Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
1999-11-16
2001-01-09
Mis, David (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C331S03600C, C331S096000, C331S1170FE, C331S175000, C331S17700V
Reexamination Certificate
active
06172578
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an oscillation circuit and, more particularly, an oscillation circuit suitable for use as a local oscillator of an upper heterodyne receiver.
2. Description of the Related Art
For example, in the case of frequency-converting a television signal in a band of tens MHz to hundreds MHz to a television intermediate frequency signal, the television signal is once frequency-converted to a first intermediate frequency signal in a high band of 1300 MHz. At this time, a local oscillator oscillates at a frequency higher than 1300 MHz.
A conventional oscillation circuit used as such a local oscillator is shown in FIG.
5
. The oscillation circuit is of a common collector type. The collector of an oscillation transistor
31
to which a source voltage (E) is applied is connected to the ground in a high frequency manner by a d.c. blocking capacitor
32
and feedback capacitors
33
and
34
are connected between the base and emitter and between the emitter and collector, respectively. Inductance means
35
is connected between the base and the ground. The inductance means
35
is connected in parallel to the feedback capacitors
33
and
34
which are connected in series in a high frequency manner and becomes equivalently inductive at an oscillation frequency.
In the inductance means
35
, a clap capacitor
36
, a varactor diode
37
, and an inductor
38
are connected in series. An oscillation frequency is determined by a parallel resonance frequency obtained by an equivalent inductance of the inductance means
35
and a series capacity of the feedback capacitors
33
and
34
which are connected in series.
A resistor
39
is connected between the emitter of the oscillator transistor
31
and the ground and a resistor
40
is connected between the base and the ground. A source voltage (E) is supplied to the base via a resistor
41
. The resistor
39
serves as an emitter-bias resistor for supplying a bias voltage to the emitter. The resistors
40
and
41
serve as base-bias resistors for applying a bias voltage to the base.
An oscillation signal outputted from the emitter of the oscillation transistor
31
is supplied to an amplifier
43
via a pickup capacitor
42
and supplied to a mixing circuit (not shown) from the amplifier
43
.
At this time, a control voltage V is applied to the cathode of the varactor diode
37
by a choke coil
44
. The capacity of the varactor diode
37
is changed by changing the voltage V, thereby varying the oscillation frequency in correspondence with the frequency of the television signal to be received.
Specifically, the capacity of the varactor diode
37
decreases as the control voltage V applied to the varactor diode
37
is made higher, an inductance equivalent value of the inductance means
35
decreases and the oscillation frequency becomes higher.
As the control voltage V applied to the varactor diode
37
is decreased, the capacity of the varactor diode
37
increases, an inductance equivalent value of the inductance means
35
increases, and the oscillation frequency becomes lower.
Generally, the level of the oscillation signal outputted from the oscillation circuit becomes higher as the oscillation frequency is lowered. Noises are also produced from the oscillation circuit and the level of the noises also becomes higher as the frequency is lowered.
When the oscillation circuit is used as a local oscillation circuit of an upper heterodyne receiver, high-level noise in a first intermediate frequency band which is lower than the oscillation frequency is carried to a mixing circuit. Consequently, there is a drawback that the S/N ratio of the first intermediate frequency signal deteriorates.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an oscillation circuit in which the S/N ratio of a first intermediate frequency signal of a receiver is increased by suppressing noise at frequencies lower than an oscillation frequency.
In order to achieve the object, according to the invention, there is provided an oscillation circuit comprising a feedback capacitor and first inductance means which constructs a parallel resonance circuit together with the feedback capacitor, wherein the first inductance means is comprised of second inductance means whose inductance equivalent value increases as the frequency is lowered and third inductance means which is connected to the second inductance means in series, and an oscillation signal is outputted from both ends of the third inductance means.
The second inductance means of the oscillation circuit of the invention comprises a first inductor and a variable capacitor which is connected to the first inductor in series, and the frequency of the oscillation signal is controlled by varying the capacity value of the variable capacitor.
The third inductance means of the oscillation circuit of the invention is constructed by a second inductor, the first inductor and the second inductor are connected in series and are integrated as a first microstrip line, and the oscillation signal is outputted from a some midpoint in the longitudinal direction of the first microstrip line.
The second inductance means of the oscillation circuit of the invention comprises a third inductor and a variable capacitor which is connected to the third inductor in parallel, and the frequency of the oscillation signal is controlled by changing the capacity value of the variable capacitor.
The third inductance means of an oscillation circuit of the invention is constructed by a fourth inductor, the third inductor and the fourth inductor are connected in series and are integrated as a second microstrip line, and the oscillation signal is outputted from a some midpoint in the longitudinal direction of the second microstrip line.
According to the oscillation circuit of the invention, the variable capacitor is constructed by a varactor diode and the frequency of the oscillation signal is controlled by changing a control voltage which varies the capacity of the varactor diode.
According to the oscillation circuit of the invention, one end of the third inductance means is connected to the ground in a high frequency manner.
REFERENCES:
patent: 4249262 (1981-02-01), Fenk
patent: 4639691 (1987-01-01), Iigima
patent: 5694092 (1997-12-01), Oba et al.
patent: 5712596 (1998-01-01), Van Amesfoort
Alps Electric Co. Ltd
Brinks Hofer Gilson & Lione
Mis David
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