Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
1999-08-30
2001-05-08
Grimm, Siegfried H. (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C330S277000, C326S121000
Reexamination Certificate
active
06229405
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a low voltage oscillation amplifying circuit having an insulated gate field effect transistor (hereinafter referred to a MOSFET), and also to a portable electronic instrument using the circuit. This low voltage oscillation amplifying circuit can be operated at a very low voltage and prevent a leakage current when an operation of the circuit is stopped.
BACKGROUND ART
A conventional oscillation amplifying circuit using a MOSFET, which is incorporated in a semiconductor integrated circuit device, uses a circuit based on a CMOS inverter circuit typified by the circuit construction as shown in
FIGS. 2 and 3
. An amplifying circuit
50
shown in
FIGS. 2 and 3
includes a P-type MOSFET
51
and an N-type MOSFET
52
. The gate electrodes of these MOSFETs are connected to each other and the drain electrodes are also connected to each other. The circuit shown in
FIG. 3
further includes a switching circuit
60
having a single P-type MOSFET
61
. In the case where the amplifying circuit
50
is operated at a low voltage, each of the MOSFETs
51
and
52
is channel-doped so as to specially lower the threshold voltage.
Further, the miniaturization of the integrated circuit has been progressed in recent years, and it is required to lower the power source voltage in order to prevent the elevation in the intensity of the electric field involved in the development of the miniaturization. Because of the increase in demand for portable electronic instruments, an integrated circuit operable at a low voltage is required to achieve the power saving. In general, it is desirable to decrease the threshold voltage of the MOSFET in order to make the integrated circuit operable at a low voltage. A simple logic circuit can be operated if the power source voltage exceeds the threshold voltage of the P-type MOSFET or the N-type MOSFET, whichever of a higher threshold voltage. However, an oscillation circuit using a CMOS inverter circuit as an amplifying circuit is not operated if the power source voltage is not higher than the sum of the threshold voltages of the P-type MOSFET and the N-type MOSFET, due to the characteristics as an analog circuit. Therefore, for the low voltage oscillation, it is necessary to make the threshold voltage lower than the case of a logic circuit. However, if the threshold voltage is made very low, the voltage-current characteristics of the MOSFET can not necessarily permit the MOSFET to satisfactorily perform a sharp ON/OFF position against the gate voltage in general, even if the threshold voltage is set at a positive value. It follows that a leakage current takes place to some extent during OFF time of the MOSFET.
Under the circumstances, various problems are brought about if the threshold voltage is lowered in the conventional circuit construction described above in order to permit the circuit to be operated at a low voltage. The problems are such that, for example, the leakage current is increased during the OFF time, the yield in the manufacturing process is lowered, the channel doping step has to be added twice, leading to a high manufacturing cost, or a clock signal has to be supplied to the oscillating circuit that is separated from other components.
The present invention is devised to overcome these problems and has an objective thereof the provision of a low voltage oscillation amplifying circuit and a portable electronic instrument using the circuit. This low voltage oscillation amplifying circuit can be operated at a low voltage, can prevent leakage current when an operation of the circuit is stopped, and does not incur an increased manufacturing cost derived from an additional channel-doping step.
DISCLOSURE OF THE INVENTION
According to the present invention, there is provided a low voltage oscillation amplifying circuit, comprising:
a switching circuit including first and second MOSFETs of the same conductivity type being connected in series and having the gate electrodes connected to each other;
an amplifying circuit connected to the switching circuit and including a third MOSFET of a first conductivity type and a fourth MOSFET of a second conductivity type, drain electrodes of the third and fourth MOSFETs being connected to each other to provide a common drain electrode, and gate electrodes of the third and fourth MOSFETs being connected to each other to provide a common gate electrode;
a feedback resistor connected between the common gate electrode and the common drain electrode of the third and fourth MOSFETs;
a control circuit including a control signal terminal and an inverter circuit for outputting an inverted signal obtained by inverting a control signal inputted to the control signal terminal;
a power source of a first polarity connected to the switching circuit; and
a power source of a second polarity connected to the amplifying circuit;
wherein a body of each of the third and fourth MOSFETs is insulatively isolated, a voltage of the body of the fourth MOSFET is controlled by the control signal of the control circuit, and a voltage of the body of the third MOSFET is controlled by the inverted signal.
According to the present invention, when the amplifying circuit is operated by the control signal, the body voltage of each of the third and fourth MOSFETs collectively constituting the amplifying circuit is controlled, so that the threshold voltage of each of the MOSFETs is equivalently lowered by the back gate effect. Thus, each of these MOSFETs is operated at a lower voltage. On the other hand, when the operation of the amplifying circuit is stopped by the control signal, the body voltage of each of the third and fourth MOSFETs is brought back to the original level so as to bring the threshold voltage back to the original high level. At the same time, the switching circuit is turned off by the control signal. In addition, since the switching circuit has a structure that the first and second MOSFETs of the same conductivity type are connected to each other in series, the gates electrodes of which are connected to each other, the leakage circuit in the switching circuit can be prevented even if each of these first and second MOSFETs exhibits a threshold voltage of such a level as to bring about the leakage current in a single MOSFET. To be more specific, when each of these first and second MOSFETs is in a turned off state, the connecting point between these first and second MOSFETs bears a voltage intermediate between a power source voltage of a first polarity and a power source voltage of a second polarity. The intermediate voltage is applied to the source electrode of the second MOSFET, and the power source voltage of the first polarity is applied to the gate electrode of the second MOSFET, so that a voltage difference is produced between the gate and the source of the second MOSFET. Because of the voltage difference, it becomes difficult for a leakage current to flow through the second MOSFET when the second MOSFET is in the turned off state, compared with the case where the voltage difference is zero as in the case where the power source voltage of the first polarity is applied to each of the gate and the source of the second MOSFET. This is seemingly equivalent to the condition that the threshold voltage of the second MOSFET has been increased. Accordingly, flow of a leakage current can be prevented even when the amplifying circuit is not operated.
As described above, the switching circuit includes MOSFETs of the same conductivity type that are connected in series and have the gate electrodes connected to each other. Also, the amplifying circuit includes the third and fourth MOSFETs for controlling the body voltages. By these switching and amplifying circuits, the threshold voltages of the third and fourth MOSFETs can be seemingly lowered to operate the amplifying circuit at a very low voltage, and in the OFF state, the threshold voltage of the second MOSFET in the switching circuit can be seemingly increased to prevent the leakage current almost completely.
During the operation of the amplifying
Grimm Siegfried H.
Oliff & Berridg,e PLC
Seiko Epson Corporation
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