Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
2001-12-26
2004-04-20
Pascal, Robert (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C330S311000
Reexamination Certificate
active
06724270
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-399217 filed Dec. 27, 2000, the entire contents of which are incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an oscillation circuit, and more particularly, to an oscillation circuit of a cascode connection type. Further, the invention relates to a technique for preventing a phenomenon in which the oscillation frequency of an oscillation circuit varies due to changes in power supply voltage.
2. Description of the Related Art
To construct an oscillation circuit for generating a high-frequency oscillation signal, a cascode connection is being widely used. The cascode connection is a connection method for connecting a grounded-emitter transistor circuit to a grounded-base transistor circuit in series. The cascode connection is characterized in that it can provide an oscillation circuit with both a total gain equivalent to that of the grounded-emitter transistor circuit and a bandwidth up to the cutoff frequency of the grounded-base transistor circuit. Accordingly, the cascode connection is very useful in constructing a high-frequency oscillation circuit.
FIG. 1
is a circuit diagram illustrating a conventional grounded-collector oscillation circuit
10
of a cascode connection type. As shown, the oscillation circuit
10
comprises two bipolar transistors
11
and
12
, bias resistance elements
13
-
15
, a resistance element
16
, a load
17
, a capacitance element
18
and an LC oscillator section
19
.
The transistor
11
includes a base connected to respective ends of the bias resistance elements
13
and
14
, a collector connected to an end of the load
17
, and an emitter connected to the collector of the transistor
12
. The transistor
12
includes a base connected to the other end of the bias resistance element
14
, an end of the bias resistor
15
and the output terminal of the LC oscillator section
19
, a collector connected to one electrode of the capacitance element
18
, and an emitter connected to an end of the resistance element
16
. The other ends of the bias resistance element
13
and the load
17
are connected to a power supply potential Vcc. The other ends of the bias resistance element
15
and the resistance element
16
, and the other electrode of the capacitance element
18
are connected to the ground potential. In other words, the grounded-base transistor
11
and the grounded-emitter transistor
12
are connected in series. A capacitance element
20
interposed between the base and collector of the transistor
12
is a parasitic capacitance element. The capacitance element
20
is created because of a depletion layer which occurs in a pn-junction between the base region and collector region of the transistor
12
. Therefore, the capacitance Cbc of the capacitance element
20
depends upon the width of the depletion layer. The width of the depletion layer depends upon the base-collector voltage Vbc of the transistor
12
.
In the oscillation circuit constructed as above, the difference in potential between the bases of the transistors
11
and
12
(a voltage drop occurring at the bias resistance element
14
) is (R
2
·Vcc)/(R
1
+R
2
+R
3
) (R
1
·R
3
: the respective resistances of the bias resistance elements
13
-
15
). Thus, the potential difference is directly determined from the resistances of the bias resistance elements
13
-
15
. Accordingly, the base-collector voltage Vbc of the transistor
12
is ((R
2
·Vcc)/(R
1
+R
2
+R
3
)−Vbe). Vbe represents the base-emitter voltage of the transistor
11
, which is substantially constant. As is evident from the above equation, a change in the power supply potential Vcc causes a change in the base-collector voltage Vbc of the transistor
12
.
Moreover, as aforementioned, the depletion layer width that determines the capacitance Cbc of the capacitance element
20
depends upon the base-collector voltage Vbc of the transistor
12
. Further, the base-collector voltage Vbc depends upon the power supply potential Vcc. Consequently, the capacitance Cbc depends upon the power supply potential Vcc, which means that a change in the power supply potential Vcc causes a change in the capacitance Cbc.
The oscillation frequency fosc of an oscillation signal output from the oscillation circuit
10
is basically determined from an oscillation signal output by the LC oscillator section
19
. However, the oscillation frequency is, of course, influenced by the capacitance Cbc of the capacitance element
20
. This being so, a change in the power supply potential Vcc causes a change in the base-collector voltage Vbc of the transistor
12
, which causes a change in the capacitance Cbc of the capacitance element
20
and hence a change in the oscillation frequency fosc of the oscillation circuit
10
.
As described above, a phenomenon in which power supply potential Vcc fluctuation causes oscillation frequency fosc fluctuation (this phenomenon is called “pushing”) occurs in the conventional cascode-connection-type oscillation circuit.
BRIEF SUMMARY OF THE INVENTION
An oscillation circuit according to an aspect of the present invention comprises:
a first transistor including a base inputted an oscillation signal, an emitter connected to a ground potential, and a collector;
a second transistor including a collector connected to a power supply potential, a base and an emitter; and
a first resistance element having one end connected to the collector of the first transistor, and another end connected to the emitter of the second transistor, the first resistance element causing a voltage drop proportional to the power supply potential,
wherein the a resistance of the first resistance element is set such that a change in a potential appearing across the first resistance element is equal to a change in a potential difference between the bases of the first and second transistors when the power supply potential changes.
REFERENCES:
patent: 5245298 (1993-09-01), Pham
patent: 5502420 (1996-03-01), Barclay
patent: 6147559 (2000-11-01), Fong
patent: 407221545 (1995-08-01), None
U.S. patent application Ser. No. 09/892,447, filed Jun. 28, 2001, pending.
Chang Joseph
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pascal Robert
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