JP2002299957A - Method for correcting temperature characteristics of crystal oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature characteristics correcting method for a crystal oscillator which simplifies a manufacturing process and reduces temperature characteristics measuring time. SOLUTION: This method includes a process for reading basic data inherent to a crystal resonator to an external terminal 7 from the crystal resonator (S2), a process for calculating temperature correction data of the crystal oscillator by a temperature correction function on the basis of the basic data (S2 and S3), a process for writing the calculated temperature correction data with bit values a writeable read-only memory (S4), and a process for applying a control voltage based on the written bit values to a varicap diode 4 and measuring the frequency temperature characteristics of the crystal oscillator A (S5).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting a temperature characteristic of a crystal oscillator in a crystal oscillator including a crystal resonator, a varicap diode, a temperature compensation circuit, and the like.

[0002]

2. Description of the Related Art Conventionally, a temperature-compensated crystal oscillator oscillates a crystal oscillator mounted on a circuit board and oscillates the crystal oscillator, since the inherent frequency-temperature characteristic of the crystal oscillator differs for each crystal oscillator. The operation of the crystal oscillation circuit section having a temperature compensation circuit that can flatten the inherent frequency-temperature characteristic is very important.

As shown in FIG. 1, a conventional crystal oscillation circuit section B includes an oscillation circuit 6 for driving a crystal oscillator 1, a temperature sensor 2 for detecting an ambient temperature, and a temperature sensor 3 for measuring the ambient temperature.
A temperature compensating circuit 3 which converts the voltage value into a voltage value having the following function:
Varicap diode 4, PROM (Programmable Read Only) for storing temperature compensation data for a predetermined temperature
Memory 5), which are LSI
(Large-scale integrated circuit).

The temperature-compensated crystal oscillator A is constructed by connecting the crystal resonator 1 and the crystal oscillation circuit section B on a circuit board (not shown) or a ceramic package.

Referring to FIG. 6, a description will be given of a temperature characteristic correcting step of the temperature compensated crystal oscillator A. In adjusting the frequency-temperature characteristics of the temperature-compensated crystal oscillator A, since the frequency-temperature characteristics of the crystal unit 1 itself are unknown, first, the oscillation frequency at room temperature of 25 ° C. and the voltage control sensitivity (AFC Initialize (sensitivity) (P
1). Then, the output voltage of the varicap diode 4 is measured from the Input / Output terminal 8 by the temperature compensation circuit 3 which is fixed to an arbitrary set value at each temperature of 5 points or more (P
2) While monitoring the oscillation frequency output from the Input / Output terminal 8, a predetermined voltage is applied to the varicap diode 4 so that the oscillation frequency output from the Input / Output terminal 8 can be set to a certain value. The cap input voltage is measured (P3).

Here, a varicap capable of compensating for the varicap input voltage-temperature characteristic (VC-Out) in a state where the temperature compensation circuit 3 is set to an arbitrary set value at each temperature and the frequency temperature characteristic of the crystal unit 1. Two voltage-temperature characteristic curves of cap input voltage-temperature characteristic (VC-IN) are obtained. These respective voltage-temperature characteristic curves are expressed by the following cubic functions. These coefficients can be calculated by the least square method or the like. VC-OUT = α ₁ (T−Ti ₁ ) ³ + β ₁ (T−Ti ₁ ) + γ ₁ ... VC-IN = α ₂ (T−Ti ₂ ) ³ + β ₂ (T −Ti ₂ ) + γ ₂ ... Α _* : third-order coefficient, β _* : first-order coefficient, γ _* : zero-order coefficient T _* : temperature characteristic rotation center temperature coefficient In the next step, this VC The coefficients of the -OUT characteristic and the VC-IN characteristic are compared, and to what value the set value in the PROM (RAM) 5 is changed, the temperature compensated values α, β, γ, Ti
Is calculated (P4). That is, α = α ₂ −α ₁ , β
= Β ₂ −β ₁ , γ = γ ₂ −γ ₁ , and T = T ₂ −T ₁ , temperature compensation of the crystal resonator becomes possible. Then, the calculated set value is reset in the PROM (RAM) 5 (P5).

However, even if the adjustment is performed in this manner and the set value of the PROM (RAM) 5 connected to the temperature compensation circuit 3 is changed,
Due to the variation in capacity, a desired voltage is not always output correctly in the setting. Therefore, in the next step, after the adjustment is completed, the frequency temperature characteristic of the temperature compensated crystal oscillator A is measured again for the purpose of confirmation (P
6) As a result, the quality of the product is determined (P7),
The measurement has been completed.

Therefore, in order to determine the set value of the PROM (RAM) 5, it is necessary to measure the actual temperature characteristics after measuring the varicap input / output voltage in steps P1 to P5.

[0009]

SUMMARY OF THE INVENTION The present small size, light weight,
In the parts industry where cost reduction is advancing, the cost reduction of the temperature compensated crystal oscillator is also progressing. Therefore, in order to reduce costs, it is necessary to simplify the manufacturing process without deteriorating the conventional characteristics, and it is particularly necessary to reduce the time-consuming measurement time of the frequency temperature characteristic.

The present invention has been devised in view of the above problems, and has as its object to simplify the manufacturing process and reduce the time for measuring the temperature characteristics without deteriorating the conventional characteristics. A method of manufacturing a temperature compensated crystal oscillator is provided.

[0011]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a quartz oscillator having an AT-cut quartz substrate, an oscillation circuit for oscillating the quartz oscillator, and an oscillation circuit connected to the oscillation circuit. A varicap diode for adjusting the oscillation frequency of the oscillation circuit by changing the capacitance by application of a control voltage, and generating a control voltage of a cubic function with respect to an ambient temperature, and applying the control voltage to the varicap diode. A temperature-compensated crystal oscillator comprising a temperature-compensation circuit for compensating the fluctuation of the oscillation frequency of the oscillation circuit due to a temperature change by application, a writable read-only memory storing information of the control voltage as a bit value, Basic data including the frequency-temperature characteristic coefficient, temperature characteristic rotation center temperature coefficient, and varicap sensitivity of the varicap diode are registered. Having an external terminal having a database and a temperature correction function of calculating temperature correction data of the crystal oscillator based on the basic data, and connecting the external terminal to a writable read-only memory of the crystal oscillator. In the temperature characteristic correction method of the crystal oscillator for correcting the temperature characteristic, the basic data is described in advance in the crystal oscillator, and the step of reading the basic data from the crystal oscillator to the external terminal is performed based on the basic data. Calculating the temperature correction data of the crystal oscillator by the temperature correction function, writing the calculated temperature correction data to the writable read-only memory as bit values, and controlling the control voltage based on the written bit values. Applying a voltage to the varicap diode to measure the frequency temperature characteristic of the crystal oscillator. To provide a temperature characteristic correction method for a crystal oscillator according to symptoms.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. It is to be noted that the same reference numerals are used for the same configurations as the conventional technology.

FIG. 1 shows a block diagram of a temperature-compensated crystal oscillator A according to the present invention. Temperature compensated crystal oscillator A
Is mainly composed of a crystal oscillator 1, a temperature sensor 2, a temperature compensation circuit 3, a varicap diode 4, a PROM (RAM) 5, and an oscillation circuit 6.

In the crystal unit 1, a crystal substrate composed of vibration electrodes facing both main surfaces is housed in a container 10, and the crystal substrate is formed by AT cutting. The crystal unit 1 has a unique temperature-frequency characteristic represented by a cubic curve, and a code describing frequency-temperature characteristic information unique to the crystal unit is attached to the surface of the container 10 shown in FIG. The contents described on the crystal unit 1 are not limited to numbers, and may be bar codes. This is because the miniaturization of the product is progressing, so only the minimum contents can be described, and if it is forcibly packed, a reading error may occur. This is because it is only necessary to access the database of the above and fetch the unique frequency temperature characteristic information.

The temperature sensor 2 has a circuit for generating a voltage represented by a linear function with respect to the ambient temperature, and is connected to the temperature compensation circuit 3.

The temperature compensation circuit 3 has a circuit for converting a voltage value generated by the temperature sensor 2 into a voltage value represented by a cubic function. -30 to 85 ° C in actual use area
When viewed from inside, the temperature compensation circuit 3 generates the following cubic curve. VC = α (T−Ti) ³ + β (T−Ti) + γ ················ VC: Varicap applied voltage α: Cubic coefficient of varicap applied voltage β: Varicap applied voltage Γ: Zero-order coefficient of varicap applied voltage Ti: Temperature characteristic rotation center temperature coefficient of varicap applied voltage The oscillation circuit 5 is a circuit that is connected to the excitation electrode of the crystal unit 1 and causes thickness shear vibration. is there.

The PROM (RAM) 5 is connected to the external terminal 7, and information for converting a primary voltage generated by the temperature sensor 2 to a cubic function voltage generated by the temperature compensation circuit 3 is described from the external terminal 7. Is done. Specifically, a third-order coefficient, a first-order coefficient, and a temperature characteristic rotation center temperature coefficient obtained by correcting the frequency-temperature characteristic inherent to the crystal unit are stored as bit values.

The PROM (RAM) 5 is a PROM (RAM).
Mode and RAM mode. This RA
Temporary bit setting is performed in the M mode, and frequency measurement is performed at each temperature. Only products that are finally determined to be good are P
In the ROM mode, writing of bits is performed. This is because it is no longer possible to change the bits that are written in the defective product, resulting in a completely defective product.

Here, the frequency temperature characteristic inherent in the crystal unit is obtained by measuring the temperature and frequency at 5 points or more.
From the least squares method, it is represented by the following cubic curve. _{f X 'tal = α X'} tal (T-Ti X 'tal) 3 + β X' tal (T-Ti X 'tal) + γ X' t al ··· f X 'tal: crystal oscillator frequency α _{X ' tal} : third order coefficient of crystal oscillator frequency β _{X ' tal} : first order coefficient of crystal oscillator frequency γ _{X ' tal} : zero order coefficient of crystal oscillator frequency Ti _{X ' tal} : temperature characteristic of crystal oscillator frequency Temperature coefficient of rotation center External terminal 7 is PROM (RAM) via Data Input 9
The basic data of α _{x ' tal} , β _{x ' tal} , γ _{x ' tal} , Ti _{x ' tal} , and varicap sensitivity are stored in a database in advance as shown in FIG. Further, as will be described later, a temperature correction function for calculating temperature correction data of the crystal oscillator A based on the basic data is provided. If the frequency value is directly input as the product-specific temperature characteristic data on the database, the coefficient must be calculated at the time of measuring the product, which may affect the tact time of the product measurement. Therefore, the third-order coefficient, the first-order coefficient, the zero-order coefficient, which are previously calculated from the inherent frequency temperature characteristics by the least square method or the like are stored in the database.
The temperature characteristic rotation center temperature coefficient and the varicap sensitivity coefficient are input.

Here, since the varicap sensitivity changes depending on the variation in the capacitance of the varicap diode 4 itself and the capacitance ratio of the crystal unit 1 combined with the crystal unit 1, the frequency sensitivity is measured before setting. Varicap sensitivity needs to be determined. Here, the varicap sensitivity can be obtained by directly applying a voltage to the varicap diode 4 from the outside and measuring the frequency at that time. It is desirable that the applied voltage be changed within the temperature compensation voltage range actually applied to the varicap in order to increase the accuracy of the temperature compensation.

The varicap diode 4 changes the capacitance component by applying the voltage generated by the temperature compensating circuit 3, and changes the oscillation frequency of the oscillation circuit 5.

Next, a method of manufacturing the temperature compensated crystal oscillator of the present invention will be described.

First, the crystal resonator 1 and the crystal oscillation circuit section B are connected and arranged on a ceramic package (not shown), and thereafter, a temperature characteristic correction step is performed. In order to efficiently perform the temperature compensation in the temperature correction step, it is necessary that the frequency temperature characteristic unique to the crystal unit 1 is known. This is because the variation after the adjustment can be greatly reduced by considering the variation of the crystal resonator itself. Therefore, the value of the frequency temperature characteristic unique to the crystal unit 1 in FIG. 3 is measured in advance as a database in the external terminal 7. Further, the varicap is measured at room temperature (25 ° C.) and registered in the database.

Next, the temperature characteristic correction step of the present invention starts.
You. As shown in FIGS. 2 and 5, the quartz resonator 1 is attached to a container.
The character information of the crystal unit 1 is recognized by the code (S
1) The code information is stored in the database of the external terminal 7.
Inserted and recognized crystal oscillator 1 has codes ZZX0001 to ZZX02
00 (S2), and the coefficient α
_{X ' tal}, Β_{X ' tal}, Γ_{X ' tal}, Ti_{X ' tal}Frequency temperature
Set value in LSI from characteristic information and varicap sensitivity
Is calculated by the temperature correction function of the external terminal 7 (S3).
Write the output data to PROM (RAM) 5 described later
No. The temperature is determined by the value of the PROM (RAM) 5 after this setting.
The degree compensation circuit 3 has a voltage value V expressed by the following equation:_{I c}Occurs
Let it. V_{I c}= Α_ICV(T-Ti_ICV)^Three + Β_ICV(T-Ti_ICV) + Γ_ICV・ ・ ・ ・ ・ Α_ICV, Β_ICV, Γ_ICV, Ti_ICV: Count value of control voltage Note that the third order coefficient, first order coefficient, temperature characteristic rotation center temperature
The degree coefficient is actually set in the PROM (RAM) 5.
Bit α_{I c}, β_{I c}, Ti_{I c}Is the temperature compensator of the external terminal 7
The function is calculated as follows. <Third order coefficient> First, the third order set value α_{I c}Is the crystal oscillator 1
Existent third order coefficient α_{X ' tal}, And its varicap sensitivity VC
It can be calculated from: That is, for each product,
Α ′ indicating the third-order characteristic in a state including C is obtained. This
Is α '= α_{X ' tal}/ VC.

Then, the range of α ′ in which the crystal oscillation circuit section B can be adjusted is determined in advance, and α ′ calculated for each product is determined.
The set value α _IC is calculated backward. That is, it is obtained by the following equation. α _IC = α _S + α _P ······ α _S : Bit value set when α 'is the center α _P : Deviation from coefficient α _S For example, the range of α' is specific to the crystal unit The minimum value of the coefficient is α _{X ' tal} = 85 ppm / ° C ³ , and the varicap sensitivity VC at that time
= Alpha in the case of a 21 ppm / V 'becomes 4.04V / ℃ ^3. Also,
The maximum value of the coefficient specific to the crystal unit α _{X ' tal} = 115 ppm / ° C ³ ,
When the varicap sensitivity VC at that time is VC = 17 ppm / V, α ′ is 6.76 V / ° C. ³ . Since the central value of α 'is 5.4 V / ° C ³ from the maximum value and the minimum value, α _P is α _P = (α'-5.4) / ｛(6.76-4.04) / αBit number｝ ・ ・ ・ ・ ・ ・αBit number: alpha = time 5Bit of (11111) can calculate the alpha _IC than 31 (decimal) below. <Primary coefficient> Primary set value β _IC is the primary coefficient β _{X ′} of crystal
_It can be calculated from _tal . In advance, β _{X ' tal}
Is calculated for each product individually. β _IC = coefficient1 × β _{X ' tal} + coeffICient2... Here, coefficient1 and coefficient2 are coefficients determined by the cut angle of the quartz substrate. Set value Ti _IC of <Temperature characteristics rotation center temperature coefficient> Ti can be calculated from Ti coefficient Ti _{X 'tal} crystal. However, since the temperature sensor 2 has variations, it is necessary to adjust the voltage of the temperature sensor 2 near 25 ° C. first. It is determined in advance how many degrees Celsius the temperature sensor changes by changing one bit (referred to as Ti_sensitivity), and Ti _{X ' tal}
And Ti_sensitivity. _{Ti IC = Ti y + {(} Ti X 'tal -25 ℃) / Ti_sensitivity} ······ Incidentally, a set bit after Ti _y Temperature sensor voltage regulation. <Γ _IC > Since γ _IC is a bit for setting the oscillation frequency at normal temperature (25 ° C.), it is set so that the oscillation frequency becomes the target oscillation frequency while actually measuring the oscillation frequency.

As described above, α _IC , β _IC , Ti _IC and γ _IC are calculated and stored in the database of FIG. Then, the setting bits obtained as a result are set in the RAM 5 (S4), and the quality is judged by measuring the frequency-temperature characteristic of the temperature-compensated crystal oscillator A with the corrected value. After the pass / fail judgment is completed, only the PROM
Set it to 5 and end.

[0027]

As described above, according to the present invention, after the varicap input / output voltage is measured, the actual temperature characteristic is measured once without deteriorating the characteristic. The pass / fail can be determined by the measurement, and the manufacturing cost can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of a temperature compensated crystal oscillator according to the present invention.

FIG. 2 is a flowchart in a temperature correction step of the present invention.

FIG. 3 is a diagram illustrating contents in a database of an external terminal used in the present invention.

FIG. 4 is a diagram for explaining contents after temperature correction in a database of an external terminal used in the present invention.

FIG. 5 is a diagram illustrating code information described in the crystal resonator of the present invention.

FIG. 6 is a flowchart in a conventional temperature correction step.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Crystal oscillator 2 ... Temperature sensor 3 ... Temperature compensation circuit 4 ... Varicap diode 5 ... PROM (RAM) 6 ... Oscillation circuit 7 ... External terminal

Claims (1)

[Claims] 1. A quartz oscillator having an AT-cut quartz substrate, an oscillation circuit for oscillating the quartz oscillator, and an oscillation circuit connected to the oscillation circuit, the capacitance of which is changed by application of a control voltage to change the oscillation of the oscillation circuit. A varicap diode for adjusting the frequency, and a control voltage having a cubic function with respect to the ambient temperature is generated, and the control voltage is applied to the varicap diode to compensate for a change in the oscillation frequency of the oscillation circuit due to a temperature change. Temperature-compensated crystal oscillator comprising a temperature compensating circuit that performs the operation, a writable read-only memory that stores the information of the control voltage as bit values, a coefficient of frequency temperature characteristic inherent to the crystal oscillator, and a temperature characteristic rotation center temperature coefficient. And a database in which basic data including varicap sensitivity of a varicap diode and a crystal oscillation based on the basic data are registered. An external terminal having a temperature correction function of calculating temperature correction data of the device, and a temperature of the crystal oscillator for correcting the temperature characteristic by connecting the external terminal to a writable read-only memory of the crystal oscillator. In the characteristic correction method, the basic data is described in advance in the crystal oscillator, the step of reading the basic data from the crystal oscillator to the external terminal, and the temperature of the crystal oscillator by the temperature correction function based on the basic data. Calculating the correction data, writing the calculated temperature correction data as a bit value to the writable read-only memory, applying a control voltage based on the written bit value to the varicap diode, Measuring the temperature characteristic of the frequency of the crystal oscillator.