CN114726316A - A Voltage Controlled Oscillator and Signal Generation Device with Octave Band Low Phase Noise - Google Patents

Abstract

The invention discloses a voltage-controlled oscillator with multiple frequency bands and low phase noise and a signal generating device, belonging to the technical field of circuit design.A coupling resonant cavity network comprises a first coupling resonator and a second coupling resonator, wherein the first coupling resonator and the second coupling resonator generate different resonant frequency signals under the control of tuning voltage; the emitters of the transistors are respectively connected to the output ends of the first coupling resonator and the second coupling resonator and used for amplifying resonant frequency signals; and the broadband negative resistance network is connected with the base electrode of the transistor and is used for generating uniform or constant negative resistance on the tuning frequency band. The negative resistance network is coupled with the base level of the transistor, and provides a negative resistance value which is uniformly changed in the whole passband, thereby ensuring that the VCO can maintain stable oscillation in the whole S waveband and simultaneously keep good noise performance.

Description

A Voltage Controlled Oscillator and Signal Generation Device with Octave Band Low Phase Noise

technical field

The invention relates to the technical field of circuit design, in particular to a voltage-controlled oscillator and a signal generating device with an octave frequency band and low phase noise.

Background technique

Voltage Controlled Oscillator (VCO) refers to an oscillator circuit whose output frequency corresponds to the input control voltage. The size of the output signal depends on the design of the VCO circuit, and the operating frequency is determined by the resonator that provides the input signal; clock generation and clock Recovery circuits typically generate clocks using the VCO within a phase-locked loop (PLL) as an external reference, so the VCO is critical to the performance of the phase-locked loop. Phase-locked loops are particularly important in wireless networks because they enable communication devices to quickly lock onto the carrier frequency on which communications are transmitted.

The dynamic operating range and noise performance of the VCO may limit or affect the performance of the phase-locked loop itself, which in turn affects the performance of devices with a phase-locked loop, such as RF transceivers, mobile phones, modem cards, etc. The effect of controlled oscillator performance. Wideband tunability of a VCO is one of the most fundamental properties to consider in VCO design, and is related to the technology and topology used. The dynamic time-averaged quality factor (Q factor, which is generally inversely proportional to the VCO's operating frequency range) of the resonator and the noise of the tuning diodes affect the noise performance of the VCO.

The development of current radio frequency technology puts forward higher requirements for VCO design: low phase noise, low power consumption and wide frequency tuning range. Although VCO technology continues to improve, low phase noise is usually still a bottleneck, and the existing technologies mainly have the following defects and deficiencies:

1. From the perspective of tuning bandwidth, the existing VCO based on LC resonator does not have a tuning range covering the entire S-band, while the VCO based on YIG resonator can achieve a wider tuning range, but it is expensive and bulky. There are certain disadvantages for today's miniaturization needs;

2. From the perspective of phase noise, the phase noise level of VCOs with wider bandwidths is generally around -80dBc/Hz@10kHz, and the phase noise level still needs to be improved.

To sum up, the invention of a voltage-controlled oscillator with octave band and low phase noise is very necessary.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the problems of the prior art, and to provide a voltage-controlled oscillator and a signal generating device with an octave frequency band and low phase noise.

The purpose of the present invention is achieved through the following technical solutions: a voltage-controlled oscillator with multiplier frequency band and low phase noise, the voltage-controlled oscillator includes a coupled resonant cavity network, a quartz crystal or a transistor, and a broadband negative resistance network.

Wherein, the coupled resonator network includes a first coupled resonator and a second coupled resonator, and the first coupled resonator and the second coupled resonator generate signals of different resonant frequencies under the control of the tuning voltage. Specifically, the tuning voltage is provided by a power supply module or device with an adjustable output voltage, and its value is 0V-20V. The two coupled resonators are used to generate resonant frequencies, which can be LC oscillators, RC oscillators, etc., and will generate different resonant frequencies when excited by different tuning voltages. Preferably, the first coupled resonator and the second coupled resonator use the same resonator, and generate the same resonance frequency under the excitation of the same tuning voltage.

The emitters of the transistors are respectively connected to the output ends of the first coupled resonator and the second coupled resonator for amplifying the resonant frequency signal, and the VCO operating frequency is output by the collectors of the transistors. Specifically, the VCO of the present invention selects parallel emitter transistors for amplification, and two identical tuning networks (coupled resonators) are coupled to the two emitters of the parallel emitter transistors. By suppressing and superimposing even-order modes, the output frequency can be adjusted within twice the range of the fundamental frequency, which increases the range of tuning frequencies.

A broadband negative resistance network, connected to the transistor base, is used to maintain a constant resistance over the entire passband of the resonator, specifically, while changing the oscillation frequency of the coupled resonator network by tuning the voltage to change the VCO operating frequency, the negative resistance The network creates a uniform or constant negative resistance across the tuning band, which ensures that the VCO can maintain stable oscillations over the entire S-band while maintaining good noise performance.

In an example, according to the oscillation principle of the negative resistance circuit (broadband negative resistance network), the starting condition of the circuit is:

R _IN +R _L <0

Among them, R _IN represents the real part of the input impedance; _RL represents the real part of the load impedance; the conditions for oscillation balance are:

R _IN = -R _L , and X _{IN =} -XL

Among them, X _IN represents the imaginary part of the input impedance; _XL represents the imaginary part of the load impedance. In practical applications, it is usually necessary to meet:

R _L = -R _IN /3

However, it is a difficulty in the current broadband VCO design to make the negative resistance of the circuit meet the start-up condition in a wider passband. The impedance calculation formula of the 1.6G-4.1G frequency band of the present invention is:

Zin=Vin/Iin

Among them, Vin represents the input voltage; Iin represents the input current; the triode circuit is AC equivalent to obtain:

Zin=[(1+β)X _c X _vr +h _ie (X _c +X _vr )]/X _c +h _ie

Among them, β is the parameter characterizing the current amplification ability of the triode; Xc is the equivalent capacitive reactance of the negative resistance circuit; _Xvr is the equivalent capacitive _reactance of the varactor diode; It reflects the ability of the base voltage to control the base current when the output voltage Uce remains unchanged. When X _c << h _ie , there are:

Zin≈(1+β)/h _ie *X _c X _vr +(X _c +X _vr )=-gm/ω2C*C _vr +1/jω(C*C _vr /(C+C _vr ))

R _IN =-gm/ω ² C*C _vr ,X _IN =1/jω(C*C _vr /(C+C _vr ))

Among them, gm represents the control ability of the input voltage of the transistor to the output current, that is, the amplification effect; C is the equivalent capacitance of the negative resistance circuit; C _vr is the equivalent capacitance of the varactor diode. After obtaining the impedance that meets the 1.6G-4.1G frequency band through calculation, make the load impedance and input impedance meet the start-up conditions, and then build a negative resistance circuit that meets the impedance required in the 1.6G-4.1G frequency band based on capacitance and inductance. As a preferred option, a broadband negative resistance network inductor L9, one end of the inductor L9 is connected with a grounding capacitor C10, the other end is connected with a grounding capacitor C11, and an inductor L10 is connected between the inductor L9 and the grounding capacitor C10, and the other end of the inductor L10 is connected with a grounding capacitor The values of C12, L9, L10, C10, C11, and C12 are specific to meet the impedance required in the 1.6G-4.1G frequency band. Under the condition that the impedance requirements can be met, the value of the capacitor should be increased as much as possible to reduce phase noise. .

In an example, the VCO further includes a filter network for filtering the tuning voltage to filter out clutter signals in the tuning voltage, thereby improving the anti-interference capability of the VCO.

In one example, the filter network is an LC filter circuit. As a preferred option, the LC filter circuit includes a first LC filter sub-circuit and a second LC filter sub-circuit, and the tuning voltage is respectively input to the first coupling after being filtered by the first LC filter sub-circuit and the second LC filter sub-circuit. resonator, second coupled resonator. Specifically, the first LC filter sub-circuit includes an inductor L6 and an inductor L5 connected in sequence, a grounding capacitor C7 is connected between the inductor L6 and the inductor L5, and a grounding capacitor C6 is connected to the other end of the inductor L5 (the end away from the inductor L6). The second LC filter subcircuit includes an inductor L8 and an inductor L7 connected in sequence, a grounding capacitor C9 is connected between the inductor L8 and the inductor L7, and a grounding capacitor C8 is connected to the other end of the inductor L7 (the end far from the inductor L8).

In an example, the first coupled resonator and the second coupled resonator are both LC oscillators, and the resonant frequency f satisfies:

Among them, L represents the inductance value of the oscillator; C represents the capacitance value of the oscillator.

In an example, the LC oscillator includes two varactor diodes connected in parallel, a microstrip line is provided between the two varactor diodes, and the output end of the LC oscillator is drawn between the microstrip line and a varactor diode. In this example, the use of two varactors connected in parallel can increase the capacitance variation range of the varactors, thereby broadening the tuning frequency range of the VCO to cover the entire S-band.

In an example, the specifications of the two varactor diodes in the LC oscillator are the same, and the specification here refers to the performance parameters of the varactor diode, including the capacitance value of the diode and the like. In this example, the Q value of two identical varactors in parallel is the same as that of a single varactor, resulting in a low-noise output without deteriorating phase noise.

In one example, the microstrip line is an arc-shaped microstrip line. At this time, the model expression of the LC oscillator composed of two parallel-connected varactors and microstrip lines is:

At this time, the F factor is expressed as:

In the above two formulas, Δω represents the angular frequency variation; T represents the temperature; R represents the loss resistance in the LC oscillator; V ₀ represents the output voltage; Q represents the dynamic time-averaged quality factor of the resonator; ω ₀ represents the initial angular frequency; I _T represents the tail current; g _m,tail represents the transconductance of the tail current source transistor; γ represents the transistor noise figure. In the resonant network, the Q value of the inductance is much lower than that of the MIM capacitor and the varactor diode, so the Q value in the resonant network (coupled resonant cavity network) is mainly determined by the spiral inductance, so it is necessary to improve the resonant network. For the Q value, it is necessary to select an inductance with a high Q value as much as possible. In this example, the equivalent inductance obtained by a section of arc-shaped microstrip line resonates, which effectively improves the Q value of the inductance.

In an example, the first coupled resonator and the second coupled resonator use varactor diodes and microstrip lines of the same specification. At this time, the circuit of the tuning voltage to the two resonators and then to the transistor emitter is completely mirrored, so at Vt During the change process, the outputs of the two resonators are the same, which ensures the efficiency of signal coupling.

In an example, the voltage-controlled oscillator further includes an output matching network, which is connected to the collector of the transistor, thereby obtaining a stable operating frequency at the output end of the output matching network.

In one example, the output matching network includes a first capacitor for matching the output of the transistor with the subsequent stage, and a capacitor and an inductor for impedance matching with the output of the voltage-controlled oscillator. Preferably, the output matching network includes a capacitor C3, a resistor R1, a capacitor C2, and a capacitor C1 connected in sequence. A grounding inductor L2 is provided between the resistor R1 and the capacitor C2, and a grounding inductor L1 is provided between the capacitor C2 and the capacitor C1. Among them, C3 is used for the matching between the transistor output and the subsequent stage, and is also used for DC blocking. C1, C2, L1, and L2 match the output impedance line in order to take into account the error in the actual project.

In an example, the VCO further includes a DC power supply network, which is connected to the broadband negative resistance network and the base of the transistor. As a preferred option, the voltage VCC of the DC power supply network is sequentially connected with a resistor R2 and a resistor R3, and the other end of the resistor R3 is connected with a broadband negative resistance network; a grounding capacitor C4 is also connected between the resistor R2 and the resistor R3, while the resistor R2 and the resistor R3 are connected to the grounding capacitor C4. R3 is also connected to an inductor L3, one end of the inductor L3 is connected to one side of the ground capacitor C4, the other end of the inductor L3 is connected to a ground capacitor C5, and the inductor L3 and the capacitor C5 are connected to the transistor collector.

The present invention also includes a signal generating device, which includes a voltage-controlled oscillator formed by any one or more of the above examples, and is used to generate a signal of a specific frequency.

Compared with the prior art, the beneficial effects of the present invention are:

1. In an example, the coupling resonator network of the present invention provides the required oscillation frequency, and the negative resistance network is coupled with the base level of the transistor to provide a negative resistance value that changes uniformly in the entire passband, thereby ensuring that the VCO can S-band can maintain stable oscillation while maintaining good noise performance.

2. In an example, the clutter signal in the tuning voltage is filtered out by the filtering network, which improves the anti-interference ability of the VCO.

3. In an example, using two varactor diodes connected in parallel can increase the capacitance variation range of the varactor diodes, thereby broadening the tuning frequency range of the VCO to cover the entire S-band.

4. In an example, the Q value after using two identical varactor diodes in parallel is the same as the Q value of a single varactor diode, which will not deteriorate phase noise and achieve low-noise output.

5. In an example, resonance is performed based on the equivalent inductance obtained from the arc-shaped microstrip line, which effectively improves the Q value of the inductance.

6. In an example, using resonators of the same specification can output the same resonant frequency to the transistor emitter when the tuning voltage changes, ensuring signal coupling efficiency.

Description of drawings

The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. The accompanying drawings described herein are used to provide further understanding of the present application and constitute a part of the present application. In these drawings, the same reference numerals are used to denote the same or similar parts, the exemplary embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation of the present application.

1 is a system block diagram in an example of the present invention;

2 is a schematic circuit diagram of a coupled resonant cavity network and a filter network in an example of the present invention;

3 is a circuit schematic diagram of a broadband negative resistance network and a DC power supply network in an example of the present invention;

4 is a schematic circuit diagram of an output matching network in an example of the present invention;

5 is a noise test diagram in an example of the present invention;

FIG. 6 is a noise test chart in another example of the present invention.

Detailed ways

The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

In the description of the present invention, it should be noted that "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. The indicated direction or positional relationship is based on the direction or positional relationship described in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the indicated device or element must have a specific orientation or a specific orientation. construction and operation, and therefore should not be construed as limiting the invention. Furthermore, ordinal numbers (eg, "first and second," "first to fourth," etc.) are used to distinguish between objects, are not limited to that order, and should not be construed to indicate or imply relative importance.

In the description of the present invention, it should be noted that, unless otherwise expressly specified and limited, “installation”, “connection” and “connection” should be understood in a broad sense, for example, it may be a fixed connection or a detachable connection Connection, or integral connection; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be internal communication between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood in specific situations.

In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

A voltage-controlled oscillator with octave band low phase noise, a preferred example of which is shown in Figure 1, includes a coupled resonant cavity network, an NPN transistor, a broadband negative resistance network, a filter network, an output matching network and a DC power supply network.

As shown in FIG. 2 , the coupled resonator network includes a first coupled resonator and a second coupled resonator with the same circuit structure. The first coupled resonator includes a first varactor diode VR1 and a second varactor diode VR2 connected in parallel, and a first arc-shaped microstrip is arranged between the cathode of the first varactor diode VR1 and the cathode of the second varactor diode VR2 line, the first arc-shaped microstrip line and the cathode of the second varactor diode VR2 are connected to the emitter of the transistor; the second coupled resonator includes a third varactor diode VR3 and a fourth varactor diode VR4 connected in parallel, And a second arc-shaped microstrip line is arranged between the cathode of the third varactor diode VR3 and the cathode of the fourth varactor diode VR4, and the second arc-shaped microstrip line and the cathode of the fourth varactor diode VR4 are connected to the transistor. the emitter.

Further, as shown in FIG. 2 , the filtering network is an LC filtering circuit, including a first LC filtering subcircuit and a second LC filtering subcircuit. The first LC filter sub-circuit includes an inductance L6 and an inductance L5 connected in sequence, a grounding capacitor C7 is connected between the inductance L6 and the inductance L5, and the other end of the inductance L5 (the end away from the inductance L6) is connected with a grounding capacitor C6; the second LC The filter sub-circuit includes an inductance L8 and an inductance L7 connected in sequence, a grounding capacitor C9 is connected between the inductance L8 and the inductance L7, and a grounding capacitor C8 is connected to the other end of the inductance L7 (the end away from the inductance L8). The tuning voltage Vt is respectively filtered by the first LC filter sub-circuit and the second LC filter sub-circuit and then loaded onto the four varactor diodes, and the specifications and parameters of the four varactor diodes are the same.

Further, as shown in FIG. 3 , the broadband negative resistance network inductor L9, one end of the inductor L9 is connected with a grounding capacitor C10, the other end of the inductor L9 is connected with a grounding capacitor C11, and an inductor L10 is connected between the inductor L9 and the grounding capacitor C10. The other end of the L10 is connected to the ground capacitor C12, and the capacitor L9 and the ground capacitor C11 are connected to the base of the transistor.

Further, as shown in FIG. 3 , the voltage VCC of the DC power supply network is sequentially connected with a resistor R2 and a resistor R3, and the other end of the resistor R3 is connected with a grounding capacitor C10; a grounding capacitor C4 is also connected between the resistor R2 and the resistor R3, and at the same time The resistor R2 and the resistor R3 are also connected with an inductor L3, one end of the inductor L3 is connected to one side of the ground capacitor C4, the other end of the inductor L3 is connected to the ground capacitor C5, and the inductor L3 and the capacitor C5 are connected to the collector of the transistor.

Further, as shown in FIG. 4 , the output matching network includes a capacitor C3, a resistor R1, a capacitor C2, and a capacitor C1 connected in sequence. The other end of the capacitor C3 is connected to the collector of the transistor, and a ground is provided between the resistor R1 and the capacitor C2. A grounding inductor L1 is arranged between the inductor L2, the capacitor C2, and the capacitor C1, and the operating frequency of the VCO is output from the capacitor C1 end. Among them, C3 is used for the matching between the transistor output and the rear stage, and is also used for DC blocking. C1, C2, L1, L2 match the 50Ω impedance line at the output end in order to take into account the error in the actual project.

In this example, the capacitance value of the varactor diode is changed by changing the tuning voltage Vt, thereby changing the resonant frequency of the resonator, thereby changing the working frequency of the VCO, and at the same time, the negative resistance network generates a uniform or constant negative resistance in the tuning frequency band. Horseshoe-shaped resonator structure, designed a 1.6G-4.1G voltage-controlled oscillator that covers the entire S-band, and the phase noise can reach -90dBc/Hz@10kHz.

The above VCO was prepared by using a rogers5880 printed board, and the thickness of the printed board was 0.8 mm. According to the above principle and layout, the actual circuit test results designed are as follows:

When the Vt voltage is 0V, the output frequency is 1.599GHz, the harmonic suppression is less than 15, and the output power is 4.1dBm; when the Vt voltage is 18V, the output frequency is 4.195GHz, the harmonic suppression is less than 40, and the output power is 2.1dBm. In the process of voltage increase, the frequency is gradually increased, the harmonic suppression is gradually increased, and the output power is gradually decreased. According to the noise test diagram Figure 5, it can be seen that the phase noise of the VCO can reach -92.67dBc/Hz at 10KHz offset, -109.50dBc/Hz at 100KHz offset, and -109.50dBc/Hz at 1MHz offset. The phase noise can reach -128.91dBc/Hz.

计算出所需输出频率下谐振腔中的变容二极管取值，即振荡器的电感器；根据R_L＝-R_IN/3， X_IN＝-X_L计算出负阻网络中电容和电感的取值，以此实现其他频段输出的压控振荡器。例如一款3GHz-6GHz的压控振荡器。此时当Vt电压为0V时，输出 2.760GHz的频率，谐波抑制＜15，输出功率3.44dBm；当Vt电压为18V时，输出频率6.300GHz，谐波抑制＜20，输出功率-0.9dBm。在电压增加过程中，频率逐步提高，谐波抑制逐步提高，输出功率逐渐降低。基于噪声测试图图6中可以看出，根据相噪计算公式计算压控振荡器在10KHz偏移处的相噪，具体计算公式为：In another example, using the same circuit principle as the above example, according to

_Calculate the value of the _{varactor diode} in the _resonant cavity under the required output frequency, that is, the inductor of the oscillator; value, so as to realize the voltage-controlled oscillator output in other frequency bands. For example, a 3GHz-6GHz voltage controlled oscillator. At this time, when the Vt voltage is 0V, the output frequency is 2.760GHz, the harmonic suppression is less than 15, and the output power is 3.44dBm; when the Vt voltage is 18V, the output frequency is 6.300GHz, the harmonic suppression is less than 20, and the output power is -0.9dBm. In the process of voltage increase, the frequency is gradually increased, the harmonic suppression is gradually increased, and the output power is gradually decreased. As can be seen in Figure 6 based on the noise test chart, the phase noise of the voltage controlled oscillator at the 10KHz offset is calculated according to the phase noise calculation formula. The specific calculation formula is:

L(Δω)=(Pn)dBm-(Psig)dBm-10lg(Δf)

Among them, L(Δω) represents the phase noise of the output frequency; Pn represents the effective power of the signal; Psig represents the effective power of the noise floor of the spectrum analyzer. It can be seen from Figure 6 that the value of (Pn)dBm-(Psig)dBm in this example is 54.47dB; Δf represents the resolution bandwidth, or RES BW, which is 1KHz in this example. Based on the phase noise calculation formula, it can be concluded that the phase noise of the voltage-controlled oscillator at a 10KHz offset in this example is calculated to be -84.47dBc/Hz.

The above specific embodiment is a detailed description of the present invention, and it cannot be considered that the specific embodiment of the present invention is limited to these descriptions. Some simple deductions and substitutions should be considered as belonging to the protection scope of the present invention.

Claims (10)

1. A voltage-controlled oscillator with low phase noise in an octave band, characterized in that: the voltage-controlled oscillator comprises: A coupled resonator network, comprising a first coupled resonator and a second coupled resonator, the first coupled resonator and the second coupled resonator generate signals of different resonant frequencies under the control of a tuning voltage; a transistor, the emitters of the transistors are respectively connected to the output ends of the first coupled resonator and the second coupled resonator for amplifying the resonance frequency signal; A broadband negative resistance network, connected to the transistor base, used to create a uniform or constant negative resistance over the tuning frequency band. 2 . The voltage-controlled oscillator with octave frequency band and low phase noise according to claim 1 , wherein the voltage-controlled oscillator further comprises a filter network for filtering the tuning voltage. 3 . 3 . The voltage-controlled oscillator with octave band and low phase noise according to claim 2 , wherein the filter network is an LC filter circuit. 4 . 4 . The voltage controlled oscillator with octave frequency band and low phase noise according to claim 1 , wherein the first coupled resonator and the second coupled resonator are both LC oscillators. 5 . 5 . The voltage controlled oscillator with multiplier frequency band and low phase noise according to claim 4 , wherein the LC oscillator comprises two varactor diodes connected in parallel, and a micro-channel is arranged between the two varactor diodes. 6 . with line. 6 . The voltage-controlled oscillator with octave band and low phase noise according to claim 5 , wherein the specifications of the two varactors in the LC oscillator are the same. 7 . 7 . The voltage-controlled oscillator with octave frequency band and low phase noise according to claim 5 , wherein the microstrip line is an arc-shaped microstrip line. 8 . 8 . The voltage-controlled oscillator with octave frequency band and low phase noise according to claim 5 , wherein the first coupled resonator and the second coupled resonator use varactor diodes and microstrip lines of the same specification. 9 . . 9 . The voltage-controlled oscillator with octave frequency band and low phase noise according to claim 1 , wherein the voltage-controlled oscillator further comprises an output matching network, which is connected to the collector of the transistor. 10 . 10. A signal generating device, characterized in that: the device comprises the voltage-controlled oscillator according to any one of claims 1-9.

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