Oscillators – Electromechanical resonator – Crystal
Reexamination Certificate
1998-01-08
2001-04-10
Mis, David (Department: 2817)
Oscillators
Electromechanical resonator
Crystal
C337S116000
Reexamination Certificate
active
06215370
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a crystal oscillating circuit and an integrated circuit for crystal oscillation.
2. Description of the Related Art
FIG. 16
is an electric circuit diagram showing a conventional oscillating circuit using a crystal resonator. Numeral
161
designates a crystal resonator, numeral
162
designates a CMOS (Complementary Metal Oxide Semiconductor) invertor, numeral
163
designates a feedback resistor and numerals
164
and
165
designate capacitors. The crystal resonator
161
and the feedback resistor
163
are connected between input and output terminals of the CMOS invertor
162
. Terminals on one side of the capacitors
164
and
165
are respectively connected to the input terminal and the output terminal of the CMOS invertor and terminals on the other side thereof are connected to a power source VSS (OV).
At present, according to such an oscillating circuit, downsizing of the crystal resonator has progressed in response to a need for speed-up of operational frequency and downsizing a total of a crystal oscillation module.
However, with downsizing a crystal resonator, a problem caused by crystal current (current flowing in a crystal in oscillation) cannot be neglected. For example, an increase in an amplitude by an excessive crystal current makes frequency unstable and brings about destruction of a crystal resonator in the worst case.
Further, although there has been proposed a circuit where the crystal current is reduced by providing a resistor
166
between the CMOS invertor
162
and the crystal resonator
161
as shown by
FIG. 17
, a resistance value thereof cannot be increased since the resistance value effects a significant influence on the negative resistance. Further, according to such a circuit, not only the crystal current but the amplitude voltage are lowered. Therefore, setting of the circuit becomes difficult in which the duty of a CMOS invertor at a next stage is significantly changed in view of a threshold voltage of the CMOS invertor at the next stage and the like.
SUMMARY OF THE INVENTION
Hence, according to the present invention, the crystal current is reduced by providing resistors not on paths formed by the input terminal and the output terminal of the CMOS invertor and the crystal resonator, but either of paths formed by the input terminal of the CMOS invertor, a first capacitance element and a power source terminal and/or either of paths formed by the output terminal of the CMOS invertor, a second capacitance element and a power source terminal.
According to an aspect of the present invention, there is provided a crystal oscillating circuit constituted by a CMOS invertor, a crystal resonator connected between input and output terminals of the CMOS invertor, a feedback resistor connected between the input terminal and the output terminal of the CMOS invertor, a first capacitance element provided between a first connection point of connecting the input terminal of the CMOS invertor and the crystal resonator and a power source terminal at a predetermined potential, a second capacitance element provided between a second connection point of connecting the output terminal of the CMOS invertor and the crystal resonator and a power source terminal at the predetermined potential, and resistors provided at either of one or a plurality of portions between the first connection point and the first capacitance element, between the second connection point and the second capacitance element, between the first capacitance element and the power source terminal and between the second capacitance element and the power source terminal. And it is desirable to provide an integrated circuit for crystal oscillation capable of constituting such a crystal oscillating circuit.
Further, it is preferable that the resistors are provided between the first connection point and the first capacitance element and between the second connection point and the second capacitance element, respectively.
It is preferable that the resistors are provided between the first capacitance element and the power source terminal and between the second capacitance element and the power source terminal, respectively.
It is preferable that the resistors are provided between the first capacitance element and the power source terminal and between the second connection point and the second capacitance element, respectively.
It is preferable that the resistors are provided between the first connection point and the first capacitance element and between the second capacitance element and the power source terminal, respectively.
REFERENCES:
patent: 3803828 (1974-04-01), Keeler et al.
patent: 3939642 (1976-02-01), Morozumi
patent: 3958187 (1976-05-01), Suzuki et al.
patent: 5457433 (1995-10-01), Westwick
patent: 57-26903 (1982-02-01), None
patent: 0079603 (1990-03-01), None
patent: 5-191144 (1993-07-01), None
Uno, T. et al; “A New Digital TCXO Circuit Using a Capicitor-Switch Array”;Proc. 37th Annual Frequency Control Symposium; 1983 pp. 434-441.
Hasegawa Eiichi
Otsuka Haruhiko
Jordan and Hamburg LLP
Mis David
Nippon Precision Circuits Inc.
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