JPH1127045A - Voltage control oscillator and communication unit using the oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the attenuation of a basic wave via a simple output circuit part and attenuating selectively the levels of a higher harmonic that is double or more as high as the fundamental wave by connecting the output circuit part consisting of a parallel resonance circuit of a capacitive element and an inductive element in series to the signal output terminal of an amplifier circuit part. SOLUTION: An output circuit part 11 of a voltage control oscillator 10 consists of a parallel circuit of a capacitor C3 and an inductor L1. Thus, the frequency characteristic of the signal passing through the part 11 shows the characteristic of a band elimination filter which has a large loss with the resonance frequency due to the C3 and the L1 and has the small losses with frequency levels set before and after the resonance frequency. Thereby, the resonance frequency of the part 11 is set at the frequency of a double wave of the oscillator 10. As a result, the loss is reduced with the frequency of a fundamental wave and then increased with the frequency of the double wave. Accordingly, the levels of unnecessary signals are lowered among those signals that undergone the conversion of frequency and the performance of a communication unit is improved.

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 used as a local signal source for a portable telephone or the like and a communication device using the same.

[0002]

2. Description of the Related Art FIG. 8 is a circuit diagram of a conventional voltage controlled oscillator. In FIG. 8, a voltage controlled oscillator 1 includes an amplification circuit section 2 including two transistors for oscillation and buffer amplification, a capacitor, an inductor and a resistor, a dielectric resonator 3a as a resonator, and a capacitor. It comprises a resonance circuit section 3, a frequency variable section 4 composed of a varactor diode, a capacitor and an inductor, an output circuit section 5, an output terminal 6, a power supply terminal 7, and a control terminal 8 for inputting a frequency variable signal. The amplifier circuit section 2 is connected to the frequency variable section 4 via the resonance circuit section 3, the amplifier circuit section 2 is connected to the output terminal 6 via the output circuit section 5, and the power supply terminal 7 is connected to the amplifier circuit section 2. , Control terminal 8
Are connected to the frequency variable unit 4 respectively. And
In the output circuit section 5, the amplifying circuit section 2 and the output terminal 6 are connected in series via a capacitor C1 for cutting a DC component, and a capacitor C2 is connected between the capacitor C1 and the output terminal 6 for removing harmonic components. Grounded.

[0003] The voltage controlled oscillator 1 configured as described above
Of the resonance system composed of the resonance circuit unit 3 and the frequency variable unit 4 oscillates mainly with the resonance frequency determined by the resonance circuit unit 3 as a fundamental wave, and the frequency variable unit 4 is controlled by a voltage applied to the control terminal 8. By changing the capacitance value of the varactor diode, the resonance frequency of the resonance system, that is, the oscillation frequency of the voltage controlled oscillator 1 can be changed.

[0004]

FIG. 9 shows only the output circuit section 5 of the conventional voltage controlled oscillator 1. As shown in FIG. Also,
FIG. 10 shows transmission characteristics (insertion loss) of a signal passing through the output circuit unit 5. In FIG. 10, fo represents the oscillation frequency of the voltage controlled oscillator 1, and 2fo represents the frequency of its second harmonic. A and b represent insertion loss at frequencies fo and 2fo, respectively.

As described above, in the conventional voltage controlled oscillator 1, the output circuit section 5 is connected in parallel between the output terminal 6 and the ground, and the capacitor C1 inserted in series between the amplifier circuit section 2 and the output terminal 6. Since it is constituted by the inserted capacitor C2, the frequency characteristic of the signal passing through the output circuit unit 5 of the voltage controlled oscillator 1 depends on the capacitors C1 and C2.
There is some loss even at low frequencies,
As the frequency increases, the loss tends to increase gradually due to the effect of the capacitor C2.

Next, FIG. 11 shows a spectrum of a signal output from the voltage controlled oscillator 1. In FIG. 11, x1
Represents a fundamental wave, and x2 represents a second harmonic. Here, the third harmonic wave or more is omitted. As described above, the level difference between the fundamental wave x1 and the second harmonic wave x2 is 15 dB due to the difference in the insertion loss in the output circuit unit 5 in addition to the original level difference.

However, in this example, the fundamental wave x
1 also causes a loss, and since the suppression amount of the second harmonic x2 is not sufficient as the characteristic of the voltage controlled oscillator, a low-pass filter is further added to the output terminal 6 to reduce the attenuation amount of the second harmonic. Ingenuity such as increase is necessary. And
In this case, there is a problem that the attenuation of the fundamental wave x1 is further increased, and the circuit scale is increased, which hinders downsizing of the voltage controlled oscillator.

Accordingly, the present invention provides a voltage controlled oscillator that reduces attenuation of a fundamental wave and increases attenuation of a harmonic including a second harmonic with a simple output circuit section, and a communication device using the same. Aim.

[0009]

In order to solve the above problems, a voltage controlled oscillator according to the present invention is a voltage controlled oscillator comprising an amplifier circuit section, a resonance circuit section, and a frequency variable section. An output circuit section comprising a parallel resonance circuit of a capacitance element and an inductive element is connected in series to a signal output terminal of the amplifier circuit section.

In the voltage controlled oscillator according to the present invention, the resonance frequency of the parallel resonance circuit is set to be twice the resonance frequency of the resonance circuit.

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

With such a configuration, the voltage controlled oscillator of the present invention can increase the amount of suppression of the second harmonic.

Further, the communication device of the present invention can improve the performance and reduce the cost.

[0014]

FIG. 1 is a circuit diagram showing an embodiment of a voltage controlled oscillator according to the present invention. In FIG. 1, the same reference numerals are given to the same or equivalent parts as in the conventional example shown in FIG. 8, and the description thereof will be omitted.

In FIG. 1, an output circuit section 11 of a voltage controlled oscillator 10 is constituted by a parallel circuit of a capacitor C3 as a capacitive element and an inductor L1 as an inductive element.
Portions other than the output circuit section 11 are the same as in the conventional example shown in FIG.

Here, only the output circuit section 11 of the voltage controlled oscillator 10 is shown in FIG. FIG. 3 shows the output circuit unit 11.
Shows the pass characteristics (insertion loss) of a signal passing through. In FIG. 3, c and d are the frequencies fo and 2f, respectively.
5 shows the insertion loss at o. As described above, by configuring the output circuit unit 11 by the parallel circuit of the capacitor C3 and the inductor L1, the frequency characteristic of the signal passing through the output circuit unit 11 is determined by the capacitor C3 and the inductor L1.
1 shows the characteristic of the band elimination filter that the loss is large at the resonance frequency according to No. 1 and small at the frequencies before and after the resonance frequency. Therefore, as shown in FIG.
By adjusting the resonance frequency of 1 to the frequency of the second harmonic of the voltage controlled oscillator 10, the loss is small at the frequency of the fundamental wave and the loss is large at the frequency of the second harmonic.

Next, FIG. 4 shows a spectrum of a signal output from the voltage controlled oscillator 10. In FIG. 4, y1 indicates a fundamental wave, and y2 indicates a second harmonic. Here, the third harmonic wave or more is omitted. By configuring the output circuit unit 11 in this manner, the level of the fundamental wave y1 becomes +5 dBm, and the fundamental wave x of the conventional example shown in FIG.
1 +3 dBm, and the fundamental waves y1 and y2
The difference between the harmonics y2 is also 30 dB, which is larger than the conventional example.

As described above, since the output circuit section 11 is constituted by the parallel circuit of the capacitor C3 and the inductor L1, the loss of the fundamental wave can be reduced and the second harmonic wave can be suppressed with a simple circuit having the same number of components. Thus, the level difference between the fundamental wave and the second harmonic can be increased.

FIG. 5 shows another example of the output circuit section of the voltage controlled oscillator according to the present invention. 5, the same parts as those in FIG. 2 are denoted by the same reference numerals, and the description thereof will be omitted. In the output circuit section 12 of FIG. 5, a parallel circuit of the capacitor C3 and the inductor L1 is connected to an amplifier circuit section (not shown) via a capacitor C4 for cutting a DC component in series.

Normally, the output of the voltage controlled oscillator is connected to the next circuit by capacitive coupling on the set side, so that the output circuit section 11 of FIG.
However, there is no problem, but in some cases, it is necessary to cut the DC component on the voltage controlled oscillator side. In that case,
By configuring the output circuit unit 12 in this way, it is possible to sufficiently suppress the second harmonic with respect to the fundamental wave and also cut the DC component.

FIG. 6 shows still another example of the output circuit section of the voltage controlled oscillator of the present invention. 6, the same components as those in FIG. 2 are denoted by the same reference numerals, and the description thereof will be omitted. In FIG. 6, the output circuit unit 13 includes a capacitor C3 and an inductor L1.
The connection between the parallel circuit and an output terminal (not shown) is grounded via a capacitor C5 for removing harmonic components.

By configuring the output circuit section 13 as described above, it is possible to suppress the second harmonic by the capacitor C3 and the third harmonic or more by the capacitor C5, as well as to suppress the second harmonic by the capacitor C3 and the inductor L1. Can be further increased.

In each of the embodiments shown in FIGS. 5 and 6, the capacitor C4 or the capacitor C5 is connected to the parallel circuit of the capacitor C3 and the inductor L1 in the output circuit unit. A configuration having both the effect of cutting the component and the effect of increasing the suppression of the third or higher harmonic wave may be adopted.

FIG. 7 is a block diagram showing an embodiment of the communication device according to the present invention. In FIG. 7, a communication device 20 includes a signal processing circuit 21, band-pass filters 22, 26, 30, 34,
It comprises amplifiers 23, 27, 31, 35, mixers 25, 33, duplexer 28, antenna 29, and voltage-controlled oscillators 24, 32 of the present invention. Here, the output of the signal processing circuit 21 is output from the bandpass filter 22 and the amplifier 2.
3 are connected to the mixer 25 via a series connection. Also,
The output of the voltage controlled oscillator 24 is also connected to the mixer 25. The output of the mixer 25 is output to a bandpass filter 26.
And an amplifier 27 connected in series to a duplexer 28. The duplexer 28 is connected to the antenna 29. The duplexer 28 is also connected to a mixer 33 via a band-pass filter 30 and an amplifier 31 in series. The output of the voltage controlled oscillator 32 is also
It is connected to the. The output of the mixer 33 is connected to the signal processing circuit 21 via a band-pass filter 34 and an amplifier 35 in series.

In the communication device 20 configured as described above, first, at the time of transmission, an unnecessary signal is removed from the output signal generated by the signal processing circuit 21 by the band-pass filter 22, amplified by the amplifier 23, and Is multiplied by a signal from the voltage controlled oscillator 24 to be frequency-converted into an RF signal, an unnecessary signal is removed by a band-pass filter 26, amplified by an amplifier 27, and radiated from an antenna 29 via a duplexer 28. At the time of reception, the RF signal received by the antenna 29 is input to the band-pass filter 30 through the duplexer 28, unnecessary signals are removed by the band-pass filter 30, amplified by the amplifier 31, and controlled by the mixer 33. The signal is multiplied by a signal from an oscillator 32 and frequency-converted into an IF signal. An unnecessary signal is removed by a band-pass filter 34, amplified by an amplifier 35, and input to the signal processing circuit 21. Signal transmission and reception are performed in this manner.

As described above, by using the voltage controlled oscillator of the present invention as a local oscillator for frequency conversion at the time of transmission and reception, unnecessary components included in a signal after frequency conversion caused by harmonics of the voltage controlled oscillator are caused. The signal level is reduced, and the performance of the communication device 20 can be improved. In addition, since the level of the unnecessary signal is reduced, a circuit for removing the unnecessary signal after the frequency conversion such as a band-pass filter can be simplified, and the cost of the communication device 20 can be reduced.

[0027]

According to the voltage controlled oscillator of the present invention, the output circuit section comprising the parallel resonance circuit of the capacitive element and the inductive element is provided.
By connecting in series to the signal output terminal of the amplifier circuit section,
The attenuation of the fundamental wave can be reduced by a simple output circuit section, and the level of a harmonic that is two or more harmonics of the fundamental wave can be selectively attenuated. Further, by setting the resonance frequency to twice the resonance frequency of the voltage controlled oscillator, it is possible to particularly increase the attenuation of the level of the second harmonic.

According to the communication device of the present invention, it is possible to improve the performance and reduce the cost.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram of an output circuit unit of the voltage controlled oscillator of FIG.

FIG. 3 is a diagram illustrating pass characteristics of an output circuit unit of the voltage controlled oscillator of FIG. 1;

FIG. 4 is a diagram showing a spectrum of an output signal of the voltage controlled oscillator of FIG. 1;

FIG. 5 is a circuit diagram of another example of the output circuit section of the voltage controlled oscillator of the present invention.

FIG. 6 is a circuit diagram of still another example of the output circuit unit of the voltage controlled oscillator according to the present invention.

FIG. 7 is a block diagram showing one embodiment of the communication device of the present invention.

FIG. 8 is a circuit diagram of a conventional voltage controlled oscillator.

9 is a circuit diagram of an output circuit unit of the voltage controlled oscillator of FIG.

FIG. 10 is a diagram illustrating a pass characteristic of an output circuit unit of the voltage controlled oscillator in FIG. 8;

11 is a diagram showing a spectrum of an output signal of the voltage controlled oscillator of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 2 ... Amplification circuit part 3 ... Resonance circuit part 3a ... Dielectric resonator 4 ... Frequency variable part 6 ... Output terminal 7 ... Power supply terminal 8 ... Control terminal 10 ... Voltage control oscillator 11 ... Output circuit part L1 ... Inductor C3 ... Capacitor 20 … Communication equipment

Claims (3)

[Claims] 1. A voltage controlled oscillator comprising an amplifier circuit section, a resonance circuit section, and a frequency variable section, wherein an output circuit section comprising a parallel resonance circuit of a capacitive element and an inductive element is connected to a signal of the amplifier circuit section. A voltage controlled oscillator connected in series to an output terminal. 2. The voltage controlled oscillator according to claim 1, wherein a resonance frequency of the parallel resonance circuit is set to be twice a resonance frequency of the resonance circuit unit. 3. A communication device using the voltage controlled oscillator according to claim 1.