Low-noise broadband voltage-controlled oscillator based on cross coupling differential structure

Abstract

The invention relates to the technical field of oscillators, and discloses a low-noise broadband voltage-controlled oscillator based on a cross coupling differential structure, which comprises a resonant cavity, a differential negative resistance circuit and a current bias circuit, and is characterized in that the resonant cavity adopts an LC resonant structure and is used for determining frequency selection and phase characteristics of the low-noise broadband voltage-controlled oscillator; the differential negative resistance circuit adopts a cross coupling differential pair structure formed by two bipolar junction transistors and is used for providing enough gain and positive feedback so as to generate a negative resistance effect; the current bias circuit uses a bipolar junction transistor to construct a bias circuit structure and is used for providing stable bias current and ensuring that the bipolar junction transistor in the differential negative resistance circuit works in an amplification region.

Description

Technical Field

[0001] The present invention relates to the technical field of oscillators, and in particular to a low-noise, wide-bandwidth voltage-controlled oscillator based on a cross-coupled differential structure. Background Art

[0002] As the core component of the RF communication system, the RF front end is responsible for processing the reception and transmission of electromagnetic signals. Its performance directly affects the performance of the entire RF communication system, including the reliability of signal transmission, the coverage of the communication range, and the anti-interference ability. It usually includes a series of RF modules, covering key functions such as signal reception, transmission, amplification, filtering, and mixing. The voltage-controlled oscillator VCO (Voltage-Controlled Oscillator) is one of the cores of the phase-locked loop (PLL). It is a circuit that generates an oscillation signal with adjustable frequency. Its output frequency is determined by the input control voltage. It is responsible for generating RF signals with adjustable frequencies. Its frequency stability and adjustability directly affect the spectrum utilization and signal quality of the communication system.

[0003] Nowadays, although VCO is very important in many applications, people usually pursue VCO structures with low phase noise, excellent stability and linearity characteristics, low power consumption, high integration and wide bandwidth coverage. However, the existing technology still faces some challenges and problems, such as phase noise, frequency stability, linearity, power consumption, integration, frequency band coverage and other issues, and in analog design, many aspects cannot be well balanced. Usually LC-VCO uses a cross-coupled differential pair structure based on CMOS process or a π-type structure based on bipolar junction transistors to achieve better indicators. Many scholars have also explored and studied the above issues, such as the patent "A low-noise voltage-controlled oscillator based on capacitor three-point" (CN116094517A). The VCO invention structure proposed in this patent is as follows Figure 1 As shown in the figure, a bipolar junction transistor π-type structure based on a three-point capacitor is used, which achieves some advantages such as low phase noise and multi-band coverage, but the frequency stability, linearity and power consumption have not been well optimized. Specifically, there are the following disadvantages:

[0004] 1. The π-type structure based on bipolar junction transistors in the patent uses the low noise characteristics of bipolar junction transistors, but the π-type structure is inferior to the cross-coupled differential pair structure used in this patent in terms of signal anti-interference, frequency stability and nonlinear distortion;

[0005] 2. The current bias structure in its patent uses two current bias branches, which increases power consumption, increases debugging difficulty, and also hinders miniaturization, and is lacking in power consumption and integration;

[0006] 3. The overall structure of the patent is relatively complex, resulting in an increase in the number of components, thereby increasing costs and manufacturing difficulty;

[0007] 4. The inductor Q value of the resonant cavity and tail current in traditional VCO is generally not high, resulting in increased phase noise;

[0008] 5. The variable capacitance range in conventional VCOs is smaller, resulting in a smaller tuning voltage VTUNE range, which in turn results in a smaller frequency band range. Summary of the invention

[0009] The present invention provides a low-noise, wide-band voltage-controlled oscillator based on a cross-coupled differential structure, which solves the technical problems of the existing oscillator, such as complex structure, high noise, poor stability, etc.

[0010] The present invention can be achieved through the following technical solutions:

[0011] A low-noise, wide-bandwidth voltage-controlled oscillator based on a cross-coupled differential structure comprises a resonant cavity, a differential negative resistance circuit and a current bias circuit. The resonant cavity adopts an LC resonance structure to determine the frequency selection and phase characteristics of the low-noise, wide-bandwidth voltage-controlled oscillator; the differential negative resistance circuit uses a cross-coupled differential pair structure composed of two bipolar junction transistors to provide sufficient gain and positive feedback, thereby generating a negative resistance effect; the current bias circuit uses a bipolar junction transistor to construct a bias circuit structure, which is used to provide a stable bias current to ensure that the bipolar junction transistor in the differential negative resistance circuit operates in an amplification region.

[0012] Further, the resonant cavity includes an inductor L1 and an inductor L2 which are symmetrically arranged, one end of the inductor L1 and the inductor L2 are both connected to the VCC power supply, and the other end of the inductor L1 and the inductor L2 are both connected to the variable capacitor array;

[0013] The differential negative resistance circuit includes a bipolar junction transistor Q1 and a bipolar junction transistor Q2 which are symmetrically arranged, wherein the base of the bipolar junction transistor Q1 and the collector of the bipolar junction transistor Q2 are commonly connected to the other end of the inductor L2 of the resonant cavity, the base of the bipolar junction transistor Q2 and the collector of the bipolar junction transistor Q1 are commonly connected to the other end of the inductor L1 of the resonant cavity, and the emitters of the bipolar junction transistor Q1 and the bipolar junction transistor Q2 are commonly connected to a current bias circuit;

[0014] The current bias circuit includes a bipolar junction transistor Q3, whose emitter is connected to the inductor L3 and the resistor R1 in sequence and then grounded, whose base is connected to the VCC power supply, whose collector is connected to the capacitor C1 and then grounded, and is also directly connected to the emitters of the bipolar junction transistors Q1 and Q2.

[0015] Furthermore, the variable capacitor array includes multiple pairs of varactors connected in parallel, whose positive terminals are connected to the tuning voltage VTUNE, and whose negative terminals on both sides are connected together and then connected to the other ends of the inductor L1 and the inductor L2 and the collectors of the bipolar junction transistors Q1 and the bipolar junction transistors Q2 respectively.

[0016] Furthermore, each of the varactor pairs includes two varactor diodes connected in a mirror-symmetrical manner.

[0017] Furthermore, the inductor L1 and the inductor L2 adopt a microstrip line structure.

[0018] Furthermore, the resonant cavity also includes a plurality of parallel branches connected in parallel with the variable capacitor array, each of the parallel branches includes a fixed capacitor array and a control switch connected in series, and each of the control switches is used to control the connection or disconnection of the fixed capacitor array in the parallel branch.

[0019] Further, the collectors of the bipolar junction transistor Q1 and the bipolar junction transistor Q2 are connected to the first buffer circuit and the second buffer circuit respectively, and the collectors of the bipolar junction transistor Q1 and the bipolar junction transistor Q2 are respectively connected to the resonant cavity with fixed capacitors C2 and C3, and the fixed capacitors C2 and C3 act together with the variable capacitor array to enable the low-noise wide-band voltage-controlled oscillator to obtain a wider frequency band;

[0020] A current mirror circuit is also connected between the current bias circuit and the VCC power supply, and the current mirror circuit is used to provide a stable operating current for the current bias circuit.

[0021] Further, the current mirror circuit includes a bipolar junction transistor Q6, the base and collector of the bipolar junction transistor Q6 are connected together, then connected to the VCC power supply through the current source Current_I1, and directly connected to the base of the bipolar junction transistor Q3, and the emitter of the bipolar junction transistor Q6 is grounded through the resistor R2;

[0022] The first buffer circuit includes a bipolar junction transistor Q4, the collector of which is connected to the VCC power supply via a resistor R3, and is used as an output terminal OUTP via a bypass capacitor C4, the emitter of which is grounded, and the base of which is connected to the collector of the bipolar junction transistor Q1;

[0023] The second buffer circuit includes a bipolar junction transistor Q5, the collector of which is connected to the VCC power supply through a resistor R4 and serves as an output terminal OUTN through a bypass capacitor C5, the emitter of the bipolar junction transistor Q5 is grounded, and the base is connected to the collector of the bipolar junction transistor Q2.

[0024] The beneficial technical effects of the present invention are:

[0025] 1) The low-noise, wide-bandwidth voltage-controlled oscillator of the present invention uses a differential negative resistance circuit structure to replace the commonly used π-type structure of the bipolar junction transistor. Since the differential structure is symmetrical, it can effectively suppress common-mode noise, improve the anti-interference ability of the signal, increase the frequency stability of the circuit, and make the feedback network more concise, so that the area is reduced, the integration can be increased, and the cost is reduced;

[0026] Since the two signal paths in the differential structure are complementary, the differential structure can be used to improve the nonlinear distortion of the voltage-controlled oscillator and reduce even harmonics.

[0027] Compared with CMOS process bipolar junction transistors (BJTs), due to its material and process characteristics, it has lower noise and better thermal stability in high-power and high-power applications;

[0028] 2) The low-noise, wide-bandwidth voltage-controlled oscillator of the present invention uses a single-tube bipolar junction transistor as a current bias circuit. Compared with a multi-tube structure, the single-tube design of the present invention is simpler and easier to adjust the working current according to the oscillation amplitude and to match the appropriate bias voltage of the bipolar junction transistor in the differential negative resistance circuit structure, so that it can provide sufficient gain in the amplification region and keep the noise at a low level, thereby minimizing power consumption;

[0029] 3) The present invention uses a single bipolar junction transistor as a current bias circuit, and the emitter of the bipolar junction transistor Q3 is connected to the resistor R1 to form an emitter negative feedback, which not only stabilizes the oscillation (because the working current is stabilized), but also occupies a small area and has a simple structure, so the cost is reduced and it is easy to integrate with other circuits, or form a multi-mode VCO and other purposes;

[0030] At the same time, a large capacitor C1 is connected to the collector of the bipolar junction transistor Q3 to form a low-pass filter to absorb high-frequency components. The large capacitor C1 can store charges and smooth the signal. When the voltage-controlled oscillator is disturbed or the bias voltage changes suddenly, the capacitor absorbs these changes and prevents them from propagating to the output of the voltage-controlled oscillator, which can reduce noise and instability in the signal.

[0031] Connect a high-quality inductor L3 to the emitter of the bipolar junction transistor Q3, and the tail current noise formula is It can be seen that due to the high Q value (e.g. greater than 15), the loss is lower at a specific frequency, thereby reducing the noise inside the oscillator;

[0032] 4) The present invention uses microstrip lines instead of traditional inductors to increase the Q value during layout, thereby reducing the resonance cavity noise;

[0033] 5) The present invention uses multiple varactor pairs to form a variable capacitor array, so that the tuning voltage Vtune range is increased to -2 to 5V, and the structure is simple and easy to add fixed capacitors, thereby achieving a wide-band effect;

[0034] In summary, based on the simple structure of each module, the present invention is easy to transform and integrate, which reduces the area and cost, and provides a template for the development of voltage-controlled oscillator IP. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A circuit schematic diagram of a π-type VCO in the prior art;

[0036] Figure 2 It is a circuit principle structure diagram of the present invention;

[0037] Figure 3 is a circuit structure diagram of a variable capacitance diode array of the present invention;

[0038] Figure 4 is a CV characteristic curve diagram of the varactor of the present invention;

[0039] Figure 5 The microstrip line inductor layout of the present invention;

[0040] Figure 6 It is a Q value curve diagram of the inductance value of the microstrip line inductor at different frequencies of the present invention;

[0041] Figure 7 A phase noise curve diagram of the low-noise, wide-bandwidth voltage-controlled oscillator of the present invention;

[0042] Figure 8 A frequency sweep characteristic curve diagram of the low-noise, wide-bandwidth voltage-controlled oscillator of the present invention;

[0043] Fig. 9 It is a graph of various harmonics of the low-noise wide-band voltage-controlled oscillator of the present invention;

[0044] Fig.10 A power consumption curve diagram of the low-noise, wide-bandwidth voltage-controlled oscillator of the present invention;

[0045] Fig.11 This is a schematic diagram of the first deformation circuit principle of the present invention;

[0046] Fig.12 This is a schematic diagram of the second deformation circuit principle of the present invention. DETAILED DESCRIPTION

[0047] The specific implementation of the present invention is described in detail below with reference to the accompanying drawings and preferred embodiments.

[0048] like Figure 2As shown, the present invention provides a low-noise, wide-bandwidth voltage-controlled oscillator based on a cross-coupled differential structure, including a resonant cavity, a differential negative resistance circuit and a current bias circuit. The resonant cavity adopts an LC resonance structure to determine the frequency selection and phase characteristics of the low-noise, wide-bandwidth voltage-controlled oscillator; the differential negative resistance circuit uses a cross-coupled differential pair structure composed of two bipolar junction transistors to provide sufficient gain and positive feedback, thereby generating a negative resistance effect; the current bias circuit uses a bipolar junction transistor to construct a bias circuit structure, which is used to provide a stable bias current to ensure that the bipolar junction transistor in the differential negative resistance circuit operates in the amplification region. The low-noise, wide-bandwidth voltage-controlled oscillator of the present invention has the advantage of low phase noise. A cross-coupled differential pair negative resistance unit structure, i.e., a differential negative resistance circuit, is used to replace the π-type structure commonly used in bipolar junction transistor voltage-controlled oscillators. On the basis of this structure, a capacitor array composed of multiple variable capacitance diodes is used to achieve a wider frequency modulation range. In addition, a current bias structure composed of a single transistor is used, so that the overall effects of high anti-interference, low phase noise, wide bandwidth, simple structure, convenient regulation and control, and low cost are achieved.

[0049] Circuit structure:

[0050] 1. The resonant cavity includes symmetrically arranged inductors L1 and L2, one end of the inductors L1 and L2 are connected to the VCC power supply, and the other end is connected to the variable capacitor array.

[0051] The variable capacitor array includes multiple pairs of varactors connected in parallel, the positive terminals of which are connected to the tuning voltage VTUNE, and the negative terminals on both sides of which are connected together and then connected to the other ends of the inductor L1 and the inductor L2 and the collectors of the bipolar junction transistors Q1 and Q2. Figure 3 As shown, there are three pairs of varactor pairs connected in parallel, the positive terminals of the varactor pairs are connected to the tuning voltage VTUNE, and after the negative terminals of the three pairs of varactor pairs are connected, they are also connected to the resonant cavity and the collectors of the bipolar junction transistors Q1 and Q2, so that the tuning voltage VTUNE can range from -2 to 5V, and the structure is simple, and it is easy to add fixed capacitors, thereby achieving a wide-band effect.

[0052] like Figure 4 As shown, it is a CV characteristic curve diagram of the variable capacitance diode of the present invention, and the variable capacitance value range is 493fF-1291fF.

[0053] like Figure 5 , 6As shown, the inductor layout and inductor parameters in the LC resonant cavity of the present invention include the inductance value and the Q value of the microstrip line inductance. The original inductors L1 and L2 are circular inductors, which are replaced by microstrip lines in the layout. While the inductance value remains unchanged, the Q value of the inductance is greatly improved, thereby reducing the resonant cavity noise.

[0054] 2. The differential negative resistance circuit includes a symmetrically arranged bipolar junction transistor Q1 and a bipolar junction transistor Q2, wherein the base of the bipolar junction transistor Q1 and the collector of the bipolar junction transistor Q2 are commonly connected to the other end of the inductor L2 of the resonant cavity, the base of the bipolar junction transistor Q2 and the collector of the bipolar junction transistor Q1 are commonly connected to the other end of the inductor L1 of the resonant cavity, and the emitters of the bipolar junction transistor Q1 and the bipolar junction transistor Q2 are commonly connected to a current bias circuit.

[0055] The differential negative resistance circuit of the present invention is mostly used for the differential structure of the CMOS process, thereby replacing the π-type structure commonly used in the bipolar junction transistor in the existing voltage-controlled oscillator, and can effectively suppress common-mode noise, improve the anti-interference ability of the signal, increase the frequency stability of the circuit, improve the nonlinear distortion of the voltage-controlled oscillator, and reduce even harmonics. At the same time, the feedback network is more concise, the area is reduced, the integration is increased, and the cost is reduced.

[0056] Compared with CMOS process bipolar junction transistors (BJTs), they have lower noise and better thermal stability in high-power and high-power applications.

[0057] 3. The current bias circuit includes a bipolar junction transistor Q3, whose emitter is connected to the inductor L3 and the resistor R1 in sequence and then grounded, whose base is connected to the VCC power supply, whose collector is connected to the capacitor C1 and then grounded, and is also directly connected to the emitters of the bipolar junction transistor Q1 and the bipolar junction transistor Q2.

[0058] Compared with the current bias circuit of the multi-tube structure, the single-tube structure of the present invention is simpler and easier to adjust the working current according to the oscillation amplitude and match the appropriate bias voltage of the bipolar junction transistor in the differential negative resistance structure, so that it can provide sufficient gain in the amplification area and keep the noise at a low level, thereby minimizing power consumption;

[0059] At the same time, the emitter negative feedback structure formed with the resistor R1 not only stabilizes the oscillation (because the working current is stabilized), but also occupies a small area and has a simple structure, so the cost is reduced and it is easy to integrate with other circuits, or form a multi-mode VCO and other uses;

[0060] And the emitter of the bipolar junction transistor Q3 is connected to the inductor L3, which has a higher Q value and lower loss at a specific frequency. It can be seen that the high-Q tail inductor can reduce the noise in the tail current; its collector is connected to the large capacitor C1 to form a low-pass filter to absorb high-frequency components, and the large capacitor can store charge and smooth the signal. When the voltage-controlled oscillator is disturbed or the bias voltage changes suddenly, the capacitor absorbs these changes and prevents them from propagating to the voltage-controlled oscillator output, which can reduce noise and instability in the signal.

[0061] like Figure 7 As shown, this is a phase noise curve diagram of the present invention at the center frequency of 3.9GHz, and its phase noise is -78.841dBc / Hz@10kHz, -98.841dBc / Hz@100kHz, and -118.843dBc / Hz@1MHz, respectively, achieving the function of reducing the phase noise by 20dBc / Hz for every 10 times increase in frequency from 10kHz to 1MHz. The phase noise at the near-end 10kHz, 100kHz and 1MHz also performs very well, achieving better phase noise characteristics.

[0062] like Fig.10 As shown, it is the power consumption curve of the present invention. By using a single bipolar junction transistor Q3 to form a current bias circuit, the three factors of amplitude, noise and power consumption are balanced, so that the power consumption is lower than that of a conventional structure.

[0063] Oscillation conditions

[0064] To achieve stable oscillation, the circuit must satisfy the Barkhausen oscillation conditions:

[0065] 1) The loop gain is greater than or equal to 1

[0066] 2) The loop phase shift is an integer multiple of 2π (positive feedback)

[0067] In the VCO, the LC resonant cavity and the differential negative resistance structure jointly meet these conditions

[0068] Oscillation Mechanism - Oscillation Process

[0069] In fact, the oscillation is the result of the combined effect of the entire circuit (including the LC resonant cavity and the differential negative resistance structure), such as Figure 2 shown.

[0070] Working point: The current bias circuit makes the bipolar junction transistor in the cross-coupled differential pair work in the amplification region

[0071] In the present invention, a current bias circuit of an emitter negative feedback structure composed of a bipolar junction transistor Q3 and a resistor R1 connected to its emitter provides a suitable bias current, so that the bipolar junction transistors Q1 and Q2 in the cross-coupled differential pair work in the amplification region.

[0072] Oscillation: A small noise or initial disturbance generates an initial signal in the LC resonant cavity.

[0073] In the present invention, a tiny noise or initial disturbance generates an initial signal in the LC resonant cavity composed of the inductor L1, the inductor L2 and the variable capacitor array.

[0074] Positive feedback: The differential negative resistance circuit amplifies the initial signal and generates a negative resistance effect through the positive feedback mechanism to offset the loss of the resonant cavity and maintain the oscillation signal.

[0075] In the present invention, the initial signal generated in the LC resonant cavity is amplified by positive feedback formed by a differential negative resistance circuit composed of bipolar junction transistors Q1 and Q2, and the resonant cavity loss is offset by the generated negative resistance effect to maintain the oscillation signal.

[0076] Frequency stability: The LC resonant cavity ensures that the oscillation frequency is stable near its resonant frequency

[0077] In the present invention, after maintaining stable oscillation through a differential negative resistance circuit, the inductance and capacitance values ​​set in the LC resonant cavity composed of inductors L1, L2 and a variable capacitor array make the oscillation frequency stabilized at the set resonant frequency. The capacitance value of the variable capacitor array can also be changed by changing the tuning voltage VTUNE so that the resonant frequency changes as required.

[0078] In the voltage-controlled oscillator, the LC resonant cavity is responsible for selecting and stabilizing the oscillation frequency, while the differential negative resistance circuit provides positive feedback by generating a negative resistance effect to maintain oscillation. In this way, a stable oscillator is formed through the joint action of the resonant cavity and the negative resistance structure. Therefore, the oscillation is the result of the entire circuit, in which the resonant cavity provides frequency selection, and the positive feedback mechanism ensures the continued existence of the oscillation signal.

[0079] like Figure 8 As shown, the frequency sweep characteristic curve of the oscillator of the present invention is in the range of 3.75 GHz-4.05 GHz.

[0080] like Fig. 9 As shown in the figure, the harmonic curves of the oscillator of the present invention are obtained. The second harmonic characteristic is better than the conventional structure, which is -20dBc, through the high-quality tail inductor L1, the large capacitor filter C1, the emitter negative feedback current bias circuit composed of the bipolar junction transistor Q3 and the cross-coupled differential pair composed of the bipolar junction transistors Q1 and Q2.

[0081] The first deformation circuit:

[0082] like Fig.11 , a deformation circuit schematic diagram of the present invention, compared with the Figure 2The circuit structure shown is the basic circuit structure, which is based on a voltage-controlled oscillator composed of a cross-coupled differential pair of bipolar junction transistors, and also includes a buffer circuit, a fixed capacitor and a current mirror circuit, which can make the circuit work more stably and achieve better phase noise characteristics and a more universal frequency band range.

[0083] Specifically, the buffer circuit buffer includes a first buffer circuit and a second buffer circuit, which are respectively composed of a bipolar junction transistor Q4 and a bipolar junction transistor Q5, which are symmetrically distributed. The base of the bipolar junction transistor Q4 is connected to the original output end OUTP of the basic circuit structure, that is, the collector of the bipolar junction transistor Q1, and its collector is connected to the VCC power supply through a resistor R3, and is used as the output end OUTP through a bypass capacitor C4, and its emitter is connected to the ground; symmetrically, the base of the bipolar junction transistor Q5 is connected to the original output end OUTN of the basic circuit structure, that is, the collector of the bipolar junction transistor Q2, and its collector is connected to the VCC power supply through a resistor R4, and is used as the output end OUTN through a bypass capacitor C5, and its emitter is connected to the ground. The buffer circuit buffer makes the output signal and circuit operation more stable;

[0084] Fixed capacitors C2 and C3 are respectively connected between the collectors of the bipolar junction transistors Q1 and Q2, that is, the original output terminals OUTP and OUTN, and the resonant cavity. The fixed capacitors C2 and C3 work together with the variable capacitor array to enable the low-noise wide-band voltage-controlled oscillator to obtain a wider frequency band.

[0085] A current mirror circuit is also connected between the current bias circuit and the VCC power supply. The current mirror circuit is used to provide a stable operating current for the current bias circuit. The base and collector of the bipolar junction transistor Q6 are connected together, and then connected to the base of the bipolar junction transistor Q3. It is also directly connected to the VCC power supply through the current source Current_I1. The emitter of the bipolar junction transistor Q6 is grounded through the resistor R2, thereby forming a current mirror circuit to reduce noise.

[0086] The second deformation circuit:

[0087] like Fig.12 , a deformation circuit schematic diagram of the present invention, compared with the Figure 2The circuit structure shown is the basic circuit structure, and also includes a fixed capacitor array and a control switch, that is, the resonant cavity also includes a plurality of parallel branches connected in parallel with the variable capacitor array, each parallel branch includes a fixed capacitor array and a control switch connected in series, and each control switch is used to control the access or disconnection of the fixed capacitor array in the parallel branch. In other words, n fixed capacitor arrays can be designed, and one of the fixed capacitor arrays can be selected to work by controlling the switch, so that each LC resonant cavity works in a different frequency band. The design is simple, and only one control signal is needed to achieve frequency band switching; it is highly flexible and has a simple structure, so more fixed capacitor arrays can be added as needed to achieve more frequency band selection.

[0088] Although specific embodiments of the present invention are described above, those skilled in the art should understand that these are merely examples and that various changes or modifications may be made to these embodiments without departing from the principles and essence of the present invention. Therefore, the scope of protection of the present invention is limited by the appended claims.

Claims

1. A low-noise, wide-bandwidth voltage-controlled oscillator based on a cross-coupled differential structure, characterized in that: It includes a resonant cavity, a differential negative resistance circuit and a current bias circuit. The resonant cavity adopts an LC resonance structure to determine the frequency selection and phase characteristics of a low-noise wide-band voltage-controlled oscillator. The differential negative resistance circuit uses a cross-coupled differential pair structure composed of two bipolar junction transistors to provide sufficient gain and positive feedback, thereby generating a negative resistance effect. The current bias circuit uses a bipolar junction transistor to construct a bias circuit structure, which is used to provide a stable bias current and ensure that the bipolar junction transistor in the differential negative resistance circuit works in the amplification region.

2. The low-noise, wide-bandwidth voltage-controlled oscillator based on a cross-coupled differential structure according to claim 1, characterized in that: The resonant cavity comprises an inductor L1 and an inductor L2 which are symmetrically arranged, one end of the inductor L1 and the inductor L2 are both connected to a VCC power supply, and the other end of the inductor L1 and the inductor L2 are both connected to a variable capacitor array; The differential negative resistance circuit includes a bipolar junction transistor Q1 and a bipolar junction transistor Q2 which are symmetrically arranged, wherein the base of the bipolar junction transistor Q1 and the collector of the bipolar junction transistor Q2 are commonly connected to the other end of the inductor L2 of the resonant cavity, the base of the bipolar junction transistor Q2 and the collector of the bipolar junction transistor Q1 are commonly connected to the other end of the inductor L1 of the resonant cavity, and the emitters of the bipolar junction transistor Q1 and the bipolar junction transistor Q2 are commonly connected to a current bias circuit; The current bias circuit includes a bipolar junction transistor Q3, whose emitter is connected to the inductor L3 and the resistor R1 in sequence and then grounded, whose base is connected to the VCC power supply, whose collector is connected to the capacitor C1 and then grounded, and is also directly connected to the emitters of the bipolar junction transistors Q1 and Q2.

3. The low-noise, wide-bandwidth voltage-controlled oscillator based on a cross-coupled differential structure according to claim 2, characterized in that: The variable capacitor array includes multiple pairs of varactors connected in parallel, whose positive terminals are connected to the tuning voltage VTUNE, and whose negative terminals on both sides are connected together and then connected to the other ends of the inductor L1 and the inductor L2 and the collectors of the bipolar junction transistors Q1 and Q2.

4. The low-noise, wide-bandwidth voltage-controlled oscillator based on a cross-coupled differential structure according to claim 3, characterized in that: Each of the varactor pairs includes two varactor diodes connected in mirror symmetry.

5. The low-noise, wide-bandwidth voltage-controlled oscillator based on a cross-coupled differential structure according to claim 2, characterized in that: The inductor L1 and the inductor L2 adopt a microstrip line structure.

6. The low-noise, wide-bandwidth voltage-controlled oscillator based on a cross-coupled differential structure according to claim 2, characterized in that: The resonant cavity also includes a plurality of parallel branches connected in parallel with the variable capacitor array, each of the parallel branches includes a fixed capacitor array and a control switch connected in series, and each of the control switches is used to control the connection or disconnection of the fixed capacitor array in the parallel branch.

7. The low-noise, wide-bandwidth voltage-controlled oscillator based on a cross-coupled differential structure according to claim 2, characterized in that: The collectors of the bipolar junction transistor Q1 and the bipolar junction transistor Q2 are connected to the first buffer circuit and the second buffer circuit respectively, and the collectors of the bipolar junction transistor Q1 and the bipolar junction transistor Q2 are further connected to the resonant cavity with fixed capacitors C2 and C3 respectively, and the fixed capacitors C2 and C3 act together with the variable capacitor array to enable the low-noise wide-band voltage-controlled oscillator to obtain a wider frequency band; A current mirror circuit is also connected between the current bias circuit and the VCC power supply, and the current mirror circuit is used to provide a stable operating current for the current bias circuit.

8. The low-noise, wide-bandwidth voltage-controlled oscillator based on a cross-coupled differential structure according to claim 7, characterized in that: The current mirror circuit includes a bipolar junction transistor Q6, wherein the base and collector of the bipolar junction transistor Q6 are connected together, and then connected to the VCC power supply through a current source Current_I1, and directly connected to the base of the bipolar junction transistor Q3, and the emitter of the bipolar junction transistor Q6 is grounded through a resistor R2; The first buffer circuit includes a bipolar junction transistor Q4, the collector of which is connected to the VCC power supply via a resistor R3, and is used as an output terminal OUTP via a bypass capacitor C4, the emitter of which is grounded, and the base of which is connected to the collector of the bipolar junction transistor Q1; The second buffer circuit includes a bipolar junction transistor Q5, the collector of which is connected to the VCC power supply through a resistor R4 and serves as an output terminal OUTN through a bypass capacitor C5, the emitter of the bipolar junction transistor Q5 is grounded, and the base is connected to the collector of the bipolar junction transistor Q2.

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