JPH07202638A - Voltage controlled oscillator - Google Patents

Abstract

PURPOSE:To shorten the lock up time of a PLL circuit by providing plural coils for determining a resonance frequency, switching these coils according to a frequency band to be used and reducing the changing range of control voltage to be imparted to a VCO. CONSTITUTION:Coils L1,2 and a varactor diode 11 compose the resonance circuit of the VCO of a PLL circuit. The coils L1,2 are set to oscillate the frequency bands of 160 to 161 and 130 to 131MHz frequency bands, for instance, respectively. The control part of the PLL circuit transmits a signal S to a changeover switch 10 and selects a desired coil according to a frequency band to be used. The varactor diode 11 changes capacitance and resonates to a desired frequency by DC controlled voltage V where the signal from the phase comparator of the PLL circuit is integrated. When the frequencies of a transmission and a reception is largely apart, for instance, an only necessary frequency range is oscillated at the changing range of narrow DC controlled voltage V by switching to the resonance coil according to each 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 used in a radio device or the like which requires a large frequency shift.

[0002]

2. Description of the Related Art FIG. 5 shows a PLL (Pha) using a conventional voltage controlled oscillator used as a local oscillator circuit of a radio device or the like.
FIG. 3 is a block diagram showing a configuration of a se Locked Loop) frequency synthesizer.

The operation of the PLL frequency synthesizer and the voltage controlled oscillator shown in FIG. 5 will be described below.

First, the PLL means a circuit structure in which a phase difference is detected so as to match the frequency and phase of a reference signal, and the oscillation frequency is controlled by the detected signal.
As shown in FIG. 5, the L frequency synthesizer comprises a reference frequency oscillator 1, a phase comparator 2, a low pass filter 3, a voltage controlled oscillator 4, a frequency divider 5, and a control unit 6.

The control unit 6 sets a frequency division value in the frequency divider 5 such that the output frequency of the voltage controlled oscillator 4 becomes equal to the reference signal of the reference frequency oscillator 1. The reference signal from the reference frequency oscillator 1 and the signal divided by the frequency divider 5 so as to have a frequency equal to this reference signal are input to the phase comparator 2, and the phase difference between the two signals is detected, A pulse-shaped signal proportional to the phase difference is output. The low-pass filter 3 integrates the output of the phase comparator 2 to remove harmonic components, and adds a DC control voltage signal to the voltage controlled oscillator 4. The oscillating frequency of the voltage controlled oscillator 4 changes according to the applied DC control voltage as shown in FIG.

FIG. 7 shows a modified Clapp oscillator circuit as a circuit example of the voltage controlled oscillator 4 shown in FIG. Resistance R ₁ ,
R ₂ and R ₃ give a bias voltage for operating the transistor Tr23. Reference numeral 21 is a varactor diode whose capacity changes depending on the reverse bias voltage of the diode, 22 is a coil, and C ₁ , C ₂ , C ₃ , C ₄ are capacitors. The oscillating frequency f of this circuit is determined by the parallel resonance frequency of the coil and the capacitor, but by the DC control voltage V applied to the varactor diode 21,
Let C _{D be} the capacitance value of L and the inductance of the coil 22 be L, which is given by (Equation 1).

[0007]

[Equation 1]

Therefore, the oscillation frequency can be changed by changing the capacitance value C _D of the varactor diode 21, and the output characteristic of the oscillation frequency f with respect to the DC control voltage V is as shown in FIG.

[0009]

As described above, in the PLL frequency synthesizer using the conventional voltage controlled oscillator, the transmission frequency band is 160 MHz to 161 MHz and the reception frequency band is 130 MHz.
In order to realize a local oscillating circuit for communication equipment having a wide frequency band of ~ 131 MHz and a narrow frequency band, it is necessary to increase the range of the DC control voltage V to the voltage controlled oscillator and oscillate a wide range. . Further, since the DC control voltage V is largely changed, there is a problem that the lockup time until the oscillation frequency f becomes stable becomes long.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to shorten the lock-up time by making it possible to oscillate only the required frequency range with a narrow DC control voltage.

[0011]

In order to achieve the above object, the present invention provides a plurality of coils for changing the oscillation frequency, a switch for switching the coils by a switching signal, or a plurality of capacitors and a switching signal for changing the capacitance value. It is characterized by having a switch for changing.

[0012]

According to the present invention, with the above structure, the oscillation frequency can be shifted by switching the coil or the capacitor that determines the parallel resonance frequency with the switch and greatly changing the inductance or the capacitance value.

[0013]

1 is a block diagram showing the structure of a frequency synthesizer using a voltage controlled oscillator according to an embodiment of the present invention. FIG. 5 shows a conventional example in which the control unit 6 controls the voltage controlled oscillator 4. different. 2 and 3 show circuit diagrams of respective examples of the voltage controlled oscillator 4.

In FIG. 2, 11 is a varactor diode,
12 is a coil L ₁ used when oscillating a transmission frequency of 160 MHz to 161 MHz, 13 is a coil L ₂ used when oscillating a reception frequency of 130 MHz to 131 MHz, and 10 is a coil L ₁ and a coil L.
_This is a changeover switch for changing over _{2 according} to the changeover signal S.

The operation will now be described with reference to FIGS. 1 and 2. First, when the transmission frequency of 160 MHz is output, the control unit 6 makes the output frequency of the voltage controlled oscillator 4 equal to the reference signal of the reference frequency oscillator 1. Such a frequency division value is set in the frequency divider 5, the changeover signal S is turned ON, and the changeover switch 10
Is connected to the coil L ₁ 12. The phase comparator 2 receives the reference signal from the reference frequency oscillator 1 and the signal divided by the frequency divider 5 so as to have a frequency equal to this reference signal, and the DC control voltage V is supplied as in the conventional example. It is applied to the voltage controlled oscillator 4 and outputs a desired oscillation frequency f. The output characteristic of the voltage controlled oscillator 4 with respect to the DC control voltage V at this time is shown by the characteristic A in FIG.

Next, when the reception frequency of 130 MHz is output, the control section 6 divides the frequency division value so that the output frequency of the voltage controlled oscillator 4 becomes equal to the reference signal of the reference frequency oscillator 1.
And the switching signal S is turned off, and the changeover switch 10 connects to the coil L ₂ 13. Phase comparator 2
The reference signal from the reference frequency oscillator 1 and the signal divided by the frequency divider 5 so as to have the same frequency as this reference signal are input to the voltage control oscillator 4 as in the conventional example. And outputs the desired oscillation frequency f. The output characteristic of the voltage controlled oscillator 4 with respect to the DC control voltage V at this time is shown in the characteristic B of FIG.

As described above, the oscillating frequency of the voltage controlled oscillator 4 is changed by the applied DC control voltage V and the switching signal S as shown in FIG.

FIG. 3 shows a case where a plurality of capacitors are switched by the switching signal S from the control section 6 in place of the plurality of coils L ₁ and L ₂ of FIG. In this case, instead of the inductance shown in FIG. 2, the oscillation frequency is shifted by changing the capacitance value.

[0019]

As described above, according to the present invention, the voltage controlled oscillator is provided with a plurality of coils or capacitors for changing the oscillation frequency and a switch for switching these coils or capacitors. Can be output at a required frequency without significantly changing the control voltage.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a frequency synthesizer using a voltage controlled oscillator according to an embodiment of the present invention.

FIG. 2 is an example of a circuit diagram of the voltage controlled oscillator in FIG.

3 is another example of a circuit diagram of the voltage controlled oscillator in FIG. 1. FIG.

FIG. 4 is an output characteristic diagram with respect to a control voltage of the voltage controlled oscillator according to the present invention.

FIG. 5 is a block diagram showing a configuration of a frequency synthesizer using a voltage controlled oscillator in a conventional example.

FIG. 6 is an output characteristic diagram with respect to a control voltage of a conventional voltage controlled oscillator.

FIG. 7 is a circuit diagram of the voltage controlled oscillator shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reference frequency oscillator, 2 ... Phase comparator, 3 ... Low pass filter, 4 ... Voltage controlled oscillator, 5 ... Frequency divider, 6 ... Control part, 10 ... Changeover switch, 11, 21 ... Varactor diode, 12, 13, 22 ... coil, 23 ... transistor.

Claims (2)

[Claims] 1. A voltage controlled oscillator, comprising: a plurality of inductances for changing an oscillation frequency; a switch for switching the inductances; and a variable capacitance diode for changing an oscillation frequency according to a control voltage. 2. A voltage controlled oscillator, comprising: a plurality of capacitors for changing the oscillation frequency; a switch for switching the capacitors; and a variable capacitance diode for changing the oscillation frequency according to a control voltage.