JPS6062727A - Frequency stabilizer to temperature change in crystal oscillator - Google Patents

Abstract

PURPOSE:To obtain the temperature frequency characteristic with high stability by digitizing an output from a temperature sensor and converting a compensated digital data into an anlog data so as to control a crystal oscillator. CONSTITUTION:An input of the temperature sensor 2 is written in an address of a PROM4 through an A/D converter 3 so as to read the compensated digital data Cn stored therein, a temperature compensation DC voltage Vo is applied to the crystal oscillator 1 through a D/A converter 5 so as to obtain the temperature frequency characteristic with high stability. Then a frequency comparator 6 of a data processing unit 10 mounted removably outputs a frequency difference between an output frequency and the stadard frequency, and a microcomputer 7 outputs the compensated digital data Cn and writes it in the PROM4.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for responding to temperature changes in crystal oscillators used in wireless communication devices, quartz lock electronic devices, etc. that require highly stable temperature-frequency characteristics. This invention relates to a frequency stabilizing device.

[Prior art]

Generally, wireless communication devices, such as personal radios, MCA
The temperature-frequency characteristics of the AT-cut crystal oscillator used in radio equipment, SSB land mobile equipment, Rinconvex radio equipment, GHz band wireless radio equipment, narrow FM radio equipment, or quartz lock electronic equipment, etc. It is known that it has a cubic curve as shown in FIG. 2, and that its frequency characteristics change as shown by curves a and b in FIG. 2 depending on the cutting angle.

Therefore, various compensation circuits have been considered in the past to compensate for changes in frequency characteristics due to temperature changes.
A typical example is ocxo.

There is something called TCXO.

OCXO uses an oven to keep the environmental temperature of the crystal oscillator constant, while TCXO uses a temperature variable element such as a thermistor to change the constant of the crystal oscillator depending on the temperature. This is aimed at stabilization.

A simple example of a TCXO will be explained using the conventionally used circuit diagram shown in Fig. 1 and the characteristic diagram shown in Fig. 2.The crystal oscillator 1a has a temperature-frequency characteristic curve shown in Fig. 2 b. is selected. In other words, the oscillation frequency fQ shown in Fig. 1 is now f
s: Series resonant frequency Co of the crystal oscillator; parallel capacitance of the crystal oscillator, r: ratio of series capacitance to parallel capacitance, CL: load capacity of the crystal oscillator In the above equation, OL is R1 in Figure 1.
, C, , C2° C3, C4, CII, C6 and transistor T 1 cQ Determined by Haas capacitance, Ca@
If the C51TrO capacitance has a small influence on the entire TCX0 (temperature compensated crystal oscillator) and is therefore ignored, then CX is the combined capacitance of R1 and 01.

In this CL equation, CX changes rapidly to reduce the influence of the small n Ct when the temperature becomes lower than room temperature because of the combined capacity of the thermistor positive and C positive. In addition, since the thermistor R1 is normally a nonlinear element, the resistance change is very small above room temperature, and the value of CX is kept almost constant. As a result, its temperature-frequency characteristics are as shown by the dotted line C in Figure 2. However, the heater current of the crystal oscillator circuit in the OCXO constant temperature oven is large, making it unsuitable for use as a portable device, and when used as a mopil device. It also takes time to warm up when turning on the device.
There is a problem with lack of responsiveness.

In addition, in the TCXO, since the amount of compensation of the thermistor R1 is limited within a predetermined range, the temperature frequency characteristics of the crystal oscillator 1a should be selected in advance, or the amount of compensation of the thermistor R1 should be adjusted to match that of the crystal oscillator 1a. The crystal oscillator 1 itself becomes very expensive because the selection is time-consuming and has a low yield. In addition, the crystal oscillator 1 shown in FIG. 1 is not compensated for on the high temperature side.
In order to mass-produce products with high stability of ±2 ppm or less at 0°C to 60°C, even at low temperatures, the slope curve of the temperature-frequency characteristic curve of the crystal oscillator 1a and the temperature-frequency characteristic of the thermistor R11, which is a compensation element. Since the slope of the curve does not match closely with the curve, it is very difficult to obtain high stability.

In addition, using a crystal oscillator 1a with a large room temperature deviation,
When the C rises, a trimmer capacitor C is used to adjust it.
As a result of moving the capacitor 4, the mutual relationship between the crystal oscillator 1a and thermistor 1a described above cannot be maintained constant, and the crystal oscillator 1 cannot be used as a crystal oscillator 1 having highly stable frequency characteristics. In addition, the frequency drift of the crystal oscillator 1 due to temperature changes in the power supply voltage Vcc, and the temperature changes and dispersion of the crystal oscillator in the case of using a parallel converter, must also be taken into account, making mass production extremely difficult. It also had problems.

[Purpose of Hon'ei'g]

This item was invented after considering the various problems mentioned above.
Its purpose is to provide quick response, enable miniaturization, and provide highly stable temperature-frequency characteristics regardless of the temperature-frequency characteristics of the crystal oscillator. The present invention provides a frequency stabilizing device for temperature changes in a crystal oscillator used in a nine-crystal oscillator, which eliminates the need to worry about variations and linearity, and is also excellent in terms of mass production and cost reduction of the oscillator. It is in.

[Summary of the Invention] In order to achieve the above object, the device of the present invention includes a temperature sensor that converts ambient temperature into a DC voltage value, and an A/D converter that converts the voltage value output from the temperature sensor into digital data. , a dedicated memory for reading compensation digital data stored in accordance with the digital data output from the A/D converter, and a D/A converter for converting the compensation digital data output from the dedicated memory into a DC voltage; The D/
It has a crystal oscillator whose output frequency changes according to the application of the DC voltage output from the A converter, and further inputs the output frequency output from the crystal oscillator and a standard frequency from a separately provided standard frequency generator. A frequency comparator to be compared and a frequency output difference outputted from the comparator are taken in, the compensation data is calculated and inputted to the D/A converter, and the data is stored in the dedicated memory as the ambient temperature changes. The device is equipped with a removable data processing device consisting of a microcomputer that sequentially specifies the address of the compensation digital data stored in the crystal oscillator, and the compensation digital data corresponding to the temperature frequency change of the crystal oscillator is stored in a dedicated memory as a digital value. , addressing a compensation value in the memory according to temperature changes, so that the crystal oscillator always oscillates at a stable frequency even in the presence of temperature changes based on the compensation value read from the memory; □It is characterized by being able to deal with oscillation errors due to temperature changes in the crystal oscillator itself.

[Example of the present invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the apparatus of the present invention will be described below with reference to the drawings.

In Fig. 3 (a), 1 is the applied DC voltage VOv
The crystal oscillator 1 has an output frequency f toward the output side 9.
It is designed to oscillate O.

In the figure, 2 is a temperature sensor that converts the ambient temperature into a voltage value VT and outputs it. 5 is an A/D converter which converts the voltage value VT inputted from the temperature sensor 2 into digital data Tn. 4 is FR, which is a writable reading-only memory.
In the OM, this PROM 4 temporarily sets the frequency for each temperature change, which is input from a microcomputer (described later) and written and stored in the address, based on temperature digital data Tn input from the A/D converter 3. The compensated digital data Cn is read out, and the D/A converter 5
The terminal is designed to output compensation digital data On. The D/A converter 5 inputs the compensation digital data Cn output from the PROM 4, converts it to an analog value, and applies a large DC voltage vO to the crystal oscillator 1. In other words, it compensates the FROM 4 address. The digital data Cn is commanded to read in each temperature at a data processor 10, and the data processor 10 inputs and compares the output frequency fO and the standard frequency fs outputted from a standard frequency generator (not shown). and set the difference as digital data Rn, and set the difference as digital data Rn.
A frequency comparator 6 outputs as n, and digital data Rn output from the frequency comparator 6 is converted into compensation digital data Cn from digital data Rn set for each temperature.
It is composed of a microcomputer 7 that calculates and issues a write command to the FROM 4 address.

Note that the data processing device 10 is removably installed,
Once the compensation digital data Cn is written and stored in the FROM 4, it can be removed as appropriate and used as shown in Figure 3.

Next, the operation of PROM 4 and microcomputer 7 will be explained. Although the operation will be explained in terms of 8-bit operation, the operation is not limited to this, and in principle, the same operation and effect will be achieved no matter how many bits are used.

First, at room temperature, the microcomputer 7 is 00H to FF.
Compensation digital data O is sent to the D/A converter 5 in sequence up to H.
Output n. At this time, the DC voltage 0 applied to the crystal oscillator 1 changes approximately linearly as shown in FIG. 5, and the frequency of the crystal oscillator 1 changes accordingly. Then, the frequency comparator 6 outputs the output frequency fO and the reference frequency f8.
The data between 0OH and FFHO is sequentially input to the microcomputer 7 as digital data Rn. Therefore, the compensation digital data Cn and the digital data R output from the microcomputer 7
A certain correlation can be obtained with n. For example, for 0n-00H, Rn=+04H, 1
For on, it is 15H, and this relationship is almost not similar to the graph shown in FIG.

The mutually corresponding temporary digital data Ca and Rn thus obtained are temporarily stored in the microcomputer 7.Next, the crystal oscillator 1, temperature sensor 2, and A/D converter a
, the D/A converter 5 is placed in a temperature-changeable constant temperature bath, and the ambient temperature other than the data processing device 10 is set within a desired temperature range (
For example, -30°C to 60°C).

At this time, the microcomputer 7 continues to output temporarily set digital data Ca (for example, 7FH) as a reference. Further, the microcomputer 7 takes in the output digital data Tn of the Φ converter 3 and the output digital data Rn of the frequency comparator 6, calculates compensation digital data On for the Rn, and calculates the compensation digital data On for the Tn. Specify the FROM 4 address. Next, the compensation digital data Cn addressed by the Tn
is written to the FROM 4 address.

After performing the above operation over the desired temperature range, several crystal oscillators such as 1 are taken out of the thermostatic chamber, and compensation digital data On is written at each temperature in the address of FROM 4 as shown in the graph in Figure 5. It will be.

Here, to describe the calculations inside the microcomputer 7, the captured digital data 几n (referred to as R1)
The digital data Rn corresponding to the computer output of the microcomputer 7, which was stored at room temperature, is checked and it is determined which computer's compensation digital data On output R1 corresponds to.

If the estimated value is Cn, then CnmF
Compensation digital data Cn can be obtained by calculating FH-Ca.

[Operation of the present invention]

According to the present invention configured in this manner, after the data processing device 10 is removed, the digital data Tn, which changes from moment to moment due to temperature changes, directly specifies the address of the PIEtOM 4, and is transferred from the PR, OM 4 to the address of the PIEtOM 4. If the contents of the output compensation digital data On are directly input to the D/A converter 5, the D/A converter 5 will apply the DC voltage VO that varies depending on the temperature to the crystal oscillator 1. The frequency stability of the crystal oscillator 1 with respect to temperature is kept constant as shown in FIG. By compensating the digital data graph Rn shown in FIG. 5 with the compensated digital data graph Cn, a constant output frequency fO can be obtained even if there is a temperature change.

As described above, it is possible to easily obtain frequency stability of approximately ±0.5 ppm even with temperature changes over a wide range of, for example, -30°C to 60°C.

Further, the immediate response to temperature changes is also stored in the FROM 4 via the microcomputer 7.
Since the configuration allows the compensation digital data Cn to be called out immediately from the ROM 4, the data processing device 10 can be removed when writing of the compensation digital data Cn to the FROM 4 is completed, resulting in miniaturization.

[Effects of the present invention]

As is clear from the above slots, according to the device of the present invention,
The instantaneous response of the crystal oscillator to temperature changes is improved, the number of attached parts is reduced, the size can be reduced, and moreover, highly stable temperature-frequency characteristics can be obtained. Furthermore, if the variations and linearity of the parts used in the crystal oscillator are compensated for, there is no need to take these effects into consideration, which will improve the mass production and cost reduction of the crystal oscillator. This will bring about various effects.

[Brief explanation of the drawing]

Figures 1 and 2 show a conventional example of a TCX crystal oscillator.
The circuit diagram used for O, its frequency characteristic diagram, and Figures 3 (A), (B) to Figure 5 are book diagrams showing an embodiment of the device of the present invention, and the data processing device has been removed, respectively. They are a block diagram in the state, a characteristic diagram of the applied DC voltage ■0, and a characteristic diagram of compensation digital data. 1...Crystal oscillator 2...Temperature sensor 6...A/
D converter 4...PROM5...D/A converter 6
... Frequency comparator 7 ... Microcomputer 10 ... Data processing device ■0 ... Applied DC voltage VT ... DC voltage Ca ... Digital data Cn ... Compensation digital data Rn. ...Digital data patent applicant Nippon Marantz Co., Ltd.

Claims (1)

[Claims] (1) A temperature sensor that converts ambient temperature into a DC voltage value, an A/D converter that converts the voltage value output from the temperature sensor into digital data, and the digital data output from the A/D converter. A dedicated memory for reading compensation digital data stored in the data, a D/A converter for converting the compensation digital data output from the dedicated memory into a DC voltage, and a DC voltage output from the D/A converter. a crystal oscillator whose output frequency changes according to the application of the crystal oscillator; (1) taking the difference in frequency output from the comparator, calculating compensation digital data thereof, and inputting it to the D/A converter, and compensating digital data stored in the dedicated memory as the ambient temperature changes; Frequency stabilization device for crystal oscillator temperature changes, which is equipped with a removable data processing device consisting of a microcomputer that sequentially specifies the address of the crystal oscillator.