JPH10270942A - Temperature compensation crystal oscillator and its adjusting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily adjust a frequency temperature characteristic and to shorten adjusting time by providing switches for a first and third order function voltage generation circuits and independently adjusting the coefficients of the first and third order function voltage generation circuits. SOLUTION: When a first order coefficient of a first order function generation circuit 1 is adjusted for obtaining the first order coefficient of the first order function generation circuit 3, the switch SW1 is turned off and first order coefficient adjusting resistance R1 is adjusted while a voltage measuring means monitors the output voltage of a terminal A. Then, it is adjusted so that desired first order temperature compensated voltage is obtained. For obtaining the third order coefficient of temperature compensated voltage, SW3 is turned off, resistance R3 for a third order coefficient adjusting is adjusted while the output voltage of a terminal B is monitored and desired third order temperature compensated voltage is obtained so as to adjust the third order coefficient of a third order function generation circuit 4. Thus, the first order voltage and the third order voltage can independently be adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting a temperature-compensated crystal oscillator, and more particularly to a method for adjusting a temperature-compensated crystal oscillator having a temperature sensor, a linear function and a cubic function voltage generating circuit.

[0002]

2. Description of the Related Art In recent years, demands for improving the frequency stability, reducing the size, and reducing the price of crystal oscillators have been particularly increasing in the field of portable telephone terminals and the like. In a crystal oscillator using a crystal oscillator as a frequency control element, the oscillation frequency changes in accordance with a change in ambient temperature due to the frequency temperature characteristics of the crystal oscillator used in the crystal oscillator. Therefore, a temperature-compensated crystal oscillator (TCXO) using an AT-cut crystal resonator has been used in a field requiring higher frequency stability than ever before.
The TXCO performs temperature compensation by inserting and connecting a variable capacitance means in an oscillation loop including a crystal resonator, and changing the variable capacitance value so as to cancel out the frequency temperature characteristic of the crystal resonator. For example, a variable-capacitance diode is inserted into an oscillation loop, and both ends of the variable-capacitance diode of a voltage-controlled crystal oscillator (VCXO) configured such that a change in voltage applied to both ends thereof and a change in oscillation frequency are proportional to each other. In some cases, a temperature compensation voltage that suppresses a change in the frequency of the crystal oscillator is applied from outside the oscillation loop to perform temperature compensation of the crystal oscillator.

The amount of change in the frequency corresponding to the output voltage of the temperature compensation voltage generating circuit is determined by the sensitivity of the capacitance change to the fluctuation of the voltage applied to both ends of the variable capacitance element, for example, the variable capacitance diode, and the capacitance of the variable capacitance diode. It is determined by the sensitivity of the frequency change of the voltage controlled crystal oscillator corresponding to the change. In the temperature-compensated crystal oscillator of this method, a method of generating a temperature-compensated voltage to be applied to a variable capacitance diode from a circuit network using a thermistor and a resistor has been generally used. Recently, a method as shown in FIG. 3 has also been proposed, in which the first-order function voltage generation circuit 13 and the third-order function voltage generation circuit 14 are respectively based on the temperature information from the temperature sensor 12. A function voltage is generated, and the combined output Vcomp is supplied to both ends of the variable capacitance diode of the voltage controlled crystal oscillator to perform temperature compensation.

[0004]

However, in the temperature compensated crystal oscillator using the compensation voltage generation circuit including the thermistor and the resistor, the measurement of the frequency-temperature characteristics of the TCXO and the adjustment of the element value of the compensation voltage generation circuit are performed. The adjustment is repeated by trial and error so that the characteristics converge little by little within a predetermined standard. Further, in a compensation voltage generating circuit using a circuit for generating a first-order function voltage and a third-order function voltage with respect to temperature as shown in FIG. Since it is difficult to approximate the circuit with a first-order function with high accuracy, it is actually necessary to vary R1 and R2 provided in each voltage generation circuit and fine-tune by trial and error. There was a disadvantage. The present invention has been made in order to solve the above-described disadvantages, and in advance, a temperature-output voltage characteristic of a temperature sensor and a temperature-applied voltage characteristic for maintaining an oscillation frequency of a voltage-controlled crystal oscillator at a constant frequency are obtained. It is an object of the present invention to provide a temperature-compensated crystal oscillator in which the temperature-temperature compensation of TCXO is extremely easy in a method of obtaining the first-order and third-order coefficients of a compensation voltage generating circuit from the characteristics and performing frequency temperature compensation of TCXO. .

[0005]

In order to achieve the above object, according to the first aspect of the present invention, there is provided a voltage controlled crystal oscillator and a compensation required for canceling a temperature-frequency characteristic of the voltage controlled oscillator. A temperature generating crystal oscillator comprising a voltage generating circuit for generating a voltage, wherein the voltage generating circuit includes a plurality of function voltage generating circuits each of which has a temperature as a variable, and synthesizes an output of each function voltage generating circuit to generate the voltage control crystal. A temperature-compensated crystal oscillator for supplying a voltage to an oscillator, wherein a switch is provided in at least one of the output short-circuits of the function voltage generation circuit. The invention according to claim 2 is the temperature compensated crystal oscillator according to claim 1, wherein the function voltage generation circuit is a linear function voltage generation circuit and a cubic function voltage generation circuit. The invention according to claim 3, wherein the coefficient is adjusted for each function voltage generation circuit while monitoring the output voltage of each function voltage generation circuit by opening the switch. This is a method for adjusting the compensation crystal oscillator.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the drawings. FIG. 1 is a block diagram showing a configuration of a TCXO according to the present invention. The compensation voltage generation circuit includes a temperature sensor 2, a first-order function voltage generation circuit 3, a third-order function voltage generation circuit 4 that receives temperature information output from the temperature sensor, and an output terminal of the first-order function voltage generation circuit 3. It comprises a switch SW1 connected in series and a switch SW3 connected in series to the output terminal of the cubic function voltage generation circuit 4. In addition,
Each voltage generating circuit is provided with adjusting resistors R1 and R3, which are variable resistors for coefficient adjustment. A feature of the present invention is that switches SW1 and SW3 are provided in the primary and cubic function voltage generating circuits so that the coefficients of the primary and cubic function voltage generating circuits can be adjusted independently. During normal operation, SW1 and SW2 are both closed, and the output voltage Vs of the TCXO temperature sensor 2 shown in FIG.
ens is input to the first-order function voltage generation circuit 3 and the third-order function voltage generation circuit 4, and a first-order voltage and a third-order voltage relating to temperature are generated from the respective function voltage generation circuits. Applied to the variable capacitance element. As a result, the capacitance of the variable capacitance element in the oscillation loop changes, and the frequency of the oscillation loop fluctuates so as to suppress the frequency temperature characteristics of the crystal resonator.

Next, a method of adjusting TCXO according to the present invention will be described. First, the temperature-voltage characteristic of the temperature sensor 2 is measured in advance, and thereafter, the applied voltage Vc of VCXO necessary for maintaining the oscillation frequency of the voltage controlled crystal oscillator 1 at a constant value (F ₀ ) with respect to a temperature change is determined. The applied voltage value V obtained over the entire temperature range to be compensated and corresponding to the temperature
_{Get C.} By using the measurement result to calculate a cubic approximate expression relating to the temperature of the applied voltage V _C, obtaining the primary and third-order coefficients of the applied voltage V _C. VCXO is calculated by calculating the temperature compensation voltage of each of the first-order function generation circuit and the third-order function voltage generation circuit at an arbitrary temperature using the first-order and third-order coefficients, and combining the temperature-generation voltage of the temperature sensor 2. Temperature compensation voltage to be applied to the variable capacitance element can be obtained. In this case, the fine adjustment of the temperature compensation voltage is performed using the first and third order coefficient adjusting resistors R1 and R3 of the function voltage generating circuit.

To obtain a first order coefficient of the temperature compensation voltage,
When adjusting the first order coefficient of the first order function generation circuit, SW
After turning 1 off, while adjusting the output voltage of the terminal A with a voltage measuring means such as a digital voltmeter, the primary coefficient adjusting resistor R1 is adjusted so as to obtain a desired primary temperature compensation voltage. I do. Similarly, in order to obtain the third order coefficient of the temperature compensation voltage, the adjustment of the third order coefficient of the third order function generation circuit is performed by turning off the switch SW3 and monitoring the output voltage of the terminal B while adjusting the third order coefficient. The resistance R3 is adjusted so that a desired third-order temperature compensation voltage is obtained. After these adjustments are completed, SW1 and SW3 are closed and the primary compensation voltage and 3
It is sufficient to confirm that a temperature compensation voltage to be applied to the VCXO can be obtained by adding the following compensation voltages.

FIG. 2 is a block diagram of a TCXO according to the present invention, which differs from that of FIG. 1 in that the switch of the linear function voltage generating circuit is omitted and only the switch SW3 is used. In this case, the adjustment of the primary coefficient is performed by turning off the switch SW3 and setting the terminal Vco
mp while monitoring the output voltage of mp
Is adjusted to obtain a desired first-order temperature compensation voltage. Thereafter, the third-order coefficient is adjusted while monitoring the output voltage of the terminal B with the switch SW3 turned off, and adjusting the third-order coefficient adjustment resistor R3 so as to obtain a desired third-order temperature compensation voltage. . After completing the adjustment, close SW3 to VCX
The fact that the temperature compensation voltage to which O is applied can be obtained
You just have to check at the terminal.

In the above description of the embodiment, the adjusting method according to the present invention has been described by using a combination of a linear function voltage generating circuit and a cubic function voltage generating circuit. However, the present invention is not limited to this. Instead, the present invention may be applied to a combination of a plurality of cubic function voltage generation circuits or a combination of multidimensional function voltage generation circuits.

[0011]

As described above, according to the present invention, in a TCXO in which a temperature compensating circuit comprising a temperature sensor and a function voltage generating circuit is combined with a voltage controlled crystal oscillator, the voltage generated by the temperature sensor and the oscillation of the voltage controlled crystal oscillator are determined in advance. A temperature-applied voltage Vc for keeping the frequency constant is obtained, and 1 is obtained from the temperature characteristic of the temperature sensor and the temperature-applied voltage Vc.
Since the primary and tertiary voltages can be adjusted independently of each other by determining the secondary and tertiary coefficients, the adjustment method is much easier than the conventional adjustment method, and the frequency temperature characteristics are measured many times. There is no need to perform the adjustment, and the adjustment time can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a method of adjusting a temperature compensated crystal oscillator according to the present invention.

FIG. 2 is a diagram showing another embodiment of the method of adjusting the temperature compensated crystal oscillator according to the present invention.

FIG. 3 is a diagram illustrating a method of adjusting a conventional temperature compensated crystal oscillator.

[Explanation of symbols]

 1. Voltage controlled crystal oscillator 2. Temperature sensor 3. Linear function voltage generator 4. Linear function voltage generator R1, R3. Resistor SW1, SW3. Switch A, B, Vcomp.

Claims (3)

[Claims] 1. A temperature-compensated crystal oscillator comprising a voltage-controlled crystal oscillator and a voltage-generating circuit for generating a compensation voltage necessary for canceling the temperature-frequency characteristic of the voltage-controlled oscillator, wherein the voltage-generating circuit controls the temperature. A plurality of function voltage generating circuits each serving as a variable, and combining the outputs of the function voltage generating circuits to supply a voltage to the voltage controlled crystal oscillator, wherein at least one of the output terminals of the function voltage generating circuit is provided. A temperature-compensated crystal oscillator characterized in that a switch is provided for the crystal oscillator. 2. The temperature compensated crystal oscillator according to claim 1, wherein said function voltage generation circuit is a first-order function voltage generation circuit and a third-order function voltage generation circuit. 3. The temperature compensated crystal oscillator according to claim 1, wherein said switch is opened to adjust the coefficient of each function voltage generation circuit while monitoring the output voltage of each function voltage generation circuit. Adjustment method.