JP4476299B2 - Method for correcting temperature characteristics of crystal oscillator - Google Patents

Description

  The present invention relates to a method for correcting temperature characteristics of a crystal oscillator in a crystal oscillator including a crystal resonator, a varicap diode, a temperature compensation circuit, and the like.

  Conventionally, the temperature-compensated crystal oscillator has its own frequency temperature characteristics that differ from crystal oscillator to crystal oscillator mounted on a circuit board. The operation of the crystal oscillation circuit portion having the temperature compensation circuit capable of flattening is very important.

  As shown in FIG. 1, the conventional crystal oscillation circuit section B includes an oscillation circuit 6 that drives the crystal resonator 1, a temperature sensor 2 that detects the ambient temperature, and a measured temperature that is a voltage composed of a cubic function. A temperature compensation circuit 3 that converts values, a varicap diode 4, and a PROM (Programmable Read Only Memory) 5 that stores temperature compensation data for a predetermined temperature are mainly composed of 1 by LSI (Large Scale Integrated Circuit). Consisted of two chips.

  The crystal oscillator 1 and the crystal oscillation circuit section B are connected to a circuit board (not shown) or a ceramic package to constitute a temperature compensated crystal oscillator A.

  Based on FIG. 6, the temperature characteristic correction process of the temperature compensated crystal oscillator A will be described. In adjusting the frequency-temperature characteristic of the temperature-compensated crystal oscillator A, since the frequency-temperature characteristic of the crystal unit 1 itself is unknown, first, the oscillation frequency at 25 ° C. and the voltage control sensitivity (AFC) at room temperature. (Sensitivity) is initially set (P1). Then, the output voltage of the varicap diode 4 is measured from the Input / Output terminal 8 by the temperature compensation circuit 3 fixed at an arbitrary set value at each temperature of 5 points or more (P2), and output from the Input / Output terminal 8 While monitoring the oscillation frequency, a predetermined voltage is applied to the varicap diode 4, and the varicap input voltage that can make the oscillation frequency output from the Input / Output terminal 8 a certain value is measured (P3).

Here, 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 varicap input voltage capable of compensating the frequency temperature characteristic of the crystal unit 1. -Two voltage-temperature characteristic curves of temperature characteristics (VC-IN) are obtained. Each voltage temperature characteristic curve is represented by the following cubic function. 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 (1)
VC-IN = α ₂ (T-Ti ₂ ) ³ + β ₂ (T-Ti ₂ ) + γ ₂ (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-OUT characteristic (1) and VC-IN characteristic (2 ) And the values set in the PROM (RAM) 5 are changed to which values α, β, γ, and Ti of the temperature compensated values are calculated (P4). In other words, the temperature compensation of the crystal resonator becomes possible by setting α = α ₂ −α ₁ , β = β ₂ −β ₁ , γ = γ ₂ −γ ₁ , and T = T ₂ −T ₁ . Then, the calculated set value is reset in the PROM (RAM) 5 (P5).

  However, even if adjustment is made in this way and the setting value of the PROM (RAM) 5 connected to the temperature compensation circuit 3 is changed, the desired voltage is output correctly by the setting due to the capacitance variation of the varicap diode 4 in practice. Not necessarily. Therefore, in the next step, when this adjustment is finished, the frequency temperature characteristic of the temperature compensated crystal oscillator A is measured for the purpose of confirmation again (P6), thereby determining whether the product is good or bad (P7). ), The measurement was finished.

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.
JP-A-8-237030

  In the parts industry where the current miniaturization, weight reduction, and cost reduction are progressing, temperature-compensated crystal oscillators are also moving toward cost reduction. For this reason, in order to reduce the cost, it is necessary to simplify the manufacturing process without degrading the conventional characteristics, and it is particularly necessary to reduce the time required for measuring the frequency temperature characteristics.

  The present invention has been devised in view of such problems, and its purpose is to provide a temperature compensation type in which the manufacturing process is simplified and the temperature characteristic measurement time is reduced without degrading the conventional characteristics. A method for manufacturing a crystal oscillator is provided.

In order to solve the above problems, the present invention provides a bit value of information on a crystal resonator, a varicap diode that adjusts an oscillation frequency of an oscillation circuit that oscillates the crystal resonator, and a control voltage applied to the varicap diode. And a temperature characteristic correction method for a crystal oscillator having a built-in writable read-only memory and a plurality of the crystal oscillators and LSI elements, and the frequency of each crystal oscillator The temperature characteristic coefficient, the temperature characteristic rotation center temperature coefficient, and the varicap sensitivity of the varicap diode built in each LSI element are measured, and the measured value is associated with a predetermined code in the first database of the external terminal. Registering and attaching the code to each crystal resonator, and recognizing the code attached to each crystal resonator (S1) The step (S2) of collating the code recognized in the step (S1) with the code on the first database, and the coefficient of the frequency temperature characteristic of the crystal unit corresponding to the code collated in the step (S2) Temperature coefficient of rotation center temperature coefficient , varicap sensitivity of varicap diode, minimum and maximum coefficient specific to crystal unit, coefficient determined by crystal substrate cut angle, temperature sensor temperature change with 1 bit change The temperature correction data is calculated based on the value set to the target oscillation frequency while actually measuring the oscillation frequency because of the value of and the bit for setting the oscillation frequency at room temperature (25 ° C.) , The temperature correction data is registered in the second database of the external terminal so as to correspond to the code (S3) and calculated in the step (S3) A step (S4) of writing temperature correction data corresponding to each code to the writable read-only memory of each LSI element with a bit value, and a control voltage based on the bit value written in the step (S4) Providing a crystal oscillator temperature characteristic correction method comprising: measuring a frequency temperature characteristic of a crystal oscillator whose temperature is corrected by applying to a cap diode, and determining whether the crystal oscillator is good or bad (S5). To do.

  According to the present invention, after measuring the varicap input / output voltage, it is possible to make a pass / fail judgment with a single measurement without degrading the actual temperature characteristics, and the manufacturing cost is reduced. Can be greatly reduced.

  Embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol shall be used for the same structure as a prior art.

  FIG. 1 shows a block diagram of a temperature compensated crystal oscillator A of the present invention.

  The 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 quartz crystal resonator 1, a quartz crystal substrate composed of an example vibration electrode facing both main surfaces is accommodated in a container 10, and the quartz crystal substrate is formed by AT cut. The crystal unit 1 has a unique temperature frequency characteristic indicated 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. In addition, it is not limited to a number, About the description content on the crystal oscillator 1, a barcode may be sufficient. This is because the miniaturization of the product is progressing, so the description content can be described only minimally, there is a possibility that reading mistakes will occur if packed forcibly, and from the unique description content read, it will be described later This is because it is only necessary to access the above database and take in the specific frequency temperature characteristic information.

  The temperature sensor 2 has a circuit that generates 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 that converts the voltage value generated by the temperature sensor 2 into a voltage value represented by a cubic function expression. When viewed within −30 to 85 ° C. of the actual use region, the temperature compensation circuit 3 generates the following cubic curve.

VC = α (T−Ti) ³ + β (T−Ti) + γ (3)
VC: Varicap applied voltage
α: Third-order coefficient of varicap applied voltage
β: First-order coefficient of varicap applied voltage
γ: 0th order coefficient of varicap applied voltage
Ti: Temperature characteristic of varicap applied voltage Rotational center temperature coefficient The oscillation circuit 5 is connected to the excitation electrode of the crystal unit 1 to cause a thickness shear vibration.

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

  The PROM (RAM) 5 has PROM mode and RAM mode types. Temporary bit setting is performed in this RAM mode, and frequency measurement is performed at each temperature. Only the product finally determined to be non-defective is written in the PROM mode. This is because a bit written to a defective product cannot be changed, resulting in a completely defective product.

  Here, the frequency-temperature characteristic unique to the crystal resonator is indicated by the following cubic curve by the least square method by measuring the temperature and frequency of 5 points or more.

f _X'tal = α _X'tal (T-Ti _X'tal ) ³ + β _X'tal (T-Ti _X'tal ) + γ _X'tal (4)
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 : _Zeroth order coefficient of crystal oscillator frequency
Ti _X'tal : Temperature characteristic of crystal resonator frequency Rotational center temperature coefficient The external terminal 7 is connected to the PROM (RAM) 5 via the Data Input 9, and α _{X '} in the equation (4) as shown in FIG. Basic data of _tal , β _X'tal , γ _X'tal , Ti _X'tal , and varicap sensitivity are stored in advance in the database. Further, as will be described later, there is a temperature correction function for calculating temperature correction data of the crystal oscillator A based on this basic data. If the frequency value is directly input as product-specific temperature characteristic data on the database, coefficient measurement will be required at the time when measuring the product, which may affect the tact of product measurement. Therefore, the third-order coefficient, first-order coefficient, zero-order coefficient, temperature characteristic rotation center temperature coefficient, and varicap sensitivity coefficient calculated in advance from the inherent frequency temperature characteristic by the least square method or the like are input on the database.

  Here, the varicap sensitivity varies depending on the capacitance variation of the varicap diode 4 itself and the capacitance ratio of the crystal resonator 1 combined with the crystal resonator 1, and therefore, the frequency sensitivity is measured before setting, and the varicap sensitivity. It is necessary to ask for. Here, the varicap sensitivity can be obtained by applying a voltage directly to the varicap diode 4 from the outside and measuring the frequency at that time. It is desirable to change the applied voltage within the temperature compensation voltage range that is actually applied to the varicap in order to increase the accuracy of temperature compensation.

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

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

  First, the crystal resonator 1 and the crystal oscillation circuit unit B are connected and arranged on a ceramic package (not shown), and then a temperature characteristic correction step is performed.

  In order to efficiently perform temperature compensation in the temperature correction process, the frequency temperature characteristic unique to the crystal unit 1 needs to be known. This is because the variation after adjustment can be greatly reduced if the variation of the crystal unit itself is taken into consideration. Therefore, the value of the frequency temperature characteristic specific 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 on the database.

Next, the temperature characteristic correction process of the present invention starts. As shown in FIGS. 2 and 5, the character information of the crystal unit 1 attached to the container of the crystal unit 1 is recognized by a code (S1), and the code information is taken into the database of the external terminal 7 and recognized. The crystal resonator 1 is selected from the codes ZZX0001 to ZZX0200 (S2), and its coefficients α _X'tal , β _X'tal , γ _X'tal , Ti _X'tal frequency temperature characteristic information and A setting value inside the LSI is calculated from the varicap sensitivity by the temperature correction function of the external terminal 7 (S3), and the calculated data is written in a PROM (RAM) 5 described later. The temperature compensation circuit 3 generates a voltage value V _IC represented by the following expression (5) by the value of the PROM (RAM) 5 after this setting.

V _IC = α _ICV (T−Ti _ICV ) ³ + β _ICV (T−Ti _ICV ) + γ _ICV (5) α _ICV , β _ICV , γ _ICV , Ti _ICV : _Count value of control voltage The bits α _IC , β _IC , and Ti _{IC that} are actually set in the PROM (RAM) 5 with respect to the third order coefficient, the first order coefficient, and the temperature characteristic rotation center temperature coefficient of the equation (5) are It is calculated as follows.

<Third order coefficient>
First, the third-order set value α _IC can be calculated from the third-order coefficient α _X′tal unique to the crystal unit 1 and its varicap sensitivity VC. That is, α ′ indicating the third-order characteristics in a state including the crystal resonator and the IC is obtained for each product. This can be obtained as α ′ = α _X′tal / VC.

Then, a range of α ′ that can be adjusted by the crystal oscillation circuit section B is obtained in advance, and the set value α _IC is calculated backward from α ′ calculated for each product. That is, it is obtained by the following equation (6).

α _IC = α _S + α _P (6)
α _S : Set bit value when α 'is the center α _P : Deviation amount from coefficient α _S For example, the range of α' is the minimum value of the coefficient specific to the crystal unit α _X'tal = 85ppm / ° C ³ In this case, α ′ when the varicap sensitivity VC = 21 ppm / V is 4.04 V / ° C. ³ . Furthermore, crystal oscillator-specific coefficient maximum value α _X'tal = 115ppm / ℃ ³ of, alpha in the case of a varicap sensitivity VC = 17 ppm / V at that time 'becomes 6.76V / ℃ ^3. Since the center value of α ′ is 5.4 V / ° C ³ from the maximum and minimum values, α _P is α _P = (α′-5.4) / {(6.76-4.04) / αBit number} (7)
αBit number: 31 (decimal number) when α = 5Bit (11111)
(6) α _IC can be calculated from equation (7).

<First order coefficient>
The primary set value β _IC can be calculated from the primary coefficient β _X'tal of the crystal. In advance, each product is calculated from the relationship with β _X′tal by the following equation (8).

β _IC = coefficient1 × β _X'tal + coeffICient2 (8)
Coefficient1 and coefficient2 are coefficients determined by the cut angle of the quartz substrate.

<Temperature characteristic coefficient of rotation center temperature>
The set value Ti _IC of Ti can be calculated from the Ti coefficient Ti _{X'tal of} quartz. However, since the temperature sensor 2 varies, it is necessary to first adjust the voltage of the temperature sensor 2 in the vicinity of 25 ° C. The number of degrees Celsius the temperature sensor changes by changing 1 bit is obtained in advance (Ti_sensitivity), and calculation is performed from Ti _X'tal and Ti_sensitivity.

Ti _IC = Ti _y + {(Ti _X'tal −25 ° C.) / Ti_sensitivity} (9)
It is a setting bit after adjusting the Ti _y temperature sensor voltage.

<Γ _IC >
Since γ _IC is a bit for setting the oscillation frequency at room temperature (25 ° C.), it is set so that the target oscillation frequency is obtained 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 set bit obtained as a result is set in the RAM 5 (S4), and the pass / fail judgment is performed by measuring the frequency temperature characteristic of the temperature compensated crystal oscillator A with the corrected value. This pass / fail determination is completed, and only non-defective products are set in the PROM 5 and the process ends.

  As described above, according to the present invention, after measuring the varicap input / output voltage, the measurement of the actual temperature characteristic is performed. Manufacturing costs can be greatly reduced.

1 is a block diagram of a temperature compensated crystal oscillator of the present invention. It is a flowchart in the temperature correction process of this invention. It is a figure explaining the content in the database of the external terminal used for this invention. It is a figure explaining the content after the temperature correction in the database of the external terminal used for this invention. It is a figure explaining the code information described in the crystal oscillator of this invention. It is a flowchart in the conventional temperature correction process.

Explanation of symbols

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

Claims (1)

Built-in quartz resonator, varicap diode that adjusts the oscillation frequency of the oscillation circuit that oscillates the quartz resonator, and writable read-only memory that stores information on the control voltage applied to the varicap diode in bit values A temperature characteristic correction method for a crystal oscillator including an LSI element,
Prepare a plurality of the crystal resonators and LSI elements, measure the frequency temperature characteristic coefficient of each crystal oscillator, the temperature characteristic rotation center temperature coefficient and the varicap sensitivity of the varicap diode built in each LSI element, Registering the measured value in correspondence with a predetermined code in the first database of the external terminal, and attaching the code to each crystal unit;
A step of recognizing a code attached to each crystal resonator (S1);
A step (S2) of collating the code recognized in the step (S1) with the code on the first database;
The frequency temperature characteristic coefficient of the crystal unit corresponding to the code verified in the step (S2), the temperature characteristic rotation center temperature coefficient , the varicap sensitivity of the varicap diode, the minimum and maximum values of the coefficient specific to the crystal unit The coefficient determined by the cut angle of the quartz substrate, the value of the temperature change of the temperature sensor in the change of 1 bit, and the bit for setting the oscillation frequency at room temperature (25 ° C.), while actually measuring the oscillation frequency A step of calculating temperature correction data based on a value set to obtain a target oscillation frequency, and registering the temperature correction data in the second database of the external terminal so as to correspond to the code (S3) When,
Writing temperature correction data corresponding to each code calculated in the step (S3) into a writable read-only memory of each LSI element with a bit value (S4);
A step of measuring a frequency temperature characteristic of the crystal oscillator whose temperature is corrected by applying a control voltage based on the bit value written in the step (S4) to the varicap diode, and determining a quality of the crystal oscillator (S5). And a method of correcting the temperature characteristics of the crystal oscillator.

Images