Oscillators – Electromechanical resonator – Crystal
Reexamination Certificate
2000-12-20
2004-09-28
Kinkead, Arnold (Department: 2817)
Oscillators
Electromechanical resonator
Crystal
C331S1160FE, C310S338000, C310S311000, C310S316010, C073S702000, C073S514340, C073S514130, C324S623000
Reexamination Certificate
active
06798306
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a high-frequency oscillation circuit, and more particularly, to a high-frequency oscillation circuit useful for enhancing sensitivity of various measuring instruments used as weight sensor, chemical sensor, biosensor, viscosity sensor, film thickness meter, gas sensor, floating dust sensor, immunity sensor or the like.
BACKGROUND OF THE INVENTION
While recently various measuring instruments using crystal as weight sensor, chemical sensor, biosensor, viscosity sensor, film thickness meter or the like have been numerously developed, it has been needed urgently to develop a high precision and highly sensitive measuring instruments to cope with such a demand for diversity of materials to be detected and precise quantitative determination of materials to be detected.
As is generally known, however, a wafer used for a crystal resonator has such a nature as to cause distortion (piezo-electric effect) when a voltage is applied to thin film electrodes attached to both side faces faces thereof and return to its initial state when the voltage is removed. Because of this nature, a crystal resonator oscillates at a natural frequency determined by its thickness. Thereby, in a crystal wafer, when its thickness varies by adsorbing a substance, a basic frequency (i.e., the natural oscillation frequency or basic oscillation frequency) of the crystal resonator is varied.
The change &Dgr;f of this natural oscillation frequency is proportionate to a change in thickness. If the change in thickness dimension is replaced by a change &Dgr;m in mass, the following equation called Sauerbrey's equation can be introduced.
&Dgr;
f=−{
2
f
0
2
/(&rgr;
q×&mgr;g
)
1/2
}×(&Dgr;
m/A
)
wherein f
0
is a basic oscillation frequency, &rgr;g and &mgr;g are density and elastic modulus of the crystal, respectively, and A is the area of a portion performing piezo-electric response.
From this equation, it is understood that, since the sensitivity &Dgr;f is proportionate to the square of the basic oscillation frequency f
0
, it is desirable to use a crystal resonator whose f
0
is great. However, if f
0
becomes too great, the thickness is reduced, and the oscillator tends to be easily broken. Therefore, it is general to use a crystal resonator whose f
0
is between 5 and 10 MHz under the normal atmosphere, and even in a solution, merely a crystal resonator whose greatest oscillation frequency f
0
is 30 MHz is used, and a measurement exceeding the maximum detection limit of a general-purpose crystal resonator has not yet been attained.
While there is also an example of measurement using the seventh order overtone mode (63 MHz) of a crystal resonator whose f
0
is 9 MHz, its detection limit is reported as 0.1 ng, which showed no remarkable improvement in sensitivity, compared with the conventional method of 1 ng (“The Latest Method of Separation, Purification and Detection”, p. 441, by NTS Publishing Co., issued May 26, 1997).
On the other hand, in contrast with such a situation as above, there is also proposed a high-frequency oscillation circuit using a crystal resonator not as a weight sensor but for controlling the frequency of an oscillation circuit.
However, in many cases these circuits were analog circuits which are complicated and hard-to-adjust as numerous parts such as transistor, coupling transformer, inductance, etc., are used, and were expensive and not suitable to be used as a measuring instrument for various sensors.
A low-frequency oscillation circuits using a logic element in part is known (JP-A-3-165236 (“JP-A” means unexamined published Japanese patent application), “The Electronic Circuit Parts Utilization Handbook”, p.67, by CQ Publishing Co., issued on Nov. 1, 1985). This oscillation circuits, however, use only an oscillator having a natural frequency in a low-frequency area, so that it cannot cope with a demand for higher sensitivity, making it hard to realize a high-frequency oscillation circuit showing high-frequency stability. Furthermore, there was a need to design and constitute an oscillation circuit to suit a crystal resonator to be oscillated and its frequency (Japanese patent application No. 2000-31513).
SUMMARY OF THE INVENTION
The present invention overturns common knowledge of a conventional oscillation circuit.
The present invention aims to provide a high-frequency oscillation circuit which can keep a stable high-frequency oscillation to easily cope with the natural oscillation frequency of a crystal resonator as a sensor even if it becomes high, and yet which can be easily manufactured at a low cost.
Other and further objects, features, and advantages of the invention will appear more fully from the following description, take in connection with the accompanying drawings.
REFERENCES:
patent: 3676801 (1972-07-01), Musa
patent: 3689907 (1972-09-01), Guajardo
patent: 3760290 (1973-09-01), Epstein
patent: 3879992 (1975-04-01), Bartera
patent: 4321562 (1982-03-01), Igarashi
patent: 4735081 (1988-04-01), Luoma et al.
patent: 4862114 (1989-08-01), Kleinberg
patent: 5197028 (1993-03-01), Nakai
patent: 5801596 (1998-09-01), Sakurai
patent: A3165236 (1991-07-01), None
patent: 05-273106 (1993-10-01), None
patent: 7-131249 (1995-05-01), None
Application note AN-88, “CMOS Linear Applications” 1986 Linear Applications Databook National Semiconductor Corporation Santa Clara, CA, USA.
“Encyclopedia of Electronic Circuits, vol. 1”, R.F. Graf, Tab Books,p. 175, 1985.
Electronic Circuit Parts Utilization Handbook, p. 67, by CQ Publishing Co., issued on Nov. 1, 1985.
Kinkead Arnold
Secretary of Agency of Industrial Science and Technology
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