JP2006340243A - Piezo-oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem which does not realize an excellent noise characteristic with regard to a piezo-oscillator having an excellent power supply fluctuation characteristic. <P>SOLUTION: The piezo-oscillator which is provided with a piezoelectric vibrator, a first transistor to amplify and oscillate a frequency signal of the piezoelectric vibrator, and a second transistor to amplify an output signal of the transistor for oscillating and which cascade-connects the first transistor and the second transistor forward-directionally connects a MOSFET between a base and an earth ground of the second transistor and connects a gate of the MOSFET to an emitter of the second transistor. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a piezoelectric oscillator, and more particularly to a piezoelectric oscillator having excellent noise characteristics in addition to power supply fluctuation characteristics.

As a reference frequency source in a base station such as a mobile communication device, a thermostat crystal oscillator having high frequency stability is used. As such a crystal oscillator, a cascode disclosed in Japanese Patent Laid-Open No. 2002-135051 is used. A connection type is known.
In the crystal oscillator, if the power supply voltage value fluctuates, the setting conditions of the oscillation circuit will deviate from the appropriate values, and the crystal current flowing through the crystal unit may fluctuate and the output signal level may fluctuate. If the phenomenon is not preferred as a problem of the power supply fluctuation characteristic, it is necessary to provide a constant voltage circuit such as a Zener diode.

FIG. 5 is a circuit diagram showing a crystal oscillator including a conventional general cascode amplifier circuit.
In the crystal oscillator 100 shown in the figure, a series circuit of a resistor 103 and a resistor 104 is inserted and connected between the base of the oscillation transistor 101 and the power supply line 102, and a resistor is connected between the base of the transistor 101 and the ground. 105 is inserted and connected, and the base of the transistor 106 for constituting the grounded base amplifier circuit is connected to the connection middle point between the resistors 103 and 104, and the capacitor 107 is inserted and connected between the base of the transistor 106 and the ground. The resistor 108 is inserted and connected between the collector of the transistor 106 and the power supply line 102.
Further, a series circuit composed of a capacitor 109, a capacitor 110, and a capacitor 111 is inserted and connected between the base of the transistor 101 and the ground, and a coil 112 is connected in parallel to the capacitor 110, and a resistor 113 is connected in parallel to the capacitor 111.
A series circuit of a crystal resonator 114 and a capacitor 115 is inserted and connected between the base of the transistor 101 and the ground, and a Zener diode 116 and a capacitor 117 as a bypass capacitor are inserted and connected between the power supply line 102 and the ground. Further, the power supply line 102 is connected to the power supply Vcc through the resistor 118, and the collector of the transistor 106 is connected to the output OUT through the capacitor 119.
In the crystal oscillator 100 having such a configuration, even when the voltage value of the power supply Vcc fluctuates, the voltage between the power supply line 102 and the ground is kept constant based on the Zener voltage. A stable frequency signal source can be output without any error.

However, there is a problem that a crystal oscillator with excellent noise characteristics cannot be obtained because the Zener diode becomes a noise source. Such a problem is a highly stable type that is used as a reference transmission source for base stations of communication devices in particular. It was a big thing in the crystal oscillator.
JP 2002-135051 A

  The problem to be solved is that an excellent noise characteristic cannot be realized for a piezoelectric oscillator having an excellent power supply fluctuation characteristic.

The present invention includes a piezoelectric vibrator, a first transistor for amplifying and oscillating a frequency signal of the piezoelectric vibrator, and a second transistor for amplifying an output signal of the oscillation transistor, In the piezoelectric oscillator in which the first transistor and the second transistor are cascode-connected, a MOSFET is forward-connected between the base of the second transistor and the ground, and the gate of the MOSFET is connected to the second transistor The transistor is connected to the emitter of the transistor.
The present invention also provides a piezoelectric vibrator, a first transistor for amplifying and oscillating a frequency signal of the piezoelectric vibrator, a second transistor for amplifying an output signal of the oscillation transistor, and the A piezoelectric oscillator having a cascode connection between the first transistor and the second transistor, the drain of the MOSFET being connected to the base of the second transistor, The emitter resistor is inserted and connected between the gate and source of the MOSFET.
In addition to the characteristics described in claim 1 or 2, the present invention is characterized in that a gate-source voltage of the MOSFET is equal to or higher than an element threshold voltage of the MOSFET.

  According to the present invention, there is an advantage that a piezoelectric oscillator excellent in power supply fluctuation characteristics and noise characteristics can be realized.

  The purpose of improving the noise characteristics of the piezoelectric oscillator was realized without damaging the power fluctuation characteristics.

FIG. 1 shows a piezoelectric oscillator provided with a cascode amplifier according to the present invention.
As a piezoelectric oscillator shown in the figure, for example, a crystal oscillator 1 has a series circuit of a resistor 4 and a resistor 5 inserted and connected between a base of an oscillation transistor 2 and a power supply line 3, and a base of the transistor 2 and a ground. A resistor 6 is inserted and connected between them, and a base of a transistor 7 for constituting a base-grounded amplifier circuit is connected to a connection midpoint between the resistors 4 and 5, and a capacitor is connected between the base of the transistor 7 and the ground. 8 is inserted and connected, and a resistor 9 is inserted and connected between the collector of the transistor 7 and the power supply line 3.
Further, a series circuit composed of a capacitor 10, a capacitor 11, and a capacitor 12 is inserted and connected between the base of the transistor 2 and the ground, a coil 13 is connected in parallel to the capacitor 11, and a resistor 14 is connected in parallel to the capacitor 12.

A series circuit of a crystal resonator 15 and a capacitor 16 is inserted and connected between the base of the transistor 2 and the ground, and a capacitor 17 that is a bypass capacitor is inserted and connected between the power supply line 3 and the ground. The line 3 and the power source Vcc are connected through, for example, a resistor 18, and the collector of the transistor 7 is connected to the output OUT through a capacitor 19.
Further, the drain of an N-channel MOSFET 20 (Metal Oxide Semiconductor Field Effect Transistor) is connected to the base of the transistor 7, the gate of the MOSFET 20 is connected to the connection midpoint between the capacitor 11 and the capacitor 12, and the source of the MOSFET 20 is further connected. It is configured to be grounded.
In the crystal oscillator 1 having such a configuration, when the voltage value of the power supply Vcc is changed, the emitter potential of the transistor 2 is changed, and the output signal level of the oscillator is changed. Therefore, even if the power supply line 3 is not provided with a constant voltage circuit, the power supply fluctuation characteristics are excellent.

That is, if the MOSFET20 for example enhancement mode, (the relationship between the voltage _{V GS} and the drain current _{I D} between the gate and the source) voltage-current characteristic of MOFFET, the gate-source voltage _{V GS} MOSFET as shown in FIG. 2 The drain current _ID increases as the gate-source voltage _VGS increases when the element threshold voltage _Vth increases.
Therefore, the fluctuation of the voltage value of the power source Vcc described above is, for example, a voltage drop from the voltage V1 to the voltage V2, and the voltage between the gate and source of the MOSFET 20 drops from V _GS1 to V _{GS2 due} to the voltage drop. If the bias circuit of the amplifier circuit is set in advance so that the voltages V _GS1 and V _GS2 are equal to or higher than the element threshold voltage Vth as shown in FIG. 2, the power supply Vcc is changed from the voltage V1 to the voltage V2. As a result, the base currents of the transistors 2 and 7 are reduced, and as a result, the function of lowering the output signal level of the oscillator occurs. On the other hand, the voltage drops from the voltage VGS1 to VGS2 with the voltage drop of the power supply Vcc. since the drain current _{I D} of the MOSFET20 based on the voltage-current characteristic of the MOSFET shown in Figure 2 along with decreases, the drain Since increasing control to increase the output signal level of the oscillator by the base current of the transistor 7 with decreasing emission current I _D acts, the output signal level of the two functions is cancel each other oscillator is kept constant Therefore, excellent power supply fluctuation characteristics can be obtained without using a constant voltage circuit such as a Zener diode.

FIG. 3 shows the power supply voltage fluctuation characteristics of the current (crystal current) flowing through the crystal resonator of the crystal oscillator according to the present invention.
The power supply voltage characteristic of the crystal oscillator according to the present invention is indicated and indicated as "invention circuit". Further, in order to clarify the effect of the present invention, the conventional circuit shown in FIG. The power supply voltage fluctuation characteristics of the crystal current in FIG.
As shown in the figure, the crystal oscillator according to the present invention has a small change in the value of the crystal current with respect to the change in the power supply voltage value as compared with the conventional circuit. As a result, the fluctuation of the output signal level is small. I understand that.
Although the present invention has been described using a circuit configuration using a bipolar type as an oscillation transistor, the present invention is not limited to this. For example, as shown in FIG. The present invention can also be applied to a design oscillator that uses a MOSFET.
Further, although the present invention has been described using the enhancement type as the MOSFET 20, the present invention is not limited to this, and a depletion type may be applied.

It is a circuit diagram of the piezoelectric oscillator based on this invention. It is a figure which shows the voltage-current characteristic of MOSFET. It is a figure which shows the crystal current power supply voltage characteristic of the piezoelectric oscillator based on this invention. It is a circuit diagram which shows the other Example of the piezoelectric oscillator based on this invention. The circuit diagram of the conventional piezoelectric oscillator is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crystal oscillator 2, 7 Transistor 3 Power supply line 4, 5, 6, 9, 18 Resistor 8, 10, 11, 12, 16, 17, 19 Capacitance 14 Coil 15 Crystal oscillator 20 MOSFET
100 Crystal oscillator 101, 106 Transistor 102 Power supply line 103, 104, 105, 108, 113, 118 Resistor 107, 109, 110, 111, 115, 117, 119 Capacitance 112 Coil 114 Crystal oscillator 116 Zener diode

Claims (3)

  A piezoelectric vibrator; a first transistor for amplifying and oscillating a frequency signal of the piezoelectric vibrator; and a second transistor for amplifying an output signal of the oscillation transistor; In a piezoelectric oscillator in which a transistor and a second transistor are cascode-connected, a MOSFET is forward-connected between a base of the second transistor and a ground, and the gate of the MOSFET is connected to an emitter of the second transistor. A piezoelectric oscillator characterized by being connected to A piezoelectric vibrator, a first transistor for amplifying and oscillating a frequency signal of the piezoelectric vibrator, a second transistor for amplifying an output signal of the oscillation transistor, and a second transistor for the second transistor In a piezoelectric oscillator comprising an emitter resistor, wherein the first transistor and the second transistor are cascode-connected, the drain of the MOSFET is connected to the base of the second transistor, and the gate-source between the MOSFET A piezoelectric oscillator characterized in that the emitter resistor is inserted and connected to the piezoelectric oscillator. 3. The piezoelectric oscillator according to claim 1, wherein a gate-source voltage of the MOSFET is equal to or higher than a device threshold voltage of the MOSFET.

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