JP2006121134A - Piezoelectric oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric oscillator capable of acquiring a stable oscillation output even if a current consumption in a transistor for oscillation is changed in response to different required performance. <P>SOLUTION: The piezoelectric oscillator is provided with a piezoelectric resonator resonating at a predetermined frequency, a piezoelectric oscillation circuit having an active element for oscillation for applying a current to the piezoelectric resonator to cause the piezoelectric resonator to continuously resonate, and a means for adjusting the current consumption of the active element for oscillation. The active element for oscillation is formed of a transistor. A means for adjusting a current flowing through the transistor is provided as a means for adjusting the current consumption of the transistor. The means for adjusting the current consists of a first current mirror circuit provided in an emitter of the transistor, a second current mirror circuit controlled in its output current by the first current mirror circuit, and a third current mirror circuit provided on a base bias unit of the transistor and controlled in its output current by the first current mirror circuit. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a piezoelectric oscillator that can cope with low power consumption and low phase noise and can obtain a stable oscillation output regardless of changes in power consumption.

Conventionally, piezoelectric oscillators have been widely used as reference signal source oscillators in mobile communication devices such as mobile phones and transmission devices, since stable oscillation frequencies can be obtained. Devices, transmission devices, and the like are required for effective frequency use and high efficiency. For this reason, for example, in the case of a Dual type compatible type or Triple type compatible type communication device that integrates communication devices with different transmission methods, various specifications are also required for the piezoelectric oscillator to be used to support the communication device. In particular, the phase noise characteristic of oscillation output is attracting attention as a characteristic that greatly affects the performance of the device itself, and there is a strong demand to reduce it along with the smaller size and lower power consumption of piezoelectric oscillators. Yes.
As a piezoelectric oscillator satisfying the required performance as described above, since frequency stability is particularly important, among various piezoelectric oscillators, a crystal using a crystal resonator having excellent resonance characteristics and high frequency stability. Oscillators are frequently used. Here, FIG. 2 shows a crystal oscillation circuit of a general crystal oscillator used in the communication device or the like.

FIG. 2 shows a voltage controlled crystal oscillation circuit using a Colpitts oscillation circuit. The crystal oscillation circuit includes a crystal resonator Y1 and an oscillation transistor Tr1, and an oscillation stage 101 that obtains an oscillation output by applying amplification feedback to the output of the crystal resonator Y1, and an oscillation frequency of the oscillation stage 101 And a frequency adjusting unit 102 for adjusting the frequency.
One end of the crystal resonator Y1 is connected to the base of the first transistor Tr1, and a base bias circuit including a resistor R1 and a resistor R2 is connected to the base of the first transistor Tr1. The other end of the crystal resonator Y1 is connected to one end of a load capacitor C2 for adjusting the oscillation frequency of the crystal oscillation circuit, and the other end of the load capacitor C2 slightly adjusts the oscillation frequency with one end grounded. It connects with the other end of load capacity C1 for adjustment. Further, a series circuit of a load capacitor C3 and a load capacitor C4, which are part of the load capacitor, is inserted and connected between the base and ground of the first transistor Tr1, and the connection midpoint of this series circuit and the oscillation circuit The emitter of the transistor Tr1 is connected, and the emitter of the oscillation transistor Tr1 is grounded via an emitter resistor R4. The collector of the transistor Tr1 is connected to the DC power supply Vcc line via the collector resistor R3, thereby constituting the oscillation stage 101.
The frequency adjustment unit 102 includes a voltage variable capacitance diode Vd1 connected in parallel to the load capacitance C1, and a frequency control voltage Vcont for applying a voltage to the voltage variable capacitance diode Vd1 via an AC cut resistor R8. The oscillation frequency of the crystal oscillation circuit can be changed by changing the voltage of the frequency control voltage Vcont.
The crystal oscillation circuit configured as described above oscillates at the natural frequency of the crystal resonator Y1 by applying a DC voltage to the oscillation transistor Tr1 by the DC power supply Vcc, and is stable. Oscillation output can be obtained.

In the oscillation circuit as shown in FIG. 2, there are various methods for reducing the phase noise characteristic of the oscillation output. One of the methods is to increase the collector current of the oscillation transistor Tr1 and increase the output level of the oscillator. Therefore, good phase noise characteristics can be obtained.
For example, in Japanese Patent Laid-Open No. 2003-243931, the magnitude of the collector current in the oscillation transistor Tr1 can be switched as shown in FIG. 3 in order to cope with different required performances such as reduction in phase noise characteristics and reduction in power. As described above, an emitter resistor R4 interposed between the emitter of the oscillation transistor Tr1 and the ground, and one end connected to the emitter of the oscillation transistor Tr1 and the other end grounded via a switch means Tr7 made of a switch transistor or the like. By providing the current switching means composed of the resistor R9, an invention has been made in which the collector current in the oscillation transistor Tr1 can be easily controlled.
According to the invention, when the switch means Tr7 is off, the current switching means increases the emitter current of the oscillation transistor Tr1, that is, the collector current of the transistor Tr1, thereby reducing the phase noise characteristic of the oscillation output. In addition, when the switch means Tr7 is on, the emitter current of the oscillation transistor Tr1, that is, the collector current of the transistor Tr1, decreases, so that the power consumption in the oscillation transistor Tr1 is reduced. Therefore, it is possible to easily realize low phase noise or low power consumption of the oscillator.
JP 2003-243931 A

However, in the conventional example and the circuit of the above-described invention, in order to reduce the phase noise characteristic of the oscillation output, when trying to pass a large collector current to the oscillation transistor Tr1, the base current in the oscillation transistor Tr1 is unchanged. In this state, a large collector current is passed through the oscillation transistor Tr1. Therefore, there is a possibility that the ratio of the collector current to the base current becomes abnormally large. As a result, the operation of the oscillation transistor Tr1 becomes unstable, and in the worst case, the oscillation may stop. there were.
An object of the present invention is to provide a piezoelectric oscillator capable of obtaining a stable oscillation output even when the current consumption in an oscillation transistor is changed according to different performance requirements such as low power consumption and low phase noise. .

  In order to achieve the above object, the present invention provides an oscillation circuit using a current mirror circuit which is a constant current circuit in a base bias part and an emitter part of the oscillation transistor as means for stably operating the oscillation transistor. It is characterized by comprising.

  The piezoelectric oscillator according to the present invention is configured by using a current mirror circuit, which is a constant current circuit, in the base bias part and the emitter part of the oscillation transistor, so that the collector current of the oscillation transistor is changed according to the required performance. However, since the oscillation transistor is supplied with a suitable base current according to the change in the collector current, the ratio of the base current and the collector current can be made constant, and the oscillation transistor Can operate with bias. In addition, it is possible to easily realize an oscillator that meets the demand for low phase noise or low power consumption by changing circuit constants, so there is no need to manufacture oscillators with different circuit configurations for each required performance, reducing manufacturing costs. can do. Further, since the current mirror circuit suitable for the IC is used for the oscillation circuit, the piezoelectric oscillator can be reduced in size and simplified by using an IC in which the oscillation circuit is packaged.

Hereinafter, the present invention will be described in detail based on the illustrated embodiment.
FIG. 1 is a circuit diagram showing a crystal oscillation circuit according to an embodiment of the present invention. In addition, about the structural member similar to what was shown in the above-mentioned prior art example, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

FIG. 1 shows a voltage-controlled crystal oscillation circuit using a Colpitts oscillation circuit. The crystal oscillation circuit includes a crystal resonator Y1 and an NPN-type first transistor Tr1 for oscillation, and an oscillation stage 101 that obtains an oscillation output by applying amplification feedback to the output of the crystal resonator Y1. And a frequency adjustment unit 102 that adjusts the oscillation frequency of the oscillation stage 101, and a current adjustment unit 103 that adjusts the collector current Ic1 and the base current Ib1 in the first transistor Tr1.
One end of the crystal resonator Y1 is connected to the base of the first transistor Tr1, and a base bias circuit including a resistor R1 and a resistor R2 is connected to the base of the first transistor Tr1. The other end of the crystal resonator Y1 is connected to one end of a load capacitor C2 for adjusting the oscillation frequency of the crystal oscillation circuit, and the other end of the load capacitor C2 slightly adjusts the oscillation frequency with one end grounded. It connects with the other end of load capacity C1 for adjustment. The base bias resistor R1 is connected to the collector of a PNP-type second transistor Tr2 whose emitter is connected to the DC power supply Vcc line. Further, a series circuit of a load capacitor C3 and a load capacitor C4, which are part of the load capacitor, is inserted and connected between the base and ground of the first transistor Tr1, and the connection midpoint of this series circuit is the oscillation point. The emitter of the transistor Tr1 is connected to the collector of the NPN-type fourth transistor Tr4 that is grounded via the emitter resistor R4. The collector of the first transistor Tr1 is connected to a DC power supply Vcc line via a collector resistor R3. With the circuit configuration including the second transistor Tr2 and the fourth transistor Tr4, The oscillation stage 101 is configured.
The frequency adjustment unit 102 includes a voltage variable capacitance diode Vd1 connected in parallel to the load capacitance C1, and a frequency control voltage Vcont for applying a voltage to the voltage variable capacitance diode Vd1 via an AC cut resistor R8. The oscillation frequency of the crystal oscillation circuit can be changed by changing the voltage of the frequency control voltage Vcont.

  Next, the main part of the present invention will be described. The base of the aforementioned fourth transistor Tr4 is connected to the base of an NPN-type fifth transistor Tr5, and the fifth transistor Tr5 has a collector connected to the base and a direct current via a collector resistor R7. The emitter is connected to the power supply Vcc line and the emitter is grounded via an emitter resistor R5 having the same value as the emitter resistor R4. The fourth transistor Tr4 and the fifth transistor Tr5 form a first current mirror circuit that is a constant current circuit. Further, the base of the fifth transistor Tr5 is connected to the base of an NPN-type sixth transistor Tr6, and the sixth transistor Tr6 has an emitter whose value is 10 times the emitter resistance R5. The collector is grounded through a resistor R6, and the collector is connected to the emitter and base of a PNP-type third transistor Tr3. That is, a second current mirror circuit is formed by the fifth transistor Tr5 and the sixth transistor Tr6. The collector of the third transistor Tr3 is connected to the DC power supply Vcc line, the base is connected to the emitter, and is connected to the base of the second transistor Tr2 inserted in the base bias portion of the oscillation transistor Tr1. The third transistor Tr3 and the second transistor Tr2 form a third current mirror circuit, which is a constant current circuit, and constitutes the current adjusting unit 103.

The operation of the current adjustment unit 103 configured as described above will be described below. Since the base of the fourth transistor Tr4 and the base of the fifth transistor Tr5 constituting the first current mirror circuit are common, the base potential of both transistors is the same, and both transistors have the same potential. Since the emitter resistors R4 and R5 connected to the emitters have the same value as described above, the emitter current Ie4 of the fourth transistor Tr4, that is, the emitter in the first transistor Tr1, regardless of the collector load of both transistors. The current Ie1 is equal to the emitter current Ie5 of the fifth transistor Tr5. Here, the collector current Ic, emitter current Ie, and base current Ie in the transistor circuit are Ie = Ib + Ic, and the base current Ib is very small compared to the collector current Ic. The collector current Ic1 in one transistor Tr1 is equal to the emitter current Ie1, that is, the emitter current Ie5 in the fifth transistor Tr5. Since the magnitude of the emitter current Ie5 depends on the base potential of the fifth transistor Tr5, the collector current Ic1 can be controlled by the base potential of the fifth transistor Tr5.
Next, since the base of the fifth transistor Tr5 and the base of the sixth transistor Tr6 forming the second current mirror circuit are common, the base potentials of the two transistors are the same, and Since the resistance ratio of the emitter resistors R5 and R6 connected to the emitters of both transistors is R5: R6 = 1: 10 as described above, the emitter current Ie6 of the sixth transistor Tr6 includes the fifth transistor A current that is 1/10 of the emitter current Ie5 in Tr5 flows. Therefore, as described above, the emitter current Ie6 of the sixth transistor Tr6 is also controlled by the base potential of the fifth transistor Tr5.
Further, since the current flowing through the base bias portion of the first transistor Tr1 forming the oscillation stage 101 is inserted into the base bias portion of the second transistor Tr2 forming the third current mirror circuit, It is determined by the emitter current Ie2 in the second transistor Tr2. The emitter current Ie2 in the second transistor Tr2 is the same as the base of the second transistor Tr2 and the base of the third transistor Tr3, and the base potential of both transistors is the same. It becomes equal to the emitter current Ie3 of the transistor Tr3. Here, since the emitter current Ie3 is equal to the emitter current Ie6 in the sixth transistor Tr6 serving as the collector load of the third transistor Tr3, the emitter current Ie2 of the second transistor Tr2 is It becomes equal to the emitter current Ie6. As described above, 1/10 of the emitter current Ie5 of the fifth transistor Tr5 flows in the emitter current Ie6 of the sixth transistor Tr6, and the current value is the base potential of the fifth transistor Tr5. Therefore, the emitter current Ie2 of the second transistor Tr2 is also controlled by the base potential of the fifth transistor Tr5.
Here, the collector current Ic of the transistor circuit changes greatly as the base current Ib changes, and the collector current Ic increases as the base current Ib increases, that is, the base potential increases. As described above, since the collector current Ic and the emitter current Ie of the transistor circuit are substantially equal, the emitter current Ie increases by increasing the base potential. Accordingly, each emitter current in the first to sixth transistors is increased by increasing the base potential of the fifth transistor Tr5.

By the above operation, the collector current Ic1 of the first transistor Tr1 for oscillation, that is, the emitter current Ie4 in the fourth transistor is increased by increasing the base potential of the fifth transistor Tr5. Can be increased. When the base potential of the fifth transistor Tr5 increases, the emitter current Ie6 of the sixth transistor Tr6 sharing the base increases, and the emitter current Ie3 of the third transistor equal to the emitter current Ie6, and Since the emitter current Ie2 in the second transistor Tr2 inserted in the base bias portion of the crystal oscillation circuit also increases, the current flowing through the base bias of the first transistor Tr1 for oscillation also increases, and the first The base current Ib1 of the transistor Tr1 increases.
That is, the base current Ib1 also increases in conjunction with the increase in the collector current Ic1 in the first transistor Tr1 for oscillation, so that the base current Ib1 and the collector current Ic1 in the first transistor Tr1 are constant. Therefore, even if the collector current Ic1 in the first transistor Tr1 is increased to reduce the phase noise characteristic of the oscillation output, the first transistor Tr1 always operates in a stable state. Stable oscillation output can be obtained. Further, even when the collector current Ic1 of the first transistor Tr1 is reduced in response to the demand for lower power consumption, the base current Ib1 and the collector current Ic1 of the first transistor Tr1 are constant as described above. Since the current ratio is maintained, the first transistor Tr1 operates in a stable state, and a stable oscillation output is obtained.
As described above, the crystal oscillation circuit is configured using the current mirror circuit that is a constant current circuit in the base bias part and the emitter part of the oscillation transistor in the crystal oscillation circuit. Even if the collector current is changed, a stable oscillation output can always be obtained. Further, since the current mirror circuit suitable for the IC is used for the oscillation circuit, the piezoelectric oscillator can be reduced in size and simplified by making the oscillation circuit into an IC in one package.
In the above embodiment, the voltage control type crystal oscillator has been described as an example. However, the present invention is not limited to this, and a crystal oscillator such as a temperature compensation type or an OVEN control type, and a piezoelectric vibrator other than a crystal are used. It is clear that the piezoelectric oscillator used may be used. The ratio of the base bias current Ie2 and the collector current Ic1 in the transistor circuit of the oscillation stage 101 is preferably Ie2: Ic1 = 1: 10. In this embodiment, the emitter resistance R6 in the sixth transistor Tr6 is Although the value of 1/10 of the emitter resistance R5 in the fifth transistor Tr5 is set, the emitter resistances R5 and R6 are set to the same value, and the second transistor Tr2 and the third transistor are set in the second current mirror circuit. The same effect can be obtained even if the IC is configured as a multi-emitter in which the value of the emitter current in the transistor Tr3 can be set at an arbitrary ratio.

1 is a voltage controlled crystal oscillation circuit diagram showing an embodiment according to the present invention. FIG. It is a figure which shows the structural example of the conventional crystal oscillation circuit. It is a figure which shows the other structural example of the conventional crystal oscillation circuit.

Explanation of symbols

Y1 crystal resonator Tr1 first transistor Tr2 second transistor Tr3 third transistor Tr4 fourth transistor Tr5 fifth transistor Tr6 sixth transistor Tr7 switching transistor R1 to R10 resistor C1 to C4 load capacitance Vd1 voltage variable capacitance Diode L1 Choke inductor 1a Strip conductor Vcc DC power supply Vcont Frequency control voltage Vin DC voltage 101 Oscillation stage 102 Frequency control unit 103 Current control unit

Claims (4)

A piezoelectric vibrator which vibrates at a predetermined frequency, and a current is passed through the piezoelectric vibrator to continuously
A piezoelectric oscillation circuit having an oscillation active element that vibrates an electric vibrator, and the oscillation active element;
A piezoelectric oscillator comprising: means for adjusting the amount of power consumption. As means for adjusting the magnitude of power consumption in the oscillation active element, the oscillation capability
2. The pressure according to claim 1, further comprising means for adjusting a current flowing through the moving element.
Electric oscillator. The active element for oscillation is formed by a transistor, and the current flowing through the transistor is adjusted.
As means for enabling adjustment, the base bias portion of the transistor and the emitter current flow
The piezoelectric device according to claim 2, further comprising a current control unit capable of controlling a current of the passage unit.
Oscillator. The current control unit includes a first current mirror circuit provided in the emitter of the transistor.
And a second current mirror circuit whose output current is controlled by the first current mirror circuit, and a base bias portion of the transistor, and the output current is controlled by the first current mirror circuit. 4. The piezoelectric oscillator according to claim 3, wherein the piezoelectric oscillator is configured by a third current mirror circuit.

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