JP2009224865A - Voltage controlled surface acoustic wave oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voltage controlled SAW oscillator which can perform stabilized operation. <P>SOLUTION: A voltage controlled SAW oscillator comprises an oscillation circuit having an SAW oscillator, and a temperature compensation voltage generator for supplying a control voltage to the oscillation circuit, wherein the temperature compensation voltage generator comprises a temperature detection unit 201 for detecting the ambient temperature of the SAW oscillator, an inverting amplifier circuit 202 and a noninverting amplifier circuit 203 producing an output current according to the output voltage from the temperature detection unit 201, a pair of function generating circuits 204 and 205 for producing currents which vary with square-law characteristics from the output currents of the amplifier circuits 202 and 203, a section 208 for adding the currents produced from the function generating circuits 204 and 205, a current to voltage conversion circuit 209 for converting the added current varying with square-law characteristics into a voltage convex upward, and an inverting amplifier circuit 210 producing a control voltage which is axially symmetrical with respect to a quadratic function showing the frequency temperature characteristics of an elastic surface acoustic wave oscillator and varying with square-law characteristics convex downward from the converted voltage. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a voltage-controlled surface acoustic wave oscillator that compensates for frequency fluctuations associated with changes in ambient temperature of a surface acoustic wave (SAW) oscillator.

  The SAW oscillator has a frequency-temperature characteristic in which the oscillation frequency changes when the ambient temperature changes, and the oscillation frequency is known to change along a convex curve with respect to the temperature change. , Can be approximated by a quadratic curve. The oscillation frequency of the SAW resonator has a maximum value at a certain temperature, and has a characteristic of decreasing as the temperature becomes lower or higher than the temperature (peak temperature) indicating the maximum value. The frequency temperature characteristics of this SAW oscillator exceed the allowable fluctuation range in the general operating temperature range of electronic equipment, −40 ° C. to 85 ° C., specifically exceeds 100 ppm, and are used as they are. Then, normal operation such as malfunction of electronic equipment cannot be expected.

  For this reason, in the prior art, a SAW oscillation circuit in which the oscillation frequency changes in proportion to the voltage is formed, and the differential function is line-symmetric with a quadratic function indicating frequency temperature characteristics with respect to the ambient temperature of the SAW oscillator. In addition, a control voltage represented by a convex quadratic function is generated to cancel the change in the oscillation frequency due to the temperature change.

  In addition, the oscillation frequency of the SAW oscillator is detected, the detected oscillation frequency is converted into a temperature display voltage, and a control voltage generated based on the temperature display voltage is applied to the SAW oscillator to suppress temperature fluctuation of the oscillation frequency. It has been proposed (Patent Document 1).

JP-A-5-283934

  However, according to the configuration that cancels the temperature change of the oscillation frequency using a conventional differential circuit, the amount of noise generated under the operating conditions varies, and thus there is a drawback that stable operation cannot be expected due to the influence of noise. Further, according to the configuration described in Patent Document 1, it is difficult to perform high-precision compensation, and there is a drawback that a control voltage having a fluctuation range of the oscillation frequency of the ppm level cannot be obtained. It is an object of the present invention to provide a voltage controlled SAW oscillator that eliminates such drawbacks.

  A voltage-controlled SAW oscillator according to the present invention includes a surface acoustic wave oscillator whose frequency temperature characteristic is approximated by a quadratic function, an oscillation circuit whose output frequency is controlled by a control voltage, and the oscillation circuit including the control circuit A voltage-controlled surface acoustic wave oscillator comprising a temperature-compensated voltage generator for supplying a voltage, wherein the temperature-compensated voltage generator detects the ambient temperature of the surface acoustic wave oscillator and increases the detected temperature. Correspondingly, a temperature detector that generates an output voltage that decreases at a constant rate of change, and a range in which the output voltage of this temperature detector corresponds to a temperature that does not reach a preset reference temperature, corresponds to a temperature rise. A non-inverting amplifier circuit that generates an output current that is zero in a range corresponding to a temperature equal to or higher than the reference temperature, and an output of the temperature detector Voltage Inversion that generates an output current that is zero in a range corresponding to a temperature that does not reach the reference temperature, and that generates an output current that increases at a constant rate in response to a temperature increase in a range corresponding to a temperature that is higher than the reference temperature. An amplifier circuit, a pair of function generator circuits that generate a current that changes in a square characteristic from each output current of the non-inverting amplifier circuit and the inverting amplifier circuit, and a current that changes in a square characteristic generated by each of these function generator circuits. An adding unit for adding, a current-voltage conversion circuit for converting a current changing with the added square characteristic into a voltage changing with an upward convex square characteristic, and from the converted voltage, the surface acoustic wave oscillator It comprises an inverting amplifier circuit that generates a control voltage that is line-symmetric with a quadratic function indicating frequency temperature characteristics and that changes in a square characteristic that is convex downward.

  In the above-described configuration, since the output voltage value of the temperature detection unit with respect to the reference temperature has a one-to-one correspondence, the reference voltage of the inverting amplifier circuit and the non-inverting amplifier circuit is set to the output voltage value corresponding to the reference temperature. It is preferable that a reference temperature (apex temperature) at which the oscillation frequency is maximum is set by the reference voltage. In the above-described configuration, the gain of the inverting amplifier circuit and the non-inverting amplifier circuit is adjusted, and the change rate of the output current of each amplifier circuit is adjusted so as to match the change rate of the oscillation frequency depending on the temperature of the SAW oscillator. It is preferable to set. Further, in the above-described configuration, the reference voltage of the inverting amplifier circuit that generates the control voltage has a voltage level that inverts the input voltage. Therefore, the minimum voltage corresponding to the apex temperature of the frequency temperature characteristic of the SAW oscillator is determined by this reference voltage. It is preferable to set the voltage. Furthermore, in the above-described configuration, it is preferable that a current correction circuit for improving the linearity of the change in the oscillation frequency with respect to the change in the control voltage of the oscillation circuit is provided in the subsequent stage of the pair of function generation circuits.

  According to the present invention, since the inverting amplifier circuit and the non-inverting amplifier circuit can be designed with low noise, it is possible to obtain a stable operation with low noise in the voltage controlled SAW oscillator, and the frequency temperature of the SAW oscillator. There is an effect that it is possible to obtain a control voltage that is line-symmetric with the quadratic function indicating the characteristic and changes with a square characteristic that is convex downward.

  Hereinafter, a circuit configuration of a preferred embodiment of a voltage controlled SAW oscillator according to the present invention will be described with reference to FIGS. 1 and 2 of the accompanying drawings. FIG. 1 is a circuit diagram showing a voltage controlled SAW oscillator according to the present invention. The voltage controlled SAW oscillator includes a SAW oscillation circuit 1, a temperature compensation voltage generator 2, and a memory 3.

  As shown in FIG. 1, the SAW oscillator 101 of the SAW oscillation circuit 1 is connected to the input end and the output end in parallel with the feedback resistor 103 of the inverting amplification circuit 102 made of an operational amplifier. The input terminal of the inverting amplifier circuit 102 is grounded via a capacitor 104 and a variable capacitance diode 105, and the output end is grounded via a capacitor 106 and a variable capacitance diode 107. A resistor 108 is connected to an intermediate point between the capacitor 104 and the variable capacitance diode 105, a resistor 109 is connected to an intermediate point between the capacitor 106 and the variable capacitance diode 107, and an oscillation frequency control terminal 110 is connected to each of the resistors 108 and 109. It is connected. An output terminal 111 is connected to the output terminal of the inverting amplifier circuit 102, and a coil 112 and a resistor 113 are connected in parallel between the output terminal and the SAW oscillator 101.

  When the control voltage VC, which is an oscillation frequency control signal, is input from the temperature compensation voltage generator 2 to the variable capacitance diodes 105 and 107 via the resistors 108 and 109, respectively, and the voltage value of the control voltage increases, the variable capacitance diodes The capacitance values 105 and 107 decrease and the oscillation frequency increases. The coil 112 is for increasing the fluctuation amount of the oscillation frequency, and the resistor 113 is for suppressing oscillation at an unnecessary frequency.

  Next, the circuit configuration of the temperature compensation voltage generator 2 will be described with reference to FIG. As shown in FIG. 2, the temperature compensation voltage generator 2 includes a temperature detector 201, an inverting amplifier circuit 202 for voltage-current conversion, and a non-inverted amplifier, each of which includes an operational amplifier to which the output voltage of the temperature detector 201 is input. A circuit 203, a pair of function generation circuits 204 and 205 to which output currents of the amplification circuits 202 and 203 are separately input, and output currents of the function generation circuits 204 and 205 are oscillated with respect to a control voltage change of the oscillation circuit 1. Current correction circuits 206 and 207 for correcting to improve the linearity of change, an addition unit 208 for adding the corrected current, a current-voltage conversion circuit 209 for converting the output current of the addition unit 208 into a voltage, and a conversion And an inverting amplifier circuit 210 for generating a control voltage VC from the corrected voltage.

  The temperature detector 201 detects the ambient temperature of the SAW oscillator 101, and generates an output voltage that linearly decreases with a predetermined slope as the temperature rises, as shown in FIG. Therefore, if the reference temperature is determined, the output voltage corresponding to the reference temperature is specified. Therefore, the output voltage at the vertex temperature, for example, 15 ° C., is measured in advance with the vertex temperature at which the oscillation frequency of the SAW oscillator 101 has a maximum value as the reference temperature. Then, this voltage value is written in the memory 3. The temperature detection unit 201 can be formed, for example, by connecting a pair of diode-connected transistors in series.

  The inverting amplifier circuit 202 is supplied with an output voltage corresponding to the vertex temperature of the temperature detection unit 201 previously written in the memory 3 as the reference voltage vref_To. As shown in FIG. 5, the inverting amplifier circuit 202 has a range corresponding to a temperature at which the output voltage of the temperature detection unit 201 does not reach the peak temperature (15 ° C. in the illustrated example) that is the reference temperature, in other words, a reference voltage. In a range lower than vref_To, an output current that is zero is generated, and in a range corresponding to a temperature equal to or higher than the reference temperature, in other words, in a range equal to or higher than the reference voltage vref_To, an output that linearly increases with a predetermined slope as the temperature increases. Generate current.

  Similarly to the inverting amplifier circuit 202, the non-inverting amplifier circuit 203 is supplied with an output voltage corresponding to the vertex temperature of the temperature detection unit 201 previously written in the memory 3 as the reference voltage vref_To. As shown in FIG. 4, the non-inverting amplifier circuit 203 has a range corresponding to a temperature at which the output voltage of the temperature detecting unit 201 does not reach the peak temperature (15 ° C. in the illustrated example) that is the reference temperature, in other words, the reference voltage. In a range lower than vref_To, an output current that linearly decreases with a predetermined slope as the temperature rises is generated, and in a range corresponding to a temperature equal to or higher than the reference temperature, in other words, an output that becomes zero in a range equal to or higher than the reference voltage vref_To. Generate current.

  As the inverting amplifier circuit 202 and the non-inverting amplifier circuit 203, for example, an amplifier circuit using an operational amplifier that adjusts the gain by changing the resistance value of the negative feedback circuit, which is disclosed in JP-A-2005-150982, can be used. The inverting amplifier circuit 202 and the non-inverting amplifier circuit 203 can change the vertex temperature, which is the reference temperature, by changing the reference voltage vref_To, as shown in FIG. 6, which is a combination of FIGS. That is, in FIG. 6, the dotted line indicates that the vertex temperature is 15 ° C., and the solid line indicates that the vertex temperature is 30 ° C. Further, the inverting amplifier circuit 202 and the non-inverting amplifier circuit 203 change the rate of change of the output current with respect to the temperature change by changing the resistance value of the negative feedback circuit and adjusting the gain, for example, as shown in FIG. In addition, the slope of the straight line shown in FIGS. 4 and 5 can be changed. Data for performing this gain adjustment, for example, the resistance value of the negative feedback circuit is also written in the memory 3 in advance.

  The output currents of the inverting amplifier circuit 202 and the non-inverting amplifier circuit 203 change linearly with a constant change rate. When these output currents are input to the function generation circuits 204 and 205, respectively, the function generation circuits Reference numerals 204 and 205 output linearly changing input currents as currents that change with square characteristics. Each of the function generating circuits 204 and 205 can be configured using a known translinear circuit. The currents generated by the function generation circuits 204 and 205 that change with the square characteristics are input to the current correction circuits 206 and 207, which are composed of, for example, translinear circuits. The linearity is improved and added by the adder 208, resulting in a current that changes with the square characteristic shown in FIG.

  The corrected current added by the adder 208 is input to the current-voltage conversion circuit 209, where it is converted to a voltage that changes with a square characteristic that is convex upward (see FIG. 9). , Input to the inverting amplifier circuit 210. The inverting amplification circuit 210 inverts the voltage VCin, which is input from the current-voltage conversion circuit 209, and changes with an upward convex square characteristic into a control voltage VC that changes with a downward convex square characteristic, as shown in FIG. Amplify and output.

  By changing the reference voltage vref_fo of the inverting amplifier circuit 210, the lowest control voltage value corresponding to the apex temperature of the frequency temperature characteristic of the SAW oscillator 101 is set by changing the voltage level that is inverted up and down as shown in FIG. Can do. That is, the reference voltage vref_fo indicates the upside down voltage level in the inverting amplifier circuit 210, and the value of the reference voltage vref_fo is also written in the memory 3 in advance. By appropriately setting the minimum control voltage value in this way, a control voltage that changes in a downward convex square characteristic that is axisymmetric to a quadratic function indicating the frequency temperature characteristic of the surface acoustic wave oscillator 101 can be generated more reliably. can do.

  As described above, according to the present embodiment, the frequency temperature characteristic of the SAW oscillator 101 is measured in advance, and the output voltage of the temperature detection unit 2 corresponding to the vertex temperature and the quadratic function that approximates the frequency temperature characteristic are obtained. A resistance value of the negative feedback circuit of each of the amplifier circuits 202 and 203 for obtaining a change in output current corresponding to the rate of change, and a voltage value serving as an inversion reference for obtaining the lowest control voltage value corresponding to the vertex temperature, Writing to the memory 3, the output voltage value is set as the value of the reference voltage vref_To of each amplifier circuit 202, 203, the gain of each amplifier circuit 202, 203 is set by the resistance value, and the voltage value is inverted by an inverting amplifier circuit By setting it as the value of the reference voltage vref_fo of 210, the frequency temperature characteristic of the SAW oscillator 101 is changed by an approximate convex quadratic function and a convex convex square characteristic that is axisymmetrical downward. It is possible to generate a voltage.

  The present invention is not limited to the above-described embodiment. For example, the current correction circuits 206 and 207 provided in the subsequent stage of the pair of function generation circuits 204 and 205 are not necessarily provided, and the temperature You may comprise so that the output of the detection part 201 may be input into each amplification circuit 202,203 via the impedance conversion circuit which consists of operational amplifiers.

1 is a circuit diagram showing an embodiment of a voltage controlled SAW oscillator according to the present invention. The circuit diagram of a temperature compensation voltage generation part similarly. The graph which similarly shows the output state of a temperature detection part. The graph which similarly shows the output state of a non-inverting amplifier circuit. The graph which similarly shows the output state of an inverting amplifier circuit. The graph which similarly shows the output state of the inverting amplifier circuit by the change of vertex temperature, and a non-inverting amplifier circuit. The graph which similarly shows the output state of the inverting amplifier circuit by a change of a gain, and a non-inverting amplifier circuit. The graph which similarly shows the output state of an addition part. The graph which similarly shows the control voltage which is the output of the current-voltage conversion circuit, and the output of the inverting amplifier circuit which carried out the inverting amplification of this. The graph which similarly shows the change of the minimum control voltage by the change of the inversion level by a reference voltage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 SAW oscillator 2 Temperature compensation voltage oscillation part 3 Memory 101 SAW oscillator 102 Inversion amplification circuit 105,107 Variable capacity diode 110 Oscillation frequency control terminal 201 Temperature detection part 202 Inversion amplification circuit 203 Non-inversion amplification circuit 204,205 Function generation circuit 206 207 Current correction circuit 208 Adder 209 Current-voltage conversion circuit 210 Inverting amplifier circuit

Claims (5)

An oscillation circuit having a surface acoustic wave oscillator whose frequency temperature characteristic is approximated by a quadratic function, the output frequency of which is controlled by a control voltage, and a temperature compensation voltage generator for supplying the control voltage to the oscillation circuit A voltage-controlled surface acoustic wave oscillator comprising:
The temperature compensation voltage generator is
A temperature detector that detects the ambient temperature of the surface acoustic wave oscillator and generates an output voltage that decreases at a constant rate of change in response to an increase in the detected temperature;
In a range corresponding to a temperature at which the output voltage of the temperature detection unit does not reach a preset reference temperature, an output current that decreases at a constant change rate corresponding to a temperature rise is generated, and the output voltage is In a range corresponding to a temperature equal to or higher than the reference temperature, a non-inverting amplifier circuit that generates zero output current;
The output voltage of the temperature detection unit generates an output current that is zero in a range corresponding to a temperature that does not reach the reference temperature, and is constant in response to a temperature increase in a range corresponding to a temperature that is equal to or higher than the reference temperature. An inverting amplifier circuit that generates an output current that increases with the rate of change;
A pair of function generators for generating a current that changes in a square characteristic from each output current of the non-inverting amplifier circuit and the inverting amplifier circuit;
An adder that adds currents that change with the square characteristics generated by each of these function generators;
A current-voltage conversion circuit that converts the current that changes with the added square characteristic into a voltage that changes with an upward convex square characteristic; and
It is characterized by comprising an inverting amplifier circuit that generates a control voltage that is symmetrical with a quadratic function indicating the frequency-temperature characteristic of a surface acoustic wave oscillator and that changes in a downward convex square characteristic from the converted voltage. A voltage-controlled surface acoustic wave oscillator.   2. The reference temperature is set by setting each reference voltage of the non-inverting amplifier circuit and the inverting amplifier circuit to an output voltage of a temperature detection unit corresponding to a vertex temperature at which the oscillation frequency has a maximum. The voltage-controlled surface acoustic wave oscillator described.   The rate of change of each output current of the non-inverting amplifier circuit and the inverting amplifier circuit is set by adjusting the gain of each amplifier circuit so as to match the rate of change of the oscillation frequency depending on the temperature of the surface acoustic wave oscillator. 2. The voltage-controlled surface acoustic wave oscillator according to claim 1, wherein   2. The voltage controlled surface acoustic wave oscillator according to claim 1, wherein the minimum control voltage value corresponding to the apex temperature of the frequency temperature characteristic is set by the reference voltage of the inverting amplifier circuit that generates the control voltage. 2. A voltage-controlled surface acoustic wave according to claim 1, wherein a current correction circuit for improving linearity of the oscillation frequency change with respect to the control voltage change of the oscillation circuit is provided at the subsequent stage of the pair of function generation circuits. Oscillator.

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