JP2001352218A - Voltage-controlled oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To widen the linear range of conversion characteristics of a resonance type voltage-controlled oscillator by a CMOS process. SOLUTION: This oscillator has a resonance circuit 201, a negative resistance circuit 202, and varactor elements 2031 to 2034 and a control voltage is shifted by a specific value at each time through a level shift circuit 206 and applied to the varactor elements to expand the linear range of the oscillation frequency to the control voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage controlled oscillator used for a transceiver for wireless communication and the like.
In particular, the present invention relates to a technique for connecting two or more variable capacitance elements in parallel to perform deviation correction of output frequency, modulation of oscillation frequency, improvement of linearity of conversion characteristic, switching of frequency range, and the like.

[0002]

2. Description of the Related Art A frequency synthesizer for generating a carrier wave is used in a transceiver for wireless communication. At present, local oscillators of many wireless terminals use PLLs for frequency synthesizers.
(Phase-locked loop).

As shown in FIG. 13, this PLL synthesizer comprises a hood-back loop including a phase comparator 101, a loop filter 102, a voltage controlled oscillator (VCO) 103, and a variable frequency divider 104. The control voltage of the voltage controlled oscillator 103 is controlled so that the frequency and phase of the reference signal input to the terminal 105 and the output signal of the variable frequency divider 104 match. 106 is an output terminal. Here, by switching the frequency division number of the variable frequency divider 104, the oscillation frequency of the voltage controlled oscillator 103 can be switched. The transient response characteristics and noise band characteristics of the PLL synthesizer include the gain of the phase comparator 101, the transfer characteristic of the loop filter 102, the conversion gain of the voltage controlled oscillator 103,
It is determined by the frequency division number of the variable frequency divider 104.

A voltage controlled oscillator 103 used in such a PLL synthesizer generally uses a combination of a resonance circuit 201 and a negative resistance generation circuit 202 as shown in FIG. In the case of the voltage controlled oscillator using the resonance circuit 201 and the negative resistance, the oscillation frequency is
Therefore, the oscillation frequency is controlled by changing the resonance frequency by connecting a variable capacitance element (varactor diode) to the resonance circuit 201 and changing the capacitance. 204 is a frequency control terminal, and 205 is an oscillation output terminal. Note that FIG. 14 shows that the variable capacitance element 203 is AC grounded, but not DC grounded. Therefore, the control terminal 204 is not grounded in terms of direct current. As the characteristics of such a voltage controlled oscillator, it is desirable that the oscillation frequency obtained at the oscillation output terminal 205 linearly changes over a wide range with respect to the control voltage applied to the frequency control terminal 204.

Further, as shown in FIG. 15, in the voltage controlled oscillator, a modulation control terminal 107 is newly provided, and a modulation baseband signal is inputted from the modulation control terminal 107, whereby a frequency modulation signal can be obtained at the output terminal 106. Such a circuit is widely used in a wireless communication device using the FSK modulation method.

FIG. 16 is a circuit diagram of a resonance type voltage controlled oscillator realized by a CMOS process. In this circuit, the resonance circuit includes inductors 301 and 302 and an NMOS transistor 3
The negative resistance circuit is constituted by a cross-coupled NMOS.
This is a circuit composed of transistors 305 and 306. 307 is a current source, 308 is a frequency control terminal, 30
9, 310 are oscillation output terminals. In this circuit, when a control voltage Vc is applied to the frequency control terminal 308, the gate capacitances of the transistors 303 and 304 change, and the resonance frequency changes, so that the oscillation frequency changes.

[0007]

The conversion characteristic between the oscillation frequency of the voltage controlled oscillator and the control voltage is substantially determined by the characteristic of the variable capacitance element in the case of the resonance type, but it is difficult to obtain a linear change over a wide range. In a one-chip voltage controlled oscillator based on a CMOS process that has become popular in recent years, a variable capacitance element formed by a special process such as a super step junction used as a variable capacitance element in a voltage controlled oscillator using a conventional module cannot be used. It is particularly difficult to obtain good variable capacitance characteristics.

FIG. 17 shows a conventional CMOS shown in FIG.
FIG. 7 is a characteristic diagram of an oscillation frequency with respect to a control voltage Vc of a voltage controlled oscillator by a process. FIG. 18 is a characteristic diagram of the gate capacitance with respect to the control voltage Vc (gate voltage) of the MOS transistor.

In the case of the voltage controlled oscillator shown in FIG. 16, the gate capacitance of the MOS transistors 303 and 304 is used as the capacitance of the variable capacitance element. The gate capacitance changes rapidly near the threshold voltage as shown in FIG. Therefore, a wide range of linearity cannot be obtained. As described above, the transient response characteristics and noise band characteristics of the PLL are determined by the conversion gain of the voltage-controlled oscillator. Therefore, when the linearity of the conversion gain of the voltage-controlled oscillator is poor as described above, the characteristics depend on the oscillation frequency. It is not preferable because it causes a problem such as a drastic change.

Further, since the resonance circuit of the voltage controlled oscillator is also manufactured on-chip, the oscillation frequency fluctuates due to manufacturing variations especially at high frequencies. If the variable range is increased in anticipation of the variation in order to avoid this, the conversion gain of the voltage-controlled oscillator becomes too large, and the sensitivity to voltage becomes too high, which causes a problem of deteriorating phase noise.

When a frequency modulation circuit is formed by a voltage-controlled oscillator having a wide variable range, the conversion gain is high, so that the level of the baseband signal must be reduced, and as a result, the modulation accuracy deteriorates. There is also.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to provide a voltage-controlled oscillator which has improved various problems which occur when integrated by a CMOS process as described above. It is.

[0013]

In order to solve the above-mentioned problems, a first invention has a negative resistance circuit and a first variable capacitance element forming a part of a resonance circuit. In a voltage controlled oscillator that changes an oscillation frequency obtained at an oscillation output terminal by changing a frequency control voltage applied to a control terminal of the variable capacitance element, a second variable capacitance element connected in parallel to the first variable capacitance element And a frequency correction signal generating means for applying a frequency correction signal to a control terminal of the second variable capacitance element, wherein a signal generated by the frequency correction signal generation means is supplied to a control terminal of the second variable capacitance element. , The deviation of the oscillation frequency determined by the first variable capacitance element is corrected.

According to a second aspect, in the first aspect, a measuring means for measuring an oscillation frequency is connected to the oscillation output terminal, and a measurement result obtained by the measuring means is input to the frequency correction signal generating means. Thus, it is configured to correct the deviation of the oscillation frequency.

A third invention has a negative resistance circuit and a first variable capacitance element forming a part of a resonance circuit, and varies a frequency control voltage applied to a control terminal of the first variable capacitance element. And a third variable capacitance element connected in parallel to said first variable capacitance element, said third variable capacitance element being connected to said third variable capacitance element in parallel with said third variable capacitance element.
Modulation signal generating means for applying a frequency modulation signal to the control terminal of the variable capacitance element, and applying the signal generated by the modulation signal generation means to the control terminal of the third variable capacitance element. An oscillation frequency determined by one variable capacitance element is modulated.

A fourth invention has a negative resistance circuit and a first variable capacitance element which forms a part of a resonance circuit, and changes a frequency control voltage applied to a control terminal of the first variable capacitance element. A voltage-controlled oscillator that varies an oscillation frequency obtained at an oscillation output terminal, and at least one fourth variable capacitance element connected in parallel to the first variable capacitance element, and a value obtained by inputting the frequency control voltage. And a level shift circuit for generating a plurality of voltages different from each other.
Are applied to the control terminals of the variable capacitance elements.

A fifth invention has a negative resistance circuit and a first variable capacitance element forming a part of a resonance circuit, and varies a frequency control voltage applied to a control terminal of the first variable capacitance element. A voltage-controlled oscillator that changes the oscillation frequency obtained at the oscillation output terminal, thereby controlling at least one fifth variable capacitance element connected in parallel to the first variable capacitance element, and controlling the fifth variable capacitance element A frequency range switching signal generating means for applying a signal for switching a capacitance of the variable capacitance element to one of a first capacitance value and a second capacitance value at a terminal, wherein the frequency range switching signal is generated by the frequency range switching signal generating means; By applying a signal to the control terminal of the fifth variable capacitance element, the range of the oscillation frequency determined by the first variable capacitance element is switched.

In a sixth aspect based on any one of the first to fifth aspects, a MOS transistor formed by a CMOS process is used as the variable capacitance element, and a gate capacitance of the MOS transistor is used as the capacitance. used.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Principle of the Present Invention] As shown in FIG.
31 to 2034), and a control voltage as needed can be applied to frequency control terminals 2041 to 2044 of the respective variable capacitors 2031 to 2034. Note that FIG. 1 shows that the variable capacitance elements 2031 to 2034 are AC grounded, and are not DC grounded. Therefore, the control terminals 2041 to 2044 are not DC grounded.

One of the plurality of variable capacitance elements can be used for controlling the oscillation frequency and the other one can be used for correcting the oscillation frequency, so that manufacturing variation can be corrected. One can be used for frequency modulation to prevent accuracy degradation during modulation operation, and two or more can be used for oscillation frequency control to improve the linearity of conversion characteristics.
Further, one can be used for controlling the oscillation frequency and another one or more can be used for switching the oscillation frequency range so that a wide range of frequencies can be oscillated. For example, in order to improve the linearity of the frequency variable characteristic, the control voltage applied to the frequency control terminal 204 is shifted by a predetermined voltage by using a level shift circuit 206 as shown in FIG. 2031 to 2034. Hereinafter, each case will be described in detail.

[First Embodiment] FIG. 3 shows an embodiment of a voltage controlled oscillator according to claim 1 of the present invention. This is C
A MOS transistor formed by a MOS process is used as a variable capacitance element.
This utilizes the change in the gate capacitance of the OS transistor, that is, the change in the gate-source capacitance with respect to the gate-source voltage, and the change in the gate-drain capacitance with respect to the gate-drain voltage. In FIG. 3, 1 is a current source, 2,
Reference numeral 3 denotes an inductor, 4 and 5 denote variable capacitance elements using NMOS transistors, and 6 and 7 denote cross-coupled NMOS transistors constituting a negative resistance circuit. The inductors 2 and 3 and the variable capacitance elements 4 and 5 form a resonance circuit.
A frequency control terminal 8 is connected to a control terminal (gate) of one variable capacitance element 4, and a frequency correction signal generation circuit 9 is connected to a control terminal of the other variable capacitance element 5. 1
0 and 11 are oscillation output terminals.

As described above, the voltage controlled oscillator of the present embodiment includes the two variable capacitance elements 4 and 5, one of which is used for controlling the main oscillation frequency, and the other variable capacitance element 5 is used for controlling the oscillation frequency. This is for correcting the oscillation frequency.

This voltage-controlled oscillator applies, for example, a predetermined constant voltage from a frequency control terminal 8 at the time of factory shipment inspection, and evaluates the output frequency value at that time by a circuit such as a counter for monitoring the frequency. By adjusting the voltage generated by the frequency correction signal generation circuit 9 so that the value falls within a certain reference value, it is possible to correct a frequency deviation due to a variation at the time of manufacturing.

Further, as shown in FIG. 4, a frequency monitor circuit 12 having a function of monitoring the frequency of a counter or the like is connected to the output of the voltage controlled oscillator, and the oscillation output is output at a fixed timing, for example, at the time of turning on the power or at a fixed time interval. By monitoring the frequency and controlling the voltage generated by the frequency correction signal generating circuit 9 according to the result (claim 2), it is possible to configure a voltage-controlled oscillator having a small characteristic change with time or temperature fluctuation. Become.

[Second Embodiment] FIG. 5 shows a voltage controlled oscillator according to a third embodiment of the present invention. 5, the same components as those in FIG. 3 are denoted by the same reference numerals. In the voltage controlled oscillator shown in FIG. 5, a variable capacitance element 13 composed of a transistor smaller in size than a transistor constituting the variable capacitance element 4 is connected in parallel to a main variable capacitance element 4 for controlling the oscillation frequency. The modulation signal is applied by the modulation signal generation circuit 14 there.
Reference numeral 15 denotes an input terminal for a modulation baseband signal.

Here, for example, if the size of the transistor forming the variable capacitance element 13 is 1/100 of the size of the transistor forming the variable capacitance element 4, the oscillation frequency f becomes f = 1 / (2π (LC) ^{1 /} represented by ²⁾ (L is the total inductance of the inductor 2,3, C is the total capacitance) of the variable capacitance element 4, 13, the capacity of ignoring parasitic capacitance variable capacitance element 13 is 1/100
Therefore, the change amount of the oscillation frequency becomes 1/10. In other words, since the voltage-to-frequency gain is 1/10, the baseband signal can be provided at a voltage ten times higher, and the modulation accuracy can be increased. The modulation signal generating circuit 14 filters the modulation baseband digital signal input to the terminal 15 as necessary,
The amplitude level of the signal input to the variable capacitance element 13 is adjusted.

Third Embodiment FIG. 6 shows a voltage controlled oscillator according to a fourth embodiment of the present invention. Here, the variable capacitance elements for controlling the oscillation frequency are denoted by reference numerals 4A and 4A.
B, 4C, and 4D, each of which is composed of four, and a control voltage is applied from the level shift circuit 16 to each of the variable capacitance elements 4A, 4B, 4C, and 4D. Assuming that the control voltage input from the frequency control terminal 8 is Vc, the level shift circuit 16 shifts the voltage shifted by Vd from the four output terminals such as Vc, Vc-Vd, Vc-2Vd, and Vc-3Vd, respectively. appear.

The four variable capacitance elements 4A, 4B, 4C, 4
The characteristics of the gate voltage versus the gate capacitance of the eight transistors used as D are the same as those shown in FIG.
By shifting c by the voltage Vd through the level shift circuit 16 and applying it to each of the variable capacitance elements 4A, 4B, 4C and 4D, the characteristics of the gate capacitance of each transistor with respect to their control voltages are as shown in FIG. Each of the characteristics has an offset of Vd in the voltage direction. In FIG. 7, 51A, 51B, 51C and 51D are characteristic diagrams of the gate capacitance with respect to the gate voltage of the transistors of the variable capacitance elements 4A, 4B, 4C and 4D, respectively.

Since the capacitance of the resonance circuit is the sum of the capacitances of these four variable capacitance elements 4A, 4B, 4C, and 4D, the total capacitance has the characteristic shown by the solid line 52 in FIG. Compared to the conventional capacitance characteristic 53 (same as FIG. 18), it can be seen that the control width of the control voltage is wider with respect to the change width of the capacitance, and the linear range is wider. Since the change in the oscillation frequency follows the change in the variable capacitance, the linear range of the oscillation frequency with respect to the control voltage is also widened as shown in FIG. In FIG. 9, a solid line 54 is a case according to the present embodiment, and a broken line 55 is a conventional case (same as FIG. 17).

In this embodiment, four variable capacitance elements are used. However, the linear range can be expanded by further increasing the number of variable capacitance elements.

FIG. 10 shows an example of the configuration of the level shift circuit 16. 17 to 19 are NMOS transistors connected in series to a power supply, 20 is a current source, 21 is an input terminal connected to the frequency control terminal 8, and 22 to 25 are four variable capacitance elements 4
Output terminals for connection to A, 4B, 4C, and 4D. In this circuit, since the current flowing between the drain and the source of the transistors 17 to 19 is constant, if the size of each transistor is the same, the gate-source voltage of the transistor becomes constant (Vd). Voltages sequentially shifted by a fixed voltage Vd with respect to the voltage Vc input to the terminal 21 can be obtained at the output terminals 22 to 25.

Fourth Embodiment FIG. 11 shows a voltage controlled oscillator according to a fifth embodiment of the present invention. FIG.
Is a main variable capacitance element 4 for controlling the oscillation frequency described in the voltage-controlled oscillator shown in FIG.
In addition, the variable capacitance elements 26A, 2
6B and 26C are used. 27 is a frequency range switching control circuit, and 28 is a control terminal to which a frequency range setting signal is input.

Here, the frequency range switching control circuit 27
Thus, a binary digital signal (for example, a high level signal for turning on, a high level signal for turning on / off the respective transistors) is supplied to the variable capacitance elements 26A, 26B, 26C.
For turning off, a low level signal is applied. When the transistor is turned off, the channel resistance of the transistor becomes extremely high, so that the gate capacitance becomes almost invisible (first capacitance value), and the capacitance of the variable capacitance element formed by the transistor has almost no influence on the oscillation frequency. Do not give. Conversely, when the transistor is turned on, the gate capacitance (second capacitance value) of the variable capacitance element formed by the transistor is added to the resonance circuit, and the range of the oscillation frequency is changed. As a result, the range of the oscillation frequency corresponding to the control voltage input to the frequency control terminal 8 can be switched at high speed. With this, Japanese Patent Application 200
It is possible to realize a voltage-controlled oscillator such as 0-10408 and a receiving circuit of a direct conversion on the transmitting side and a single conversion method on the receiving side using the same.

In this embodiment, three variable capacitance elements for switching the frequency range are used. However, by further increasing the number, the number of range switches can be increased.

[Fifth Embodiment] FIG. 12 shows an embodiment of a voltage controlled oscillator which includes all the structures of the first to fourth embodiments described above. Variable capacitance element 4A, 4
Control voltages B, 4C, and 4D are input with offsets through the level shift circuit 16 to improve the linearity of the conversion gain of the output frequency with respect to the control voltage of the frequency control terminal 8. The variable capacitance element 13 is a variable capacitance element 4A,
A modulation baseband signal for frequency modulation is input from the modulation signal generation circuit 14 which is composed of a variable capacitance element smaller in size than 4B, 4C and 4D. The variable capacitance element 5 receives a signal for compensating for a deviation due to a manufacturing variation of the oscillation frequency with respect to the control voltage of the frequency control terminal 8. A signal for turning on / off the MOS transistor generated by the frequency range switching control circuit 26 is input to the variable capacitance elements 26A, 26B, 26C, and the oscillation frequency of the voltage controlled oscillator is switched to a required frequency range.

As described above, this embodiment has good linearity, can compensate for manufacturing variations, can easily configure a frequency modulator, and can switch the frequency range over a wide range at high speed. A controlled oscillator can be realized.

[Other Embodiments] In the voltage controlled oscillator of each of the embodiments described above, the NMOS transistor is used for the variable capacitance element and the cross-coupled transistor. The same applies to the configuration using the PMOS transistor for each. It is possible to apply to.

[0038]

As described above, according to the voltage controlled oscillator of the present invention, it is possible to widen the linear range of the control voltage vs. frequency characteristic, whereby the loop characteristic based on the output frequency when configuring the PLL is obtained. This has the effect of suppressing the fluctuation of.

Further, conventionally, it has been difficult to obtain a variable capacitance element having a wide linear range when trying to form a CMOS process.
Also in a resonance type voltage controlled oscillator by a process, it is possible to configure a voltage controlled oscillator having a wide linear range by using a variable capacitance element having a narrow linear range.

Further, it is possible to easily correct a frequency shift due to a process variation, and to easily configure a frequency modulator having high modulation accuracy.
Frequency range can be switched at high speed, etc.
There is a great effect in practical use.

[Brief description of the drawings]

FIG. 1 is a circuit diagram for explaining the principle of a voltage controlled oscillator according to the present invention.

FIG. 2 is a circuit diagram for explaining the principle of the voltage controlled oscillator for improving the linearity of the present invention.

FIG. 3 is a diagram illustrating a first example in which the present invention is applied to a resonance type voltage controlled oscillator configured by a CMOS process to enable frequency correction.
It is a circuit diagram of the voltage controlled oscillator of the embodiment.

FIG. 4 is a circuit diagram of a voltage controlled oscillator of an example in which frequency correction of the voltage controlled oscillator of FIG. 3 is automated.

FIG. 5 shows a second embodiment in which the present invention is applied to a resonance type voltage controlled oscillator configured by a CMOS process to enable frequency modulation.
It is a circuit diagram of the voltage controlled oscillator of the embodiment.

FIG. 6 is a circuit diagram of a voltage controlled oscillator according to a third embodiment in which the present invention is applied to a resonance type voltage controlled oscillator configured by a CMOS process to improve the linearity of conversion characteristics.

7 is a characteristic diagram of a gate capacitance of a transistor of each variable capacitance element in the voltage controlled oscillator of FIG. 6 with respect to a control voltage.

8 is a characteristic diagram with respect to a control voltage of a total capacitance of each variable capacitance element in the voltage controlled oscillator of FIG.

9 is a characteristic diagram of an oscillation frequency with respect to a control voltage of the voltage controlled oscillation circuit of FIG.

FIG. 10 is a circuit diagram of a level shift circuit in the voltage controlled oscillator of FIG.

FIG. 11 is a circuit diagram of a voltage-controlled oscillator according to a fourth embodiment in which the present invention is applied to a resonance-type voltage-controlled oscillator configured by a CMOS process and enables switching of a frequency range.

FIG. 12 is a diagram illustrating an example in which the present invention is applied to a resonance type voltage controlled oscillator configured by a CMOS process,
FIG. 13 is a circuit diagram of a voltage controlled oscillator according to a fifth embodiment, in which the linearity of the oscillation frequency can be improved and the frequency range can be switched.

FIG. 13 is a block diagram of a general PLL.

FIG. 14 is a block diagram of a conventional resonance type voltage controlled oscillator.

FIG. 15 is a block diagram of a frequency modulation circuit using a PLL.

FIG. 16 is a circuit diagram of a conventional resonance type voltage controlled oscillator configured by a CMOS process.

17 is a characteristic diagram of an oscillation frequency with respect to a control voltage of the voltage controlled oscillation circuit of FIG.

18 is a characteristic diagram of the capacitance of the variable capacitance element of the voltage controlled oscillation circuit of FIG.

[Explanation of symbols]

1: current source, 2, 3: inductor, 4, 4A, 4B, 4
C, 4D, 5: variable capacitance element, 6, 7: transistor,
8: frequency control terminal, 9: frequency correction signal generation circuit, 1
0, 11: oscillation output terminal, 12: frequency monitor circuit, 1
3: Variable capacitance element, 14: Modulation signal generation circuit, 15: Modulation baseband signal input terminal, 16: Level shift circuit, 17 to 19: Transistor, 20: Current source, 21:
Input terminals, 22 to 25: output terminals, 26A, 26B, 2
6C: variable capacitance element, 27: frequency range switching control circuit, 28: control terminal 101: phase comparator, 102: loop filter, 10
3: voltage controlled oscillator, 104: variable frequency divider, 105: reference signal input terminal, 106: output terminal, 107: modulation control terminal 201: resonance circuit, 202: negative resistance circuit, 203, 2
031 to 2034: Variable capacitance element, 204, 2041
2044: frequency control terminal, 205: oscillation output terminal, 2
06: Level shift circuit 301, 302: Inductor, 303 to 306: NMO
S transistor, 307: current source, 308: frequency control terminal, 309, 310: oscillation output terminal

Continuation of the front page (72) Inventor Tsuneo Tsukahara 2-3-1 Otemachi, Chiyoda-ku, Tokyo F-term in Nippon Telegraph and Telephone Corporation (reference) 5J081 BB01 CC04 CC06 CC22 DD04 DD29 EE02 EE03 KK02 MM03 5J106 AA01 BB01 CC02 GG01 HH01 JJ01 KK02 KK12 LL01 5K004 AA04 EE07 EG08

Claims (6)

[Claims] An oscillation output is provided by changing a frequency control voltage applied to a control terminal of the first variable capacitance element, comprising a negative resistance circuit and a first variable capacitance element forming a part of a resonance circuit. In a voltage controlled oscillator for changing an oscillation frequency obtained at a terminal, a frequency correction signal is applied to a second variable capacitance element connected in parallel to the first variable capacitance element, and a control terminal of the second variable capacitance element. Frequency correction signal generating means,
By applying a signal generated by the frequency correction signal generating means to a control terminal of the second variable capacitance element,
A voltage-controlled oscillator that corrects a deviation of the oscillation frequency determined by the variable capacitance element. 2. The oscillating frequency according to claim 1, wherein a measuring means for measuring an oscillating frequency is connected to said oscillation output terminal, and a measurement result obtained by said measuring means is inputted to said frequency correction signal generating means. A voltage controlled oscillator characterized in that the deviation of the voltage is corrected. 3. An oscillation output having a negative resistance circuit and a first variable capacitance element forming a part of a resonance circuit, and changing a frequency control voltage applied to a control terminal of the first variable capacitance element. In a voltage controlled oscillator for changing an oscillation frequency obtained at a terminal, a third variable capacitance element connected in parallel to the first variable capacitance element, and a frequency modulation signal applied to a control terminal of the third variable capacitance element Modulating the oscillation frequency determined by the first variable capacitance element by applying a signal generated by the modulation signal generation means to a control terminal of the third variable capacitance element. The voltage controlled oscillator characterized by the above. 4. An oscillation output having a negative resistance circuit and a first variable capacitance element forming a part of a resonance circuit, and changing a frequency control voltage applied to a control terminal of the first variable capacitance element. A voltage-controlled oscillator for changing an oscillation frequency obtained at a terminal, wherein at least one of the voltage-controlled oscillators connected in parallel to the first variable capacitance element;
Four variable capacitance elements, and a level shift circuit that receives the frequency control voltage and generates a plurality of voltages having different values, and outputs different voltages obtained by the level shift circuit to the first and fourth variable capacitance elements. A voltage-controlled oscillator, wherein the voltage is applied to the control terminals of the variable capacitance elements. 5. An oscillation output having a negative resistance circuit and a first variable capacitance element forming a part of a resonance circuit, and changing a frequency control voltage applied to a control terminal of the first variable capacitance element. A voltage-controlled oscillator for changing an oscillation frequency obtained at a terminal, wherein at least one of the voltage-controlled oscillators connected in parallel to the first variable capacitance element;
The fifth variable capacitance element and the control terminal of the fifth variable capacitance element have the capacitance of the variable capacitance element as the first capacitance value and the second capacitance value.
Frequency range switching signal generating means for applying a signal for switching to any one of the following capacitance values, and applying a signal generated by the frequency range switching signal generating means to a control terminal of the fifth variable capacitance element. A voltage-controlled oscillator that switches a range of an oscillation frequency determined by the first variable capacitance element. 6. The variable capacitance element according to claim 1, wherein a MOS transistor formed by a CMOS process is used as the variable capacitance element, and a gate capacitance of the MOS transistor is used as the capacitance. And a voltage controlled oscillator.