JP2002135051A - Piezoelectric oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a small-sized constant-temperature oven type crystal oscillator having an excellent yield and a high frequency stability. SOLUTION: The constant-temperature oven type crystal oscillator comprises an oscillation circuit having a piezoelectric oscillator, an amplifier and a variable capacity diode, a constant-temperature oven for holding the oscillator at a predetermined temperature, and a voltage generator for outputting a control voltage for controlling the capacitance of the diode so as to suppress a change in the oscillation frequency of the oscillator due to a change in electrical characteristics of the amplifier in association with a temperature change. Thus, since the frequency change in association with the change in the electrical characteristics of the amplifier generated due to the temperature change can be compensated in a circuit manner by controlling the control voltage with a positive or negative temperature coefficient thermistor as a temperature sensitive element by the voltage generator, the crystal oscillator having an excellent frequency temperature characteristics can be easily realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric oscillator, and more particularly to a small-sized piezoelectric oscillator having excellent frequency temperature characteristics.

[0002]

2. Description of the Related Art Conventionally, as a reference frequency source for a base station, a thermostatic oven crystal oscillator having high frequency stability and a small size has been used. In general, a constant temperature oven crystal oscillator is an electronic device that stores electronic components whose electrical characteristics tend to fluctuate under the influence of environmental temperature changes in a constant temperature oven consisting of metal blocks and drives them under a constant high temperature condition. The characteristic is stabilized, and a frequency signal with high stability is output. Electronic components whose electrical characteristics tend to fluctuate easily include crystal oscillators and oscillation amplifier circuits, but storing both in a constant-temperature bath requires a large-sized constant-temperature bath. I can't.

Conventionally, when realizing a small thermostat type crystal oscillator, only a crystal oscillator which is most susceptible to a temperature change is accommodated in a thermostat, and an amplifying circuit is slightly controlled by the crystal oscillator. There has been known a method of performing electrical temperature compensation using a frequency change.

FIG. 4 is a circuit diagram of a conventional oven controlled crystal oscillator. A crystal oscillator 100 shown in FIG. 1 is a Colpitts type oscillator, in which one end of a crystal oscillator 102 is connected to a base of an oscillation transistor 101, and a base bias circuit including a resistor 103 and a resistor 104 is connected to the base. , The base and the ground are connected to the capacitor 105
And a connection point of the series circuit, the connection point of the series circuit is connected to the emitter of the transistor 101, and the connection point is connected to the ground via a resistor 107. A collector 101 is connected to a power supply voltage Vcc line via a resistor 108, and the other end of the crystal unit 102 is connected via a capacitor 109.

The operation of such a crystal oscillator 100 will be described below. Note that the oscillation circuit is of the Colpitts type as described above, and its operation is known, so description thereof will be omitted. Quartz vibrator 1 with rising environmental temperature
For example, when a change in the overall electrical characteristics of the oscillation circuit section other than 02 causes a function of lowering the oscillation frequency, as shown in FIG. The frequency temperature characteristic of 102 is set to the temperature T1 which is a positive characteristic.

The temperature T0 is a temperature at which the frequency temperature characteristic of the crystal unit 102 has a minimum value. On the other hand, the temperature of the thermostat is controlled by a temperature control circuit (not shown) so as to maintain a constant high temperature state. Since the temperature changes within a narrow range between the temperatures Ta and Tb, which is set as the point, by setting the temperature to the set temperature T1, it is possible to cause the crystal resonator 102 to generate a frequency temperature change having a positive characteristic as the environmental temperature increases.

The change in the frequency of the positive characteristic caused by the crystal unit 102 and the change in the negative characteristic caused by the change in the electric characteristics of the electronic components constituting the oscillation circuit other than the crystal unit cancel each other. Frequency temperature characteristics become stable.

[0008]

However, in the crystal oscillator 100 having the above configuration, the crystal oscillator 10
2 has a variation in frequency-temperature characteristics among individuals, and an electronic component also has variations in electrical characteristics between individuals. Therefore, as described above, the frequency-temperature characteristics of the oscillator Did not always agree symmetrically to completely cancel each other out.

In particular, an overton oscillation circuit or the like uses an electronic component having a large variation in electrical characteristics between solids, such as a coil, so that the variation width of the electrical characteristics as an oscillation circuit portion becomes large. Inevitably, the required frequency-temperature characteristics of the crystal oscillator 100 may not be obtained.

The present invention has been made in order to solve the above-mentioned problems of the piezoelectric oscillator, and has as its object to provide a small-sized constant temperature oven type piezoelectric oscillator excellent in frequency stability and yield.

[0011]

According to a first aspect of the present invention, there is provided an oscillation circuit having a piezoelectric vibrator, an amplifier circuit, and a variable capacitance diode. A thermostat for maintaining a constant temperature, and a capacitor for controlling a capacitance value of the variable capacitance diode so as to suppress a fluctuation in an oscillation frequency of the piezoelectric oscillator due to a change in electrical characteristics of the amplifier circuit due to a temperature change. A voltage generating circuit for outputting a control voltage, wherein the voltage generating circuit controls the control voltage using a thermistor having a positive characteristic or a negative characteristic as a temperature sensing element.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on illustrated embodiments. FIG. 1 is a circuit diagram showing an embodiment of a crystal oscillator according to the present invention. The crystal oscillator 1 shown in FIG. 1 includes a crystal oscillator 2, an amplification circuit 3 that forms a Colpitts oscillation circuit together with the crystal oscillator 2, and a frequency control circuit unit 4.

The amplifying circuit 3 connects a base bias circuit composed of a resistor 7, a resistor 8, and a resistor 9 to the base of the oscillation transistor 5 via a resistor 6, and connects a capacitor 10 in parallel with the resistor 9. A capacitor 11 is connected to one end of the crystal unit 2 via a capacitor 11, and a series circuit including a capacitor 12, a capacitor 13 and a capacitor 14 which bears a part of a load capacitor is connected between the connection point and the ground. A connection point between the capacitors 12 and 13 is connected to the emitter of the transistor 4, and
The capacitor 13 and the coil 15 are configured so that the capacitor 14 and the resistor 16 are connected in parallel, respectively.
7 is cascode-connected to the transistor 5, the base of the transistor 17 is connected to the connection point between the resistors 7 and 8,
Further, the collector of the transistor 17 is connected to the power supply voltage Vcc line via the resistor 18.

The frequency control circuit unit 4 connects the cathode end of the parallel circuit of the variable capacitance diode 19 and the capacitance 20 to the other end of the crystal unit 2, and connects the anode end of the diode 19 and the variable capacitance diode 21 to the capacitance. 22 is grounded through a resistor 23, and the cathode of the diode 21 is connected to a capacitor 24.
, And a resistor 2 is provided at a connection point between the resistors 8 and 9.
5 and the thermistor 26, and the other end of the series circuit is grounded via a parallel circuit of a resistor 27 and a capacitor 28. Further, the other end of the series circuit and the cathode of the diode 21 are connected. It is connected via a resistor 29.

In order to achieve a small-sized oven-controlled crystal oscillator, only the quartz oscillator 2 is housed in an oven formed of, for example, a metal block. Hereinafter, the operation of the crystal oscillator 1 will be described. Note that the operation of the oscillation circuit is a general Colpitts type as described above, and a description thereof will be omitted. As described above, the crystal oscillator 1 having the above-described configuration includes:
Since only a crystal oscillator 2 is housed in a thermostat in order to achieve a small thermostat-type crystal oscillator, other electronic components constituting the amplifier circuit unit 3 are affected by changes in environmental temperature. Thus, for example, a function of lowering the oscillation frequency (negative characteristic) due to the temperature characteristic (hereinafter referred to as temperature characteristic) of the electric characteristic of the amplifier circuit 3 occurs.

On the other hand, the resistance value of the thermistor 26 decreases as the temperature rises, so that the reverse bias voltage of the variable capacitance diode 21 increases. As a result, the capacitance value of the diode 21 decreases, so that the oscillation frequency of the oscillation circuit increases. A function of controlling (to have a positive characteristic) occurs. Therefore, the frequency change of the negative characteristic by the amplifier circuit unit 3 and the diode 2
If the temperature compensation sensitivity (.DELTA.f / .degree. C.) of the diode 21 is set so that the frequency change of the positive characteristic due to 1 is symmetrically matched, the respective frequency changes cancel each other, and as a result, a crystal oscillator with high frequency stability can be obtained. Can be.

As a method of adjusting the temperature compensation sensitivity by the diode 21, there is a method of changing the setting conditions of the value of the capacitor 22 and the reverse bias voltage value in addition to the method of using a required B constant as the thermistor 26. Thus, the frequency can be easily adjusted so as to obtain the required frequency stability. The frequency deviation accompanying this adjustment can be corrected by changing the capacitance between the terminals of the diode 19.

When the temperature characteristic of the amplifier circuit 3 causes the oscillation frequency to increase with temperature, a positive type thermistor 26 whose resistance increases with temperature rise may be used.
As another method, a crystal oscillator 1 'as shown in FIG. 2 may be used.

FIG. 2 shows another embodiment of the crystal oscillator according to the present invention. The crystal oscillator 1 'shown in the figure is characterized in that the frequency control circuit section 4 is connected to a resistor 27 at a connection point between the resistors 8 and 9, and a thermistor 26 is connected between the other end of the resistor 27 and the ground. And a parallel circuit including a series circuit including a resistor 25 and a capacitor 28 is inserted and connected, and the other end of the resistor 27 is connected to a cathode of the diode 21 via a resistor 29. The other configuration is the same as that of the crystal oscillator 1 shown in FIG.

With such a configuration, the voltage between the terminals of the diode 21 decreases due to a decrease in the resistance value of the thermistor 26 due to a rise in temperature. Accordingly, the capacitance value of the diode 21 decreases and the oscillation frequency decreases. The action to cause it occurs. Then, the frequency fluctuation due to the temperature characteristic of the amplifier circuit 3 is canceled out by this function, so that it is possible to easily realize the small-sized oven controlled crystal oscillator 1 ′ having high frequency stability.

In the above description, the present invention has been described by taking as an example a configuration using separate variable capacitance diodes for frequency adjustment and temperature compensation, but the present invention is not limited to this. As shown in FIG. 3, a configuration in which one variable capacitance diode is used for both frequency adjustment and temperature compensation may be used.

FIG. 3 shows another embodiment of the crystal oscillator according to the present invention. The feature of the crystal oscillator 1 "shown in the figure is that the frequency control circuit unit 4 is connected to the cathode of the variable capacitance diode 29 by the frequency control voltage terminal VRef.
To the diode 31 and a capacitance 32 for adjusting the sensitivity in parallel with the diode 31, and a parallel circuit composed of a series circuit including the thermistor 26 and the resistor 25 and the capacitor 28 between the anode of the diode 31 and the ground. The circuit is inserted and connected, and the connection point between the resistors 8 and 9 and the anode of the diode 31 are connected via the resistor 27.

1 and 2 for other structures.
Therefore, the description is omitted. Also, even with the crystal oscillator 1 "having such a configuration, the same temperature compensation function as that of the other two embodiments can be obtained, so that it is possible to easily realize a small-sized oven controlled crystal oscillator having high frequency stability. Furthermore, although the present invention has been described using a quartz oscillator, the present invention is not limited to this.
The present invention can be applied to an oscillator using a piezoelectric vibrator other than quartz.

[0024]

As described above, according to the first aspect of the present invention, there is provided an oscillation circuit having a piezoelectric vibrator, an amplifier circuit and a variable capacitance diode, a thermostat for keeping the piezoelectric vibrator at a constant temperature, A voltage generation circuit that outputs a control voltage for controlling a capacitance value of the variable capacitance diode so as to suppress a fluctuation in an oscillation frequency of the piezoelectric oscillator due to a change in an electrical characteristic of the amplification circuit accompanying the change. The voltage generation circuit controls a control voltage using a thermistor having a positive characteristic or a negative characteristic as a temperature sensing element, thereby compensating for a frequency change due to a change in electrical characteristics of the amplifier circuit caused by a temperature change. Therefore, it is possible to easily realize a small-sized oven controlled crystal oscillator having excellent frequency-temperature characteristics.

[Brief description of the drawings]

FIG. 1 shows a circuit diagram of an embodiment of a crystal oscillator according to the present invention.

FIG. 2 shows a circuit diagram of another embodiment of the crystal oscillator according to the present invention.

FIG. 3 shows a circuit diagram of another embodiment of the crystal oscillator according to the present invention.

FIG. 4 is a circuit diagram of a conventional crystal oscillator.

FIG. 5 is a diagram for explaining a set temperature of a thermostat.

[Explanation of symbols]

1, 1 ', 1 "crystal oscillator, 2 crystal oscillator, 3 amplifier circuit,
4 frequency control circuit section, 5, 17 transistors, 6, 7,
8, 9, 16, 18, 23, 25, 27, 29, 30 resistance, 10, 11, 12, 13, 14, 20, 22, 2,
4, 28, 32 capacitance, 15 coils, 19, 21, 31 variable capacitance diode, 26 thermistor 100 crystal oscillator,
101 transistor, 102 crystal oscillator, 103, 10
4, 107, 108 resistance, 105, 106, 109 capacity

Claims (1)

[Claims] 1. An oscillation circuit having a piezoelectric vibrator, an amplifier circuit and a variable capacitance diode, a thermostat for keeping at least the piezoelectric vibrator at a constant temperature, and a change in electrical characteristics of the amplifier circuit with a temperature change. A voltage generating circuit for outputting a control voltage for controlling the capacitance value of the variable capacitance diode so as to suppress the fluctuation of the oscillation frequency of the piezoelectric oscillator, wherein the voltage generating circuit has a positive characteristic or a negative characteristic. A piezoelectric oscillator, wherein a control voltage is controlled using a thermistor as a temperature-sensitive element.