KR20090096783A - Voltage controlled oscillator improved in phase noise and frequency - voltage tuning linearity - Google Patents

Abstract

A voltage control oscillator is provided to reduce a parasitic component of a resonant unit, thereby obtaining a more improved phase noise characteristic within a frequency tuning range. A voltage control oscillator is comprised of a voltage control oscillator power supply unit, a resonant unit and an oscillating unit. The resonant part is connected to an oscillating unit in parallel. The resonant unit outputs only a signal of a specific frequency. The oscillating unit amplifies internal noise or a small signal largely by using only DC power to generate a signal. Symmetric parallel resistances(304a,304b) are parallel connected to MOS varactors(306a,306b) and an inductor(307) respectively. A radio frequency blocking resistance(308) is serially connected to a control voltage source. The symmetric parallel resistance is made of at least a pair of parallel resistances having the same resistance size. An electric potential difference is formed between the first contact point(305a) or the second contact point(305b) and a Vctrl terminal which is a tuning voltage source.

Description

 Voltage controlled oscillator improved in phase noise and frequency-voltage tuning linearity}

The present invention relates to a voltage controlled oscillator that can be used in the signal generator of broadcasting, communication, and measurement equipment, and more particularly, to a voltage controlled oscillator bringing the linearity and stability of the oscillation frequency and extending the tuning voltage range. will be.

Recently, due to the explosive growth of the mobile communication market, many companies are forming their markets by releasing various mobile communication terminals using different frequency bands or having different functions. However, the future prospects, both at home and abroad, are expected to not only operate in various frequency bands, but also to form a mobile communication terminal market in which various functions are integrated.

In addition, miniaturization must be accompanied for this purpose, and mobile communication terminals are also miniaturizing components used in many parts for miniaturization, and in the case of RF (Radio Frequency) systems, miniaturization is being performed at various parts.

In the present invention, a part of the present invention relates to an RF system, and more particularly, to a voltage controlled oscillator. The voltage controlled oscillator may be widely used in the broadcasting and communication fields as well as the signal generator of the measurement equipment. In general, a voltage controlled oscillator does not have an input and is a device that generates and outputs a signal of a specific frequency internally.

Figure 2a is a block diagram of the internal structure of the resonator of the conventional voltage controlled oscillator.

에서 커패시턴스 C가 변하므로 공진 주파수가 변한다. 공진부는 발진부에 대해 병렬회로이므로 공진주파수에서 임피던스가 가장 크고 이외의 주파수에서의 임피던스는 작다. 발진부로부터 이득을 얻어 출력된 신호는 공진부에 의해 특정 주파수 신호만 큰 임피던스에 의해 반사되어 다시 입력으로 들어가고, 이런 포지티브 피드백 궤환을 통해 특정 주파수원만이 출력된다. RF 차단저항(203)은 외부로부터 튜닝전압(Tuning voltage) 인가시 DC 선로를 통해 전압제어발진기 핵심부로 유입될 수 있는 고주파 신호의 주입, 또는 전압제어발진기 핵심부로부터 튜닝전압소스로 유출될 수 있는 고주파 신호를 막기 위한 저항으로써, DC전압에는 영향을 주지 않으며 고주파(RF) 신호의 감쇄 효과가 있다.Referring to FIG. 2A, the resonator of the voltage controlled oscillator includes an inductor 201 and variable capacitors 202a and 202b. Since the gate-bulk depletion capacitance of the MOS varactor, which is a variable capacitor, is increased or decreased by an externally applied tuning voltage

Because the capacitance C changes at, the resonant frequency changes. Since the resonator part is a parallel circuit with respect to the oscillator part, the impedance is the largest at the resonance frequency and the impedance at the other frequency is small. The signal output by gaining the gain from the oscillator is reflected by the resonator with only a certain frequency signal by a large impedance and is input back to the input, and through this positive feedback feedback, only a specific frequency source is output. RF cut-off resistor 203 is the injection of a high frequency signal that can flow into the core of the voltage controlled oscillator through the DC line when a tuning voltage is applied from the outside, or the high frequency that can flow out of the tuning voltage source from the core of the voltage controlled oscillator As a resistor for blocking a signal, it does not affect the DC voltage and has an attenuation effect of a high frequency (RF) signal.

Basically, the resonator uses a spiral inductor and a MOS varactor during a CMOS process, and the resonant frequency is determined by these two devices. At this time, the resonance frequency is changed by changing the depletion capacitance of the gate-bulk of the MOS varactor by the tuning voltage.

The general MOS varactor used in the resonator of the voltage controlled oscillator usually shows a sudden change in capacitance even at a small tuning voltage, and has a very narrow tuning voltage range in which the frequency change characteristic is linear. In view of the characteristics of the voltage controlled oscillator, that is, the purpose of adjusting the oscillation frequency according to the tuning voltage, it is very sensitive and requires delicate tuning voltage adjustment and has unstable characteristics. The voltage controlled oscillator linearly changes the oscillation frequency according to the tuning voltage and requires a wide frequency tuning range. In addition, the resonator of the voltage controlled oscillator has a large influence on the parasitic component, so the performance index is very small and the phase noise characteristics should be considered. Therefore, the design of the resonator having a high figure of merit for further improved phase noise characteristics is required.

An object of the present invention is to solve the above problems, and to improve the linearity of the oscillation frequency with respect to the tuning voltage by changing the capacitance of the variable capacitor linearly even in a large tuning voltage range, the performance index of the resonator It is to provide a voltage controlled oscillator with improved phase noise characteristics by increasing the.

The voltage controlled oscillator according to the present invention for achieving the above object, a power supply for supplying the overall power to the voltage controlled oscillator, a resonator for determining to output only a signal of a specific frequency, and greatly amplifies the internal noise or the signal An oscillator for generating a signal, wherein the resonator includes an inductor, at least one pair of variable capacitors, and at least one pair of symmetric parallel resistors of the same size, the symmetric parallel resistors connected in parallel to the variable capacitor and the inductor, respectively It is characterized by.

The oscillator may use a single transistor or have a differential structure in which each transistor is cross-connected in a symmetrical structure.

A control voltage for controlling the frequency of the oscillation signal is applied from the tuning voltage source to the resonator, and the variable capacitor is a varactor or preferably a MOS varactor.

The symmetrical parallel resistance is characterized by having a size of several tens of kΩ.

As described above, the voltage controlled oscillator according to the present invention enables economical linearization of tuning characteristics of frequencies within a wider tuning voltage control range. In addition, more precise and stable control is possible by mitigating abrupt frequency change characteristics, and by reducing parasitic components of the resonator unit, the phase noise characteristic is improved within the frequency tuning range, and the abrupt change in capacitance according to the tuning voltage is achieved. It can be widely used in voltage controlled oscillator and its application structure to be relaxed.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following examples are provided to aid the understanding of the present invention and the present invention is not limited to the following examples.

1 is a block diagram illustrating a voltage controlled oscillator according to an embodiment of the present invention.

Referring to FIG. 1, a voltage controlled oscillator including a power supply 101, a resonator 102, and an oscillator 103 is configured, and the power supply 101 supplies power to the entire voltage controlled oscillator, and includes a resonator ( 102 determines to output only a signal of a specific frequency, and the oscillator 103 plays a role of generating a signal by amplifying a large noise or a small signal with only a DC power supply. Here, the oscillation frequency of the voltage controlled oscillator is changed by applying a control voltage to the resonator 102 from an external terminal.

Figure 2a is a block diagram of the internal structure of the resonator of the conventional voltage controlled oscillator, Figure 2b is a block diagram of the internal structure of the resonator using a symmetrical parallel resistance according to the present invention.

Referring to FIG. 2A, the resonator of the voltage controlled oscillator includes an inductor 201 and respective variable capacitors 202a and 202b. Here, the RF blocking resistor 203 is connected as above.

FIG. 2B is a configuration in which the resonator symmetric parallel resistors 204a and 204b according to the present invention are added to the configuration of FIG. 2A. The resonator symmetric parallel resistors 204a and 204b are connected in parallel with the variable capacitors 202a and 202b and the inductor, respectively. In addition, the resonator symmetric parallel resistors 204a and 204b are connected to the RF blocking resistor 203 as shown in the figure.

3A is a circuit diagram illustrating a conventional voltage controlled oscillator, and FIG. 3B is a circuit diagram illustrating a voltage controlled oscillator using a symmetrical parallel resistance according to an embodiment of the present invention.

Referring to the circuit diagram of Figure 3a, the circuit diagram of the oscillator is a voltage-controlled oscillator of a differential structure, the conventionally known voltage-controlled oscillator is composed of a voltage-controlled oscillator power supply 301, a resonator 302 and an oscillator 303, The resonator unit is connected to a parallel circuit with respect to the oscillator unit, the resonator unit 102 determines to output only a signal of a specific frequency, and the oscillator unit 103 amplifies the internal noise or a small signal with only a DC power source to generate a signal. In this embodiment, the oscillator 303 is a structure in which M3 and M4, which are RF_NMOS of the same size, are differentially connected in a symmetrical structure to induce positive feedback oscillation, so that a differential signal having a phase difference of 180 degrees is output. do. Here, M3 and M4 may be implemented with all kinds of transistors capable of implementing an oscillator.

3B is a circuit diagram in which symmetric parallel resistors 304a and 304b according to the present invention are added to FIG. 3A. Each of the symmetric parallel resistors 304a and 304b is connected in parallel with the MOS varactors 306a and 306b and the inductor 307 which are variable capacitors, respectively. In addition, the RF blocking resistor 308 is connected as shown in the figure, the RF blocking resistor 308 is connected in series with the control voltage source Vctrl.

The symmetrical parallel resistors 304a and 304b have at least a pair of parallel resistors having the same size of several tens of kΩ or more, and preferably a large resistance of 10 kΩ to 80 kΩ may be used. In this embodiment, the simulation was performed using a 20 kΩ resistor, respectively, and the RF frequency (Radio Frequency) acts as an open circuit, there is almost no high frequency loss.

에 의해 전압제어발진기 중심부의 DC전류(수백 mA)에 영향을 주지 않는 미세한 전류(수십 uA)가 흐른다. RF차단저항(308)에 흐르는 전류를 I₃₀₈라고 할 경우, 아래와 같다.In this embodiment, a 40 kΩ resistor is used as the RF blocking resistor 308, and a large resistor of several tens of kΩ or more may be used. Here, the symmetric parallel resistors 304a and 304b may be connected to a pair of resistors having the same size or more. At this time, a potential difference exists between the contact 305a or the contact 305b and the V _ctrl terminal, which is a tuning voltage source, and a current flows. The DC voltages of the contact 305a and the contact 305b are the same as the differential structure. If the tuning voltage is 0 to 3.3 V and a large resistance of several tens of kΩ or more is used as the RF blocking resistor 308,

This results in a fine current (tens of uA) that does not affect the DC current (hundreds of mA) at the center of the voltage-controlled oscillator. When the current flowing through the RF blocking resistor _{308 is} referred to as I ₃₀₈ , it is as follows.

Therefore, the voltage drop V ₃₀₈ at the RF blocking resistor ₃₀₈ is I ₃₀₈ × R ₃ .

In view of the above, the larger the voltage difference between the contacts 305a or 305b and the tuning voltage source V _ctrl , V ₃₀₈ degrees. Increases. That is, not all of the tuning voltages are applied to the source and drain of the MOS varactors 306a and 306b, but voltages other than the voltage drop are applied. Even if the tuning voltage is 0 V, the contacts 305a and 305b and the tuning voltage source V _ctrl Since a current flows due to the voltage difference between them, a voltage greater than 0 V is applied to the MOS varactors 306a and 306b. The tuning voltage applied to the MOS varactors 306a and 306b by the influence of the parallel resistors 304a and 304b is a voltage of a linear operating range of the MOS varactors 306a and 306b, that is, a tuning voltage to be actually applied externally. The range corresponds to a small range between 0V and 3.3V. V _ctrl by the parallel resistors 304a and 304b. Even if a wide range of control voltage is applied, the voltage of the actual linear operating range is applied to the MOS varactor. Thus, even if the tuning voltage range is large, fine and linear frequency tuning is possible.

Due to the distribution of the tuning voltage, the actual tuning voltage is applied to a voltage within the linear operating range of the MOS varactors 306a and 306b, thereby greatly changing the frequency tuning range secured according to the tuning voltage. This reduces the rate of change of the frequency with respect to voltage and has a linear frequency change characteristic over the entire tuning voltage range, thereby leading to a more stable and linear function of the frequency tuning characteristics of the voltage controlled oscillator under voltage control. to provide. In addition, the present invention is applicable not only to MOS varactors but also to voltage controlled oscillators including variable capacitors that must mitigate abrupt changes in capacitance in accordance with tuning voltages, and their application structures.

FIG. 4 is a graph showing oscillation frequency characteristics according to the tuning voltage V _ctrl in the circuit diagram of FIG. 3A.

Referring to FIG. 4, 1.8 V is fixedly applied to the voltage power supply VDD of FIG. 3A, and the DC tuning voltage is V _ctrl. Through the terminal Change from 0 V to 3.3 V. As a result, the frequency tuning range of the tuning voltage is very narrow and the frequency change characteristic is saturated over the range. Therefore, the range of practically available tuning voltage is very narrow, and it can be seen that the change of frequency is made very rapidly.

FIG. 5 is a graph showing oscillation frequency characteristics according to tuning voltages in the circuit diagram of FIG. 3B implementing the symmetric parallel resistors 304a and 304b.

Referring to FIG. 5, as in FIG. 4, oscillation frequency characteristics when 1.8 V is fixedly applied to the voltage power supply VDD of FIG. 3B and the DC tuning voltage is changed from 0 V to 3.3 are shown. Unlike FIG. 4, the linear oscillation frequency tuning characteristic is shown in the overall tuning voltage range, and has a gentle oscillation frequency adjusting characteristic while using a wide range of tuning voltages. Only linear control sections of the MOS varactors 306a and 306b are used in the tuning voltage range. This is the result of using the feature that the symmetric parallel resistors 304a and 304b scale the tuning voltage to have a linear and gentle oscillation frequency control characteristic within the adjustment range.

As a result, the voltage controlled oscillator of the circuit diagram of FIG. 3B according to the present invention exhibits linear characteristics over a wider tuning voltage range.

6 is a graph illustrating phase noise according to a tuning voltage in the circuit diagram of FIG. 3A.

Here, Pnmx (phase noise due to noise mixing) represents the maximum phase noise that can be generated in the voltage controlled oscillator.

Referring to Figure 6, the control voltage V _ctrl The maximum phase noise at the output terminal OUT_1 according to the offset frequency when applied from 0 to 3.3 V through the terminal. When the offset frequency was fixed at 100 kHz, the smallest phase noise appeared when 0 V was applied, and the worst phase noise appeared when 0.9 V was applied, and the width was wide. . This is a result of the parasitic component changes according to the performance index and the changed frequency of the resonator 302.

FIG. 7 is a graph illustrating phase noise according to a tuning voltage in the circuit diagram of FIG. 3B using the present invention.

Referring to FIG. 7, when the control voltage is applied to 0 to 3.3 V as in FIG. 6, the maximum phase noise at the output terminal OUT_1 according to the offset frequency is shown. When the offset frequency was fixed at 100 kHz, the smallest phase noise appeared when 0.9 V was applied, and the largest phase noise appeared when 3.3 V was applied, and the width thereof was very narrow. have. As a result, the phase change characteristics are narrower than those of FIG. 6 and the overall value is relatively low, thereby further improving phase noise characteristics. The symmetric parallel resistors 304a and 304b are connected in parallel to the inductor 307 to make the influence of the parallel parasitic resistance component of the inductor 307 even smaller. This leads to an improvement of the resonator performance index and shows more improved phase noise characteristics as shown in FIG. 7.

8 is a graph illustrating power characteristics of an oscillation frequency and an output signal according to a tuning voltage in the circuit diagram of FIG. 3A.

Referring to FIG. 8, the control voltage is V _ctrl When applied from 0 to 3.3 V through the terminal, the frequency change characteristic was saturated and no longer changed outside the tuning voltage range indicating partial linearity of the whole, and the output signal changed from -3.764 dBm to 0.077 dBm. do.

9 is a graph showing the power characteristics of the oscillation frequency and the output signal according to the tuning voltage in the circuit diagram of FIG. 3b using the present invention.

Referring to FIG. 9, a linear frequency tuning characteristic is shown in a wide tuning range of tuning voltage 0 V to 3.3 V, and a power characteristic ranging from -2.726 dBm to -0.641 dBm is shown. Does not allow much.

From the above results, by using the newly configured resonator according to the present invention, it is possible to linearize the tuning characteristic of the frequency within a wider tuning voltage control range, abruptly change the frequency change characteristic, and reduce the parasitic components of the resonator frequency tuning. It can be seen that the phase noise characteristics are further improved within the range.

The present invention is not limited to the embodiments described above, and various modifications and changes can be made by those skilled in the art, which are included in the spirit and scope of the present invention as defined in the appended claims.

1 is a block diagram illustrating a voltage controlled oscillator according to an embodiment of the present invention.

Figure 2a is a block diagram of the internal structure of the resonator of the conventional voltage controlled oscillator.

Figure 2b is a block diagram of the internal structure of the resonator according to the present invention.

3A is a circuit diagram illustrating a conventional voltage controlled oscillator, and FIG. 3B is a circuit diagram illustrating a voltage controlled oscillator using a symmetrical parallel resistance according to an embodiment of the present invention.

FIG. 4 is a graph showing oscillation frequency characteristics according to tuning voltages in the circuit diagram of FIG. 3A.

FIG. 5 is a graph showing oscillation frequency characteristics according to tuning voltages in the circuit diagram of FIG. 3B.

6 is a graph illustrating phase noise according to a tuning voltage in the circuit diagram of FIG. 3A.

FIG. 7 is a graph illustrating phase noise according to a tuning voltage in the circuit diagram of FIG. 3B.

8 is a graph illustrating power characteristics of an oscillation frequency and an output signal according to a tuning voltage in the circuit diagram of FIG. 3A.

FIG. 9 is a graph illustrating power characteristics of an oscillation frequency and an output signal according to a tuning voltage in the circuit diagram of FIG. 3B.

<Explanation of symbols for the main parts of the drawings>

101: power supply

102: resonator

103: oscillation unit

201, 307: Inductor

202a, 202b: variable capacitor

203, 308: RF cutoff resistor

204a, 204b, 304a, 304b: symmetrical parallel resistance of resonance part

205a, 205b, 305a, 305b: node

301: voltage controlled oscillator power supply

302: voltage controlled oscillator resonator

303: NMOS transistor of the oscillation part

306a, 306b: MOS varactor

Claims (7)

A power supply unit for supplying overall power to the voltage controlled oscillator, A resonator for determining to output only a signal of a specific frequency, and It includes an oscillator for generating a signal by greatly amplifying the internal noise or the signal, And the resonator comprises an inductor, at least one pair of variable capacitors, and at least one pair of symmetric parallel resistors of the same size, wherein the symmetric parallel resistors are connected in parallel to the variable capacitor and the inductor, respectively. The voltage controlled oscillator of claim 1, wherein the oscillator uses a single transistor. The oscillator of claim 1, wherein the oscillator has a differential structure in which each transistor is cross-connected in a symmetrical structure. 4. The voltage controlled oscillator according to any one of claims 1 to 3, wherein a control voltage for controlling the frequency of the oscillation signal is applied to the resonator unit from a tuning voltage source. 4. The voltage controlled oscillator according to any one of claims 1 to 3, wherein the variable capacitor is a varactor. 6. The voltage controlled oscillator of claim 5, wherein the varactor is a MOS varactor. 4. The voltage controlled oscillator according to any one of claims 1 to 3, wherein the symmetric parallel resistor has a size of several tens of kΩ.

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