagram of the low-phase-noise X-band voltage-controlled oscillator circuit in Embodiment 3 of the present invention;

[0056] Figure 14 This is a phase noise test diagram of the X-band voltage-controlled oscillator in Embodiment 3 of the present invention;

[0057] Figure 15 This is a phase noise test diagram of the low phase noise X-band voltage-controlled oscillator in Embodiment 3 of the present invention. Detailed Implementation

[0058] The preferred embodiments of the present invention will now be described with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0059] Example 1: A Low-Phase-Noise S-Band Voltage-Controlled Oscillator

[0060] like Figure 1 The diagram shown is a circuit block diagram of a traditional microwave voltage-controlled oscillator (VCO) in the prior art. During microwave oscillation, the noise of the oscillator enters the resonant network and is amplified along with the oscillation signal, thus deteriorating the phase noise. Therefore, with a fixed Q value for the resonant network and a selected oscillator, reducing the injection of oscillator noise into the resonant network can effectively improve the phase noise of the microwave VCO output signal.

[0061] This embodiment increases the isolation between the negative resistance network and the resonant network by inserting a noise reduction circuit network between the traditional negative resistance network and the resonant network, thereby improving the phase noise of the microwave voltage-controlled oscillator output signal. For example... Figure 2 The diagram shown is a circuit block diagram after adding a noise reduction circuit network. In this embodiment, the added noise reduction circuit network is as follows... Figure 3The circuit shown is a series circuit consisting of a first capacitor C1 and a second capacitor C2. Therefore, the microwave voltage-controlled oscillator provided in this embodiment includes a resonant network and a negative resistance network, as well as a noise reduction circuit network. The noise reduction circuit network consists of a first capacitor C1 and a second capacitor C2 connected in series. The oscillation signal output terminal of the resonant network is connected to one end of the first capacitor C1, the other end of the first capacitor C1 is connected to one end of the second capacitor C2, and the other end of the second capacitor C2 is connected to the oscillation signal input terminal of the negative resistance network.

[0062] The noise reduction circuit network in this embodiment can increase the isolation between the negative resistance network and the resonant network, without affecting the start-up conditions of the S-band voltage-controlled oscillator. The Q value of the noise reduction circuit network is higher than that of the resonant network. The equivalent impedance of the noise reduction circuit network satisfies the following conditions.

[0063] 1 / (2*π*f0*C 等效 Formula ① < 10;

[0064] Where f0 is the oscillation frequency of the resonant network, and also the operating frequency of the S-band voltage-controlled oscillator, C 等效 This is the equivalent capacitance of the noise reduction circuit network.

[0065] Specifically, such as Figure 4 The diagram shown is a typical circuit diagram of an S-band voltage-controlled oscillator. U1 is the first oscillating transistor; resistors R1-R4 provide DC bias for the first oscillating transistor; inductors L1-L3 are choke inductors; capacitors C3 and C4 are filter capacitors; capacitor C6 is the feedback capacitor between the emitter and base of the first oscillating transistor U1, which can be replaced by the parasitic capacitance of U1 under high-frequency conditions; capacitor C7 provides an AC path and affects the final output frequency; capacitor C5 is the output coupling capacitor; capacitor C8 is the coupling capacitor between the resonant circuit and the base of the first oscillating transistor U1, and also affects the final output frequency; the first varactor diode D1, capacitor C9, inductor L4, and inductor L5 form the resonant circuit, where inductor L4 is grounded and also provides DC bias for the first varactor diode D1.

[0066] Based on the above analysis, it can be seen that in the circuit of this S-band voltage-controlled oscillator, the first oscillating transistor U1, the first resistor to the fourth resistor R1 to R4, the first inductor to the third inductor L1 to L3, and the third capacitor to the seventh capacitor C3 to C7 form a negative resistance network; the first varactor diode D1, the fourth inductor L4, the fifth inductor L5, the eighth capacitor C8, and the ninth capacitor C9 form a resonant network.

[0067] The circuit diagram of the low-phase-noise S-band voltage-controlled oscillator obtained after modifying the above S-band voltage-controlled oscillator circuit is shown below. Figure 5As shown. In this embodiment, Figure 5 All active components in the circuit are low-noise devices, and the Q values ​​of the inductors and capacitors involved in the oscillation are very high. In this embodiment, the Q value of the noise reduction circuit network is ≥40, f0=3GHz. Substituting into equation ①, we can obtain C. 等效 >5.31pF.

[0068] like Figure 5 As shown, the negative resistance network includes the first oscillating transistor U1, the first resistor to the fourth resistor R1 to R4, the first inductor to the third inductor L1 to L3, and the third capacitor to the seventh capacitor C3 to C7.

[0069] The base of the first oscillating transistor U1 is connected to one end of the sixth capacitor C6 and one end of the second inductor L2, respectively. The other end of the sixth capacitor C6 serves as the oscillation signal input terminal of the impedance network and is connected to the other end of the second capacitor C2, the emitter of the first oscillating transistor U1, and one end of the third inductor L3, respectively. The other end of the third inductor L3 is grounded through a parallel circuit composed of the seventh capacitor C7 and the fourth resistor R4.

[0070] The other end of the second inductor L2 is connected to one end of the second resistor R2, one end of the third capacitor C3, and one end of the third resistor R3, respectively. The other end of the second resistor R2 is grounded, the other end of the third capacitor C3 is grounded, the other end of the third resistor R3 is connected to one end of the first resistor R1, one end of the fourth capacitor C4, and one end of the first inductor L1, respectively. The other end of the first resistor R1 is connected to the power supply terminal, the other end of the fourth capacitor C4 is grounded, the other end of the first inductor L1 is connected to the collector of the first oscillating transistor U1 and one end of the fifth capacitor C5, respectively. The other end of the fifth capacitor C5 serves as the oscillation signal output terminal of the negative resistance network.

[0071] The resonant network includes a first varactor diode D1, a fourth inductor L4, a fifth inductor L5, an eighth capacitor C8, and a ninth capacitor C9. The cathode of the first varactor diode D1 is connected to the electronically adjustable terminal on one side and grounded through the ninth capacitor C9 on the other side. The anode of the first varactor diode D1 is connected to one end of the fifth inductor L5 and one end of the eighth capacitor C8 and one end of the fourth inductor L4, respectively. The other end of the fourth inductor L4 is grounded. The other end of the eighth capacitor C8 serves as the oscillation signal output terminal of the resonant network and is connected to one end of the first capacitor C1.

[0072] Before the renovation Figure 4 and after renovation Figure 5 The circuits were tested separately. During the tests, the power supply filtering was good. The phase noise test curve before the modification is as follows: Figure 6 As shown, the phase noise test curve after modification is as follows: Figure 7 As shown. By comparison Figure 6 and Figure 7It can be observed that within the range of f01kHz to 1MHz, the phase noise of the S-band voltage-controlled oscillator is reduced by 6dB to 13dB, meaning that the phase noise of the low-phase-noise S-band voltage-controlled oscillator provided in this embodiment is optimized.

[0073] In this embodiment, the frequency range of the S-band voltage-controlled oscillator is 2GHz to 4GHz.

[0074] Example 2: A low-phase-noise C-band voltage-controlled oscillator

[0075] This embodiment uses the same method as in Embodiment 1 to modify a C-band voltage-controlled oscillator to obtain a low-phase-noise C-band voltage-controlled oscillator.

[0076] Similarly, the noise reduction circuit network in this embodiment can increase the isolation between the negative resistance network and the resonant network, without affecting the start-up conditions of the C-band voltage-controlled oscillator. The Q value of the noise reduction circuit network is higher than that of the resonant network. The equivalent impedance of the noise reduction circuit network satisfies the following conditions.

[0077] 1 / (2*π*f0*C 等效 Formula ① < 10;

[0078] Where f0 is the oscillation frequency of the resonant network, and also the operating frequency of the C-band voltage-controlled oscillator, C 等效 This is the equivalent capacitance of the noise reduction circuit network.

[0079] like Figure 8 The diagram shown is a typical C-band voltage-controlled oscillator (VCO) schematic. U2 is the second oscillating transistor; resistors 11 to 14 (R11 to R14) provide DC bias for U2; inductors 11 to 13 (L11 to L13) are choke inductors; capacitors C11 (eleventh) and C12 (twelfth) are filter capacitors; capacitor C14 (fourteenth) provides an AC path and affects the final output frequency; capacitor C13 (thirteenth) is the output coupling capacitor; capacitor C16 (sixteenth) is the coupling capacitor between the resonant circuit and the emitter of the oscillating transistor, also affecting the final output frequency; and the second varactor diode D2, capacitor C15 (fifteenth), and inductor L14 form the resonant circuit.

[0080] Based on the above analysis, it can be seen that the second oscillating transistor U2, the eleventh to fourteenth resistors R11 to R14, the eleventh to thirteenth inductors L11 to L13, and the eleventh to fourteenth capacitors C11 to C14 in this circuit constitute a negative resistance network; the second varactor diode D2, the fourteenth inductor L14, the fifteenth capacitor C15, and the sixteenth capacitor C15 constitute a resonant network.

[0081] This embodiment uses a noise reduction circuit network to modify the aforementioned C-band voltage-controlled oscillator, resulting in a low-phase-noise C-band voltage-controlled oscillator. The circuit schematic is shown below. Figure 9 As shown, all active devices in the circuit are low-noise devices, and the Q values ​​of the inductors and capacitors participating in the oscillation are very high. In this embodiment, the Q value of the noise reduction circuit network is ≥30, f0=6GHz. Substituting into equation ①, we can obtain C 等效 >2.65pF.

[0082] Figure 9 In the middle, the negative resistance network includes the second oscillating transistor U2, the eleventh to fourteenth resistors R11 to R14, the eleventh to thirteenth inductors L11 to L13, and the eleventh to fourteenth capacitors C11 to C14. The base U2 of the second oscillating transistor is connected to one end of the twelfth inductor L12; the other end of the twelfth inductor L12 is connected to one end of the twelfth resistor R12, one end of the eleventh capacitor C11, and one end of the thirteenth resistor R13 respectively; the other end of the twelfth resistor R12 is grounded; the other end of the eleventh capacitor C11 is grounded; the other end of the thirteenth resistor R13 is connected to one end of the eleventh resistor R11, one end of the eleventh inductor L11, and one end of the twelfth capacitor C12 respectively; the other end of the eleventh resistor R11 is connected to the power supply terminal; the other end of the twelfth capacitor C12 is grounded; the other end of the eleventh inductor L11 is connected to the collector of the second oscillating transistor U2 and one end of the thirteenth capacitor C13 respectively; the other end of the thirteenth capacitor C13 serves as the oscillation signal output terminal of the negative resistance network. The emitter of the second oscillating transistor U2 is connected to one end of the thirteenth inductor L13. The common terminal of the two is connected to the oscillation signal input terminal of the negative resistance network and the oscillation signal output terminal of the noise reduction circuit network. The other end of the thirteenth inductor L13 is grounded through a parallel circuit composed of the fourteenth capacitor C14 and the fourteenth resistor R14.

[0083] The resonant network includes a second varactor diode D2, a fourteenth inductor L14, a fifteenth capacitor C15, and a sixteenth capacitor C16. The cathode of the second varactor diode D2 is connected to the electronically adjustable terminal on one side and sequentially connected to the fifteenth capacitor C15 and the sixteenth capacitor C16 on the other side, and then connected to the oscillation signal input terminal of the noise reduction circuit network; the anode of the second varactor diode D2 is grounded; the common terminal of the fifteenth capacitor C15 and the sixteenth capacitor C16 is grounded through the fourteenth inductor L14.

[0084] Before the renovation Figure 8 and after renovation Figure 9 The circuits were tested separately. During the tests, the power supply filtering was good. The phase noise test curve before the modification is as follows: Figure 10 As shown, the phase noise test curve after modification is as follows: Figure 11 As shown. By comparison Figure 10 and Figure 11It can be observed that within the range of f01kHz to 1MHz, the phase noise of the C-band voltage-controlled oscillator is reduced by 6dB, meaning that the phase noise of the low-phase-noise C-band voltage-controlled oscillator provided in this embodiment is optimized.

[0085] In this embodiment, the frequency range of the C-band voltage-controlled oscillator is 4GHz to 8GHz.

[0086] Example 3: A low-phase-noise X-band voltage-controlled oscillator

[0087] This embodiment uses the same method as in Embodiment 1 to modify an X-band voltage-controlled oscillator to obtain a low-phase-noise X-band voltage-controlled oscillator.

[0088] Similarly, the noise reduction circuit network in this embodiment can increase the isolation between the negative resistance network and the resonant network, without affecting the start-up conditions of the X-band voltage-controlled oscillator. The Q value of the noise reduction circuit network is higher than that of the resonant network. The equivalent impedance of the noise reduction circuit network satisfies the following conditions.

[0089] 1 / (2*π*f0*C 等效 Formula ① < 10;

[0090] Where f0 is the oscillation frequency of the resonant network, and also the operating frequency of the X-band voltage-controlled oscillator, C 等效 This is the equivalent capacitance of the noise reduction circuit network.

[0091] like Figure 12 The diagram shown is a typical schematic of an X-band voltage-controlled oscillator. U3 is the third oscillating transistor; resistors R21-R24 (21-24) provide DC bias for U3; inductors L21-L23 (21-23) are choke inductors; capacitors C21 and C22 are filter capacitors; capacitor C24 provides an AC path and affects the final output frequency; capacitor C23 is the output coupling capacitor; capacitor C26 is the coupling capacitor between the resonant circuit and the base of the third oscillating transistor U3, and also affects the final output frequency; varactor diode D3, capacitor C25, and inductor L24 form the resonant circuit.

[0092] Based on the above analysis, it can be seen that the third oscillating transistor U3, the twenty-first to twenty-fourth resistors R21 to R24, the twenty-first to twenty-third inductors L21 to L23, and the twenty-first to twenty-fourth capacitors C21 to C24 in the above circuit constitute a negative resistance network; the third varactor diode D3, the twenty-fourth inductor L24, the twenty-fifth capacitor C25, and the twenty-sixth capacitor C26 constitute a resonant network.

[0093] This embodiment uses a noise reduction circuit network to modify the aforementioned X-band voltage-controlled oscillator, resulting in a low-phase-noise X-band voltage-controlled oscillator. The circuit schematic is shown below. Figure 13 As shown, all active devices in the circuit are low-noise devices, and the Q values ​​of the inductors and capacitors involved in the oscillation are very high. In this embodiment, the Q value of the noise reduction circuit network is ≥20. In this embodiment, the frequency range of the X-band voltage-controlled oscillator is 8GHz~12GHz, f0=10GHz. Substituting into equation ①, we can obtain C 等效 >1.59pF.

[0094] Figure 13 In the middle, the negative resistance network includes the third oscillating transistor U3, the twenty-first to twenty-fourth resistors R21 to R24, the twenty-first to twenty-third inductors L21 to L23, and the twenty-first to twenty-fourth capacitors C21 to C24. The base of the third oscillating transistor U3 is connected to one end of the twenty-second inductor L22, and their common terminal is connected to the oscillation signal input terminal of the negative resistance network and the oscillation signal output terminal of the noise reduction circuit network. The other end of the twenty-second inductor L22 is connected to one end of the twenty-second resistor R22, one end of the twenty-first capacitor C21, and one end of the twenty-third resistor R23, respectively. The other end of the twenty-second resistor R22 is grounded. The other end of the twenty-first capacitor C21 is grounded. The other end of the twenty-third resistor R23 is connected to one end of the twenty-first resistor R21, one end of the twenty-first inductor L21, and one end of the twenty-second capacitor C22, respectively. The other end of the twenty-first resistor R21 is connected to the power supply terminal. The other end of the twenty-second capacitor C22 is grounded. The other end of the twenty-first inductor L21 is connected to the collector of the third oscillating transistor U3 and one end of the twenty-third capacitor C23, respectively. The other end of the twenty-third capacitor C23 serves as the oscillation signal output terminal of the negative resistance network. The emitter of the third oscillating transistor U3 is connected to ground via the 23rd inductor L23 and the 24th resistor R24 ​​in sequence, and is also grounded via the 24th capacitor C24.

[0095] The resonant network includes a third varactor diode D3, a twenty-fourth inductor L24, a twenty-fifth capacitor C25, and a twenty-sixth capacitor C26. The cathode of the third varactor diode D3 is connected to the electronically regulated terminal on one side and sequentially to the twenty-fifth capacitor C25 and the twenty-sixth capacitor C26 on the other side, and then connected to the oscillation signal input terminal of the noise reduction circuit network; the anode of the third varactor diode D3 is grounded; the common terminal of the twenty-fifth capacitor C25 and the twenty-sixth capacitor C26 is grounded through the twenty-fourth inductor L24.

[0096] Before the renovation Figure 12 and after renovation Figure 13 The circuits were tested separately. During the tests, the power supply filtering was good. The phase noise test curve before the modification is as follows: Figure 14As shown, the phase noise test curve after modification is as follows: Figure 15 As shown. By comparison Figure 14 and Figure 15 It can be observed that within the range of f01kHz to 1MHz, the phase noise of the X-band voltage-controlled oscillator is reduced by 5dB, meaning that the phase noise of the low-phase-noise X-band voltage-controlled oscillator provided in this embodiment is optimized.

Claims

1. A low-phase-noise microwave voltage-controlled oscillator, comprising a resonant network and a negative-resistance network, characterized in that: It also includes a noise reduction circuit network that can increase the isolation between the negative resistance network and the resonant network; The oscillation signal input terminal of the noise reduction circuit network is connected to the oscillation signal output terminal of the resonant network, and the oscillation signal output terminal of the noise reduction circuit network is connected to the oscillation signal input terminal of the negative resistance network. The Q value of the noise reduction circuit network is higher than that of the resonant network; Furthermore, the equivalent impedance of the noise reduction circuit network satisfies the following condition. 1 / (2*π*f0*C 等效 )<Equation ①; Where f0 is the oscillation frequency of the resonant network, and C 等效 This is the equivalent capacitance of the noise reduction circuit network.

2. The low-phase-noise microwave voltage-controlled oscillator according to claim 1, characterized in that: The noise reduction circuit network consists of a first capacitor and a second capacitor connected in series. The oscillation signal output terminal of the resonant network is connected to one end of the first capacitor, the other end of the first capacitor is connected to one end of the second capacitor, and the other end of the second capacitor is connected to the oscillation signal input terminal of the negative resistance network.

3. A low-phase-noise microwave voltage-controlled oscillator according to claim 1 or 2, characterized in that: The negative resistance network includes a first oscillating transistor, a first resistor to a fourth resistor, a first inductor to a third inductor, and a third capacitor to a seventh capacitor; The base of the first oscillating transistor is connected to one end of the sixth capacitor and one end of the second inductor, respectively; the other end of the sixth capacitor serves as the oscillation signal input terminal of the impedance network, and is connected to the oscillation signal output terminal of the noise reduction circuit network, the emitter of the first oscillating transistor, and one end of the third inductor, respectively; the other end of the third inductor is grounded through a parallel circuit composed of the seventh capacitor and the fourth resistor. The other end of the second inductor is connected to one end of the second resistor, one end of the third capacitor, and one end of the third resistor, respectively. The other end of the second resistor is grounded, the other end of the third capacitor is grounded, and the other end of the third resistor is connected to one end of the first resistor, one end of the fourth capacitor, and one end of the first inductor, respectively. The other end of the first resistor is connected to the power supply terminal, the other end of the fourth capacitor is grounded, the other end of the first inductor is connected to the collector of the first oscillating transistor, and one end of the fifth capacitor is connected to the power supply terminal. The other end of the fifth capacitor serves as the oscillation signal output terminal of the negative resistance network.

4. A low-phase-noise microwave voltage-controlled oscillator according to claim 3, characterized in that: The resonant network includes a first varactor diode, a fourth inductor, a fifth inductor, an eighth capacitor, and a ninth capacitor; The cathode of the first varactor diode is connected to the power-adjustable terminal on one side and grounded through the ninth capacitor on the other side. The anode of the first varactor diode is connected to one end of the eighth capacitor and one end of the fourth inductor through the fifth inductor, respectively. The other end of the fourth inductor is grounded. The other end of the eighth capacitor serves as the oscillation signal output terminal of the resonant network and is connected to the oscillation signal input terminal of the noise reduction circuit network.

5. A low-phase-noise microwave voltage-controlled oscillator according to claim 1 or 2, characterized in that: The negative resistance network includes a second oscillating transistor, eleventh to fourteenth resistors, eleventh to thirteenth inductors, and eleventh to fourteenth capacitors; The base of the second oscillating transistor is connected to one end of the twelfth inductor; the other end of the twelfth inductor is connected to one end of the twelfth resistor, one end of the eleventh capacitor, and one end of the thirteenth resistor, respectively; the other end of the twelfth resistor is grounded; the other end of the eleventh capacitor is grounded; the other end of the thirteenth resistor is connected to one end of the eleventh resistor, one end of the eleventh inductor, and one end of the twelfth capacitor, respectively; the other end of the eleventh resistor is connected to the power supply terminal; the other end of the twelfth capacitor is grounded; the other end of the eleventh inductor is connected to the collector of the second oscillating transistor and one end of the thirteenth capacitor, respectively; the other end of the thirteenth capacitor serves as the oscillation signal output terminal of the negative resistance network. The emitter of the second oscillating transistor is connected to one end of the thirteenth inductor. The common terminal of the two is connected to the oscillation signal input terminal of the negative resistance network and the oscillation signal output terminal of the noise reduction circuit network. The other end of the thirteenth inductor is grounded through a parallel circuit composed of the fourteenth capacitor and the fourteenth resistor.

6. A low-phase-noise microwave voltage-controlled oscillator according to claim 5, characterized in that: The resonant network includes a second varactor diode, a fourteenth inductor, a fifteenth capacitor, and a sixteenth capacitor; The cathode of the second varactor diode is connected to the power-adjustable terminal on one side and to the fifteenth and sixteenth capacitors in sequence on the other side, and then connected to the oscillation signal input terminal of the noise reduction circuit network; the anode of the second varactor diode is grounded; the common terminal of the fifteenth and sixteenth capacitors is grounded through the fourteenth inductor.

7. A low-phase-noise microwave voltage-controlled oscillator according to claim 1 or 2, characterized in that: The negative resistance network includes a third oscillating transistor, resistors 21 to 24, inductors 21 to 23, and capacitors 21 to 24. The base of the third oscillating transistor is connected to one end of the twenty-second inductor, and their common terminal serves as the oscillation signal input terminal of the negative resistance network and is connected to the oscillation signal output terminal of the noise reduction circuit network. The other end of the twenty-second inductor is connected to one end of the twenty-second resistor, one end of the twenty-first capacitor, and one end of the twenty-third resistor, respectively. The other end of the twenty-second resistor is grounded. The other end of the twenty-first capacitor is grounded. The other end of the twenty-third resistor is connected to one end of the twenty-first resistor, one end of the twenty-first inductor, and one end of the twenty-second capacitor, respectively. The other end of the twenty-first resistor is connected to the power supply terminal. The other end of the twenty-second capacitor is grounded. The other end of the twenty-first inductor is connected to the collector of the third oscillating transistor and one end of the twenty-third capacitor, respectively. The other end of the twenty-third capacitor serves as the oscillation signal output terminal of the negative resistance network. The emitter of the third oscillating transistor is connected to ground in sequence through the 23rd inductor and the 24th resistor, and also grounded through the 24th capacitor.

8. A low-phase-noise microwave voltage-controlled oscillator according to claim 7, characterized in that: The resonant network includes a third varactor diode, a twenty-fourth inductor, a twenty-fifth capacitor, and a twenty-sixth capacitor. The cathode of the third varactor diode is connected to the power-adjustable terminal on one side and to the 25th and 26th capacitors in sequence on the other side, and then connected to the oscillation signal input terminal of the noise reduction circuit network; the anode of the third varactor diode is grounded; the common terminal of the 25th and 26th capacitors is grounded through the 24th inductor.

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