Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
1998-10-15
2001-07-10
Kinkead, Arnold (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C331S176000, C331S158000, C331S066000
Reexamination Certificate
active
06259333
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an oscillator. Many communication devices including handy telephone and PHS etc. are used widely for general use. Frequency accuracy used in these devices is most important, and this invention provides a quartz oscillator a highly accurate frequency for use with these devices.
2. Description of Prior Art
A quartz oscillator is used as a frequency source up to now. But the prior art crystal quartz oscillator uses an inductive region of quartz vibrator. Therefore higher frequency more than the characteristics serial resonating frequency of the quartz oscillator is generated, and many sub-frequencies are accompanied for the reason of vibrating energies propagating outside of electrode thereon.
The is an obstacle for fabricating an accurate frequency oscillation source. On the other hand, an oscillator design for decreasing the loss term of quartz vibrator is adapted to make oscillation starting of oscillation easy. This amounts to making the electrode size great, and the sub-frequency generation is increased. So it is difficult to fabricate an accurate frequency oscillation source.
Most quartz oscillators use a thickness-shear mode vibration (in following, explained as AT mode vibration). But they have a characteristic accompanying the other vibrating mode. Especially, a flexure mode vibration accompanied causes a problem that the vibration frequency is much lower than the AT mode series vibration and temperature frequency change is great. Therefore it happens for the flexure mode vibration frequency to coincide with the AT mode series vibration in any temperature within a wide range temperature. Then energy transfer occurs between both modes of vibration. This is called mode coupling, and as the result the AT mode frequency is changed suddenly.
The sudden change of frequency in AT mode has been suppressed by avoiding the coupling between the AT mode and flexure mode. It is resolved by fabrication techniques as strict management of the outline size of the quartz blank (reference number
1
of
FIG. 1
,
FIG. 2
,
FIG. 3
) which affects most to the flexure mode series vibration or beveling cut of the cross-section of quartz vibrator (reference number of
FIG. 2
) for suppressing the flexure mode vibration. However they are not essential resolving methods, and in spite of the production, management many quartz blank having the coupling mode are frequently fabricated for the reason of dispersion of outline size and beveling form of crystal blank in the fabricating process. The quartz vibrator having the mode coupling is excepted at final measuring process thereof, therefore fabrication efficiency of prior art quartz vibrator is very bad. Higher accuracy of the frequency generation source is requested, the fabrication efficiency is greatly lowered. Therefore it is difficult to keep the product quantity, as the product quantity of accurate frequency source is unstable.
SUMMARY OF THE INVENTION
This invention does not solve these problems in view of the quartz vibrator fabrication, but solves by avoiding the mode coupling in quartz vibrator by considering a principle of quartz vibration and circuit technique. An object of the present invention is to provide an accurate frequency generating source having a high production efficiency.
The fundamental characteristic of a quartz vibrator is explained in advance of explanation of a preferred embodiment.
FIG. 1
shows a cross sectional view of a disk of quartz blank
1
having electrodes
2
,
3
at the center. AT mode vibration is caused by the shear mode vibration of the quartz. A region S is a part between the electrodes
2
,
3
, and a region T is a part not having the electrodes. A quartz vibrator having a definite thickness has a proper vibration frequency Ft. The vibration frequency is a proper frequency of the part T. However the frequency Fs of the part S is less than the frequency Ft because of mass effect of the electrodes. Frequency difference of these frequencies (Ft−Fs) is called plate back value. AT mode vibration has a grave problem that it accompanies two kinds of sub-vibrations. One of the sub-vibrations is no-harmonics vibration group of which frequency is very near the AT mode vibration and higher than the frequency of AT mode vibration, it called generally spurious mode. The other is vibration caused by outline of quartz blank, the vibration is called flexure mode vibration. According to energy trapping theory, when a quartz vibrator is exited with frequency less than frequency Fs, the vibration within the region S is reflected totally on the boundary between region S and region T, and all energy is enclosed in the region S. When the excitation frequency is Fs<F<Ft, the vibration propagates freely in the region S, but the vibration amplitude decreases exponentially in propagation in the region T. When the excitation frequency F is F>Ft, the vibration can propagate freely in all region of the crystal blank without decreasing. Therefore the excitation frequency F is F<Ft, standing wave is occurred in the region S depending to the electrode size and many spurious vibration is excited. However, when the plate back value is restricted less than value calculated by the energy trapping theory, these spurious mode frequencies becomes less than frequency Ft, and the standing wave does not cause in the region S.
FIG. 4
shows an electrical equivalent circuit of ideal quartz vibrator which does not have the sub-frequency. In the AT mode vibration, the electrodes size does not affect to the fundamental vibration frequency. According to the approximate theory, parallel capacitor of quartz vibrator proportional to electrode area, and resistance is inverse proportion of electrode area. Prior art quartz oscillator excites the quartz vibrator in an inductive region thereof, therefore the effective resistance thereof is increased. In the prior art quartz oscillator, there is a tendency that the electrode radius is great for the reason of a strong request that the resistance Rs of quartz vibrator is set so as to start surely the oscillation. Under this condition, the oscillation frequency Fo is Fs<Fo<Ft, and a portion of the oscillation energy propagates the blank through the boundary and reaches to the end. As mentioned above, vibration decreases exponentially in propagation within the region T. However, when the electrode size is greater comparative to the size of the region T, enough energy rests at the end of blank. Thickness-shear mode vibration is excited in blank, during the vibration propagation thereof, transverse wave propagating to radius direction of the blank. Therefore the second sub-vibration series of flexure mode series vibration is caused.
FIG. 5
shows an example of frequency change of AT fundamental mode to temperature change. A definite radius blank causes flexure mode vibration. The flexure mode vibration is lower than AT mode frequency, and the frequency variation by temperature change is much greater than that of AT mode. As the result, a part of harmonics of the flexure mode vibration coincides with the AT fundamental frequency at a temperature, and causes mode coupling. The actual measured example of
FIG. 5
shows a mode coupling at about 40° C. This is measured between −35° C. and +85° C. and step of 15° C., and detail change is not clear at the temperature causing the mode coupling. However, such a sudden change of frequency shown in
FIG. 5
cannot be compensated with usual frequency compensation circuit. On the hand, equivalent resistance Rs of AT mode increases sharply by the mode coupling. The rapid increase of resistance happens to stop the quartz vibration temporarily.
It is known that the mode coupling is weak under the condition of low power excitation of quartz vibrator for the reason of decrease of energy for exciting the flexure vibration. However it happens that quartz oscillator excited with such a low energy does not restart, when it had been stopped during a period. It is called as a
Bitex Limited Company
Kinkead Arnold
Staas & Halsey , LLP
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