Oscillators – Electromechanical resonator – Crystal
Patent
1997-03-07
1998-09-01
Nelms, David C.
Oscillators
Electromechanical resonator
Crystal
331176, 331177V, H03B 532, H03B 100, H03L 100
Patent
active
058015949
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a crystal oscillation apparatus with built-in temperature compensation function, and a method of adjusting this crystal oscillation apparatus.
BACKGROUND OF THE INVENTION
The crystal oscillation apparatus comprises crystal oscillating circuit; the oscillation frequency of the crystal oscillating circuit significantly shifts along with the change in temperature.
In order to keep said frequency shift due to temperature variation small, a prior art crystal oscillating circuit as disclosed in Japan patent publication No.Heil-265708 controls the voltage to be applied to varactor diode, which is used as a frequency adjusting element of crystal oscillating circuit, by means of a control circuit.
Said prior art control circuit has following constitution; suppose the temperature compensation has to be performed for a range of 130.degree. C. between -35.degree. C. and 95.degree. C., the 300.degree. C. range is divided into zones of 4.degree. C. and temperature compensation data for each of the 4.degree. C. zones are put into respective memory devices.
In the prior art, data regarding the precise graduation, temperature bias point, polarity, rough graduation and fixed offset are necessary for each of said 4.degree. C. zones in order to compensate the temperature shift; which data are divided into 32 control voltage setting groups of 4.degree. C. zone and are stored in respective memory devices.
In the above described constitution, temperature is detected by a temperature sensor, one out of the data of control voltage setting groups corresponding to the temperature detected is selected and picked up out of the memory device, thereby the oscillation frequency of crystal oscillating circuit is stabilized against variation of the ambient temperature.
A problem with said prior art is that it needs memory device of large memory capacity; consequently, a large size semiconductor integrated circuits is needed to house the memory device and control circuits to control the large memory, such control circuits inevitably become complicated and consumes a large power.
Namely, in said prior art, the temperature compensation data are prepared for each of the 4.degree. C. zones, which data are stored in the memory of control voltage setting groups for performing the temperature-compensation by 4.degree. C. interval from -35.degree. C. to 95.degree. C.; which means the memory device should have a capacity large enough for momorizing as many as 32 control voltage setting groups, large and sophisticated control circuits are needed to control the large memory, as a result a semiconductor integrated circuits containing the memory and the control circuits inevitably becomes large sized.
Furthermore, control circuits to control the memory comprising 32 control voltage setting groups consume much power.
SUMMARY OF THE INVENTION
The present invention is to provide an apparatus with which a semiconductor integrated circuits comprising memories and control circuits can be made smaller, hence consuming smaller power.
In order to implement the objective, the invented apparatus comprises a crystal oscillating circuit, a frequency adjusting element electrically coupled with the crystal oscillating circuit, and a control circuit for controlling the voltage to be applied to the frequency adjusting element; said control circuit comprises a temperature sensor, a temperature detecting section electrically coupled with the temperature sensor, a memory device electrically coupled with the temperature detecting section, an amplifier to which the memory device and said temperature sensor are electrically coupled, a first D/A converter electrically intervening between said memory device and temperature detecting section, a second D/A converter electrically intervening between said memory device and amplifier; said memory device comprises actually-operative control voltage setting groups counting not more than 8 groups, each of the control voltage setting groups has in the memory a temperature detection
REFERENCES:
patent: 3719838 (1973-03-01), Peduto et al.
patent: 5081431 (1992-01-01), Kubo et al.
patent: 5126699 (1992-06-01), Kabler
patent: 5473289 (1995-12-01), Ishizaki et al.
patent: 5548252 (1996-08-01), Watanabe et al.
International Search Report.
Translation of International Search Report.
Maeda Chikao
Mizukoshi Ryuji
Mochida Yoshihisa
Muto Masaki
Matsushita Electric - Industrial Co., Ltd.
Nelms David C.
Phan Trong
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