JP2010166438A - Piezoelectric oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric oscillator achieved in accurate temperature compensation by preventing a temperature compensation function and an AFC function from influencing each other, in a circuit structure having the temperature compensation function and the AFC function. <P>SOLUTION: The piezoelectric oscillator 10 includes: an oscillation circuit 20 including a piezoelectric oscillator 26, an oscillating amplifier circuit and a voltage-controlled variable capacitance element; a temperature compensation voltage generation circuit 30 for outputting a temperature compensation voltage for compensating a frequency-temperature characteristic of the oscillation circuit 20 by increasingly and decreasingly controlling the value of a first variable capacitance element 28a; an output current-supplying voltage regulation means 50 to change the value of a second variable capacitance element 28b according to the temperature compensation voltage; and an amplifier circuit 40 having a second operational amplifier 44 for outputting a frequency control voltage for controlling the value of the second variable capacitance element 28b according to an external control voltage. The voltage regulation means 50 includes a differential amplifier circuit 52 for supplying an output current generated based on the difference between the external control voltage and a fixed voltage to the second operational amplifier 44 to control a reference current according to the temperature compensation voltage. <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. 4 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 an oscillation circuit 2 using an inverter element, a temperature compensation circuit 3 that generates a temperature compensation voltage to be applied to the voltage variable capacitance element, and an AFC circuit 4 using a variable capacitance element. And are 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, the variation in the electrical characteristics of the IC is corrected, and the adjustment is performed so as to obtain the AFC characteristics according to the user's arbitrary specifications. be able to. The AFC circuit 4 is a function used by the user, and a desired frequency variation is required for 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. 5 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 an AFC circuit coexist in a conventional temperature compensated crystal oscillator, even if the AFC circuit is optimally designed at room temperature, as shown in FIG. The slope of the characteristic changes. This is because the temperature compensation variable capacitance element undergoes capacitance change due to the temperature compensation voltage, and therefore the sensitivity of the preset variable capacitance element is affected by the change in the variable capacitance. Then, the amount of change of the oscillation frequency that is changed by the AFC circuit changes.

  SUMMARY OF THE INVENTION In order to solve the problems of the prior art, the present invention provides a piezoelectric oscillator that realizes that the AFC function is less affected by the temperature compensation in the circuit configuration having the temperature compensation function and the AFC function. It is aimed.

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 generating circuit for outputting a temperature compensation voltage for compensating the frequency temperature characteristic of the oscillation circuit, and an output current for changing the value of the second variable capacitance element in accordance with the temperature compensation voltage. And an amplifier circuit having a second operational amplifier that outputs a frequency control voltage for controlling the value of the second variable capacitance element according to an external control voltage. A differential amplifier circuit for supplying the output current generated based on a difference between a voltage based on the external control voltage and a fixed voltage to the second operational amplifier, and controlling a reference current in accordance with the temperature compensation voltage Having Piezoelectric oscillator, characterized.

  As a result, the load capacitance of the oscillation circuit due to the temperature compensation voltage changes, and even if the variable sensitivity of the variable capacitance value for the AFC circuit changes, the frequency control voltage can be finely adjusted using the output current according to the temperature compensation voltage. it can. Therefore, an AFC characteristic with small gain fluctuation can be obtained regardless of temperature change. Moreover, the variable capacitance element which outputs an AFC voltage or a temperature compensation voltage can be provided independently, and the voltage can be set individually.

Application Example 2 The first operational amplifier in which the amplifier circuit uses the external control voltage as an input signal via an input resistor, the second operational amplifier that uses the first output signal as an input signal, and the first And a feedback resistor of the first operational amplifier, wherein the base of the first transistor of the differential amplifier circuit to which the external control voltage is supplied is connected between the feedback resistors of the first operational amplifier. The piezoelectric oscillator described in Example 1.
As a result, it is not necessary to separately provide a voltage dividing circuit composed of a series resistor, and the overall configuration of the oscillator can be simplified.

Application Example 3 Application Example 1 or Application Example 2 in which a resistor is provided in the emitters of the first and second transistors to which the external control voltage and the fixed voltage of the differential amplifier circuit are supplied. A piezoelectric oscillator according to 1.
As a result, the input width of the external control voltage input to the differential amplifier circuit can be widened, and gain adjustment can be easily performed.

It is a figure which shows the structure outline of the piezoelectric oscillator of this invention. It is a graph which shows the relationship between an AFC voltage (VAFC) and an external control voltage (VCONT). It is a figure which shows the structure outline of the piezoelectric oscillator of a modification. 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, an amplification circuit 40, and a voltage adjusting means 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, and a plurality of voltage-controlled variable capacitance elements 28. For example, a MOS type voltage variable capacitance element can be applied to the variable capacitance element 28. In this case, the capacitance value is controlled by controlling the potential of the gate terminal and the potential of the back gate terminal of the MOS type voltage variable capacitance element. Will be controlled. 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. The output signal of the temperature sensor 36 is input to the primary voltage generation circuit 32 and the tertiary voltage generation circuit 34. A temperature compensation voltage obtained by synthesizing the output signals of the primary voltage generation circuit 32 and the tertiary voltage generation circuit 34 by an adder is applied to the first variable capacitance element 28a so that the temperature characteristic of the crystal resonator is canceled. The oscillation frequency is controlled by controlling the value (capacitance value) of the variable capacitance element 28a.

  The amplifier circuit 40 includes first and second operational amplifiers 42 and 44. The first operational amplifier 42 constitutes resistors Ra and Rb and an inverting amplifier circuit. A fixed voltage (VREF 1) is supplied to the non-inverting input terminal of the first operational amplifier 42. The second operational amplifier 44 constitutes resistors Rc and Rd and an inverting amplifier circuit. A fixed voltage (VREF 2) is supplied to the non-inverting input terminal of the second operational amplifier 54. The amplifier circuit 40 having such a configuration plays a role of the AFC function, and outputs the adjusted AFC voltage to the second variable capacitance element 28b.

The voltage adjusting means 50 includes a differential amplifier circuit 52, a voltage dividing circuit 54, and a voltage / current conversion circuit 56.
The differential amplifier circuit 52 includes first and second PNP transistors Tr1a and Tr1b, and first and second NPN transistors Tr2a and Tr2b.

  The first and second PNP transistors Tr1a and Tr1b have emitters connected to the power supply input (VDD) terminal 60, bases connected to each other, collectors and bases of the first PNP transistor Tr1a connected, and current mirror circuits. It is composed.

  The first and second NPN transistors Tr2a and Tr2b have collectors connected to the collectors of the first and second PNP transistors Tr1a and Tr1b. The base of the first NPN transistor Tr2a is connected to the external control voltage terminal 70 via a voltage dividing circuit 54 described later. The base of the second NPN transistor Tr2b is supplied with a fixed voltage VREF3. The emitters of the first and second NPN transistors Tr2a and Tr2b are connected to the collector of a fourth NPN transistor Tr3b constituting a current mirror of a voltage-current conversion circuit 56 described later via resistors R3 and R4, respectively. Yes.

  Since the resistors R3 and R4 are provided at the emitters of the first and second NPN transistors Tr2a and Tr2b to which the external control voltage and the fixed voltage of the differential amplifier circuit 52 are supplied, the external control input to the differential amplifier circuit 52 is provided. The voltage input width can be widened, and gain adjustment can be easily performed.

  Further, the collector of the second PNP transistor Tr1b and the collector of the second NPN transistor Tr2b are connected between the resistors Rc and Rd of the second operational amplifier, and the output current (Iout) is supplied to the second operational amplifier 44. is doing.

  One end of the voltage dividing circuit 54 is connected between the external control voltage input terminal 70 and the amplifier circuit 40, and the other end is connected to the base of the first NPN transistor Tr2a of the differential amplifier circuit 52. The voltage dividing circuit 54 is formed by connecting a plurality of resistors in series, and adjusts the external control voltage to a predetermined voltage.

The voltage-current conversion circuit 56 is a circuit that generates a current corresponding to the supplied voltage. In the present embodiment, the temperature compensation voltage specifically output from the temperature compensation voltage generation circuit 30 is input to the input side of the conversion circuit and converted into a current corresponding to the temperature compensation voltage. The voltage-to-current conversion circuit 56 is connected to the emitters of the first and second NPN transistors Tr2a and Tr2b of the differential amplifier circuit 52 via a current mirror circuit having third and fourth NPN transistors Tr3a and Tr3b connected in a current mirror connection. Connected.
With such a configuration, the differential amplifier circuit 52 uses a current corresponding to the temperature compensation voltage from the voltage-current conversion circuit 56 as a reference current.

  The operation of the piezoelectric oscillation circuit of the present invention having the above configuration will be described below. FIG. 2 is a graph showing the relationship between the AFC voltage (VAFC) and the external control voltage (VCONT). The horizontal axis of the graph shows the external control voltage (VCONT), and the vertical axis shows the AFC voltage (VAFC). A broken line indicates the AFC characteristic before correction, and a solid line indicates the AFC characteristic after correction.

First, in the current mirror circuit including the first PNP transistors Tr1a and 1b of the differential amplifier circuit 52, the same current flows in each transistor.
An external control voltage input from the external control voltage input terminal 70 is supplied to the voltage dividing circuit 54. The voltage dividing circuit 54 adjusts the external control voltage to a predetermined voltage. An external control voltage adjusted to a predetermined voltage is supplied to the base of the first NPN transistor Tr2a. On the other hand, a fixed voltage VREF3 is supplied to the base of the second NPN transistor Tr2b.

  Further, the temperature compensation voltage from the temperature compensation voltage generation circuit 30 is supplied to the voltage / current conversion circuit 56 of the voltage adjusting means 50. In the voltage-current conversion circuit 56, a current corresponding to the supplied temperature compensation voltage is generated and supplied to the base of the fourth NPN transistor Tr3b constituting the current mirror circuit. A current corresponding to the temperature compensation voltage is supplied as a reference current to the base of the fourth NPN transistor Tr3b.

  When the voltage Vin obtained by dividing the external control voltage is equal to the fixed voltage VREF3, this is a reference state in which the external control voltage is a reference value, and the base voltages of the first and second NPN transistors Tr2a and Tr2b are Will be equal. As a result, the output current Iout does not flow at all. In this case, the signal of only the external control voltage is amplified by the amplifier circuit 40 to become an AFC voltage and supplied to the second variable capacitance element 28b.

  Next, when the voltage Vin obtained by dividing the external control voltage is lower than the fixed voltage VREF3 (Vin <VREF3), the voltage of the first NPN transistor Tr2a is smaller than the voltage of the second transistor Tr2b. It becomes. As a result, the collector current of the first NPN transistor Tr2a is smaller than the collector current of the second transistor Tr2b. As a result, a difference current from the second operational amplifier 44 side of the amplifier circuit flows into the differential amplifier circuit 52. Therefore, as shown in FIG. 2A, the gain of the second operational amplifier 44 increases to compensate for the insufficient current.

  On the other hand, when the voltage Vin obtained by dividing the external control voltage is higher than the fixed voltage VREF3 (Vin> VREF3), the collector current of the first NPN transistor Tr2a is larger than the collector current of the second transistor Tr2b. It becomes a state. Then, the differential amplifier circuit 52 sends the output current to the second operational amplifier 44. Therefore, as shown in FIG. 2B, the gain of the second operational amplifier 44 decreases. When the reference current that changes according to the temperature compensation voltage increases, the slope of the AFC voltage changes like C and D, so that the slope of the AFC characteristic can be adjusted.

  FIG. 3 is a diagram showing a schematic configuration of a modification of the piezoelectric oscillator. FIG. 3 shows only the amplifier circuit 20 and the voltage adjusting means 50 for convenience of explanation. The difference in configuration between the piezoelectric oscillator 10A of the modified example and the piezoelectric oscillator 10 shown in FIG. 1 is that the voltage dividing circuit is deleted, and between the plurality of feedback resistors of the first operational amplifier 42 and the differential amplifier circuit 52. In this configuration, the base of one NPN transistor Tr2a is connected. The other configuration is the same as that of the piezoelectric oscillator shown in FIG. 1, and detailed description thereof is omitted.

  As described above, the voltage dividing circuit can be formed by connecting a plurality of resistors in series. In this embodiment, among the series resistors Ra, Rb, and Rb ′ of the first operational amplifier 42 of the amplifier circuit 20, resistors Rb, The base of the first NPN transistor Tr2a is connected between Rb ′.

  According to the piezoelectric oscillator 10A of the modified example having the above configuration, the configuration of the voltage dividing circuit can be eliminated by replacing the voltage dividing circuit shown in FIG. 1 with the series resistance of the first operational amplifier. Can be simplified. Even when the external control voltage is input from the feedback resistor of the amplifier circuit 40 to the differential amplifier circuit 52, the AFC voltage can be adjusted as in the piezoelectric oscillator 10 of FIG.

DESCRIPTION OF SYMBOLS 1 ......... Temperature compensation crystal oscillator, 2 ......... Oscillation circuit, 3 ......... Temperature compensation circuit, 4 ......... AFC circuit, 10, 10A ......... Piezoelectric oscillator, 20 ...... Oscillation circuit, 22 ... ...... Feedback resistor, 24... Inverter element, 26... Piezoelectric vibrator, 28... Variable capacitance element, 30... Temperature compensation voltage generation circuit, 32. ...... Third-order voltage generation circuit 36... Temperature sensor 40... Amplifier circuit 42... First operational amplifier 44 44 Second operational amplifier 50 Voltage adjusting means 52. ... Differential amplifier circuit 54... Voltage divider circuit 56... Voltage / current converter circuit 60... Power supply input terminal 70.

Claims (3)

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;
Voltage adjusting means for supplying an output current for changing the value of the second variable capacitance element according to the temperature compensation voltage;
An amplification circuit having a second operational amplifier that outputs a frequency control voltage for controlling the value of the second variable capacitance element according to an external control voltage;
The voltage adjusting means supplies the output current generated based on a difference between a voltage based on the external control voltage and a fixed voltage to the second operational amplifier, and controls a reference current according to the temperature compensation voltage. A piezoelectric oscillator comprising the differential amplifier circuit.   A first operational amplifier in which the amplifier circuit uses the external control voltage as an input signal via an input resistor; a second operational amplifier that uses the first output signal as an input signal; and a feedback resistor of the first operational amplifier The base of the first transistor of the differential amplifier circuit to which the external control voltage is supplied is connected between the feedback resistors of the first operational amplifier. Piezoelectric oscillator.   3. The piezoelectric oscillator according to claim 1, wherein a resistor is provided in an emitter of each of the first and second transistors to which the external control voltage and the fixed voltage of the differential amplifier circuit are supplied. .

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