JP2002100929A - Oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oscillator having superior noise characteristics. SOLUTION: The oscillator is provided with an oscillation circuit and a buffer circuit, that uses the oscillation signals of the oscillation circuit as the input signals. The buffer circuit is provided with a push-pull amplifier circuit having two base-grounded transistors. As a result, the input impedance of the buffer circuit is reduced, and distortion in the waveform of input signals is suppressed. This renders the oscillator superior in noise characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillator, and more particularly to an oscillator having excellent noise characteristics.

[0002]

2. Description of the Related Art In order for digital communication equipment such as mobile communication equipment to obtain high communication quality, it is necessary that an oscillator used as a carrier frequency source has excellent noise characteristics. FIG. 3 shows a circuit diagram of a crystal oscillator which is conventionally said to have particularly excellent phase noise characteristics as noise characteristics.

A crystal oscillator 100 shown in FIG. 1 includes a crystal oscillator 101 and an oscillation amplifier circuit 102 surrounded by a dotted line.
And a buffer circuit 103 surrounded by an alternate long and short dash line. The oscillation amplifying circuit 102 connects the collector of the transistor 104 to the power supply voltage Vcc line, and connects the base and the ground to the capacitor 105 and a capacitor
06, a connection point of the series circuit is connected to the emitter, a resistor 107 is connected between the emitter and the ground, and a resistor 108 is connected to the base.
And a base bias circuit composed of a resistor 109 and
Further, the base is connected to one end of the crystal unit 101.

The buffer circuit 103 is a grounded base circuit. The base of the transistor 110 is grounded via a capacitor 111, and a base bias circuit including a resistor 112 and a resistor 113 is connected.
A collector resistor 114 is connected between the collector of the oscillator and the power supply voltage Vcc line, the collector is connected to the output terminal OUT of the oscillator, an emitter resistor 115 is connected between the emitter and the ground, and the emitter and the crystal oscillator are connected. 101 is connected to the other end.

In the crystal oscillator 100 having such a configuration, the excitation signal of the crystal oscillator 101 is supplied to the buffer circuit 103 as an output stage without passing through the oscillation amplifier circuit 102, and thus the oscillation signal is generated in the oscillation amplifier circuit 102. Since the noise signal does not overlap with the output signal and the transistor 110 of the buffer circuit 103 is a grounded base circuit having a small input impedance, the signal waveform is less likely to be distorted when amplifying the excitation signal of the crystal unit 101. As a result, a signal having excellent phase noise characteristics can be output.

[0006]

However, when a frequency source superior to the above-described phase noise characteristic of the crystal oscillator 100 is required, the output signal of the oscillator is output through a narrow-band band-pass filter. The noise signal must be removed, but if the center frequency of the filter fluctuates due to a change in temperature, the oscillation frequency of the crystal oscillator 100 shifts to the attenuation range of the filter. As a result, the output signal level decreases and the S / N characteristics and the like decrease. In some cases, the noise characteristics of the hologram are degraded.

In order to avoid such a problem, a band-pass filter having a wide band may be used.
In this case, since a noise signal cannot be sufficiently removed, it is impossible to obtain a required noise characteristic. The present invention has been made to solve the above problems of the piezoelectric oscillator, and has as its object to provide an oscillator having excellent noise characteristics.

[0008]

According to a first aspect of the present invention, there is provided an oscillator comprising: an oscillation circuit; and a buffer circuit having an oscillation signal of the oscillation circuit as an input signal. Wherein the buffer circuit is provided with a push-pull amplifier circuit having two base-grounded transistors.

According to a second aspect of the present invention, in addition to the first aspect, the push-pull amplifier circuit has a grounded base NP.
An N-transistor and a PNP transistor, wherein the collectors of the two transistors are connected to each other, and the emitters of the two transistors are connected to the output terminal of the oscillation circuit via a capacitor. It is characterized by.

According to a third aspect of the present invention, in addition to the first or second aspect, the oscillation circuit has a piezoelectric element, and further connects one end of the piezoelectric element to an input end of the buffer circuit. It is characterized in that it is configured to perform.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on illustrated embodiments. FIG. 1 shows an embodiment of an oscillator according to the present invention. The crystal oscillator 1 shown in FIG. 1 includes a crystal oscillator 2, an oscillation amplifier circuit 3 surrounded by a dotted line, and a buffer circuit 4 surrounded by a dashed line.

The oscillation amplifying circuit 3 is an amplifying circuit part of a general Colpitts type oscillation circuit, and connects a base bias circuit composed of a resistor 6 and a resistor 7 to a base of a transistor 5 and connects a base to a ground. A series circuit of a capacitor 8 and a capacitor 9 that bears a part of a load capacitance is connected between them, an intermediate point of the series circuit is connected to the emitter, and an emitter resistor 10 is connected between the emitter and the ground. Further, the collector is connected to the power supply voltage Vcc line, and one end of the crystal unit 2 is connected to the base.

The buffer circuit 4 is a push-pull amplifier configured to cascode-connect two grounded base circuits, and includes a collector of an NPN transistor 11 and a PNP transistor.
The collector of the transistor 12 is connected, the base of the transistor 11 is connected to the base of the transistor 12 via the resistor 13, the emitter resistor 14 is connected between the emitter of the transistor 11 and the ground, and the base of the transistor 11 is connected. A parallel circuit of a resistor 15 and a capacitor 16 is connected between the ground and the ground. Further, the collector of the transistor 12 and the power supply voltage Vcc line are connected via a resistor 17, and the base of the transistor 12 and the power supply voltage Vc
A parallel circuit of a resistor 18 and a capacitor 19 is connected between the other end of the crystal unit 2 and the transistor 1
1 and the emitter of the transistor 12 are connected via capacitors 20 and 21, respectively.

Next, the operation of the crystal oscillator 1 will be described below. The operation of the components constituting the Colpitts type oscillation circuit is omitted because its operation is known. As is well known, an extremely pure excitation signal (sine wave signal) is output from the crystal unit 2 having a high Q value,
This is supplied as an input signal to the buffer circuit 4 via the capacitors 20 and 21. At this time, when the excitation signal of the plus half cycle is supplied to the buffer circuit 4, the buffer circuit 4 shifts to the cutoff state with the rise of the emitter voltage of the transistor 11, thereby increasing the collector-emitter impedance. In addition, since the collector-emitter impedance of the transistor 12 decreases as the emitter voltage increases, the voltage at the output terminal OUT increases with the amplitude level of the excitation signal, and the output terminal OUT
Generates a signal of a plus half cycle.

When an excitation signal of a minus half cycle is supplied, the transistor 11 becomes active and the impedance between the collector and the emitter decreases, while the transistor 12 shifts to the cutoff state and the impedance between the collector and the emitter increases. Therefore, a signal of a minus half cycle is output to the output terminal OUT. By repeating the above operation continuously, an output signal having the same phase as the excitation signal continues to be generated at the output terminal OUT.

Further, the crystal oscillator 1 having such a configuration has a configuration in which grounded base circuits are connected in parallel in an AC manner, so that the buffer circuit 4 is compared with a conventional crystal oscillator using a single grounded base circuit. Since the input impedance is small and the signal distortion when the excitation signal of the crystal resonator 2 is supplied to the buffer circuit 4 can be effectively suppressed, the phase noise characteristic is excellent.

FIG. 2 shows another embodiment of the crystal oscillator according to the present invention. A feature of the crystal oscillator 1 shown in FIG.
Is connected to the base of the transistor 12 via a series circuit composed of a resistor 23 and a resistor 24. Further, the connection point of the series circuit is connected to the collector of the transistor 11 and the collector of the transistor 12. is there. In such a crystal oscillator 1, it is necessary to appropriately apply a base bias determined by the resistors 14, 17, 23 and 24 to the transistors 11 and 12.

For this reason, when the excitation signal as the input signal has a positive half cycle, the transistor 11 is cut off, and when the input signal has a negative half cycle, both transistors are, for example, A so that the transistor 12 does not reach the cut off state. Bias is set to perform class amplification operation. Even in the crystal oscillator 1 having such a configuration, the impedance between the collector and the emitter of the transistor 11 and the transistor 12 changes with the change in the amplitude of the supplied excitation signal, so that the same function as the circuit of FIG. 1 is obtained. Can be

[0019]

As described above, the oscillator according to the present invention is an oscillator including an oscillation circuit and a buffer circuit using an oscillation signal of the oscillation circuit as an input signal, wherein the buffer circuit has a grounded base. Since the push-pull amplifier having the two transistors is provided, the input signal waveform is suppressed from being distorted by the low input impedance of the buffer circuit, and the noise characteristics are improved.

[Brief description of the drawings]

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

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

FIG. 3 shows a circuit diagram of a conventional oscillator.

[Explanation of symbols]

1,100 crystal oscillator, 2,101 crystal oscillator, 3,1
02 oscillation amplifier circuit, 4, 103 buffer circuit, 5, 1
1, 12, 104, 110 transistors, 6, 7, 1
0, 13, 14, 15, 17, 18, 23, 24, 10
7, 108, 109, 112, 113, 114, 115
Resistance, 8, 9, 16, 19, 22, 105, 10611
1 capacity,

Claims (3)

[Claims] 1. An oscillator comprising: an oscillation circuit; and a buffer circuit having an oscillation signal of the oscillation circuit as an input signal, wherein the buffer circuit comprises a push-pull amplifier circuit having two base-grounded transistors. An oscillator characterized in that: 2. The push-pull amplifier circuit according to claim 1, further comprising an NPN transistor and a PNP transistor whose bases are grounded. The collectors of the two transistors are connected to each other, and the emitters of the two transistors are connected to each other through a capacitor. 2. The oscillator according to claim 1, wherein the oscillator is configured to be connected to an output terminal of the circuit. 3. The oscillation circuit according to claim 1, wherein the oscillation circuit has a piezoelectric element, and further comprises a configuration in which one end of the piezoelectric element is connected to an input terminal of the buffer circuit. 2. The oscillator according to 2.