JP2005217773A - Voltage-controlled piezoelectric oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voltage-controlled piezoelectric oscillator which is likely to be influenced by stray capacitance and ensures a wide frequency variable width. <P>SOLUTION: The frequency-varying circuit 300 of the voltage-controlled piezoelectric oscillator comprises a resistor R10 connected to a voltage control terminal V<SB>CONT</SB>, variable capacitance diodes VD10, VD20 the cathodes of which are connected to the other end of the resistor R10, a resistor 20 grounded at one end and connected at the other end to the cathode of the variable capacitance diode VD10, a capacitor C10 inserted between the anode of the diode VD10 and the anode of the diode VD20, the parallel circuit of a coil L10 and a resistor R30 inserted between the anode of the diode VD20 and the ground; and a parallel circuit of a variable capacitance type capacitor VC10 and a capacitor C20, inserted between the anode of the diode VD10 and a crystal oscillator X1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a voltage-controlled piezoelectric oscillator capable of controlling an oscillation frequency, and more particularly to an improvement in circuit arrangement effective for widening a frequency variable range.

Conventionally, there is an oscillator using a piezoelectric vibrator as a stable frequency signal generation source.
As a piezoelectric vibrator used for such an oscillator, for example, crystal, ceramic, lithium niobate, lithium tantalate, lithium tetraborate or the like is used. In particular, quartz substrates obtained by polishing thin plates accurately cut from artificially grown quartz crystals according to certain rules are often used as quartz resonators because of their excellent resonance characteristics among various piezoelectric materials. ing.

In addition, a voltage controlled crystal oscillator (VCXO) is known as a piezoelectric oscillator that is often used in phase synchronization devices and frequency modulation devices that control the frequency signal generated by itself to synchronize with an external signal. It has been. A general voltage-controlled crystal oscillator is provided with a voltage-controlled variable reactance element such as a varactor diode in its oscillation loop, and the output frequency generated by the oscillator can be changed according to a control voltage given from the outside. It is configured to be able to.
In recent years, voltage controlled piezoelectric oscillators have become higher in frequency and smaller in size, and accordingly, strict circuit design conditions are required.

FIG. 7 is a circuit diagram showing a configuration example of a conventional voltage-controlled piezoelectric oscillator. Hereinafter, a voltage controlled crystal oscillator will be described as an example of the voltage controlled piezoelectric oscillator.
The voltage-controlled crystal oscillator shown in this example is roughly classified as an oscillator having a crystal resonator X1, an oscillation circuit 100, and a frequency variable circuit 200, and includes four external terminals.
The external terminals are a Vcc terminal and a GND terminal for receiving power, an f _OUT terminal for outputting a frequency, and a V _CONT terminal for inputting a control voltage.

The oscillation circuit 100 is a so-called Colpitts oscillation circuit, and includes an oscillation transistor Tr1 that feedback-amplifies a resonance frequency generated in a closed loop via the crystal resonator X1, and a base between the oscillation transistor Tr1 and the ground (GND). Divided capacitors C1 and C2 provided, bias resistors R1 and R2 for applying a bias to the base of the oscillation transistor Tr1, load resistor R4 provided between the emitter of the oscillation transistor Tr1 and ground (GND), and oscillation And a current limiting resistor R3 provided between the collector of the transistor Tr1 and the power supply voltage (Vcc). Further, a CMOS (Complementary Metal-Oxide Semiconductor) buffer IC1 is provided in the frequency signal output stage. The VD electrode of the CMOS buffer IC1 is connected to Vcc, and the Vss electrode is connected to GND. Then, a frequency signal is input to the XT electrode of the CMOS buffer IC1 via the DC blocking capacitor C3 connected to the connection point between the collector of the oscillation transistor Tr1 and the current limiting resistor R1, and f _{OUT of the} CMOS buffer IC1. A frequency signal suitable for a predetermined signal condition is output from the f _OUT terminal via the output resistor 7 from the electrode.
Further, the XT electrode of the CMOS buffer IC1 is connected to a connection point between both resistances of the signal value adjusting resistors R5 and R6 inserted in series between Vcc and GND.
A bypass capacitor C4 is inserted between the power supply voltage (Vcc) and the ground (GND).

On the other hand, the frequency variable circuit 200 includes a resistor R10 connected to the V _CONT terminal, a variable capacitance diode (varactor diode) VD10 having a cathode connected to the other end of the resistor R10, an anode side of the variable capacitance diode VD10, A parallel circuit composed of a resistor R30 and a coil L10 connected between the crystal resonator X1, a resistor R20 connected between the anode side of the variable capacitance diode VD10 and GND, and a cathode side of the variable capacitance diode VD10. The variable capacitance diode VD20 connected to the cathode side, the capacitor C10 connected between the anode side of the variable capacitance diode VD10 and the anode side of the variable capacitance diode VD20, and the anode side of the variable capacitance diode VD20 and GND Resistor R40 connected in parallel, variable capacitance type A capacitor (variable capacitor or trimmer capacitor) VC10 and a capacitor C20 are included.

The voltage controlled crystal oscillator shown in this figure operates as follows. In other words, when electric power is supplied, a frequency is generated by oscillating at a frequency in the vicinity of the resonance point of the crystal resonator X1, and a frequency output from the f _OUT terminal starts. Here, the variable capacitance type capacitor VC10 is a frequency adjustment capacitor, and is for manually operating the frequency under a certain condition to a predetermined value, for example, in the initial stage. As a result, the frequency deviation due to variations in the electronic components constituting the circuit and variations in assembly accuracy is adjusted.
Then, a voltage control signal is given to the V _CONT terminal, and the oscillation frequency changes according to the voltage level. That is, the two variable capacitance diodes VD10 and VD20 of the frequency variable circuit 200 are applied with a reverse voltage, and the capacitance value decreases when the reverse voltage is high, and the capacitance value functions when the reverse voltage is low. Since the capacitance value changes according to the level of the reverse voltage in each variable capacitance diode, the oscillation frequency can be variably controlled.

Next, FIG. 8 shows a circuit configuration example of the conventional voltage-controlled crystal oscillator shown in FIG. 7, in which 50.000 MHz is set as the center frequency f ₀ and the control voltage is varied in the range of ₀ to 3.0V. FIG. 6 is a graph showing an example of frequency variable characteristics at the time of normal temperature (constant at normal temperature), where the vertical axis indicates the amount of frequency change (ppm) and the horizontal axis indicates the control voltage (V). The broken line in the figure shows a reference of the minimum frequency variable width (Lower Limit) of a certain standard, and has a slope of 90 ppm / V.
The conventional characteristic indicated by the solid line has an average slope of about 106 ppm / V, and is within the above-mentioned standard, but it cannot be said that there is a sufficient margin in consideration of temperature characteristics and component variations. .

Among these, when an actual voltage-controlled piezoelectric oscillator circuit is formed on a printed board, stray capacitance due to wiring capacitance or the like is generated, and the influence of the stray capacitance on the oscillation frequency is large.
This is particularly noticeable when a signal wiring pattern is formed on a double-sided mounting multilayer printed circuit board, and the frequency variable width is greatly reduced by stray capacitance.

As a countermeasure against such a problem of frequency variable width reduction, for example, there is one proposed in Japanese Patent Laid-Open No. 2001-144539. This is an invention to devise a multilayer board, and the signal wiring added in parallel to the voltage variable capacitance element is a partial aerial layer in which the vertical under the signal wiring is hollowed, or the vertical under the wiring is deleted By providing the lowest layer, the parasitic capacitance (floating capacitance) generated between the reference potential wiring is reduced and a wide frequency variable width is secured.
According to this, since the generation of the stray capacitance itself is reduced, the effect of suppressing the influence of the stray capacitance on the oscillation frequency is exhibited.
JP 2001-144539 A

However, the conventional voltage controlled crystal oscillator described above has the following problems. That is, the circuit configuration itself is easily affected by stray capacitance, and there is a limit even if the printed circuit board is devised as in Patent Document 1 described above.
That is, it is necessary to reduce the generation of stray capacitance, which is an extremely effective means, but it becomes a factor incurring high costs due to the complexity of the printed circuit board and strict assembly accuracy requirements, and at the same time the distance of the hollow space Since it takes (the distance between the reference potential wiring and the signal wiring), it becomes an obstacle to miniaturization.
The present invention has been made to solve such a problem, and has been made to find a circuit configuration (component arrangement in an oscillation closed loop) that is not easily affected by stray capacitance and to secure a wide frequency variable width. is there.

  In order to solve the above-mentioned problems, a voltage-controlled piezoelectric oscillator according to claim 1 of the present invention is a voltage-controlled piezoelectric oscillator having a piezoelectric vibrator, an oscillation circuit, and a frequency variable circuit, wherein the frequency variable circuit The first resistor connected to the voltage control terminal, the first variable capacitance diode and the second variable capacitance diode having the cathode connected to the other end of the first resistor, one end grounded and the other end A second resistor connected to the anode side of the first variable capacitance diode, and a first capacitor inserted between the anode side of the first variable capacitance diode and the anode side of the second variable capacitance diode Further, a parallel circuit of a coil and a third resistor is inserted between the anode side of the second variable capacitance diode and the ground, and the variable capacitance capacitor and the second capacitor are inserted. The parallel circuit of a service, characterized by being configured by inserting between the anode side and the piezoelectric vibrator of the first variable capacitance diode.

  According to a second aspect of the voltage controlled piezoelectric oscillator of the present invention, the voltage controlled piezoelectric oscillator includes a piezoelectric vibrator, an oscillation circuit, and a frequency variable circuit, and the frequency variable circuit includes a voltage control terminal. And a first variable capacitance diode and a second variable capacitance diode having a cathode connected to the other end of the first resistor, one end being grounded and the other end being the first variable A second resistor connected to the anode side of the capacitance diode; and a first capacitor inserted between the anode side of the first variable capacitance diode and the anode side of the second variable capacitance diode. Furthermore, a parallel circuit of a coil and a third resistor is inserted between the anode side of the second variable capacitance diode and the ground, and the anode side of the first variable capacitance diode is variable in capacitance. Characterized by being configured by inserting the piezoelectric vibrator between parallel circuit of the capacitor and the second capacitor.

  The voltage controlled piezoelectric oscillator according to claim 3 of the present invention is a voltage controlled piezoelectric oscillator having a piezoelectric vibrator, an oscillation circuit, and a frequency variable circuit, wherein the frequency variable circuit includes a voltage control terminal. And a first variable capacitance diode and a second variable capacitance diode having a cathode connected to the other end of the first resistor, one end being grounded and the other end being the first variable A second resistor connected to the anode side of the capacitance diode, a first capacitor inserted between the anode side of the first variable capacitance diode and the anode side of the second variable capacitance diode, and the second A fourth resistor inserted between the anode side of the variable capacitance diode and the ground, and a parallel circuit of a coil and a third resistor is connected to the anode side of the first variable capacitance diode. Above It is inserted between the electric vibrator, a parallel circuit of a capacitance variable capacitor and a second capacitor, characterized by being configured to connect to the other end of the piezoelectric vibrator.

  The voltage-controlled piezoelectric oscillator of the present invention has a circuit configuration that is hardly affected by stray capacitance, and has an advantage that a wide frequency variable width can be secured.

  FIG. 1 is a circuit diagram showing a first embodiment of a voltage controlled piezoelectric oscillator according to the present invention. In the following description, the same functional parts as those shown as the conventional example in FIG. 7 described above are denoted by the same reference numerals and description thereof is omitted, and the oscillation circuit connected to the point A in the figure is completely omitted. Illustration is omitted because they are the same.

That is, the voltage controlled crystal oscillator shown in this example is roughly divided into a crystal resonator X1, an oscillation circuit 100, and a frequency variable circuit 300.
A characteristic feature of the present invention resides in the frequency variable circuit 300. The frequency variable circuit 300 has a resistor R10 connected to a V _CONT terminal to which a control voltage is input and a cathode side connected to the other end of the resistor R10. A variable capacitance diode VD10, a parallel circuit including a capacitor C20 and a capacitance variable capacitor VC10 connected between the anode side of the variable capacitance diode VD10 and the crystal resonator X1, and an anode side of the variable capacitance diode VD10 and the GND Connected between the resistor R20, the variable capacitance diode VD20 having the cathode side connected to the cathode side of the variable capacitance diode VD10, and the anode side of the variable capacitance diode VD20 and the anode side of the variable capacitance diode VD20. Capacitor C10 and variable capacitance diode VD2 It is comprised by the parallel circuit which consists of resistance R30 and coil L10 which are connected in parallel between the anode side of 0 and GND.
That is, as compared with the frequency variable circuit 200 shown as the conventional example, the frequency variable circuit 300 includes a position of the parallel circuit including the capacitor C20 and the capacitance variable capacitor VC10, and a position of the parallel circuit including the resistor R30 and the coil L10. It becomes the composition which replaced.

The operation of the voltage controlled crystal oscillator shown in this figure is the same as that shown in the above-described conventional example. When a voltage control signal is applied to the V _CONT terminal, the oscillation frequency changes according to the voltage level. It works as follows.

FIG. 2 shows a circuit configuration example of the voltage controlled crystal oscillator shown in FIG. 1 described above, when 50.000 MHz is set to the center frequency f ₀ and the control voltage is made variable in the range of ₀ to 3.0V ( It is a graph which shows the frequency variable characteristic example of normal temperature), and a vertical axis | shaft shows frequency variation (ppm) and a horizontal axis shows control voltage (V). The broken line in the figure shows a reference of the minimum frequency variable width (Lower Limit) of a certain standard, and has a slope of 90 ppm / V.
The frequency variable characteristic in the frequency variable circuit 300 indicated by the solid line has an average inclination of about 120 ppm / V, and a frequency variable range having a sufficient margin can be obtained even in consideration of temperature characteristics and component variations. Is done.

  As described above, since the capacitive elements (capacitor C20 and variable capacitance type capacitor CV10) functioning as load capacitances are provided at positions different from the reference potential, they are less susceptible to stray capacitance and have a wide frequency range. A variable width can be secured.

  FIG. 3 is a circuit diagram showing a second embodiment of the voltage controlled piezoelectric oscillator according to the present invention. The voltage controlled crystal oscillator shown in this example roughly includes a crystal resonator X1, an oscillation circuit 100, and a frequency variable circuit 400.

The frequency variable circuit 400 shown in this figure has a configuration in which the position of the crystal resonator X1 and the position of the parallel circuit including the capacitor C20 and the variable capacitance capacitor VC10 are interchanged as compared with the frequency variable circuit 300 described above. equal.
That is, the resistor R10 connected to the V _CONT terminal to which the control voltage is input, the variable capacitance diode VD10 having the cathode connected to the other end of the resistor R10, and the crystal resonator X1 connected to the anode of the variable capacitance diode VD10. A parallel circuit composed of a capacitor C20 and a variable capacitance capacitor VC10 connected to the other end of the capacitor, a resistor R20 connected between the anode side of the variable capacitance diode VD10 and GND, and a cathode on the cathode side of the variable capacitance diode VD10. Are connected in parallel between the anode of the variable capacitance diode VD20, the capacitor C10 connected between the anode side of the variable capacitance diode VD20 and the anode side of the variable capacitance diode VD20, and GND. Resistor R30 and coil L10 connected to It is comprised by the parallel circuit which consists of.

The operation of the voltage controlled crystal oscillator shown in this figure is the same as that shown in the above-described conventional example. When a voltage control signal is applied to the V _CONT terminal, the oscillation frequency changes according to the voltage level. It works as follows.

FIG. 4 shows a circuit configuration example of the voltage controlled crystal oscillator shown in FIG. 3 described above when 50.000 MHz is set as the center frequency f ₀ and the control voltage is made variable in the range of ₀ to 3.0 V ( It is a graph which shows the frequency variable characteristic example of normal temperature), and a vertical axis | shaft shows frequency variation (ppm) and a horizontal axis shows control voltage (V). The broken line in the figure shows a reference of the minimum frequency variable width (Lower Limit) of a certain standard, and has a slope of 90 ppm / V.
The frequency variable characteristic in the frequency variable circuit 400 indicated by the solid line has an average slope of about 153 ppm / V, and a frequency variable range having a sufficient margin can be obtained even when temperature characteristics and component variations are taken into account. Is done.

  Thus, by providing the capacitive elements (capacitor C20 and variable capacitance type capacitor CV10) functioning as load capacitances at positions different from the reference potential and on the oscillation transistor side as seen from the crystal resonator, In addition to being less susceptible to stray capacitance, a wider frequency variable width can be secured.

  FIG. 5 is a circuit diagram showing a third embodiment of the voltage controlled piezoelectric oscillator according to the present invention. The voltage controlled crystal oscillator shown in this example is roughly divided into a crystal resonator X1, an oscillation circuit 100, and a frequency variable circuit 500.

Compared with the frequency variable circuit 400 described above, the frequency variable circuit 500 shown in this figure further includes a parallel circuit including a resistor R30 and a coil L10 between the anode side of the variable capacitance diode VD10 and the crystal unit X1. Corresponds to the moved configuration.
That is, the resistor R10 connected to the V _CONT terminal to which the control voltage is input, the variable capacitance diode VD10 having the cathode connected to the other end of the resistor R10, the anode side of the variable capacitance diode VD10, and the crystal resonator X1 Between the parallel circuit composed of the inserted resistor R30 and the coil L10, the parallel circuit composed of the capacitor C20 and the variable capacitance capacitor VC10 connected to the other end of the crystal resonator X1, and the anode side of the variable capacitance diode VD10 and GND A resistor R20 connected to the cathode, a variable capacitance diode VD20 having a cathode connected to the cathode side of the variable capacitance diode VD10, and a capacitor connected between the anode side of the variable capacitance diode VD10 and the anode side of the variable capacitance diode VD20. C10 and the variable capacitance diode VD20 The resistor R40 is inserted between the node side and GND.

The operation of the voltage controlled crystal oscillator shown in this figure is the same as that shown in the above-described conventional example. When a voltage control signal is applied to the V _CONT terminal, the oscillation frequency changes according to the voltage level. It works as follows.

FIG. 6 shows a circuit configuration example of the voltage controlled crystal oscillator shown in FIG. 5 described above when 50.000 MHz is set as the center frequency f ₀ and the control voltage is made variable in the range of ₀ to 3.0V ( It is a graph which shows the frequency variable characteristic example of normal temperature), and a vertical axis | shaft shows frequency variation (ppm) and a horizontal axis shows control voltage (V). The broken line in the figure shows a reference of the minimum frequency variable width (Lower Limit) of a certain standard, and has a slope of 90 ppm / V.
The frequency variable characteristic in the frequency variable circuit 500 indicated by the solid line has an average inclination of about 130 ppm / V, and a frequency variable range having a sufficient margin can be obtained even when temperature characteristics and component variations are taken into account. Is done.

  In this manner, the capacitive reactance circuit (capacitor C20 and variable capacitance capacitor CV10) that functions as a load capacitance is provided at a position different from the reference potential and on the oscillation transistor side when viewed from the crystal resonator. In addition, since the dielectric reactance circuit (resistor R30 and coil 10) is also provided at a position different from the reference potential, it is less susceptible to stray capacitance and a wide variable frequency range can be secured.

  If the voltage controlled piezoelectric oscillator having a frequency variable circuit as in the configuration example of the present invention described above is used, there is a stray capacitance between the contact (signal wiring pattern) between each electronic component and the reference potential (GND) wiring. Even if it occurs, the reduction of the frequency variable width due to the influence is suppressed. In addition to the circuit configuration of the present invention, if the structure of the above cited reference 1 is applied, the influence of the stray capacitance on the oscillation frequency can be extremely reduced.

The correspondence between the configuration shown in the above-described embodiment and the configuration shown in the claims is described below.
The first variable capacitance diode according to the claims corresponds to the variable capacitance diode VD10 shown in the embodiment, the second variable capacitance diode corresponds to the variable capacitance diode VD20 shown in the embodiment, and the first resistor is the resistor 10 , The second resistor corresponds to the resistor 20, the third resistor corresponds to the resistor 30, the fourth resistor corresponds to the resistor 40, the first capacitor corresponds to the capacitor 10, and the second resistor The capacitor corresponds to the capacitor 20.

1 is a circuit diagram illustrating a first configuration example of a voltage controlled piezoelectric oscillator according to the present invention. FIG. It is a graph which shows the frequency variable characteristic of the circuit shown in FIG. It is a circuit diagram which shows the 2nd structural example of the voltage control type piezoelectric oscillator which concerns on this invention. It is a graph which shows the frequency variable characteristic of the circuit shown in FIG. It is a circuit diagram which shows the 3rd structural example of the voltage control type piezoelectric oscillator which concerns on this invention. It is a graph which shows the frequency variable characteristic of the circuit shown in FIG. It is a circuit diagram which shows the structural example of the conventional voltage control type piezoelectric oscillator. It is a graph which shows the frequency variable characteristic of the circuit shown in FIG.

Explanation of symbols

Tr1 ... Oscillation transistor IC1 ... C MOS buffer R1, R2 ... Bias resistor R3 ... Current limiting resistor R4 ... Load resistor R5, R6 ... Signal value adjusting resistor R7 ... Output Resistor R10 ... resistor (first resistor)
R20... Resistance (second resistance)
R30: Resistance (third resistance)
R40: Resistance (fourth resistance)
C1, C2: Split capacitors C3: DC element capacitors C4: Bypass capacitors C10: Capacitors (first capacitors)
C20: Capacitor (second capacitor)
L10 ... Coil VD10 ... Varactor diode (first variable capacitance diode)
VD20 ... Varactor diode (second variable capacitance diode)
VC10 ・ ・ ・ Variable capacitor (Capacitance variable capacitor)
X1 ... Crystal resonator (piezoelectric resonator)
DESCRIPTION OF SYMBOLS 100 ... Oscillation circuit 200 ... Frequency variable circuit 300 ... Frequency variable circuit 400 ... Frequency variable circuit 500 ... Frequency variable circuit

Claims (3)

A voltage-controlled piezoelectric oscillator having a piezoelectric vibrator, an oscillation circuit, and a frequency variable circuit,
The frequency variable circuit is:
A first resistor connected to the voltage control terminal; a first variable capacitance diode and a second variable capacitance diode having a cathode connected to the other end of the first resistor; one end is grounded and the other end is the first resistor A second resistor connected to the anode side of the first variable capacitance diode, and a first capacitor inserted between the anode side of the first variable capacitance diode and the anode side of the second variable capacitance diode. Has
Further, a parallel circuit of a coil and a third resistor is inserted between the anode side of the second variable capacitance diode and the ground,
A voltage-controlled piezoelectric oscillator, wherein a parallel circuit of a variable capacitance capacitor and a second capacitor is inserted between the anode side of the first variable capacitance diode and the piezoelectric vibrator. A voltage-controlled piezoelectric oscillator having a piezoelectric vibrator, an oscillation circuit, and a frequency variable circuit,
The frequency variable circuit is:
A first resistor connected to the voltage control terminal; a first variable capacitance diode and a second variable capacitance diode having a cathode connected to the other end of the first resistor; one end is grounded and the other end is the first resistor A second resistor connected to the anode side of the first variable capacitance diode, and a first capacitor inserted between the anode side of the first variable capacitance diode and the anode side of the second variable capacitance diode. Has
Further, a parallel circuit of a coil and a third resistor is inserted between the anode side of the second variable capacitance diode and the ground,
A voltage-controlled piezoelectric oscillator comprising the piezoelectric vibrator inserted between an anode side of the first variable capacitance diode and a parallel circuit of a variable capacitance capacitor and a second capacitor. A voltage-controlled piezoelectric oscillator having a piezoelectric vibrator, an oscillation circuit, and a frequency variable circuit,
The frequency variable circuit is:
A first resistor connected to the voltage control terminal; a first variable capacitance diode and a second variable capacitance diode having a cathode connected to the other end of the first resistor; one end is grounded and the other end is the first resistor A second resistor connected to the anode side of the first variable capacitance diode; a first capacitor inserted between the anode side of the first variable capacitance diode and the anode side of the second variable capacitance diode; A fourth resistor inserted between the anode side of the second variable capacitance diode and the ground,
Further, a parallel circuit of a coil and a third resistor is inserted between the anode side of the first variable capacitance diode and the piezoelectric vibrator,
A voltage controlled piezoelectric oscillator comprising a parallel circuit of a variable capacitance capacitor and a second capacitor connected to the other end of the piezoelectric vibrator.

Images