JP2002009548A - Piezoelectric oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric oscillator with high accuracy that can simply avoid spurious radiation even when employing a piezoelectric vibrator where a design method to avoid the spurious radiation is not established. SOLUTION: The piezoelectric oscillator 10 drives an AT-cut crystal vibrator X by a low power of 10 μW or over and 150 μW or below and more preferably by 100 μW or below. In this case, a feedback amplifier circuit employs a bipolar transistor (Q1) so as to be easily driven by the low power.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric oscillator, and more particularly, to a 30 MHz oscillator using an AT-cut crystal resonator.
The present invention relates to a piezoelectric oscillator in a band of about 50 MHz.

[0002]

2. Description of the Related Art Conventionally, for example, an AT-cut crystal resonator is used for a piezoelectric oscillator having an oscillation frequency of several MHz or more. Here, the AT-cut crystal resonator is a crystal resonator in a thickness-shear vibration mode, in which the oscillation frequency is determined by the thickness of the AT resonator, and the frequency-temperature characteristic is controlled by the cut angle of the AT resonator. I am a child.

[0003]

By the way, recent ADs
With the advent of high-speed digital transmission technology such as SL (asymmetric digital subscriber line), for oscillators that can oscillate high frequencies of several MHz or more,
High frequency stability and temperature stability are required. However, for example, 35.3 required by ADSL related equipment
Oscillation frequency such as 28 [MHz] is 30MHz to 50M
Since the demand for the piezoelectric oscillator in the Hz band has rapidly increased in recent years, there is a problem that an optimal design method for avoiding spurious due to another vibration mode has not been established yet. Here, the design method is a countermeasure method such as performing an optimal aspect ratio of the vibrator for avoiding spurious and performing convex processing for processing the end face of the vibrator into a lens shape. For this reason, in a piezoelectric oscillator that oscillates at a frequency of several MHz or more, the oscillation frequency greatly changes at a certain temperature due to the influence of spurious noise, and there has been a problem that the accuracy required for communication equipment cannot be satisfied.

Accordingly, an object of the present invention is to provide a high-precision piezoelectric oscillator that can easily avoid spurious even if a piezoelectric vibrator for which a design method for avoiding spurious has not been established is used. .

[0005]

According to a first aspect of the present invention, there is provided a piezoelectric oscillator which oscillates a piezoelectric vibrator having an oscillation frequency of at least several MHz. It is characterized by being driven at 150 μW or less. According to a second aspect of the present invention, in the piezoelectric oscillator according to the first aspect, the piezoelectric vibrator is driven at 100 μW or less.
According to a third aspect of the present invention, in the piezoelectric oscillator according to the first or second aspect, a transistor used for a feedback amplifier circuit of the piezoelectric oscillator is a bipolar transistor. According to a fourth aspect of the present invention, there is provided the first aspect.
The piezoelectric oscillator according to any one of claims 3 to 3,
The piezoelectric vibrator has an oscillation frequency of 30 MHz to 50 M
Hz piezoelectric vibrator is used.
According to a fifth aspect of the present invention, in the piezoelectric oscillator according to any one of the first to fourth aspects, the piezoelectric vibrator may have an A
It is a T-cut quartz resonator. According to a sixth aspect of the present invention, in the piezoelectric oscillator according to any one of the first to fifth aspects, a circuit unit excluding the piezoelectric vibrator is formed of a one-chip IC. According to a seventh aspect of the present invention, in the piezoelectric oscillator according to the sixth aspect, the one-chip IC and the piezoelectric vibrator are housed in one package.

[0006]

Embodiments of the present invention will be described below with reference to the drawings.

(1) Embodiment (1-1) Configuration of Embodiment FIG. 1 is a circuit diagram of a piezoelectric oscillator according to an embodiment of the present invention. In this piezoelectric oscillator 10, the fundamental mode is 4
A Colpitts-type oscillation circuit is configured by connecting a 1-MHz AT-cut crystal resonator X, a phase shift circuit composed of oscillation capacitors C1 and C2, and a bipolar transistor Q1. That is, this piezoelectric oscillator 1
0 indicates that the output signal of the bipolar transistor Q1 is rotated by 360 ° by the phase shift circuit and is fed back to the base terminal of the bipolar transistor Q1, so that the feedback signal always has a gain of 1 or more at the base terminal. , The AT-cut quartz resonator X is excited. The bipolar transistor Q2 is a buffer for driving a load (not shown) connected to the output terminal OUT. In this example, the bipolar transistor Q2 is configured by an emitter follower circuit. This buffer is not limited to the emitter follower circuit.
Needless to say, various types can be used. Resistance R
1 and R2 are bias resistors for setting the base potential of the bipolar transistor Q1, and the resistor Rc is
Collector resistance and resistance Re of the bipolar transistor Q1
Is an emitter resistance of the bipolar transistor Q1, and Vcc is a power supply terminal for inputting driving power for the piezoelectric oscillator 10.

FIG. 2A shows a conventional piezoelectric oscillator 2.
As shown in the logic circuit diagram of FIG. 2, in the conventional piezoelectric oscillator 20, from the viewpoint of low power consumption and high integration, the oscillation circuit is replaced by the CMOS inverters INV1 and INV1 shown in FIG.
In contrast to the general configuration using NV2, the piezoelectric oscillator 10 according to the present embodiment has an oscillation circuit configured using the bipolar transistor Q1 as described above. Hereinafter, the reason why the oscillation circuit is configured using the bipolar transistor Q1 will be described.

First, the inventors changed the drive level of the AT-cut quartz resonator X in various ways, and measured the frequency temperature characteristics thereof. Then, the drive level is set to 10 μW, 75
μW, 100μW, 150μW, 200μW, 250μ
As shown in FIG. 3, the measurement results when W was set to W, it was found that the influence of spurious tends to increase in the AT-cut crystal resonator X with an increase in the drive level. From these measurement results, if the drive level of the AT-cut quartz resonator X is 150 μW or less, the deviation of the frequency temperature characteristic from the ideal characteristic curve (cubic curve) is within 1.5 × 10 ^{-6 in} frequency deviation. It turned out to be practical, even if the variation during mass production was considered. Furthermore, if the drive level is 100 μW or less, the deviation from the ideal characteristic curve (cubic curve) falls within 1.0 × 10 ^{-6 in} frequency deviation, and a high-precision that can satisfy the precision required for communication equipment. It has been found that a piezoelectric oscillator can be obtained. If the drive level is lower than 10 μW, stable oscillation cannot be obtained in mass production.
It is necessary to be 0 μW or more.

However, in the conventional piezoelectric oscillator 20 using the CMOS inverter shown in FIG.
The MOS inverter INV1 itself is originally a logic circuit, and the oscillation signal output from the drain terminal is applied between the power supplies (VDD).
(Between −GND), it is difficult to accurately control the drive level of the AT-cut crystal resonator X, and it is difficult to reduce the drive level from about 200 μW to 150 μW or less. On the other hand, when a bipolar transistor is used for an amplifier, it is suitable for linearly amplifying a small signal since a bipolar transistor is conventionally used for an analog signal amplifier. Therefore, the piezoelectric oscillator 10 according to the present embodiment uses the bipolar transistor Q1 for the oscillation circuit as shown in FIG. 1 in order to drive the AT-cut crystal resonator X simply and reliably at the above-described drive level. It is configured.

As a result, the piezoelectric oscillator 10 according to the present embodiment is designed to avoid spurious by driving the AT-cut quartz resonator X at 10 μW or more and 150 μW or less, more preferably 100 μW or less. Even when a high-frequency AT-cut crystal resonator X for which a technique has not been established is used, spurious can be easily reduced, and the accuracy of an oscillation signal can be improved. In addition, since the piezoelectric oscillator 10 is configured using a bipolar transistor, the drive level can be accurately controlled.

(2) Modification (2-1) First Modification The piezoelectric oscillator of the present invention is not limited to the circuit configuration shown in FIG.
Various modifications are possible. For example, FIG. 4 is an example of a circuit diagram when applied to a cascode oscillation circuit.
FIG. 6 is an example of a circuit diagram in a case where frequency-adjusting capacitive elements (CT1 to CTn) are added, and FIG. 6 is an example of a circuit diagram in a case where the present invention is applied to a voltage controlled oscillator (VCXO).

(2-2) Second Modification In the above-described embodiment, the case where all the transistors used for the piezoelectric oscillator are constituted by bipolar transistors has been described. However, the present invention is not limited to this. The transistor used for the feedback amplification circuit of the circuit may be a bipolar transistor.

(2-3) Third Modification In the above-described embodiment, the case where the present invention is applied to a piezoelectric oscillator having an AT-cut crystal resonator having a fundamental mode of 41 MHz has been described. The present invention can be simplified by applying the present invention to a piezoelectric oscillator having a piezoelectric vibrator such as a crystal vibrator or a ceramic vibrator having an oscillation frequency of at least several MHz because the influence of spurious can be reduced by reducing the drive level of the vibrator It can be widely used as a simple spurious avoidance method.

(2-4) Fourth Modification The piezoelectric oscillator 10 is actually a piezoelectric vibrator X
Components are formed of one-chip IC except 7mm ×
It is housed in one package such as a 5 mm ceramic package or a plastic package. Further, the one-chip IC is manufactured by a bipolar process or a Bi-CMOS process.

[0016]

As described above, the piezoelectric oscillator of the present invention has the following features.
Even if a piezoelectric vibrator for which a design method for avoiding spurious has not been established, spurious can be easily avoided and accuracy can be increased.

[Brief description of the drawings]

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

FIG. 2A is a logic circuit diagram of a conventional piezoelectric oscillator, and FIG. 2B is a diagram showing a configuration of a CMOS inverter.

FIG. 3 is a measurement result of frequency temperature characteristics when a drive level of an AT-cut crystal resonator is changed.

FIG. 4 is a circuit diagram showing another circuit configuration of the piezoelectric oscillator according to the first modification.

FIG. 5 is a circuit diagram showing another circuit configuration of the piezoelectric oscillator according to the first modification.

FIG. 6 is a circuit diagram showing another circuit configuration of the piezoelectric oscillator according to the first modification.

[Explanation of symbols]

 10, 20: Piezoelectric oscillator, X: AT-cut crystal oscillator, C1, C2: Oscillating capacitor, Q1, Q2: Bipolar transistor, R1, R2, Rc, Re: Resistor, INV1, INV2 ... CMOS inverter.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Kinoshita 3-3-5 Yamato, Suwa-shi, Nagano F-term in Seiko Epson Corporation (reference) 5J079 AA04 BA35 BA47 FA14 FA21 GA02 GA03 KA05

Claims (7)

[Claims] 1. A piezoelectric oscillator for oscillating a piezoelectric vibrator having an oscillation frequency of at least several MHz, wherein the piezoelectric vibrator is driven at 10 μW or more and 150 μW or less. 2. The piezoelectric oscillator according to claim 1, wherein the piezoelectric vibrator is driven at 100 μW or less. 3. The piezoelectric oscillator according to claim 1, wherein a transistor used for a feedback amplifier circuit of the piezoelectric oscillator is a bipolar transistor. 4. The piezoelectric oscillator according to claim 1, wherein the piezoelectric vibrator has an oscillation frequency of 30 MHz to 50 MHz.
Hz piezoelectric oscillator is used. 5. The piezoelectric oscillator according to claim 1, wherein said piezoelectric vibrator is an AT-cut quartz crystal vibrator. 6. The piezoelectric oscillator according to claim 1, wherein a circuit unit excluding the piezoelectric vibrator is formed of a one-chip IC. 7. The piezoelectric oscillator according to claim 6, wherein the one-chip IC and the piezoelectric vibrator are housed in one package.