Oscillators – With frequency adjusting means – With voltage sensitive capacitor
Reexamination Certificate
2001-07-26
2003-08-26
Tokar, Michael (Department: 2819)
Oscillators
With frequency adjusting means
With voltage sensitive capacitor
C331S167000, C331S105000, C331S17700V
Reexamination Certificate
active
06611179
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to voltage-controlled oscillators and communication apparatuses incorporating the same. More particularly, the present invention relates to voltage-controlled oscillators generating high frequency signals in different frequency bands and communication apparatuses incorporating the oscillators.
2. Description of the Related Art
Recently, multiple communication systems using different frequency bands have come into widespread use. The recent tendency has permitted a single communication apparatus to be used to handle multiple communication systems. In this case, in the communication apparatus, it is necessary for a high frequency oscillation circuit such as a voltage-controlled oscillator defining a local oscillation circuit to generate signals having different frequency bands according to the multiple communication systems.
FIG. 7
shows a circuit diagram of a conventional voltage-controlled oscillator. In this figure, there is shown a voltage-controlled oscillator
50
generating high frequency signals of two different frequency bands disclosed in Japanese Unexamined Patent Application Publication No. 10-163750. The voltage-controlled oscillator
50
includes first and second resonant circuits
51
a
and
51
b,
first and second oscillation circuits
52
a
and
52
b
oscillating at resonance frequencies of the first and second resonant circuits
51
a
and
51
b,
an amplifying circuit
53
amplifying oscillation signals of the first and second oscillation circuits
52
a
and
52
b,
a control terminal
54
applying a control voltage to each of the first and second resonant circuits
51
a
and
51
b,
power-source terminals
55
a
and
55
b
of the first and second oscillation circuits
52
a
and
52
b,
a power-source terminal
56
of the amplifying circuit
53
, and an output terminal
57
outputting a high frequency signal.
The first resonant circuit
51
a
includes a variable-capacitance diode D
51
a,
a stripline S
51
a
defining a resonator, a frequency adjusting capacitor C
51
a,
a coil L
51
a,
and a capacitor C
52
a.
The second resonant circuit
51
b
includes a variable-capacitance diode D
51
b,
a stripline S
51
b
defining a resonator, a frequency adjusting capacitor C
51
b,
a coil L
51
b,
and a capacitor C
52
b.
The stripline S
51
a
and the variable-capacitance diode D
51
a
constitute a parallel resonant circuit, and the stripline S
51
b
and the variable-capacitance diode D
51
b
also constitute a parallel resonant circuit.
The first oscillation circuit
52
a
includes a transistor Q
51
a,
capacitors C
53
a
to C
55
a,
and resistors R
51
a
to R
53
a.
The second oscillation circuit
52
b
includes a transistor Q
51
b,
capacitors C
53
b
to C
55
b,
and resistors R
51
b
to R
53
b.
The amplifying circuit
53
includes a transistor Q
52
, a coil L
52
, capacitors C
56
to C
60
, and resistors R
54
to R
56
.
The first resonant circuit
51
a
is connected to the first oscillation circuit
52
a
via a coupling capacitor C
61
a,
and the second resonant circuit
51
b
is connected to the second oscillation circuit
52
b
via a coupling capacitor C
61
b.
The first and second oscillation circuits
52
a
and
52
b
are connected to the amplifying circuit
53
via coupling capacitors C
62
a
and C
62
b.
Next, a description will be provided of the operation of the voltage-controlled oscillator
50
shown in FIG.
7
. When a power source is supplied to the power-source terminal
55
a
of the first oscillation circuit
52
a
and a power source is not supplied to the power-source terminal
55
b
of the second oscillation circuit
52
b,
only the first oscillation circuit
52
a
is driven whereas the second oscillation circuit
52
b
is not driven. In addition, when a power source is supplied to the amplifying circuit
53
from the power-source terminal
56
, the amplifying circuit
53
is driven. In this case, in a range permitting oscillation of the first oscillation circuit
52
a,
a high frequency signal according to a direct current voltage applied by the control terminal
54
is output from the output terminal
57
. In contrast, when a power source is supplied to the power-source terminal
55
b
of the second oscillation circuit
52
b
and a power source is not supplied to the power-source terminal
55
a
of the first oscillation circuit
52
a,
in a range permitting oscillation of the second oscillation circuit
52
b,
a high frequency signal according to a direct current voltage applied by the control terminal
54
is output from the output terminal
57
.
The above-described operation can be performed by roughly coupling the first and second oscillation circuits
52
a
and
52
b
and the amplifying circuit
53
defining the voltage-controlled oscillator
50
via the coupling capacitors C
62
a
and C
62
b
having low capacitances so that no frequency change occurs even though the impedance of the output terminal
57
of the voltage-controlled oscillator
50
changes. For example, when the first oscillation circuit
52
a
is driven and the second oscillation circuit
52
b
is not driven, of the oscillation signals of the first oscillation circuit
52
a,
most of signals passing through the coupling capacitor C
62
a
flow into the amplifying circuit
53
and hardly flow into the second oscillation circuit
52
b,
which is not driving, via the coupling capacitor C
62
b.
In other words, since the coupling capacitors C
62
a
and C
62
b
are capacitors provided for rough coupling, as compared with the impedance of an input terminal of the amplifying circuit
53
, each of the capacitors C
62
a
and C
62
b
has significantly high impedance. As a result, most of the oscillation signals of the first oscillation circuit
52
a
flow into the amplifying circuit
53
having low impedance. This is also applied to the case in which the second oscillation circuit
52
b
oscillates and the first oscillation circuit
52
a
does not oscillate. With this arrangement, without causing any mutual influence between the first and second oscillation circuits
52
a
and
52
b,
the first and second oscillation circuits
52
a
and
52
b
can be connected to the amplifying circuit
53
.
However, the above conventional voltage-controlled oscillator requires a plurality of oscillation circuits to respond to different frequency bands. Thus, there is a problem in that the size of the voltage-controlled oscillator tends to be larger.
Furthermore, when characteristic deterioration occurs in the coupling capacitors connecting the plurality of oscillation circuits and the amplifying circuit, the oscillation signals of the driving oscillation circuit flow into the oscillation circuit that is not driving. As a result, the characteristics of the voltage-controlled oscillation circuit are deteriorated.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a voltage-controlled oscillator having a greatly reduced size and a structure that prevents characteristic deterioration. In addition, preferred embodiments of the present invention provide a communication apparatus including a voltage-controlled oscillator having a greatly reduced size and a structure that prevents characteristic deterioration.
A voltage-controlled oscillator according to a preferred embodiment of the present invention includes a first resonant circuit resonating in a first frequency band, a second resonant circuit resonating in a second frequency band that is higher than the first frequency band, an oscillation circuit oscillating at respective resonance frequencies of each of the first and second resonant circuits, and an amplifying circuit amplifying an oscillation signal transmitted from the oscillation circuit. In this oscillator, the first resonant circuit has high impedance in the second frequency band.
In addition, the first resonant circuit may be a series resonant circuit including a variable-capacitance diode and a resonator, and the second resonant circuit m
Keating & Bennett LLP
Mai Lam T.
Murata Manufacturing Co. Ltd.
Tokar Michael
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