JPH05251932A - Temperature compensation type crystal oscillator - Google Patents

Abstract

PURPOSE:To obtain high frequency stability over a wide temperature range by devising the oscillator such that a temperature compensation element section makes analog temperature compensation and a variable capacitive element section whose capacitance is varied with a control voltage added to the temperature compensation element section makes digital temperature compensation in addition. CONSTITUTION:When temperature around a crystal vibrator 33 changes, a temperature sensor detects the change and a temperature compensation element section 32 also detects it. The temperature compensation element section 32 makes analog temperature compensation so that a frequency fluctuation of the crystal vibrator 33 is set within a range from + or -2ppm to + or -3ppm (at -30 deg.C to +80 deg.C). Then a control voltage is applied to a variable capacitive element section 31 via a digital circuit network according to the temperature information detected by the temperature sensor. Since the variable capacitance element section 31 is controlled by the control voltage, the frequency fluctuation of the crystal vibrator 33 is set within a range of + or -0.15ppm (at -30 deg.C to +80 deg.C).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature compensated crystal oscillator.

[0002]

2. Description of the Related Art Recently, mobile communication has been in the limelight. Among them, mobile communication systems represented by car telephones are required to have high frequency stability over a wide temperature range. Currently, in this type of mobile communication system, an analog type temperature-compensated crystal oscillator (hereinafter referred to as AT
CXO) and a digital temperature-compensated crystal oscillator (hereinafter referred to as DTCXO) are used. Both of these oscillators have the following performance.

(A) The frequency f stability of the ATCXO for mobile stations is ± 2 p within the temperature range of -30 ° C to + 80 ° C.
Performance of ± 3 ppm from pm, (b) D for mobile station
The frequency f stability of TCXO is +8 from -30 ° C.
The performance is from ± 1ppm to ± 1.5ppm within the range of 0 ° C, and the frequency stability of (c) DTCXO for fixed station is
± 0.1ppm in the temperature range of -10 ℃ to + 60 ℃
To ± 0.5 ppm performance.

[0004]

FIG. 3 shows the temperature-frequency characteristics of a single crystal unit of the ATCXO for mobile stations. As is clear from FIG. 3, the frequency fluctuation with respect to temperature is about 25 ppm when the crystal unit is alone,
Quite big.

Therefore, as shown in FIG. 4, the thermistor 1
When the temperature compensator 15 in which the capacitors 1 and 12 and the capacitors 13 and 14 are connected in parallel as shown in the figure is connected in series with the crystal oscillator 16, the frequency stability of the ATCXO is ±, as shown in FIG.
Within 2 ppm. However, in the ATCXO, there is a problem that it is difficult to adjust the stability more than this due to variations in the thermistor and the capacitor.

For this reason, recently, as shown in FIG. 6, the temperature sensor 21 detects the temperature around the crystal unit, and the detected temperature information is converted into analog-digital converters 22 and RO.
DTCXO means for supplying temperature to a digital circuit consisting of M23 and digital-analog converter 24 and compensating the temperature of the voltage-controlled crystal oscillator VCXO with a control voltage output from this digital circuit has come to be adopted. .. Here, the operation of the digital circuit network will be described. The analog-to-digital converter 22 converts the temperature information into a digital signal and then supplies it to the ROM 23 as a temperature address for the temperature compensation data. The ROM 23 stores in advance information of temperature compensation data, data corresponding to the temperature address is sequentially read, and the read signal is converted into an analog voltage by the digital-analog converter 24. This analog voltage is supplied to the VCXO as a control voltage, and the frequency of the crystal unit is controlled according to the temperature change.

FIG. 7A is a temperature-frequency characteristic diagram of a single crystal unit of the VCXO. When temperature compensation is not performed, the VCXO is a VCXO.
O indicates that there is a frequency variation of ± 10 ppm. 7B shows the amount of frequency change per unit temperature of VCXO, and FIG. 7C is a temperature-frequency characteristic diagram when temperature compensation (as in the block diagram shown in FIG. 6) is performed. In FIG. 7C, the portion indicated by reference numeral C ₁ indicates that a frequency deviation due to sampling occurs.

In the DTCXO shown in FIG. 6, in order to keep the frequency stability high in a wide temperature range, if the number of bits of the analog-digital converter 22 and the digital-analog converter 24 is increased, the information amount of temperature compensation is increased. Although the number is increased and the accuracy is increased, there is a problem that cost is increased and miniaturization is difficult. Further, since the DTCXO performs stepwise control compensation by digital sampling, there is also a problem that a temperature deviation causes a sawtooth frequency deviation.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a temperature-compensated crystal oscillator capable of increasing frequency stability over a wide temperature range.

[0010]

In order to achieve the above object, the present invention provides a temperature sensor for detecting the ambient temperature of a crystal unit and a temperature information obtained by analog-digital conversion of temperature information detected by the temperature sensor. A ROM provided as a temperature address for the compensation data, and a digital-analog converter provided by sequentially reading the temperature compensation data stored in the ROM according to the temperature address,
In a crystal oscillator provided with a control voltage sent from this converter, and a voltage control crystal oscillation circuit that obtains a stable frequency output with respect to ambient temperature changes by the control voltage, the voltage control crystal oscillation circuit is A crystal unit, a variable capacitance element unit whose capacitance changes according to a control voltage, a temperature compensation element unit inserted in an electric path connecting the variable capacitance unit unit and one end of the crystal unit, and the crystal vibration unit. It is characterized in that it is provided with an oscillating circuit section which is connected to the other end of the child and obtains an oscillating output as an output.

[0011]

In the voltage controlled crystal oscillating circuit of the present invention, analog temperature compensation is performed in the temperature compensating element section, and ± 2 ppm to ± 3
to obtain ppm. The frequency stability of the crystal unit is increased by adding digital temperature compensation including a variable capacitance element unit that is variable by the control voltage.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 31 is a voltage variable capacitance element 31a.
A variable capacitance element section including a capacitor 31b and a resistor 31c is provided at one end of the resistor 31c of the element section 31 as shown in FIG.
The control voltage of the digital-analog converter 24 shown in is applied. Reference numeral 32 denotes a temperature compensating element portion. This element portion 32 is a series connection of parallel circuits each including a thermistor 32a and a capacitor 32b and a thermistor 32c and a capacitor 32d. One end is connected to the variable capacitance element portion 31 and the other end Is connected to the base of a transistor 34a forming the oscillation circuit section 34 via the crystal oscillator 33. In the oscillator circuit section 34, 34b is a resistor and 34c is a capacitor.

The voltage controlled crystal oscillating circuit configured as described above is replaced with the VCXO shown in FIG. Now, if there is a change in the temperature around the crystal unit 33, the temperature sensor 21 detects this and the temperature compensation element unit 3
2 also detects this. The temperature compensating element unit 32 performs analog temperature compensation so that the frequency fluctuation of the crystal unit 33 is ± 2 pp.
Temperature compensation is performed so as to be within ± 3 ppm (−30 ° C. to + 80 ° C.) from m. Then, according to the temperature information detected by the temperature sensor 21, the control voltage is applied to the variable capacitance element section 31 via the digital circuit network. By this voltage, the element portion 31
Is controlled, the frequency fluctuation of the crystal unit 33 is ±
It becomes 0.15 ppm (-30 ° C to + 80 ° C).

FIG. 2A is a temperature-frequency characteristic diagram of the oscillator circuit in the temperature-controlled crystal oscillator circuit of the above-mentioned embodiment only, and FIG. 2B is a characteristic diagram showing the frequency change amount per unit temperature of the oscillator circuit. FIG. 2C is a temperature-frequency characteristic diagram when the temperature control of the voltage controlled crystal oscillation circuit of the above embodiment is controlled by both the temperature compensation element section 32 (analog temperature compensation) and the variable capacitance element section 31 (digital temperature compensation).
The temperature-frequency characteristic diagram of FIG. 2C shows that the frequency fluctuation in the oscillation circuit in this embodiment is within the range of ± 0.15 ppm, and the frequency deviation due to the conventional sampling does not occur. Shows.

Generally, in the DTCXO, if the information stored in the ROM or the like is accurate, the frequency deviation amount δfd (ppm) of the DTCXO is expressed by the following equation.

[0016]

[Equation 1]

In the above equation, D of this embodiment and the conventional example of FIG.
The following table shows the results of substituting the values obtained by TCXO.

[0018]

[Table 1]

From the above table, in the DTCXO, the maximum frequency deviation of the DTCXO also increases in proportion to the amount of frequency change per unit temperature of the VCXO to be compensated. Therefore, if the frequency change amount is reduced, the sawtooth frequency deviation can be reduced. Therefore, if the embodiment of the present invention in which analog temperature compensation is performed is replaced with a conventional VCXO, the estimated values in the above table can be obtained. So ± 0.15ppm (-30
It is possible to obtain a voltage controlled crystal oscillating circuit of ℃ to + 80 ℃.

[0020]

As described above, according to the present invention,
There is an advantage that the frequency can be highly stabilized over a wide temperature range.

[Brief description of drawings]

FIG. 1 is a connection diagram showing a main part of an embodiment of the present invention.

FIG. 2A is a temperature-frequency characteristic diagram only for analog temperature compensation used in the embodiment of the present invention, B is a frequency change amount characteristic diagram per unit temperature, and C is the present invention in which analog and digital temperature compensation is performed. 3 is a temperature-frequency characteristic diagram of the example of FIG.

FIG. 3 is a temperature-frequency characteristic diagram of a crystal unit for ATCXO.

FIG. 4 is a connection diagram showing an analog temperature compensation network.

FIG. 5 is a characteristic diagram of ATCXO after temperature compensation.

FIG. 6 is a block diagram showing a conventional example of DTCXO.

FIG. 7A is a temperature-frequency characteristic diagram of VCXO, and B is VC.
Frequency change amount characteristic chart of XO per unit temperature, C is temperature-frequency characteristic chart of conventional DTCXO.

[Explanation of symbols]

21 ... Temperature sensor, 22 ... Analog-digital converter,
23 ... ROM, 24 ... Digital-analog converter, 31
... Variable capacitance element section, 32 ... Temperature compensation element section, 33 ... Crystal oscillator, 34 ... Oscillation circuit section.

Claims (1)

[Claims] 1. A temperature sensor for detecting an ambient temperature of a crystal unit, a ROM which is subjected to analog-digital conversion of temperature information detected by the temperature sensor to be given as a temperature address for temperature compensation data, and stored in this ROM. The temperature-compensated data is read out sequentially according to the temperature address, and the digital-analog converter and the control voltage sent from this converter are supplied. This control voltage stabilizes the ambient temperature. In a crystal oscillator including a voltage control crystal oscillation circuit that obtains a variable frequency output, the voltage control crystal oscillation circuit includes a crystal resonator, a variable capacitance element unit whose capacitance changes according to a control voltage, and the variable capacitance element unit. And a temperature compensation element section inserted in an electric path connecting one end of the crystal unit and the other end of the crystal unit, Temperature compensated crystal oscillator characterized in that it comprises an oscillation circuit portion for obtaining a vibration output.