JP2010161532A - Piezoelectric oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric oscillator capable of achieving highly accurate temperature compensation without mutually exerting influence between a temperature compensation function and an AFC function in a circuit configuration provided with the temperature compensation function and the AFC function. <P>SOLUTION: The piezoelectric oscillator 10 includes: an oscillation circuit 20 provided with a piezoelectric vibrator 26, an oscillating amplifier circuit, and voltage control type first and second variable capacitance elements 28, 28b; a temperature compensation voltage generation circuit 30 for outputting a temperature compensation voltage for compensating the frequency temperature characteristics of the oscillation circuit 20 by controlling a value of the first variable capacitance element 28a so as to increase/decrease the value; a compensation voltage detection circuit 40 for outputting an adjustment signal for changing the value of the second variable capacitance element 28b so as to suppress increase/decrease in the AFC sensitivity of the oscillation circuit 20 when the value of the first variable capacitance element 28a is changed due to the temperature compensation voltage; a gain adjustment circuit 60 for receiving the adjustment signal and adjusting an amplification factor of an external control voltage; and an amplifier circuit 50 for outputting a frequency control voltage for controlling the second variable capacitance element 28b. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a piezoelectric oscillator that performs temperature compensation of the oscillation frequency of a crystal resonator, and more particularly, to a piezoelectric oscillator having a temperature compensation function and an AFC (Auto Frequency Control) function.

FIG. 6 is an explanatory diagram showing a circuit configuration of a conventional temperature compensated crystal oscillator. As shown in the figure, a temperature compensated crystal oscillator 1 includes a temperature compensation circuit 3 using a MOS type voltage variable capacitance element in an oscillation circuit 2 using an inverter element, an AFC circuit 4 using a MOS type voltage variable capacitance element, Is added. The temperature compensation circuit 3 includes a primary voltage generation circuit and a tertiary voltage generation circuit. In order to cancel the original frequency temperature characteristic of the crystal resonator itself, a temperature is applied to the variable capacitance element in the oscillation circuit 2. By applying a compensation voltage, for example, the frequency is varied so as to cancel the temperature characteristic of the cubic curve of the crystal resonator, thereby stabilizing the oscillation frequency. In the oscillator formed as an IC, the AFC circuit 4 is composed of an operational amplifier. In other words, the gain of the external control voltage is arbitrarily changed by controlling the resistance value of the operational amplifier, and the variation in the electrical characteristics of the IC is corrected, so that the AFC characteristics that match the user's arbitrary specifications can be obtained. can do. The AFC circuit 4 is a function used by the user, and is a function for obtaining a desired frequency variation with respect to the external control voltage. The AFC function has different external control voltage ranges and required frequency variable widths for each user.
Patent Documents 1 and 2 disclose a crystal oscillator including such a temperature compensation circuit and an AFC circuit.

JP 2002-217743 A JP 2007-19565 A

  FIG. 7 is an explanatory diagram showing the AFC characteristics of a conventional temperature-compensated crystal oscillator. In the figure, the horizontal axis indicates the external control voltage (V), and the vertical axis indicates the oscillation frequency deviation (ppm). In the case of a temperature compensated crystal oscillator in which a temperature compensated crystal oscillator and a temperature compensated crystal oscillator coexist in a conventional temperature compensated crystal oscillator, even if the AFC circuit is optimally designed at room temperature, which is the reference state, the AFC characteristic is the temperature as shown in the figure. Because there is a characteristic, it will be different depending on the temperature. This is because the variable capacitance element D1 for temperature compensation changes its capacitance depending on the temperature compensation voltage, and thereby the load capacitance of the oscillation circuit changes, but the control condition of the variable capacitance element D2 by the external control voltage of the AFC circuit Is the same as that in the reference state, so that a difference occurs in the frequency change characteristic (AFC sensitivity) with respect to the change in the external control voltage between the reference state and other temperature states.

  In order to solve the problems of the prior art, the present invention realizes highly accurate temperature compensation in a circuit configuration having a temperature compensation function and an AFC function without the temperature compensation function and the AFC function affecting each other. An object of the present invention is to provide a piezoelectric oscillator that can be used.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.
[Application Example 1] An oscillation circuit including a piezoelectric vibrator, an oscillation amplifier circuit, and voltage-controlled first and second variable capacitance elements, and increase / decrease control of the value of the first variable capacitance element A temperature compensation voltage generation circuit for outputting a temperature compensation voltage for compensating the frequency temperature characteristic of the oscillation circuit, a compensation voltage detection circuit for outputting an adjustment signal controlled by the temperature compensation voltage, and the adjustment signal. And a gain adjustment circuit for adjusting an amplification factor of the external control voltage, and an amplification circuit for outputting a frequency control voltage for controlling the second variable capacitance element.

  An adjustment signal controlled by the temperature compensation voltage is generated by the compensation voltage detection circuit, the gain of the external control voltage is adjusted by the gain adjustment circuit, and the adjusted frequency control voltage is output to the second variable capacitance element. it can. Therefore, even if the variable capacitance for temperature compensation is changed by the temperature compensation voltage, the AFC voltage is controlled according to the temperature compensation voltage, so that the influence on the variable capacitance on the AFC side is avoided and stable AFC characteristics are obtained. Can be obtained.

  Application Example 2 When the frequency change amount in the unit voltage of the external control voltage increases or decreases as compared with the reference state because the temperature compensation voltage controls the value of the first variable capacitance element to increase or decrease, the frequency change The compensation voltage detection circuit controls the gain adjustment circuit to adjust the gain of the amplification circuit so as to generate the frequency control voltage for controlling the second variable capacitance element so as to suppress the increase and decrease of the amount. The piezoelectric oscillator according to Application Example 1, wherein the adjustment signal is output.

  In the piezoelectric oscillator of the present invention, the state in which the AFC voltage is adjusted so as to obtain a desired AFC characteristic in a state where the temperature compensation voltage at normal temperature is applied to the second variable capacitance element is used as a reference state. When the frequency change amount in the unit voltage of the external control voltage is increased / decreased compared to the reference state because the temperature compensation voltage is controlled to increase / decrease the value of the first variable capacitance element, the increase / decrease in the frequency change amount is suppressed. The gain of the amplifier circuit is adjusted so as to generate a frequency control voltage for controlling the two variable capacitance elements. Therefore, even if the variable capacitance for temperature compensation is changed by the temperature compensation voltage, the AFC voltage is controlled according to the temperature compensation voltage, so that the influence on the variable capacitance on the AFC side is avoided and stable AFC characteristics are obtained. Can be obtained.

  Application Example 3 In the piezoelectric oscillator according to Application Example 1 or Application Example 2, the amplifier circuit includes an operational amplifier and a variable resistance circuit, and the gain adjustment circuit is configured to output the variable resistance circuit according to the adjustment signal. A piezoelectric oscillator characterized by controlling a resistance value.

  Accordingly, the resistance value of the operational amplifier can be controlled based on the adjustment signal output from the compensation voltage detection circuit. Therefore, the gain of the external control voltage can be digitally adjusted.

  Application Example 4 In the piezoelectric oscillator according to Application Example 1 or Application Example 2, the amplifier circuit includes an operational amplifier and a series resistor including a plurality of resistors, and the gain adjustment circuit includes a resistance of the series resistor. A piezoelectric oscillator comprising a switch control circuit for controlling an on / off state of a switch element by the adjustment signal between the input terminal and the input terminal of the operational amplifier.

  Accordingly, the resistance value of the operational amplifier can be controlled by controlling the on / off states of the plurality of switch elements based on the adjustment signal output from the compensation voltage detection circuit. Therefore, the gain of the external control voltage can be digitally adjusted.

  Application Example 5 A feature is that a latch circuit is provided between the amplifier circuit and the compensation voltage detection circuit to latch until the external control voltage is input and the center value of the external control voltage is output. The piezoelectric oscillator according to Application Example 4.

  Thereby, the gain adjustment timing can be adjusted when the external control voltage is the center value, and the frequency fluctuation can be suppressed. Therefore, it is possible to prevent the frequency from fluctuating due to the AFC voltage being changed by gain adjustment other than the center value.

It is a figure which shows the structure outline of the piezoelectric oscillator of this invention. It is explanatory drawing which shows the relationship between temperature, a temperature compensation voltage, and the capacitance value of a 1st variable capacitance element. It is explanatory drawing which shows the AFC characteristic of the piezoelectric oscillator of this invention. It is a figure which shows the structure outline of the modification 1 of the piezoelectric oscillator of this invention. It is a figure which shows the structure outline of the modification 2 of the piezoelectric oscillator of this invention. It is explanatory drawing which shows the circuit structure of the conventional temperature compensation type | mold crystal oscillator. It is explanatory drawing which shows the AFC characteristic of the conventional temperature compensation type | mold crystal oscillator.

  Embodiments of a piezoelectric oscillator according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of a piezoelectric oscillator according to the present invention. As shown in the figure, the piezoelectric oscillator 10 of the present invention mainly includes an oscillation circuit 20, a temperature compensation voltage generation circuit 30, a compensation voltage detection circuit 40, and an amplification circuit 50.

  The oscillation circuit 20 includes a feedback resistor 22 and an inverter element 24 that form an oscillation amplifier circuit, a piezoelectric vibrator 26, a plurality of voltage-controlled variable capacitance elements 28, and capacitors C1 and C2.

  For example, a MOS type voltage variable capacitor can be applied to the variable capacitor 28. The gate terminal of the second variable capacitance element 28b is connected to the input end side of the inverter element 24 via the capacitor C1, and the gate terminal of the first variable capacitance element 28a is the output of the inverter element 24 via the capacitor C2. The back gate terminals of the first and second variable capacitance elements 28a and 28b are connected to the end side and grounded. Then, an AFC voltage (frequency control voltage) from an amplifier circuit 50 described later is supplied to the connection point between the gate terminal of the second variable capacitance element 28b and the capacitor C1 via the resistor R1. On the other hand, a temperature compensation voltage (Vcomp) from a temperature compensation voltage generation circuit 30 described later is supplied to a connection point between the gate terminal of the first variable capacitance element 28a and the capacitor C2 via a resistor R2.

  The temperature compensation voltage generation circuit 30 includes a primary voltage generation circuit 32, a tertiary voltage generation circuit 34, and a temperature sensor 36. When high-precision temperature compensation is required, a voltage generation circuit having an order of 4th or higher is provided. The primary voltage generation circuit 32 and the tertiary voltage generation circuit 34 are connected so that the output voltage of the temperature sensor 36 is input. Then, a temperature compensation voltage obtained by adding the output voltage of the primary voltage generation circuit and the output voltage of the tertiary voltage generation circuit is applied to the first variable capacitance element 28a, and the output voltage of the temperature sensor 36 is determined. The oscillation frequency is finely adjusted.

  The compensation voltage detection circuit 40 includes a plurality of comparators. The compensation voltage detection circuit 40 is connected between the temperature compensation voltage generation circuit 30 and the first variable capacitance element 28a. The compensation voltage detection circuit 40 determines which voltage range the compensation voltage output from the temperature compensation voltage generation circuit belongs to the voltage range divided by a predetermined reference voltage, and according to the state of the compensation voltage. This circuit outputs an adjustment signal for changing the value of the second variable capacitance element 28b in order to perform temperature compensation of the AFC characteristic. The compensation voltage detection circuit 40 of the present embodiment is composed of first and second comparators 42 and 44, and two arbitrary reference voltages (reference voltage 1> reference voltage 2) are set. The first and second comparators 42 and 44 receive the temperature compensation voltage from the temperature compensation voltage generation circuit 30, respectively. The reference voltage 1 and the temperature compensation voltage are input to the first comparator 42. The second comparator 44 receives the reference voltage 2 and the temperature compensation voltage.

The amplifier circuit 50 includes first and second operational amplifiers 52 and 54, a series resistor R that is a variable resistance circuit, and a gain adjustment circuit 60.
The inverting input terminal of the first operational amplifier 52 is connected to a terminal between the series resistors R via a plurality of switch elements described later. A fixed voltage (VREF1) is input to the non-inverting input terminal.

In this embodiment, the series resistor R includes four resistors (Ra, Rb, Rc, Rd) arranged in series, one end of the resistor Ra is connected to the external control voltage input terminal 70, and one end of the resistor Rd is connected to the first resistor Rd. And between the second operational amplifiers 52 and 54 (between the output terminal of the first operational amplifier 52 and the inverting input terminal of the second operational amplifier 54). The number of resistors forming the series resistor R can be set arbitrarily. The gain of the first operational amplifier 52 is the resistance value between the terminal of the external control voltage VCONT and the inverting input terminal of the first operational amplifier 52, the inverting input terminal of the first operational amplifier 52, and the first operational amplifier 52. It is determined by the ratio to the resistance value (feedback resistance value) between the output terminal.
The second operational amplifier 54 configures resistors Re and Rf and an inverting amplifier circuit. A fixed voltage (VREF2) is input to the non-inverting input terminal of the second operational amplifier 54.

  The gain adjustment circuit 60 includes a switch element 62 and a switch control circuit 64. The switch element 62 is connected in parallel between a plurality of terminals between the series resistors R and the inverting input terminal of the first operational amplifier. In the present embodiment, three switch elements 62a, 62b, and 62c are connected in parallel. A control signal from a switch control circuit 64 (described later) is input to the switch element 62, and the series resistor R and the first operational amplifier 52 are connected and disconnected by the control signal.

  The switch control circuit 64 is a circuit that controls the switch element 62 in accordance with a comparison result between the temperature compensation voltage and a predetermined reference voltage. In the present embodiment, the on / off states of the plurality of switch elements 62a to 62c are switched based on the adjustment signal of the compensation voltage detection circuit 40.

  The amplifier circuit 50 having such a configuration plays a role of an AFC function, and outputs the adjusted AFC voltage to the second variable capacitance element 28b. Specifically, in the amplifier circuit 50, the external control voltage (VCONT) from the external control voltage input terminal 70 is input to the first operational amplifier 52 constituting the gain adjustment circuit 60. The gain of the first operational amplifier 52 is adjusted by adjusting a plurality of resistors R. This voltage is amplified by the second operational amplifier 54 to be an AFC voltage and applied to the second variable capacitance element 28b.

The operation of the piezoelectric oscillator 10 of the present invention having the above configuration will be described below.
The temperature compensation voltage from the temperature compensation voltage generation circuit 30 is input to the compensation voltage detection circuit 40. The compensation voltage detection circuit 40 compares the temperature compensation voltage with predetermined reference voltages 1 and 2.

  FIG. 2 is an explanatory diagram showing the relationship between the temperature, the temperature compensation voltage, and the capacitance value of the first variable capacitance element 28a. In FIG. 1A, the horizontal axis indicates the temperature (° C.), and the vertical axis indicates the temperature compensation voltage (V) and the capacitance value (pF) of the first variable capacitance element 28a. Also, the wavy lines in the figure are two predetermined reference voltages 1 and 2 (reference voltage 1> reference voltage 2), and a reference region A of the temperature compensation voltage is between the reference voltages 1 and 2. A voltage region higher than the reference region A is C, and a low voltage region is B. The temperature range of the reference region A between the voltage region B and the voltage region C includes normal temperature (about 25 ° C.) that is the temperature of the reference state.

  The reference state of the piezoelectric oscillator 10 is a state in which the gain adjustment circuit 60 is set and the AFC voltage is adjusted so as to obtain a desired AFC characteristic in a state where a temperature compensation voltage at normal temperature is applied to the second variable capacitance element 28b. It is.

  Adjustment of the AFC gain in accordance with the temperature compensation voltage outputs an adjustment signal for outputting the external control voltage itself when the temperature compensation region is the reference region A, as shown in FIG. Specifically, in this embodiment, the switch control circuit 64 outputs a switch control signal that turns on the switch element 62b and turns off the switch elements 62a and 62c. The external control voltage is amplified by the first and second operational amplifiers 52 and 54, and the AFC voltage is output to the second variable capacitance element 28b.

  Further, when the temperature compensation voltage is in the region C, an adjustment signal for increasing the AFC gain is output as compared with the case of the reference region A sandwiched between the regions B and C. Specifically, in this embodiment, the switch control circuit 64 outputs a switch control signal that turns on the switch element 62a and turns off the switch elements 62b and 62c. The external control voltage is increased by the first and second operational amplifiers 52 and 54, and the AFC voltage is output to the second variable capacitance element 28b.

  On the other hand, when the temperature compensation voltage is in the region B, an adjustment signal for reducing the AFC gain is output as compared with the case of the reference region A sandwiched between the regions B and C. Specifically, in this embodiment, the switch control circuit 64 outputs a switch control signal that turns on the switch element 62c and turns off the switch elements 62a and 62b. The external control voltage is reduced by the first and second operational amplifiers 52 and 54, and the AFC voltage is output to the second variable capacitance element 28b.

  Thus, when the temperature compensation voltage is controlled so as to reduce the capacitance value of the first variable capacitance element with respect to the reference voltage (reference state), for example, the change in the capacitance value per unit of the second variable capacitance element. The amount of change in the load capacitance of the oscillation circuit is reduced, and as a result, the AFC sensitivity expressed as the amount of change in frequency with respect to the change in voltage per unit of the external control voltage VCONT is reduced, but the compensation voltage detection circuit 40 Works to suppress the decrease in the AFC sensitivity. That is, in order to suppress the decrease in the AFC sensitivity as described above, the amplification factor of the amplifier circuit 50 is increased to increase the amount of change in the AFC voltage with respect to the voltage change per unit of the external control voltage VCONT. The amount of change in the capacitance value of the second variable capacitance element with respect to the voltage change per unit of the voltage VCONT may be adjusted largely. Therefore, the compensation voltage detection circuit 40 outputs an adjustment signal necessary for controlling the gain adjustment circuit 60 so that the gain of the amplification circuit 50 increases.

  FIG. 3 is an explanatory diagram of AFC characteristics of the piezoelectric oscillator of the present invention. In the figure, the horizontal axis represents the external control voltage (V), and the vertical axis represents the oscillation frequency deviation (ppm). As shown in the figure, according to the piezoelectric oscillator of the present invention, the adjustment signal controlled by the temperature compensation voltage can be output to the gain adjustment circuit, and the gain of the external control voltage can be adjusted by the gain adjustment circuit. The adjusted frequency control voltage is output to the second variable capacitance element, and the effect of suppressing the influence of the AFC characteristic due to the temperature change can be obtained.

  Next, Modification 1 of the piezoelectric oscillator of the present invention will be described below. FIG. 4 is a diagram showing a schematic configuration of Modification 1 of the piezoelectric oscillator of the present invention. The piezoelectric oscillator 10A according to the first modification includes an amplifier circuit 50A having an ON resistance and a compensation voltage control circuit 80 to which a temperature compensation voltage is input. The oscillation circuit 20A has a plurality of variable capacitance elements 28c, 28d, 28e, and 28f connected in parallel. Other configurations are the same as those shown in FIG. 1, and the same reference numerals are given, and detailed descriptions thereof are omitted.

  The compensation voltage control circuit 80 includes an operational amplifier 82 and resistors Rg and Rh. A fixed voltage (VREF3) is input to the inverting input terminal of the operational amplifier 82, and the temperature compensation voltage generation circuit 30 is provided to the non-inverting input terminal. The temperature compensation voltage from is input.

  The amplifier circuit 50A includes a variable resistance circuit 66. An adjustment signal from the compensation voltage control circuit 80 is input to the variable resistance circuit 66. As an example, the variable resistance circuit 66 of this embodiment can use an Nch MOS transistor or the like as the ON resistance of the transistor.

  In the piezoelectric oscillator 10A of Modification 1 having the above-described configuration, the compensation voltage control circuit 80 to which the temperature compensation voltage is input is amplified according to the change amount of the temperature compensation voltage. Next, the adjustment signal is input to the variable resistance circuit 66 of the gain adjustment circuit 60A. In the variable resistance circuit 66, the resistance value changes according to the input adjustment signal, so that the gain amplification amount can be adjusted. In the oscillation circuit 20A of the first modification, a plurality of variable capacitance elements 28 are connected in parallel. For this reason, the adjustment is reverse to the configuration in which the variable capacitance elements shown in FIG. 1 are connected in series. That is, when the AFC sensitivity of the oscillation circuit changes due to the increase / decrease control of the capacitance value of the first variable capacitance element by the temperature compensation voltage with respect to the reference voltage (reference state), the compensation voltage control circuit 80 changes this AFC sensitivity. An adjustment signal for adjusting the gain of the amplifier circuit 50 is output so as to suppress the change of the signal.

  According to the piezoelectric oscillator of the first modification, AFC characteristics can be obtained by fine adjustment of gain adjustment with respect to a change in load capacitance due to temperature compensation voltage, and a stable frequency can be obtained. In addition, AFC and temperature compensation variable capacitance elements can be provided independently, and independent and independent voltage settings can be made. The AFC gain can be varied not only by linear temperature compensation but also by a complicated temperature compensation method.

  Next, Modification 2 of the piezoelectric oscillator of the present invention will be described below. FIG. 5 is a diagram showing a schematic configuration of a second modification of the piezoelectric oscillator of the present invention. The piezoelectric oscillator 10 </ b> B according to the second modification has a configuration in which a latch circuit 100 is provided between the amplifier circuit 50 and the compensation voltage detection circuit 40 in the configuration of the piezoelectric oscillator 10 illustrated in FIG. 1. The plurality of variable capacitance elements 28 of the piezoelectric oscillator 10B are connected in parallel. Other configurations are the same as those of the piezoelectric oscillator 10, and the same reference numerals are given, and detailed descriptions thereof are omitted.

  As an example, the latch circuit 100 of the piezoelectric oscillator 10 </ b> B of the second modification is formed between the switch element 62 and the switch control circuit 64. The latch circuit 100 receives an external control voltage and an adjustment signal from the switch control circuit 64. The latch circuit 100 predetermines the center value of the external control voltage as a reference value, transmits the signal of the switch control circuit 64 to the switch element when the center value is the center value, and changes the signal of the switch control circuit 64 when the center value is other than the center value. However, it operates so as not to be transmitted to the switch element. A hysteresis function may be provided in the input portion of the VCONT voltage so that the latch circuit does not malfunction due to noise of the reference center value voltage.

  The piezoelectric oscillator 10B of Modification 2 having the above configuration outputs an adjustment signal to the switch control circuit 64 based on the reference voltages 1 and 2 and the temperature compensation voltage in the compensation voltage detection circuit 40 as in FIG. At this time, since the piezoelectric oscillator 10B of the second modification has a plurality of variable capacitance elements connected in parallel, as shown in the first modification, the capacitance of the first variable capacitance element by the temperature compensation voltage with respect to the reference voltage. When the value increases, the gain of the amplifier circuit 50 is increased, or the capacitance value of the first variable capacitance element is controlled to increase or decrease with respect to the reference voltage by the temperature compensation voltage. When decreased, an adjustment signal for decreasing the gain of the amplifier circuit 50 is output.

  When the temperature compensation region is the reference region A as shown in FIG. 2A, the switch control circuit 64 outputs an adjustment signal for outputting the external control voltage itself. Specifically, in this embodiment, a switch control signal for turning on the switch element 62b and turning off the switch elements 62a and 62c is output from the switch control circuit 64 to the latch circuit 100 in the subsequent stage.

  Further, when the temperature compensation voltage is in the region C, an adjustment signal for reducing the AFC gain is output as compared with the case of the reference region A sandwiched between the region B and the region C. Specifically, in this embodiment, a switch control signal for turning on the switch element 62c and turning off the switch elements 62a and 62b is output from the switch control circuit 64 to the latch circuit 100 in the subsequent stage.

  On the other hand, when the temperature compensation voltage is in the region B, an adjustment signal for increasing the AFC gain is output as compared with the case of the reference region A sandwiched between the region B and the region C. Specifically, in this embodiment, a switch control signal that turns on the switch element 62a and turns off the switch elements 62b and 62c is output from the switch control circuit 64 to the latch circuit 100 in the subsequent stage.

  In the latch circuit 100, when the switch control signal from the switch control circuit 64 in the previous stage and the external control voltage are input from the external control voltage input terminal 70, and the center value of the predetermined external control voltage is input, the switch control circuit The switch control signal from 64 is output to the switch elements 62a, 62b and 62c.

  According to the piezoelectric oscillator 10B of Modification 2 as described above, the gain adjustment timing can be adjusted when the external control voltage is the center value, and the frequency fluctuation can be suppressed. Therefore, it is possible to prevent the frequency from fluctuating due to the change in the AFC voltage caused by changing the gain when the external control voltage is other than the center value.

DESCRIPTION OF SYMBOLS 1 ......... Temperature compensated crystal oscillator, 2 ......... Oscillator circuit, 3 ......... AFC circuit, 4 ......... Temperature compensation circuit, 10, 10A, 10B ......... Piezoelectric oscillator, 20 ......... Oscillator circuit, 22 ......... Feedback resistor, 24 ......... Inverter element, 26 ......... Piezoelectric vibrator, 28 ......... Variable capacitance element, 30 ......... Temperature compensated voltage generating circuit, 32 ......... Primary voltage generating circuit, 34... Tertiary voltage generation circuit 36... Temperature sensor 40... Compensation voltage detection circuit 42 42 First comparator 44 44 Second comparator 50 Amplifier circuit 52... First operational amplifier 54... Second operational amplifier 60... Gain adjustment circuit 62... Switch element 64 64 Switch control circuit 66 Variable resistor Circuit, 70... External control voltage input terminal, 80... Compensation voltage control circuit 90 ......... AFC circuit, 100 ......... latch circuit.

Claims (5)

An oscillation circuit including a piezoelectric vibrator, an oscillation amplifier circuit, and voltage-controlled first and second variable capacitance elements;
A temperature compensation voltage generation circuit that outputs a temperature compensation voltage for compensating the frequency temperature characteristic of the oscillation circuit by increasing or decreasing the value of the first variable capacitance element;
A compensation voltage detection circuit that outputs an adjustment signal controlled by the temperature compensation voltage;
An amplifying circuit that includes a gain adjusting circuit that receives the adjustment signal and adjusts an amplification factor of an external control voltage, and that outputs a frequency control voltage for controlling the second variable capacitance element;
A piezoelectric oscillator comprising:   When the frequency change amount in the unit voltage of the external control voltage increases or decreases as compared with the reference state because the temperature compensation voltage controls the value of the first variable capacitance element to increase or decrease, the increase or decrease in the frequency change amount is suppressed. The compensation voltage detection circuit controls the gain adjustment circuit so as to generate the frequency control voltage for controlling the second variable capacitor so as to output the adjustment signal for adjusting the gain of the amplifier circuit The piezoelectric oscillator according to claim 1. The piezoelectric oscillator according to claim 1 or 2,
The amplifier circuit includes an operational amplifier and a variable resistance circuit,
The gain adjustment circuit controls a resistance value of the variable resistance circuit according to the adjustment signal. The piezoelectric oscillator according to claim 1 or 2,
The amplifier circuit includes an operational amplifier and a series resistor composed of a plurality of resistors,
2. The piezoelectric oscillator according to claim 1, wherein the gain adjustment circuit includes a switch control circuit that controls an on / off state of a switch element between the resistors of the series resistors and an input terminal of the operational amplifier by the adjustment signal.   The latch circuit which latches until the said external control voltage is input between the said amplifier circuit and the said compensation voltage detection circuit until it becomes the output of the center value of the said external control voltage is provided. The piezoelectric oscillator as described.

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