Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
2001-02-05
2002-06-25
Mis, David (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C331S132000
Reexamination Certificate
active
06411170
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an oscillation circuit used in high-frequency circuits of various communication equipment such as BS tuner, digital TV tuner and cellular telephone.
2. Description of the Related Art
FIG. 12
shows an example of circuit diagram of an oscillation circuit having differential configuration of the prior art. This oscillation circuit has such a configuration as one terminal of a current source I
1N
is connected to a power terminal to which a power voltage V
CC
is applied, and one terminal each of inductance elements L
1
, L
2
is connected to other terminal of the current source I
1N
. The other terminals of the inductors L
1
, L
2
are connected to anode terminals of varactor diodes C
11
, C
21
used as adjustable capacitance elements, and cathode terminals of the varactor diodes C
11
, C
21
are connected with each other while a frequency tuning voltage V
TX
is applied thereto. The inductance elements L
1
, L
2
and the varactor diodes C
11
, C
21
constitute an LC resonance circuit RC
3
.
Junction of the inductance element L
1
and the varactor diode C
11
is connected to the collector of a bipolar transistor (hereafter referred to as transistor) T
IN1
which is a 3-terminal active element, while the emitter of the transistor T
IN1
is grounded via an emitter resistor R
E1
. Junction of the inductance element L
2
and the varactor diode C
21
is connected to the collector of a transistor T
IN2
which is a 3-terminal active element, while the emitter of the transistor T
IN2
is grounded via an emitter resistor R
E2
. The base of the transistor T
IN1
is connected to the collector of the transistor T
IN2
, and the base of the transistor T
IN2
is connected to the collector of the transistor T
IN1
.
Junction of the inductance element L
1
, the varactor diode C
11
, and the transistor T
IN1
is connected to the base of the transistor Q
P1
that constitutes an emitter follower circuit. Collector of the transistor Q
P1
is connected to a power terminal, while the emitter is grounded via a current source I
P1
and is, at the same time, connected to the base of a transistor Q
P2
that constitutes the emitter follower circuit. Collector of the transistor Q
P2
is connected to the power terminal, while the emitter is grounded via a current source I
P2
, so that one of oscillation outputs V
OUT
(+) is obtained at the emitter of the transistor Q
P2
.
Junction of the inductance element L
2
, the varactor diode C
21
, and the transistor T
IN2
is connected to the base of the transistor Q
N1
that constitutes an emitter follower circuit. Collector of the transistor Q
N1
is connected to a power terminal, while the emitter is grounded via a current source I
N1
and is, at the same time, connected to the base of a transistor Q
N2
that constitutes the emitter follower circuit. Collector of the transistor Q
N2
is connected to the power terminal, while the emitter is grounded via the current source I
N2
, so that the other oscillation outputs V
OUT
(−) is obtained at the emitter of the transistor Q
N2
.
In the oscillation circuit having such a constitution as described above, the inductance elements L
1
, L
2
and the varactor diodes C
11
, C
21
constitute an LC parallel resonance circuit (hereafter abbreviated as LC resonance circuit), while a resonance signal of the LC resonance circuit that is connected as a load to the collectors of the transistors T
IN1
, T
IN2
is fed to the bases of the transistors T
IN1
, T
IN2
in positive feedback, thereby carrying out oscillation operation.
In this oscillation circuit, LC resonance frequency is changed and the oscillation frequency is accordingly changed by varying the voltage V
TX
applied to the cathode terminals of the varactor diodes C
11
, C
21
thereby varying the capacitances of the varactor diodes C
11
, C
21
.
In the oscillation circuit of the prior art described above, the inductance elements L
1
, L
2
of the LC resonance circuit includes not only pure inductance component but also a series resistive component. In such an oscillation circuit, when the resonance frequency is changed in order to change the oscillation frequency, Q factor of oscillation also varies in concert therewith, thus resulting in such a problem that the oscillation output level changes and stable oscillation cannot be maintained.
Also because the varactor diodes C
11
, C
21
are used as adjustable capacitance elements in the LC resonance circuit for the tuning of oscillation frequency, the tunable range of the oscillation frequency is determined by the adjustable range of capacitances of the varactor diodes C
11
, C
21
. Thus since the varactor diodes C
11
, C
21
do not have large adjustable range of capacitances due to the characteristics thereof, it has been difficult to achieve oscillation over a large frequency range.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an oscillation circuit that is capable of maintaining stable oscillation when the oscillation frequency is changed.
Another object of the present invention is to provide an oscillation circuit that is capable of making stable oscillation over a large range of frequencies.
An oscillation circuit of the first invention comprises a 3-terminal active element and an LC resonance circuit, the LC resonance circuit being connected with two terminals of the 3-terminal active element and output signal of the 3-terminal active element being fed back to the input terminal of the 3-terminal active element, wherein a voltage-current converter circuit that converts the voltage across the LC resonance circuit to a current and a current path for supplying the output current of the voltage-current converter circuit to the LC resonance circuit are provided. The voltage-current converter circuit and the current path function as Q-factor tuning voltage-current converter circuit that tunes the Q factor of the LC resonance circuit.
An oscillation circuit of the second invention comprises a pair of transistors that supply signals to bases or gates of a plurality of transistors of which emitters or sources are connected with each other and output a signal from the collector or the drain thereof, and a plurality of LC resonance circuits with one end each thereof being ac-grounded, wherein the other ends of the LC resonance circuits are connected to same type terminals of the transistors that constitute the transistor pair, and the signal from the collector or drain of each transistor of the transistor pair is fed back to the base or gate of the other transistor.
The oscillation circuit is characterized in that the voltage-current converter circuit that converts the voltage across the LC resonance circuit into a current and the current path for supplying the output current of the voltage-current converter circuit to the LC resonance circuit are provided. The voltage-current converter circuit and the current path function as Q-factor tuning voltage-current converter circuit that tunes the Q factor of the LC resonance circuit.
With these constitutions, when the oscillation frequency is changed by changing the resonance frequency of the LC resonance circuit, C/N characteristic deteriorates because the resistive component included in the LC resonance circuit causes the Q factor of the LC resonance circuit to change in concert therewith, although the change in the Q factor of the LC resonance circuit can be compensated for by means of the Q-factor tuning voltage-current converter circuit. As a result, it is made possible to stabilize the oscillation output level and the C/N characteristic when the oscillation frequency is changed.
The LC resonance circuit may be provided, for example, in the following two constitutions. An LC resonance circuit of the first constitution comprises an LC resonance main circuit consisting of an inductance element and a capacitance element, a current sensing resistor provided in series with the capacitance element and a frequency tuning voltage-current converter circuit that con
Matsushita Electric - Industrial Co., Ltd.
Mis David
Stevens Davis Miller & Mosher LLP
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