JP2001320235A - Voltage controlled oscillator - Google Patents

Abstract

(57) [Problem] To provide a high frequency band voltage controlled oscillator suitable for integration capable of obtaining a continuous wide oscillation frequency band. SOLUTION: A resonator is constituted by an inductor 2 and variable capacitance diodes 3 to 7 connected in parallel to the inductor 2,
Excited by the active element circuit 1 to form a voltage controlled oscillator. The on-state capacitance values of the variable capacitance diodes 4 to 7 are 2
C, 2C, 4C, and 8C. The off-state capacitance values are 1C, 1C, 2C, and 4C, respectively. By controlling the variable capacitance diodes 4 to 7 with the 4-bit control signals b0 to b3, the total capacitance value Ct of the variable capacitance diodes is controlled.
From 8C to 16C in 1C steps. The oscillation frequency can be changed stepwise at substantially equal intervals, and a wide oscillation frequency band can be obtained. Since Ct can be reduced, it is suitable for a voltage controlled oscillator in a high frequency band.

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, and more particularly to a voltage controlled oscillator suitable for a semiconductor integrated circuit, capable of obtaining a wide oscillation frequency band.

[0002]

2. Description of the Related Art As a conventional voltage controlled oscillator, a differential voltage controlled oscillator described in US Pat. No. 5,648,744 is known. FIG. 9 is a circuit diagram showing a configuration of this conventional voltage controlled oscillator. The voltage-controlled oscillator shown in FIG. 9 includes a resonator including a variable capacitance diode connected in parallel with an inductor 2 and an active element circuit 1. The capacitance values of the variable capacitance diodes 3 and 9 change continuously according to the control voltage Vt. Variable capacitance diode 4 ~
Switches 7 and 10 to 13 are respectively connected in series. The control signals b0 to b3 perform on / off control of each switch. The capacitance value of the variable capacitance diodes 4, 10 is C, the capacitance value of the variable capacitance diodes 5, 11 is 2C, the capacitance value of the variable capacitance diodes 6, 12 is 4C, and the capacitance of the variable capacitance diodes 7, 13 is The value is 8C.

Next, the operation of the voltage controlled oscillator will be described. The control signals b0 to b3 shown in FIG. 9 are generated by a 4-bit binary counter. The total capacitance value of the variable capacitance diodes 4 to 7 or the variable capacitance diodes 10 to 13 connected in parallel is the sum of the values when the switches connected in series are on. FIG. 10 shows a change in the total capacitance value of the variable capacitance diodes 4 to 7 or the variable capacitance diodes 10 to 13 with respect to the control signals b0 to b3. FIG.
As shown in the figure, when the control signals b0 to b3 increase by 1, the total capacitance value of the variable capacitance diode changes by C. Assuming that the capacitance value of the variable capacitance diode 3 is Co, the total capacitance value of the variable capacitance diodes 4 to 7 is Ct, and the inductance of the inductor 2 is L, the oscillation frequency of the voltage controlled oscillator is expressed by the following equation (1). .

[0004]

(Equation 1)

FIG. 11 shows a change in the oscillation frequency of the voltage controlled oscillator with respect to the control voltage Vt. Since the total capacitance Ct changes stepwise according to the control signal, the oscillation frequency band also changes stepwise. Further, the oscillation frequency changes because the capacitance value Co of the variable capacitance diode 3 changes continuously by the control voltage Vt. Therefore, even when the change ratio of the capacitance value of the variable capacitance diode 3 is small, the oscillating frequency band changes stepwise at substantially equal intervals due to the stepwise change of the total capacitance value Ct, and the Bandwidth is obtained.

In the integration, the variable capacitance diode 4
, 7 and 10 to 13 are connected in series, respectively.
It is composed of an OS transistor or a bipolar transistor. For this reason, in the off state, the capacitance value remains without being completely opened, and the change in the total capacitance value of the variable capacitance diode does not become C with respect to the change in which the control signals b0 to b3 increase by one. Therefore, the interval of the stepwise change of the oscillation frequency is not constant, and the oscillation frequency may be discontinuous. In order to avoid discontinuity of the oscillation frequency, there is a method of increasing the number of control bits to increase the number of stepwise frequency changes. In order to increase the number of bits, it is necessary to increase the number of variable capacitance diodes connected in parallel, but the total capacitance value Ct of the variable capacitance diodes also increases.
As is clear from equation (1), it is necessary to reduce the inductance L in order to keep the oscillation frequency constant.
That is, in order to make the off-state capacitance of the variable capacitance diode negligible, the on-state capacitance needs to be sufficiently large, and C cannot be reduced below a certain value.
Therefore, the inductance L must be reduced.

[0007]

However, in the above-described conventional voltage controlled oscillator, when a high frequency band voltage controlled oscillator is formed, the absolute value of the inductance L becomes very small. There is a limit on the minimum value of the inductance that can be actually configured, and there is a problem that it is difficult to configure a voltage controlled oscillator in a high frequency band.

The present invention solves the above-mentioned problem and can easily change the number of control bits while keeping the total capacitance value Ct of the variable capacitance diode constant, and gradually changes the oscillation frequency at substantially equal intervals. It is an object of the present invention to provide a high-frequency integrated voltage controlled oscillator capable of obtaining a continuous wide oscillation frequency band.

[0009]

In order to solve the above-mentioned problems, according to the present invention, an inductor, a variable capacitance block connected in parallel to the inductor, and a resonator composed of the inductor and the variable capacitance block are excited. The variable-capacitance block includes an analog variable-capacitance diode having a capacitance that is continuously changed by an analog control signal, and an on-time capacitance controlled by a digital control signal. A configuration was adopted in which a plurality of double variable capacitance diodes were connected in parallel. With this configuration, when the voltage-controlled oscillator is integrated, the oscillation frequency can be changed stepwise at substantially equal intervals. Further, the number of bits of the digital control signal can be easily changed while keeping the total capacitance value Ct of the digital variable capacitance diode constant.

Further, the digital variable capacitance diode is a variable capacitance element in which a capacitor and a transistor switch are connected in series. With this configuration, it is possible to increase the change ratio of the capacitance value between when the transistor switch is on and when it is off, and it is possible to widen the interval between the stepwise changes in the oscillation frequency.

[0011] Further, a plurality of digital variable capacitance diodes are composed of first and second variable capacitance diodes having the same capacitance value;
A third variable capacitance diode having a capacitance value twice that of the first and second variable capacitance diodes, and a fourth variable capacitance diode having a capacitance value four times that of the first and second variable capacitance diodes. With this configuration, the oscillation frequency can be changed stepwise at substantially equal intervals in the integration.

Further, the resonator is a balanced resonance circuit in which a variable capacitance block is symmetrically connected to an inductor, and the active element circuit is a circuit for exciting the resonator differentially. With this configuration, the external noise mixed in the differential signal path can be removed in-phase. For this reason, signal isolation between other circuit blocks can be ensured in integration.

[0013] Further, a communication device including an antenna, a transmission / reception unit having a voltage-controlled oscillator, and a communication control unit is provided. The voltage-controlled oscillator includes an inductor, a variable capacitance block connected in parallel to the inductor, and an inductor. An active element circuit that excites a resonator composed of a variable capacitance block, the variable capacitance block has an analog variable capacitance diode whose capacitance is continuously changed by an analog control signal,
A plurality of digital variable capacitance diodes whose on-time capacitance is twice the off-time capacitance controlled by the digital control signal are connected in parallel, and the plurality of digital variable capacitance diodes have the same capacitance value. The variable capacitance diode includes two variable capacitance diodes and third to ^n-th variable capacitance diodes having capacitance values twice to 2 ⁿ⁻² times that of the first and second variable capacitance diodes. With this configuration,
With a voltage-controlled oscillator suitable for integration, a communication device can be downsized.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to FIGS.

(First Embodiment) In a first embodiment of the present invention, a four-bit variable-capacitance diode whose on-time capacity is twice the off-time capacity is connected in parallel to form a 4-bit circuit. This is a voltage controlled oscillator that controls the total capacitance value by a control signal.

FIG. 1 is a circuit diagram showing a configuration of a voltage controlled oscillator according to a first embodiment of the present invention. In FIG. 1, an active element circuit 1 is a feedback amplifier for oscillating by a resonance circuit. The inductor 2 is an inductive element forming a resonance circuit. The variable capacitance diode 3 is an element whose capacitance value changes continuously according to the control voltage Vt. The variable capacitance diodes 4 to 7 are elements whose capacitance values change according to the control signals b0 to b3.

This voltage controlled oscillator comprises a resonator and an active element circuit 1. The resonator is an inductor 2
And a variable capacitance diode connected in parallel to the inductor 2. The capacitance value of the variable capacitance diode 5 is 2C when the control signal b0 is High and 1C when the control signal b0 is Low. The capacitance value of the variable capacitance diode 6 is 4C when the control signal b1 is High and 2C when it is Low. The capacitance value of the variable capacitance diode 7 is 8C when the control signal b2 is high and 4C when the control signal b2 is low. The capacitance value of the variable capacitance diode 4 is 2C when the control signal b3 is High and 1C when the control signal b3 is Low.

FIG. 2 is a diagram showing a change in the total capacitance value of the variable capacitance diodes 4 to 7 with respect to the control signals b0 to b3. FIG. 3 is a diagram showing a change in the oscillation frequency with respect to the control voltage Vt of the voltage controlled oscillator.

The operation of the voltage controlled oscillator according to the first embodiment of the present invention configured as described above will be described. The control signals b0 to b3 shown in FIG. 1 are generated by a 4-bit binary counter. This 4-bit counter operates so that all bits are set to 1 when a carry to the MSB occurs.

Variable capacitance diodes 4 to 7 connected in parallel
The total capacitance value of
It is the sum of the capacities at the time. FIG. 2 shows variable capacitance diodes 4 to
7 shows the change of the total capacitance value of No. 7 with respect to the control signals b0 to b3. As shown in FIG. 2, when the control signals b0 to b3 increase by 1, the total capacitance value of the variable capacitance diode changes by 1C. Assuming that the capacitance value of the variable capacitance diode 3 is Co, the capacitance value of the capacitor 30 is Cc, the total capacitance value of the variable capacitance diodes 4 to 7 is Ct, and the inductance of the inductor 2 is L, the oscillation frequency of the voltage controlled oscillator becomes , Equation (2). Since the capacity of the decoupling capacitor is sufficiently large, its influence can be ignored.

[0021]

(Equation 2)

The solid line in FIG. 3 shows a change in the oscillation frequency with respect to the control voltage Vt of the voltage controlled oscillator shown in FIG. Since the total capacitance Ct changes stepwise according to the control signal, the oscillation frequency band also changes stepwise. Further, the oscillation frequency changes because the capacitance value Co of the variable capacitance diode 3 changes continuously by the control voltage Vt.

As described above, in the first embodiment of the present invention, the voltage-controlled oscillator is formed by connecting in parallel four variable capacitance diodes whose on-time capacity is twice the off-time capacity. Since the total capacitance value is controlled by the bit control signal, the oscillation frequency of the integrated voltage controlled oscillator can be changed stepwise at substantially equal intervals.

(Second Embodiment) In a second embodiment of the present invention, five variable-capacitance diodes whose on-capacitance is twice as large as off-capacitance are connected in parallel to form a 5-bit circuit. This is a voltage controlled oscillator that controls the total capacitance value by a control signal.

FIG. 4 is a circuit diagram showing a configuration of a voltage controlled oscillator according to a second embodiment of the present invention. In FIG. 4, variable capacitance diodes 5 to 7, 41, and 42 are elements whose capacitance values change according to control signals b0 to b4. The capacitance value of the variable capacitance diode 42 is 1C when the control signal b0 is High and 0.5C when the control signal b0 is Low. The capacitance value of the variable capacitance diode 5 is 2C when the control signal b1 is High and 1C when the control signal b1 is Low. The capacitance value of the variable capacitance diode 6 is 4C when the control signal b2 is High and 2C when the control signal b2 is Low. The capacitance value of the variable capacitance diode 7 is 8C when the control signal b3 is high and 4C when the control signal b3 is low. The capacitance value of the variable capacitance diode 41 is such that the control signal b4 is H
It is 1C at igh and 0.5C at Low. The variable capacitance diodes 41 and 42 are obtained by dividing the variable capacitance diode 4 shown in FIG. 1 into two equal parts. Therefore, the total capacitance value Ct of the variable capacitance diode is the same as in FIG.

FIG. 5 shows variable capacitance diodes 5 to 7, 41,
FIG. 42 is a diagram illustrating a change in a total capacitance value of 42 with respect to control signals b0 to b4.

The operation of the voltage controlled oscillator according to the second embodiment of the present invention configured as described above will be described. The operation of the voltage controlled oscillator shown in FIG. 4 is basically the same as that of the circuit shown in FIG. FIG.
The change of the total capacitance value of 7, 41 and 42 with respect to the control signals b0 to b4 is shown. As shown in FIG. 5, the control signals b0 to b4 are 1
For an increasing change, the total capacitance value of the variable capacitance diode changes by 0.5C.

The solid line and the dotted line in FIG. 3 show changes in the oscillation frequency with respect to the control voltage Vt of the voltage controlled oscillator shown in FIG. It is apparent from FIG. 3 that the change in the oscillation frequency indicated by the dotted line is added so as to complement the space between the solid lines indicating the change in the oscillation frequency of the voltage controlled oscillator shown in FIG. Therefore, even when the change ratio of the capacitance value of the variable capacitance diode 3 is small, the interval of the stepwise change of the oscillation frequency can be reduced while the total capacitance value Ct of the variable capacitance diode is kept constant. Therefore, a wide oscillation frequency band without discontinuity of the oscillation frequency can be obtained.

It is also possible to further increase the number of variable capacitance diodes. The first and second variable capacitance diodes having the same capacitance value, and the third to ^n-th variable capacitance diodes having capacitance values twice to 2 ⁿ⁻² times the first and second variable capacitance diodes, respectively. The interval between the stepwise changes of the oscillation frequency can be further reduced.

As described above, in the second embodiment of the present invention, the voltage-controlled oscillator is formed by connecting in parallel five variable capacitance diodes whose on-time capacity is twice the off-time capacity. Since the total capacitance value is controlled by the bit control signal, the number of control bits can be increased while keeping the total capacitance value Ct of the variable capacitance diode constant, and the interval between the oscillation frequencies can be narrowed.

(Third Embodiment) In a third embodiment of the present invention, a capacitor and a transistor switch are connected in series to form a variable capacitance diode whose on-time capacity is twice the off-time capacity. This is a voltage-controlled oscillator configured to connect four variable capacitance diodes in parallel and to control the total capacitance value with a 4-bit control signal.

FIG. 6 is a circuit diagram showing a configuration of a voltage controlled oscillator according to a third embodiment of the present invention. In FIG. 6, capacitors 14 to 17 are fixed capacitance elements that determine the capacitance at the time of ON. The transistor switches 20 to 23 are
This is a switch composed of S transistors. A switch constituted by a bipolar transistor may be used.

The operation of the voltage controlled oscillator according to the third embodiment of the present invention configured as described above will be described. The capacitors 14 to 17 shown in FIG. 6 are connected in series with the transistor switches 20 to 23, respectively. Control signals b0 to b3
Perform on / off control of the transistor switches. The capacitance values of the capacitors 14 and 15 are 2C, the capacitance value of the capacitor 16 is 4C, and the capacitance value of the capacitor 17 is 8C.

Assuming that the size of the transistor switch 20 is 1, the size of the transistor switch 21 is 1, the size of the transistor switch 22 is 2, and the size of the transistor switch 23 is 4. The size ratio of the transistor switch is the ratio of the value of the capacitance component that the transistor has in the off state. Further, the capacitance value of the transistor switch connected in series with each capacitor is the capacitance value of the capacitor when the transistor switch is on, and the capacitance value of the transistor switch when the transistor is off. Assuming that the capacitance value of the transistor switches 20 and 21 in the off state is 1C, the capacitance value of the transistor switch 22 in the off state is 2C, and the capacitance value of the transistor switch 23 in the off state is 4C.
C.

That is, by turning on / off the transistor switch, each capacitance value changes in the same manner as the change due to the operation of the variable capacitance diode shown in FIG. 1 or FIG. Therefore, the oscillation frequency can be changed stepwise by the control signals b0 to b3, and the operation is the same as that of the voltage controlled oscillator of FIG. Further, by adjusting the capacitance component that the transistor has in the off state, it is possible to adjust the interval of the change of the oscillation frequency with respect to the change of the control signal by one.

As described above, in the third embodiment of the present invention, the voltage-controlled oscillator is formed by connecting a capacitor and a transistor switch in series, and a variable capacitor whose on-time capacity is twice the off-time capacity. A diode is formed, and four variable capacitance diodes are connected in parallel to control the total capacitance value by a 4-bit control signal. Therefore, the change ratio of the capacitance value when the transistor switch is on and off is large. Therefore, the interval of the stepwise change of the oscillation frequency can be widened.

(Fourth Embodiment) A fourth embodiment of the present invention is a voltage controlled oscillator having a differential configuration of a resonator and an active element circuit.

FIG. 7 is a circuit diagram showing a configuration of a voltage controlled oscillator according to a fourth embodiment of the present invention. In FIG. 7, variable capacitance diodes 4 to 7 and 10 to 13 are elements whose capacitance values change according to control signals b0 to b3. The variable capacitance diode 9 is an element whose capacitance value changes continuously according to the control voltage Vt.

The operation of changing the oscillation frequency is the same as that of the voltage controlled oscillator shown in FIG. Variable capacitance diodes 4 to 7
The change of the total capacitance value of the control signals with respect to the control signals b0 to b3 is shown in FIG.
Is the same as that shown in FIG. Control voltage V of voltage controlled oscillator
The change of the oscillation frequency with respect to t is the same as that shown by the solid line in FIG.

Since the resonator and the active element circuit have a differential configuration, external noise mixed in the differential signal path can be removed in-phase. For this reason, in integration, isolation from other circuit blocks can be ensured.

As described above, in the fourth embodiment of the present invention, the voltage controlled oscillator has a differential configuration of the resonator and the active element circuit, so that the external noise mixed in the differential signal path is in-phase. Since it can be removed, signal isolation between other circuit blocks can be ensured in integration.

(Fifth Embodiment) In a fifth embodiment of the present invention, a variable capacitance diode whose on-time capacity is twice the off-time capacity is connected in parallel, and the total capacity is controlled by a control signal. This is a PLL circuit using a voltage controlled oscillator for controlling a value.

FIG. 8 is a functional block diagram showing the configuration of the PLL circuit according to the fifth embodiment of the present invention. PL
The L circuit includes a voltage controlled oscillator 52, a frequency divider 53, a phase comparator 50, a low-pass filter 51, a phase detector 54, and a binary counter 55. In FIG. 8, the voltage controlled oscillator 52 is the voltage controlled oscillator described in the first to fourth embodiments. The frequency divider 53 is a circuit that divides the output signal of the voltage controlled oscillator 52. The phase comparator 50 is a circuit that compares the phase of the signal (fdiv) divided by the frequency divider 53 with the phase of the reference signal (fref) and outputs a phase difference signal. The low-pass filter 51 is a circuit that averages the output signal of the phase comparator 50. The phase detector 54 is a circuit that detects a frequency difference based on the output signal of the phase comparator 50. Binary counter
55 is a binary up / down counter.

The operation of the PLL circuit according to the fifth embodiment of the present invention configured as described above will be described. In the initial state of the PLL circuit shown in FIG. 8, the control voltage Vt is fixed. The voltage controlled oscillator 52 outputs a signal having a frequency according to the initial value of the control signal. The frequency divider 53 includes a voltage-controlled oscillator 52
Is divided. The phase comparator 50 is a frequency divider.
The phase of the signal (fdiv) divided by 53 and the reference signal (fref) are compared, and a phase difference signal is output.

The phase detector 54 detects a frequency difference based on the output signal of the phase comparator 50. At this time, the detection accuracy of the phase difference is a frequency change interval when the control signal of the voltage controlled oscillator 52 changes by one. The binary counter 55 is counted up or down by the frequency difference signal detected by the phase detector 54, and the control signal is changed so that the frequency difference is minimized.

Next, the output signal frequency of the voltage controlled oscillator is controlled by the control voltage Vt obtained by averaging the output signal of the phase comparator 50 with the low-pass filter 51 by fixing the bit state of the control signal that minimizes the frequency difference. I do. The PLL circuit is stabilized when the frequency and phase of fdiv and fref match, and an output signal of a constant frequency is obtained from the voltage controlled oscillator 52. By this operation, first, the output signal frequency of the voltage controlled oscillator is changed stepwise, and the lock-up time of the PLL circuit is shortened in order to draw a stable state by the control voltage Vt while approaching the desired oscillation frequency. it can.

As described above, in the fifth embodiment of the present invention, the capacity of the PLL circuit is two times smaller than that of the off state.
Since a variable-capacitance diode that is doubled is connected in parallel to use a voltage-controlled oscillator that controls the total capacitance value by a control signal, the communication device can be downsized with a voltage-controlled oscillator suitable for integration.

[0048]

As is apparent from the above description, according to the present invention, an active element circuit for exciting a resonator composed of an inductor, a variable capacitance block connected in parallel to the inductor, and an inductor and a variable capacitance block. The variable capacitance block includes an analog variable capacitance diode whose capacitance is continuously changed by an analog control signal, and an on-time capacitance that is controlled by a digital control signal to be twice the off-time capacitance. Since a plurality of digital variable capacitance diodes are connected in parallel, when the voltage controlled oscillator is integrated, the oscillation frequency can be changed stepwise at approximately equal intervals, and the total capacitance of the digital variable capacitance diodes The effect that the number of bits of the digital control signal can be easily changed while keeping the value Ct constant is obtained. You.

Further, since the digital variable capacitance diode is a variable capacitance element in which a capacitor and a transistor switch are connected in series, a large change ratio of the capacitance value when the transistor switch is turned on and when the transistor switch is turned off can be obtained. The effect that the interval of the step change of the frequency can be widened is obtained.

Further, a plurality of digital variable capacitance diodes are defined as first and second variable capacitance diodes having the same capacitance value,
Since a third variable capacitance diode having a capacitance value twice as large as the first and second variable capacitance diodes and a fourth variable capacitance diode having a capacitance value four times as large as the first and second variable capacitance diodes, integrated. In this case, the effect is obtained that the oscillation frequency can be changed stepwise at substantially equal intervals.

Further, the resonator is a balanced resonance circuit in which a variable capacitance block is symmetrically connected to an inductor, and the active element circuit is a circuit for exciting the resonator differentially. The mixed external noise can be removed in-phase, and an effect of securing signal isolation between other circuit blocks during integration can be obtained.

A communication device including an antenna, a transmitting / receiving unit including a voltage controlled oscillator, and a communication control unit includes a voltage controlled oscillator including an inductor, a variable capacitance block connected in parallel to the inductor, and an inductor. An active element circuit that excites a resonator composed of a variable capacitance block, the variable capacitance block has an analog variable capacitance diode whose capacitance is continuously changed by an analog control signal,
A plurality of digital variable capacitance diodes whose on-time capacitance is twice the off-time capacitance controlled by the digital control signal are connected in parallel, and the plurality of digital variable capacitance diodes have the same capacitance value. Since the variable capacitance diode is composed of ^two variable capacitance diodes and third to nth variable capacitance diodes having a capacitance value twice to 2 ⁿ⁻² times the first and second variable capacitance diodes, it is suitable for integration. With the voltage-controlled oscillator, the communication device can be downsized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a voltage controlled oscillator according to a first embodiment of the present invention;

FIG. 2 is a diagram showing a change in Ct with respect to a control signal of a voltage controlled oscillator according to the first and fourth embodiments of the present invention;

FIG. 3 is a diagram showing a change in an oscillation frequency with respect to a control voltage Vt of the voltage controlled oscillator according to the first, second, and fourth embodiments of the present invention;

FIG. 4 is a circuit diagram showing a configuration of a voltage controlled oscillator according to a second embodiment of the present invention;

FIG. 5 is a diagram showing a change in Ct with respect to a control signal of a voltage controlled oscillator according to a second embodiment of the present invention;

FIG. 6 is a circuit diagram showing a configuration of a voltage controlled oscillator according to a third embodiment of the present invention;

FIG. 7 is a circuit diagram showing a configuration of a voltage controlled oscillator according to a fourth embodiment of the present invention;

FIG. 8 is a functional block diagram showing a configuration of a PLL circuit according to a fifth embodiment of the present invention;

FIG. 9 is a circuit diagram illustrating a configuration of a conventional voltage controlled oscillator.

FIG. 10 shows C with respect to a control signal of a conventional voltage controlled oscillator.
Diagram showing the change in t,

FIG. 11 is a diagram showing a change in oscillation frequency with respect to a control voltage Vt of a conventional voltage controlled oscillator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Active element circuit 2 Inductor 3-7 Variable capacitance diode 9-13 Variable capacitance diode 14-17 Capacitor 20-23 Transistor switch 50 Phase comparator 51 Low pass filter 52 Voltage controlled oscillator 53 Divider 54 Phase detector Vt External control voltage fref reference signal fdiv frequency-divided signal

Claims (7)

[Claims] 1. A voltage controlled oscillator comprising: an inductor; a variable capacitance block connected in parallel to the inductor; and an active element circuit for exciting a resonator constituted by the inductor and the variable capacitance block. The variable capacitance block is composed of an analog variable capacitance diode whose capacitance changes continuously by an analog control signal and a plurality of digital variable capacitance diodes controlled by a digital control signal and whose on-time capacitance is twice the off-time capacitance. A voltage controlled oscillator having a connected configuration. 2. The voltage controlled oscillator according to claim 1, wherein the digital variable capacitance diode is a variable capacitance element in which a capacitor and a transistor switch are connected in series. 3. The plurality of digital variable capacitance diodes have first and second variable capacitance diodes having the same capacitance value.
A third variable capacitance diode having a capacitance value twice that of the first and second variable capacitance diodes, and a capacitance value of the first and second variable capacitance diodes;
2. The voltage controlled oscillator according to claim 1, further comprising a fourth variable capacitance diode that is four times as large as the variable capacitance diode. 4. The plurality of digital variable capacitance diodes have first and second variable capacitance diodes having the same capacitance value.
A third variable capacitance diode having a capacitance value twice that of the first and second variable capacitance diodes, and a capacitance value of the first and second variable capacitance diodes;
A fourth variable capacitance diode that is four times as large as the variable capacitance diode, and a capacitance value equal to 8 of the first and second variable capacitance diodes.
2. The voltage controlled oscillator according to claim 1, comprising a fifth variable capacitance diode that is doubled. 5. The plurality of digital variable capacitance diodes have first and second variable capacitance diodes having the same capacitance value.
2. The voltage controlled oscillator according to claim 1, wherein the voltage controlled oscillator comprises third to ^n-th variable capacitance diodes each having a capacitance value twice to 2 ^n-2 times that of the first and second variable capacitance diodes. 6. The resonator according to claim 1, wherein the resonator is a balanced resonance circuit in which the variable capacitance block is symmetrically connected to the inductor, and the active element circuit is a circuit for exciting the resonator differentially. The voltage controlled oscillator according to claim 1, wherein 7. A communication device including an antenna, a transmission / reception unit including a voltage controlled oscillator, and a communication control unit,
The voltage-controlled oscillator includes an inductor, a variable capacitance block connected in parallel to the inductor, and an active element circuit that excites a resonator including the inductor and the variable capacitance block. A configuration in which an analog variable capacitance diode whose capacitance changes continuously by an analog control signal and a plurality of digital variable capacitance diodes controlled by a digital control signal and whose on-time capacitance is twice the off-time capacitance are connected in parallel. The plurality of digital variable capacitance diodes have first and second variable capacitance diodes having the same capacitance value, and a second variable capacitance diode having a capacitance value twice to 2 ^n-2 times that of the first and second variable capacitance diodes. A communication device comprising: a third to an n-th variable capacitance diode.