JPH0515082B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a frequency signal output device that outputs a stable reference frequency signal using a crystal resonator.

[Prior art]

2. Description of the Related Art Devices that use the resonant frequency of a crystal oscillator as a reference signal are conventionally known.

Since the resonant frequency of a crystal resonator is affected by temperature, conventional equipment requires placing the crystal resonator in a constant temperature bath or using a VCOX (voltage controlled crystal oscillator) or TCXO (temperature controlled crystal oscillator). ) is used.

However, these have the disadvantage that they require means for temperature detection and are complicated in construction.

Also, for example, as disclosed in Japanese Patent Application Laid-open No. 55-163481, using one piezoelectric vibrator,
Constructs first and second self-oscillation loops, obtains temperature information from the difference between two oscillation frequency signals obtained from the two oscillation loops, corrects one frequency signal, and uses a time reference frequency that does not affect temperature. There is a time reference generator configured to obtain a signal.

However, the time reference generator disclosed herein assumes that the piezoelectric vibrator uses fundamental vibration and its harmonic vibration, and the two oscillation frequencies have similar temperature characteristics. Therefore, there was a problem that temperature information could not be obtained accurately.

[Purpose of the invention]

The present invention has been made in view of such prior art, and aims to realize a signal output device that can obtain a stable frequency signal without using a temperature detection means.

[Summary of the invention]

The device according to the present invention includes a tuning fork-shaped crystal resonator, a first self-excited oscillation loop that causes the crystal resonator to vibrate in a bending manner, a second self-excited oscillation loop that causes the crystal resonator to vibrate in a torsional manner, and Input the resonance frequency signals ₁ and ₂ obtained from the two self-excited oscillation loops ( ₁ −
Regarding ₂ ), it is characterized in that it is composed of a control loop that controls the load capacity of the crystal resonator or the temperature of the crystal resonator.

[Explanation of Examples]

FIG. 1 is a block diagram showing an example of a device according to the present invention. In the figure, 1 indicates arms 1a and 1b.
This is a tuning fork-shaped crystal resonator having an excitation electrode that excites the crystal resonator and a detection electrode that detects vibrations (not shown). This crystal resonator 1 has a thickness t of, for example, 0.025 to 0.2 mm.
The length l of both arms 1a and 1b is 2.5 to 20 mm.
(100.t), the width w of both arms 1a and 1b is 0.05 to 0.5
The size is about mm, and the manufacturing of the shape and the formation of each electrode are performed using photolithography and etching techniques. 21 and 22 are filter circuits coupled to the vibration detection electrodes; one filter circuit 21 is a low-pass filter through which the bending vibration frequency ₁ of the crystal resonator 1 passes; It is a band filter that allows the torsional vibration frequency ₂ to pass through. 31, 32
4 is an amplifier that amplifies the frequency signal from each filter circuit 21, 22, and 4 is an adder circuit that adds the signals from each amplifier 31, 32 and outputs this added signal to an excitation electrode.

A loop formed including the low-pass filter circuit 21, the amplifier 31, and the adder circuit 4 constitutes a self-oscillation loop OSC1 that bends the crystal resonator 1,
Low-pass filter circuit 22, amplifier 32, addition circuit 4
The loop formed including the above constitutes a self-oscillation loop OSC2 that causes the crystal resonator 1 to torsionally vibrate.

₅ is a control loop that inputs frequency signals ₁ and ₂ obtained from the two self-oscillation loops OSC1 and OSC2 and controls the load capacity of the crystal resonator 1 according to the difference ( ₁ - ₂ ) between the frequency signals; and ₂ , a load capacitance 52 connected to the crystal resonator 1, and a calculation circuit 51 that calculates the difference signal between
The drive circuit 53 is configured to be changed by a signal from the drive circuit 53.

FIG. 2 is an explanatory diagram of the bending vibration of the crystal resonator 1. The vibration of both arms 1a and 1b of the tuning fork-shaped crystal oscillator 1 as shown by the arrows (the vibration mode is symmetrical vibration) is bending vibration, and its resonance frequency is
₁ can be expressed by equation (1) if each dimension of the vibrator 1 is taken as shown.

However, α: Eigenvalue k: Correction coefficient ρ: Density of the crystal resonator S ₂₂ ′: Value related to the Young's modulus of the crystal resonator S ₄₄ ′: Value related to the torsional rigidity of the crystal resonator FIG. 2 is an explanatory diagram of torsional vibration of the vibrator 1. FIG. Torsional vibration is when the arms 1a and 1b of the tuning fork-shaped vibrator 1 vibrate as shown by the arrows (the vibration mode may be symmetrical or asymmetrical), and its resonance frequency ₂ can be expressed by equation (2). I can do it.

However, β: Eigenvalue λ=w/t S' ₄₄ /S' ₆₆ S' ₆₆ : Value related to torsional rigidity of the crystal resonator n: Order of vibration mode Figure 4 shows the crystal substrate for making the crystal resonator 1. Using the Z plate (Z cut plate) as a reference, we use a plate whose first rotation is within ±10° with respect to the X axis and ±10° with respect to the Y axis, and when this is subjected to flexural vibration. 3 is a diagram showing temperature characteristics at resonance frequency _1. FIG.

In this diagram, the change in resonant frequency ₁ of bending vibration with respect to temperature is small overall, especially at 20°C.
The temperature coefficient α ₁ near normal temperature of ~30°C becomes very small, for example, α ₁ =0.04 ppm/°C ² or so.

Here, if temperature coefficients after the second order are ignored, the resonance frequency ₁ of the bending vibration and the first order temperature coefficient α ₁ of the bending vibration have a relationship with respect to the temperature T as shown in equation (3).

₁ = ₀₁ {1+α ₁ (T-T ₀ )} (3) However, ₀₁ : Frequency of bending vibration at temperature ₀ Also, as is clear from equation (1), ₁ is the shape and dimension w/l, etc. By choosing these to specific values, it is possible to make ₁ correspond to 2 ⁿ , for example 32.768 kHz, at temperature T ₀ .

FIG. 5 is a diagram showing the temperature characteristics of the resonance frequency ₂ when the crystal resonator 1 is subjected to torsional vibration.

In this diagram, the resonance frequency of torsional vibration ₂
The change with respect to temperature changes linearly, and the temperature coefficient α ₂ changes the size and shape of the crystal resonator, for example, t/
When w≒0.4 and l=2.5mm, α ₂ =40ppm/℃
It will be about.

In FIG. 1, a crystal oscillator 1 simultaneously performs bending vibration and torsional vibration through two self-excited oscillation loops OSC1 and OSC2, and receives frequency signals ₁ and ₂ from each self-excited oscillation loop OSC1 and OSC2. Output. Usually, the resonance frequency ₂ of torsional vibration is
higher than the resonance frequency of bending vibration ₁ ( ₂ > ₁ ),
These frequency signals are passed through a low-pass filter circuit 21,
The self-oscillation loops are separated by a bandpass filter circuit 22, and the self-oscillation loops maintain self-oscillation asynchronously with each other.

The control circuit 5 includes self-excited oscillation loops OSC1,
Input frequency signals ₁ and ₂ from OSC2, ₁ - ₂
By performing the following calculation, a temperature-dependent difference signal t is obtained. This difference signal t is the drive circuit 53
is applied, and the drive circuit 53 continuously changes the capacitance of the load capacitor 52 so as to compensate for the drift of the resonance frequencies ₁ and ₂ due to temperature.

Through this kind of operation, the self-oscillation loop OSC
The resonance frequency ₁ of 1 becomes a stable reference frequency signal that is not affected by temperature.

FIG. 6 is a block diagram showing another example of the apparatus according to the present invention. In this embodiment, the crystal resonator 1 is placed in a container 10, and a heater 54 for heating the crystal resonator 1 with the output of a drive circuit 53 is provided. This heater 54
As a result, the crystal resonator 1 is heated in response to changes in the ambient temperature, and the resonant frequency ₁ becomes a stable reference frequency signal that is not affected by temperature.

FIGS. 7 and 8 show examples of forming electrodes provided on the crystal resonator 1, and in each case, a is a perspective view;
b is a sectional view taken along line X-X in figure a.

In each case, opposing electrodes 15, 16 and 17, 18 are formed on both surfaces of both arms of the crystal resonator 1, and are arranged in parallel with each other. As is well known, since crystal is an elastic body and also a piezoelectric body, for example, by applying an excitation signal from the adding circuit 4 between the electrodes 15 and 16, it causes bending vibration and torsional vibration. A voltage signal corresponding to the vibration of the crystal resonator 1 is generated between 17 and 18.

Note that the electrodes may be provided on the side surfaces of each arm 1a, 1b.

[Effects of the present invention]

As described above, according to the present invention, it is possible to realize a device that can obtain a stable reference frequency signal without being affected by ambient temperature without using a temperature detection means.

Further, the present invention is characterized in that the tuning fork-shaped crystal resonator is vibrated in different vibration modes of bending vibration and torsional vibration. This results in
The temperature coefficients of the frequency signals obtained by bending vibration and the frequency signals obtained by torsional vibration are significantly different, resulting in a special effect in that temperature information can be obtained accurately.

Therefore, it is possible to control the load capacitance of the crystal resonator or the temperature of the crystal resonator based on accurate temperature information, and the oscillation loop including the crystal resonator can be directly controlled with accurate temperature information. A reference frequency signal can be obtained.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram showing an example of a device according to the present invention, FIG. 2 is an explanatory diagram of bending vibration of a crystal resonator, and FIG. 3 is an explanatory diagram of torsional vibration of a crystal resonator.
FIG. 4 is a diagram showing the relationship between the resonant frequency ₁ of the bending vibration of the crystal oscillator used in the present invention and temperature, and the fifth is a diagram showing the relationship between the resonant frequency ₂ of the torsional vibration and temperature. FIG. 6 is a block diagram of another embodiment of the device according to the present invention, and FIGS.
The figure is an explanatory diagram showing an example of forming electrodes provided on a crystal resonator. 1...Crystal resonator, OSC1, OSC2...Self-excited oscillation loop, 4...Addition circuit, 5...Control loop, 52...Load capacity, 54...Heater.

Claims (1)

[Scope of Claims] 1. A tuning fork-shaped crystal resonator, a first self-excited oscillation loop that causes the crystal resonator to vibrate in a bending manner, a second self-excited oscillation loop that causes the crystal resonator to vibrate in a torsional manner, and a control loop that inputs resonant frequency signals f ₁ and f ₂ obtained from two self-excited oscillation loops and controls the load capacity of the crystal oscillator or the temperature of the crystal oscillator in relation to the difference between the two frequency signals, A frequency signal output device configured to output a resonant frequency signal f ₁ obtained from the first self-oscillation loop as a reference frequency signal.