JP2002141745A - Voltage controlled oscillator and communication unit using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage controlled oscillator that can obtain an excellent phase noise characteristic and to provide a communication unit employing the voltage controlled oscillator. SOLUTION: The voltage controlled oscillator 10 selects either of two different frequencies, is in operation under the selected frequency and provided with a resonance circuit 11, an oscillation circuit 2 and a buffer circuit 3. The resonance circuit 11 selects either of the two different frequencies and provides an output of a signal resonated at the selected frequency, and is provided with a varactor diode VD11, a diode D11, resistors R11-R13, 1st and 2nd strip lines L11, L12, and capacitors C11-C13. The oscillation circuit 2 is provided with a transistor(TR) Q1, an inductor L3 and capacitors C4-C7.

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 a communication device using the same, and more particularly to a voltage controlled oscillator that operates by switching a plurality of different frequencies and a communication device using the same.

[0002]

2. Description of the Related Art In recent years, a plurality of communication systems using different frequencies have become widespread. Along with this, there is a demand that one communication device can use these plural communication systems. In this case, a high-frequency oscillation circuit such as a voltage-controlled oscillator constituting a local oscillation circuit of a communication device needs to operate by switching a plurality of different frequencies according to the communication system.

FIG. 3 is a circuit diagram showing a conventional voltage controlled oscillator. The voltage controlled oscillator 50 that operates by switching between two different frequencies is disclosed in Japanese Patent Application Laid-Open No. H11-186844, and includes a resonance circuit 1, an oscillation circuit 2, and a buffer circuit 3.

The resonance circuit 1 is a circuit that selects one of two different frequencies and outputs a signal resonated at the selected frequency. The variable capacitance diode VD1, the diode D1, the resistors R1, R2, The first and second strip lines L1 and L2, and the capacitors C1 to C3
Is provided. The anode of the variable capacitance diode VD1 is grounded, and the cathode is connected to the voltage supply terminal 4 via the resistor R1. The connection point between the variable capacitance diode VD1 and the resistor R1 is connected to the oscillation circuit 2 via the capacitors C1 and C2. Further, one ends of the first and second strip lines L1 and L2 are connected to each other, the other end of the first strip line L1 is connected to a connection point of the capacitors C1 and C2, and the other end of the second strip L2 is connected to Grounded. Also, the first and second strip lines L1,
L2 is connected to a diode D1 via a capacitor C3.
And the cathode of the diode D1 is grounded. Further, a capacitor C3 and a diode D1
Is connected to the control terminal 5 via the resistor R2.
Note that the capacitor C1 is for coupling the variable capacitance diode VD1 to the first strip line L1, and the capacitor C2 is for coupling the first strip line L1 to the oscillation circuit 2.

The oscillating circuit 2 is a Colpitts-type oscillating circuit having a common collector and including a transistor Q1, and a capacitor C4 for generating a feedback capacitance to the transistor Q1 is connected between the base and the emitter of the transistor Q1. The emitter of the transistor Q1 is connected to the buffer circuit 3 via the capacitor C5, and is grounded via the capacitor C6. Further, the collector of the transistor Q1 is connected to the power supply terminal 6 via an inductor L3 as a choke coil, and a capacitor C7
Grounded.

[0006] The voltage controlled oscillator 50 constructed as described above.
, The signal resonated by the resonance circuit 1 is
Input to the base of the transistor Q1 of the
It oscillates at 4. After this oscillation signal is amplified by the buffer circuit 3, it is output from the output terminal 7. Further, by controlling on / off of the diode D1 by a voltage applied to the control terminal 5, two different frequencies can be switched and used for oscillation. That is, when no voltage is applied to the control terminal 5, the diode D1 is turned off,
The capacitor C3 and the diode D1 are electrically disconnected from the first and second strip lines L1 and L2, and the inductance component is changed to the first and second strip lines L1 and L2.
1, L2.

On the other hand, when a voltage is applied to the control terminal 5, the diode D1 is turned on, the connection point of the first and second strip lines L1 and L2 is grounded via the capacitor C3 and the diode D1, and the inductance is reduced. The components are defined only by the first strip line L1. Therefore, diode D1 is turned off, and the frequency is higher than in the case where the inductance component is defined by first and second striplines L1 and L2.

As described above, the frequency can be switched by turning on / off the diode D1.

[0009]

However, according to the above-mentioned conventional voltage controlled oscillator, when a high inductance, that is, an inductance component defined by the first and second strip lines is used, a voltage is applied to the control terminal. Since the diode is turned off without applying the voltage, the operation of the diode becomes unstable. As a result, there is a problem that the Q value of the resonance circuit is reduced and the phase noise characteristic is deteriorated.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems, and an object of the present invention is to provide a voltage-controlled oscillator capable of obtaining good phase noise characteristics and a communication device using the same. I do.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a voltage controlled oscillator according to the present invention comprises an inductance component defined by first and second inductance elements connected in series with each other. A voltage-controlled oscillator, comprising: a resonance circuit that switches between an inductance component defined by an inductance element and resonates at a plurality of different frequencies; and an oscillation circuit that oscillates an output signal of the resonance circuit. The circuit includes a diode and always applies a voltage to a cathode of the diode.

Further, the voltage controlled oscillator of the present invention switches between an inductance component defined by the first and second inductance elements connected in series with each other and an inductance component defined by the first inductance element. A resonant circuit that resonates at a plurality of different frequencies,
A voltage controlled oscillator connected to an oscillation circuit that oscillates an output signal of the resonance circuit, wherein the resonance circuit includes a diode, a first control terminal connected to an anode of the diode, And a second control terminal connected to the cathode, wherein a voltage is constantly applied from the second control terminal to the cathode of the diode.

The voltage controlled oscillator according to the present invention is characterized in that an anode of the diode is grounded and connected to a connection point of the first and second inductance elements via a capacitor.

In the voltage controlled oscillator according to the present invention, a positive voltage is always applied to the first control terminal, and when the diode is turned on, a positive voltage is applied to the second control terminal. When turning off the diode, a negative voltage is applied to the second control terminal.

A communication device according to the present invention is characterized by using the above-mentioned voltage controlled oscillator.

According to the voltage controlled oscillator of the present invention, since a voltage is always applied to the cathode of the diode included in the resonance circuit, the operation of the diode can be stabilized even when the diode is off.

According to the communication device of the present invention, since a voltage controlled oscillator that can obtain good phase noise characteristics is used, a communication device having good phase noise characteristics at a plurality of different frequencies, particularly at low frequencies, is configured. be able to.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. In the embodiments, the same or equivalent parts as those of the conventional example are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 is a circuit diagram of one embodiment according to the voltage controlled oscillator of the present invention. The voltage controlled oscillator 10 operates by switching between two different frequencies, and includes a resonance circuit 11, an oscillation circuit 2, and a buffer circuit 3.

The resonance circuit 11 is a circuit that selects one of two different frequencies and outputs a signal resonated at the selected frequency.
1, a diode D11, resistors R11 to R13, first and second striplines L11 and L12 as first and second inductance elements, and a capacitor C11
To C13.

The anode of the variable capacitance diode VD11 is grounded, and the cathode is connected to the voltage supply terminal 12 via the resistor R11. The connection point between the variable capacitance diode VD11 and the resistor R11 is connected to the capacitor C11,
It is connected to the oscillation circuit 2 via C12.

Further, one ends of the first and second strip lines L11 and L12 are connected to each other, and the other end of the first strip line L11 is connected to a connection point of the capacitors C11 and C12. The other end is grounded. Further, the first and second strip lines L1
1 and L12 are connected to the anode of a diode D11 via a capacitor C13, and the connection point between the capacitor C13 and the diode D11 is connected to the first node via a resistor R12.
Is connected to the control terminal 13. Further, the diode D1
1 is connected to a second control terminal 14 via a resistor R13.
Connected to.

The capacitor C11 is for coupling the variable capacitance diode VD11 to the first strip line L11, and the capacitor C12 is for coupling the first strip line L11 to the oscillation circuit 2. is there. The oscillation circuit 2 and the buffer circuit 3
Has the same circuit configuration as the conventional voltage controlled oscillator 50 (FIG. 3).

The voltage controlled oscillator 10 constructed as described above
In, the signal resonated by the resonance circuit 11 is input to the base of the transistor Q1 of the oscillation circuit 2, and is oscillated by the capacitor C4. After this oscillation signal is amplified by the buffer circuit 3, it is output from the output terminal 7. Further, by controlling the on / off of the diode D11 with the voltage applied to the first and second control terminals 13 and 14, a different 2
The two frequencies can be switched and used for oscillation.

That is, a positive voltage is applied to the first control terminal 13,
For example, when a voltage of 0.7 V and a negative voltage, for example, -0.1 V, are applied to the second control terminal 14, the diode D11 is turned off, and the capacitor C13 and the diode D11 are connected to the first and second strip lines L11 and L12. From the first and second components,
Are defined by the strip lines L11 and L12.

On the other hand, a positive voltage, for example, 0.7 V, is applied to the first control terminal 13, and a positive voltage, for example, 3 V, is applied to the second control terminal 14.
Is applied, the diode D11 is turned on, the connection point of the first and second striplines L11 and L12 becomes a negative potential via the capacitor C13 and the diode D11, and the inductance component is only the first stripline L11. Is defined by Therefore, the diode D11 is turned off, and the inductance component is reduced to the first and second strip lines L11, L11,
The frequency is higher than the case defined by L12.

As described above, the first and second control terminals 1
Diode D11 while voltage is always applied to 3, 14
The frequency can be switched by turning on / off the.

Here, phase noise characteristics of the voltage controlled oscillator 10 (FIG. 1) of the embodiment and the voltage controlled oscillator 50 (FIG. 3) of the conventional example were examined. At an offset frequency of 25 kHz, the voltage-controlled oscillator 10 of the embodiment has an output frequency of 101.5 dBc.
/ Hz, which is 100./Hz of the conventional voltage controlled oscillator 50.
Good phase noise characteristics were obtained as compared with 5 dBc / Hz.

According to the voltage controlled oscillator of the above embodiment,
Since a voltage is always applied to the cathode of the diode included in the resonance circuit, the operation of the diode can be stabilized even when the diode is in the off state. Therefore, the Q value of the resonance circuit is improved, and good phase noise characteristics can be obtained.

FIG. 2 is a block diagram of one embodiment according to the communication device of the present invention. The communication device 20 includes an antenna 21, a duplexer 22, amplification units 23a and 23b, a mixing unit 24a,
24b, a voltage controlled oscillator 25, a PLL control circuit 26,
It includes a low-pass filter 27, a temperature-compensated crystal oscillation circuit 28, a transmitting unit Tx, and a receiving unit Rx.

The PLL control circuit 26 receives the output signal of the voltage control oscillator 25, compares the phase with the oscillation signal of the temperature compensated crystal oscillation circuit 28, and outputs a control voltage so as to have a predetermined frequency and phase. .

The voltage-controlled oscillator 25 receives the control voltage at the control terminal via the low-pass filter 27, and outputs a high-frequency signal corresponding to the control voltage. This high-frequency signal is supplied to the mixing units 24a and 24b as local oscillation signals.

The mixing section 24a mixes the intermediate frequency signal output from the transmission section Tx with the local oscillation signal and converts it into a transmission signal. This transmission signal is amplified by the amplifier 23a,
Radiated from the antenna 21 via the duplexer 22.

The signal received from the antenna 21 is amplified by the amplifier 23b via the duplexer 22. Mixing section 24
b mixes the received signal amplified by the amplifier 23b with the local oscillation signal from the voltage controlled oscillator 25 and converts it into an intermediate frequency signal. This intermediate frequency signal is subjected to signal processing in the receiving unit Rx.

The voltage controlled oscillator 25 of the communication device 20 is replaced by the voltage controlled oscillator 10 of the embodiment shown in FIG.
Is used.

According to the communication device of the above-described embodiment, since the voltage controlled oscillator that can obtain good phase noise characteristics is used, a communication device having good phase noise characteristics at a plurality of different frequencies, especially at low frequencies, can be used. Can be configured.

In the voltage controlled oscillator according to the above-described embodiment, the case where the anode of the diode included in the resonance circuit is connected to the first control terminal and the voltage is applied has been described. However, the anode is connected to the ground. Similar effects can be obtained even when no voltage is applied. That is, as long as the voltage is always applied to the cathode of the diode, the voltage may or may not be applied to the anode.

Although the case where the first and second inductance elements are the first and second strip lines has been described, the same effect can be obtained by using a chip inductor or a dielectric resonator.

Further, the configuration of the oscillation circuit and the buffer circuit described in the voltage controlled oscillator of the above-described embodiment is a general circuit configuration, and the voltage controlled oscillator of the present invention can be realized even with a circuit having another configuration. be able to.

Further, it is also possible to integrate the voltage controlled oscillator of the above-described embodiment into one module.

Further, a combination of a plurality of different frequencies includes a European DCS (Digital Cellular System: 1.8).
GHz band) system and GSM (Global System for Mobile commu
nications: 900MHz band, North American PCS (Persona
l Communication Services: 1.9GHz band) and AM
PS (Advanced Mobile Phone Services: 800MHz)
DECT (Digital European Cordless Telephone:
1.9 GHz band) system and GSM system, PHS (Personal) in Japan
Handy-phone System: 1.9GHz and PDC (Perso
nal Digital Cellular: 800 MHz band).

[0042]

According to the voltage controlled oscillator of the present invention, since a voltage is always applied to the cathode of the diode provided in the resonance circuit, the operation of the diode can be stabilized even when the diode is off. Therefore, the Q value of the resonance circuit is improved, and good phase noise characteristics can be obtained.

According to the communication device of the present invention, since a voltage controlled oscillator that can obtain good phase noise characteristics is used, a communication device having good phase noise characteristics at a plurality of different frequencies, particularly at low frequencies, is configured. be able to.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of one embodiment according to a voltage controlled oscillator of the present invention.

FIG. 2 is a block diagram of one embodiment according to the communication device of the present invention.

FIG. 3 is a circuit diagram of a conventional voltage controlled oscillator that operates by switching between two different frequencies.

[Explanation of symbols]

2 Oscillation Circuit 10 Voltage Controlled Oscillator 11 Resonant Circuit 13 First Control Terminal 14 Second Control Terminal 20 Communication Device D11 Diode C13 Capacitor L11 First Inductance Element (First Stripline) L12 Second Inductance Element (First 2 strip lines)

Claims (5)

[Claims] The present invention switches between an inductance component defined by first and second inductance elements connected in series and an inductance component defined by a first inductance element to resonate at a plurality of different frequencies. A voltage-controlled oscillator comprising a resonance circuit and an oscillation circuit for oscillating an output signal of the resonance circuit, wherein the resonance circuit includes a diode and always applies a voltage to a cathode of the diode. Characteristic voltage controlled oscillator. 2. Switching between an inductance component defined by first and second inductance elements connected in series and an inductance component defined by the first inductance element to resonate at a plurality of different frequencies. What is claimed is: 1. A voltage controlled oscillator comprising a resonance circuit connected to an oscillation circuit for oscillating an output signal of the resonance circuit, wherein the resonance circuit includes a diode, a first control terminal connected to an anode of the diode, , A second control terminal connected to the cathode of the diode,
A voltage is always applied from the control terminal of the diode to the cathode of the diode. 3. The device according to claim 1, wherein an anode of the diode is grounded and connected to a connection point of the first and second inductance elements via a capacitor. Voltage controlled oscillator. 4. A positive voltage is always applied to the first control terminal, and when the diode is turned on, the second voltage is applied to the second control terminal.
4. The voltage controlled oscillator according to claim 2, wherein a positive voltage is applied to a control terminal of the second control terminal, and a negative voltage is applied to the second control terminal when the diode is turned off. . 5. A communication device using the voltage-controlled oscillator according to claim 1.