JPH02174407A - Temperature compensated frequency crystal oscillator - Google Patents

Abstract

PURPOSE:To obtain a crystal oscillator with high accuracy and high reliability by using a temperature characteristic of a sub vibration mode not coupled with the main vibration mode, detecting directly the temperature of the substrate in a form of the frequency and applying temperature compensation control to the main vibration frequency of the substrate at the same time. CONSTITUTION:Exciting electrode pairs 3, 4 are provided independently of the front and rear sides of a crystal vibrator 2. A temperature compensation circuit TC and an oscillation circuit OS2 are connected to the electrode pair 4 to oscillate the main vibration mode, and an oscillation circuit OS1 is connected to the electrode pair 3 to oscillate the sub vibration mode. The temperature of the crystal substrate 2 is detected depending on the temperature characteristic of the frequency F1 of the sub vibration mode. The frequency F1 is converted into a voltage by an FV conversion circuit and the voltage is matched with an input voltage by the voltage/load capacitor conversion of the compensation circuit TC. Through the constitution above, a temperature compensated frequency crystal oscillator small in size, low in power consumption and high in accuracy is obtained.

Description

Detailed Description of the Invention (Industrial Field of Application) A high-temperature constant temperature chamber designed to output a constant oscillation frequency by compensating the frequency-temperature characteristics of a crystal resonator, particularly at a high temperature (prior art) Highly stable thermostatic bath crystal oscillators with built-in crystal oscillators are limited to special uses because they require power to maintain constant temperature and the thermostatic chamber itself prevents miniaturization.

In order to improve this drawback, a temperature-sensitive element such as a thermistor is used to convert the temperature-electrical resistance change into a voltage-capacitance value, and this is used as a change in the equivalent load capacitance of the crystal resonator. This enables us to create a small non-temperature oven type frequency temperature compensated crystal oscillator (
(hereinafter referred to as TCXO) are widely used.

This TCXO has been further improved to create a digital frequency temperature compensation oscillator (hereinafter referred to as DTCXO), which processes and stores the frequency vs. temperature data specific to the crystal resonator and uses this data for frequency temperature compensation. It has been developed and is in the practical stage.

(Ld to be solved by the invention) Conventionally, a temperature sensing element such as a thermistor or a posistor has been used to detect the temperature of a TCXO or DTCXO, but it is not necessarily the case that the temperature sensing element is at an equivalent position and equivalent to the crystal resonator of the object of temperature measurement. Since heat capacity cannot be measured, a sudden change in environmental temperature inevitably causes a temperature difference between the temperature sensing element and the crystal resonator, leading to deterioration of frequency temperature compensation characteristics.

Further, temperature-sensitive elements are often manufactured by hybrid sintering of compound semiconductor materials, and changes over time, which are thought to be caused by the instability of the compound components, are unavoidable, impairing stability and reliability.

In order to improve this, the use of a thermoelectric cone was considered, but it is rarely used today due to its low sensitivity and low impedance.

Furthermore, since the resistance value of a temperature sensing element made of a semiconductor material changes greatly exponentially with respect to temperature, it is completely impossible to compensate for temperature over the entire temperature Iat with a single element. Therefore, two or three with different characteristics
It was necessary to create a circuit configuration in which the individual temperature sensing elements were divided into narrow temperature ranges and combined into one.

Figure 5 shows a conventional example where the temperature compensation range is T CL, T C
The variable capacitance element V is divided into three parts, M and TCH.
An example of a TCXO controlling CI, VO2, and VO2 is shown.

However, it is extremely difficult to match the characteristics of this temperature-sensitive element to the requirements, and it has been difficult to select from a large number of elements to obtain an element with the desired characteristics.

Therefore, the circuit adjustment work is extremely complicated, and even if a computer is used, adjustment and measurement Z still require a long time.

Even with this method, it is becoming extremely difficult to perform temperature compensation within the frequency deviation specifications over the entire compensation temperature range, and there has been a strong desire to develop new technical means.

The DTCXO has the advantage of easily performing ideal frequency temperature compensation based on compensation data matched to the natural frequency temperature characteristics of the crystal resonator, and can theoretically compensate within any frequency deviation standard.

FIG. 6 shows a conventional example of a DTCXO that uses a switched capacitor to perform temperature compensation control by selectively opening and closing an optimum compensation capacitance Cn of 5n (n is a natural number).

However, due to the roughness of temperature sampling performed for control purposes, the frequency to be compensated for is difficult to flatten, and sampling quantization noise or jitter occurs. The disadvantages include that the power consumption of the processing circuit is relatively large, and it does not meet the requirements for small size and low power consumption.

The present invention has been made in view of these drawbacks, and an object of the present invention is to realize a frequency-temperature compensated oscillator that is small, has low power consumption, and has high accuracy and high reliability.

(Means for solving the rR problem) There are various unique motion states of a crystal substrate, and we focus on one of them, the ti motion state, and extract and use it as the main vibration state (hereinafter referred to as "principal vibration"). do.

Various crystal resonators have been put into practical use by determining a cutting angle that includes an inflection point in the frequency-temperature characteristics so that the frequency temperature change is minimized within the operating temperature range.

However, since the dimensions and shape of the crystal substrate are finite, it satisfies the boundary W condition that enables the generation of many resonance (natural) vibration states in addition to the main vibration, and as a result, many undesirable secondary vibrations are generated in addition to the main vibration. (Spurious JH motion') φB (hereinafter referred to as sub-vibration) may be observed.

Secondary vibrations are classified into two types based on their generation form.

When the main vibration frequency and the secondary vibration (higher harmonic) frequency match for some reason and are acoustically coupled to occur (coupled resonance), the secondary vibration frequency happens to satisfy the oscillation conditions of the oscillation circuit. The coupling between the vibration and the main vibration is weak and occurs almost independently (non-coupled resonance). Generally, in order to maintain the stability of a crystal oscillator, much effort has been made to reduce the coupling of the coupled resonance with the sub-oscillation to obtain a purer main vibration.

On the other hand, the secondary vibration of non-coupled resonance can be suppressed more easily than the case of coupled resonance by design means such as providing a frequency selection means in the oscillation circuit or changing the shape and dimensions of the vibrator.

The present invention pays particular attention to this non-coupled sub-vibration, simultaneously oscillates the sub-vibration that has little influence on the main vibration as an independent vibration state, separates it into each frequency, and reverses the sub-vibration frequency based on the temperature characteristics of the sub-vibration frequency. The temperature of the crystal substrate is detected and the temperature characteristics of the main vibration frequency are compensated and controlled.

This will be explained using an AT cut crystal resonator as an example.

As shown in Figure 4 (1)), an AT designed in a flat plate shape
On the surface of the cut crystal substrate 1, a partially excitation type RI15a
, 5b is caused to resonate in the thickness shear vibration state TS shown in the same figure (c), the plane slip Wi motion state shown in the same figure (d), which is equivalent to the CT cut where the cutting angle is close to the AT cut, is generated. The FS can be made to resonate simultaneously without using acoustic coupling between both pregnancy motion states.

This is because there are four nodes in this vibration mode in the center of the periphery in addition to the center, which makes it easy to match the support of the AT cafe and vibrator, and the thickness of the crystal substrate is the optimum thickness for the CT force and oscillator. The main reason why both resonances can coexist is that they are close to each other.

However, as shown in FIG. 4(d), the crystal substrate 1
When operated as a CT-cut crystal oscillator in the plane-sliding vibration mode FS, the inflection point of its frequency-temperature characteristic FS is not at room temperature, as shown in Figure (a), and the frequency as an AT-cut quartz crystal oscillator is Near room temperature, where the temperature characteristic TS is at its flattest point, it shows an almost linear and rapid change.

This difference in temperature characteristics is determined unilaterally by the design of the crystal substrate, and does not change much due to accompanying processing such as frequency adjustment, so it can be regarded as a characteristic unique to the crystal substrate 1. The frequency F of this secondary vibration
Conversely, by extracting the temperature characteristics of the crystal substrate l, the temperature of the crystal substrate l can be accurately detected.

The present invention applies this principle to detect the temperature of the crystal substrate itself and utilizes it for temperature compensation control.

That is, in a frequency temperature compensated crystal oscillator in which a crystal resonator, an oscillation circuit, and a temperature compensation circuit are connected, two independent excitation electrode pairs are provided on the front and back surfaces of the crystal substrate of the crystal resonator, and one excitation electrode pair is The temperature mfr4 circuit and the first oscillation circuit are connected to oscillate the main vibration, and the second oscillation circuit is connected to the other excitation electrode pair to oscillate the sub-oscillation. From the temperature characteristics of the sub-oscillation frequency, the temperature of the crystal substrate is determined. Detect the temperature and set up the temperature compensation circuit;l
/J to temperature compensate the main oscillation frequency of the first oscillation circuit, or provide a pair of excitation electrodes on the front and back surfaces of the crystal substrate of the crystal resonator, and connect the temperature compensation circuit and the The first oscillation circuit is connected to oscillate the main vibration, and the first filter circuit and the second oscillation circuit are connected to the same excitation electrode pair to oscillate the sub vibration at the same time as the main vibration. oscillating frequency, detecting the temperature of the crystal substrate from the temperature characteristics of the auxiliary oscillating frequency, controlling a temperature compensation circuit, and temperature-compensating the main oscillating frequency of the first oscillating circuit. This constitutes a temperature compensated crystal oscillator.

(Operation of the invention) In the frequency temperature compensated oscillator configured as described above, the temperature detection light of the crystal substrate and the target for temperature compensation of its main vibration frequency are the same crystal substrate itself, and the frequency temperature compensation function is the same. This is done smoothly and with high precision using a data format called frequency.

However, in order to guarantee highly reliable frequency-temperature compensation, the secondary vibration of temperature detection and the main vibration to be compensated for frequency-temperature characteristics must have independent vibration modes with less acoustic coupling so that they do not directly interfere with each other on the crystal substrate. It is important to choose.

When using non-coupled resonance, it is possible to cause a pair of excitation electrodes to simultaneously oscillate both the main vibration and the sub-vibration, and separate them into their respective frequencies (see Figures 2, 3 and 4). b)).

Alternatively, by providing a groove or the like between the main vibration vibration part and the secondary vibration vibration part to structurally isolate them, it is possible to almost completely prevent mutual interference between the two locks (first Figure (b)).

In this case, if the two excitation electrode pairs can be acoustically isolated,
A vibration mode in which both vibrations are combined and resonated can also be implemented as the present invention.

Typically, frequency-temperature compensation is performed in sequence from temperature-frequency conversion, frequency-voltage value, and voltage value-load capacitance value conversion.

In this case, the voltage value-load capacitance value conversion of the frequency temperature compensation control method implemented in the conventional analog method can be directly applied to the present invention.

Although not shown, by using a PLL loop control system for this conversion, it can be implemented as a direct frequency-to-frequency conversion.

(Example) FIG. 1(a) shows the necessary components for the crystal resonator shown in FIG. This is an embodiment of the present invention in which circuits are connected to form a frequency temperature compensated crystal oscillator.

That is, one excitation electrode pair 4 is connected to a first oscillation circuit 052 and a temperature compensation circuit TC, and the other excitation electrode pair 3 is connected to a second oscillation circuit oSl. It oscillates in a plane-sliding vibration state equivalent to a CT cut, and a frequency Fl is obtained.

The excitation electrode pair 4 oscillates in an AT-cut thickness-shear vibration mode to obtain a frequency F2.

Since the surface sliding vibration frequency Fl, which is a sub-vibration, is a monovalent value of temperature, the temperature of the crystal substrate 2Φ is detected from this.

This sub-oscillation frequency Fl is converted into a voltage by the frequency-voltage conversion circuit FV, which is matched to the voltage value required for voltage-load capacitance conversion of the temperature compensation circuit TC.

Although not shown, the main vibration frequency F2 can also be directly controlled by passing the secondary vibration frequency F1 through a frequency processing circuit such as a PLL instead of the frequency-voltage conversion circuit FV. In this case, if the frequency-temperature characteristics of the main vibration and the sub-vibration have a one-to-one correspondence, for example, a Y-cut resonator with the least spurious, etc., has no inflection point within the operating temperature range. The linearly changing frequency-temperature characteristic vibration IJJ configuration, which has rarely been used, can be actively utilized as the main vibration.

If the vibration state of the crystal substrate 2a is made into a surface sliding vibration state corresponding to a DT cut, it is also possible to make the crystal substrate 2b into a thickness shear vibration state by using a BT cut.

Alternatively, since the crystal substrates 2a and 2b are physically separated by a grooved structure or the like at the center of the substrate, it is also possible to utilize, for example, the vibration state of bending and thickness shear in the coupling resonance relationship. In this case, it is important to maintain a non-integer multiple relationship up to high-order harmonics, taking into account non-linear coupling in circuits, etc., and to always make the frequencies of the main vibration and sub-vibration different (
Hereinafter, for the sake of simplicity, this will only be referred to as a different frequency).

FIG. 2(a) shows another embodiment of the present invention constructed by connecting the necessary circuits to the crystal resonator of FIG. 4(b) in which a single excitation electrode pair 5 is arranged on a crystal substrate 1. .

That is, by utilizing the non-coupled resonance relationship between the surface-slip vibration state FS of the sub-vibration and the thickness-shear vibration state TS of the main vibration, superimposed oscillation can be simultaneously performed in the excitation electrode pair 5 without mutual interference. , the frequencies Fl and F2 of both vibration modes are always made different, and the oscillation circuit oS1 and the low-pass filter FIL are connected to the excitation electrode pair 5, and the oscillation circuit OS2 and the temperature compensation circuit TC are connected. , is an example of further parallel connection.

Temperature compensation control can be performed by converting the output frequency F1 of the oscillation circuit O9I into the control voltage V of the temperature compensation circuit TC through the frequency-voltage conversion port 'PtFV.

In this example, it is desirable to support the crystal substrate 1 at the center of the four sides in consideration of both target motions.

FIG. 3(a) shows the oscillation waveform (F 1 +F2) of the excitation electrode pair 5 in the embodiment of FIG. 2, and FIG. 3(b) shows the oscillation output waveform (F2) of the oscillation circuit oS2. Figure (c
) respectively show the oscillation output waveform (F1) of the oscillation circuit OSI.

Note that although each oscillation circuit is shown as being connected separately, the image frequencies are far apart, for example, C
The T-cut oscillation frequency F1 is expressed as IL (k=3080kHz - mm) where L is the side length of the crystal substrate, so in the case of 10MHz and 11XI 1mm,
The frequency is approximately 280 KHz, and it is possible to perform superimposed oscillation with one oscillation circuit.

The excitation electrode pair 5 of the crystal substrate 1 in FIG. 4(1)) is
C), ((1) Partial electrode pairs are used to suppress spurious vibrations that occur in other than the two vibration states shown here, but on the other hand, since the surface slip vibration state FS takes a node at the center of the surface, thickness slip This is very convenient in the sense that it does not overlap with the maximum displacement part of the vibration 6BTS and avoids interference.

(Effects of the Invention) Since the present invention is configured as detailed above, the substrate temperature can be directly measured from the substrate in the form of a frequency by using the temperature characteristics of the sub-vibration mode that is not coupled to the main vibration mode of the crystal substrate. Since it detects and simultaneously controls the main vibration frequency of the substrate with temperature compensation, it has no disadvantages associated with conventional temperature measurement and control and has an ideal temperature.

The imaging mode to be used is not limited to those conventionally used, but can also be used as long as it does not have an inflection point in the frequency-temperature characteristic within the temperature range. Certain methods have not been used due to poor P1 wavenumber temperature characteristics, but can now be applied to various cuts such as Y-cuts.
It has a great technical contribution.

As long as the vibration mode to be utilized can be separated into a non-coupling state as described above, it can be applied to other piezoelectric materials, and is not limited to crystal.

[Brief explanation of the drawing]

FIG. 1(a) is a configuration diagram of an embodiment of the present invention, and FIG. 1(1)
) is a perspective view of a crystal resonator substrate applied thereto, FIG. 2 is a configuration diagram of another embodiment of the present invention, and FIGS. 3(a), (b) (
c) is a waveform diagram of frequencies F1+F2, Fl, and F2 in FIG. Figure 4 (a) is a frequency temperature characteristic diagram of the vibration v1 state of the AT-cut crystal resonator, Figure 4 (b) is a perspective view of the crystal resonator substrate applied to Figure 2, and Figure 4 (C) is a diagram of thickness slip. A diagram illustrating a photographing state; FIG. FIG. 5 is an explanatory diagram of the TCXO function of a conventional example, and FIG. 6 is an explanatory diagram of the DTCXO function of the conventional example. 1.2...Crystal substrate 3, IL, 5...Excitation electrode pair O81, O8
2,05C--Oscillation circuit TC, T (I, ~TCH... Temperature compensation circuit FV... Frequency voltage conversion circuit FIL...
・・Low-pass filter circuit TS・・・・Thickness shear vibration mode FS・・・・
・・Surface sliding vibration mode・
...Switching circuit VCI~VC3...Variable capacitance diode 1st! ! ! (Q) 41st! I Kan 4 Sen (C) (d)

Claims (1)

[Scope of Claims] 1) In a frequency temperature compensated crystal oscillator formed by connecting a crystal resonator, an oscillation circuit, and a temperature compensation circuit, two two excitation electrode pairs (3, 4) are arranged, and the temperature compensation circuit (TC) and the first oscillation circuit (OS2) are connected to one excitation electrode pair (4) to oscillate the main vibration mode, and the other excitation electrode pair (
3) is connected to a second oscillation circuit (OS1) to oscillate the sub-vibration mode, detects the temperature of the crystal substrate (2) from the temperature characteristics of the frequency (F1) of the sub-vibration mode, and activates the temperature compensation circuit. (
TC) by controlling the first oscillation circuit (OS2).
1. A frequency temperature compensated crystal oscillator, characterized in that the frequency (F2) of the main vibration mode of is temperature compensated. 2) In a frequency temperature compensated crystal oscillator formed by connecting a crystal resonator, an oscillation circuit and a temperature compensation circuit, one excitation electrode pair (5) is provided on the front and back surfaces of the crystal substrate (1) of the crystal resonator.
), and the temperature compensation circuit (T
C) and the first oscillation circuit (OS2) to oscillate the main vibration state, and a low-pass filter circuit (
FIL) and a second oscillation circuit (OS1) are connected to oscillate a sub-vibration mode at the same time as the main vibration mode, and the frequency (F2) of the main vibration mode and the frequency (F1) of the sub-vibration mode are set respectively. The temperature of the crystal substrate is detected from the temperature characteristic of the frequency (F1) of the sub-vibration mode, and the temperature compensation circuit (T
A frequency temperature compensated crystal oscillator, characterized in that the frequency (F2) of the main vibration state of the first oscillation circuit (OS2) is temperature compensated by controlling the frequency (F2) of the first oscillation circuit (OS2).