JPH0326663Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a piezoelectric oscillation circuit for a logic IC that is capable of oscillating higher-order modes of a piezoelectric vibrator.

[Conventional technology]

As an oscillation circuit using a crystal resonator, which is particularly commonly used among piezoelectric resonators, those using a CMOS IC inverter are widely used because of their low power consumption. Figure 3 shows CMOS
This is a general configuration of an oscillation circuit.

An amplifier is formed by connecting a DC feedback resistor 12 to an inverter 11 of the CMOS IC, and an AC signal feedback circuit is formed by a crystal oscillator 13 and load capacitors 34 and 15, and a crystal oscillation circuit is formed as a whole. There is. Note that the inverter 16 is a buffer and also serves as a waveform generator.

The crystal resonator 13 generally utilizes the thickness shear vibration of an AT plate, which includes odd-order higher-order mode vibrations in addition to the fundamental wave. However, the oscillation circuit shown in FIG. 3 oscillates at the lowest frequency fundamental wave because the feedback circuit is a low-pass filter.

On the other hand, when this crystal oscillation circuit is used in a calculator or a watch, it is not necessary to increase the operating speed so much, but when used in a microcomputer, etc., a fast operating speed is desired. This requires increasing the oscillation frequency. However, in order to raise the fundamental frequency of a crystal oscillator, there is a limit in processing due to the need to reduce the thickness, and it would be convenient if the higher-order mode vibration of the crystal oscillator could be utilized. However, in order to oscillate a higher-order mode with the piezoelectric oscillation circuit of this CMOS IC, it is necessary to provide a resonant circuit with L, C, etc., which increases the number of parts and is inconvenient when downsizing.

[Problems to be solved by the invention] The present invention provides a piezoelectric oscillation circuit that uses a logic IC inverter and enables a piezoelectric vibrator to oscillate in a higher order mode.

[Structure of the present invention]

In order to achieve the purpose of this invention, this invention uses logic.
In a piezoelectric oscillator circuit that oscillates a piezoelectric vibrator in a high-order mode using an IC, there is a high coupling vibration between the input and ground and/or output and ground of the logic IC with a larger electromechanical coupling coefficient than that of the piezoelectric vibrator. This is a piezoelectric oscillator circuit with a configuration in which two terminals are connected.

[Function and Examples]

FIG. 1a shows a crystal oscillation circuit showing an embodiment of the present invention. This is the logic IC in Figure 3.
In the oscillation circuit of CMOS IC, inverter 1
Load capacitor 34 between the input of 1 and ground
is replaced with a high-coupling resonator 14 having a larger electromechanical coupling coefficient than the crystal resonator 13.
As the high-coupling resonator 14, lithium niobate,
A vibrator made from materials such as lithium tantalate or piezoelectric ceramic, and has a large electromechanical coupling coefficient, so it has a large piezoelectric effect.

FIG. 1b shows the crystal oscillator 13 and the high-coupling oscillator 1.
4, the fundamental wave frequency of the crystal resonator 13 is f ₀ and the third-order resonance frequency is 3f ₀ .
On the other hand, the high coupling oscillator 14 also has a fundamental frequency
f ₁ , and the third-order resonance frequency is 3f ₁ . Note that the frequencies of the fundamental waves of the crystal resonator 13 and the high-coupling resonator 14 are approximately matched.

A crystal resonator has a higher Q and a lower electromechanical coupling coefficient than resonators made of piezoelectric ceramics, lithium tantalate, or the like. When these vibrators are provided with excitation electrodes and the electrodes are made thicker for frequency adjustment, the frequency decreases due to piezoelectric reaction. This is particularly noticeable in a vibrator with a large coupling coefficient than in a vibrator with a low coupling coefficient. The fundamental wave has a greater influence than the higher-order mode vibration and decreases in inverse proportion to the square of the resonance order. As a load is applied to the electrodes of the highly coupled resonator, the higher-order mode vibration frequency decreases little, but the frequency of the fundamental wave decreases a lot, and as shown in Figure 1b, it overlaps with the fundamental wave f ₀ of the crystal resonator. The frequency difference between the fundamental wave f ₁ of the piezoelectric ceramic contour-coupled resonator and the overtone frequency 3f ₁ (3f ₁ − f ₁ ) is wider than the frequency difference between the tone frequency 3f ₀ (3f ₀ − f ₀ ). Become. That is, if the fundamental wave frequencies of the crystal resonator and the high-coupling resonator are made to match, the resonance frequency of the higher-order mode will be higher in the high-coupling resonator than in the crystal resonator. When this is utilized in the oscillation circuit of the present invention, the fundamental wave is grounded through the high-order coupled oscillator,
Only higher-order mode vibrations oscillate, and higher-order modes have different frequencies, so they have no effect. In addition, a crystal resonator has a high Q, so the interval between the resonance point and anti-resonance point of the fundamental wave is narrow, but a piezoelectric ceramic equal-height coupling resonator has a low Q, and the resonance point and anti-resonance point of the fundamental wave are wide, making it difficult for filters to When considering a highly coupled resonator as Since the anti-resonance point is wide, it is easy to match the frequency.

Since the high-coupling resonator 14 is connected between the input of the inverter 11 and the ground instead of the load capacitor, the high-coupling resonator 14 acts as a trap, and the third-order resonance frequency of the crystal resonator 13 increases. It functions simply as a capacitor. Therefore, the fundamental frequency of the crystal resonator 13 is suppressed, and it stably oscillates at the third-order resonance frequency.

FIGS. 2a and 2b are oscillation circuit diagrams showing another embodiment. Figure 2a shows a CMOS IC oscillation circuit in which a high-coupling resonator 14 with a larger electromechanical coupling coefficient than the crystal resonator 13 is installed between the output of the inverter 11 and the ground. is similar to FIG. 1a. Furthermore, FIG. 2b shows a configuration in which high-coupling resonators 14 are provided both between the input and the ground of the inverter 11 and between the output and the ground, which also has the same effect as in FIG. 1a.

In this invention, a crystal resonator is used as a piezoelectric resonator, but if the one with a lower electromechanical coupling coefficient is used as an oscillator and the one with a higher electromechanical coupling coefficient is used as a resonator, any combination of piezoelectric resonators can be used. You can. In addition, although CMOS has been given as an example of the logic IC, it is of course possible to use TTL or the like.

[Effects of this invention]

The present invention is a piezoelectric oscillator circuit that uses a logic IC to oscillate in a higher-order mode of a piezoelectric resonator, and a resonator with higher coupling than the piezoelectric resonator is installed between the logic IC's input and ground and/or between the output and ground. It is something that
This made it possible to easily obtain higher-order mode oscillations and increase the operating speed, making it possible to use it in memory, microcontrollers, etc. It also eliminates the need for resonant circuits such as inductors and capacitors used in conventional high-order mode oscillators, reducing the number of parts and contributing to miniaturization.

[Brief explanation of drawings]

Figure 1a and Figures 2a and b are logic ICs of the present invention.
piezoelectric oscillation circuit. FIG. 1b is a diagram showing the state of the oscillation frequency. Figure 3 shows the piezoelectric oscillator circuit of a general logic IC. 11...Logic IC, 13...Piezoelectric vibrator, 14
...Highly coupled oscillator.

Claims (1)

[Claims for Utility Model Registration] (1) In a piezoelectric oscillator circuit that uses a logic IC to oscillate a piezoelectric vibrator in a higher-order mode, the logic IC
A high-coupling resonator whose fundamental wave frequency matches that of the piezoelectric resonator and whose electromechanical coupling coefficient is larger than that of the piezoelectric resonator is connected between the input and ground and/or between the output and the ground side of the piezoelectric resonator. Piezoelectric oscillation circuit. (2) The piezoelectric oscillator circuit according to claim 1, wherein the piezoelectric vibrator is a crystal vibrator.