Data processing: generic control systems or specific application – Specific application – apparatus or process – Specific application of temperature responsive control system
Reexamination Certificate
1999-11-03
2003-06-24
Picard, Leo (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Specific application of temperature responsive control system
C331S158000
Reexamination Certificate
active
06584380
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an approximate third-order function generator, for example, for use with a temperature compensated crystal oscillator, a temperature compensated crystal oscillation circuit made by using the function generator, and a temperature compensation method.
BACKGROUND ART
An example of an approximate third-order function generator of this type is the invention described, for example, on Japanese Patent Laid-Open No. 9-55624 which the present applicant proposed before.
This prior art discloses an approximate third-order curve generation circuit which comprises three differential amplifiers, each comprising a pair of MOS field effect transistors receiving a common first-order input signal and a fixed level signal, the respective fixed level signals to the three differential amplifiers being different in level, and providing a non-inverted output and an inverted output, and the non-inverted outputs and the inverted outputs from the three differential amplifiers being added respectively in group.
However, although the above prior art generator can generate an approximate third-order function, it cannot arbitrarily control its variable independently, which is a unsolved problem.
A general form of the third-order function is represented by:
f
(
x
)=
a
3
x
3
+a
2
x
2
+a
1
x+a
0
(1)
By transforming the variable in the expression (1), the expression (1) is rewritten as follows:
f
(
x
)=
a
3
′(
x−x
0
)
3
+a
1
′(
x−x
0
)+
a
0
′
a
3
=a
3
′
a
2
3′
x
0
a
1
=3
a
3
′x
0
2
+a
1
′
a
0
=a
0
′−a
3
x
0
3
−a
1
′x
0
(2)
Since in the prior art the three differential amplifiers are used to generate an approximate third-order function, the output approximate third-order function is shown in
FIG. 15
, which is represented by the following expression (3).
This expression (3) contains a second term component of the expression (2) thereby and variables a
3
′ and a
1
′ in the expression (2) cannot be controlled independently, which is an unsolved problem.
f
(
x
)=&agr;{
a
3
″(
x−x
0
)
3
+a
1
″(
x−x
0
)}+a″ (3)
Especially, when the approximate third-order function generator is used for temperature compensation of an voltage-controlled crystal oscillation circuit, an approximate third-order function which compensates a temperature characteristics of the crystal oscillator is required to be generated, but an accurate temperature compensated crystal oscillation circuit cannot be constituted, which is an unsolved problem.
DISCLOSURE OF THE INVENTION
The present invention is made in view of those unsolved problems with the prior art. It is a first object of the present invention to provide an approximate third-order function generator capable of accurately outputting only a first term component of the expression (2) and controlling the respective variables independently.
A second object of the present invention is to provide a temperature compensated crystal oscillation circuit which uses an approximate third-order function generator to perform accurate temperature compensation.
A third object of the present invention. is to provide a method of performing temperature compensation for a temperature compensated crystal oscillation circuit.
In order to achieve the first object, an approximate third-order function generator of claim
1
comprises a first amplifier, a second amplifier and a third amplifier each receiving a common input signal and a different fixed level signal, the three different fixed level signals received respectively by the first, second and third amplifiers sequentially increasing in level in this order, each amplifier having an input-output characteristics in which a non-inverted or inverted output signal is provided based on the common input signal and the fixed level signal concerned, that amplifier also having a function to limit the output signal to within a range defined by a maximum predetermined value and a minimum predetermined value; a fourth amplifier receiving the common input signal and the same fixed level signal as the second amplifier receives, the fourth amplifier having an input-output characteristics in which a non-inverted or inverted output signal is provided based on the common input signal and the fixed level signal concerned, and having a function to limit the output signal to within a range defined by a maximum predetermined value and a minimum predetermined value; and a fixed level signal generation circuit for supplying the fixed level signals having the different fixed levels to the first, second, third, and fourth amplifiers, respectively, the output characteristics of the first, third and fourth amplifiers being set so as to have the same polarity, the output characteristics of the second amplifier being set so as to be reverse to those of the first, third and fourth amplifiers, wherein the output signals from the first, second, third and fourth amplifiers being added to generate a third-order function component free from a first-order component.
In the invention of claim
1
, the second amplifier which has a characteristics reverse to those of the first, third and fourth amplifiers is provided, so that only a third-order component free from the first-order component as the first term of the expression (2) produced by the first, second and third amplifiers can be generated. Thus, the variables of the first and second terms of the expression (2) can be controlled independently.
An approximate third-order function generator of claim
2
comprises a third-order component generation unit which includes a third-order component generation circuit having the composition of claim
1
supplied with an input added voltage as a first-order input voltage which includes the sum of a first-order input voltage signal and a variable voltage signal, and a variable gain amplifier which receives an amplified version of the differential between the non-inverted and inverted output signals from the third-order component generation circuit; a first-order component generation unit for receiving the input added voltage and for generating a first-order component; a constant generation unit for receiving a constant voltage signal and for generating a constant component; and an addition circuit for adding output signals from the third-order component generation unit, the first-order generation unit, and the constant generation unit.
The invention of the claim
2
is constructed so as to comprise the third-order component generator, the first-order component generation unit and the constant generation unit which have the respective compositions described in claim
1
and their outputs are added. Thus, the third-order function of the expression (2) can be generated accurately and the respective variables can be controlled independently.
An approximate third-order function generator of claim
3
is characterized in that in the invention of claim
1
or
2
, the fourth amplifier has an output characteristics reverse in inclination to the inverted output characteristics of the second amplifier, and the distance between the maximum and minimum values of the output signal is set so as to be longer than that of the second amplifier.
In the invention of claim
3
, an approximate first-order straight line can be generated in a range of input voltages which can be approximated by a third-order function which has been generated by the first-third amplifiers to thereby ensure that the first-order component contained in the third-order component is offset.
An approximate third-order function generator of claim
4
is characterized in that the first-fourth amplifiers each comprise a differential amplifier having a pair of MOS field effect transistors.
In the invention of claim
4
, the approximate third-order function generator includes CMOSs to thereby achieve higher density integration and reduced power consumption.
A te
Asahi Kasei Microsystems Co. Ltd.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Picard Leo
Rapp Chad
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