JP2002246840A - Voltage controlled oscillator and communication unit using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage controlled oscillator capable of realizing stable oscillation in a wide frequency range, and to provide a communication unit using the oscillator. SOLUTION: The voltage controlled oscillator 10 is provided with a resonance circuit 1 and an oscillation circuit 11. The oscillation circuit 11 is provided with an oscillation transistor Q11, resistances R11-R14, a capacitor C11, and a second variable capacity diode VD11. The emitter of the oscillation transistor Q11 is connected to an output terminal 4, and grounded through a parallel circuit constituted of the second variable capacity diode VD11 and a resistance R12. Also, the cathode of the second variable capacity diode VD11 is connected through a resistance R14 to a control circuit 3 of the resonance circuit 1.

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, for example, to a voltage controlled oscillator that stably oscillates in a wide band and a communication device using the same.

[0002]

2. Description of the Related Art A voltage controlled oscillator is widely used as a component of an FM modulator, an FM demodulator, a phase locked loop (PLL), a frequency synthesizer and the like. The required performance of this voltage controlled oscillator differs depending on the purpose of use, but in general, the variable range of the oscillation frequency, the linearity of the relationship between the control voltage and the oscillation frequency, the stability of the output level, and the low noise characteristics Etc. For example, since the output frequency of a frequency synthesizer is limited by the frequency range that can be generated by a voltage-controlled oscillator, a voltage-controlled oscillator with a wide variable range of oscillation frequency is indispensable to realize a synthesizer with a wide frequency range. Become. Further, an FM modulator that performs FM modulation of a video signal and transmits the RF signal at a radio frequency requires linearity in which a change in output frequency with respect to a change in control voltage is constant over a wide frequency range. As described above, there is a demand for a voltage-controlled oscillator to expand the variable range of the oscillation frequency, improve linearity, stabilize the output level, and the like.

FIG. 4 is a circuit diagram showing a conventional voltage controlled oscillator. The voltage controlled oscillator 50 includes a resonance circuit 1 and an oscillation circuit 2. The resonance circuit 1 includes a first variable capacitance diode VD1, a resonator L1, capacitors C1 and C2, and a resistor R
1 is a circuit that outputs a signal resonated at a frequency determined by the first variable capacitance diode VD1 and the resonator L1. The anode of the first variable capacitance diode VD1 is grounded, the cathode is connected to the oscillation circuit 2 via the resonator L1 and the capacitor C2, and is connected to the control terminal 3 via the resistor R1. The control terminal 3 side of the resistor R1 is grounded via the capacitor C1. Note that the capacitor C2 is for coupling the resonator L1 and the oscillation circuit 2.

The oscillation circuit 2 includes an oscillation transistor Q1, resistors R2 to R4, and a capacitor C3. Oscillation transistor Q is connected between the emitter and base of oscillation transistor Q1.
A capacitor C3 for generating a feedback capacitance to 1 is connected,
A resistor R2 is connected between the collector and the base. Also,
The emitter of the oscillation transistor Q1 is connected to the output terminal 4 and is grounded via the resistor R3. further,
The collector of the oscillation transistor Q1 is connected to the power supply terminal 5, and the base is grounded via the resistor R4.

[0005]

However, according to the conventional voltage controlled oscillator, the variable range of the oscillation frequency is determined by the amount of change in the impedance of the resonance circuit as viewed from the oscillation circuit. Has the property of decreasing. Therefore, even if the amount of change in the impedance of the resonance circuit is increased for broadening the band, the oscillation circuit cannot compensate for the loss of the resonance circuit on the high frequency side, and there is a problem that oscillation stops.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to provide a voltage controlled oscillator capable of stably oscillating over a wide frequency range and a communication device using the same. And

[0007]

In order to solve the above-mentioned problems, a voltage controlled oscillator according to the present invention comprises: a resonance circuit which resonates in a plurality of frequency bands according to a control voltage from a control terminal; An oscillation circuit that oscillates at a frequency, wherein the resonance circuit includes a first variable capacitance diode, and the oscillation circuit includes a second variable capacitance diode. Connecting the second variable capacitance diode,
The control terminal is connected to a connection point between the emitter of the oscillation transistor and the second variable capacitance diode.

The voltage controlled oscillator of the present invention includes a resonance circuit that resonates in a plurality of frequency bands according to a control voltage from a control terminal, and an oscillation circuit that oscillates at a resonance frequency of the resonance circuit. The circuit includes a first variable capacitance diode, and the oscillation circuit includes a second variable capacitance diode. The control voltage is applied to the first variable capacitance diode to control an oscillation frequency, and
The control voltage is applied to the variable capacitance diode to control the impedance of the second variable capacitance diode.

Further, the voltage controlled oscillator according to the present invention is characterized in that an LC parallel circuit comprising an inductor and a capacitor is connected between the second variable capacitance diode and ground.

The voltage controlled oscillator according to the present invention is characterized in that a capacitor is connected in parallel with the second variable capacitance diode.

[0011] A communication device according to the present invention is characterized by using the above-described voltage controlled oscillator.

According to the voltage controlled oscillator of the present invention, the second transistor connected between the emitter of the oscillation transistor and the ground.
In order to control the variable capacitance diode by the control voltage,
The impedance of the oscillation circuit can be changed according to the oscillation frequency.

According to the communication device of the present invention, a voltage-controlled oscillator capable of stably oscillating in a wide frequency range is used, so that a communication device having good communication characteristics in a wide frequency range can be constructed. it can.

[0014]

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 a first embodiment of the voltage controlled oscillator according to the present invention. The voltage controlled oscillator 10 includes a resonance circuit 1 and an oscillation circuit 11.

The oscillation circuit 11 includes an oscillation transistor Q1
1, a resistor R11 to R14, a capacitor C11, and a second variable capacitance diode VD11. The oscillation transistor Q1 is connected between the emitter and the base of the oscillation transistor Q11.
A capacitor C11 for generating a feedback capacitance to 1 is connected, and a resistor R11 is connected between the collector and the base.

Further, the emitter of the oscillation transistor Q11 is connected to the output terminal 4, and the capacitor C12 and the second variable capacitance diode VD11 connected in series.
Parallel circuit consisting of a resistor R12 and an inductor L
11 and a capacitor C13 are grounded via a parallel circuit.

Further, the collector of the oscillation transistor Q11 is connected to the power supply terminal 5, and the base is grounded via the resistor R13. Also, the second variable capacitance diode VD1
1 is connected to the control terminal 3 of the resonance circuit 1 via the resistor R14.

Next, the operation of the voltage controlled oscillator 10 will be described. The control voltage from the control terminal 3 is applied to the first variable capacitance diode VD1 of the resonance circuit 1 via the resistor R1 to change the resonance frequency of the resonance circuit 1 and the resonance voltage of the oscillation circuit 11 via the resistor R14. This is applied to the second variable capacitance diode VD11 to change the capacitance value of the second variable capacitance diode VD11.

Further, a capacitor C11 is connected between the emitter and the base of the oscillation transistor Q11, and the output signal is fed back to the base as the input side of the oscillation transistor Q11. Further, the power supply voltage from the power supply terminal 5 is equal to the resistance R
11, and divided by R13 and applied to the base as a bias voltage.

At this time, the oscillation circuit 11 viewed from the resonance circuit 1
The impedance of

[0022]

(Equation 1)

The first term is the amplification degree of the oscillation circuit 11,
The second term represents the reactance of the oscillation circuit 11. Incidentally, C ₂ is the capacitance value of the capacitor C2, C _x indicates a composite capacitance value of the second variable capacitance diode VD11 and the capacitor C12.

According to this equation, when the capacitance value of the second variable capacitance diode VD11 changes according to the control voltage from the control terminal 3, not only the amplification degree (first term) of the oscillation circuit 11 but also the reactance (first term) is obtained. 2) also changes. Normally, the variable range of the oscillation frequency is determined by the change in the reactance of the resonance circuit 1.
In the case of, not only the reactance of the resonance circuit 1 but also the reactance of the oscillation circuit 11 changes, so that the variable range of the oscillation frequency can be expanded.

The second variable capacitance diode VD11
And the combined capacitance value C of the capacitor C12 _xIs control terminal 3
The control voltage decreases monotonically in response to these control voltages.
Even if the oscillation frequency increases and the oscillation frequency increases,
The amplification does not decrease. Therefore, increase the oscillation frequency
Even if oscillation does not stop, the range of oscillation frequency
I can do it.

FIG. 2 is a circuit diagram of a second embodiment of the voltage controlled oscillator according to the present invention. The voltage controlled oscillator 20 includes a resonance circuit 1 and an oscillation circuit 21.

The oscillation circuit 21 includes an oscillation transistor Q1
1, resistors R11 to R14, capacitors C11 and C21,
A second variable capacitance diode VD11 is provided. A capacitor C11 for generating a feedback capacitance to the oscillation transistor Q11 is connected between the emitter and the base of the oscillation transistor Q11, and a resistor R11 is connected between the collector and the base.

The emitter of the oscillation transistor Q11 is connected to the output terminal 4 and is grounded via a parallel circuit including the second variable capacitance diode VD11, a resistor R12 and a capacitor C21. Further, the collector of the oscillation transistor Q11 is connected to the power supply terminal 5, and the base is grounded via the resistor R13.

The second variable capacitance diode VD11
Is connected to the control terminal 3 of the resonance circuit 1 via the resistor R14.

Next, the operation of the voltage controlled oscillator 20 will be described. The control voltage from the control terminal 3 is applied to the first variable capacitance diode VD1 of the resonance circuit 1 via the resistor R1 to change the resonance frequency of the resonance circuit 1 and the resonance voltage of the oscillation circuit 11 via the resistor R14. This is applied to the second variable capacitance diode VD11 to change the capacitance value of the second variable capacitance diode VD11.

Further, a capacitor C11 is connected between the emitter and the base of the oscillation transistor Q11, and the output signal is fed back to the base as the input side of the oscillation transistor Q11. Further, the power supply voltage from the power supply terminal 5 is equal to the resistance R
11, and divided by R13 and applied to the base as a bias voltage.

At this time, the oscillation circuit 21 viewed from the resonance circuit 1
The impedance of

[0033]

(Equation 2)

The first term is the amplification degree of the oscillation circuit 21,
The second term represents the reactance of the oscillation circuit 21. Incidentally, C ₂ is the capacitance value of the capacitor C2, C _y denotes the combined capacitance value between the second variable capacitance diode VD11 and the capacitor C12, C21.

According to this equation, similarly to the voltage controlled oscillator 10 of the first embodiment (FIG. 1), the capacitance value of the second variable capacitance diode VD11 changes according to the control voltage from the control terminal 3. It can be seen that not only the amplification degree (first term) of the oscillation circuit 21 but also the reactance (second term) changes. Therefore, not only the reactance of the resonance circuit 1 but also the reactance of the oscillation circuit 21 changes, so that the variable range of the oscillation frequency can be expanded.

In particular, the second variable capacitance diode VD11
Is connected in parallel with the capacitor C21.
Even when the variable capacitance diode VD11 has a variation, the variation in the combined capacitance value of the second variable capacitance diode VD11 and the capacitor C21 is reduced. Therefore, as compared with the voltage controlled oscillator 10 of the first embodiment, the variable range of the oscillating frequency can accurately determine the amount of change.

For example, 10 pF having a variation of 10%
The capacitance value of the second variable capacitance diode VD11 is 10 ±
Although it is 1 pF, the combined capacitance value of the second variable capacitance diode VD11 and the capacitor C21 is 20 pF ± 1 pF by connecting the capacitor C21 of 10 pF which can ignore the variation in parallel, and the variation is suppressed to 5%. Become.

The voltage-controlled oscillator 10 of the first embodiment
Like the combined capacitance value C _y and the second variable capacitance diode VD11 and the capacitor C12, C21 is, the control terminal 3
Since the voltage decreases monotonically in response to the control voltage from the control circuit, even if the control voltage increases and the oscillation frequency increases, the oscillation circuit 11
Does not decrease. Therefore, the oscillation does not stop even if the oscillation frequency is increased, so that the variable range of the oscillation frequency can be expanded.

According to the voltage controlled oscillators of the first and second embodiments, the capacitance value of the second variable capacitance diode connected between the emitter of the oscillation transistor and the ground is controlled by the control voltage. The impedance of the oscillation circuit can be changed according to the oscillation frequency.

Therefore, since a decrease in the degree of amplification of the oscillation circuit can be prevented and the variable range of the oscillation frequency can be widened, it is possible to provide a voltage-controlled oscillator capable of performing stable oscillation in a wide frequency range.

When a capacitor is connected in parallel with the second variable capacitance diode, the combined capacitance value of the second variable capacitance diode and the capacitor can be obtained even if the second variable capacitance diode has variation. Is small. Therefore, the variable range of the oscillation frequency can accurately determine the amount of change. Therefore, it is possible to provide a voltage-controlled oscillator capable of performing more stable oscillation in a wide frequency range.

FIG. 3 is a block diagram of one embodiment according to the communication device of the present invention. The communication device 30 includes an antenna 31, a duplexer 32, amplification units 33a and 33b, a mixing unit 34a,
34b, a voltage control oscillator 35, a PLL control circuit 36,
It includes a low-pass filter 37, a temperature-compensated crystal oscillation circuit 38, a transmitting unit Tx, and a receiving unit Rx.

The PLL control circuit 36 receives the output signal of the voltage controlled oscillator 35, compares the phase with the oscillation signal of the temperature compensated crystal oscillation circuit 38, and outputs a control voltage so as to have a predetermined frequency and phase. .

The voltage-controlled oscillator 35 receives the control voltage via a low-pass filter 37 at a control terminal, and outputs a high-frequency signal corresponding to the control voltage. This high frequency signal is provided to each of the mixing units 34a and 34b as a local oscillation signal.

The mixing section 34a 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 33a,
Radiated from the antenna 31 via the duplexer 32.

The signal received from the antenna 31 is amplified by the amplifier 33b via the duplexer 32. Mixing section 34
b mixes the received signal amplified by the amplifier 33b with the local oscillation signal from the voltage controlled oscillator 35 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 oscillators 35 of the embodiment shown in FIGS. 1 and 2 are used as the voltage controlled oscillator 35 in the communication device 30.

According to the communication device of the above-described embodiment, a voltage-controlled oscillator capable of stably oscillating in a wide frequency range is used, so that a communication device having good communication characteristics in a wide frequency range is configured. be able to.

The configuration of the resonance circuit and the oscillation circuit described in the voltage controlled oscillator of the above-described embodiment is a general circuit configuration, and the circuit of another configuration can realize the voltage controlled oscillator of the present invention. It is possible.

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

[0051]

According to the voltage controlled oscillator of the present invention, the impedance of the oscillation circuit is oscillated because the capacitance value of the second variable capacitance diode connected between the emitter of the oscillation transistor and the ground is controlled by the control voltage. It can be changed according to the frequency.

Therefore, since a decrease in the amplification degree of the oscillation circuit can be prevented and the variable range of the oscillation frequency can be widened, it is possible to provide a voltage-controlled oscillator capable of performing stable oscillation in a wide frequency range.

When a capacitor is connected in parallel with the second variable capacitance diode, the combined capacitance value of the second variable capacitance diode and the capacitor can be obtained even if the second variable capacitance diode has variation. Is small. Therefore, the variable range of the oscillation frequency can accurately determine the amount of change. Therefore, it is possible to provide a voltage-controlled oscillator capable of performing more stable oscillation in a wide frequency range.

According to the communication device of the present invention, a voltage-controlled oscillator capable of stably oscillating in a wide frequency range is used, so that a communication device having good communication characteristics in a wide frequency range can be constructed. it can.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram of a second embodiment according to the voltage controlled oscillator of the present invention.

FIG. 3 is a block diagram of an embodiment according to the communication device of the present invention.

FIG. 4 is a circuit diagram of a conventional voltage controlled oscillator.

[Explanation of symbols]

 10, 20 voltage controlled oscillator 1 resonance circuit 11, 21 oscillation circuit 30 communication device Q11 oscillation transistor VD11 second variable capacitance diode C21 capacitor

Claims (5)

[Claims] 1. A resonance circuit that resonates in a plurality of frequency bands according to a control voltage from a control terminal, and an oscillation circuit that oscillates at a resonance frequency of the resonance circuit, wherein the resonance circuit is a first variable capacitance diode. Wherein the oscillation circuits each include a second variable capacitance diode, wherein the second variable capacitance diode is connected between an emitter of an oscillation transistor constituting the oscillation circuit and ground, and an emitter of the oscillation transistor is connected to the ground. A voltage controlled oscillator, wherein the control terminal is connected to a connection point with the second variable capacitance diode. 2. A resonance circuit that resonates in a plurality of frequency bands according to a control voltage from a control terminal, and an oscillation circuit that oscillates at a resonance frequency of the resonance circuit, wherein the resonance circuit is a first variable capacitance diode. The oscillation circuits each include a second variable capacitance diode, the control voltage is applied to the first variable capacitance diode to control an oscillation frequency, and the control voltage is applied to the second variable capacitance diode. To control the impedance of the second variable capacitance diode. 3. The voltage controlled oscillator according to claim 1, wherein an LC parallel circuit including an inductor and a capacitor is connected between the second variable capacitance diode and a ground. 4. The voltage controlled oscillator according to claim 1, wherein a capacitor is connected in parallel with said second variable capacitance diode. 5. A communication device using the voltage-controlled oscillator according to claim 1.