JPH09181561A - Sc cut crystal resonator and crystal oscillator using the resonator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an oscillation output with high purity by simple constitution by forming an SC cut crystal chip, 1st electrodes opposed to the surface and rear plate faces of the chip and a pair of 2nd electrodes formed on one plate face of the chip at a prescribed gap from the 1st electrode. SOLUTION: A crystal chip 1 is obtained by rotating a face rectangular to the Y axis of an artificial quartz crystal around the X axis by about 33 deg., rotating the rotated face around the Z axis from the rotated position by about 22 deg. and cutting out the rotated face like a round plate. The 1st electrodes 2 to be used for vertical field excitation are formed oppositely to the centers of the front and rear plate faces of the chip 1. A pair of 2nd electrodes 3 to be used for parallel field excitation are formed on one plate face at a prescribed gap from the 1st electrode 2. The 2nd electrodes 3 are formed so as to be mutually separated by a gap of 0.03mm or 0.2mm. Consequently sub-vibration can be sufficiently suppressed, and even in the case of using the quartz resonator for a crystal oscillator, stable operation can be executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal oscillator having a vertical electric field excitation electrode and a parallel electric field excitation electrode, and a crystal oscillator using the same.

[0002]

2. Description of the Related Art Recently, attention has been paid to SC-cut crystal oscillators having excellent performances such as stress sensitivity, thermal shock characteristics, and phase noise performance. Such an SC-cut crystal unit rotates about 33 ° about the X axis on the plane perpendicular to the Y axis of the crystal of the crystal, and about 22 ° about the Z axis from this rotated position. The electrodes are formed on the crystal piece cut out from the surface.

Conventionally, there have been SC-cut crystal oscillators in which electrodes for vertical electric field excitation are formed and those in which electrodes for parallel electric field excitation are formed. However, regardless of whether the electric field is excited vertically or in parallel, the SC-cut crystal resonator produces a sub-vibration which is a vibration of the same thickness system as the main vibration. Some of these sub-vibrations exist near the frequency of the main vibration, so they are easily coupled to the main vibration. When an SC-cut crystal oscillator is used in a crystal oscillator, when the main vibration is coupled with the sub-vibration, it causes an abnormal operation such as a jump of the oscillation frequency.

In the design of the SC cut crystal unit,
It was desired to suppress the secondary vibration. As means for suppressing the sub-vibration of the SC cut crystal resonator, for example, a parallel electric field excitation electrode is used instead of the vertical electric field excitation electrode,
It has been considered to perform asymmetric bevel processing on the crystal piece. However, the former means requires a special oscillation circuit because the equivalent resistance of the crystal oscillator becomes large, and the latter means has a problem that the sub-vibration cannot be sufficiently suppressed.

Therefore, in the crystal oscillator using the SC cut crystal oscillator, a narrow band filter is used to filter and output the oscillation output so that only the oscillation output of the main vibration is passed. . However, in such a device, an expensive narrow band filter is required, and it is necessary to match the oscillation frequency of the SC-cut crystal unit with the pass frequency of the filter, which easily causes deterioration of the frequency aging characteristics. There was a problem.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances and is capable of sufficiently suppressing secondary vibrations, operates stably even when used in a crystal oscillator, and has high purity. It is an object of the present invention to provide an SC-cut crystal oscillator capable of obtaining an oscillation output with a simple structure and a crystal oscillator using the same.

[0007]

According to the present invention, there is provided an SC-cut crystal piece, a first electrode formed to face the front and back plate surfaces of the crystal piece, and a first plate surface of the crystal piece. The present invention is characterized by an SC-cut crystal resonator including a pair of second electrodes formed with a predetermined gap with respect to one electrode.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to a plan view of electrodes formed on a crystal blank shown in FIG. In the figure, reference numeral 1 is a crystal piece, which is a surface rotated about 33 ° about the X-axis about the plane orthogonal to the Y-axis of the crystal of artificial quartz, and about 22 ° about the Z-axis from this rotated position. It is a round plate cut out from.

Then, a first electrode 2 used for vertical electric field excitation is formed facing the center of the front and back plate surfaces of the crystal blank 1. In addition, a pair of second electrodes 3 used for parallel electric field excitation are formed on one plate surface with a predetermined gap in the first electrodes 2. The second electrodes 3 are connected to each other, for example 0.03.
It is formed with a gap of mm to 0.2 mm.

FIG. 2 shows a first electrode 2 used for vertical electric field excitation.
When a signal with a voltage of 0 dBm is input to, the size of the gap between the second electrodes 3 used for parallel electric field excitation, the B mode that is the secondary vibration output from the second electrode 3, and the C that is the main vibration It is a graph which shows the voltage level of the signal of a mode.
The crystal unit used here is a circular crystal unit having a diameter of 14 mm and a 5 MHz SC cut with a third overtone.

As is clear from this graph, the output in the B mode has a substantially constant value, but the output in the C mode is the second value.
The level rises as the gap between the electrodes 3 of N becomes narrower. That is, the narrower the distance between the second electrodes 3, the larger the output voltage difference between the B and C modes. For example, when the distance between the second electrodes 3 is narrowed to 0.03 mm, the C-mode output of the main vibration becomes significantly large, and a large level difference of 45 dB or more with respect to the B-mode output voltage of the secondary vibration. It is possible to sufficiently suppress the secondary vibration.

The distance between the second electrodes 3 is set to 0.2.
When it is widened to mm, the level difference between the B and C modes approaches 20 dB, and when the gap is further extended, the secondary vibration cannot be suppressed sufficiently. Also, if the size of the gap between the second electrodes 3 is made narrower than 0.03 mm, both electrodes may be short-circuited. Therefore, the distance between the second electrodes 3 is preferably 0.03 mm to 0.2 mm.

Further, the first electrode 2 and the second electrode 3 are formed with a gap of, for example, 0.05 mm to 0.1 mm. The reason for defining the gap between the first electrode 2 and the second electrode 3 in this way is that if the gap is narrower than 0.05 mm, both electrodes may be short-circuited, and the gap is 0.1 m.
This is because if it is wider than m, the equivalent resistance becomes too large and it becomes difficult to use. The graph shown in FIG. 3 shows changes in the equivalent resistance with respect to the size of the gap between the first electrode 2 and the second electrode 3. That is, it is shown that the narrower the gap, the smaller the equivalent resistance, and the larger the gap, the larger the equivalent resistance. If the gap between both electrodes is larger than 0.1 mm, the equivalent resistance will be 18
Since it exceeds 00Ω, it is not practically preferable.

The table shown in FIG. 4 shows the equivalent resistance of the main vibration and the sub vibration to the size of the gap between the first electrode 2 and the second electrode 3. That is, the equivalent resistance of the sub-vibration is infinite regardless of the size of the gap, whereas the equivalent resistance of the main vibration tends to be substantially proportional to the size of the gap. The equivalent resistance also tends to decrease.

FIG. 5 shows the first and second embodiments described in the above embodiment.
FIG. 6 is a circuit diagram of a crystal oscillator using an SC-cut crystal resonator having the electrodes of FIG. Reference numeral 11 in the drawing is an SC-cut crystal resonator having a first electrode 11a and a second electrode 11b. 12 is an active circuit, which uses an inverting amplifier in this case. The first electrode 11a of the crystal oscillator 11 is connected to the input and output of the inverting amplifier 12, respectively. A feedback resistor 13 is provided between the input and output of the inverting amplifier 12.
And a phase control capacitor 14 is connected between the input and output and the ground potential. Then, the second electrodes 11b are connected to the differential inputs of the differential amplifier 15, respectively, and the oscillation output is obtained from the output.

In this way, an oscillation circuit can be constructed by connecting the inverting amplifier 12 which is an active circuit to the first electrode 11a. The oscillation output is output from the second electrode 11b. And the first and second electrodes 1
1a and 11b are provided on the plate surface of the crystal blank 1 so as to be electrically insulated from each other. Therefore, an electric signal does not flow directly from the first electrode 2 to the second electrode 3,
It is only coupled through mechanical vibration. Therefore, it is possible to obtain an oscillation output with extremely high purity and little phase noise from the second electrode 11b.

Conventionally, when such a high-purity oscillation output is required, the output of the oscillation circuit is output via a crystal filter having a narrow band. However, such a device has a problem that the number of components is increased and the cost is increased because a narrow band crystal filter or the like is required, and the aging characteristic of the oscillation frequency is deteriorated due to a change with time of the filter. On the other hand, in the crystal oscillator of the above-mentioned embodiment, it is possible to obtain a high-purity oscillation output without using an expensive narrow band filter or the like. Further, it is possible to suppress the sub-vibration at a frequency near the main vibration of the crystal oscillator, and it is possible to further improve the purity of the oscillation output.
And since the number of parts can be reduced, the configuration becomes simple,
Cost can be reduced.

The electrical characteristics of the crystal unit having only a pair of electrodes are, for example, IEC pub. The measurement is performed by the measurement method represented by 444. However, the electrical characteristics of the SC-cut crystal unit having the first and second electrodes as described in the above embodiment cannot be measured by the same measuring method as that of the crystal unit having only a pair of electrodes. . The reason for this is that in the case of a crystal oscillator having two types of excitation electrodes, it becomes a four-terminal circuit with two terminals on the input side and two terminals on the output side, and the measurement method of the two-terminal circuit with a pair of electrodes formed is applied as is. I can't.

In such a case, for example, as shown in FIG. 6, the control signal output terminal of the network analyzer 21 is impedance-matched and connected to the vertical electric field excitation electrode 11a of the crystal resonator 11 for excitation. Then, the parallel electric field excitation electrode 11b of the crystal resonator 11 is connected to the input terminal of the network analyzer 21 by impedance matching.
Then, by operating the network analyzer 21, it is possible to measure the equivalent circuit constant and the secondary vibration of the crystal unit.

The table shown in FIG. 7 shows the 5M used in the above embodiment.
It shows the result of measuring the vibration characteristics of 20 crystal oscillators of SC cut of Hz. From these results, the average Q value is 1514300, R1 is 2151Ω, and C1 is 97.
72fF and L1 were 10.37mH.

[0021]

As described in detail above, according to the present invention,
It is possible to provide an SC-cut crystal oscillator capable of sufficiently suppressing secondary vibration and capable of operating stably even when used in a crystal oscillator, and a crystal oscillator using the same.

[Brief description of the drawings]

FIG. 1 is a plan view showing an arrangement of electrodes of a crystal resonator according to an embodiment of the present invention.

FIG. 2 is a graph showing changes in output voltage in B and C modes with respect to a gap between parallel electric field excitation electrodes.

FIG. 3 is a graph showing a change in equivalent resistance with respect to a gap between a vertical electric field excitation electrode and a parallel electric field excitation electrode.

FIG. 4 is a table showing changes in equivalent resistance of main vibration and sub vibration with respect to a gap between a vertical electric field excitation electrode and a parallel electric field excitation electrode.

FIG. 5 is a circuit diagram of a crystal oscillator using the crystal resonator of the present invention.

FIG. 6 is a block diagram for measuring the electrical characteristics of the crystal unit of the present invention.

7 is an example of electrical characteristics of the crystal resonator of the present invention measured by the measuring method shown in FIG.

[Explanation of symbols]

 1 ·· Quartz piece 2 ·· First electrode 3 ·· Second electrode 11 ·· Crystal oscillator 11a ·· First electrode 11b ·· Second electrode 12 ·· Active circuit 13 · · Feedback resistor 14 ..Phase control capacitors 15 ..Differential amplifier 20 ..Network analyzer

Claims (5)

[Claims] 1. An SC-cut crystal piece, a first electrode formed facing the front and back plate surfaces of the crystal piece, and a predetermined gap from the first electrode on one plate surface of the crystal piece. An SC-cut crystal resonator, comprising: a pair of second electrodes that are formed by existing. 2. The SC-cut crystal resonator according to claim 1, wherein the first electrode is used for vertical electric field excitation and the second electrode is used for parallel electric field excitation. 3. The device according to claim 1, wherein the gap between the first electrode and the second electrode is 0.05 mm to 0.1 m.
SC cut crystal unit characterized by m. 4. The crystal oscillator of SC cut according to claim 1, wherein the second electrodes are formed at intervals of 0.03 mm to 0.2 mm. 5. A first electrode formed facing the front and back surfaces of an SC-cut crystal piece is connected to an active circuit to oscillate,
An SC cut, characterized in that an oscillation output derived from a pair of second electrodes formed on the one plate surface of the crystal piece from the first electrode with a predetermined gap therebetween is output via a differential amplifier. Crystal oscillator using the above crystal oscillator.