Oscillators – With frequency adjusting means – Step-frequency change
Reexamination Certificate
2002-03-11
2004-04-20
Kinkead, Arnold (Department: 2817)
Oscillators
With frequency adjusting means
Step-frequency change
Reexamination Certificate
active
06724274
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a frequency-switching oscillator and an electronic device using the same, and more particularly relates to a frequency-switching oscillator for switching oscillation frequencies by switching the feedback capacitance of a resonance system or an amplification system, and to an electronic device using the same.
2. Description of the Related Art
Generally, an oscillator has a resonance system and an amplification system, and the relationship between the resonance system and the amplification system must satisfy conditions for oscillation in order for the oscillator to oscillate. The conditions for oscillation are that the impedance of the amplification system has a negative resistance to compensate the impedance loss of the resonance system. In addition, the imaginary part of the impedance of the resonance system and the imaginary part of the impedance of the amplification system must have reverse signs, and the same absolute values. Further, in the Colpitts oscillator used in the following explanation, it is required for the impedance of the resonance system to be inductive to satisfy a condition of oscillation.
FIG. 8
is a Smith chart showing frequency characteristics of the impedance of the resonance system and the amplification system. The top half portion of the circle shows that the impedance is inductive, and the bottom half portion of the circle shows that the impedance is capacitive. The inner portion of the circle shows that the impedance is a resistance, and the outer portion of the circle shows that the impedance is a negative resistance. Then, the point where the impedance on the right end of the circle is extremely high is called a resonance point. The phase q of the impedance is shown counterclockwise from the right end of the circle from 0 degrees to 360 degrees. In
FIG. 8
, the solid lines show the frequency characteristics of the impedance. The impedance at a higher frequency is shown as it moves clockwise from an impedance at a certain frequency on the solid line. For example, frequency fb is higher than frequency fa. Furthermore, the impedance at frequency fa and frequency fb is a resistance, and the impedance at frequency fc is a negative resistance. Moreover, the difference in phase of the impedance at frequency fa and at frequency fb is approximately 340 degrees. As an example of phase difference and a resonance point, in the Smith chart, the phase difference between an impedance at a given frequency on the solid line and an impedance at a frequency two cycles to the right from that impedance is 720 degrees, in which case the resonance point is passed twice.
A frequency-switching oscillator is an oscillator which outputs two or more oscillation frequency signals, and conditions for oscillation must be satisfied at each of the different oscillation frequencies. Conventional frequency-switching oscillators comprise a switch element as switching member in the resonance system, and output two or more oscillation frequencies, satisfying the conditions for oscillation at each of the different oscillation frequencies, by switching the state of the switch element.
FIG. 9
shows a conventional frequency-switching oscillator
11
. The basic concept of the frequency-switching oscillator
11
shown in
FIG. 9
is disclosed in Japanese Unexamined Patent Publication No. 9-307354.
In
FIG. 9
, the frequency-switching oscillator
11
is a Colpitts oscillator with oscillation frequencies f
11
and f
12
, and is provided with a resonance system
12
and an amplification system
13
being connected.
Firstly, the resonance system
12
has a coil L
12
, a coil L
13
, a coil L
14
, a diode D
11
, a capacitor C
13
, and a switching voltage input terminal a
15
. These elements are important in determining the impedance of the resonance system. One end of the coil L
12
is connected via a resonance output terminal a
12
to the amplification system
13
, and the other end is connected to the anode of the diode D
11
and one end of the coil L
14
. The other end of the coil L
14
is connected to the switching voltage input terminal a
15
, and is grounded via the capacitor C
13
. The cathode of the diode D
11
is grounded via the coil L
13
.
Then, when a switching voltage is applied to the switching voltage input terminal a
15
, the diode D
11
becomes conductive, thereby operating as a resonator which is termination-grounded by the coil L
12
and the coil L
13
; when no switching voltage is applied, the diode D
11
becomes nonconductive, thereby operating as a resonator which is termination-opened by the coil L
12
. Here, the coil L
14
is a choke coil, and C
13
is a ground capacitor.
The frequency-switching oscillator
11
is a voltage-controlled oscillator, having a coil L
11
, a capacitor C
11
, a capacitor C
12
, a variable-capacitance diode VD
11
, and a control voltage input terminal, which are all corresponding to the voltage-controlled portion. The capacitance value of the variable-capacitance diode VD
11
is adjusted by a control voltage inputted from the control voltage input terminal via the coil L
11
which is a choke coil. The variable-capacitance diode VD
11
is connected via the capacitor C
12
to one end of the coil L
12
.
The impedance of the resonance system
12
of such a frequency-switching oscillator
11
is the impedance seen from the resonance output terminal a
12
of the resonance system
12
when the frequency-switching oscillator
11
is separated into the resonance system
12
and the amplification system
13
.
FIGS. 10A and 10B
show frequency characteristics of the impedance of the resonance system
12
using a Smith chart.
FIG. 10A
shows the impedance when the diode D
11
is conductive, and
FIG. 10B
shows the impedance when the diode D
11
is nonconductive. Furthermore, the impedances at oscillation frequencies f
11
and f
12
are shown by reference numerals f
11
and f
12
.
As shown in
FIGS. 10A and 10B
, when the diode D
11
is conductive or nonconductive as a result of application of a switching voltage to the switching voltage input terminal a
15
, the impedance of the resonance system
12
greatly changes.
FIG. 10A
shows the case when a switching voltage is applied to the switching voltage input terminal a
15
, and the impedance of the resonance system
12
is inductive at f
11
and f
12
. Then,
FIG. 10B
shows a case when no switching voltage is applied, whereby the impedance of the resonance system
12
is capacitive at f
11
, and inductive at f
12
.
Furthermore, in
FIG. 9
, in the amplification system
13
, a transistor TR
11
is an amplification element. The collector of the transistor TR
11
is connected to a power supply input terminal a
14
, one end of a capacitor C
19
, and one end of a capacitor C
17
, and also is connected via a capacitor C
14
to the resonance system
12
. The base of the transistor TR
11
is connected to the other end of the capacitor C
17
, and is grounded via the capacitor C
15
. In addition, a power supply voltage voltage-divided by a resistance R
11
and a resistance R
12
is input to the base of the transistor TR
11
. The emitter of transistor TR
11
is connected to the other end of the capacitor C
19
, is grounded via a capacitor C
16
and a resistance R
13
, and is connected via a capacitor C
18
to an oscillation output terminal a
16
. Thus, the amplification system
13
has no switching member, and the frequency characteristics of the impedance of the amplification system
13
are not switched.
The impedance of amplification system
13
is the impedance seen from the oscillation input terminal a
13
when the frequency-switching oscillator
11
is separated into the resonance system
12
and the amplification system
13
.
FIG. 11
shows the impedance of the amplification system
13
, and the impedance at the oscillation frequencies f
11
and f
12
is shown by reference numerals f
11
and f
12
. In
FIG. 11
, the impedance of the amplification system
13
is a negative resistance at the oscillation frequencies f
11
Fujidai Masanori
Hata Toshio
Burns Doane , Swecker, Mathis LLP
Kinkead Arnold
Murata Manufacturing Co. Ltd.
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