Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
2001-07-10
2003-12-16
Lam, Tuan T. (Department: 2816)
Oscillators
Solid state active element oscillator
Transistors
C331S10800D, C331S1170FE
Reexamination Certificate
active
06664862
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to oscillators, and more particularly to an oscillator including an oscillation circuit unit and an amplification circuit unit for amplifying an oscillation signal output from the oscillation circuit unit.
2. Description of the Related Art
FIG. 2
is a circuit diagram of a conventional oscillator. Referring to
FIG. 2
, an oscillation circuit unit
40
includes an oscillation transistor
41
and a resonance circuit
42
. The collector of the oscillation transistor
41
is grounded via a ground capacitor
43
in the high-frequency range (i.e. at high frequencies), and the emitter thereof is grounded via an emitter bias resistor
44
. Furthermore, capacitors
45
and
46
are connected for feedback purposes between the base and the emitter and between the emitter and the ground, respectively.
The resonance circuit
42
is implemented by a two-port circuit including a resonance line
42
a
implemented by a microstrip line, a varactor diode
42
b
, etc. One end of the resonance line
42
a
and the anode of the varactor diode
42
b
are grounded, and the other end of the resonance line
42
a
is connected to the base of the oscillation transistor
41
via a coupling capacitor
42
c
and to the cathode of the varactor diode
42
b
via a DC blocking capacitor
42
d
. Thus, the oscillation circuit unit
40
constitutes an oscillation circuit of the common-collector type.
The cathode of the varactor diode
42
b
is connected to a control terminal
48
via a choke inductor
47
. The control terminal
48
is grounded via a ground capacitor
49
in the high-frequency range. A voltage for changing the capacitance of the varactor diode
42
b
is applied to the control terminal
48
.
An amplification circuit unit
50
includes an amplification transistor
51
, the emitter thereof being connected to the collector of the oscillation transistor
41
, and the collector thereof being connected to a power supply terminal
53
via an inductor
52
. A voltage Vb is applied to the power supply terminal
53
. The power supply terminal
53
is grounded via a ground capacitor
54
in the high-frequency range. The collector is grounded via a capacitor
55
, and connected to an output terminal
57
via an output matching circuit formed by the inductor
52
and a coupling capacitor
56
.
In association with base bias resistors
58
,
59
, and
60
connected in series between the power supply terminal
53
and the ground, bias voltages are applied to the bases of the oscillation transistor
41
and the amplification transistor
51
. Thus, a common bias current flows into the oscillation transistor
41
and the amplification transistor
51
. Thus, the amplification circuit unit
50
constitutes an amplification circuit of the common-emitter type.
A coupling capacitor
61
is connected between the emitter of the oscillation transistor
41
and the base of the amplification transistor
51
, so that an oscillation signal is input to the base of the amplification transistor
51
.
The oscillation frequency changes according to the voltage applied to the control terminal
48
.
In the above-described conventional oscillator, the emitter of the oscillation transistor
41
is connected to the base of the amplification transistor
51
via the coupling capacitor
61
. Since the reactance of the coupling capacitor
61
depends on frequency, the level of the oscillation signal input to the base of the amplification transistor
51
is higher when the oscillation frequency is high and lower when the oscillation frequency is low.
Thus, the level of the oscillation signal output from the amplification circuit unit
50
also changes depending on the oscillation frequency. It would be desirable to provide an oscillator having a substantially constant level of oscillation signal over the entire range of oscillation frequencies.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an oscillator in which the level of the oscillation signal is substantially constant over the entire oscillation frequency range.
To this end, the present invention provides an oscillator comprising an oscillation circuit unit having an oscillation transistor and a resonance circuit, the collector of the oscillation transistor being grounded via a first capacitor; and an amplification circuit unit of the common base type, having an amplification transistor, the emitter of the amplification transistor being directly connected to the collector of the oscillation transistor, and the base of the amplification transistor being grounded via a second capacitor. The resonance circuit is connected between the base of the oscillation transistor and the ground, an oscillation signal output from the collector of the oscillation transistor is input to the emitter of the amplification transistor while partially being bypassed to the ground via the first capacitor, and a negative feedback is provided to the amplification transistor in association with the second capacitor.
Thus, the level of the oscillation signal output from the amplification circuit unit is substantially constant even if the oscillation frequency changes.
Preferably, the reactance of each of the first capacitor and the second capacitor is in a range of a few ohms to dozens of ohms at the oscillation frequency.
Thus, the level of the oscillation signal-input to the emitter of the amplification transistor is maintained sufficiently high while a sufficient gain is provided in the amplification circuit unit.
More preferably, the reactance of either the first capacitor or the second capacitor is within three times the reactance of the other.
Thus, substantial flatness is achieved in the level of the oscillation signal over the oscillation frequency range.
More preferably, the reactance of the first capacitor is larger than the reactance of the second capacitor.
Thus, the level of higher harmonics input to the amplification circuit unit is decreased.
More preferably, the oscillation circuit unit oscillates in a range of approximately 3.5 GHz to 3.9 GHz, the capacitance of the first capacitor is approximately 2 pF, and the capacitance of the second capacitor is approximately 4 pF.
Thus, the level of the oscillation signal output from the oscillation circuit unit is substantially constant in the oscillation frequency range of 3.5 GHz to 3.9 GHz.
REFERENCES:
patent: 5187451 (1993-02-01), Nakamoto et al.
patent: 5379003 (1995-01-01), Bizen
patent: 5440276 (1995-08-01), Kim
patent: 5905414 (1999-05-01), Motoi
patent: 6008702 (1999-12-01), Yamamoto
patent: 6060954 (2000-05-01), Liu et al.
patent: 6188295 (2001-02-01), Tsai
patent: 6-085536 (1994-03-01), None
Kukita Hiroaki
Ueda Kazuhiko
Yoshisato Akiyuki
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Lam Tuan T.
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