Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
2002-03-13
2004-09-14
Lam, Tuan T. (Department: 2816)
Oscillators
Solid state active element oscillator
Transistors
C331S158000
Reexamination Certificate
active
06791424
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to piezo oscillators, and particularly to piezo oscillators with the start-up time taken to reach the steady oscillating state from the non-oscillating state shortened.
BACKGROUND
To make longer continuous use of cell phones possible, the crystal oscillators used as the reference oscillation source in cell phones are intermittently put into operation to reduce power consumption.
For crystal oscillators thus intermittently put into operation, the start-up time taken to generate desired output signals from beginning to be driven is desired to be short. Therefore, the crystal oscillator of the configuration disclosed in the patent application laid open under Laid Open No. 1996-51017 has been put into practical use.
FIG. 38
is a schematic diagram of the conventional crystal oscillator with an improved start-up characteristics, disclosed in the above gazette.
The crystal oscillator
100
shown in the figure is a typical Colpitts crystal oscillator, but characterized in the configuration in which one terminal of the crystal resonator
103
is connected to the base of a transistor
100
through a capacitor
102
, and the other terminal of the crystal resonator
103
is connected to the power supply voltage Vcc line. Since the power supply voltage Vcc line is usually connected to the ground through a capacitor
104
of a comparatively large capacitance, the terminal of the crystal oscillator
103
connected to the power supply voltage Vcc line is also connected to the ground via the power supply voltage Vcc line.
Further, in this configuration, resistors
105
and
106
are base-biasing circuit, resistor
107
is an emitter resistor of the transistor
101
, and capacitors
108
and
109
serve as part of load capacitance.
By this configuration, a voltage of the same level as the power supply voltage Vcc is applied to the crystal resonator
103
like a pulse wave, and the crystal resonator
103
vibrates in a large level of vibration. As a result, the start-up time taken for the oscillation signal to reach the required level becomes shorter.
However, in the crystal oscillator of the configuration described above, the power supply voltage Vcc line is contained in the oscillation loop, and hence noises contained in the supply voltage and those that come in via the power supply voltage Vcc line are directly applied to the crystal oscillator
103
. The phase noise characteristics of this crystal resonator therefore can degrade because of the influence of noises.
Specifically, although the capacitor
104
connected between the power supply voltage Vcc line and the ground serves as a bypass capacitor in the crystal oscillator
100
of the configuration described above, it is not possible to completely remove the noises that comes in from the supply voltage and everywhere on the power supply voltage Vcc line even by using a plurality of bypass capacitors.
Since the noises are amplified by the amplification circuit in the oscillating circuit and output along with the oscillation signal, they can cause the degradation of the phase noise characteristics of the crystal oscillator
100
.
If the output signal of such a crystal oscillator is used for digital processing, there is the possibility that bit errors occur in data processing because of the noise signals mixed in the output signal.
Further, when this crystal oscillator is built in apparatuses such as cell phones, the stray capacitance of other circuits connected to the power supply voltage Vcc line comes into the oscillation loop, and causes the problem that the oscillation frequency shifts from the set frequency.
Specifically, in addition to the capacitance of the capacitors and the stray capacitance associated with the circuit elements and wiring patterns of the crystal oscillator, the capacitance of the bypass capacitors connected to the power supply voltage Vcc line and the stray capacitance of circuits in the apparatus in which the crystal oscillator is built in, the oscillation frequency of the crystal oscillator
100
must be set taking into account the capacitance in the apparatus beforehand.
However, this adjustment method can lower the productivity of the apparatuses in which the crystal oscillator is used, since the capacitance of bypass capacitor used in apparatuses differs with models, and hence the adjustment condition must be change accordingly.
The present invention is made to solve these problems with conventional piezo oscillators. The object of the present invention is therefore to provide piezo oscillators having an improved start-up characteristics without degradation in the phase noise characteristics and the frequency stability characteristics.
SUMMARY OF THE INVENTION
The above object is accomplished by the following piezo oscillators.
The piezo oscillator of first embodiment is characterized in that: the piezo oscillator contains a crystal resonator, amplifying circuit, and quick start-up circuit; the quick start-up circuit has a configuration in which an NPN transistor is connected between the power supply voltage Vcc line and one terminal of the crystal resonator in forward polarity, and a capacitor is connected between the power supply voltage Vcc line and the base of the NPN transistor; and a start-up quickening voltage is applied to the piezo resonator from the power supply voltage Vcc line through the NPN transistor for a predetermined length of time after the application of power supply voltage Vcc.
The piezo oscillator of second embodiment is characterized in that: the piezo oscillator contains a piezo resonator, amplifying circuit, and quick start-up circuit; the quick start-up circuit has a configuration in which a first NPN transistor is connected between the power supply voltage Vcc line and one terminal of the piezo resonator in forward polarity, a resistor is connected between the base and the emitter of the first NPN transistor, a second NPN transistor is connected to the power supply voltage Vcc line and the base of the first NPN transistor in forward polarity, and a capacitor is connected between the power supply voltage Vcc line and the base of the second NPN transistor; and a start-up quickening voltage is applied to the piezo resonator from the power supply voltage Vcc line through the NPN transistor for a predetermined length of time after the application of power supply voltage Vcc.
The piezo oscillator of third embodiment is characterized in that: the piezo oscillator contains a piezo resonator, amplifying circuit, and quick start-up circuit; the quick start-up circuit has a configuration in which a PNP transistor is connected between the power supply voltage Vcc line and one terminal of the piezo resonator in forward polarity, and a capacitor and a diode are connected in parallel between the base of the PNP transistor and the ground; and a start-up quickening voltage is applied to the piezo resonator from the power supply voltage Vcc line through the NPN transistor for a predetermined length of time after the application of power supply voltage Vcc.
The piezo oscillator of fourth embodiment is characterized in that: the piezo oscillator contains a piezo resonator, amplifying circuit, and quick start-up circuit for applying a start-up quickening voltage of a desired level to one terminal of the piezo resonator after the application of power supply voltage Vcc; and the quick start-up circuit begins to operate with a delay determined according to the rise of voltage of the power supply voltage Vcc after the application of the power supply voltage Vcc and outputs the start-up quickening voltage with a steeper rise than the rise characteristics of the power supply voltage Vcc.
The piezo oscillator of fifth embodiment is characterized in that: the piezo resonator, amplifying circuit, and quick start-up circuit for applying a start-up quickening voltage of a desired level to one terminal of the piezo resonator after the application of power supply voltage Vcc; the quick start-up circuit having a transistor switch and a voltage dividing circuit f
Adachi Takehiko
Hosaka Koji
Ishikawa Masayuki
Izumiya Shoji
Oinuma Yuuichi
Koda & Androlia
Lam Tuan T.
Toyo Communication Equipment Co., Ltd.
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