CN112953393A - Broadband voltage-controlled oscillator with low phase noise - Google Patents
Broadband voltage-controlled oscillator with low phase noise Download PDFInfo
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- CN112953393A CN112953393A CN202110382648.XA CN202110382648A CN112953393A CN 112953393 A CN112953393 A CN 112953393A CN 202110382648 A CN202110382648 A CN 202110382648A CN 112953393 A CN112953393 A CN 112953393A
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03B—GENERATION OF OSCILLATIONS, DIRECTLY OR BY FREQUENCY-CHANGING, BY CIRCUITS EMPLOYING ACTIVE ELEMENTS WHICH OPERATE IN A NON-SWITCHING MANNER; GENERATION OF NOISE BY SUCH CIRCUITS
- H03B5/00—Generation of oscillations using amplifier with regenerative feedback from output to input
- H03B5/08—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element comprising lumped inductance and capacitance
- H03B5/12—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element comprising lumped inductance and capacitance active element in amplifier being semiconductor device
Abstract
The invention discloses a broadband voltage-controlled oscillator with low phase noise, which comprises an active amplification circuit and a frequency selection feedback network; the frequency selective feedback network comprises a loop phase shift network and a filter. The loop phase shift network adopts a structure that two pairs of back-to-back connected anti-series variable capacitance diodes are inserted into a suspension stripline in pairs to provide correct phase shift for a circuit and increase the working bandwidth; the filter is composed of a tuning voltage source, a coupling transmission line and a pair of anti-series variable capacitance diode pairs connected back to back, the middle of the anti-series variable capacitance diode pair is also connected into a suspension stripline, and the coupling transmission line adopts a suspension stripline structure to reduce phase noise. Two ends of the frequency selection feedback network are respectively connected with a base electrode and a collector electrode of a bipolar transistor in the active amplifying circuit. Compared with other voltage-controlled oscillators adopting microstrip structures to design filters, the voltage-controlled oscillator realizes a low-phase-noise voltage-controlled oscillator on the basis of broadband.
Description
Technical Field
The invention relates to the field of microwave and millimeter wave active devices, in particular to a broadband voltage-controlled oscillator with low phase noise.
Background
In recent years, with the high-speed development of microwave and millimeter wave circuits and systems, the functions of the circuits and the systems are more and more complex, meanwhile, the working frequency of the systems is higher and higher, the working bandwidth is also larger and higher, the requirements on the technical indexes of wireless mobile communication systems are more and more strict, and a voltage-controlled oscillator is a core module in a phase-locked loop. The basic phase-locked loop circuit structure is shown in fig. 3, and is composed of the following main modules: phase Detector (PD), Loop Filter (LF), Voltage Controlled Oscillator (VCO). The phase detector is used to compare the phase of the input signal Fref with the output signal Fout of the voltage controlled oscillator whose output voltage is a function of the phase difference corresponding to the two signals. The loop filter is used for filtering high-frequency components and noise output by the phase detector. The voltage-controlled oscillator is controlled by the output voltage of the loop filter, so that the oscillation frequency is close to the frequency of the input signal until the frequency of the oscillation frequency is the same as that of the input signal. The design of a voltage-controlled oscillator with wide band and low phase noise is related to the performance of the whole phase-locked loop, and the performance of the phase-locked loop is related to the performance of the whole microwave millimeter wave system.
The voltage-controlled oscillator is a core basic device of a microwave millimeter wave circuit and is used for generating a microwave millimeter wave source. Tunable bandbroadening and phase noise are key performance indicators for voltage controlled oscillators. Lower phase noise requires a high quality factor filter to achieve. In practical applications, the advantages of low cost, small size and easy integration of an oscillator using a planar structure filter make it more and more popular in communication systems, such as a microstrip structure oscillator. However, the oscillator of the microstrip structure has difficulty in realizing low phase noise because its unloaded Q value is very low. As shown in fig. 4, this is a microstrip-coupled transmission line electric field pattern, where 4, 5, and 6 are metal conduction bands, 7 is a dielectric plate, 8 is a metal floor, and a solid line with arrows is an electric field line. The microstrip planar circuit is a semi-open structure, so that the radiation loss is large; meanwhile, the dielectric loss of the microstrip line is also large, so that the Q value is low, which means that the oscillator with the microstrip structure is difficult to realize low phase noise. And because the dielectric plate of the microstrip coupling transmission line is thinner, it is more difficult to realize tighter coupling.
The suspended stripline is also a planar structure, as shown in fig. 5, which is a coupled transmission line electric field layout based on the suspended stripline, wherein 9 is a metal wall, 10, 11, 12 are metal conduction bands, 13 is a dielectric plate, and the solid line with arrows is an electric field line. Since this is a closed structure, there is no radiation loss; because the dielectric plate is thinner, the other parts in the metal cavity are air, and the equivalent dielectric constant is close to 1, the dielectric loss is also lower. The structure has the advantages of low transmission loss, high Q value and simple structure, and is suitable for replacing microstrip lines to manufacture low-phase noise filters. Meanwhile, the height adjusting range of the metal cavity is large, so that the adjusting range of the coupling tightness is large; in addition, in the aspect of processing and manufacturing, the circuit board is compatible with the manufacturing of the existing circuit board, and has the advantage of simple and convenient manufacturing. However, no clear scheme is provided for further designing a voltage controlled oscillator for a filter with a suspended strip line structure, so that a low-phase-noise wideband voltage controlled oscillator is realized.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to overcome the defects of the prior art and provide a broadband voltage-controlled oscillator with low phase noise.
The technical scheme is as follows: in order to achieve the purpose, the invention adopts the following technical scheme:
a broadband voltage-controlled oscillator with low phase noise comprises an active amplifying circuit and a frequency selection feedback network; the frequency selection feedback network comprises a loop phase shift network and a filter; the loop phase shift network comprises two pairs of anti-series variable capacitance diodes which are connected back to back, and a suspension strip line is connected between the anti-series variable capacitance diodes to provide correct phase shift for the circuit and ensure the normal oscillation of the circuit in the working bandwidth. The suspended strip line is a closed structure, and has the advantages of low transmission loss, high Q value and simple structure. The filter is made of a coupling transmission line based on a suspended strip line structure, so that the phase noise is reduced.
Furthermore, the filter comprises a tuning voltage source, a coupling transmission line and a pair of anti-series variable capacitance diode pairs connected back to back, and a suspension stripline is connected between the anti-series variable capacitance diode pairs. The capacitance value of the variable capacitance diode can be changed by adjusting a tuning voltage source in the frequency selection feedback network, so that the center frequency of the filter is adjusted, and the tunable broadband is realized.
Furthermore, the coupling transmission line is of a suspended strip line structure, and the real object comprises a first metal upper cover, a first circuit board and a first metal lower cover; the first metal upper cover and the first metal lower cover are buckled together to form a cavity, the first circuit board is clamped in the middle, and the transmission line on the first circuit board, the first metal upper cover and the first metal lower cover form a suspended stripline structure.
Furthermore, the active amplification circuit comprises a bipolar transistor and a direct current bias network, and sufficient gain is provided for the circuit. And two ends of the frequency selection network are respectively connected with a base electrode and a collector electrode of a bipolar transistor in the active amplification circuit.
Has the advantages that: the invention discloses a broadband voltage-controlled oscillator with low phase noise.A structure that two pairs of back-to-back connected anti-series variable capacitance diodes are inserted into a suspension stripline in pairs is used as a loop phase shift network to provide correct phase shift for a circuit and expand the working bandwidth; a coupling transmission line based on a suspended strip line structure and a variable capacitance diode are used as frequency selection units. Compared with a microstrip filter circuit, the phase noise is lower on the basis of broadband of the voltage-controlled oscillator.
Drawings
FIG. 1 is a circuit diagram of a low phase noise wideband voltage controlled oscillator of the present invention
FIG. 2 is an exploded view of the physical model, in which the rectangular blocks on the first circuit board 2 are schematic diagrams of circuit components;
FIG. 3 is a circuit configuration diagram of a phase-locked loop in the background art;
FIG. 4 is a diagram of an electric field distribution of a microstrip coupled transmission line in the prior art;
fig. 5 is a prior art coupling transmission line electric field layout based on a suspended stripline structure.
Detailed Description
The invention will be further explained with reference to the drawings.
The present embodiment discloses a wideband voltage controlled oscillator with low phase noise, as shown in fig. 1, including an active amplifying circuit and a frequency selective feedback network. The active amplification circuit comprises a bipolar transistor and a direct current bias circuit; the frequency selection feedback network comprises a loop phase shift network and a filter; two ends of the frequency selection feedback network are respectively connected with a base electrode and a collector electrode of a bipolar transistor in the active amplifying circuit.
The active amplification circuit provides enough gain for the system, the Q1 is a bipolar transistor, and the direct current bias circuit is arranged according to the selected bipolar transistor, so that the active amplification circuit can provide enough gain in the whole working frequency bandwidth, the starting oscillation condition that the amplitude in the Barkhausen criterion is greater than 1 is met, and the normal work of the circuit is ensured; in addition to selecting the desired frequency response, the frequency selective feedback network should provide the correct phase shift such that the total phase shift of the entire circuit is equal to 0 ° or an integer multiple of 360 °, and the barkhausen criterion can be satisfied based on the sufficient gain provided by the active amplification circuit: the loop gain is larger than 1, the loop phase shift is equal to 0 degree or integral multiple of 360 degrees, and the normal oscillation starting of the circuit is ensured.
The loop phase shift network consists of a suspension strip line and a variable capacitance diode, the SSL1 and the SSL2 are the suspension strip line, and compared with a microstrip line which is a semi-open structure, the suspension strip line is a closed structure, and is low in transmission loss, high in Q value and simple in structure. VD1, VD2, VD3 and VD4 are varactor diodes. Although a single varactor can tune the filter over a wide frequency band, the desired phase shift cannot be maintained over a wide range to keep the oscillator running. Therefore, the circuit adopts a plurality of diodes and adds the suspension strip line to jointly adjust the loop phase shift, and the length of the suspension strip line needs to be optimized according to frequency tuning to ensure a very wide tuning range. Meanwhile, the voltage-capacitance characteristic of the variable capacitance diode has nonlinearity, which can cause nonlinear distortion of the voltage-controlled oscillator, and the nonlinear distortion of the voltage-controlled oscillator can be reduced by adopting a back-to-back connected anti-series variable capacitance diode pair mode, so that a structure that a suspension stripline is inserted between the back-to-back connected anti-series variable capacitance diode pairs is adopted in the circuit, so that correct phase shift is provided for the circuit, the bandwidth is expanded, and the nonlinear distortion is reduced.
The filter is composed of a tuning voltage source, a coupling transmission line and a variable capacitance diode. Coupled Line1 and Coupled Line2 are coupling transmission lines based on a suspended stripline structure, SSL3 is the suspended stripline, and VD5 and VD6 are varactor diodes. The varactor not only provides correct phase shift for the circuit, but also plays a role in adjusting the center frequency of the filter, and under the action of a tuning voltage source Vtune, the varactor can change the capacitance value along with the change of the voltage and adjust the center frequency of the filter together with the suspended strip line, so that the oscillator can adjust the oscillation frequency under the control of the tuning voltage.
The resistor in the frequency selective feedback network is 22k ohms and is used as a resonance-free radio frequency choke to apply the same tuning voltage to the six varactor diodes without being affected by high frequency signals. R1 and R2 in the active amplifying circuit are bias resistors and are used for direct current bias of the bipolar transistor; the capacitors C1 and C2 are used for isolating direct current signals and coupling high-frequency signals.
Coupled Line1 and Coupled Line2 connected with three pairs of varactors are coupling transmission lines based on a suspended strip Line structure, and because the microstrip planar circuit is a semi-open structure, the transmission loss is large, the Q value is low, which means that a filter with a microstrip structure is difficult to realize low phase noise. The filter is thus implemented with a suspended stripline structure. Firstly, modeling simulation is carried out on a coupling transmission line Structure model based on a suspended strip line Structure in three-dimensional electromagnetic field simulation software, such as High Frequency Structure Simulator (HFSS), tuning optimization is carried out, the width and the length of a metal conduction band and the distance between the conduction bands are determined so as to meet the requirement of Frequency selection, then an S parameter model is led out to be connected with other elements of a circuit in Advanced Design System (ADS) software, collaborative simulation optimization is carried out, and performance is evaluated.
One end of a power supply VCC in the active amplifying circuit is grounded, the other end of the power supply VCC is connected with one end of a resistor R1, and the other end of a resistor R1 is connected with a collector of a bipolar transistor, one end of a resistor R2 and one end of a capacitor C1. The emitter of the bipolar transistor is grounded, the base of the bipolar transistor is connected with the other end of the resistor R2 and one end of the capacitor C2, the other end of the capacitor C1 is connected with one end of the resistor R3 and the anode of the variable capacitance diode VD1, and the other end of the resistor R3 is grounded. The cathode of the variable capacitance diode VD1 is connected with one end of a suspension strip Line SSL1, the other end of the suspension strip Line SSL1 is connected with one end of a resistor R5 and the cathode of the variable capacitance diode VD3, the anode of the variable capacitance diode VD3 is connected with one end of a resistor R7 and the upper right end of a coupling transmission Line Coupled Line1, the other end of the resistor R7 is grounded, the other end of the capacitor C2 is connected with one end of the resistor R4 and the anode of the variable capacitance diode VD2, and the other end of the resistor R4 is grounded. The cathode of the variable capacitance diode VD2 is connected with one end of a suspension strip Line SSL2, the other end of the suspension strip Line SSL2 is connected with one end of a resistor R6 and the cathode of the variable capacitance diode VD4, the anode of the variable capacitance diode VD4 is connected with one end of a resistor R8 and the right lower end of a coupling transmission Line Coupled Line1, and the other end of the resistor R8 is grounded.
The left three ends of the coupling Line1 are respectively connected with the right three ends of the coupling Line2, the left middle end of the coupling Line1 is connected with one end of a resistor R9 between the right middle end of the coupling Line2, the other end of the resistor R9 is grounded, the left middle end of the coupling Line2 is connected with the anode of a varactor VD6, the cathode of the varactor VD6 is connected with one end of a suspension stripline SSL3, the other end of the suspension stripline SSL3 is connected with the cathode of the varactor VD5 and one end of the resistor R10, the anode of the varactor VD5 is grounded, one end of a power source Vtune is connected with the other end of the resistor R5, the other end of the resistor R6, the other end of the resistor R10, and the other end of the power source Vtune is grounded.
The voltage-controlled oscillator with low phase noise and wide band can be realized by the method and the circuit structure provided by the invention.
Claims (4)
1. A low phase noise wideband voltage controlled oscillator, comprising: the frequency selection feedback circuit comprises an active amplification circuit and a frequency selection feedback network; the frequency selection feedback network comprises a loop phase shift network and a filter; the loop phase shift network comprises two pairs of anti-series variable capacitance diodes which are connected back to back, and the middle of the anti-series variable capacitance diode pair is connected into a suspension stripline.
2. A low phase noise wideband voltage controlled oscillator as claimed in claim 1, characterized in that: the filter comprises a tuning voltage source, a coupling transmission line and a pair of anti-series variable capacitance diode pairs connected back to back, wherein the middle of the anti-series variable capacitance diode pair is connected with a suspension stripline.
3. A low phase noise wideband voltage controlled oscillator as claimed in claim 2, characterized in that: the coupling transmission line is of a suspended strip line structure, and the real object comprises a first metal upper cover (1), a first circuit board (2) and a first metal lower cover (3); the first metal upper cover and the first metal lower cover are buckled together to form a cavity, the first circuit board (2) is clamped in the middle, and a transmission line on the first circuit board (2), the first metal upper cover (1) and the first metal lower cover (3) form a suspension strip line structure.
4. A low phase noise wideband voltage controlled oscillator as claimed in claim 1, characterized in that: the active amplification circuit comprises a bipolar transistor and a direct current bias network, and two ends of the frequency selection network are respectively connected with a base electrode and a collector electrode of the bipolar transistor in the active amplification circuit.
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| CN202110382648.XA CN112953393B (en) | 2021-04-09 | 2021-04-09 | Broadband voltage-controlled oscillator with low phase noise |
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| CN202110382648.XA CN112953393B (en) | 2021-04-09 | 2021-04-09 | Broadband voltage-controlled oscillator with low phase noise |
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| CN112953393B CN112953393B (en) | 2023-09-29 |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115498962A (en) * | 2022-11-16 | 2022-12-20 | 成都世源频控技术股份有限公司 | Low-phase-noise crystal oscillator circuit and implementation method |
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| CN112953393B (en) | 2023-09-29 |
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