CN114301393A

CN114301393A - Low-phase-noise voltage-controlled oscillating circuit

Info

Publication number: CN114301393A
Application number: CN202111513992.4A
Authority: CN
Inventors: 鲁浩
Original assignee: Wuhan Gewei Electronic Technology Co Ltd
Current assignee: Wuhan Gewei Electronic Technology Co Ltd
Priority date: 2021-12-13
Filing date: 2021-12-13
Publication date: 2022-04-08

Abstract

The invention discloses a low-phase-noise voltage-controlled oscillation circuit, wherein a main circuit of the low-phase-noise voltage-controlled oscillation circuit comprises an oscillation triode, and a charge pump input port, a VCC power supply port and an RF output port are arranged on the main circuit; wherein: an oscillation circuit is arranged between the input port of the charge pump and the emitter electrode of the oscillation triode, the oscillation circuit is a frequency continuous variable oscillation circuit and comprises a variable capacitance diode; a power supply filter circuit is arranged between the VCC power supply port and the collector of the oscillation triode; the RF output port is an alternating current signal output port and is connected with a collector electrode of the oscillation triode, the signal output of the oscillation triode is divided into two paths, one path of the output signal provides a feedback signal to the PLL chip, and the other path of the output signal outputs a radio frequency signal with continuously variable frequency. The invention can adjust the working frequency of the oscillator, so that the oscillation frequency range of the oscillator meets the design requirement.

Description

Low-phase-noise voltage-controlled oscillating circuit

Technical Field

The invention relates to the field of oscillating circuits, in particular to a low-phase-noise voltage-controlled oscillating circuit.

Background

A voltage Controlled oscillator (vco), which generally forms a phase-Locked loop with a pll (phase Locked loop) chip and a loop filter. By controlling a charge pump cp (charge pump) of the PLL chip, a voltage change is generated at a pin to which the VCO is connected, thereby causing a change in the output frequency of the VCO.

The phase-locked loop is generally composed of a Phase Detector (PD), a Loop Filter (LF) and a Voltage Controlled Oscillator (VCO), the phase-locked loop is composed of a feedback circuit, the phase detector detects the phase difference between an input signal (Ui) and a feedback signal (Ud) and converts the phase difference into a direct current voltage signal (Ud) to be output, stray and noise of the signal are filtered by the LF, and the control voltage (Uc) of the VCO is output. The VCO is an important component of the phase-locked loop and is a voltage-controlled oscillator, and the output pulse frequency can be changed within a certain range along with the amplitude of the control voltage (Uc).

Because a closed loop tracking loop is formed, the phase-locked loop realizes the real-time automatic tracking of the frequency of the input signal by the frequency of the output signal, when the frequency of the input signal of the phase-locked loop is equal to the frequency of the output signal, the input voltage and the output voltage of the phase discriminator keep a fixed phase difference, namely the phase of the output voltage and the input voltage is locked, and the phase-locked function is formed.

In a transceiver of a communication system, a VCO usually forms a phase-locked local oscillator together with a PLL chip and a loop filter. In a receiving circuit of a transceiver of a frequency conversion scheme, a radio frequency signal received by an antenna is amplified through a Low Noise Amplifier (LNA), and is mixed with a local oscillator to mix a useful signal into an intermediate frequency; in a transmitting circuit of a transceiver of a frequency conversion scheme, an intermediate frequency signal output by a DAC is mixed with a local oscillator signal, and a useful signal is restored to a transmitting frequency from an intermediate frequency.

The VCO plays an important role in a communication system, and the radio frequency performance of the transceiver is indistinguishable from it.

However, the voltage-controlled oscillation circuit in the prior art has poor performance, cannot reasonably adjust the oscillation frequency, and cannot obtain higher oscillation frequency, higher output power, wider frequency tuning range and good phase noise in the full frequency band of the oscillation range.

Disclosure of Invention

The invention mainly aims to provide a voltage-controlled oscillating circuit with better output signal quality.

The technical scheme adopted by the invention is as follows:

the main circuit of the low-phase-noise voltage-controlled oscillation circuit comprises an oscillation triode, and a charge pump input port, a VCC power supply port and an RF output port are arranged on the main circuit; wherein:

an oscillation circuit is arranged between the input port of the charge pump and the emitter electrode of the oscillation triode, the oscillation circuit is a frequency continuous variable oscillation circuit and comprises a variable capacitance diode;

a power supply filter circuit is arranged between the VCC power supply port and the collector of the oscillation triode;

the RF output port is an alternating current signal output port and is connected with a collector electrode of the oscillation triode, the signal output of the oscillation triode is divided into two paths, one path of the output signal provides a feedback signal to the PLL chip, and the other path of the output signal outputs a radio frequency signal with continuously variable frequency.

In connection with the above technical solution, the emitter electrode of the oscillating triode is further connected with two ground loops including an emitter ac loop and an emitter dc loop.

According to the technical scheme, an inductor is arranged between the VCC power supply port and the collector of the oscillating triode.

According to the technical scheme, the collector electrode of the oscillation triode is grounded through an alternating current load capacitor.

According to the technical scheme, the shielding cover is arranged outside the low-phase-noise voltage-controlled oscillating circuit, and a distance of a preset distance is arranged between a circuit component in the low-phase-noise voltage-controlled oscillating circuit and the shielding cover.

According to the technical scheme, the circuit components in the low-phase-noise voltage-controlled oscillation circuit are arranged close to the corresponding polarities of the oscillation triodes connected with the circuit components, and the circuit components connected with different polarities are separately placed.

According to the technical scheme, all GND grounds in a top layer ground loop of the low-phase-noise voltage-controlled oscillation circuit are completely and continuously connected, and at least 10 ground holes are placed on each GND of the top layer to be connected with a bottom layer ground.

The invention has the following beneficial effects: the invention is provided with an independent oscillation circuit, the direct current voltage output by the pin of the charge pump is changed by controlling the PLL, so that the input current of the input port of the charge pump of the oscillation circuit is changed, the capacitance value is changed along with the input current by arranging the variable capacitance diode in the oscillation circuit, so that the frequency of the oscillation circuit is changed, an oscillator with continuously variable frequency is formed, the working frequency of the oscillator can be adjusted by adjusting the component value in the independent oscillator, and the oscillation frequency range of the oscillator meets the design requirement.

In addition, because the circuit for adjusting the oscillation frequency is relatively independent, the oscillation loop is not directly connected with the collector, and a part of the active device in the oscillation loop is less connected, so that a stable voltage feedback ratio is provided, and a good condition is provided for adjusting the oscillation frequency.

Furthermore, an alternating current load capacitor is arranged at the emitter of the triode, so that the oscillator forms a high-frequency common base electrode amplifying circuit. In the adjustment process of the oscillating circuit, the direct current loop and the alternating current loop of the emitter of the oscillating triode are relatively independent, so that the change of the oscillating frequency and the stop of the oscillator are not easy to cause when the working point of the oscillating tube is adjusted.

Furthermore, at the output end of the oscillator, a triode collector load capacitor is used as an oscillator output load to provide effective load traction for the output signal of the oscillator. On the direct current upper loop, the VCC provides direct current supply voltage to the triode collector, and because the inductor and the filter capacitor are arranged in the loop, the alternating current component is effectively filtered, and the parasitic parameters on the collector are reduced to the maximum extent. And the load capacitor is directly grounded, does not participate in the adjustment of the working frequency of the oscillator, and only adjusts the working state of the oscillator to be matched with the load of the output signal.

Furthermore, the GND of the same layer is complete and continuous, so that the partial GND is prevented from being cut into small areas, and at least 10 ground holes can be placed on each GND of the top layer to be connected with the ground of the bottom layer; avoiding GND from forming a line shape so as to form a lead inductor; the smaller the area of GND, the denser the arrangement of ground holes, and the number of ground holes to be arranged should be as large as possible, so as to reduce parasitic parameters to the greatest extent.

Drawings

The invention will be further described with reference to the accompanying drawings and examples, in which:

FIG. 1 is a low phase noise voltage controlled oscillator circuit model according to an embodiment of the present invention;

FIG. 2 is an AC equivalent circuit diagram of FIG. 1;

fig. 3 is a diagram of a low phase noise voltage controlled oscillator circuit according to an embodiment of the invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Fig. 1 shows a 1.7GHz VCO voltage-controlled oscillator circuit model of the present invention, and fig. 2 shows an ac equivalent circuit of the 1.7GHz VCO model, and the structure of the ac equivalent circuit is based on the evolution of a circler oscillator.

Table 1 below illustrates the electrical performance parameters of a 1.7GHz VCO oscillator implemented using the present invention.

TABLE 1- -1.7GHz VCO Electrical Performance

As shown in fig. 1, the model designs an independent oscillation circuit, and the C6, C2, C3 and L4 devices determine the frequency of the oscillation circuit, wherein C6 is a varactor diode. The PLL is controlled to change the direct current voltage output by the charge pump pin, and after filtering of the loop filter, the capacitance value of the C6 varactor is changed along with the change of the capacitance value, so that the frequency of the oscillation loop is changed, and the oscillator with continuously variable frequency is formed. The working frequency of the oscillator is adjusted by adjusting the device values of C2, C3 and L4, so that the oscillation frequency range of the oscillator meets the design requirement.

In the VCO oscillation circuit realized by applying the technology, a circuit for adjusting oscillation frequency is relatively independent, and an oscillation loop is not directly connected with a collector. The active device in the oscillation loop is connected to a small part, so that a stable voltage feedback ratio is obtained, and a good condition is provided for adjusting the oscillation frequency.

The voltage-controlled oscillator circuit model also designs a flexible oscillation tube working point adjusting mode, R1, R2 and R3 are direct current bias resistors of the oscillation triode, and the working point of the triode Q1 is in an amplifying region and in the optimal state in the target oscillation frequency by adjusting the resistance value of the resistors. C5 is the bypass capacitor of the transistor, which can be regarded as the ac load capacitor of the emitter of the transistor, making the oscillator form a high frequency common base amplifier circuit.

By applying the technology, the direct current loop and the alternating current loop are relatively independent in the adjustment process of the oscillating circuit, and the change of the oscillating frequency and the stop of the oscillator are not easily caused when the working point of the oscillating tube is adjusted.

The voltage-controlled oscillator circuit model also has stable oscillation frequency signal output. At the oscillator output, the triode collector load capacitor C1 acts as the oscillator output load, providing efficient load pulling for the oscillator output signal. On the direct current upper loop, the VCC provides direct current supply voltage to the triode collector, and because the inductor and the filter capacitor are arranged in the loop, the alternating current component is effectively filtered, and the parasitic parameters on the collector are reduced to the maximum extent. And the load capacitor is directly grounded, does not participate in the adjustment of the working frequency of the oscillator, and only adjusts the working state of the oscillator to be matched with the load of the output signal.

Therefore, the alternating current output part of the VCO oscillator realized by the technology does not directly participate in the adjustment of the oscillation frequency, and is relatively isolated from the direct current power supply, so that the output oscillation frequency signal has good index and stability in the whole frequency range.

As shown in fig. 3, in the low-phase-noise voltage-controlled oscillation circuit according to the embodiment of the present invention, a main circuit includes an oscillation triode, and the main circuit is provided with a charge pump input port, a VCC power port, and an RF output port; wherein: an oscillation circuit is arranged between the input port of the charge pump and the emitter electrode of the oscillation triode, the oscillation circuit is a frequency continuous variable oscillation circuit and comprises a variable capacitance diode; a power supply filter circuit is arranged between the VCC power supply port and the collector of the oscillation triode; the RF output port is an alternating current signal output port and is connected with a collector electrode of the oscillation triode, the signal output of the oscillation triode is divided into two paths, one path of the output signal provides a feedback signal to the PLL chip, and the other path of the output signal outputs a radio frequency signal with continuously variable frequency.

The emitter electrode of the oscillating triode is also connected with two ground loops, including an emitter alternating current loop and an emitter direct current loop.

An inductor is arranged between the VCC power supply port and the collector of the oscillating triode.

Further, the collector of the oscillating triode is grounded through an alternating current load capacitor.

A shielding case is arranged outside the low-phase-noise voltage-controlled oscillating circuit, and a distance of a preset distance is arranged between a circuit component in the low-phase-noise voltage-controlled oscillating circuit and the shielding case.

The circuit components in the low-phase-noise voltage-controlled oscillation circuit are arranged close to the corresponding polarities of the oscillation triodes connected with the circuit components, and the circuit components connected with different polarities are separately arranged.

All GND grounds in a top layer ground loop of the low-phase-noise voltage-controlled oscillation circuit are connected completely and continuously, and at least 10 ground holes are placed on each GND of the top layer to be connected with a bottom layer ground.

Specifically, as shown in fig. 3, in the application in the phase-locked loop type local oscillation:

and the port Charge Pump, the Charge Pump pin and the Charge Pump pin of the PLL chip output a voltage control signal to a Charge Pump port of the VCO through a loop filter. By designing the loop filter, noise and spurious in the loop are suppressed, and a relatively pure direct-current voltage signal is provided for a Charge Pump port of the VCO, so that a signal at an output end of the VCO has lower phase noise.

The port VCC provides DC supply voltage for the oscillation triode, and its voltage amplitude should satisfy the power supply requirement of triode, if want to make VCO have better performance, the DC supply that the VCC provided needs very stable, increases power filter circuit, stray, noise and ripple on the filtering circuit. In the VCO design circuit, decoupling and filter capacitors are also required to be placed, so that the oscillation triode is in a stable working state.

The port RF out, the alternating current signal output port of the oscillating circuit, its signal output divides into two routes, one route provides the feedback signal to PLL chip, another route outputs the frequency continuously variable radio frequency signal.

As can be seen from fig. 2, C4 connects the emitter and the base of the oscillating transistor, forming the feedback cut-in point of the oscillator. The device values of C6 (varactor), C2, C3, and L4 together determine the oscillation frequency of the oscillation circuit.

Thus, the oscillation frequency

Determined by C3, C2, C6, L4:

c6 is a varactor, and in the oscillation circuit, its main parameters are capacitance dynamic range and Q value, where the capacitance dynamic range determines the frequency tunable range of the oscillator, the Q value affects the phase noise of the output signal of the oscillator, and these two parameters need to be measured when the type of the varactor is selected.

As shown in fig. 3, the emitter of the oscillator tube Q1 forms two loops to ground, and C5 forms an ac loop of the emitter, so that the emitter of the oscillator tube obtains ac ground potential; l3 and R3 form a direct current loop of the emitter of the oscillation tube, and determine the working point of the oscillation triode together with R1, R2 and L2.

The L1 is a DC power supply inductor of the collector of the oscillating triode, and by utilizing the characteristics of the direct current and the alternating current of the inductor, the AC component of the collector of the oscillating triode can not reversely flow back to a power supply end, thereby reducing the parasitic parameters introduced by the power supply end. C1 is the AC load capacitance of the collector of the oscillator tube, provides impedance adaptation for the AC output of the collector of the oscillator tube, and also provides capacitive load pulling for the oscillator, so that the oscillator parameters have good consistency in the whole tuning range.

The low-phase-noise voltage-controlled oscillating circuit adopts a unique PCB design, and is purposefully designed on the PCB layout aiming at the difficulty of realizing the high-frequency VCO:

a. and (3) narrowing the device pitch:

in order to obtain a higher oscillation frequency, when designing a PCB of the VCO, parasitic parameters in the oscillation circuit need to be reduced as much as possible, which makes the oscillation frequency of the high-frequency VCO more stable and the quality of the output signal better. In an oscillating circuit, parasitic parameters are usually caused by unreasonable layout and too long microstrip routing between devices. Many VCO design schemes usually only focus on the performance and parameters of devices, neglect the influence caused by connection and matching between devices, and do not consider that unnecessary parasitic parameters are introduced due to too large space between some key devices. As the frequency requirements of the VCO increase, the parasitic parameters introduced thereby become more significant, which directly affect the performance of the VCO.

The PCB design difference from other VCO schemes is that when the high-frequency VCO of the technology is applied to PCB design, the placement of key devices needs to be compact as much as possible, and the distance between the devices is reduced as much as possible, so that radio frequency microstrip routing on the PCB is reduced to the maximum extent, and parasitic parameters in a high-frequency oscillation circuit are reduced.

b. Complete peer-to-peer loop:

in the VCO oscillating circuit, the PCB design and routing of the oscillating circuit portion is performed according to the rules of radio frequency routing. In the ac loop of the oscillating circuit, all the devices participating in the frequency oscillation form a loop with the GND (ground) of the PCB.

In many VCO designs, the influence of ground loops is often ignored in PCB design, and for layout reasons, a section of lead is used as a ground connection of a device, or when the ground cannot be directly connected to a top layer, a via is used to connect to a bottom layer. Due to the unreasonable loop design, a large number of parasitic parameters are introduced into the VCO oscillation loop, which directly causes the overall performance of the VCO to be greatly reduced.

The difference with the design of other VCO schemes PCB is that when the high frequency VCO applying the present technology performs PCB design, the ground loop requirement for the top layer is as follows: all GND must be complete and continuous, so as to avoid cutting partial GND into small areas, and at least 10 ground holes can be placed on each GND of the top layer to be connected with the ground of the bottom layer; avoiding GND from forming a line shape so as to form a lead inductor; the smaller the area of GND, the denser the arrangement of ground holes, and the number of ground holes to be arranged should be as large as possible, so as to reduce parasitic parameters to the greatest extent.

c. Reasonable device placement:

when the layout of the VCO oscillation circuit PCB is carried out, reasonable planning is carried out according to the principle and the characteristics of the circuit.

In many VCO designs, the designer does not consider the rational placement of the devices in the VCO tank when designing the PCB of the VCO to be miniaturized. For example, the matching device which should belong to a certain polarity of the triode is placed near the other polarities; the charge Pump circuit is close to the oscillating tube power supply circuit, and the like, and the unreasonable arrangement of the devices can directly influence the quality of the output signal of the VCO oscillating circuit and directly worsen the phase noise of the VCO output signal.

As can be seen from fig. 3, the devices of the entire VCO oscillating circuit can be laid out around the oscillating transistor. The PCB design difference from other VCO schemes is that when the high-frequency VCO adopting the technology is used for PCB design, all devices should be placed as close as possible to the base electrode, the emitter electrode and the collector electrode of the oscillation triode connected with the high-frequency VCO and as far as possible away from other polarities which are not connected with the high-frequency VCO, so that the interference formed in an oscillation loop can be reduced to the greatest extent, and the oscillation frequency is more stable. The VCO oscillating circuit often becomes an independent module for use in the whole system, and a shielding case needs to be manufactured to shield the whole module spatially, and it should be noted that devices in the whole VCO oscillating circuit need to be as far away from 4 vertical edges formed by the shielding case and the PCB as possible, so as to avoid that excessive radiation of alternating current signals generated by the oscillating circuit on the shielding case affects the quality of output signals of the oscillating circuit.

The 1.7GHz VCO oscillator realized by the innovative design of the technology can obtain higher oscillation frequency, higher output power, wider frequency tuning range and good phase noise in the full frequency band of the oscillation range. In an oscillation loop applied by the technology, when the oscillation frequency, the working point of the oscillation tube and the oscillation frequency output signal load are adjusted, the mutual influence is not obvious, so that the VCO technology can more conveniently carry out debugging work such as frequency shift, phase noise optimization and the like in practical application, and the debugging period of the VCO oscillator is effectively shortened. Due to the unique PCB design, the VCO oscillating circuit can achieve higher frequency, and the output signal quality is better. In the VCO oscillator, fewer devices are used, high-frequency, high-power and high-performance oscillation frequency signal output is obtained, and the occupied area of a PCB in practical application is reduced, so that the VCO oscillator is more suitable for portable and miniaturized communication equipment.

In a radio frequency transceiving base station, the voltage-controlled oscillator is applied to a receiving circuit, so that the noise coefficient of a link can be effectively reduced, the anti-interference capability of the receiving circuit is improved, and the overall performance of the receiving circuit is improved; when the voltage-controlled oscillator is applied to a transmitting circuit, indexes such as a noise coefficient of a transmitting signal, an EVM (error Vector magnetic), discrete parasitics and the like are obviously improved.

It will be understood that modifications and variations can be made by persons skilled in the art in light of the above teachings and all such modifications and variations are intended to be included within the scope of the invention as defined in the appended claims.

Claims

1. A low-phase-noise voltage-controlled oscillation circuit is characterized in that a main circuit of the low-phase-noise voltage-controlled oscillation circuit comprises an oscillation triode, and a charge pump input port, a VCC power supply port and an RF output port are arranged on the main circuit; wherein:

2. The low phase noise voltage controlled oscillator circuit of claim 1, wherein the emitter of the oscillator transistor is further connected to two ground loops, including an emitter ac loop and an emitter dc loop.

3. The low phase noise voltage controlled oscillator circuit of claim 1, wherein an inductor is disposed between the VCC power port and the collector of the oscillator transistor.

4. The low phase noise voltage controlled oscillator circuit of claim 1, wherein the collector of the oscillating transistor is connected to ground through an ac load capacitor.

5. The low-phase-noise voltage-controlled oscillator circuit as claimed in claim 1, wherein a shielding case is disposed outside the low-phase-noise voltage-controlled oscillator circuit, and a distance of a predetermined distance is provided between circuit components of the low-phase-noise voltage-controlled oscillator circuit and the shielding case.

6. The low-phase-noise voltage-controlled oscillation circuit according to any one of claims 1 to 5, wherein circuit components in the low-phase-noise voltage-controlled oscillation circuit are arranged close to the polarities corresponding to the oscillation triodes connected thereto, and circuit components connected to different polarities are separately disposed.

7. The low phase noise voltage controlled oscillator circuit as claimed in any one of claims 1 to 5, wherein all GND ground in the top layer ground loop of the low phase noise voltage controlled oscillator circuit are connected completely and continuously, and at least 10 ground holes are placed on each GND of the top layer to be connected with the bottom layer ground.