Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
2000-08-03
2002-06-25
Kinkead, Arnold (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C331S158000, C331S185000
Reexamination Certificate
active
06411169
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an oscillation circuit, an electronic circuit using that oscillation circuit, and a semiconductor device, electronic equipment, and timepiece using that oscillation circuit or electronic circuit.
2. Description of the Related Art
Oscillation circuits that use crystal oscillators are widely employed in the art in devices such as portable timepieces, portable telephones, and computer terminals. It is necessary to design such portable items of electronic equipment in such a manner that they are economical in their power consumption and have longer battery lives.
This crystal oscillation circuit comprises an inverting amplifier and a feedback circuit that is provided with a crystal oscillator. The inverting amplifier comprises a pair of transistors where the gate of each of these transistors is used as an input side and the drain thereof is used as an output side, by way of example. In this case, the drain sides of these two transistors are connected together and the source sides thereof are connected to ground and a power voltage side, respectively.
If the power voltage is applied to the inverting amplifier in the crystal oscillation circuit of this configuration, the phase of the output of the inverting amplifier is inverted through 180 degrees and the thus inverted signal is fed back to the gate of each transistor as an input. The transistors configuring the inverting amplifier are turned on and off alternately by the operation of this feedback, the oscillation output of the crystal oscillation circuit gradually increases, and thus the oscillator starts to oscillate stably.
However, the absolute value of a voltage V
reg
applied to the inverting amplifier in this prior-art crystal oscillation circuit is set to be greater than the total of the absolute values of the threshold voltages V
TP
and V
TN
of the transistors in this circuit, as follows:
|
V
reg
|>|V
TP
|+|V
TN
| (1)
The current inventors have discovered that this is the cause of a short-circuiting current I
S
that flows from the high potential side to the low potential side within the inverting amplifier, which causes a problem when trying to reduce the power consumption of the entire circuit.
SUMMARY OF THE INVENTION
An objective of this invention is to reduce the above short-circuiting current that flows through the inverting amplifier and thus provide an oscillation circuit that can oscillate with a low power consumption, an electronic circuit that uses such an oscillation circuit, and a semiconductor device, electronic equipment, and timepiece that use this oscillation circuit or electronic circuit.
In order to achieve the above objective, an oscillation circuit in accordance with a first aspect of this invention comprises an inverting amplifier including a first semiconductor switching element and a second semiconductor switching element;
wherein the first and second semiconductor switching elements are prevented from being on simultaneously to limit a short-circuiting current flowing through the inverting amplifier when the first and second semiconductor switching element is driven.
This configuration makes it possible to limit the short-circuiting current flowing through the inverting amplifier, making it possible to provide an oscillation circuit that can oscillate with a low power consumption.
The sum of the absolute value of the threshold voltage of the first semiconductor switching element and the absolute value of the threshold voltage of the second semiconductor switching element may be set to be greater than or equal to the absolute value of the power voltage of the inverting amplifier, to limit a short-circuiting current flowing through the inverting amplifier.
The oscillation circuit of this invention may further comprise a feedback circuit having a crystal oscillator connected between the output and input sides of the inverting amplifier, for causing the phase of an output signal from the inverting amplifier to invert and feeding the thus inverted signal back to the inverting amplifier as an input;
wherein the inverting amplifier comprises a first circuit including the first semiconductor switching element, and a second circuit including the second semiconductor switching element;
wherein the first semiconductor switching element is connected to the side of a first potential and is driven to be turned on and off by the feedback input, to excite the crystal oscillator;
wherein the second semiconductor switching element is connected to the side of a second potential that differs from the first potential and is driven to be turned on and off by the feedback input at a timing that differs from that of the first semiconductor switching element, to excite the crystal oscillator; and
wherein the sum of the absolute value of the threshold voltage of the first semiconductor switching element and the absolute value of the threshold voltage of the second semiconductor switching element is set to be greater than or equal to the absolute value of the power voltage of the inverting amplifier, to limit a short-circuiting current flowing through the inverting amplifier.
In this case, when a voltage is applied to the inverting amplifier in the crystal oscillation circuit, excitation of the crystal oscillator starts. The phase of the output of the inverting amplifier is inverted by the feedback circuit and is fed back as an input. The operations of inverting, amplifying, and outputting this feedback input signal by the inverting amplifier are repeated.
During this time, the first and second semiconductor switching elements that configure the inverting amplifier are driven to be turned on and off at mutually different timings by this feedback input, to excite the crystal oscillator.
As stated above, the sum of the absolute values of the threshold voltages of the first and second semiconductor switching elements can be set to be greater than or equal to the absolute value of the power voltage of the inverting amplifier. This prevents the first and second semiconductor switching elements from being driven to turn on simultaneously when the circuit is operating, and, as a result, the short-circuiting current flowing through the inverting amplifier can be greatly reduced, making it possible to reduce the power consumption.
In particular, by forming the first and second transistors in such a manner that the threshold voltage conditions are satisfied, there is no further need for means for dealing with this short-circuiting current, making it unnecessary to use special circuit components for counteracting this short-circuiting current. This makes it possible to reduce the power consumption of the crystal oscillation circuit without adversely affecting the degree of integration of the entire circuit.
Note that it is necessary to set each of the absolute values of the threshold voltages of these first and second semiconductor switching elements to be less than the absolute value of the power voltage of the inverting amplifier.
The oscillation circuit may further comprise a bias circuit for applying a first direct current bias voltage and a second direct current bias voltage to gates of the first semiconductor switching element and the second semiconductor switching element, respectively;
wherein the first and second direct current bias voltages shift the values of the direct current potentials of feedback inputs that are input from the inverting amplifier to the gates of the first and second semiconductor switching elements, to prevent the first and second semiconductor switching elements from being on simultaneously.
The oscillation circuit may further comprise:
a feedback circuit having a crystal oscillator connected between the output and input sides of the inverting amplifier, for causing the phase of an output signal from the inverting amplifier to invert and feeding the thus inverted signal back to the inverting amplifier as an input; and
a bias circuit for applying a direct curren
Kadowaki Tadao
Makiuchi Yoshiki
Nakamiya Shinji
Yabe Hiroshi
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