Oscillators – Frequency stabilization – Temperature or current responsive means in circuit
Reexamination Certificate
2002-06-21
2004-05-04
Wells, Kenneth (Department: 2816)
Oscillators
Frequency stabilization
Temperature or current responsive means in circuit
C331S17700V
Reexamination Certificate
active
06731181
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a temperature compensated oscillator in which temperature characteristics of a crystal oscillator using a crystal resonator are compensated.
BACKGROUND TECHNOLOGY
A crystal oscillator using a crystal resonator is superior in stability of frequency to other oscillators, but when it is used as a reference oscillator for mobile radio communication in recent years, variations in oscillation frequency caused by temperature characteristics of the crystal resonator present a problem. In order to solve the problem, a so-called temperature compensated oscillator is widely used in which temperature characteristics of a crystal resonator are compensated.
Among the temperature compensated oscillators, one by a method called indirect method has been reduced in the number of parts and improved in performance with recent developments in the integrated circuit technology.
The principle of compensating temperature of the temperature compensated oscillator by the indirect method is explained using FIG.
17
.
A temperature detection circuit
91
in
FIG. 17
generates a temperature detection voltage depending on a temperature. The voltage is inputted to a high temperature part/low temperature part separation circuit
92
and a gradient correction voltage generation circuit
93
. The high temperature part/low temperature part separation circuit
92
separates the voltage inputted thereto into two for a low temperature part and for a high temperature part and inputs them to a low temperature part cubic curve voltage generation circuit
94
and a high temperature part cubic curve voltage generation circuit
95
, respectively.
Voltages individually outputted from the low temperature part cubic curve voltage generation circuit
94
, the high temperature part cubic curve voltage generation circuit
95
, the gradient correction voltage generation circuit
93
, and a standard frequency adjustment voltage generation circuit
96
are inputted to an adding circuit
97
to be added, and outputted to a frequency adjustment circuit
98
.
The frequency adjustment circuit
98
controls an oscillation frequency of an oscillation circuit
99
, having a crystal resonator
90
by the inputted voltage. Further, the frequency adjustment circuit
98
adjusts a standard oscillation frequency at a prescribed temperature by the voltage outputted from the standard frequency adjustment voltage generation circuit
96
.
The cubic curve voltage generation circuit only generates a voltage obtained by cubing the inputted voltage, and thus it can only generate a voltage in a first quadrant which is half of a cubic curve in a two-dimensional plane of the input voltage and the output voltage.
Hence, in order to obtain sequential cubic curve voltages, it is necessary to use the low temperature part cubic curve voltage generation circuit
94
which generates a cubic curve voltage by inverting the input voltage and the output voltage and the high temperature part cubic curve voltage generation circuit
95
which generates a cubic curve voltage by an normal operation, and to add the respective output voltages.
This requires the high temperature part/low temperature part separation circuit
92
, the low temperature part cubic curve voltage generation circuit
94
, and the high temperature part cubic curve voltage generation circuit
95
.
In the above-described series of operations, the low temperature part cubic curve voltage generation circuit
94
and the high temperature part cubic curve voltage generation circuit
95
generate voltages such that the frequency adjustment circuit
98
compensates cubic temperature characteristics of an AT cut crystal, and the gradient correction voltage generation circuit
93
generates a voltage such that the frequency adjustment circuit
98
compensates linear temperature characteristics of the AT cut crystal.
These voltages are added in the adding circuit
97
and inputted to the frequency adjustment circuit
98
, so as to compensate the oscillation frequency of the oscillation circuit
99
changing due to temperature. In such a manner, the oscillation frequency of the temperature compensated oscillator can be held constant, even if the temperature changes.
Such a conventional technique, however, has problems that since the high temperature part/low temperature part separation circuit for separating the voltage from the temperature detection circuit for a low temperature part and a high temperature part, the two cubic curve voltage generation circuits, the gradient correction voltage generation circuit, and the adding circuit are required in order to compensate the temperature characteristics of the AT cut crystal as described above, the circuit increases in size, and that the above circuits individually require complicated adjustment in order to correct variations in fabrication.
Hence, it is an object of the present invention to solve the problems and to provide a temperature compensated oscillator that has a simple circuit configuration suitable for downsizing and requires just easy adjustment.
DISCLOSURE OF THE INVENTION
In order to attain the above object, a temperature compensated oscillator according to the invention, which comprises: an oscillation circuit; a frequency adjustment circuit for changing an oscillation frequency of the oscillation circuit by a control voltage; a temperature detection circuit for detecting a temperature in the vicinity of the oscillation circuit and generating at least one output voltage based on the detected temperature; and a control voltage generation circuit including a cubic term voltage generation circuit for generating a cubic term voltage as the control voltage based on the output voltage from the temperature detection circuit, is characterized in that the cubic term voltage generation circuit is configured as follows:
Specifically, the cubic term voltage generation circuit comprises: a first MOS transistor having a source connected to a first power line; a second MOS transistor having a conduction type different from that of the first MOS transistor and a source connected to a second power line; and a first gate voltage generation circuit for generating a first gate voltage and a second gate voltage generation circuit for generating a second gate voltage respectively based on the output voltage of the temperature detection circuit.
Further, an output terminal for outputting the first gate voltage of the first gate voltage generation circuit is connected to a gate of the first MOS transistor, an output terminal for outputting the second gate voltage of the second gate voltage generating circuit is connected to a gate of the second MOS transistor, and a drain of the first MOS transistor and a drain of the second MOS transistor are commonly connected to be an output terminal of the control voltage.
It is preferable that the second power line has a polarity opposite to that of the first power line or is at the ground potential.
Further, in the case of a temperature compensated circuit in which the control voltage generation circuit includes, in place of the cubic term voltage generation circuit, a quadratic term voltage generation circuit for generating a quadratic term voltage as the control voltage based on the output voltage from the temperature detection circuit, only the following points of the configuration of the cubic term voltage generation circuit should be changed to obtain a configuration of the quadratic term voltage generation circuit.
Specifically, the second MOS transistor has the same conduction type as that of the first MOS transistor and a source is connected to the second power line.
The second power line in this case preferably has the same polarity as that of the first power line or may be the same as the first power line.
In these temperature compensated oscillators, the output terminal of the control voltage is preferably connected to at least one arbitrary voltage source via a resistance element having a resistance value of 100 kilohms or more.
In the case of the temperature compens
Fukayama Hiroyuki
Sakurai Yasuhiro
Citizen Watch Co. Ltd.
Wells Kenneth
Westerman Hattori Daniels & Adrian LLP
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