Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2002-02-04
2004-02-03
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C327S538000, C327S512000, C327S378000, C331S1160FE
Reexamination Certificate
active
06686792
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to an electronic circuit, a semiconductor device, electronic equipment, and a timepiece.
2. Description of Related Art
An electronic circuit that is known in the art comprises a constant-voltage generation circuit that outputs a constant voltage and a crystal oscillation circuit that is driven by this constant voltage. This kind of electronic circuit is widely used in applications such as timepieces, telephones, and computer terminals.
Recent trends in the miniaturization of electronic equipment have made it particularly common to fabricate such electronic circuitry as compact, low-power ICs.
However, electronic circuitry formed as an IC has a problem in that a constant voltage that is output from the constant-voltage generation circuit varies with the effects of temperature.
This is particularly important with a crystal oscillation circuit that is driven by a constant voltage output by a constant-voltage generation circuit because, if that constant voltage should change, the oscillation frequency of the crystal oscillation circuit will also change. This causes a problem in an electronic circuit that generates a reference clock signal for operation based on the oscillation frequency of this crystal oscillation circuit, in that accurate time-keeping is not possible. If a wristwatch is taken by way of example, the environment in which such a wristwatch is used can range from low temperatures to high temperatures. If prior-art electronic circuitry is used in such a wristwatch, therefore, variations in the constant voltage that is output from the constant-voltage generation circuit can cause errors in the time displayed thereby.
It is necessary to set the absolute value of the constant voltage that is output from the constant-voltage generation circuit to be always greater than the absolute value of the oscillation-stopped voltage of the crystal oscillation circuit. If this voltage falls below the oscillation-stopped voltage, the crystal oscillation circuit will no longer be able to operate.
It is known that the power consumption of the crystal oscillation circuit is proportional to the square of the constant voltage supplied from the constant-voltage generation circuit. To reduce the power consumption of the electronic circuitry, therefore, it is necessary to set the value of the constant voltage that is output from the constant-voltage generation circuit to be as small as possible, within a range that satisfies the condition that it is greater than the oscillation-stopped voltage of that crystal oscillation circuit.
If such electronic circuitry is formed as a semiconductor integrated circuit, the effects of factors such as errors in impurity implantation will cause subtle changes in the value of the constant voltage output from the constant-voltage generation circuit and the value of the oscillation-stopped voltage of the crystal oscillation circuit.
Since it is not possible to finely adjust the value of the constant voltage that is output from the constant-voltage generation circuit in prior-art electronic circuitry, it is necessary to set the value of this constant voltage to have a sufficiently large margin over the expected value of the oscillation-stopped voltage, from consideration of the risk of a large variation therein. This means that the crystal oscillation circuit is driven by a voltage that is larger than necessary, raising a problem in that it is difficult to reduce the power consumption of the electronic circuitry from this aspect too.
The present invention is devised in the light of the above problems and has as a first objective thereof the provision of an electronic circuit, semiconductor device, electronic equipment, and timepiece wherein the value of the constant voltage that is output from the constant-voltage generation circuit is not affected greatly by changes in temperature.
Another objective of this invention is to provide an electronic circuit, semiconductor device, electronic equipment, and timepiece wherein the value of the constant voltage that is output from the constant-voltage generation circuit can be adjusted finely.
SUMMARY OF THE INVENTION
In order to achieve the first of the above objectives, there is provided an electronic circuit having a constant-voltage generation circuit for creating a constant voltage, according to a first aspect of this invention. This constant-voltage generation circuit comprises a first voltage creation circuit for creating a reference voltage, and a second voltage creation circuit for creating the constant voltage to have a predetermined relationship with the reference voltage. The first voltage creation circuit comprises a first constant-current source for supplying a constant current, and a circuit having a first voltage-control transistor through which the constant current is passed and which outputs the reference voltage with reference to a predetermined potential. The constant current is set to a value within a saturated operating region of the first voltage-control transistor.
The second voltage creation circuit may comprise a differential amplifier for amplifying the difference between the reference voltage and a comparison voltage, a second constant-current source for supplying a constant current, a circuit having a second voltage-control transistor to which the constant current is supplied, and an output transistor which is connected in series with the circuit having the second voltage-control transistor to be supplied with the constant current, the resistance of the output transistor being controlled by an output of the differential amplifier; wherein the comparison voltage is output from one end of the circuit having the second voltage-control transistor, using a predetermined potential as reference, while the constant voltage being output from another end of the circuit having the second voltage-control transistor; and wherein the constant current is set to a value within a saturated operating region of the second voltage-control transistor.
According to a second aspect of this invention, there is provided an electronic circuit having a constant-voltage generation circuit for creating a constant voltage. This constant-voltage generation circuit comprises a first voltage creation circuit for creating a reference voltage, and a second voltage creation circuit for creating the constant voltage and a comparison voltage having a predetermined relationship with the constant voltage. The second voltage creation circuit comprises: a differential amplifier for amplifying the difference between the reference voltage and the comparison voltage; a second constant-current source for supplying a constant current; a circuit having a second voltage-control transistor to which the constant current is supplied; and an output transistor which is connected in series with the circuit having the second voltage-control transistor to be supplied with the constant current, the resistance of the output transistor being controlled by an output of the differential amplifier. The comparison voltage is output from one end of the circuit having the second voltage-control transistor, using a predetermined potential as reference, while the constant voltage being output from another end of the circuit having the second voltage-control transistor. The constant current is set to a value within a saturated operating region of the second voltage-control transistor.
This aspect of invention makes it possible to reduce variations in the voltage between the ends of the voltage-control transistor to an ignorable level, even if the value of the constant current supplied from the constant-current source varies slightly because of temperature changes in the environment in which the electronic circuit is used, by setting the value of the constant current supplied by the constant-current source to be within the saturated operating region of the voltage-control transistor. Therefore, the value of at least one of the reference voltage and the comparison voltage output from at le
Kadowaki Tadao
Makiuchi Yoshiki
Nakamiya Shinji
Callahan Timothy P.
Luu An T.
Oliff & Berridg,e PLC
Seiko Epson Corporation
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