JPH09102714A - Voltage controlled oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the increase of phase noises of an oscillation frequency that is caused by the noise signal included in the inputted control signal. SOLUTION: The 1st load capacitances 11I and 11o consisting of the MOS transistors TR 5i and 5o and the capacitors 6i and 6o which are connected in series to the TR 5i and 5o, and the 2nd load capacitors 2li and 2lo consisting of the capacitors 7i and 7o having the prescribed capacitance are connected in parallel to the input and output sides of an amplifier 2 respectively. The equivalent capacitance of the capacitors 11i and 11o vary up to the capacitance C2 of the capacitors 6i and 6o from zero when the TR 5i and 5o are operated in response to the gate voltage supplied from a frequency control circuit 91. On the other hand, the total load capacitance CA of a voltage controlled oscillator varies up to C1 +C2 from C2 since the capacitance C1 of the capacitors 2li and 2lo are fixed. As a result, the noise signal is eliminated out of the control signal that is supplied as the gate voltage.

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 improvement of a voltage controlled oscillator using a piezoelectric vibrator such as a crystal.

[0002]

2. Description of the Related Art Conventionally, in the field of communication and AV (Audio-V)
In the field of (idual) equipment, an oscillator having a stable oscillation frequency and low jitter is required. As such a voltage controlled oscillator, for example, the one described in Japanese Patent Laid-Open No. 4-304704 is known. This is an oscillator using a piezoelectric element 4 such as a crystal whose oscillation frequency is variable, as shown in FIG. 6, in which a load capacitance is formed by connecting a MOS transistor 5 and a capacitance 6 in series. The oscillating frequency is variably controlled by the control voltage input applied to the gate of No. 5.

Further, for example, as shown in FIG. 7, as a system for switching the capacity, there is an "aye ai ai".
1988 Custom Integrated Circuits Conference 9.5 (IEEE 1988 CO
STOMINTEGRATED CIRCUITS C
ONFERENCE 9.5) ”. This is to variably control the oscillation frequency by switching the load capacitance connected to the amplifier 2 and changing the load capacitance value of the entire voltage controlled oscillator.

[0004]

However, in the above-mentioned conventional voltage controlled oscillator, when the oscillation frequency is made variable by controlling the gate voltage of the MOS transistor, the MOS transistor is in the off state. At times, it becomes equivalent to the state where no load is connected, and the total load capacitance becomes zero. On the contrary, when it can be considered that the MOS transistor is in the ON state and its ON resistance is sufficiently small, only the capacitance is the load. Becomes Therefore, the sensitivity, which is the ratio of the change in the oscillation frequency to the change in the control voltage applied to the gate of the MOS transistor, is high, and as a result, the phase noise increases due to the influence of the voltage noise of the control voltage. There are challenges.

Further, when the load capacitance is changed to make the total load capacitance value variable and the oscillation frequency is changed, the phase at the time of switching is discontinuous in order to switch the load capacitance having a predetermined capacitance value. Therefore, there is a problem that the jitter becomes large as a result and the phase noise is significantly deteriorated. Therefore, the present invention has been made in view of the above-mentioned unsolved problems of the related art, and an object thereof is to provide a voltage controlled oscillator having a low phase noise characteristic.

[0006]

In order to achieve the above object, a voltage controlled oscillator according to claim 1 of the present invention comprises:
An amplifier, a piezoelectric vibrator that forms a feedback circuit of the amplifier, a load circuit that forms a feedback circuit of the amplifier in parallel with the piezoelectric vibrator, and has a variable capacitance value by voltage control, and a capacitance value of the load capacitance. In the voltage-controlled oscillator including a capacitance value control means for controlling, the load capacitance is variable in capacitance with a predetermined value larger than zero as a minimum value.

According to another aspect of the voltage controlled oscillator, the amplifier, the piezoelectric vibrator forming the feedback circuit of the amplifier, the feedback circuit of the amplifier formed in parallel with the piezoelectric vibrator, and the voltage In a voltage controlled oscillator comprising a load capacitance whose capacitance value is variable by control, and a capacitance value control means for controlling the capacitance value of the load capacitance, the load capacitance is responsive to a control signal from the capacitance value control means. It is characterized in that it is composed of a first load capacity whose capacity value is controlled and a second load capacity connected in parallel with the first load capacity and having a predetermined capacity value.

According to another aspect of the voltage controlled oscillator, the amplifier, the piezoelectric vibrator forming the feedback circuit of the amplifier, the feedback circuit of the amplifier formed in parallel with the piezoelectric vibrator, and the voltage In a voltage controlled oscillator comprising a load capacitance whose capacitance value is variable by control, and a capacitance value control means for controlling the capacitance value of the load capacitance, the load capacitance is responsive to a control signal from the capacitance value control means. A first load capacitance whose capacitance value is controlled is connected in parallel and selectively switchable to a plurality of sensitivity setting load capacitances, and a predetermined capacitance value is connected in parallel with the sensitivity setting load capacitances. And a capacitance value control means for selecting the plurality of first load capacitances and setting sensitivity, and a capacitance value of the first load capacitance. Control the frequency It is characterized by having a frequency adjusting means for performing.

According to a fourth aspect of the voltage controlled oscillator, an amplifier, a piezoelectric vibrator forming a feedback circuit of the amplifier, a feedback circuit of the amplifier formed in parallel with the piezoelectric vibrator, and a voltage In a voltage controlled oscillator comprising a load capacitance whose capacitance value is variable by control, and a capacitance value control means for controlling the capacitance value of the load capacitance, the load capacitance is responsive to a control signal from the capacitance value control means. A first load capacitance whose capacitance value is controlled is connected in parallel and at least one or more to the amplifier so as to be selectively switchable, and a sensitivity setting load capacitance connected in parallel with the sensitivity setting load capacitance A second load capacitance having a capacitance value of ## EQU1 ## and a frequency setting load capacitance that is selectively switchably connected to the amplifier, and the capacitance value control means selects the first load capacitance. Sensitivity setting means for setting the sensitivity, frequency setting means for selecting the second load capacitance and setting the oscillation frequency, and adjusting the oscillation frequency by controlling the capacitance value of the first load capacitance. And a frequency adjusting means.

Further, according to the voltage controlled oscillator of the present invention, an amplifier, a piezoelectric vibrator forming a feedback circuit of the amplifier, a feedback circuit of the amplifier formed in parallel with the piezoelectric vibrator, and a voltage In a voltage controlled oscillator comprising a load capacitance whose capacitance value is variable by control, and a capacitance value control means for controlling the capacitance value of the load capacitance, the load capacitance is responsive to a control signal from the capacitance value control means. A first load capacitance whose capacitance value is controlled is connected in parallel and selectively switchable to a plurality of sensitivity setting load capacitances, and a predetermined capacitance value is connected in parallel with the sensitivity setting load capacitances. A second load capacitance having a frequency setting load capacitance connected to the amplifier in parallel so as to be selectively switchable, and the capacitance value control means selects the plurality of first load capacitances. Sensitivity setting means for setting sensitivity and selecting the second load capacitance capable of canceling the change in the oscillation frequency due to the change in the capacitance value of the load capacitance for sensitivity setting, and the second load capacitance. And an oscillation frequency setting unit that selects the first load capacitance capable of canceling a change in sensitivity due to a change in the capacitance value of the frequency setting load capacitance that accompanies the setting of the oscillation frequency. And a frequency adjusting unit for adjusting the oscillation frequency by controlling the capacitance value of the load capacitance of No. 1.

Therefore, according to the voltage controlled oscillator of the first aspect, since the capacitance value of the load capacitance is set to a value greater than or equal to a predetermined value larger than zero, a noise signal accompanying the capacitance value control by the capacitance value control means is generated. Removed by load capacity. Also,
According to the voltage controlled oscillator of claim 2, by connecting the second load capacitance in parallel with the first load capacitance, the capacitance value of the entire load capacitance is changed from the capacitance value of the second load capacitance to the first load capacitance. Is set to a value between the maximum capacity value of the load capacity and the capacity value of the second load capacity.

According to another aspect of the voltage-controlled oscillator, the first load capacitance is connected to a plurality of amplifiers so as to be selectively switchable, and these amplifiers are switched so that the control signal from the capacitance value control means is changed. The sensitivity, which is the ratio of the change amount of the oscillation frequency to the change amount, is variably controlled. Further, according to the voltage controlled oscillator of the fourth aspect, the second load capacitance is connected to a plurality of amplifiers so that the second load capacitance can be selectively switched and the second load whose oscillation frequency is selected is switched. The oscillation frequency is set according to the capacitance value of the capacitance, and the oscillation frequency is adjusted by the frequency adjusting means with respect to the set oscillation frequency.

Further, according to the voltage controlled oscillator of the present invention, a change in the oscillation frequency due to a change in the capacitance value of the sensitivity setting load capacitance is offset by the second load capacitance, and the capacitance value of the oscillation frequency load capacitance is offset. Change in sensitivity due to change in
Since it is canceled out by the load capacitance of, the oscillation frequency and the sensitivity are controlled without depending on each other.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 shows a first voltage-controlled oscillator according to the present invention.
1 shows an embodiment of the present invention. The voltage controlled oscillator 1 according to the first embodiment includes an amplifier 2 and the amplifier 2
The feedback circuit includes a resistor 3, a piezoelectric vibrator 4 such as a crystal, and a load capacitor 5. And the amplifier 2
The output side and the input side of are connected via a parallel circuit of the resistor 3 and the piezoelectric vibrator 4. Further, on the input side of the amplifier 2, a first load capacitance 11i composed of a MOS transistor 5i and a capacitance 6i connected in series with the MOS transistor 5i is connected, and in parallel with the first load capacitance 11i. The second load capacitance 21i including the capacitance 7i is connected to the.

Similarly, on the output side of the amplifier 2, a first load capacitance 11o consisting of a MOS transistor 5o and a capacitance 6o connected in series with the MOS transistor 5o is connected, and the first load capacitance 11o and The second load capacitance 21o including the capacitance 7o is connected in parallel. The other ends of these capacitors 6i, 6o, 7i, 7o are respectively connected to the ground potential.

The MOS transistors 5i and 5o are P
Either a channel MOS transistor or an N channel MOS transistor may be used, and it is also possible to use them in combination. A frequency adjusting circuit 91 (capacitance value control means) that outputs a DC analog control voltage is connected to the gates of the MOS transistors 5i and 5o. The output voltage from the frequency adjusting circuit 91 causes the MOS transistors 5i and The gate voltage of 5o is variably controlled, and the MOS transistors 5i. The source-drain current of 5o is controlled.

At this time, the MOS transistors 5i and 5o
When the on-resistance of is 0, the first load capacitances 11i, 1
The equivalent capacitance of 1o matches the capacitance values of the capacitors 6i and 6o. Further, when the on-resistance is infinite, that is, when the MOS transistors 5i and 5o are in the off state, it can be considered that there is no capacity as a load, and the capacity values of the capacitors 6i and 6o can be considered to be zero. . That is, the equivalent capacitance of the first load capacitors 11i and 11o is changed from zero to the capacitances 6i and 6 according to the gate voltage of the MOS transistors 5i and 5o.
The capacitance value of o can be made variable.

The oscillation frequency of the oscillator using the piezoelectric element depends on the capacitance value of the load, and the oscillation frequency decreases as the load capacitance increases. Further, it is known that the frequency change amount Δf depends on the capacitance change amount Δc. That is, the frequency change amount Δf when the load capacity is changed from C ₀ to C ₀ + Δc can be expressed by the following equation (1).

Δf = α · Δc / C ₀ (1) In the equation (1), α can be regarded as the sensitivity of the oscillation frequency to the rate of change in capacitance. Also, Δc
If is smaller than C ₀ , the frequency change amount Δf is considered to change substantially linearly with respect to the capacitance change amount Δc, and therefore (1) above is approximately effective.

In FIG. 1, the capacitance values of the capacitances 6i and 6o are
C₁, The capacity values of the capacity 7i and 7o are C _TwoAnd then M
The on resistance value of the OS transistors 5i and 5o is from zero to infinity
When it changes to a large extent, it connects to the input and output sides of amplifier 2, respectively.
The combined load capacity of the continued first and second load capacities is C
_TwoTo C₁+ C_TwoTo change. Therefore,
In equation (1), C₀Has the lowest value of C_TwoBecomes

Here, in FIG. 1, the second load capacitance 2
If there is no 1i or 21o, the MOS transistor 5
The fact that the on-resistance value of i, 5o becomes large means that
Since this is equivalent to the decrease of C ₀ in the equation (1), the frequency change amount Δf with respect to the change of the gate voltage becomes very large. That is, the sensitivity of the gate voltage to the oscillation frequency remarkably depends on the on-resistance values of the MOS transistors 5i and 5o, and the higher the on-resistance value, the higher the sensitivity becomes.

However, when the first and second load capacitors are provided as shown in FIG. 1, the MOS transistor 5
Even when the on-resistance values of i and 5o become large, the capacitance value C of the capacitances 6i and 6o is at least C ₀ in the equation (1).
Since the _2, the frequency change amount Δf is, MOS transistors 5i, will depend on the on-resistance of 5o and the capacitance value C _2. Therefore, since the frequency variation Δf does not depend only on the ON resistance value, the sensitivity of the gate voltage to the oscillation frequency does not become extremely high, and the dependency of the sensitivity of the gate voltage on the oscillation frequency can be reduced. .

Therefore, since the sensitivity of the gate voltage to the oscillation frequency is less dependent, the influence of the voltage noise of the gate voltage on the oscillation frequency is mitigated, and the phase noise can be reduced. Further, in the conventional voltage controlled oscillator, since it is only necessary to provide the second load capacitance composed of the capacitances 7i and 7o, there is no need to change the design, and the voltage having the low phase noise characteristic can be easily and inexpensively provided. A controlled oscillator can be realized.

Next, a second embodiment of the present invention will be described. This second embodiment, as shown in FIG.
In the first embodiment shown in FIG. 3, the configuration is the same except that a plurality of first load capacitances are provided and the first load capacitance and the amplifier 2 are connected via a changeover switch. , The same reference numerals are given to the same parts, and detailed description thereof will be omitted.

As shown in FIG. 2, the first load capacitance 11i is connected to the input side of the amplifier 2 via the changeover switch 31i, and in parallel with this, the first load capacitances 12i, 13i are similarly formed. Are changeover switches 32i, 33i
And the second load 21i.
Are connected in parallel. Similarly, the first load capacitance 11o is connected to the output side of the amplifier 2 via the changeover switch 31o, and in parallel with this, the first load capacitance 12o is connected.
o and 13o are connected via changeover switches 32o and 33o, respectively, and a second load 21o is further connected in parallel.

Here, two corresponding first load capacities (for example, 11i) on the input side and the output side of the amplifier 2, respectively.
And 11o) correspond to the first load capacity described in the claims,
Similarly, two corresponding second load capacitances on the input side and the output side of the amplifier 2 correspond to the second load capacitances described in the claims. Also, the first load capacities 11i to 13
o corresponds to the load capacity for sensitivity setting.

The first load capacitors 12i, 12o, 13
i and 13o are respectively composed of MOS transistors 5i and 5o and capacitors 6i and 6o connected in series to the MOS transistors 5i and 5o, like the first load capacitors 11i and 11o.
The other ends of the capacitors 6i and 6o are connected to the ground potential. Then, the MOS of each of the first load capacitances 11i to 13o
The transistors 5i and 5o operate according to the gate voltage supplied from the frequency adjusting circuit 91 (frequency adjusting means). Also, each changeover switch 31i
Numerals 33o are switches having normally open contacts, which are controlled by a control signal from the sensitivity setting circuit 92 (sensitivity setting means). Then, the change-over switches 31i and 31o are operated by the control signal a1 from the sensitivity setting circuit 92, and when the control signal a1 has the logical value "1", the changeover switches 31i and 31o are in the closed state and the first load capacitances 11i and 11o.
And the amplifier 2 are brought into conduction. Similarly, the changeover switches 32i and 32o are activated by the control signal a2 to bring the first load capacitors 12i and 12o and the amplifier 2 into conduction, and the changeover switches 33i and 3o.
3o is activated by the control signal a3 to bring the first load capacitors 13i and 13o and the amplifier 2 into conduction.

Here, the transistor size of the MOS transistors 5i, 5o of the first load capacitors 11i, 11o is W ₁₁ / L ₁₁ , the capacitance value of the capacitors 6i, 6o is C ₁₁ , and the first load capacitors 12i, 12o are the same. MOS transistors 5i, 5o
Of the transistor size of W ₁₂ / L ₁₂ , the capacitance value of the capacitors 6i and 6o is C ₁₂ , and the first load capacitors 13i and 13o are MOS transistors.
The transistor size of the transistors 5i and 5o is W ₁₃ /
The capacitance value of L ₁₃ and the capacitances 6i and 6o is C ₁₃ .

Further, the first load capacitors 11i, 11o and
12i, 12o MOS transistors 5i, 5o transistor
The ratio of the transistor sizes is the ratio of the capacitance values of the capacitors 6i and 6o.
Suppose it is an example. In other words, the following equation (2) holds
Shall be. W₁₁/ L₁₁: W₁₂/ L₁₂= C₁₁: C₁₂ ...... (2) In this state, the frequency adjustment circuit 91 outputs each MOS transistor.
A gate voltage is applied to the star. Each first at this time
Load capacity 11i, 11o and 12i, 12o equivalent capacity
Each quantity value is C₁₁′, C₁₂′, These equivalent contents
Quantity C₁₁′, C ₁₂′ Is the capacitance value C₁₁, C₁₂Proportional to
Therefore, the following equation (3) is established from the equation (2).

W ₁₁ / L ₁₁ : W ₁₂ / L ₁₂ = C ₁₁ ′: C ₁₂ ′ (3) Here, only the changeover switches 31i and 31o are closed and the first load capacities 11i and 11o are set. Assuming that the amplifier 2 is electrically connected to the amplifier 2, the frequency change amount Δf is expressed by the following equation (4) from the equation (1). Δf ₁₁ = α · Δc ₁₁ ′ / (C ₁₁ ′ + C ₂ ) ... (4) Similarly, only the changeover switches 32i and 32o are closed, and the first load capacitors 12i and 12o are brought into conduction with the amplifier 2. If so, the frequency change amount Δf is expressed by the following equation (5) from the equation (1).

Δf ₁₂ = α · Δc ₁₂ ′ / (C ₁₂ ′ + C ₂ ) ... (5) Therefore, from the above equations (4) and (5), each capacitance value C ₁₁ , C ₁₂ is C ₁₁ ≧ C _{If 12} , then Δf ₁₁ ≧ Δf ₁₂ , and if C ₁₁ <C ₁₂ , then Δf ₁₁ <Δf ₁₂ . Therefore, each capacitance and the MOS transistor are configured so that the above equation (2) is satisfied, and the capacitance 6i,
If the capacitance value of 6o is set differently, the frequency change amount Δf can be changed by switching the first load capacitance, that is, the frequency change amount Δf with respect to the change amount of the gate voltage, that is, the gate voltage. It is possible to change the sensitivity of the oscillation frequency to.

Therefore, it is possible to obtain the same effect as that of the first embodiment, and it is possible to change the sensitivity of the oscillation frequency with respect to the gate voltage.
By setting the respective capacitances 6i and 6o of the load capacitances of 1 to predetermined values, it is possible to easily obtain a voltage controlled oscillator having arbitrary sensitivity characteristics by operating the changeover switches 31i to 33o.

In the above second embodiment,
The case where the first load capacities 11i, 11o and 12i, 12o are switched has been described. However, the present invention is not limited to this. Obtainable. Further, in the above-described second embodiment, the case where three first load capacitors are provided has been described, but the present invention is not limited to this, and it is possible to provide an arbitrary number of first load capacitors. If each of the first load capacitors is connected to the amplifier 2 via the changeover switch, the same effect as the above can be obtained.

Further, in the second embodiment described above,
Although the case where one first load capacitance is selected has been described, for example, it is possible to select a plurality of first load capacitances in combination and adjust the sensitivity by the combined capacitance. Next, a third embodiment of the present invention will be described. As shown in FIG. 3, this third embodiment is different from the second embodiment shown in FIG. 2 in that a plurality of second load capacitors are provided and are connected to the amplifier 2 via a changeover switch. Other than that, the configuration is the same, the same reference numerals are given to the same portions, and detailed description thereof will be omitted.

As shown in FIG. 3, first load capacitors 11i to 13i are connected in parallel to the input side of the amplifier 2 via changeover switches 31i to 33i. Then, in parallel with this, the second load capacitors 21i, 2
2i and 23i are changeover switches 41i to 43, respectively.
It is connected to the input side of the amplifier 2 via i. Similarly, on the output side of the amplifier 2, the first load capacitors 11o to 1o
3o are respectively connected in parallel via the changeover switches 31o to 33o, and in parallel with this, the second load capacitance 21o.
23o are connected via changeover switches 41o to 43o, respectively.

Here, the first load capacities 11i to 13o correspond to the sensitivity setting load capacities, and the second load capacities 21i to 13o.
23o corresponds to the load capacitance for frequency setting. Each of the first load capacitors 11i to 13o is composed of a MOS transistor 5i (5o) and a capacitor 6i (6o) connected in series to the MOS transistor 5i (5o), similarly to the above.
The other end of o) is connected to the ground potential, and similarly the second load capacitance is composed of the capacitance 7i (7o).

Then, as in the second embodiment,
Each MOS transistor 5i (5o) is controlled by the gate voltage supplied from the frequency adjusting circuit 91 (frequency adjusting means), and the changeover switches 31i to 33o are also controlled.
Are operated by the control signals a1 to a3 from the sensitivity setting circuit 92 (sensitivity setting means). Further, the changeover switches 41i to 43o are formed by switches having normally open contacts and are controlled by a control signal from the frequency setting circuit 93 (frequency setting means). Then, the changeover switches 41i and 41o are operated by the control signal b1 from the frequency setting circuit 93, and when the control signal b1 has the logical value "1", the changeover switches 41i and 41o are in the closed state, and the second load capacitors 21i and 21o and the amplifier 2 are connected. And become conductive. Similarly, the changeover switches 42i,
42o is activated by the control signal b2 to bring the second load capacitors 22i and 22o and the amplifier 2 into a conductive state, and the changeover switches 43i and 43o are activated by the control signal b3 so that the second load capacitors 23i and 23o are activated. The amplifier 2 and the amplifier 2 are brought into conduction.

Here, the capacitance values of the second load capacitors 21i, 21o and 22i, 22o are C ₂₁ , C ₂₂ , respectively,
Similar to the second embodiment, the capacitance value of each first load capacitance 11i, 11o and 12i, 12o when the gate voltage is applied from the frequency adjusting circuit 91 to each MOS transistor 5i, 5o is C ₁₁ ', C _12' and. In this state, for example, only the changeover switches 31i, 31o and 41i, 41o are closed, and the first load capacitance 11
The amplifiers 2 and 11 and the second load capacitors 21i and 21o are brought into conduction. The oscillation frequency at this time is f ₂₁ .

At this time, the total load capacitance C _A of the voltage controlled oscillator 1 becomes the combined capacitance of the first and second load capacitances, which is expressed by the following equation (6). C _A = C ₁₁ ′ + C ₂₁ (6) Similarly, the changeover switches 31i, 31o and 42i,
Only 42o is closed, and the first load capacitances 11i, 11
o and the second load capacitors 22i and 22o are brought into conduction with the amplifier 2. The total load capacitance C _A of the voltage controlled oscillator 1 at this time is expressed by the following equation (7). The oscillation frequency at this time is f ₂₂ .

C_A= C₁₁′ + C_{twenty two} (7) Here, the oscillation frequency depends on the load capacitance, and the load capacitance is large.
The lower the oscillation frequency, the smaller the load capacity.
If so, the oscillation frequency will increase, so the second load capacitance
21i, 21o and 22i, 22o capacitance value C_{twenty one}, C_{twenty two}
But C_{twenty one}≤C_{twenty two}If so, each oscillation frequency at that time
f_{twenty one}, F_{twenty two}Is f_{twenty one}≧ f_{twenty two}And C_{twenty one}> C _{twenty two}If
f_{twenty one}<F_{twenty two}Becomes

Therefore, by selecting the second load capacitance by the changeover switches 41i to 43o,
The oscillation frequency can be easily set. Therefore, it is possible to obtain the same effect as that of the second embodiment and to set an arbitrary oscillation frequency. Therefore, with respect to the oscillation frequency set by the selected second load capacitance, By adjusting the oscillation frequency according to the gate voltage supplied from the frequency adjustment circuit 91, the oscillation frequency can be set to a higher performance.

In the third embodiment, the second load capacitance 21 is different from the first load capacitance 11i and 11o.
The case where i, 21o and 22i, 22o are switched has been described, but the present invention is not limited to this, and any combination of the first and second load capacities can achieve the same effect. Further, in the third embodiment, the case where three first load capacitors and three second load capacitors are provided on each of the input side and the output side has been described, but the present invention is not limited to this, and an arbitrary number of first load capacitors are provided. It is possible to provide first and second load capacitors.

Also, the case where the first load capacity and the second load capacity are selected one by one has been described, but the present invention is not limited to this, and a plurality of combinations may be selected. Next, a fourth embodiment of the present invention will be described. In the fourth embodiment, as shown in FIG. 4, a load capacitance 5a for sensitivity setting on the input side and the output side of the amplifier 2 and a frequency correction for canceling the frequency fluctuation due to the load capacitance for sensitivity setting. A load capacity 5a ', a frequency setting load capacity 5b, and a sensitivity correcting load capacity 5b' for canceling the sensitivity fluctuation due to the frequency setting load capacity. Here, the load capacity 5a for sensitivity setting and the load capacity 5b 'for sensitivity correction correspond to the load capacity for sensitivity setting, and the load capacity 5b for frequency setting and the load capacity 5a' for frequency correction are for frequency setting. Supports load capacity.

Since each load capacitance has the same functional configuration on the input side and the output side, the load capacitance on the output side will be described here. In FIG. 4, the changeover switches 71i to 78i correspond to 71o to 78o, and the first load capacities 51i to 54i are 51, respectively.
The second load capacitors 61i to 64i correspond to 61o to 64o, respectively.

The load capacitance 5a for sensitivity setting is composed of first load capacitances 51o and 52o, and these first load capacitances 51o and 52o are connected in parallel to the output side of the amplifier 2 via changeover switches 71o and 72o. It is connected to the. Then, the MO of the first load capacities 51o and 52o
The S transistor is controlled according to the gate voltage supplied from the frequency adjusting circuit 91 (frequency adjusting means).

The load capacitors for frequency correction are composed of second load capacitors 61o and 62o, and these second load capacitors 61o and 62o are connected to the amplifier 2 in parallel via changeover switches 73o and 74o. Has been done.
The changeover switches 71o to 74o are formed by switches having normally open contacts, and are controlled by a control signal from a sensitivity setting data decoder 94 (sensitivity setting means). Then, the changeover switches 71o and 73o operate in response to the control signal c1 from the sensitivity setting data decoder 94, and when the control signal c1 has the logical value "1", the changeover switches 71o and 73o are in the closed state, and the first and second switches. The load capacitors 51o and 61o and the amplifier 2 are electrically connected. Similarly, changeover switches 72o and 7
4o operates in response to the control signal c2 from the sensitivity setting data decoder 94, is closed when the control signal c2 has the logical value "1", and has the first and second load capacitances 52o, 6
2o and the amplifier 2 are brought into conduction.

Then, the first load capacitors 51o, 52
The capacity values of o and the second load capacities 61o and 62o are set so that the combined capacity of the load capacities 51o and 61o and the combined capacity of the load capacities 52o and 62o are the same value.
Moreover, when the capacitance values of the first load capacitors 51o and 52o are C ₅₁ and C ₅₂ , C ₅₁ <C ₅₂ is set to be satisfied. That is, when the first load capacitance connected to the amplifier 2 is changed to change the sensitivity, the capacitance value changes, so that the total equivalent load capacitance C _{A of the} entire voltage controlled oscillator changes, and therefore the oscillation frequency is changed. Changes. Therefore, the change in the total equivalent load capacity C _A associated with the change in the capacity value of the first load capacity is offset by changing the capacity value of the second load capacity.

In other words, when increasing the sensitivity, the first
When the capacitance value of the load capacitance is increased, the total equivalent capacitance value C _{A of the} entire voltage controlled oscillator increases, and the sensitivity increases as can be seen from the equation (1). At this time, since the total equivalent capacitance value C _A increases, the oscillation frequency decreases. In order to avoid this, as can be seen from the equation (1),
Since the total equivalent capacitance value C _A may be reduced, the capacitance value of the second load capacitance may be decreased.

On the contrary, when the sensitivity is reduced, the sensitivity is reduced by decreasing the capacitance value of the first load capacitance.
At this time, since the total equivalent capacitance value C _A decreases, the capacitance value of the second load capacitance is increased by the decrease amount. Therefore,
Since the total equivalent capacitance value C _A is always the predetermined value, only the sensitivity changes without changing the oscillation frequency. On the other hand, the load capacitance 5b for frequency setting is composed of the second load capacitances 63o and 64o.
4o is connected in parallel to the amplifier 2 via changeover switches 75o and 76o. The load capacitance 5b 'for sensitivity correction is the first load capacitance 53o and 54o.
And the first load capacities 53o and 54o are
Each of them is connected to the amplifier 2 in parallel via the changeover switches 77o and 78o.

Then, these switching switches 75o-7
8o is composed of a switch having a normally open contact, and is controlled according to a control signal from a frequency setting data decoder 95 (oscillation frequency setting means). Then, the changeover switches 75o and 77o operate in response to the control signal d1 from the frequency setting data decoder 95, and similarly, the changeover switches 76o and 78o operate in response to the control signal d2, and the respective control signals are logical. When the value is "1", it is in the closed state and the corresponding first
Also, the second load capacitance and the amplifier 2 are brought into conduction.

The first load capacities 53o and 54o and the second load capacities 63o and 64o are set according to the combined capacities of the load capacities 53o and 63o and the combined capacities of 54o and 64o, respectively. Total load capacity C
The capacitance values of the first load capacitances 53o and 54o are set to C ₅₃ and C ₅₄ and the second load capacitances 63o and 64o are set to values that can obtain a predetermined oscillation frequency according to _A. When C ₆₃ and C ₆₄ , respectively, C ₅₃ > C ₅₄ , and
It is set to satisfy C ₆₃ > C ₆₄ . That is, when the second load capacitance connected to the amplifier 2 is changed to change the oscillation frequency, the capacitance value changes, so that the total equivalent load capacitance C _{A of the} entire voltage controlled oscillator changes, and therefore the sensitivity is increased. Changes. Therefore, the change in sensitivity due to the change in the total equivalent load capacity C _A due to the change in the capacity value of the second load capacity is offset by changing the capacity value of the first load capacity.

That is, when the oscillation frequency is reduced, if the capacitance value of the second load capacitance is increased, the equivalent load capacitance value C _{A of the} entire voltage controlled oscillator increases, so the oscillation frequency decreases. However, at this time, as can be seen from the equation (1), the sensitivity decreases as the overall equivalent load capacitance value C _A increases. In order to offset this decrease in sensitivity, it is sufficient to increase the first load capacitance value as can be seen from the equation (1). On the contrary, when increasing the oscillation frequency, decreasing the capacitance value of the second load capacitance increases the oscillation frequency and increases the sensitivity. Therefore, the first
If the load capacitance value of is decreased, the sensitivity is reduced accordingly, and as a result, the sensitivity becomes constant regardless of the change of the oscillation frequency.

Therefore, by considering the change in the oscillation frequency due to the sensitivity setting and the change in the sensitivity due to the frequency setting and selecting the first and second load capacitances in a combination that cancels the change, the sensitivity and The oscillation frequency can be made variable without depending on each other. Therefore, it is possible to obtain a voltage-controlled oscillator in which the same operational effect as that of the third embodiment can be obtained, and the sensitivity and the oscillation frequency can be made variable without depending on each other.

In the fourth embodiment, the case where the sensitivity and the oscillation frequency are set in two stages has been described. However, the present invention is not limited to this, and the stages can be set in any stages. In each of the second to fourth embodiments described above, a changeover switch is provided between each first load capacitance and the amplifier 2, and the changeover switch is provided between the first load capacitance and the amplifier 2. Depending on whether to make it conductive,
Although the case where the first load capacitance is selected has been described, the present invention is not limited to this, and for example, a changeover switch is provided between the frequency adjustment circuit 91 and each MOS transistor, and a gate voltage from the frequency adjustment circuit 91 is provided. It is also possible to connect the amplifier 2 and any one of the first load capacitors by switching and supplying the gate voltage for turning off the MOS transistor.

Further, for example, as shown in FIG. 5, a changeover switch S1 is provided between the frequency adjusting circuit 91 and each MOS transistor, and further, a changeover switch S1 and the MOS transistor are provided via a changeover switch S2. It may be connected to the ground voltage. In this case, when only the switch S1 is closed, the MOS
The gate voltage supplied from the frequency adjusting circuit 91 is applied to the gate of the transistor. And the switch S
When only 2 is closed, the voltage supplied to the MOS transistor becomes the ground potential. Therefore, MOS
With the transistor turned off, a circuit equivalent to the circuit shown in FIG. 2 can be formed. In this case, since the oscillator body and the switch for switching between the plurality of load capacitors are not directly connected, the oscillator body is not affected by the parasitic capacitance, the ON resistance of the switch, etc. A stable oscillation frequency can be obtained.

In the third and fourth embodiments, a case has been described in which a plurality of second load capacitors are provided and one of them is selected, but the present invention is not limited to this, and for example, the second load capacitor is used. The load capacitance can be variably controlled,
You may change this capacitance value. Further, in each of the above embodiments, the case where the first load capacitance is configured by connecting the MOS transistor and the capacitance in series has been described, but these may be connected in parallel.
Not only the MOS transistor but also a bipolar transistor can be applied.

[0057]

As described above, according to the first aspect of the present invention,
According to the voltage controlled oscillator according to the above, since the load capacitance is set to be equal to or greater than the predetermined value larger than zero, the noise signal associated with the capacitance value control by the capacitance value control means is removed by the load capacitance. Phase noise generated at the oscillation frequency due to the noise signal can be reduced.

According to the voltage controlled oscillator of the second aspect, the load capacitance is composed of the first load capacitance having a variable capacitance value and the second load capacitance having a predetermined capacitance value, and the load capacitance is always maintained. Since it is set to be equal to or larger than the capacitance value of the second load capacitance, the phase noise can be reduced easily and inexpensively only by providing the second load capacitance. Claim 3
According to the voltage controlled oscillator of the present invention, the sensitivity can be easily changed by selecting the first load capacitance.

According to the voltage controlled oscillator of the fourth aspect, the oscillation frequency can be set with higher performance by selecting the second load capacitance. Furthermore, according to the voltage controlled oscillator of the fifth aspect, the oscillation frequency and the sensitivity can be made variable without depending on each other.

[Brief description of the drawings]

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

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

FIG. 3 is a block diagram of a voltage controlled oscillator according to a third embodiment of the present invention.

FIG. 4 is a block diagram of a voltage controlled oscillator according to a fourth embodiment of the present invention.

FIG. 5 is another example of the method for selecting each load capacitance in the second to fourth embodiments of the present invention.

FIG. 6 is an example of a conventional voltage controlled oscillator.

FIG. 7 is an example of a conventional voltage controlled oscillator.

[Explanation of symbols]

 1 Voltage Controlled Oscillator 2 Amplifier 3 Resistor 4 Piezoelectric Element 5 MOS Transistor 6,7 Capacitance

Claims (5)

[Claims] 1. An amplifier, a piezoelectric vibrator that forms a feedback circuit of the amplifier, a feedback circuit of the amplifier that is formed in parallel with the piezoelectric vibrator, and a load capacitance having a variable capacitance value by voltage control, and the load. A voltage-controlled oscillator comprising: a capacitance value control means for controlling a capacitance value of a capacitance; wherein the load capacitance has a variable capacitance with a predetermined value larger than zero as a minimum value. 2. An amplifier, a piezoelectric vibrator that forms a feedback circuit of the amplifier, a feedback circuit of the amplifier that is formed in parallel with the piezoelectric vibrator, and has a variable capacitance value by voltage control, and the load. In a voltage controlled oscillator, comprising: a capacitance value control means for controlling a capacitance value of a capacitance; wherein the load capacitance is a first load capacitance whose capacitance value is controlled according to a control signal from the capacitance value control means. And a second load capacitance connected in parallel with the first load capacitance and having a predetermined capacitance value, the voltage controlled oscillator. 3. An amplifier, a piezoelectric vibrator forming a feedback circuit of the amplifier, a feedback circuit of the amplifier formed in parallel with the piezoelectric vibrator, and a load capacitance having a variable capacitance value by voltage control, and the load. In a voltage controlled oscillator comprising: a capacitance value control means for controlling a capacitance value of a capacitance, the load capacitance is a first load capacitance whose capacitance value is controlled according to a control signal from the capacitance value control means. A plurality of sensitivity setting load capacitors connected to the amplifier in parallel and selectively switchable; and a second load capacitor connected in parallel with the sensitivity setting load capacitors and having a predetermined capacitance value. The capacity value control means selects sensitivity from the plurality of first load capacities and sets sensitivity, and frequency adjusting means that controls the capacity value of the first load capacities to adjust the frequency.
A voltage-controlled oscillator having: 4. An amplifier, a piezoelectric vibrator that forms a feedback circuit of the amplifier, a load capacitor that forms a feedback circuit of the amplifier in parallel with the piezoelectric vibrator, and has a variable capacitance value by voltage control, and the load. In a voltage controlled oscillator comprising: a capacitance value control means for controlling a capacitance value of a capacitance, the load capacitance is a first load capacitance whose capacitance value is controlled according to a control signal from the capacitance value control means. At least one or more sensitivity setting load capacitors connected in parallel and selectively switchable to the amplifier and a second load capacitor connected in parallel with the sensitivity setting load capacitor and having a predetermined capacitance value are selected. A plurality of frequency setting load capacitors connected to the amplifier so as to be dynamically switchable, and the capacitance value control means,
Sensitivity setting means for selecting the first load capacitance to set the sensitivity, frequency setting means for selecting the second load capacitance and setting the oscillation frequency, and controlling the capacitance value of the first load capacitance And a frequency adjusting means for adjusting the oscillation frequency. 5. An amplifier, a piezoelectric vibrator that forms a feedback circuit of the amplifier, a feedback circuit of the amplifier that is formed in parallel with the piezoelectric vibrator, and has a variable capacitance value by voltage control, and the load. In a voltage controlled oscillator comprising: a capacitance value control means for controlling a capacitance value of a capacitance, the load capacitance is a first load capacitance whose capacitance value is controlled according to a control signal from the capacitance value control means. A plurality of sensitivity setting load capacitors connected to the amplifier in parallel and selectively switchable, and a second load capacitor connected in parallel with the sensitivity setting load capacitors and having a predetermined capacity value can be selectively switched. And a plurality of frequency setting load capacitors connected in parallel to the amplifier, wherein the capacitance value control means selects the plurality of first load capacitors to set sensitivity, Sensitivity setting Sensitivity setting means for selecting the second load capacitance capable of canceling the change in the oscillation frequency due to the change in the capacitance value of the constant load capacitance, and the oscillation frequency is set by selecting the second load capacitance. Oscillation frequency setting means for selecting the first load capacitance capable of canceling a change in sensitivity due to a change in the capacitance value of the frequency setting load capacitance, and controlling the capacitance value of the first load capacitance to control the capacitance value of the first load capacitance. A voltage control oscillator, comprising: a frequency adjusting unit that adjusts an oscillation frequency.