JP2002261546A - Piezoelectric oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a means of suppressing abnormal oscillations which occur at the side of frequency lower than the specified frequency of a Colpitts piezoelectric oscillator. SOLUTION: The Colpitts piezoelectric oscillator is composed of transistors, a piezoelectric vibrator, capacitances and resistors. A serial circuit composed of the piezoelectric vibrator and a capacitance C3 and a serial circuit composed of capacitances C1 and C2 are connected in parallel. A capacitance C0 is connected to the circuit in series, and the circuit is interposed between the base and the ground of the transistor. A resistor R1 is interposed between the emitter and the ground of the transistor, and the middle point of the capacitances C1 and C2 is connected to the emitter of the transistor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric oscillator,
In particular, the present invention relates to a piezoelectric oscillator that suppresses abnormal oscillation on the low frequency side.

[0002]

2. Description of the Related Art In recent years, piezoelectric oscillators have high frequency stability,
Due to its small size, light weight, low price, etc., it is used in all fields of electronic equipment. Particularly, a crystal oscillator using an AT-cut crystal resonator as a piezoelectric element has excellent frequency temperature characteristics and aging characteristics, and is used as a reference oscillator of a mobile phone. The crystal oscillation circuit shown in FIG. 7 is a conventional Colpitts type crystal oscillation circuit which is widely and generally used.
As is well known, a Colpitts oscillation circuit is an oscillation circuit formed by connecting a crystal oscillator as an inductive element between a collector and a base and connecting a capacitive element between a base and an emitter and between a collector and an emitter. The actual Colpitts-type crystal oscillator has a circuit configuration as shown in FIG. 7A. As an inductive element between the collector and base of the transistor TR1, a crystal resonator X and a capacitor C are connected between the base and ground.
3 (C3 is for fine adjustment of the oscillation frequency) is inserted in series. Since the power supply Vcc and the ground GND are short-circuited in terms of high frequency, an inductive element mainly composed of a crystal oscillator is inserted between the collector and the base. Further, a series connection element of the capacitors C1 and C2 is connected between the base and the ground, and a resistor R1 is inserted between the emitter and the ground to connect the midpoint of the capacitors C1 and C2 to the emitter. The transistor TR1 has a configuration in which a base current controlling resistor R2 is connected to the base of the transistor TR1. Here, the crystal resonator is used as the piezoelectric resonator because the Q value is large and the frequency stability with respect to temperature is excellent.

[0003] A Colpitts crystal oscillator shown in FIG.
Is a circuit configuration in which amplifiers (buffers) with a common base are connected in cascade. The resistors R5 and R6 are bleeder resistors of the transistors, and the capacitors C5, C6, C
Reference numeral 7 denotes a bypass capacitor, and a capacitance C4 denotes an output capacitor.

In such a Colpitts-type crystal oscillation circuit, the degree of amplification, that is, the so-called negative resistance R (Ω), as viewed from the circuit side from both ends of the crystal oscillator X (the crystal oscillator and the variable capacitor C3 in FIG. 7). Is the square of the capacitance C1, C2 and the frequency (ω ² )
It is known to be inversely proportional to and to the collector current. That is, as shown in FIG. 8, as the frequency increases, the absolute value of the negative resistance R (Ω) increases, reaches a peak value at a predetermined frequency, and thereafter decreases as the frequency increases.
The curve in FIG. 8 indicates that the resistance R1 in FIG.
Each of the resistors R2, R4, and R6 is 10 kΩ, and the resistors R3 and R
5 is 15 kΩ, 100 Ω, respectively, capacitances C1, C2, C3 are 200pF, 140pF, 20pF, capacitances C4, C5, C
6 and C7 are each 0.1 μF, transistors TR1 and T
It is a negative resistance curve when R2 is set to 2SC3732 and the power supply voltage Vcc is set to 5 Vdc. The curve shown in FIG. 9 is a load capacitance curve on the circuit side when the circuit side is viewed from the crystal unit X. After reaching a local minimum with increasing frequency, it increases monotonically with increasing frequency.

If the oscillation frequency of the crystal oscillator shown in FIG. 7B is set to about 10 MHz from the curves of FIGS. 8 and 9, the negative resistance is about -400Ω and the load capacitance is about 60 pF as shown in FIG.
It turns out that it becomes. As described above, the oscillation frequency is generally set to a frequency having a large capacitance on the circuit side and a small gain variation and a frequency higher than a value at which the negative resistance exhibits a peak.

[0006]

However, in the conventional Colpitts-type crystal oscillator, as is apparent from FIG. 8, the frequency range where the absolute value of the negative resistance is large, that is, the gain is large, is located on the low frequency side of the oscillation frequency. However, if spurious components exist on the lower side of a predetermined resonance frequency in the crystal resonator incorporated in the oscillation circuit, there is a problem that oscillation may occur due to the spurious components. The present invention has been made to solve the above problem, and has as its object to provide a piezoelectric oscillator in which spurious vibration is suppressed.

[0007]

According to a first aspect of the present invention, there is provided a piezoelectric oscillator according to the present invention, comprising: a series connection circuit of a piezoelectric vibrator and a capacitor C3;
2 in parallel with a circuit connected in series with a capacitor C0.
Is inserted between the base and the ground of the transistor, and the resistor R1 is connected between the emitter and the ground of the transistor.
And the midpoint of the series connection of the capacitors C1 and C2 and the emitter of the transistor are connected. According to a second aspect of the present invention, in addition to the first aspect, a first parallel resonance circuit is inserted and connected between the capacitor C0 and the base of the transistor.
According to a third aspect of the present invention, in addition to the first or second aspect, a second parallel circuit configured to connect an inductance to the resistor R1 in series and connect the series circuit and the capacitor C2 in parallel is provided. It is characterized by having.
According to a fourth aspect of the present invention, in addition to the second or third aspect, the piezoelectric vibrator is an SC-cut crystal vibrator,
The parallel resonance frequency of the first parallel resonance circuit is substantially equal to the B-mode frequency of the piezoelectric vibrator. According to a fifth aspect of the present invention, in addition to the third or fourth aspect, the piezoelectric vibrator is an SC-cut quartz crystal vibrator, and the parallel resonance frequency of the second parallel resonance circuit is the same as that of the piezoelectric vibrator. 5. The Colpitts type piezoelectric oscillator according to claim 3, wherein the oscillator substantially coincides with a mode frequency.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the drawings. FIGS. 1A and 1B are diagrams showing an example of a circuit configuration of a crystal oscillator according to the present invention.
In the Colpitts type crystal oscillator shown in FIG. 1A, a capacitor C0 is connected in series to a circuit in which a series connection circuit of a crystal resonator X and a capacitor C3 and a series connection circuit of capacitors C1 and C2 are connected in parallel. The circuit is inserted between the base of the transistor TR1 and the ground, the resistor R1 is inserted between the emitter of the transistor TR1 and the ground, and the midpoint of the capacitors C1 and C2 is connected to the emitter of the transistor TR1. further,
A base current control resistor R2 is connected to the base of the transistor TR1. FIG. 1B is a diagram showing a practical circuit configuration example of the oscillator according to the present invention. In the Colpitts-type crystal oscillation circuit shown by a broken line α, a grounded base amplifier (buffer) including a transistor TR2 shown by a broken line β ) Has a cascade-connected circuit configuration.

A feature of the present invention is that a transistor in which a capacitor C0 is connected in series to a circuit in which a series connection circuit including a crystal unit and a capacitor C3 and a series connection circuit including capacitors C1 and C2 are connected in parallel. It is inserted between the base of TR1 and the ground. That is, the feature is that the capacitance C0 is added. In the Colpitts type crystal oscillation circuit according to the present invention, the amplification seen from both ends of the crystal unit X (the crystal unit and the variable capacitor C3 in FIG. 1), that is, the so-called negative resistance R (Ω) is shown in FIG. As shown in curves B and C of FIG. 2, it can be seen that the absolute value of the negative resistance on the lower frequency side is significantly smaller than the curve A of the conventional circuit. That is,
The change in the absolute value of the negative resistance with respect to the frequency change is small. The negative resistance curve shown in FIG. 2 indicates that in the crystal oscillation circuit shown in FIG.
R4 and R6 are 10 kΩ, and resistors R3 and R5 are each 15 kΩ.
Ω, 100 Ω, and capacitances C1, C2, and C3 are respectively 124 pF, 1
48pF, 20pF, capacitance C4, C5, C6, C7 respectively
0.1 μF, the transistors TR1 and TR2 are set to 2SC3732, the power supply voltage Vcc is set to 5 Vdc, the capacitance C0 is set to 20 pF,
Curves B and C show the case of 62 pF. Curve A is a curve of the negative resistance of the conventional Colpitts type crystal oscillator when the same parameters are used. Curves A and B, C
Compared with the above, the peak of the absolute value of the negative resistance R on the low frequency side becomes smaller, so that the amplification at that frequency becomes smaller, which indicates that the abnormal oscillation phenomenon is unlikely to occur even if spurious is present at the frequency. . Further, the capacitance C0
It is also clear that the negative resistance curve can be freely controlled by selecting the value of.

The curves shown in FIGS. 3B and 3C are load capacitance curves on the circuit side when the circuit side is viewed from the crystal resonator X of the Colpitts type crystal oscillator according to the present invention. Circuit constants use the same parameters as in FIG. 2, and curves B and C are curves when the capacitance C0 is 20 pF and 62 p, respectively. The load capacity curve A of the conventional Colpitts type crystal oscillator was overwritten for comparison. It has been found that the load capacity curve changes more gradually as the frequency increases, as compared with that of the conventional Colpitts type crystal oscillator. The reason that the frequency dependence of the negative resistance becomes smaller is that the oscillation loop signal is input to the base of the oscillation amplifier circuit (TR1) via the capacitor C0, and thus the input level depends on the frequency. Change. That is, since the reactance of the capacitor C0 decreases with an increase in the frequency, the amount of positive feedback in a low frequency region may decrease. Further, by adding the capacitance C0 to the effect of the change in the capacitance Cbe between the base and the emitter of the transistor TR1 by the above operation, an effect of reducing the effect can be estimated. As shown in FIG. 3, the small slope of the load capacitance curve with respect to the frequency fluctuation means that the change in the oscillation frequency is small with respect to the change around the crystal oscillator, for example, the temperature change, and the stability is improved. It represents that it is. In addition, it is possible to control the load capacity curve by selecting the value of the capacity C0, and to make the load capacity curve nearly flat.

A curve C shown in FIG. 4 is a graph showing a frequency deviation of the Colpitts type crystal oscillator according to the present invention with respect to the fluctuation of the power supply voltage Vcc. For comparison, a curve of the power supply voltage Vcc-frequency deviation A of the conventional Colpitts type crystal oscillator is also shown. When the power supply voltage Vcc changes to a larger value, it can be seen that the Colpitts crystal oscillator of the present invention is superior to the conventional Colpitts crystal oscillator.

In the oscillating circuits shown in FIGS. 1A and 1B, instead of connecting the connection point between the capacitors C1 and C2 inserted between the base and the ground of the transistor TR1 and the emitter of the transistor TR1. If a frequency selection circuit, for example, an L or C tuning circuit or an anti-tuning circuit is inserted, S
It can be used for B-mode suppression of a C-cut quartz resonator. FIG. 5 is a circuit diagram of another embodiment of the present invention in which a capacitance C0 is added and the effect of a tuning circuit or an anti-tuning circuit of LC is used. That is, the crystal oscillator 1 shown in FIG. 1 enables B mode suppression in a crystal oscillator using, for example, an SC-cut crystal resonator X. The features of the crystal oscillator 1 shown in FIGS. 6A and 6B are that the capacitor C0 and the transistor TR1 are connected via the parallel circuit 2 of the inductance L1 and the capacitor C8, and the parallel resonance frequency of the parallel circuit 2 (A) is a circuit diagram in the case where a bipolar transistor is used as the oscillation transistor TR1, and FIG. 2 (b) is a circuit diagram in which an FET is used as the oscillation transistor TR1. FIG. 3 is a circuit diagram in the case of using. According to the crystal oscillator 1 having such a configuration, the level of the B-mode frequency signal supplied to the transistor TR1 is suppressed because the parallel circuit 2 has a high impedance at the B-mode frequency, and the negative resistance has a positive polarity. Alternatively, the absolute value is reduced, and as a result, in addition to the function of the capacitor C0 described above, the B-mode oscillation is further suppressed, so that the noise characteristics are excellent. FIG. 6 shows another embodiment of the crystal oscillator according to the present invention. The characteristic of the crystal oscillator 1 shown in the figure is that, like the crystal oscillator shown in FIG. 5, a parallel resonance circuit 2 including a capacitor C8 and an inductance L1 is provided.
The capacitor C0 and the base of the transistor TR1 are connected via a capacitor C2, and a series circuit of an inductance L2 and a resistor R1 is connected in parallel with the capacitor C2. FIG. FIG. 4B shows a circuit diagram in which a bipolar transistor is used for TR1 and an FET is used for the oscillation transistor TR1. Further, the parallel resonance circuit 2 is set so that the parallel resonance frequency substantially matches the B mode frequency of the SC cut crystal resonator X, and the inductance L2, the resistance R1, and the capacitance C2 are set to the C mode frequency of the SC cut crystal resonator X. Are set so that the parallel resonance frequency of the parallel resonance circuit 3 composed of In the crystal oscillator 1 having such a configuration, the B-mode oscillation is extreme-pressured by the parallel resonance circuit 2 and the impedance of the parallel resonance circuit 3 increases at the C-mode frequency. Since this corresponds to the case where the capacitance C2 is reduced, a large negative resistance can be obtained only at the C-mode frequency. .

In the above description, a quartz oscillator is used as the piezoelectric oscillator. However, the present invention is not limited to this, and the present invention is not limited to this, and may be configured using other piezoelectric oscillators such as a langasite oscillator and a ceramic oscillator. Needless to say, the present invention can be applied to the piezoelectric oscillator described above.

[0014]

As described above, the present invention has an excellent effect that abnormal oscillation due to spurious can be suppressed on the lower frequency side than a predetermined oscillation frequency. The invention described in claim 2 is
In addition to the features of claim 1, the present invention is a Colpitts type piezoelectric oscillator having a more practical circuit configuration.

[Brief description of the drawings]

FIG. 1 is a diagram showing a circuit configuration of a Colpitts type piezoelectric oscillator according to the present invention.

FIG. 2 is a diagram showing a negative resistance curve with respect to frequency of the Colpitts type piezoelectric oscillator according to the present invention.

FIG. 3 is a diagram showing a load capacitance curve with respect to a frequency of the Colpitts type piezoelectric oscillator according to the present invention.

FIG. 4 is a diagram showing a frequency change with respect to a power supply voltage fluctuation of the Colpitts type piezoelectric oscillator according to the present invention.

5A and 5B are diagrams showing a circuit configuration of a Colpitts type piezoelectric oscillator according to the present invention.

6A and 6B are diagrams showing a circuit configuration of a Colpitts type piezoelectric oscillator according to the present invention.

FIG. 7 is a diagram showing a circuit configuration of a conventional Colpitts type piezoelectric oscillator.

FIG. 8 is a diagram showing the relationship between the frequency and the negative resistance of a conventional Colpitts type piezoelectric oscillator.

FIG. 9 is a diagram showing the relationship between the frequency and the load capacitance of a conventional Colpitts type piezoelectric oscillator.

[Explanation of symbols]

TR1, TR2 ··· Transistors R1, R2, R3, R4, R5, R6 ··· Resistors C0, C1, C2, C3, C4, C5, C6, C7, C
8. Capacitance L1, L2 inductance X Piezoelectric oscillator Vcc Power supply voltage GND Ground 1 Crystal oscillator, 2 or 3 parallel resonance circuit

Claims (5)

[Claims] 1. A circuit in which a series connection circuit of a piezoelectric vibrator and a capacitor C3 and a series connection circuit of capacitors C1 and C2 are connected in parallel, and a circuit in which a capacitor C0 is connected in series is connected between the base of the transistor and the ground. A resistor R1 is inserted between the emitter of the transistor and the ground, and the capacitors C1, C
2. A Colpitts-type piezoelectric oscillator, wherein a midpoint of the series connection of No. 2 and an emitter of the transistor is connected. 2. A Colpitts-type piezoelectric oscillator according to claim 1, wherein a first parallel resonance circuit is inserted and connected between said capacitor C0 and a base of said transistor. 3. A circuit according to claim 1, further comprising a second parallel circuit configured to connect an inductance to said resistor R1 in series and to connect said series circuit and said capacitor C2 in parallel. The Colpitts type piezoelectric oscillator according to claim 2. 4. The piezoelectric vibrator is an SC-cut quartz vibrator, and a parallel resonance frequency of the first parallel resonance circuit is substantially equal to a B mode frequency of the piezoelectric vibrator. The Colpitts type piezoelectric oscillator according to claim 2 or 3. 5. The piezoelectric vibrator is an SC cut quartz crystal vibrator, and a parallel resonance frequency of the second parallel resonance circuit is substantially equal to a C mode frequency of the piezoelectric vibrator. The Colpitts type piezoelectric oscillator according to claim 3.